ball mill inlet feeding pot desingn

construction of ball mill/ ball mill structure | henan deya machinery co., ltd

construction of ball mill/ ball mill structure | henan deya machinery co., ltd

Structurally, each ball mill consists of a horizontal cylindrical shell, provided with renewable wearing liners and a charge of grinding medium. The drum is supported so as to rotate on its axis on hollow trunnions attached to the end walls (attached figure 1 ball mill). The diameter of the mill determines the pressure that can be exerted by the medium on the ore particles and, in general, the larger the feed size the larger needs to be the mill diameter. The length of the mill, in conjunction with the diameter, determines the volume, and hence the capacity of the mill.

The feed material is usually fed to the mill continuously through one end trunnion, the ground product leaving via the other trunnion, although in certain applications the product may leave the mill through a number of ports spaced around the periphery of the shell. All types of mill can be used for wet or dry grinding by modification of feed and discharge equipment.

Mill shells are designed to sustain impact and heavy loading, and are constructed from rolled mild steel plates, buttwelded together. Holes are drilled to take the bolts for holding the liners. Normally one or two access manholes are provided. For attachment of the trunnion heads, heavy flanges of fabricated or cast steel are usually welded or bolted to the ends of the plate shells, planed with parallel faces which are grooved to receive a corresponding spigot on the head, and drilled for bolting to the head.

The mill ends, or trunnion heads, may be of nodular or grey cast iron for diameters less than about 1 m. Larger heads are constructed from cast steel, which is relatively light, and can be welded. The heads are fibbed for reinforcement and may be flat, slightly conical, or dished. They are machined and drilled to fit shell flanges(attached figure 2 tube mill end and trunnion). figure 2 Tube mill end and trunnion Trunnions and bearings The trunnions are made from cast iron or steel and are spigoted and bolted to the end plates, although in small mills they may be integral with the end plates. They are highly polished to reduce bearing friction. Most trunnion bearings are rigid highgrade iron castings with 120-180 degree lining of white metal in the bearing area, surrounded by a fabricated mild steel housing, which is bolted into the concrete foundations (attached figure 3 oil-lubricated trunnion bearing). figure 3 oil-lubricated trunnion bearing The bearings in smaller mills may be grease lubricated, but oil lubrication is favoured in large mills, via motor-driven oil pumps. The effectiveness of normal lubrication protection is reduced when the mill is shut down for any length of time, and many mills are fitted with manually operated hydraulic starting lubricators, which force oil between the trunnion and trunnion bearing, preventing friction damage to the beating surface, on starting, by re-establishing the protecting film of oil (attached figure 4 Hydraulic starting lubricator). figure 4 Hydraulic starting lubricator Some manufacturers install large roller bearings, which can withstand higher forces than plain metal bearings (attached figure 5 Trunnion with roller-type bearings ). Trunnion with roller-type bearings Drive Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated. Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing. The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry. Liners The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

The trunnions are made from cast iron or steel and are spigoted and bolted to the end plates, although in small mills they may be integral with the end plates. They are highly polished to reduce bearing friction. Most trunnion bearings are rigid highgrade iron castings with 120-180 degree lining of white metal in the bearing area, surrounded by a fabricated mild steel housing, which is bolted into the concrete foundations (attached figure 3 oil-lubricated trunnion bearing). figure 3 oil-lubricated trunnion bearing The bearings in smaller mills may be grease lubricated, but oil lubrication is favoured in large mills, via motor-driven oil pumps. The effectiveness of normal lubrication protection is reduced when the mill is shut down for any length of time, and many mills are fitted with manually operated hydraulic starting lubricators, which force oil between the trunnion and trunnion bearing, preventing friction damage to the beating surface, on starting, by re-establishing the protecting film of oil (attached figure 4 Hydraulic starting lubricator). figure 4 Hydraulic starting lubricator Some manufacturers install large roller bearings, which can withstand higher forces than plain metal bearings (attached figure 5 Trunnion with roller-type bearings ). Trunnion with roller-type bearings Drive Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated. Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing. The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry. Liners The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

The bearings in smaller mills may be grease lubricated, but oil lubrication is favoured in large mills, via motor-driven oil pumps. The effectiveness of normal lubrication protection is reduced when the mill is shut down for any length of time, and many mills are fitted with manually operated hydraulic starting lubricators, which force oil between the trunnion and trunnion bearing, preventing friction damage to the beating surface, on starting, by re-establishing the protecting film of oil (attached figure 4 Hydraulic starting lubricator). figure 4 Hydraulic starting lubricator Some manufacturers install large roller bearings, which can withstand higher forces than plain metal bearings (attached figure 5 Trunnion with roller-type bearings ). Trunnion with roller-type bearings Drive Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated. Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing. The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry. Liners The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

Some manufacturers install large roller bearings, which can withstand higher forces than plain metal bearings (attached figure 5 Trunnion with roller-type bearings ). Trunnion with roller-type bearings Drive Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated. Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing. The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry. Liners The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated.

Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing.

The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry.

The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used.

Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost.

Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings.

The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts.

A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported.

To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines.

Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner.

The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

mill trunnion liner

mill trunnion liner

This worm acts like an auger or a screw. As the mill turns the spiral will pull the feed into the mill. Part of the feed chute will be a seal between itself and the mill. This seal is required to prevent spillage.

It is in the form of a plate with a circular hole cut in the centre of it. The seal is bolted over the end of the trunnion liner. This is to allow the feed chute to come down through this hole into the mill. The material that forms the seal will be attached around the hole. It may be made from rubber Teflon or maybe just plywood. The other half of the seal is connected to the feed chute. When the chute is in place the two halves of the seal come together holding the solids in the mill. This seal requires a fair amount of attention and up keep. With one half of the seal moving and the other half stationary, any grit and small rocks that get into the seal will cause a great deal of friction. This will wear the seal out rather quickly.

In most cases the trunnion liners are already mounted in the trunnions of the mills. If not, they should be assembled with attention being given to match marks or in some cases to dowel pins which are used to locate the trunnion liners in their proper relation to other parts.

Assemble the oil seal with the spring in place, and with the split at the top. Encircle the oil seal with the band, keeping the blocks on the side of the bearing at or near the horizontal center line so that when in place they will fit between the two dowel pins on the bearing, which are used to prevent rotation of the seal.

Moderately tighten up the cap screws at the blocks, pulling them together to thus hold the seal with its spring in place. If the blocks cannot be pulled snuggly together, then the oil seal may be cut accordingly. Oil the trunnion surface and slide the entire seal assembly back into place against the shoulder of the bearing and finish tightening. Install the retainer ring and splash ring as shown.

If a scoop feeder, combination drum scoop feeder or drum feeder is supplied with the mill, it should be mounted on the extended flange of the feed trunnion liner, matching the dowel pin with its respective hole. The dowel pin arrangement is provided only where there is a spiral in the feed trunnion liner. This matching is important as it fixes the relationship between the discharge from the scoop and the internal spiral of the trunnion liner. Tighten the bolts attaching the feeder to the trunnion liner evenly, all around the circle, seating the feeder tightly and squarely on its beveled seat. Check the belts holding the tips and other bolts that may reduce tightening. The beveled seat design is used primarily where a feeder is provided for the trunnion to trunnion liner connection, and the trunnion liner to feeder connection. When a feeder is not used these connecting joints are usually provided by a simple cylindrical or male and female joints. If a spout feeder is to be used, it is generally supplied by the user, and should be mounted independently of the mill. The spout should protect inside the feed trunnion liner, but must not touch the liner or spiral.

Ordinarily the feed box for a scoop feeder is designed and supplied by the user. The feed box should be so constructed that it has at least 6 clearance on both sides and at the bottom of the scoop. The clearance is measured from the outside of the feed scope. The feed box may be constructed of 2 wood, but more often is made of 3/16 or plate steel reinforced with angles. In the larger size mills, the lower portion is sometimes made of concrete. Necessary openings should be provided for the original feed and the sand returns from the classifiers when in closed circuit. Horizontal and vertical joints should be provided for maintenance of the feeder. These joints should be designed with consideration for head room and accessibility.

A plate steel gear guard is furnished with the mill for safety in operation and to protect the gear and pinion from dirt or grit. As soon as the gear and pinion have been cleaned and coated with the proper lubricant, the gear guard should be assembled and set on its foundation.

Wedoes not attempt to build a cheap grinding mill. Engineering based on long experience with mill manufacture enters into the production of BallMills, with the result that in field operation this equipment yields the lowest possible operating costs, maximum operating time, and years of useful service. As such then it is not an expensive mill.

Every Mill is engineered and designed to meet the specific grinding conditions under which it will be used. The speed of the mill, type of liners, grate openings for ball mills, size and type of feeder, size and type of bearings, trunnion openings, mill diameter and length, as well as many other smaller factors are all given careful consideration in designing the BallMill.

Each mill is of proper design, constructed in a workmanlike manner, and guaranteed to be free from defects in material or workmanship. All Ball Mills are built to jigs and templates so any part may be duplicated whenever required. All parts are accurately machined for fits with close tolerances. Before shipment each mill is assembled in our shops, carefully checked and match marked to facilitate field erection. The mill is given a heavy coat of paint especially prepared for this type of machinery and all machined surfaces are thoroughly coated with protecting grease.

A complete set of detailed drawings is made for each mill and kept in a fireproof vault. This assures the future supply of perfectly fitting replacement parts for the life of the mill. Wearing parts embodying the latest developments are supplied on all orders.

In these descriptions you will find the word MEEHANITE. This is a trade name for metal castings poured under a licensed agreement with The Meehanite Metal Corporation. A complete description of its characteristics and inherent nature is found on page 19.

Ball Mill shells are fabricated from rolled plate steel. Under special conditions they can be cast of Meehanite, steel, or special alloys. The plate steel shells are rolled accurately to diameter and are welded according to ASME specifications, using a Union Melt Automatic Welding Machine. This equipment provides an even flow, uniform strength weld with full penetration.

On each end of the shell are steel flange rings bored to fit the shell, set in place and welded to the shell inside and out by the Union Melt machine. Large diameter shells are stress relieved under temperature and atmosphere control after welding is completed. Such heat treatment relieves any stresses or strains set up during rolling and welding operations.

The method of attaching the flange rings leaves the inside surface of the shell free from any pockets or depressions which would cause pulp racing and wear. The flanges are then machined true with the shell axis and with each other and counterbored to gauge for male and female fit with the separate mill heads. This construction eliminates any possibility of bolt shearing.

Ball Mill shells are generally 5 to 7 greater in diameter than the nominal mill diameter figure. In other words the diameter of a ball Mill is the measurement inside the average thickness of new linersnot inside the shell as designated by some manufacturers.

Ball mill feed and discharge heads are detachable, cast of Meehanite metal of ample thickness, either of GA or GC, depending on the size of mill and with consideration to bending stresses. These heads are generally ribbed for extra strength and stiffness. Such ribs terminate near the center of the head in a trunnion seat. A male and female fit to the shell flange ring is provided and the back of the connecting flange is faced or spot faced to furnish a true seat for the joint connecting bolts.

The head to which the gear will be attached has a seat or flange with a shoulder turned accurately to size providing a seat for the gear. All turning and boring is done in one setting to assure perfect concentricity.

Smaller Ball Mills are constructed with separate trunnions; larger diameter mills have trunnions cast integral with the heads. Separate trunnions are attached to the heads with bolted flanges for male and female fit. Flanges are faced and counter bored. All trunnions are cast of Meehanite metal, turned and carefully polished. All trunnions have a large bearing surface capable of carrying the heavy mill load and to avoid heating during operation. The outer ends of the trunnions are faced and drilled to receive the trunnion liners, protecting the inside surface from wear. Liner bolt holes are drilled to template and spot faced on the outside of the head.

This head is of considerable depth providing a pulp lifting chamber, and is designed to contain the discharge grates, clamp bars, and the lifters which elevate the mill product through the trunnion. See pages 20 and 21.

For rod mill work the discharge head is conical in shape causing the rods to travel by rotation laterally and away from the exceptionally large discharge opening. The discharge opening is larger than the inlet opening, thus providing the ball millLow Pulp Line principle of grinding.

The feed end trunnion liner is also constructed of Meehanite and can be furnished of several designs to meet each specific application. For normal closed circuit grinding work a spiral liner is furnished to screw new feed and return sands into the mill. For spout fed mills a plain tapered liner is generally furnished.

The mill trunnions are machined with a taper bored seat to receive the trunnion liner. Such arrangement permits the trunnion liner weight to be carried by the seat rather than by the connecting studs. This is of particular importance on the feed end since the shearing effect of the added feeder would cause breakage of the feeder connecting bolts.

ball mill design/power calculation

ball mill design/power calculation

The basic parameters used in ball mill design (power calculations), rod mill or anytumbling millsizing are; material to be ground, characteristics, Bond Work Index, bulk density, specific density, desired mill tonnage capacity DTPH, operating % solids or pulp density, feed size as F80 and maximum chunk size, productsize as P80 and maximum and finally the type of circuit open/closed you are designing for.

In extracting fromNordberg Process Machinery Reference ManualI will also provide 2 Ball Mill Sizing (Design) example done by-hand from tables and charts. Today, much of this mill designing is done by computers, power models and others. These are a good back-to-basics exercises for those wanting to understand what is behind or inside the machines.

W = power consumption expressed in kWh/short to (HPhr/short ton = 1.34 kWh/short ton) Wi = work index, which is a factor relative to the kwh/short ton required to reduce a given material from theoretically infinite size to 80% passing 100 microns P = size in microns of the screen opening which 80% of the product will pass F = size in microns of the screen opening which 80% of the feed will pass

Open circuit grinding to a given surface area requires no more power than closed circuit grinding to the same surface area provided there is no objection to the natural top-size. If top-size must be limited in open circuit, power requirements rise drastically as allowable top-size is reduced and particle size distribution tends toward the finer sizes.

A wet grinding ball mill in closed circuit is to be fed 100 TPH of a material with a work index of 15 and a size distribution of 80% passing inch (6350 microns). The required product size distribution is to be 80% passing 100 mesh (149 microns). In order to determine the power requirement, the steps are as follows:

The ball mill motorpower requirement calculated above as 1400 HP is the power that must be applied at the mill drive in order to grind the tonnage of feed from one size distribution. The following shows how the size or select thematching mill required to draw this power is calculated from known tables the old fashion way.

The value of the angle a varies with the type of discharge, percent of critical speed, and grinding condition. In order to use the preceding equation, it is necessary to have considerable data on existing installations. Therefore, this approach has been simplified as follows:

A = factor for diameter inside shell lining B = factor which includes effect of % loading and mill type C = factor for speed of mill L = length in feet of grinding chamber measured between head liners at shell- to-head junction

Many grinding mill manufacturers specify diameter inside the liners whereas othersare specified per inside shell diameter. (Subtract 6 to obtain diameter inside liners.) Likewise, a similar confusion surrounds the length of a mill. Therefore, when comparing the size of a mill between competitive manufacturers, one should be aware that mill manufacturers do not observe a size convention.

In Example No.1 it was determined that a 1400 HP wet grinding ball mill was required to grind 100 TPH of material with a Bond Work Index of 15 (guess what mineral type it is) from 80% passing inch to 80% passing 100 mesh in closed circuit. What is the size of an overflow discharge ball mill for this application?

ball mill end cover, stationary inlet and outlet factory and suppliers | special metal

ball mill end cover, stationary inlet and outlet factory and suppliers | special metal

Ball mill head Shanghai Special Metal Co., Ltd supplies ball mill head. Thematerialsof mill head are normally selectedlow carbon steelandlow alloy steel.Itsproduced by casting, used in ball grinding mill, including the feed end andoutlet end, our head/cap for the bellow ball grinding mill. Ball mill data: Model(mmxmm) Speed of bucket(r/min) Weightof ball(t) Size offeed opening(mm) Production(t/h) Power(kw) 9001800 38 1.5 20 0.65-2 18.5 12002400 32 3.8 25 1.5-4....

Shanghai Special Metal Co., Ltd supplies ball mill head. Thematerialsof mill head are normally selectedlow carbon steelandlow alloy steel.Itsproduced by casting, used in ball grinding mill, including the feed end andoutlet end, our head/cap for the bellow ball grinding mill.

henan mining machinery and equipment manufacturer - ball mill inlet design

henan mining machinery and equipment manufacturer - ball mill inlet design

ball mill inlet design - Grinding Mill China types of of ball mill inlet for cement milling... feed chute liner for ... ball mill can be either wet or dry designs.IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 ...

Ore beneficiation equipment, sand making equipment, crushing equipment and powder grinding equipment, which are widely used in various industries such as metallurgy, mine, chemistry, building material, coal, refractory and ceramics.

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 ball mill end cover, stationary inlet and outlet special metal factory and suppliers | special metal

factory outlets for balcony grill design - ball mill end cover, stationary inlet and outlet special metal factory and suppliers | special metal

Ball mill head Shanghai Special Metal Co., Ltd supplies ball mill head. Thematerialsof mill head are normally selectedlow carbon steelandlow alloy steel.Itsproduced by casting, used in ball grinding mill, including the feed end andoutlet end, our head/cap for the bellow ball grinding mill. Ball mill data: Model(mmxmm) Speed of bucket(r/min) Weightof ball(t) Size offeed opening(mm) Production(t/h) Power(kw) 9001800 38 1.5 20 0.65-2 18.5 12002400 32 3.8 25 1.5-4....

Shanghai Special Metal Co., Ltd supplies ball mill head. Thematerialsof mill head are normally selectedlow carbon steelandlow alloy steel.Itsproduced by casting, used in ball grinding mill, including the feed end andoutlet end, our head/cap for the bellow ball grinding mill.

henan zhengzhou mining machinery co., ltd.. supplier from china. view company

henan zhengzhou mining machinery co., ltd.. supplier from china. view company

Gas Burner is research and developing for rotary kiln that burning with single or various gas fuel, which not only ensure all the advantages and specificity of four-channel burner, but also enhance the application of burning. The burner have special structure and reasonable technical parameters, guarantee the gas fuel fully mixing with air, primary air and secondary air, which to ensure stronger heating intensity, higher burning efficiency, easier adjustment. Burner can be applicable for various metallurgy and chemical rotary kiln. Application Burning System for Rotary kiln on industry fields like Power, Chemical, Metallurgy, Building material etc. Its special advantages as follows: 1.Stability flame with regular flame shapes, no phenomenon like fluctuation and sweep kiln liner, that will outstanding extend the life time of kiln liner.  2.Good mixing performance with gas fuel, primary air and secondary air, burning abundantly, that can be enhance heating intensity and reduce primary air proportion at same time, then will improve kiln capacity and reduce energy consumption.  3.No strong eddy between flame and bowl effect produced by flame cover, can avoid appearance of temperature peak and make evenly distribution of flame temperature, then effectively protect cylinder and guard plate of kiln inlet. 4.Due to more fully mixing with combustion air and fuel gas, the burning will be more quickly and fully, which will reduce the content of CO and NOX from kiln inlet, but also better for safety operating and realizing green production.  5. The nozzle has made by special material with advantages like heat-resistance and easy to change. 6.Simple operation and adjustment. When operating, erupt speed of each air pipe can be change via adjust sectional area, then will realize goals like adjustment of flame shape and strength. Gas Burner is mainly composed with Pipe, Nozzle, Ignition device, Metal corrugated compensator, Butterfly valve, Pressure measurement and Protection layer etc. The mainly features are: 1. Pipeline From outside to inside respectively, the pipeline has consist of Axial wind channel, Swirling wind channel, Gas wind channel, central wind channel and ignition channel. And the ignition is just for igniting, so called four-channel burner. 2. Nozzle Nozzle made by special material, spray mouth sectional area of axial wind channel, swirling wind channel and gas wind channel are adjustable, so that can adjust the spray speed of each channel. The nozzle is the key part to ensure flame shape. 3.Ignition Device Located in the central wind channel, used for automatic igniting. 4.Metal Corrugated Compensator Which is the key part to connect each channel, sealing and adjust flame shape, and allowed process axial movement with connected channel.

Ore ball mill is used to separate and screening different ore minerals, separate ore tailing. It also be used for ore grinding, non-ferrous metal beneficiation, new-type building material producing. According to the discharge method, the ball mill divided to dry-type mill and wet-type mill. Our products advantages of ore ball mill: High grinding efficiency, low consumption 2. Product fineness is adjustable and uniform. 3.Low energy consumption, low wear, low operating costs. 4. Small vibration, low noise, environmental friendly 5. Liner is made of high-quality wear resistant material with high strength, wear resistance and long working life. Ore ball mill is mainly consisting of feeding device, big gear, discharge device, cylinder, diaphragm plate, hollow shaft, liner, drive device and other components. 1. The feeding device is consisting of inlet chute and screw. There are liners in the inlet chute, which can extend the working life of the feeding device. 2. There is pre-gap on the inlet hallow shaft, that can reduce the tolerance which is made of temperature changes and installation mistake to ensure the gear mesh. 3. Inside the ball mill, different parts have different liner structure, which will greatly improve the grinding efficiency. 4. Dry-type ball mill adopt sliding bearing, which is good of strength, ductility, antifriction, abrasion resistance, lubricity and thermal conductivity. It is able to meet the lubrication requirements of the hollow shaft. That is suitable for the environment of low speed and heavy load in metallurgical & ore dressing industry. 5. Wet-type ball mill adopt roller bearing, reduce useless work consumption and easy to replace.

This rotary cooler equipment can quickly cool higher-temperature of granular compound fertilizer directly Approximately to normal atmospheric temperature, which is convenient for timely and quick packing and Prevents compound fertilizer from forming block during store. It can achieve adverse Flow cooling, which can reduce pollution and improve working environment. It has many characteristics such as reasonable structure, stable run, strong adaptability etc.. Features of cooler: 1.High cooling efficiency 2.Simple structure, low rate malfunction, convenient operation, low cost of maintenance, stable operation. 3.Wide usage, can be used for the drying of different materials in powder, granule, strip, lump, large elasticity Of operation. Output is allowed to have larger fluctuations in manufacturing, but not allowed to influence the Quality of the products. 4.Easy to install and remove Application range of cooler: 1. Chemical industry: ammonium sulfate, sodium sulphide, anfu powder, ammonium nitrate, Urea, oxalic acid, bichromate potassium, pvc, nitrophosphate fertilizer, fytic acid, Phosphate compound fertilizer. 2. Food industry: glucose, salt, sugar, vitamin malted milk, granular sugar. 3. Mining products: ceramic sand , coal, coal slime, manganese ore, limestone, pyrite, peat, etc. 4. Others: iron powder, flat soybean

Performance characteristics: Bag Filter is widely applied for dust collection applications in mining industry, chemical industry, pharmaceutical industry, and the production of flour, glass, metallurgy, mine, cement, building materials, etc. The bag filter is made up of the top chest, middle chest, bottom chest, dust exhauster, and jet cleaning system. There is spray tube and air outlet at the top chest. The middle box consists of perforated plate, venturi tube, filter bag, keel, pulse valve and gas cleaning system. The bottom chest is comprised of ash bucket, air inlet, access door, ash exhauster (which is composed of rotary dust valve or spiral conveyer) It could be made of carbon steel or stainless steel upon request. Dust collector is generally used with a temperature less than 12C. Customized dust collector for usage at high temperatures (less 23C) is also available.

Advantages of magnetic separator: 1)Newest CTB series magnetic separator In China 2)Simple structure, high yield; 3)Covenient operation; 4)Granularity blow 0.5m Application of magnetic separator: Newest STB Series magnetic separator In China. This series of products is used in wet magnetic separation of materials with granularity below 3mm like magnetite, pyrrhotine, bake ore and washingtonite. It is also used for deironing materials like non-metal ores, coal and building materials. Average magnetic induction of barrel surface is 100-600mT. According to customer's demands, it can provide magnetic separation with different magnetic induction like forward flow, semi counter flow and counter flow. The products have features, such as simple structure, high yield, convenient operation and easy maintenance. Characteristics of Magnetic separator: The products have geatures, such as simple structure, high yield, convenient operation and easy maintenance.

Performance characteristics: Bag Filter is widely applied for dust collection applications in mining industry, chemical industry, pharmaceutical industry, and the production of flour, glass, metallurgy, mine, cement, building materials, etc. The bag filter is made up of the top chest, middle chest, bottom chest, dust exhauster, and jet cleaning system. There is spray tube and air outlet at the top chest. The middle box consists of perforated plate, venturi tube, filter bag, keel, pulse valve and gas cleaning system. The bottom chest is comprised of ash bucket, air inlet, access door, ash exhauster (which is composed of rotary dust valve or spiral conveyer) It could be made of carbon steel or stainless steel upon request. Dust collector is generally used with a temperature less than 120C. Customized dust collector for usage at high temperatures (less 230C) is also available.

NE Plate Chain Elevator takes advanced technology from home and abroad. This products is suitable for vertical transportation of powder, granular, and bulk materials, also for high hardness materials. The temperature of materials should not be higher than 200 degree celsius. Max. Elevation height 40m. Advantages: Wide range of elevating height. Strong capacity and small driving power. Feeding materials by automatic flowing and discharge through gravity induction. Long service life and good leak tightness. Stable and liable operation, easy maintenance. Low running cost. Bucket elevator The description of bucket elevator: Bucket elevators are designed to move flowing powders or bulk solids vertically. Bucket elevators use an endless belt or chain and have a series of buckets attached to it. Bulk material is spread into an inlet hopper. Buckets (or cups) dig into the material and convey it up and over the head sprocket/pulley, and then throw the material out a discharge throat. Bucket elevator can be divided into belt type and chain type, and the common characteristic is used for vertical transportation of powder, granulated and small lump materials. It has compact structure, small covering area, large hoisting height, good sealed performance. Tape bucket conveyor is lightweight, flexible, simple handling maintenance and low noise, which can be used to transport density 1.5 t/m3 granular or small conveying of bulk materials. Advantage of Bucket Elevator: The bucket conveyor has the advantages of big conveying capacity, high hoisting height, stable and reliable running and long service life. The machine is applicable for the crushed materials, and block materials, such as coal, cement, block, sand, clay and ore. The bucket elevator is allowed to convey materials with high temperature when armed with special circle chain tructure. Henan Zhengzhou Mining Machinery Co., Ltd. Specializes in manufacturing bucket elevator. Henan Zhengzhou Mining Machinery Co., Ltd. Designs and manufactures a wide variety of bucket elevators based on the characteristics of the bulk material and the process requirements. Designed to handle a wide variety of bulk materials from average to very free-flowing. Welcome to consult and order.

Gz series electromagnetic vibrating feeder Vibrating feeder is widely used in crushing, screening production line of mining, cement, metallurgy, building materials, chemical, mineral processing, coal mining and industries. The vibrating feeder is used to mine material from a storage silo or other material storage equipment in uniform or quantitative supply to the equipment of subject material, and is the necessary equipment to practice routine automation. Introduction of the vibrating feeder: Gz series electromagnetic vibrating feeder mainly used for mining, metallurgical, chemical, coal, machinery and other industries in to the accepting machine. Being diversification, this series of products can be specially designed and produced according to the customers' need. Furthermore, all types of electromagnetic vibration feeder can be easily implemented manual or automatic control. Henan zhengzhou mining machinery co., ltd. Is a large professional manufacturer of vibrating feeder. We can provide our customer with a good consultant and assistant, to ensure our customer's investment will be rewarded with great profit. At the same time, select the right model of equipment for customer. To meet our customer's special needs, we can design and develop customized products.

Introduction: PF Series Impact Crusher is one kind of equipment to crushing the brittle material which compression strength no more than 350 Map, the advantage including high crushing ratio, uniform product grain and low over crushing, low energy consumption, high adjustment range of product grain size and optional crushing etc, which is mainly used in mine, metallurgy, cement, construction material, coal etc for secondary crushing and fine crushing the medium hardness material. PF Series Impact Crusher is mainly used in secondary crushing, and can crush material o f crushing compression strength no more than 320 Maps. It is suitable to produce high rank highway, hydroelectric and building material and such industry as stone. (1)Even crushing function of multi-cavities which is suitable to crush hard material. (2)Reasonable design of leveling plate making the finished material finer and cubic-shaped without internal cracks. (3)Low and big feed opening make the production line easy to arrange and increase the size of feeding material. (4)Hydraulic start-up which is convenient for maintenance and replacement of wear-parts. (5)New anti-abrasive material which prolong service life of impact hammer, impact plate and liner. Advantages: 1 Large feeding port and high crushing cavity, suitable to crushing the material with high hardness and big grain size, and less powder. 2 The gap between impact plate and hammer plate is adjustable, so the discharging grain size can be effective control and the grain shape is well. 3 The hammer, impact plate and lining plate are made of new type abrasion-proof material with long working life and impact protection, wear protection. 4 Because of the function of three-stage crushing and plastic, so the crushing ratio is high, and the product shape is cube and can optional crushing. 5 The multi-function hydraulic station has many function of hydraulic discharge gap with high speed, impact plate stable vibration and the body open automatically.

Pulse Jet Bag Filter incorporates the advantages of the several kinds of bag filters and is equipped with high performance pulse valve. This kind of bag filter can be used in building material, metallurgy, chemical and refractory industries, especially the crushing, packing, clinker cooling and grinding workshops in cement production. It is also suitable for dust collection of coal grinding after some modification. Application: Building material, metallurgy, chemical and refractory industries. Output: Volume(m/h): 67300-314000 Filtration area(m2): 935-4361 Net filtration area(m2): 4205 Dust content at inlet(g/m):

ball mills - an overview | sciencedirect topics

ball mills - an overview | sciencedirect topics

A ball mill is a type of grinder used to grind and blend bulk material into QDs/nanosize using different sized balls. The working principle is simple; impact and attrition size reduction take place as the ball drops from near the top of a rotating hollow cylindrical shell. The nanostructure size can be varied by varying the number and size of balls, the material used for the balls, the material used for the surface of the cylinder, the rotation speed, and the choice of material to be milled. Ball mills are commonly used for crushing and grinding the materials into an extremely fine form. The ball mill contains a hollow cylindrical shell that rotates about its axis. This cylinder is filled with balls that are made of stainless steel or rubber to the material contained in it. Ball mills are classified as attritor, horizontal, planetary, high energy, or shaker.

Grinding elements in ball mills travel at different velocities. Therefore, collision force, direction and kinetic energy between two or more elements vary greatly within the ball charge. Frictional wear or rubbing forces act on the particles, as well as collision energy. These forces are derived from the rotational motion of the balls and movement of particles within the mill and contact zones of colliding balls.

By rotation of the mill body, due to friction between mill wall and balls, the latter rise in the direction of rotation till a helix angle does not exceed the angle of repose, whereupon, the balls roll down. Increasing of rotation rate leads to growth of the centrifugal force and the helix angle increases, correspondingly, till the component of weight strength of balls become larger than the centrifugal force. From this moment the balls are beginning to fall down, describing during falling certain parabolic curves (Figure 2.7). With the further increase of rotation rate, the centrifugal force may become so large that balls will turn together with the mill body without falling down. The critical speed n (rpm) when the balls are attached to the wall due to centrifugation:

where Dm is the mill diameter in meters. The optimum rotational speed is usually set at 6580% of the critical speed. These data are approximate and may not be valid for metal particles that tend to agglomerate by welding.

The degree of filling the mill with balls also influences productivity of the mill and milling efficiency. With excessive filling, the rising balls collide with falling ones. Generally, filling the mill by balls must not exceed 3035% of its volume.

The mill productivity also depends on many other factors: physical-chemical properties of feed material, filling of the mill by balls and their sizes, armor surface shape, speed of rotation, milling fineness and timely moving off of ground product.

where b.ap is the apparent density of the balls; l is the degree of filling of the mill by balls; n is revolutions per minute; 1, and 2 are coefficients of efficiency of electric engine and drive, respectively.

A feature of ball mills is their high specific energy consumption; a mill filled with balls, working idle, consumes approximately as much energy as at full-scale capacity, i.e. during grinding of material. Therefore, it is most disadvantageous to use a ball mill at less than full capacity.

Grinding elements in ball mills travel at different velocities. Therefore, collision force, direction, and kinetic energy between two or more elements vary greatly within the ball charge. Frictional wear or rubbing forces act on the particles as well as collision energy. These forces are derived from the rotational motion of the balls and the movement of particles within the mill and contact zones of colliding balls.

By the rotation of the mill body, due to friction between the mill wall and balls, the latter rise in the direction of rotation until a helix angle does not exceed the angle of repose, whereupon the balls roll down. Increasing the rotation rate leads to the growth of the centrifugal force and the helix angle increases, correspondingly, until the component of the weight strength of balls becomes larger than the centrifugal force. From this moment, the balls are beginning to fall down, describing certain parabolic curves during the fall (Fig. 2.10).

With the further increase of rotation rate, the centrifugal force may become so large that balls will turn together with the mill body without falling down. The critical speed n (rpm) when the balls remain attached to the wall with the aid of centrifugal force is:

where Dm is the mill diameter in meters. The optimum rotational speed is usually set at 65%80% of the critical speed. These data are approximate and may not be valid for metal particles that tend to agglomerate by welding.

where db.max is the maximum size of the feed (mm), is the compression strength (MPa), E is the modulus of elasticity (MPa), b is the density of material of balls (kg/m3), and D is the inner diameter of the mill body (m).

The degree of filling the mill with balls also influences the productivity of the mill and milling efficiency. With excessive filling, the rising balls collide with falling ones. Generally, filling the mill by balls must not exceed 30%35% of its volume.

The productivity of ball mills depends on the drum diameter and the relation of drum diameter and length. The optimum ratio between length L and diameter D, L:D, is usually accepted in the range 1.561.64. The mill productivity also depends on many other factors, including the physical-chemical properties of the feed material, the filling of the mill by balls and their sizes, the armor surface shape, the speed of rotation, the milling fineness, and the timely moving off of the ground product.

where D is the drum diameter, L is the drum length, b.ap is the apparent density of the balls, is the degree of filling of the mill by balls, n is the revolutions per minute, and 1, and 2 are coefficients of efficiency of electric engine and drive, respectively.

A feature of ball mills is their high specific energy consumption. A mill filled with balls, working idle, consumes approximately as much energy as at full-scale capacity, that is, during the grinding of material. Therefore, it is most disadvantageous to use a ball mill at less than full capacity.

Milling time in tumbler mills is longer to accomplish the same level of blending achieved in the attrition or vibratory mill, but the overall productivity is substantially greater. Tumbler mills usually are used to pulverize or flake metals, using a grinding aid or lubricant to prevent cold welding agglomeration and to minimize oxidation [23].

Cylindrical Ball Mills differ usually in steel drum design (Fig. 2.11), which is lined inside by armor slabs that have dissimilar sizes and form a rough inside surface. Due to such juts, the impact force of falling balls is strengthened. The initial material is fed into the mill by a screw feeder located in a hollow trunnion; the ground product is discharged through the opposite hollow trunnion.

Cylindrical screen ball mills have a drum with spiral curved plates with longitudinal slits between them. The ground product passes into these slits and then through a cylindrical sieve and is discharged via the unloading funnel of the mill body.

Conical Ball Mills differ in mill body construction, which is composed of two cones and a short cylindrical part located between them (Fig. 2.12). Such a ball mill body is expedient because efficiency is appreciably increased. Peripheral velocity along the conical drum scales down in the direction from the cylindrical part to the discharge outlet; the helix angle of balls is decreased and, consequently, so is their kinetic energy. The size of the disintegrated particles also decreases as the discharge outlet is approached and the energy used decreases. In a conical mill, most big balls take up a position in the deeper, cylindrical part of the body; thus, the size of the balls scales down in the direction of the discharge outlet.

For emptying, the conical mill is installed with a slope from bearing to one. In wet grinding, emptying is realized by the decantation principle, that is, by means of unloading through one of two trunnions.

With dry grinding, these mills often work in a closed cycle. A scheme of the conical ball mill supplied with an air separator is shown in Fig. 2.13. Air is fed to the mill by means of a fan. Carried off by air currents, the product arrives at the air separator, from which the coarse particles are returned by gravity via a tube into the mill. The finished product is trapped in a cyclone while the air is returned in the fan.

The ball mill is a tumbling mill that uses steel balls as the grinding media. The length of the cylindrical shell is usually 11.5 times the shell diameter (Figure 8.11). The feed can be dry, with less than 3% moisture to minimize ball coating, or slurry containing 2040% water by weight. Ball mills are employed in either primary or secondary grinding applications. In primary applications, they receive their feed from crushers, and in secondary applications, they receive their feed from rod mills, AG mills, or SAG mills.

Ball mills are filled up to 40% with steel balls (with 3080mm diameter), which effectively grind the ore. The material that is to be ground fills the voids between the balls. The tumbling balls capture the particles in ball/ball or ball/liner events and load them to the point of fracture.

When hard pebbles rather than steel balls are used for the grinding media, the mills are known as pebble mills. As mentioned earlier, pebble mills are widely used in the North American taconite iron ore operations. Since the weight of pebbles per unit volume is 3555% of that of steel balls, and as the power input is directly proportional to the volume weight of the grinding medium, the power input and capacity of pebble mills are correspondingly lower. Thus, in a given grinding circuit, for a certain feed rate, a pebble mill would be much larger than a ball mill, with correspondingly a higher capital cost. However, the increase in capital cost is justified economically by a reduction in operating cost attributed to the elimination of steel grinding media.

In general, ball mills can be operated either wet or dry and are capable of producing products in the order of 100m. This represents reduction ratios of as great as 100. Very large tonnages can be ground with these ball mills because they are very effective material handling devices. Ball mills are rated by power rather than capacity. Today, the largest ball mill in operation is 8.53m diameter and 13.41m long with a corresponding motor power of 22MW (Toromocho, private communications).

Modern ball mills consist of two chambers separated by a diaphragm. In the first chamber the steel-alloy balls (also described as charge balls or media) are about 90mm diameter. The mill liners are designed to lift the media as the mill rotates, so the comminution process in the first chamber is dominated by crushing. In the second chamber the ball diameters are of smaller diameter, between 60 and 15mm. In this chamber the lining is typically a classifying lining which sorts the media so that ball size reduces towards the discharge end of the mill. Here, comminution takes place in the rolling point-contact zone between each charge ball. An example of a two chamber ball mill is illustrated in Fig. 2.22.15

Much of the energy consumed by a ball mill generates heat. Water is injected into the second chamber of the mill to provide evaporative cooling. Air flow through the mill is one medium for cement transport but also removes water vapour and makes some contribution to cooling.

Grinding is an energy intensive process and grinding more finely than necessary wastes energy. Cement consists of clinker, gypsum and other components mostly more easily ground than clinker. To minimise over-grinding modern ball mills are fitted with dynamic separators (otherwise described as classifiers or more simply as separators). The working principle is that cement is removed from the mill before over-grinding has taken place. The cement is then separated into a fine fraction, which meets finished product requirements, and a coarse fraction which is returned to mill inlet. Recirculation factor, that is, the ratio of mill throughput to fresh feed is up to three. Beyond this, efficiency gains are minimal.

For more than 50years vertical mills have been the mill of choice for grinding raw materials into raw meal. More recently they have become widely used for cement production. They have lower specific energy consumption than ball mills and the separator, as in raw mills, is integral with the mill body.

In the Loesche mill, Fig. 2.23,16 two pairs of rollers are used. In each pair the first, smaller diameter, roller stabilises the bed prior to grinding which takes place under the larger roller. Manufacturers use different technologies for bed stabilisation.

Comminution in ball mills and vertical mills differs fundamentally. In a ball mill, size reduction takes place by impact and attrition. In a vertical mill the bed of material is subject to such a high pressure that individual particles within the bed are fractured, even though the particles are very much smaller than the bed thickness.

Early issues with vertical mills, such as narrower PSD and modified cement hydration characteristics compared with ball mills, have been resolved. One modification has been to install a hot gas generator so the gas temperature is high enough to partially dehydrate the gypsum.

For many decades the two-compartment ball mill in closed circuit with a high-efficiency separator has been the mill of choice. In the last decade vertical mills have taken an increasing share of the cement milling market, not least because the specific power consumption of vertical mills is about 30% less than that of ball mills and for finely ground cement less still. The vertical mill has a proven track record in grinding blastfurnace slag, where it has the additional advantage of being a much more effective drier of wet feedstock than a ball mill.

The vertical mill is more complex but its installation is more compact. The relative installed capital costs tend to be site specific. Historically the installed cost has tended to be slightly higher for the vertical mill.

Special graph paper is used with lglg(1/R(x)) on the abscissa and lg(x) on the ordinate axes. The higher the value of n, the narrower the particle size distribution. The position parameter is the particle size with the highest mass density distribution, the peak of the mass density distribution curve.

Vertical mills tend to produce cement with a higher value of n. Values of n normally lie between 0.8 and 1.2, dependent particularly on cement fineness. The position parameter is, of course, lower for more finely ground cements.

Separator efficiency is defined as specific power consumption reduction of the mill open-to-closed-circuit with the actual separator, compared with specific power consumption reduction of the mill open-to-closed-circuit with an ideal separator.

As shown in Fig. 2.24, circulating factor is defined as mill mass flow, that is, fresh feed plus separator returns. The maximum power reduction arising from use of an ideal separator increases non-linearly with circulation factor and is dependent on Rf, normally based on residues in the interval 3245m. The value of the comminution index, W, is also a function of Rf. The finer the cement, the lower Rf and the greater the maximum power reduction. At C = 2 most of maximum power reduction is achieved, but beyond C = 3 there is very little further reduction.

Separator particle separation performance is assessed using the Tromp curve, a graph of percentage separator feed to rejects against particle size range. An example is shown in Fig. 2.25. Data required is the PSD of separator feed material and of rejects and finished product streams. The bypass and slope provide a measure of separator performance.

The particle size is plotted on a logarithmic scale on the ordinate axis. The percentage is plotted on the abscissa either on a linear (as shown here) or on a Gaussian scale. The advantage of using the Gaussian scale is that the two parts of the graph can be approximated by two straight lines.

The measurement of PSD of a sample of cement is carried out using laser-based methodologies. It requires a skilled operator to achieve consistent results. Agglomeration will vary dependent on whether grinding aid is used. Different laser analysis methods may not give the same results, so for comparative purposes the same method must be used.

The ball mill is a cylindrical drum (or cylindrical conical) turning around its horizontal axis. It is partially filled with grinding bodies: cast iron or steel balls, or even flint (silica) or porcelain bearings. Spaces between balls or bearings are occupied by the load to be milled.

Following drum rotation, balls or bearings rise by rolling along the cylindrical wall and descending again in a cascade or cataract from a certain height. The output is then milled between two grinding bodies.

Ball mills could operate dry or even process a water suspension (almost always for ores). Dry, it is fed through a chute or a screw through the units opening. In a wet path, a system of scoops that turn with the mill is used and it plunges into a stationary tank.

Mechanochemical synthesis involves high-energy milling techniques and is generally carried out under controlled atmospheres. Nanocomposite powders of oxide, nonoxide, and mixed oxide/nonoxide materials can be prepared using this method. The major drawbacks of this synthesis method are: (1) discrete nanoparticles in the finest size range cannot be prepared; and (2) contamination of the product by the milling media.

More or less any ceramic composite powder can be synthesized by mechanical mixing of the constituent phases. The main factors that determine the properties of the resultant nanocomposite products are the type of raw materials, purity, the particle size, size distribution, and degree of agglomeration. Maintaining purity of the powders is essential for avoiding the formation of a secondary phase during sintering. Wet ball or attrition milling techniques can be used for the synthesis of homogeneous powder mixture. Al2O3/SiC composites are widely prepared by this conventional powder mixing route by using ball milling [70]. However, the disadvantage in the milling step is that it may induce certain pollution derived from the milling media.

In this mechanical method of production of nanomaterials, which works on the principle of impact, the size reduction is achieved through the impact caused when the balls drop from the top of the chamber containing the source material.

A ball mill consists of a hollow cylindrical chamber (Fig. 6.2) which rotates about a horizontal axis, and the chamber is partially filled with small balls made of steel, tungsten carbide, zirconia, agate, alumina, or silicon nitride having diameter generally 10mm. The inner surface area of the chamber is lined with an abrasion-resistant material like manganese, steel, or rubber. The magnet, placed outside the chamber, provides the pulling force to the grinding material, and by changing the magnetic force, the milling energy can be varied as desired. The ball milling process is carried out for approximately 100150h to obtain uniform-sized fine powder. In high-energy ball milling, vacuum or a specific gaseous atmosphere is maintained inside the chamber. High-energy mills are classified into attrition ball mills, planetary ball mills, vibrating ball mills, and low-energy tumbling mills. In high-energy ball milling, formation of ceramic nano-reinforcement by in situ reaction is possible.

It is an inexpensive and easy process which enables industrial scale productivity. As grinding is done in a closed chamber, dust, or contamination from the surroundings is avoided. This technique can be used to prepare dry as well as wet nanopowders. Composition of the grinding material can be varied as desired. Even though this method has several advantages, there are some disadvantages. The major disadvantage is that the shape of the produced nanoparticles is not regular. Moreover, energy consumption is relatively high, which reduces the production efficiency. This technique is suitable for the fabrication of several nanocomposites, which include Co- and Cu-based nanomaterials, Ni-NiO nanocomposites, and nanocomposites of Ti,C [71].

Planetary ball mill was used to synthesize iron nanoparticles. The synthesized nanoparticles were subjected to the characterization studies by X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques using a SIEMENS-D5000 diffractometer and Hitachi S-4800. For the synthesis of iron nanoparticles, commercial iron powder having particles size of 10m was used. The iron powder was subjected to planetary ball milling for various period of time. The optimum time period for the synthesis of nanoparticles was observed to be 10h because after that time period, chances of contamination inclined and the particles size became almost constant so the powder was ball milled for 10h to synthesize nanoparticles [11]. Fig. 12 shows the SEM image of the iron nanoparticles.

The vibratory ball mill is another kind of high-energy ball mill that is used mainly for preparing amorphous alloys. The vials capacities in the vibratory mills are smaller (about 10 ml in volume) compared to the previous types of mills. In this mill, the charge of the powder and milling tools are agitated in three perpendicular directions (Fig. 1.6) at very high speed, as high as 1200 rpm.

Another type of the vibratory ball mill, which is used at the van der Waals-Zeeman Laboratory, consists of a stainless steel vial with a hardened steel bottom, and a single hardened steel ball of 6 cm in diameter (Fig. 1.7).

The mill is evacuated during milling to a pressure of 106 Torr, in order to avoid reactions with a gas atmosphere.[44] Subsequently, this mill is suitable for mechanical alloying of some special systems that are highly reactive with the surrounding atmosphere, such as rare earth elements.

In spite of the traditional approaches used for gas-solid reaction at relatively high temperature, Calka etal.[58] and El-Eskandarany etal.[59] proposed a solid-state approach, the so-called reactive ball milling (RBM), used for preparations different families of meal nitrides and hydrides at ambient temperature. This mechanically induced gas-solid reaction can be successfully achieved, using either high- or low-energy ball-milling methods, as shown in Fig.9.5. However, high-energy ball mill is an efficient process for synthesizing nanocrystalline MgH2 powders using RBM technique, it may be difficult to scale up for matching the mass production required by industrial sector. Therefore, from a practical point of view, high-capacity low-energy milling, which can be easily scaled-up to produce large amount of MgH2 fine powders, may be more suitable for industrial mass production.

In both approaches but with different scale of time and milling efficiency, the starting Mg metal powders milled under hydrogen gas atmosphere are practicing to dramatic lattice imperfections such as twinning and dislocations. These defects are caused by plastics deformation coupled with shear and impact forces generated by the ball-milling media.[60] The powders are, therefore, disintegrated into smaller particles with large surface area, where very clean or fresh oxygen-free active surfaces of the powders are created. Moreover, these defects, which are intensively located at the grain boundaries, lead to separate micro-scaled Mg grains into finer grains capable to getter hydrogen by the first atomically clean surfaces to form MgH2 nanopowders.

Fig.9.5 illustrates common lab scale procedure for preparing MgH2 powders, starting from pure Mg powders, using RBM via (1) high-energy and (2) low-energy ball milling. The starting material can be Mg-rods, in which they are processed via sever plastic deformation,[61] using for example cold-rolling approach,[62] as illustrated in Fig.9.5. The heavily deformed Mg-rods obtained after certain cold rolling passes can be snipped into small chips and then ball-milled under hydrogen gas to produce MgH2 powders.[8]

Planetary ball mills are the most popular mills used in scientific research for synthesizing MgH2 nanopowders. In this type of mill, the ball-milling media have considerably high energy, because milling stock and balls come off the inner wall of the vial and the effective centrifugal force reaches up to 20 times gravitational acceleration. The centrifugal forces caused by the rotation of the supporting disc and autonomous turning of the vial act on the milling charge (balls and powders). Since the turning directions of the supporting disc and the vial are opposite, the centrifugal forces alternately are synchronized and opposite. Therefore, the milling media and the charged powders alternatively roll on the inner wall of the vial, and are lifted and thrown off across the bowl at high speed.

In the typical experimental procedure, a certain amount of the Mg (usually in the range between 3 and 10g based on the vials volume) is balanced inside an inert gas atmosphere (argon or helium) in a glove box and sealed together with certain number of balls (e.g., 2050 hardened steel balls) into a hardened steel vial (Fig.9.5A and B), using, for example, a gas-temperature-monitoring system (GST). With the GST system, it becomes possible to monitor the progress of the gas-solid reaction taking place during the RBM process, as shown in Fig.9.5C and D. The temperature and pressure changes in the system during milling can be also used to realize the completion of the reaction and the expected end product during the different stages of milling (Fig.9.5D). The ball-to-powder weight ratio is usually selected to be in the range between 10:1 and 50:1. The vial is then evacuated to the level of 103bar before introducing H2 gas to fill the vial with a pressure of 550bar (Fig.9.5B). The milling process is started by mounting the vial on a high-energy ball mill operated at ambient temperature (Fig.9.5C).

Tumbling mill is cylindrical shell (Fig.9.6AC) that rotates about a horizontal axis (Fig.9.6D). Hydrogen gas is pressurized into the vial (Fig.9.6C) together with Mg powders and ball-milling media, using ball-to-powder weight ratio in the range between 30:1 and 100:1. Mg powder particles meet the abrasive and impacting force (Fig.9.6E), which reduce the particle size and create fresh-powder surfaces (Fig.9.6F) ready to react with hydrogen milling atmosphere.

Figure 9.6. Photographs taken from KISR-EBRC/NAM Lab, Kuwait, show (A) the vial and milling media (balls) and (B) the setup performed to charge the vial with 50bar of hydrogen gas. The photograph in (C) presents the complete setup of GST (supplied by Evico-magnetic, Germany) system prior to start the RBM experiment for preparing of MgH2 powders, using Planetary Ball Mill P400 (provided by Retsch, Germany). GST system allows us to monitor the progress of RBM process, as indexed by temperature and pressure versus milling time (D).

The useful kinetic energy in tumbling mill can be applied to the Mg powder particles (Fig.9.7E) by the following means: (1) collision between the balls and the powders; (2) pressure loading of powders pinned between milling media or between the milling media and the liner; (3) impact of the falling milling media; (4) shear and abrasion caused by dragging of particles between moving milling media; and (5) shock-wave transmitted through crop load by falling milling media. One advantage of this type of mill is that large amount of the powders (100500g or more based on the mill capacity) can be fabricated for each milling run. Thus, it is suitable for pilot and/or industrial scale of MgH2 production. In addition, low-energy ball mill produces homogeneous and uniform powders when compared with the high-energy ball mill. Furthermore, such tumbling mills are cheaper than high-energy mills and operated simply with low-maintenance requirements. However, this kind of low-energy mill requires long-term milling time (more than 300h) to complete the gas-solid reaction and to obtain nanocrystalline MgH2 powders.

Figure 9.7. Photos taken from KISR-EBRC/NAM Lab, Kuwait, display setup of a lab-scale roller mill (1000m in volume) showing (A) the milling tools including the balls (milling media and vial), (B) charging Mg powders in the vial inside inert gas atmosphere glove box, (C) evacuation setup and pressurizing hydrogen gas in the vial, and (D) ball milling processed, using a roller mill. Schematic presentations show the ball positions and movement inside the vial of a tumbler mall mill at a dynamic mode is shown in (E), where a typical ball-powder-ball collusion for a low energy tumbling ball mill is presented in (F).

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