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In all ore dressing and milling Operations, including flotation, cyanidation, gravity concentration, and amalgamation, the Working Principle is to crush and grind, often with rob mill & ball mills, the ore in order to liberate the minerals. In the chemical and process industries, grinding is an important step in preparing raw materials for subsequent treatment.In present day practice, ore is reduced to a size many times finer than can be obtained with crushers. Over a period of many years various fine grinding machines have been developed and used, but the ball mill has become standard due to its simplicity and low operating cost.

A ball millefficiently operated performs a wide variety of services. In small milling plants, where simplicity is most essential, it is not economical to use more than single stage crushing, because the Steel-Head Ball or Rod Mill will take up to 2 feed and grind it to the desired fineness. In larger plants where several stages of coarse and fine crushing are used, it is customary to crush from 1/2 to as fine as 8 mesh.

Many grinding circuits necessitate regrinding of concentrates or middling products to extremely fine sizes to liberate the closely associated minerals from each other. In these cases, the feed to the ball mill may be from 10 to 100 mesh or even finer.

Where the finished product does not have to be uniform, a ball mill may be operated in open circuit, but where the finished product must be uniform it is essential that the grinding mill be used in closed circuit with a screen, if a coarse product is desired, and with a classifier if a fine product is required. In most cases it is desirable to operate the grinding mill in closed circuit with a screen or classifier as higher efficiency and capacity are obtained. Often a mill using steel rods as the grinding medium is recommended, where the product must have the minimum amount of fines (rods give a more nearly uniform product).

Often a problem requires some study to determine the economic fineness to which a product can or should be ground. In this case the 911Equipment Company offers its complete testing service so that accurate grinding mill size may be determined.

Until recently many operators have believed that one particular type of grinding mill had greater efficiency and resulting capacity than some other type. However, it is now commonly agreed and accepted that the work done by any ballmill depends directly upon the power input; the maximum power input into any ball or rod mill depends upon weight of grinding charge, mill speed, and liner design.

The apparent difference in capacities between grinding mills (listed as being the same size) is due to the fact that there is no uniform method of designating the size of a mill, for example: a 5 x 5 Ball Mill has a working diameter of 5 inside the liners and has 20 per cent more capacity than all other ball mills designated as 5 x 5 where the shell is 5 inside diameter and the working diameter is only 48 with the liners in place.

Ball-Rod Mills, based on 4 liners and capacity varying as 2.6 power of mill diameter, on the 5 size give 20 per cent increased capacity; on the 4 size, 25 per cent; and on the 3 size, 28 per cent. This fact should be carefully kept in mind when determining the capacity of a Steel- Head Ball-Rod Mill, as this unit can carry a greater ball or rod charge and has potentially higher capacity in a given size when the full ball or rod charge is carried.

A mill shorter in length may be used if the grinding problem indicates a definite power input. This allows the alternative of greater capacity at a later date or a considerable saving in first cost with a shorter mill, if reserve capacity is not desired. The capacities of Ball-Rod Mills are considerably higher than many other types because the diameters are measured inside the liners.

The correct grinding mill depends so much upon the particular ore being treated and the product desired, that a mill must have maximum flexibility in length, type of grinding medium, type of discharge, and speed.With the Ball-Rod Mill it is possible to build this unit in exact accordance with your requirements, as illustrated.

To best serve your needs, the Trunnion can be furnished with small (standard), medium, or large diameter opening for each type of discharge. The sketch shows diagrammatic arrangements of the four different types of discharge for each size of trunnion opening, and peripheral discharge is described later.

Ball-Rod Mills of the grate discharge type are made by adding the improved type of grates to a standard Ball-Rod Mill. These grates are bolted to the discharge head in much the same manner as the standard headliners.

The grates are of alloy steel and are cast integral with the lifter bars which are essential to the efficient operation of this type of ball or rod mill. These lifter bars have a similar action to a pump:i. e., in lifting the product so as to discharge quickly through the mill trunnion.

These Discharge Grates also incorporate as an integral part, a liner between the lifters and steel head of the ball mill to prevent wear of the mill head. By combining these parts into a single casting, repairs and maintenance are greatly simplified. The center of the grate discharge end of this mill is open to permit adding of balls or for adding water to the mill through the discharge end.

Instead of being constructed of bars cast into a frame, Grates are cast entire and have cored holes which widen toward the outside of the mill similar to the taper in grizzly bars. The grate type discharge is illustrated.

The peripheral discharge type of Ball-Rod Mill is a modification of the grate type, and is recommended where a free gravity discharge is desired. It is particularly applicable when production of too many fine particles is detrimental and a quick pass through the mill is desired, and for dry grinding.

The drawings show the arrangement of the peripheral discharge. The discharge consists of openings in the shell into which bushings with holes of the desired size are inserted. On the outside of the mill, flanges are used to attach a stationary discharge hopper to prevent pulp splash or too much dust.

The mill may be operated either as a peripheral discharge or a combination or peripheral and trunnion discharge unit, depending on the desired operating conditions. If at any time the peripheral discharge is undesirable, plugs inserted into the bushings will convert the mill to a trunnion discharge type mill.

Unless otherwise specified, a hard iron liner is furnished. This liner is made of the best grade white iron and is most serviceable for the smaller size mills where large balls are not used. Hard iron liners have a much lower first cost.

Electric steel, although more expensive than hard iron, has advantage of minimum breakage and allows final wear to thinner section. Steel liners are recommended when the mills are for export or where the source of liner replacement is at a considerable distance.

Molychrome steel has longer wearing qualities and greater strength than hard iron. Breakage is not so apt to occur during shipment, and any size ball can be charged into a mill equipped with molychrome liners.

Manganese liners for Ball-Rod Mills are the world famous AMSCO Brand, and are the best obtainable. The first cost is the highest, but in most cases the cost per ton of ore ground is the lowest. These liners contain 12 to 14% manganese.

The feed and discharge trunnions are provided with cast iron or white iron throat liners. As these parts are not subjected to impact and must only withstand abrasion, alloys are not commonly used but can be supplied.

Gears for Ball-Rod Mills drives are furnished as standard on the discharge end of the mill where they are out of the way of the classifier return, scoop feeder, or original feed. Due to convertible type construction the mills can be furnished with gears on the feed end. Gear drives are available in two alternative combinations, which are:

All pinions are properly bored, key-seated, and pressed onto the steel countershaft, which is oversize and properly keyseated for the pinion and drive pulleys or sheaves. The countershaft operates on high grade, heavy duty, nickel babbitt bearings.

Any type of drive can be furnished for Ball-Rod Mills in accordance with your requirements. Belt drives are available with pulleys either plain or equipped with friction clutch. Various V- Rope combinations can also be supplied.

The most economical drive to use up to 50 H. P., is a high starting torque motor connected to the pinion shaft by means of a flat or V-Rope drive. For larger size motors the wound rotor (slip ring) is recommended due to its low current requirement in starting up the ball mill.

Should you be operating your own power plant or have D. C. current, please specify so that there will be no confusion as to motor characteristics. If switches are to be supplied, exact voltage to be used should be given.

Even though many ores require fine grinding for maximum recovery, most ores liberate a large percentage of the minerals during the first pass through the grinding unit. Thus, if the free minerals can be immediately removed from the ball mill classifier circuit, there is little chance for overgrinding.

This is actually what has happened wherever Mineral Jigs or Unit Flotation Cells have been installed in the ball mill classifier circuit. With the installation of one or both of these machines between the ball mill and classifier, as high as 70 per cent of the free gold and sulphide minerals can be immediately removed, thus reducing grinding costs and improving over-all recovery. The advantage of this method lies in the fact that heavy and usually valuable minerals, which otherwise would be ground finer because of their faster settling in the classifier and consequent return to the grinding mill, are removed from the circuit as soon as freed. This applies particularly to gold and lead ores.

Ball-Rod Mills have heavy rolled steel plate shells which are arc welded inside and outside to the steel heads or to rolled steel flanges, depending upon the type of mill. The double welding not only gives increased structural strength, but eliminates any possibility of leakage.

Where a single or double flanged shell is used, the faces are accurately machined and drilled to template to insure perfect fit and alignment with the holes in the head. These flanges are machined with male and female joints which take the shearing stresses off the bolts.

The Ball-Rod Mill Heads are oversize in section, heavily ribbed and are cast from electric furnace steel which has a strength of approximately four times that of cast iron. The head and trunnion bearings are designed to support a mill with length double its diameter. This extra strength, besides eliminating the possibility of head breakage or other structural failure (either while in transit or while in service), imparts to Ball-Rod Mills a flexibility heretofore lacking in grinding mills. Also, for instance, if you have a 5 x 5 mill, you can add another 5 shell length and thus get double the original capacity; or any length required up to a maximum of 12 total length.

On Type A mills the steel heads are double welded to the rolled steel shell. On type B and other flanged type mills the heads are machined with male and female joints to match the shell flanges, thus taking the shearing stresses from the heavy machine bolts which connect the shell flanges to the heads.

The manhole cover is protected from wear by heavy liners. An extended lip is provided for loosening the door with a crow-bar, and lifting handles are also provided. The manhole door is furnished with suitable gaskets to prevent leakage.

The mill trunnions are carried on heavy babbitt bearings which provide ample surface to insure low bearing pressure. If at any time the normal length is doubled to obtain increased capacity, these large trunnion bearings will easily support the additional load. Trunnion bearings are of the rigid type, as the perfect alignment of the trunnion surface on Ball-Rod Mills eliminates any need for the more expensive self-aligning type of bearing.

The cap on the upper half of the trunnion bearing is provided with a shroud which extends over the drip flange of the trunnion and effectively prevents the entrance of dirt or grit. The bearing has a large space for wool waste and lubricant and this is easily accessible through a large opening which is covered to prevent dirt from getting into the bearing.Ball and socket bearings can be furnished.

Scoop Feeders for Ball-Rod Mills are made in various radius sizes. Standard scoops are made of cast iron and for the 3 size a 13 or 19 feeder is supplied, for the 4 size a 30 or 36, for the 5 a 36 or 42, and for the 6 a 42 or 48 feeder. Welded steel scoop feeders can, however, be supplied in any radius.

The correct size of feeder depends upon the size of the classifier, and the smallest feeder should be used which will permit gravity flow for closed circuit grinding between classifier and the ball or rod mill. All feeders are built with a removable wearing lip which can be easily replaced and are designed to give minimum scoop wear.

A combination drum and scoop feeder can be supplied if necessary. This feeder is made of heavy steel plate and strongly welded. These drum-scoop feeders are available in the same sizes as the cast iron feeders but can be built in any radius. Scoop liners can be furnished.

The trunnions on Ball-Rod Mills are flanged and carefully machined so that scoops are held in place by large machine bolts and not cap screws or stud bolts. The feed trunnion flange is machined with a shoulder for insuring a proper fit for the feed scoop, and the weight of the scoop is carried on this shoulder so that all strain is removed from the bolts which hold the scoop.

High carbon steel rods are recommended, hot rolled, hot sawed or sheared, to a length of 2 less than actual length of mill taken inside the liners. The initial rod charge is generally a mixture ranging from 1.5 to 3 in diameter. During operation, rod make-up is generally the maximum size. The weights per lineal foot of rods of various diameters are approximately: 1.5 to 6 lbs.; 2-10.7 lbs.; 2.5-16.7 lbs.; and 3-24 lbs.

Forged from the best high carbon manganese steel, they are of the finest quality which can be produced and give long, satisfactory service. Data on ball charges for Ball-Rod Mills are listed in Table 5. Further information regarding grinding balls is included in Table 6.

Rod Mills has a very define and narrow discharge product size range. Feeding a Rod Mill finer rocks will greatly impact its tonnage while not significantly affect its discharge product sizes. The 3.5 diameter rod of a mill, can only grind so fine.

Crushers are well understood by most. Rod and Ball Mills not so much however as their size reduction actions are hidden in the tube (mill). As for Rod Mills, the image above best expresses what is going on inside. As rocks is feed into the mill, they are crushed (pinched) by the weight of its 3.5 x 16 rods at one end while the smaller particles migrate towards the discharge end and get slightly abraded (as in a Ball Mill) on the way there.

We haveSmall Ball Mills for sale coming in at very good prices. These ball mills are relatively small, bearing mounted on a steel frame. All ball mills are sold with motor, gears, steel liners and optional grinding media charge/load.

Ball Mills or Rod Mills in a complete range of sizes up to 10 diameter x20 long, offer features of operation and convertibility to meet your exactneeds. They may be used for pulverizing and either wet or dry grindingsystems. Mills are available in both light-duty and heavy-duty constructionto meet your specific requirements.

All Mills feature electric cast steel heads and heavy rolled steelplate shells. Self-aligning main trunnion bearings on large mills are sealedand internally flood-lubricated. Replaceable mill trunnions. Pinion shaftbearings are self-aligning, roller bearing type, enclosed in dust-tightcarrier. Adjustable, single-unit soleplate under trunnion and drive pinionsfor perfect, permanent gear alignment.

Ball Mills can be supplied with either ceramic or rubber linings for wet or dry grinding, for continuous or batch type operation, in sizes from 15 x 21 to 8 x 12. High density ceramic linings of uniform hardness male possible thinner linings and greater and more effective grinding volume. Mills are shipped with liners installed.

Complete laboratory testing service, mill and air classifier engineering and proven equipment make possible a single source for your complete dry-grinding mill installation. Units available with air swept design and centrifugal classifiers or with elevators and mechanical type air classifiers. All sizes and capacities of units. Laboratory-size air classifier also available.

A special purpose batch mill designed especially for grinding and mixing involving acids and corrosive materials. No corners mean easy cleaning and choice of rubber or ceramic linings make it corrosion resistant. Shape of mill and ball segregation gives preferential grinding action for grinding and mixing of pigments and catalysts. Made in 2, 3 and 4 diameter grinding drums.

Nowadays grinding mills are almost extensively used for comminution of materials ranging from 5 mm to 40 mm (3/161 5/8) down to varying product sizes. They have vast applications within different branches of industry such as for example the ore dressing, cement, lime, porcelain and chemical industries and can be designed for continuous as well as batch grinding.

Ball mills can be used for coarse grinding as described for the rod mill. They will, however, in that application produce more fines and tramp oversize and will in any case necessitate installation of effective classification.If finer grinding is wanted two or three stage grinding is advisable as for instant primary rod mill with 75100 mm (34) rods, secondary ball mill with 2540 mm(11) balls and possibly tertiary ball mill with 20 mm () balls or cylpebs.To obtain a close size distribution in the fine range the specific surface of the grinding media should be as high as possible. Thus as small balls as possible should be used in each stage.

The principal field of rod mill usage is the preparation of products in the 5 mm0.4 mm (4 mesh to 35 mesh) range. It may sometimes be recommended also for finer grinding. Within these limits a rod mill is usually superior to and more efficient than a ball mill. The basic principle for rod grinding is reduction by line contact between rods extending the full length of the mill, resulting in selective grinding carried out on the largest particle sizes. This results in a minimum production of extreme fines or slimes and more effective grinding work as compared with a ball mill. One stage rod mill grinding is therefore suitable for preparation of feed to gravimetric ore dressing methods, certain flotation processes with slime problems and magnetic cobbing. Rod mills are frequently used as primary mills to produce suitable feed to the second grinding stage. Rod mills have usually a length/diameter ratio of at least 1.4.

Tube mills are in principle to be considered as ball mills, the basic difference being that the length/diameter ratio is greater (35). They are commonly used for surface cleaning or scrubbing action and fine grinding in open circuit.

In some cases it is suitable to use screened fractions of the material as grinding media. Such mills are usually called pebble mills, but the working principle is the same as for ball mills. As the power input is approximately directly proportional to the volume weight of the grinding media, the power input for pebble mills is correspondingly smaller than for a ball mill.

A dry process requires usually dry grinding. If the feed is wet and sticky, it is often necessary to lower the moisture content below 1 %. Grinding in front of wet processes can be done wet or dry. In dry grinding the energy consumption is higher, but the wear of linings and charge is less than for wet grinding, especially when treating highly abrasive and corrosive material. When comparing the economy of wet and dry grinding, the different costs for the entire process must be considered.

An increase in the mill speed will give a directly proportional increase in mill power but there seems to be a square proportional increase in the wear. Rod mills generally operate within the range of 6075 % of critical speed in order to avoid excessive wear and tangled rods. Ball and pebble mills are usually operated at 7085 % of critical speed. For dry grinding the speed is usually somewhat lower.

The mill lining can be made of rubber or different types of steel (manganese or Ni-hard) with liner types according to the customers requirements. For special applications we can also supply porcelain, basalt and other linings.

The mill power is approximately directly proportional to the charge volume within the normal range. When calculating a mill 40 % charge volume is generally used. In pebble and ball mills quite often charge volumes close to 50 % are used. In a pebble mill the pebble consumption ranges from 315 % and the charge has to be controlled automatically to maintain uniform power consumption.

In all cases the net energy consumption per ton (kWh/ton) must be known either from previous experience or laboratory tests before mill size can be determined. The required mill net power P kW ( = ton/hX kWh/ton) is obtained from

Trunnions of S.G. iron or steel castings with machined flange and bearing seat incl. device for dismantling the bearings. For smaller mills the heads and trunnions are sometimes made in grey cast iron.

The mills can be used either for dry or wet, rod or ball grinding. By using a separate attachment the discharge end can be changed so that the mills can be used for peripheral instead of overflow discharge.

mill charge - an overview | sciencedirect topics

mill charge - an overview | sciencedirect topics

Rod mill charges usually occupy about 45% of the internal volume of the mill. A closely packed charge of single sized rods will have a porosity of 9.3%. With a mixed charge of small and large diameter rods, the porosity of a static load could be reduced even further. However, close packing of the charge rarely occurs and an operating bed porosity of 40% is common. Overcharging results in poor grinding and losses due to abrasion of rods and liners. Undercharging also promotes more abrasion of the rods. The height (or depth) of charge is measured in the same manner as for ball mill. The size of feed particles to a rod mill is coarser than for a ball mill. The usual feed size ranges from 6 to 25mm.

For the efficient use of rods it is necessary that they operate parallel to the central axis and the body of the mill. This is not always possible as in practice, parallel alignment is usually hampered by the accumulation of ore at the feed end where the charge tends to swell. Abrasion of rods occurs more in this area resulting in rods becoming pointed at one end. With this continuous change in shape of the grinding charge, the grinding characteristics are impaired.

The bulk density of a new rod charge is about 6.25t/m3. With time due to wear the bulk density drops. The larger the mill diameter the greater is the lowering of the bulk density. For example, the bulk density of worn rods after a specific time of grinding would be 5.8t/m3 for a 0.91m diameter mill. Under the same conditions of operation, the bulk density would be 5.4t/m3 for a 4.6m diameter mill.

During normal operation the mill speed tends to vary with mill charge. According to available literature, the operating speeds of AG mills are much higher than conventional tumbling mills and are in the range of 8085% of the critical speed. SAG mills of comparable size but containing say 10% ball charge (in addition to the rocks), normally, operate between 70 and 75% of the critical speed. Dry Aerofall mills are run at about 85% of the critical speed.

The breakage of particles depends on the speed of rotation. Working with a 7.32m diameter and 3.66m long mill, Napier-Munn etal. [4] observed that the breakage rate for the finer size fractions of ore (say 0.1mm) at lower speeds (e.g., 55% of the critical speed) was higher than that observed at higher speeds (e.g., 70% of the critical speed). For larger sizes of ore (in excess of 10mm), the breakage rate was lower for mills rotating at 55% of the critical speed than for mills running at 70% of the critical speed. For a particular intermediate particle sizerange, indications are that the breakage rate was independent of speed. The breakage ratesize relation at two different speeds is reproduced in Figure9.7.

The blending of different ore types is a common practice to provide a consistent feed to a process in terms of uniform hardness or assay. When several different ore deposits of varying grindabilities are blended prior to closed circuit grinding, the work index of the ore is not an average or even a weighted average of the work indices of the components. The reason for this is that the circulating load will consist predominantly of the harder component and if the circulating load is high then the mill charge will also consist of mostly the harder components. Thus, the work index of the blend will be weighted towards the harder components [39]. Figure3.16 shows the Bond work index of a blend of hard and soft ores as a function of the volume fraction of the softer ore in the blend. The dotted line between the two extremes indicates the weighted average work index based on volume fraction. The work index values of the Magdalinovic method agree with this average Bond work index because the method does not simulate the recycling of harder components into the mill charge. On the other hand, the work index obtained using the standard Bond test shows the weighting of the work index towards the harder component as a result of the circulating load.

Yan and Eaton [39] also measured the breakage rates and breakage distribution functions of the different ore blends in order to predict the work index of the blend by simulation of the Bond batch grinding test. Qualitative analysis of the breakage properties suggests that there is an interaction between the components of the blend that affect their individual breakage rates. The breakage properties of the harder material appear to have a greater influence on the overall breakage properties and the Bond work index of the blend than the softer material.

Whereas most of the ball-milled systems usually prepared with using ball-to-powder weight ratio (Wb:Wp) in the range between 10:1 and 20:1, the effect Wb:Wp on the amorphization reaction of Al50Ta50 alloy powders in a low-energy ball mill was investigated in 1991 by El-Eskandarany etal.[42] They have used 90, 30, 20, 10, and 3g of powders to obtain Wb:Wp ratios of 12:1, 36:1, 54:1, 108:1, and 324:1, respectively.

The XRD patterns of mechanically alloyed Al50Ta50 powders as ball-milled for 1440ks (400h) as a function of the Wb:Wp ratio is presented in Fig.4.32. Single phase of amorphous alloys is obtained when ratios 36:1 and 108:1 were used. The Bragg peaks of elemental Al and Ta crystals still appear when the Wb:Wp ratio is 12:1, indicating that the amorphization reaction is not completed. In contrast, when the Wb:Wp ratio is 324:1, the amorphous phase coexists with the crystalline phases of AlTa, AlTa2, and AlTaFe.

Based on their results,[42] it is concluded that the rate of amorphization depends strongly on the kinetic energy of the ball mill charge and this depends on the number of opportunities for the powder particles to be reacted and interdiffused. Increasing the Wb:Wp ratio accelerates the rate of amorphization, which is explained by the increase in the kinetic energy of the ball mill charge per unit mass of powders. It has been shown in this study that the volume fraction of the amorphous phase in the mechanically alloyed ball-milled powders increases during the early stage of milling, 86173ks (48h) with increasing Wb:Wp ratio. It is noted that further increasing this weight ratio leads to the formation of crystalline phases and this might be related to the high kinetic energy of the ball mill charge which is transformed into heat. When the Wb:Wp ratio was reduced to 12:1, however, the amorphization reaction was not completed. This indicates that the kinetic energy of the mill charge is insufficient for complete transition from the crystalline to the amorphous phase.

It is worth noting that powder particles reached the minimum of extreme fineness when using a high Wb:Wp ratio. One disadvantage of using such a high weight ratio is being the high concentration of iron contamination which is introduced to the milled powders during the MA process, as presented in Fig.4.33.

Romankova etal.[43] have applied the vibration ball milling for coating of stainless steel balls during milling of TiAl powders. They examined metallographically the development of the TiAl coating structure after milling for 60min as a function of the ball-to-powder weight ratio for 6mm balls (Fig.4.34).

The results showed that the milling energy increased with increasing the number of balls. When the weight ratio was 3:1, the substrate could be covered with a thin Al layer (Fig.4.34A). For this case, only small Ti particles were embedded into the Al matrix. It should be noted that the substrate underwent plastic deformation under the ball impacts and its surface became slightly bent. When the weight ratio was increased to 4:1, the energy was sufficient to embed larger Ti particles in the Al layer than at ratio 3:1 (Fig.4.34B). Al bound these Ti particles to the substrate. They notified that, at the 4:1 ratio, the growth for the TiAl coating across the substrate was clustered; this resulted in a hillock-like morphology and increased the surface roughness. Upon further increasing the ball-to-powder weight ratio from 6:1 to 14:1, the coating roughness gradually decreased. They also reported that the lamellar structure was refined when the ball-to-powder weight ratio was 14:1, as presented in Fig.4.34E.

More recently, Waje etal.[44] have studied the effect of the ball-to-powder weight ratio (BPR) on the crystallite size of ball-milled CoFe2O4 nanoparticles, using XRD (Fig.4.35). From their results it can be seen that the particle size decreases linearly from 15.3 to 11.4nm when used BPR of 8:1 and 30:1, respectively.

The mass-size balance models as written above are in the time-domain. To be more practical they need to be converted to the energy-domain. One way is by arguing that the specific rate of breakage parameter is proportional to the net specific power input to the mill charge (Herbst and Fuerstenau, 1980; King, 2012). For a batch mill this becomes:

where SiE is the energy-specific rate of breakage parameter, P the net power drawn by the mill, and M the mass of charge in the mill excluding grinding media (i.e., just the ore). The energy-specific breakage rate is commonly given in t kWh1. For a continuous mill, the relationship is:

where is the mean retention time, and F the solids mass flow rate through the mill. Assuming plug flow, Eq. (5.17) can be substituted into Eq. (5.15) to apply to a grinding mill in closed circuit (where t=).

The distinctive feature of tumbling mills is the use of loose crushing bodies, which are large, hard, and heavy in relation to the ore particles, but small in relation to the volume of the mill, and which occupy (including voids) slightly less than half the volume of the mill.

Due to the rotation and friction of the mill shell, the grinding medium is lifted along the rising side of the mill until a position of dynamic equilibrium is reached (the shoulder), when the bodies cascade and cataract down the free surface of the other bodies, about a dead zone where little movement occurs, down to the toe of the mill charge (Figure 7.3).

The driving force of the mill is transmitted via the liner to the charge. The speed at which a mill is run and the liner design governs the motion and thus nature of the product and the amount of wear on the shell liners. For instance, a practical knowledge of the trajectories followed by the steel balls in a mill determines the speed at which it must be run in order that the descending balls shall fall on to the toe of the charge, and not on to the liner, which could lead to liner damage. Simulation of charge motion can be used to identify such potential problems (Powell et al., 2011), and acoustic monitoring can give indication of where ball impact is occurring (Pax, 2012).

At relatively low speeds, or with smooth liners, the medium tends to roll down to the toe of the mill and essentially abrasive comminution occurs. This cascading leads to finer grinding and increased liner wear. At higher speeds the medium is projected clear of the charge to describe a series of parabolas before landing on the toe of the charge. This cataracting leads to comminution by impact and a coarser end product with reduced liner wear. At the critical speed of the mill centrifuging occurs and the medium is carried around in an essentially fixed position against the shell.

In traveling around inside the mill, the medium (and the large ore pieces) follows a path which has two parts: the lifting section near to the shell liners, which is circular, and the drop back to the toe of the mill charge, which is parabolic (Figure 7.4(a)).

Consider a ball (or rod) of radius r meters, which is lifted up the shell of a mill of radius R meters, revolving at N rev min1. The ball abandons its circular path for a parabolic path at point P (Figure 7.4(b)), when the weight of the ball is just balanced by the centrifugal force, that is when:

Mills are driven, in practice, at speeds of 5090% of critical speed. The speed of rotation of the mill influences the power draw through two effects: the value of N and the shift in the center of gravity with speed. The center of gravity first starts to shift away from the center of the mill (to the right in Figure 7.4(a)) as the speed of rotation increases, causing the torque exerted by the charge to increase and draw more power (see Section 7.2.2). But, as critical speed is reached, the center of gravity moves toward the center of the mill as more and more of the material is held against the shell throughout the cycle, causing power draw to decrease. Since grinding effort is related to grinding energy, there is little increase in efficiency (i.e., delivered kWh t1) above about 4050% of the critical speed. It is also essential that the cataracting medium should fall well inside the mill charge and not directly onto the liner, thus excessively increasing steel consumption.

At the toe of the load the descending liner continuously underruns the churning mass, and moves some of it into the main mill charge. The medium and ore particles in contact with the liners are held with more firmness than the rest of the charge due to the extra weight bearing down on them. The larger the ore particle, rod, or ball, the less likely it is to be carried to the breakaway point by the liners. The cataracting effect should thus be applied in terms of the medium of largest diameter.

As already discussed, this control loop is provided to maintain the PA header pressure before the mixing of hot and cold PA duly controlled for temperature. FigureVIII/4-2 is also applicable for this type of mill when the PA is common to all the mills. The control loop is of course different for individual PA fan systems, as the above is applicable for the common PA system only. For control loop description, see Section 4.3.2.3 of this chapter. Common PA fans are provided with suction normally from the atmosphere or it may be from the FD discharge header. Header pressure control is performed through various types of final control elements.

As the fuel/load control is solely done by position adjustments to the PA damper near the mill, this control loop assists smooth and bumpless control of the fuel flow transported by the PA flow to the mill as the upstream PA header pressure control takes responsibility for providing an adequate quantity of air at any environmental condition without sacrificing the required downstream pressure,

FigureVIII/5.3-3 later in the chapter depicts the simple control loop. Any of the mill DP transmitters or level (sound-detector) transmitters is selected and the selected signal is connected to the controller as the process or measured variables against a fixed-level set point. Sufficient redundancy in measurement may vary according to the plants operating philosophy. The controller output is utilized for adjustment of feeder speed with the help of a VFD or SCR control for the gravimetric feeder/feeder speed variator.

At the higher load the charge level inside the drum decreases and the feeder speed should increase accordingly to replenish the material. For a decreasing load, the reverse action takes place. To take care of the sudden load change, the deviation between characterized PA flow and DP acrossthe mill is used to modify the controller output to achieve the desired mill charge level.

Mill load or fuel flow control follows the fuel demand from the boiler master demand control signal and is achieved by regulating the quantity of PA that is transporting agent only. Figures VIII/5.2-4 and VIII/5.2-4 depict the functioning of the control loop, which is similar to that of other mill types. For other mills the fuel demand signal from the boiler master demand is first taken care of by the mill-wise PA flow control system if the demand is less than the prevailing air flow control system. The characterized PA flow is then construed as the feeder speed demand. The ball-and-tube mill control system, on the other hand, uses feeder speed control for maintaining mill level control only and so the fuel flow control is achieved through control of the feeder-wise PA flow to mill itself.

However, the feeder-wise PA flow as measured after redundant transmitters voting selection and density compensated through temperature correction is again determined to get equivalent fuel flow. The total fuel flow is then computed by summing all the fuel (PF) flow of the running feeders and the supporting fuel (oil or gas) if any are being utilized at that time with proper weightage, taking consideration of their thermal or calorific value. The higher selection of this total equivalent fuel flow signal and the air flow demand signal from the boiler master demand (FigureVIII/2.1) is then taken as actual air demand just as in other type of mills.

As already discussed in Section 5.2.1, there is another feeder-wise control system associated with fuel flow control known as a bypass damper control. This feeder-wise damper is provided for each mill end for preheating the raw feed, which is an essential requirement during startup. No process measurement signal is utilized in this subloop. The same fuel demand from the boiler master demand (FigureVIII/ 2-1) is taken as the set point for the position demand of the bypass damper after due characterization, as shown (refer to Figures VIII/5.2-4 and VIII/5.2-5) in the control strategy and the graphical representation of approximate positions of the two final control elements. The previously mentioned two-position demands operate in opposite directions. After being in a fully open position for a certain load, ensuring elimination of initial moisture, this bypass damper begins to close gradually as the load increases.

There are two main types of fuel flow controls achieved through the proportionate PA flow only: (1) common PA fans with individual PA dampers and (2) individual PA fans with vane or speed control. There is also one known as a mill-wise PA flow control that is common to both sides.

FigureVIII/5.2-4 may be referred to for this type of control along with FigureVIII/5.2-2. Here the mill PA flow and bypass PA flows are combined to form the total mill-wise PA flow to the furnace. The boiler master demand acts as a set point here, where the mill-wise PA flow is the measured value as this air flow is only responsible for transporting the fuel to the furnace. The controller output is the demand signal for the individual PA damper. For bypass dampers, the boiler master demand generates the set point while the actual position of this damper acts as the measured value for the controller output, which is the demand signal for the bypass damper.

For any load change, the two flows readjust their positions to deliver the required PA flow. For higher load the bypass damper tends to close to allow less flow for preheating of raw feed and the PA damper to the mill opens more to take care of the load demand.

FigureVIII/5.2-5 may be referred to for this type of control along with FigureVIII/5.2-2(a). Here bypass PA flows need to be subtracted from the total mill-wise PA flow for the fuel flow control, and the total mill-wise PA flow to the furnace is required for air flow control. The reason for this is that the final control element and the flow element are both located in the common primary air path to the individual mill. The boiler master demand acts as a set point here, where the PA flow to the mill is the measured value. The controller output is the demand signal for the individual PA vane or variable speed drive as the case may be.

This type of mill design vis--vis operation is somewhat different from other types, as discussed earlier. FigureVIII/5.2-2(b), which is mainly followed by manufacturers, such as the Foster Wheeler Energy AG corporation, may be referred to for information. Here the boiler combustion control signal regulates the output of the mill by PA flow control dampers placed in the common line to both the ends or sides. The predrying of coal feed is done at the entry of each side before it enters the drum, unlike what is done by the bypass PA damper in many types of tube mills.

Another significant difference is the provision of an auxiliary air and purge air supply line taken from the cold PA for each side of the mill drum. The same is designed to the required minimum velocities of the PA/fuel mixture for maintaining proper flow inside the coal duct and to prevent fuel settling during startup or in extreme low-load operation. This feature extends the individual mill load range without encountering drifting or pulsating fuel flow to the burners. The other purpose is to purge the coal air line automatically when burners are taken out of service.

The feed level control in the drum, classifier outlet temperature control, and seal air DP control are very much similar to those in the other type of mills with the exception of the source of the seal air. Here the seal air supply is taken from the cold PA without any provision of a seal air fan.

Selecting dispersion equipment for a specific application is a complex task. Dispersion of the mixture must be complete and the process and equipment must meet economic constraints. But much more is involved. In practice, such simple criteria are complicated by a variety of parameters related to fillers and to the materials in which they are dispersed. These parameters complicate the problem to the degree that it is not easy to formulate general guidelines. In this discussion we will consider the available equipment types most frequently used for filler dispersion and illustrate their applicability with some examples.

A ball mill is an effective means of dispersing solid materials in solids or liquids.8,9 Ball mills have several advantages which include versatility, low cost of labor and maintenance, the possibility of unsupervised running, no loss of volatiles, and a clean process. The disadvantages are related to discharging viscous and thixotropic mixtures, and considerably lower efficiency when compared with other mixing equipment. The millbase viscosity is usually restricted to about 15-20 Poise, and therefore ball mills are most frequently found in production applications such as paints, flexographic, publication gravure, and letterpress news inks, and carbon paper inks which are dispersed at elevated temperatures.

The mill should rotate at 50-65% of the theoretical centrifugal speed in order to allow balls to cascade, since the cascading balls grind most effectively and do not cause an excessive loss of ball material

Viscosity, the order of filler addition, and the quantity of material should be chosen so as not to cause a viscosity increase above the specified range, since the milling efficiency drastically decreases at that point

The degree of dispersion and jetness achieved when grinding carbon black depends on the wetting properties of the dispersing material and to some degree on the filler form. For instance, pelletized carbon black is easier to disperse than a fluffy type

The sandmill has some drawbacks. It is a two stage process (premixing followed by milling). Milling develops high temperatures in the mixture which causes loss of volatiles and requires cooling. If the millbase is high in viscosity or dilatant, the sandmill process may not work at all. Agglomerated or extremely hard pigments are difficult or impossible to disperse

Both ball and sand mills operate based on a viscous shear principle, thus the viscosity of the millbase is a critical factor in achieving dispersion. The size of filler particles is critical, especially in sandmills. It was found that the shearing force is inversely proportional to the square of the linear size of filler agglomerate. An agglomerate of diameter of 7 m attains 100 times the shear stress of an agglomerate of 70 m diameter. The difference between the ball mill and the sand mill is in the size and density of the grinding media, which is reflected in their performance. Sandmilling uses small particles of low density, and therefore, there is no noticeable reduction in the size of the sand particle, whereas the balls in ballmills are very much larger and may have a high density (steel), which results in a more complex mechanism of grinding including shattering and impacting which cause this mill to be more effective in disintegrating hard particles and agglomerates containing sintered particles.

There is another mill type called an attritor, which is similar to both the ball mill and the sandmill. In construction, it is similar to a sandmill. It also has a vertical shaft, but in the attritor the agitator bars replace the milling discs of the sandmill. It is also similar to a ball mill because it uses balls, usually ceramic ones having 5-15 mm in diameter. Because the motion of the balls is independent of gravity, an attritor can handle thixotropic materials and slightly higher viscosity of millbases, but the principle of action and type of forces operating are similar to those of the ball mill. An attritor applied to pigment dispersion gives several advantages. These include rapid dispersion, the possibility of either a continuous or batch process, low power consumption, small floor space, and easy cleaning and maintenance. Their main disadvantage is high heat generation. Attritors are equipped with a cooling water jacket which can control the heat flow to some extent, but conditions are often too severe for some resins, which may degrade during the process.

Three-roll, one-roll, and stone mills constitute a more mature dispersion technology still in use with medium viscosity millbases. A three-roll mill consists of the feed, center, and apron rolls. In roll mill operation:

The speeds of feed and apron rolls are adjustable, and each roll rotates with a different speed in order to induce shear in the material at the nip and facilitate the material transfer from one roll to the other

For mechanical reasons the gap between rolls cannot be less than 10 m and it usually ranges from 40 to 50 m.7 Small particles will not be affected as they pass through the nip, but agglomerates smaller than the distance between rolls will be disintegrated due to the shear stress imposed on the material

The one-roll mill works on a similar principle but the nip is regulated by a pressure bar. Shearing takes place between the roller and the shearing bar. Stone mills have similar principles of operation. The rotor turns on a stator to achieve shearing

With current raw materials, both the primary particles and agglomerates are very small, and if any positive action can be achieved during the milling process, it can only be done by affecting these small particles. It is thus necessary to operate these machines at very tight gaps which causes abrasion of the mechanical elements, rapid deterioration of equipment, and contamination of the product by the abraded material. This affects the properties of the millbase and the color of the product

The high-speed impeller or shear mixer is the most common equipment to prepare dispersions of solids in liquid. High speed shear mills and kinetic shear mills have retained their usefulness because of their ability to deagglomerate material that is not adequately dispersed in the premixing step. A high-speed shear mill is composed of two elements a container and an impeller. These factors are important in the design:

In the first stage, the viscosity changes from low to high as fillers are incorporated; in the second stage, viscosity remains constantly high because of the disintegration of particles which occurs during the application of the highest shear stress

Long mixing increases temperature and decreases viscosity. This does not provide the conditions for the best filler dispersion. By extending mixing over, for example, a 15 min period, the degree of dispersion is not improved, but the resin may actually be degraded

If the quality of dispersion is not satisfactory, the parameters of mixing should be changed. If the expected result cannot be attained, the range of conditions available is not adequate in this particular mill

In the third stage, the viscosity changes from high to low due to the addition of diluent. The viscosity range which can be handled by high speed mixers is similar to the range of a three-roll mill, i.e., up to about 200 Poise

The range of shear rates available in high-speed mixers is not broad. The flow rate of fluid in motion decreases as viscosity increases and is inversely proportional to the width of the flow passage which, in this case, is the distance between the disperser and the container which is very large in a high speed mixer. It is not so much due to an improvement in mixing equipment that high-speed mixers have become so popular, it is mostly because of the high quality raw materials (pigments, fillers) which are available now. High structure carbon blacks can be more easily dispersed. But with the increased structure, the size of the primary particles decreases, inhibiting dispersion. Because of the interrelation between both parameters, only the medium structure, coarser particles of carbon blacks can be dispersed by high-speed mixers. Other carbon black types demand further treatment. It should be noted that this is only true of a few fillers which are known to possess strongly bonded, small sized particles. In most cases, fillers can be successfully dispersed in high-speed mixers. However, care should be taken that the filler is selected with an appropriate particle size.

High-speed mixers have several important advantages over other existing equipment including the possibility of processing a batch in the same vessel, easy cleaning, and flexibility in color changes. The main disadvantage is that the final dispersion depends greatly on the chosen composition and technology, and these are sometimes limiting factors. Frequently, the proper conditions for quality dispersion cannot be achieved at all.

The basic construction of a high-speed mixer can easily be modified to one's special requirements. For example, a change from impeller to turbine rotor changes both the principle of dispersion and the range of application. The tangential velocities of filler particles can be as high as 500 m/sec. Such particles have a very high kinetic energy, sufficient to cause size reduction. Size reduction is due to particle-particle or particle-wall collisions, and this in turn, is related in efficiency to the relative velocities at the moment of collision. Relative velocity can be increased by decreasing the viscosity of the millbase. The upper limit of millbase viscosity is somewhere around 3 to 4 Poise. It is not viscosity alone which is important but the entire rheological character of the millbase. The best results are obtained when the millbase is nearly Newtonian. For this reason, the dispersion process is best performed in a diluted millbase. As is the case with high-speed mixers, a proper dispersion should be achieved in a matter of 10-20 min. If such is not the case, the conditions of processing should be modified. Once dispersion has been achieved, it should be stabilized, with the mixer continuously running, by the addition of more resin to increase the viscosity in order to prevent sedimentation or flocculation of the pigment.

The other possible modification to such a mixer can be achieved by a substantial lowering of the speed and a change in the motion of the mixing element to planetary. This configuration can process material of a much higher viscosity, up to several thousand Poise. The high speed mixer can be modified in various ways to match its capabilities to the process requirements. Stationary baffles may be added to increase the shear rate. The distance between the rotating and stationary elements can be decreased again increasing the shear rate. The mixer may be designed to work under both pressure and vacuum and with inert gas blanketing which permits deaeration and processing of volatile or moisture sensitive materials.

The other group includes heavy-duty mixers, such as the Banbury mixer and double-arm kneading mixers. The Banbury mixer with a power input of up to 6000 kW/m3 is the strongest and the most powerful mixing unit used by industry. Nearly solid materials are mixed by a rotor which is a heavy shaft with stubby blades rotating at up to 40 rpm. The clearance between the walls and rotor is very small, which induces a very high shear in the material. The high shear generates a great amount of heat which melts the polymer rapidly and allows for quick incorporation of filler. After the filler is incorporated, the dispersion process begins, with rapid distributive mixing along and between two rotors and between the chamber walls and rotor tips. Within 2-3 min, mixing is normally completed and the compound discharged into a pelletizing extruder or a two-roll mill which converts it to a sheet form.8 Carbon black, which is most frequently processed in a Banbury mixer, is usually placed between two layers of polymeric material in order to reduce dusting.

Double-arm kneading mixers are very popular in some industries. They consist of two counter-rotating blades in a rectangular trough carved at the bottom to form two longitudinal half cylinders and a saddle section. A variety of blade shapes are used, with a clearance between them and the blades and the side walls of up to 1 mm. The most popular blade shapes include: sigma, dispersion, multiwiping overlapping, single-curve, and double-naben blades. It is important for filler dispersion in this mixer that the viscosity of the millbase be kept high enough to create the required shearing force to disperse the material. The strong construction of the mixer and its high power allow one to work with concentrated compositions of pigments which could not be processed by any other method.

High volume production is done by mixing in an extruder.11 This method offers several advantages such as a continuous process, material uniformity, a clean environment, high output, and low labor. The biggest disadvantage of this method is a high investment cost. The twin-screw extruder is the most flexible type of extruder and most appropriate for compounding. Their screw designs can be varied as can the method of dosing and the output rate. The abrasiveness of the filler may affect the life-span of the equipment, and particle size and its distribution may influence the quality of filler dispersion and material uniformity. But in general, there is adequate machinery available for almost all requirements. For instance, glass-fiber reinforced materials can be produced by this technique with little change to the initial structure and dimensions of the glass fibers, which shows the versatility of the technology. The production rate of this method is comparable to the Banbury mixer, and an additional advantage comes from the fact that the material can be completely processed in one pass through the machinery.

The importance of the proper dispersion of fillers and the complexity of techniques for measuring the degree of dispersion are reflected in numerous publications. Further information on the mixing of fillers is included in Chapter 18.

The renewable power sources are being explored due to possibility of lack in availability of conventional resources in future. The major drawback of Renewable energy resources are dependency on geographical locations and environmental conditions however, the high initial cost, increased maintenance cost, and different rates of depreciation are the main challenges associated with these hybrid systems[18]. The irregular pattern of natural resources necessitates developing a hybrid system which can generate maximum conceivable energy for continuous and reliable operations [17]. The design of hybrid system is influenced by various factors such as condition of sites, energy availability, efficiency of energy sources as well as technical and social limitation In this specific situation, a combination of optimal sizing method is an indispensable factor to accomplish higher reliability quality with least expense [21,79,87,149]. The fundamental parts of the hybrid energy systems are renewable power source, nonrenewable generators, control unit, storage system, load or grid some times, sources and load may be AC/DC [102].

An arrangement of the renewable power generation with appropriate storage and feasible amalgamation with conventional generation system is considered as hybrid energy system or some time referred as a micro grid [155]. This system may be any probable combination of Photovoltaic, wind, micro turbines, micro hydro, conventional diesel generation, battery storage, hydrogen storage and Fuel Cell in grid-connected or off grid arrangement,

An assembly of interconnected loads, conventional distributed energy resources like distributed generators (DG), renewable resources and energy storage systems in a specified boundary as a controllable single entity referred as micro grid. It may be eternally connected to grid, or isolated by grid. There are worldwide numerous remote communities those are not directly connected to grid, and fulfill electricity demand from distributed generators based on fossil fuel in isolated Microgrids[97,165]. In this paper a assimilated arrangement of solar PV and wind renewable energy resources is discussed which is slightly different from the concept of microgrid.

Solar Photovoltaic /Wind based Hybrid Energy System shows its adequacy to provide the essential electrical demand for off grid utilization. The at most imperative feature of a Solar Photovoltaic (PV) and Wind based Hybrid Energy System is that it uses at least two sustainable power sources which enhances reliability, efficiency and financial restrictions emerges from single energy resources of renewable nature [18,89,133]. Solar Photovoltaic and Wind based Hybrid Energy System is considered as amalgamation of solar PV panel, Wind mills, charge controller, storage system, power conditioning units, diesel based generator set and load [19]. The assessment of performance of Hybrid system can be done by recreating their models at Simulink platform for the accessible insulation, speed of wind, electrical load and various components [20].

The essential objective for evaluation of Hybrid System are building up the suitable models for various components and their simulation in a sequential manner as firstly availability of speed wind, accessibility of sunlight and the demand of load models are simulated after that model of battery storage and diesel generator can be Simulated. Last strides in the entire procedure of assessment is deciding the coveted criteria and exploring the optimum structure of system. [21]. The optimal hybrid system arrangement should satisfy and compromise the objectives of power reliability and cost of system. The load demand frequently considered as limitation of the optimization issue and ought to be totally satisfied [22]. The solar PV/wind hybrid system is mostly reliant on execution of individual segments. To estimate the performance of solar PV/wind hybrid system, individual components are modeled initially after that entire system evaluated to meet the demand [23]. In general key aspects to analyze a hybrid system are hybrid system configuration with respect to the available resources, the optimization of the available renewable resources exploitation and the optimization of the output power quality [24].

Solar energy and wind energy are analogous to each other in nature and both are well appropriate to develop a hybrid system [26]. Availability of solar radiations are relatively greater in summer, winds are more accessible in the evening times of winters. This hybrid renewable energy systems give a more reliable output throughout the year can be planned to fulfill craved qualities on more decreased possible cost [27]. The constraints of Photo voltaic system, the assessed energy of wind energy system and the battery storage are the majorly considered parameters for evaluation of solar and wind based hybrid energy system. In addition, the precise angular attitude of Photo voltaic panels and the tower height of wind turbines are considered for achieving the minimum levelised cost of energy. Ribeiro [31] proposed multi-criteria based analytical decision scheme abbreviated as MCDA which consider several issues like economic, quality of life, technical and environmental issues of local populations.

Metrological data based on technological, economical, socio-political and environmental factors having major impact for estimation and selection of various components of Solar Photovoltaic and Wind based Hybrid Energy System [32]. Hourly climate information as sun oriented radiation, wind speed and temperature are raw information illustrates the inconstancy of the parameter input. Place to place data is hard to obtain for designing purpose at remote location [3,73]. Statistical metrological climatic information can be delivered by the average of month to month meteorological information. The information of climate can be anticipated from an adjacent site or synthetically can be produced [32]. Simulation for performance of Solar PV/Wind Hybrid Energy System required climate data including solar radiation, speed of wind and temperature which can be find from web sources and also from local meteorological station, it is best to find realistic solution preference should be given to the specified location based weather data [28]. To optimize solar photovoltaic and wind based hybrid energy system are hourly or day by day climate information of solar and wind energy are considered as required significant inputs [29]. Meteorological data determined the receptiveness and amount of sunlight based radiation and wind energy sources at a particular region. An investigation of characteristics of sun based emission and availability of wind at a specific location ought to be concluded before starting [28]. Bianchini A et al. gives stress on the metrological data in the form of solar irradiance and wind distribution and considered hybrid renewable energy system as a amalgamation of PV panel of rated power, horizontal axis wind turbine of rated power, a diesel generator of precise nominal power able to manage peak load and a battery bank of specific storage capacity [33]. Hall et al. [34] proposed the well-known engineered climate information term Typical meteorological year (TMY) utilized in simulation of solar energy model is first time. It is observational technique picking particular months from different years using the Fleckenstein Schafer accurate system [35].

load demand play a very important role in establishment of solar PV/wind hybrid renewable energy system provides more reliable power for off-grid and standalone applications compared to individual systems [21] The most of the reviewed studies are about the alone Solar Photovoltaic /Wind based Hybrid Energy System and few studies are available for grid connected system. The unsatisfied load request is procured from the grid. Along this way the hybrid system became noticeably trustworthy. The stand-alone systems with storage infused surplus energy to the grid at a prime cost. Along these lines, the grid connected system becomes more financially acceptable.

wet ball mill/wet type ball mill/wet ball milling machine--zhengzhou bobang heavy industry machinery co.,ltd

wet ball mill/wet type ball mill/wet ball milling machine--zhengzhou bobang heavy industry machinery co.,ltd

Wet type ball mill are mostly used in the industry production. It is to increase the high grinding efficiency under the ball mill grinding and striking, from which the granularity is even and no flying dust with little noise, being the most universal powder machine in the benefication as powder grinding the ferrous metal like gold, silver, plumbum, zinc,copper,molybdenum,manganese,tungsten etc, as the nonmetal powder grinding like graphite,feldspar, potash feldspar, phosphorus ore, fluorite, clay, and swell soil etc. The wet type ball mill need to add the liquid into the grinding ball media auxiliary (water or ethanol). The material output gate is trumpet shape, with screw device inside, easy to discharging the material.

Copyright Zhengzhou Bobang Heavy Industry Machinery Co.,Ltd. E-mail : [email protected] Tel0086- 86656957 Address No.11 West Construction Road, Zhongyuan District,Zhengzhou City,Henan Province, China

chocolate, controlled and automated operations - italian food tech

chocolate, controlled and automated operations - italian food tech

Roasting is used to release the aromas of cocoa beans. This process is important because roasting contributes to reduce acidity and astringent substances present in cocoa beans. Furthermore, the heat causes a denaturation of the enzymes, which can adversely affect the organoleptic properties of cocoa butter.

Cocoa beans can be roasted as whole beans, but in this case the product will be less homogeneous; or they can be crushed in grain for a more uniform roasting; or, even better, they can be transformed into a paste with better results, but with higher costs. Some studies have demonstrated that keeping the cocoa roasting temperature below 140C best preserves the initial concentration of flavonols.

In addition, at lower temperatures the resulting product has a lower acidity, that allows to obtain a product with a lower total acidity. In order to preserve all the nutritional properties of cocoa, and especially its thermolabile components, even raw chocolate is available on the market; raw chocolate is processed at temperatures that never exceed 42C. Instead of roasting, cocoa beans are dried slowly in a controlled atmosphere.

Even during the fermentation process, which provides constant mixing, aeration and drying of the beans, the temperature never exceeds 40C. In this particular type of process, the refining may be performed using a ball mill that, thanks to the friction produced, causes the temperature to rise to 45C, with consequent melting of the cocoa butter and separation of this from the cocoa paste. The ball mill is equipped with a water cooling system, used to keep a constant low temperature and to preserve the aromatic components of cocoa.

The suitably processed mass is transferred by scrolls to the refining unit. If crystal sugar is used, a pre-refining process is required in order to reduce the particle size of sugar between 80 and 120 micron, and obtain a more compact mass thanks to the passage between two or three water-cooled rollers of variable length and diameter.

This step is not required if icing sugar is used. As the pre-refiner, the refining machine is equipped with rollers typically 5 whose distance is electronically adjusted in order to obtain the desired fineness, also thanks to the combined crushing and stretching effect. The chocolate film is then detached from the roller surface by means of blades. The refining process can be also carried out by means of a ball mill, i.e. a double chamber roller used for heating and cooling, inside which steel balls are moved by a central shaft equipped with special arms or disks. Ball mills are used to produce cream spreads, anhydrous pastes for the production of ice cream, pralines and soft chocolates.

They can be equipped with a chiller to control the heat produced by the friction of the balls, thus protecting the organoleptic properties of the product. The refining cylinder is temperature controlled to prevent residual fats to solidify between the balls during work stops. The line productivity may vary depending on the raw materials used and the percentage of sugar in the recipe. Again, by replacing crystalline sugar with icing sugar, the refining time is significantly reduced with relevant increase in production.

After the mixing and blending of the basic ingredients, chocolate paste must be finely ground, so that sugar and cocoa particles are reduced to dimensions not greater than the sensitivity threshold of taste buds. To obtain the desired creaminess, chocolate paste is processed in conching units, that mix the product for a controlled time at a controlled temperature. After that, the chocolate is stored in heated tanks (47-50C) equipped with stirrers, waiting to be processed.

It is essential that chocolate is constantly mixed inside the storage tanks to preserve the homogeneity, composition and organoleptic properties of the product. The tanks are provided with level and temperature controls. Conveying systems that maintain a constant temperature transfer the chocolate to tempering machines, which cool it to 26-28C and then heat it at 29-32C, so that cocoa butter can crystallize in its stable form, and chocolate acquires its important technological properties, as easy de-moulding, velvety and homogeneous texture, and gloss, next to a long shelf-life.

Some tempering units allow adding of hazelnut chips, cocoa gru and other products inside the chocolate for its flavouring. Depending on the processing it will undergo, chocolate is then moved to depositing, decorating, modeling machines, always maintaining a hygienic environment, without inclusion of liquids, air or foreign bodies, in order to prevent product contamination.

Cooling tunnels are used for drying chocolate and moulded chocolates placed on the conveyor belt. The products are cooled by convection with modulated temperature and airflows, with electronic temperature and humidity control. The product enters directly into the cooling tunnel consisting of modular elements, for easy inspection, cleaning and maintenance.

Ventilation is opposite to the direction of travel of the product, for an optimal cooling. The tunnels are available in different lengths. The total length and the useful width of the conveyor belt varies according to the characteristics of the product to be handled. Plastic or metal net conveyors are more indicated for moulded chocolates, bars, hollow products.

Some tunnels feature independent cooling units, and independently regulated temperatures. Even the conveying speeds of the tunnels are variable according to their length. At the beginning and at the end of the tunnel there are two automatic systems for centering and guiding the belt. Product scraps are collected and conveyed to an extractable drawer, and recycled.

Chocolate processing lines are highly automated, and equipped with control systems on all processing units, by means of dedicated hardware and software as well as scalable supervision and control systems (SCADA), through which operators can interact with the lines and check their correct operation.

Automation requires the implementation of a system that collects all production data from the PLCs of the various systems, and can handle and save the various recipes, failures, machine stops, as well as all information concerning production, in order to ensure the complete traceability of the final product. Automation systems for the chocolate industry, and for the food industry in general, must be characterized by top reliability, as they handle food products, for which safety is a basic pre-requirement, and production processes that can run on a 24/7 basis.

The possibility of dimensioning and configuring ad hoc the different machines of the system, allows considerable energy savings. Many conching machines for liquid chocolate, for instance, are equipped with evaporation towers that ensure the quick removal of unwanted volatile substances and a radical reduction in processing times and energy consumption. Energy consumption can be further reduced if the company implements cogeneration or trigeneration systems. Cogeneration, also called CHP (Combined Heat and Power), is a process of combined production of heat and power.

Cogeneration plants can reduce the amount of fuel used in power generation processes, with a reduction in energy consumption of between 35 and 40%. Furthermore, even the environment benefits of this process, because it reduces greenhouse emissions. Even more performing is the trigeneration system (CCHP Combined Cooling, Heating and Power), the simultaneous production of electricity, heat and cooling all from one single source. Thermal energy is mainly used for the production of chilled water for industrial air conditioning and refrigeration through absorption chillers.

Small chocolate manufacturers can select multi-purpose and space-saving systems. There are small lines for chocolate preparation, integrating mixing, pre-refining, refining and single-shaft conching machines. There are also systems that allow the mixing of ingredients of different consistencies, whether solid or semi-dense, to obtain different products, such as chocolate filled with creams or products containing different granular ingredients, simply by varying the setting of the recipes from the operator panel.

In order to reduce spaces, there are dosing machines equipped with double tank, designed to mould one product and its filling by one dosing. The two tanks operate at different temperatures, allowing the dosing of different products. There is a wide range of cooling tunnels on the market designed for low space requirements.

Multi-function tunnels, for instance, function as enrobing lines for pralines, and other products in one direction, and in the opposite direction, on a secondary level of handling of the product inside the chamber, the tunnel allows for cooling, with considerable advantages in terms of space and increased productivity. For work areas with space constraints, as in small and medium artisan production, products can be cooled with excellent processing results.

ball mill operation -grinding circuit startup & shutdown procedure

ball mill operation -grinding circuit startup & shutdown procedure

After the grinding circuit has been brought up to normal operating conditions, the operator must monitor the various process variables and alarms. Most of these variables are monitored in the mill control room, however, the operator is also required to sample and analyse process streams and read local indicators.

The ball mill is susceptible to variations in ore hardness resulting in various grinds at constant throughput, or alternatively, various tonnages at constant grind. The variation in grind is not directly determined. However, a changing cyclone overflow density, at a constant tonnage rate and feed density, would be indicative of changing ore hardness and in that case the tonnage fed to the ball mill should be changed accordingly.

The ore feed rate to the ball mill is controlled by the weightometer located on the mill feed conveyor which can be manually adjusted with in the control room to give a constant weight reading. The signal from the weightometer increases or decreases the belt feeder speed and adjusts the water addition to the ball mill (as a function of the actual weight reading). Both weight control and the proportion of water can be adjusted in the control room.

The water rationing controller must be adjusted programmatically to give the desired ball mill discharge density (normally 60-65% solids). The ball mill discharge density should be checked manually at regular intervals and adjustment made to water ratio controller setpoint to adjust the ball mill discharge density.

The grinding circuit operator must ensure that the ball mill runs properly loaded and gives the correct ore grind. A major practical indication of mill loading is the sound made by the mill. A properly loaded mill will have a deep rhythmic roar, while an under loaded mill will have a metallic rattling type noise and an overloaded mill will be quite silent.

The operator must manually measure the cyclone overflow and underflow densities regularly. An increase in overflowdensity is indicative of softer ore and will soon be accompanied by a lowering of power draw at the mill and a change of sound indicating that the mill is becoming under loaded. To compensate, feed tonnage must be increased. Similarity, a decrease in the cyclone overflow density is indicative of harder ore and this will be accompanied eventually by a coking of the mill. Feed to the ball mill must be reduced.

In the event of an emergency, the mill feed conveyor is shut down individually or by stopping the operating cyclone feed pump. The ball mill must be shut down separately. All equipmentshutdowns are performed locally or from the MCC located in the mill control room.

ball mill, ball grinding mill - all industrial manufacturers - videos

ball mill, ball grinding mill - all industrial manufacturers - videos

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... LN2 feeding systems, jar and ball sizes, adapter racks, materials low LN2-consumption clearly structured user interface, memory for 9 SOPs programmable cooling and grinding cycles (10 ...

The XRD-Mill McCrone was specially developed for the preparation of samples for subsequent X-ray diffraction (XRD). The mill is used for applications in geology, chemistry, mineralogy and materials science, ...

The Planetary Ball Mill PM 200, engineered by Retsch, is a milling device best suited for mixing and size reduction processes and is also capable of meeting the necessary requirements for colloidal grinding ...

... Micro Mill PULVERISETTE 0 is the ideal laboratory mill for fine comminution of medium-hard, brittle, moist or temperature-sensitive samples dry or in suspension as well as for homogenising of emulsions ...

... , fast, effective. WORKING PRINCIPLE Impact and friction The FRITSCH Mini-Mill PULVERISETTE 23 grinds the sample through impact and friction between grinding balls and the inside wall of the grinding ...

... grinding mills includes being safe throughout. When the mills are quoted we make sure to include any and all safety components needed. Long life and minimum maintenance To help you get the most of your ...

Annular gap and agitator bead mills are used for processing suspensions and highly viscous products in chemicals and cosmetics as well as in the food sector. Studies have shown that annular gap bead ...

... Pneumatic extraction from the surface of the agitated media bed Wet grinding: Separation of suspension from the agitated media by ball retaining device Flexibility Through careful selection of the size and quantity ...

... details; Agitating power: 0,37 kW Total Power Consumption : 1.44 kW Total Weight : 100 kg Metal Ball Size : 6.35 mm Metal Ball Amount : 7 kg Cold water consumption : 10 liters / hour ...

Cement Ball Mill Processing ability: - 200 t/h Max feeding size: - 25 mm Product Fineness: - 0.074-0.89mm Range of application: - limestone, calcium carbonate, clay, dolomite and other minerals ...

... grinds and classifies a product. Vilitek MBL-NK-80 mill is specially designed for grinding valuable materials, which, when grinding, the re-milled fractions are not a commodity product. In particular, this mill ...

Dimensions: Height: 1530 mm Width: 650 mm Length : 1025 mm Description: Ball mills are capable of rapidly producing chocolate, nut pastes (for gianduia), and spreadable creams. It has been ...

refining ball mill royal duyvis wiener

refining ball mill royal duyvis wiener

Low viscous products can be handled in a batch type ball mill, with a top-to-bottom flow based on gravity, mounted with a re-circulation pump. For continuous processing lines bottom-to-top operation is very important, since average pastes do have a low fat percentage resulting in high viscous mass.

The latest design of the Wiener ball mill exhibits a higher capacity while using less energy and in combination with optimal cooling possibilities, product temperatures remain very low during refining.

The ball mill is easy to maintain as all parts are manufactured from high grade materials preventing any degradation of your valuable product and are easily accessible for replacement. The design of the vessel, shaft pin configuration, and ideal parameter control, make this ball mill the most efficient in todays market.

The vertical ball mill is used for the processing of high-viscous pre-mixed pastes, like chocolate, compound, crmes, nut- and seed-paste. The continuous design vertical ball mill can be used in a 1 3 stage refining system, with 1 3 ball mills in a sequential row after the pre-mixer.

(Chocolate) Confectionary Coatings, (Chocolate) Ice-cream Coatings Processing, (Compound) Confectionary coatings, (Compound) Ice-cream Coatings Processing, Bread Spread Processing, Compound Chocolate Processing, Fillings / Creams Processing, Real Chocolate / Couverture Processing

nova s ball mill | bhler group

nova s ball mill | bhler group

The Nova Power Control (NPC) system automatically regulates the ball amount in the machine, giving you a consistently high product quality, even if viscosity during grinding varies. Single-stage grinding gives you a final product fineness of < 20 m.

The Nova Power Control (NPC) system automatically regulates the ball amount in the machine, giving you a consistently high product quality, even if viscosity during grinding varies. Single-stage grinding gives you a final product fineness of < 20 m.

Nova S ball mill is the preferred solution for fine-grinding of various masses like compounds, spreads, creams for fillings and coatings, cocoa masses, nut pastes and other fat-based masses. The unique grinding chamber delivers one-step-grinding at low temperatures, ensuring that your product has the highest and consistent quality.

This self-controlling system regulates the power input, product temperature and product throughput. Independent of operator skills and raw material quality fluctuations - a uniform product quality is always ensured.

Using our global experience across chocolate manufacturing, we can customize your solution to meet your precise requirements. Our experienced engineers can help you plan, implement and support new technology to improve quality, efficiency and safety for your plant.

Billions of people come into contact with Bhler technologies to cover their basic needs for food and mobility every day. Our motto is creating innovations for a better world. Find out more about our key topics.

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