Applied material: coal, pebble, perlite, limestone, dolomite, etc. Its outstanding features: high crushing capacity, hadraulic pressure used to adjust the distance between the rollers, and the centralization lubrication on the brearing.
The toothed roller crusher is generally used for the medium and fine crushing for brittle and medium-hard ores, and the size of the crushed product is usually not less than 20mm. Because of its simple structure, easy maintenance, and low price, it is popular to aggregate and coal ores suppliers.
A double toothed crusher with less volume is composed of two toothed rollers which is installed in parallel and rotates in opposite directions. The two-toothed rollers adopt non-meshing and non-constant speed operation to strengthen the degree of occlusion, which ideally prevents the material from slipping thus improving the crushing efficiency.
Generally speaking, materials are crushed in three stages in a double toothed roller crusher. The material enters the crushing chamber by the impact force of the deep tooth gear for the first crushing. The large-block material is cut by the teeth to complete the second crushing, and then being squeezed when they enter the toothed rollers to complete for the third crushing. Finally, the crushed material is discharged from the outlet with the rotation of the toothed roller.
1. The company makes further improvement in the aspects of feed particle size, rotor diameter, rotor channel, etc., so that this series of products can adjust the corresponding rotor structure and the corresponding speed according to different materials and feed grain levels to cooperate, and can achieve higher production volume and higher fineness modulus.
In recent years, with the transformation and upgrading of the coal industry, the requirements for coal development efficiency and environmental protection are increasing day by day. In the field of coal chemical industry, the requirements for product particle size are extremely strict, and generally the particle size is between 25 mm and 70 mm.
If the particle size is too large, the crusher chamber will be blocked, and downstream processing cannot be carried out. The toothed roll crusher is currently used in coal crushing because of its large processing capacity, low fine powder producing rate.
The crusher teeth are composed of big and small tooth phase interval, which can effectively improve the meshing capacity gear roller with the ensure of ideal particle size. Strong meshing capacity can improve the equipment processing capacity, reduce the tooth roller wear, prolong the tooth plate service life.
The connection between tooth plate and tooth roller base is made by screw fastening block, which not only guarantees the connection strength, but also has good interchangeability and replaceability.
Carbon bainite wear - resistant cast steel is used as the material of the tooth plate. The wear resistance of this material is about 40% higher than that of 40Cr surface-welded wear resistant layer. In addition, the whole tooth roller structure, including tooth plate, tooth roller seat, thread fastening block makes strength and hardness of each component more balanced and reasonable.
Besides, the motor is equipped with an electric heating system, and the hydraulic coupler and reducer are made of low temperature synthetic oil which ensures the transmission system smooth operation in the low temperature even with minus 30 .
The Indian customers coal mine adopts the single-bucket truck with semi-continuous mining process, and the raw coal has large grain size, gangue with great hardness. In the original production line, he firstly crushed the material to less than 300mm, then crushed them to less than 70mm by a ring hammer crusher. The crushed material with 70mm was transported to the coal storage bunker by conveyor belt for screening to final products of 25 ~ 70mm.
Technical improvement is urgently needed in order to reduce the operation cost and labor intensity of workers, and ensure the normal operation of the production system. So, the user finally chose Fote toothed roll crusher to replace the original ring hammer crusher.
After the double toothed roller crusher is put into use, the equipment runs stably, and the output particle size of the product has been improved obviously. The comparison shows that there is a 18.2% difference between the qualified products before and after the equipment replacement, which greatly increases the output of the qualified products and creates great economic benefits for the enterprise.
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Toothed roll crusher is widely used in coal, metallurgy, mining, chemical industry, building materials, and other industries, and it is more suitable to crush coal in large coal preparation plant and process waste. Toothed roll crusher has a high crushing capacity. The distance between the rollers can be adjusted by hydraulic pressure. The bearing of the toothed roll crusher is centralization lubrication. Whats more, it has the advantages of optimal design, high efficiency, uniform grain, and low cost.
Protective device: The motor is connected with the retarder through hydraulic coupling to avoid dynamic overload. The sensor overload protection is very reliable. If you have mining project or chemical plant, the toothed roller crusher is prepared for you in China Fote.
The toothed roll crusher is suitable for crushing raw coal in coal mines, coal preparation plants and other industries (allowing less than 30% of coal gangue in raw coal). The crusher is also used to break other brittle materials whose hardness is similar to that of raw coal.
It has the characteristics of high efficiency, long life, full sealing, low noise, and uniform granularity. The double-toothed roll crusher is equipped with a scraper to keep the groove and working surface clean. For the toothed roll crusher, the outlet-size depends on the gap between the two rollers, the size of teeth, shape of teeth, and the number.
The double-toothed roll crusher is relatively small in volume. It consists of two tooth rolls that are mounted in parallel and rotate in opposite directions. According to the crushing capacity and the size of the discharging granularity, the two crushing rolls are uniformly filled with brushing teeth.
And the double-toothed roll crusher adopts the operation way of non-circular, non-intermesh and non-uniform, which can enhance the contact face of roller teeth, and avoid material slippage and improve crushing efficiency.
When the toothed roller rotates, the teeth on the surface of the roller can bite the materials and crush them. Each roller crusher of the crushing system is driven by a separate motor. The roller crusher is generally driven by a belt, and it constitutes the deceleration system along with the reducing mechanism.
FTM double-tooth roller crusher for sand making, limestone, rock, clay crushing has a good crushing effect on wet and sticky materials. And adherence or clogging phenomenon never occurs during the work.
The silicon-aluminum raw material is an indispensable calibration material in the dry cement production process. After the mining work, the materials need to be crushed, transported and stored. and then they are sent to the raw material mill for grinding according to an appropriate ratio.
However, the silico-alumina raw materials have strong water storage capacity and high plasticity index, especially for bauxite and marlstone with water content more than 17% and plasticity index generally above 15. Because of the viscosity of materials, it can lead to blockage and arching during the process of crushing, transportation and storage, thus affecting the normal operation of the system.
In order to solve the problem of adherence and clogging of wet-adhesive materials in the crushing stage, FTM toothed roll crusher is used to break the mixture of limestone and marl. In detail, firstly, the wet and dry materials are mixed and crushed, and secondly, the wet-adhesive materials and other limestone materials with lower moisture content are mixed into the crusher. And finally, they are crushed according to an appropriate ratio.
The toothed roller crusher machine has advantages of small volume, large crushing ratio, low noise, simple structure, convenient maintenance, high productivity, uniform particle size of crushed material, low crushing rate, convenient maintenance, sensitive overload protection, safe and reliable.
In the coal industry, the requirements for the particle size of the finished product are extremely strict. Generally, the particle sizes of the finished products are between 25 and 70 mm. If it is too large, the furnace will be blocked and further coal processing can't be performed.
Toothed roll crusher is the mature coal crushing equipment applied in the current coal industry, which satisfies all the demands of customers by its advantages of large capacity and low over-crushing rate.
Based on the original toothed roll crushers, HXJQ Mining Machinery has optimized the structure and materials of rollers according to the customers' requirements, so that to adapt the nature of hard gangue and special working conditions and ensure the normal production of coal enterprises.
Traditional toothed roll crusher is usually driven by double-motors. Two sets of motors, couplers and reducers are adopted to drive the independent rollers so that the rollers have the power to crush large coal materials.
The coupler is applied between reducer and rolls to transfer torque. And the toothed rollers and drive system are connected with the machine frame respectively to eliminate the vibrating of toothed roll crusher.
Traditional toothed roll crusher with ring structure has the advantages of stable and reliable performance, and the disadvantages of low wear resistance and hard to replace. Once the traditional toothed roll crusher is damaged, it must be returned to the factory for overhaul.
The traditional rollers are connected by the bolts and tooth-holders, which offers small bearing capacity. Therefore, the traditional toothed roll crushers are mainly applied in the clean-coal crushing process, because the raw coal will cause damage to roll crusher teeth.
In terms of tooth position, the roll crusher teeth are set in the peripheral direction, adopting the setting form of large tooth alternating with a small one. Under the premise of normal discharging size, the crushing force of roller can be improved efficiently, so that to increase the capacity, wear-resistance and service life.
As the picture shows, the new-type tooth-holder adopts the form of regular octagon. The toothed rollers and toothed holders are connected by the flat kay and socket head cap screws (the traditional ones are connected by bolts).
The contacted areas between tooth and toothed holders are processed and improved completely, and torque is transferred by flat key so that can prevent the socket head cap screws from the shearing force of coal materials. And the screws can be firmer and more reliable.
Meanwhile, the fastening bolt and the toothed roller holder are connected by the screw fastening blocks, which makes that the joint strength is ensured, and the interchangeability and the replaceability are also reliable.
The teeth are the main wearing parts of the toothed roll crusher, so it is very necessary to choose a suitable material. Therefore, it is required that the material should have enough hardness, toughness, impact resistance and wear resistance. Also, the following machinability and weldability should be considered.
When parts of high manganese steel are impacted repeatedly, the surface of parts gets changed, and the hardness increases rapidly, which can reach up to HRC54. It will improve the wear resistance significantly, but the inside of parts keeps flexibly. These are the main features of high manganese steel.
However, the toothed roll crushers crush coal materials by shearing and stretching, along with less impacting and squeezing, which makes high manganese steel can't play its advantages to enhance the hardness and strength. Therefore, high manganese steel is not suitable for making teeth.
To better improve the wear-resisting performance of teeth, traditional toothed roll crusher always adopts the low-alloy quenched and tempered steel as the material to make tooth of roll crushers. In general, 40 Cr is used to process the tooth. After processing, the compressive strength and the service life of tooth are improved.
However, since there are only a few millimeters thick wear-resisting layer in the surface of the tooth, it is required to be overlaid frequently in the process of use, which brings a large workload to workers.
The teeth of the new toothed roll crusher adopt the integral casting molding process, optimizes the proportion of the main elements such as C, Cr, Mn, Mo, Si, Ni. The medium carbon bainitic steel is selected finally to be the material of toothed roll.
The medium carbon bainitic steel has good hardenability. After quenching and tempering heat treatment, bainite with high hardness and wear resistance is processed. It has an excellent comprehensive performance of HRC50 hardness and compressive strength of 1500 MPa.
In addition, the material of the entire toothed roller structure, including the toothed roller, the toothed roller holder and the threaded fastening block, is reasonably matched, so that the strength and hardness of each component are more balanced and reasonable.
The raw coal is first crushed to below 300mm by the jaw crusher, and then crushed to below 70mm by a toothed roller crusher, and then transported to the coal storage bin by the belt conveyor. After screening, the final product of 25~70mm is sold to the chemical company.
The customer said it requires technical improvement urgently in their worksite urgently to reduce the operating cost of the enterprise and the labor intensity of the workers and to ensure the normal operation of the production system.
Since the new toothed roller crusher was put into use, the equipment has been running stably, the discharge size of the products is significantly improved, the over-crushing rate reduces, and the block-forming rate is highly increased (see the following table).
It can be seen from the above table that the difference between the qualified products before and after the replacement is 18.2%, which greatly improves the output of qualified products and creates great economic benefits for the enterprise.
In addition, the new toothed roller crusher has high wear resistance, and the fastening bolt is not easy to loosen, which reduces a large amount of maintenance time, the labor intensity of workers, and the maintenance cost of the coal crushing process.
With the transformation and upgrading of the coal industry, it is an inevitable trend to vigorously develop coal chemical industry. The coal chemical industry has strict requirements on the particle size of coal, which puts higher requirements on the crushing equipment.
The new toothed roller crusher can optimize the crushing operation of the raw coal by a series of optimizations on the structure and material of the toothed roller. It has a high block rate and a small maintenance amount. With the obvious technical advantages, the promotion prospects of new-type toothed roll crusher are broad.
Although its brief period of popularity passed some thirty-odd years since, and only a few sets were installed before interest reverted to other types, the high-speed double roll crusher developed by Thomas A. Edison shortly before the end of the last century warrants a place in any discussion-of crushing equipment. In 1960, the largest machine of this type the 6 x 7 foot giant rolls were huge crushers, judged even by present-day standards; they have an unobstructed receiving opening 7 x 7 foot and their capacity on individual skip-loads of stone is enormous, although, as will be explained, they cannot maintain this peak capacity over a period of time.
Mechanically, the teethed roll crusher is a very simple machine. The two rolls are carried in bearings, supported on two very heavy and rigid bed castings which are secured on the concrete foundation by a number of large anchor bolts. The bearings, in addition to being bolted to these bed castings, are prevented from spreading by pairs of large tie-rods which pass through them above and below the roll shafts. Unlike the smooth-face crushing rolls we have described, these tension rods are not cushioned by springs. The machine is surmounted by a heavy cast rectangular hopper, all sides of which are vertical. Each roll is independently driven by a flat-belt pulley.
The roll-centres are octagonal in cross section, each face being provided with a spline groove and a series of tapped holes for securing the chilled- iron wearing plates. These wearing plates have the sledging knobs, or teeth, cast on their outer surfaces. Thus we have a roll surface that resembles that of the one rollcrusher, except that the faces of all teeth are sloped instead of radial on the advance side. The usual practice is to fit one roll entirely with so-called regular teeth, and the other roll with six rows of regulars and two rows of higher (slugger) teeth.
The peripheral speed, or tip-velocity, of these rolls is much higher than that of any of the machines we have previously described. The range of the smooth-face rolls, for example, is from about 400 ft/min for the small 12-in. rolls, to 2000-2200 feet/minute for the heavy-duty 72 machine. The single-roll crusher has a tip speed of 400-450 ft/min while the 6- x 7-ft teethed roll crusherhas a normal, no-load, surfaces speed of just under 3500 ft/min. It can be readily appreciated that this high velocity induces an extremely violent crushing action, in conjunction with the 3- to 4-in. knobs which protrude from the roll surfaces. Impact, sledging, and pressure crushing enter into the over-all performance; but impact, in this crusher, plays a far more important role than it does in the slower speed single-roll machine; and crushing, even well down along the roll faces, is more in the nature of a sledging action than it is of pressure crushing, for this action occurs in the lower-velocity crushers.
The theoretical maximum size of cube that the knobs will grip, when the rolls are set at minimum spacing, is 24; but the rolls will reduce any stone that can be introduced into the 7-ft square hopper. Large blocks will span across the tops of the two rolls; immediately the slugger teeth on the one roll so equipped go to work on these blocks and quickly shatter them into pieces that can be gripped between the sets of regular teeth; from this point on, the action is a mixture of sledging and pressure crushing. The same selective segregations which we described in connection with the single-roll machine occur in the double-roll crusher; the smaller pieces are cleared quickly, leaving the roils free to work on the larger blocks.
The entire performance on individual skip-loads of stone takes place in a very short period of time. Ten- ton loads of mixed-size medium limestone will clear the crusher in from 10 to 15 sec.; large single blocks, weighing from 6 to 8 tons, are crushed in from 5 to 20 seconds, depending upon the toughness of the individual piece, and upon the way it happens to land in the crushing chamber. These performances were clocked on ma-chines turning out a 6 product.
The short-time transfer of energy, especially when crushing large blocks, is very high; so high in fact that it would not be economically feasible to provide sufficient motive power to deliver it. The usual practice, when these rolls are driven electrically, is to drive the slugger roll with a 250 HP motor, and the regular roll with 200HP,a total of 450 HP. As compared to this motive power, instantaneous energy delivery may run as high as 4000 HP, obviously far beyond the capacity of the motive equipment. But the rolls themselves, when running at normal no-load speed, have a stored kinetic energy of upwards of 4,000,000 ft -lb , and it is this stored energy that does much of the actual crushing, the motors serving to bring the rolls back to normal speed between crushing periods. In crushing a skip-load of stone the rolls may lose anywhere from 30 to 60 RPMin speed; this loss occurs partly through slowing down of the motive equipment, and partly through belt slippage. It requires from 5 to 10 sec. to bring the machine back to speed, during which time the power input will vary from 400 to 600 HP. The power required to run the rolls empty is something less than 100 hp. The average power consumption, when crushing from 3000 to 4000 tons per 10 hour day will run in the neighbourhood of 150 HP on medium limestone.
While the average power consumption of this machine compares favorably with that of other types, the rather violent fluctuation outlined and the relatively high connected horsepower are unfavourable features. It is also natural to expect that the belt slippage we have noted would constitute something of a problem over a period of time. Performance records indicate that belt trouble accounts for about 50% of the total lost time on a set of these rolls, and about 25% of the total maintenance expense.
The type of quarry equipment most commonly used in conjunction with this crusher is the three-sided steel skip, carried on a flat-top truck or flat car. These skips are provided with a shackle on the rear end, which is engaged by a hook actuated by a small hoist. This apparatus slides the skip over against the lip of the receiving hopper, and tilts it to discharge its contents. The skips discharge over a feed-roll which retards the flow of material so that the entire load does not drop into the crushing chamber at once. When the skip is empty it is pulled back on to the truck or car by a counterweight attached to the opposite end of the same cable which performs the hoisting operation.
We have mentioned the heavily ribbed hopper which surmounts the frame and extends up to the level of the feed roll. This hopper serves the double purpose of directing the material into the crushing zone, and preventing stones thrown by the slugger teeth from flying out of the crusher. It is also necessary to cover the top of the hopper with heavy netting to contain flying spalls.The straight-sided, rectangular hopper construction, and the violent agitation in the crushing chamber, tend to minimize blocking and bridging in this crusher. When bridges do occur they are difficult and dangerous to break while the rolls are running.
Practically all that we have had to say about the application of the single-roll crusher will apply as well to the Edison toothed roll crusher. It is better adapted to handling blocky stone than is the single-roll machine, because itsslugging action is much more vigorous, and it will handle any material that will not build up on the sides of the vertical hopper. It is not as simple a machine to feed as the single roll crusher, because its narrow hopper necessitates the uses of skips, or very short-bodied cars. A heavy- duty apron feeder would of course solve this problem, but so far as we know, none of these crushers were so equipped. The high peak capacity of the crusher constitutes something of a problem in plants of medium capacity. It is not economically feasible to provide elevating or conveying equipment to handle peak loads of around 4000 TPH in a plant designed to turn out that much stone in an 8 or 10 hr day; consequently means must be provided to smooth out these high surge loads. This can be taken care of by a surge bin and feeder below the crusher, or by passing the roll product direct to a secondary crusher of uniform-capacity characteristic. A feeder ahead of the rolls would smooth out peaks on mixed feed but. once a 10 or 12 ton block of stone is dropped into the crusher, that quantity comes through very quickly as crushed stone, which would render the regulating properties of the feeder of questionable value.Modified forms of this crusher were used by Edison for secondary and tertiary stages. The crushing equipment in one large plant, for example, comprised a set of 6- x 7-ft rolls (8 product), a set of 4 x 4 feet secondary rolls (3.5 product), and a set of 4 x 3 ft tertiary rolls (1.5 product), these last rolls being in closed circuit. These smaller machines were also run at high speeds, their surface velocities being slightly over 3000 ft/min.
In recent year, mainly as a result of environmental problems, the raw material crushing sector has often had to use quarries in which the materials are imperfect or mixed with soil. This has made work difficult to traditional crushers, such as impact or jaw crushers, because they are often required to process materials for which they have not been designed.
Bedeschi machines have been installed in difficult location worldwide. The company promotes the spread and development of double-toothed roller crushers, which are employed in many different fields: cement plants, mining firms, brick and tile factories and company specialized in waste processing scrap material. They are basically very simply machines; they consist of two toothed rollers turning in opposite directions and the material to be crushed is made pass between them. The material is not crushed through compression but through a combination of shear and tensile stresses.
The processing system of the double-toothed roller crusher makes it possible to crush any type of raw material from hard (limestone and rock) to soft (clay, soil and mud) or even elastic-like wood or rubber tyres. The rotation speed, especially if compared to traditional crushers, is very low; so low, in fact, that tip speed is under 3 m/s.
These crushers have turned out to be particularly effective in situations where other crushers experience problems. They are ideal for processing wet, sticky materials, and blocks of hard material mixed with soil, in addition to crushing ordinary hard materials. Under these conditions, traditional crushers clog. Double-toothed roller crushers are equipped with scrapers, which keep the grooves and the work surface perfectly clean.
These crushers are invaluable for crushing clay, soil and sticky materials containing up to 30 % moisture content or rocks covered with a layer of soil, a situation that, as mentioned earlier, is often encountered due to environmental restrictions imposed on quarries. The majority of cement plants set up in the 1990s in the Far East where, because of the frequent rain, raw materials are very moist, are equipped with clay crushing systems with double roller crushers; most of them supplied by Bedeschi. These machines allow a maximum reduction ratio of ten at each crushing stage.
They can act as primary or secondary crushers and can be installed to suit any required arrangement, even one on top of the other, with the primary crusher discharging directly onto the secondary crusher.
The gap is adjusted in the factory according to project requirements but can be easily changed after the machine has been put into service, to improve or change crushing parameters. The roller gap of Bedeschi crushers can easily be adjusted to individual preferences.
The study and dimensioning of teeth is particularly important. Bedeschi technical staff, thanks to their calculation models defined over many years of experience, establish the characteristics and shapes that most suit the material to be crushed and the customers outlet size requirements. The most important and qualifying tooth characteristics are:
These crushers, due to their special crushing method, are characterized by their relatively low power consumption compared to traditional crushers. Many applications and tests confirm an average power absorption of 0.3 to 0.4 kWh/t.
Their special design, featuring an external reduction unit, allows compact sized machines to be made, which can be installed where space is at a premium; installations in tunnels are a particularly significant example.
Alfa Laval, irontrybex - stock.adobe.com; Nitta Corporation of Holland; Picture: Bedeschi; Profibus Nutzerorganisation; Ecoclean; Brkert; Namur ; BASF; Shell; industrieblick - stock-adobe.com; IFG Asota; Feige Filling; Emerson; Goodvibes Photo - stock.adobe.com; Steriline; Ima; Achema Pulse; Pixabay; Thordon Bearings; Leybold ; Griswold; Oleksandr - stock.adobe.com; Evonik Industries; Siemens; Siemens Energy; Siemens Energy
Roll crushers are generally not used as primary crushers for hard ores. Even for softer ores, such as chalcocite and chalcopyrite, they have been used as secondary crushers. Choke feeding is not advisable as it tends to produce particles of irregular size. Both open and closed circuit crushing is employed. For close circuit the product is screened with a mesh size much less than the set.
Figure6.4 is a typical set-up where ores crushed in primary and secondary crushers are further reduced in size by a rough roll crusher in an open circuit followed by finer size reduction in a closed circuit by a roll crusher. Such circuits are chosen as the feed size to standard roll crushers normally does not exceed 50mm.
A distinct class of roll crushers is referred to as sizers. These are more heavily constructed units with slower rotation, and direct drive of the rolls rather than belt drives. They have a lower profile, allowing material to be easily fed by loaders, and are a good choice for portable crushers at the mine that reduce the coal in size for conveying to the preparation plant. An example of these units is shown in Fig.9.4.
9.4. (a) Primary sizer with attached feeder. The large motors and gearboxes drive the relatively low-speed toothed rolls that break the coal. (b) Haulage truck dumping coal directly into the feed hopper for a primary sizer, which discharges onto a product belt. (c) Tertiary sizer for crushing coal to the desired size for a preparation plant.
Their lower speeds are claimed to reduce fines generation, while lending themselves to high throughput applications. Sizers can either have the rolls rotate towards each other to carry feed between the rolls to be broken, or can be constructed as tertiary sizers with the rolls rotating away from each other. With tertiary sizers, feed coal is added between the rolls, and much of the fine material falls through. The coarser material is then carried to the outside to be broken against fixed sizing combs. This design increases the capacity by producing two main product streams instead of one, and also minimizes overcrushing by removing a large fraction of the fines. Tertiary sizer capacities range from 440 tons/h (400 metric tons/h) for 2448 inch (61122cm) rolls producing a 2-inch (5cm) product, up to 3968 tons/h (3600 metric tons/h) for 2096 inch (51244cm) rolls producing a 10-inch (25cm) product (Alderman and Edmiston, 2010).
A typical coal handling package using sizers would comprise a dump pocket discharging to a primary sizer discharging to a product belt, as shown in Fig.9.4b. This product belt would then feed a secondary or tertiary sizer, such as is shown in Fig.9.4c, which may include intermediate screening to remove product prior to subsequent stages of breakage. Typical size ranges would start with run-of-mine coal feeding to the primary sizer at 2000mm, and reducing to 350mm. The secondary sizer would receive this coal and discharge at a nominal 125mm, followed by a tertiary sizer/screen combination to generate a 50mm topsize preparation plant feed (FLSmidth, 2011).
The intermediate crushing in the cut roll crusher is mainly used for the crushing of brittle materials like concrete and clay sintered bricks, along with the compression of rough materials like wood and fabric (to avoid being too small in size) after the coarse (primary) crushing. The selective crushing in this process is good for the separation of impurities. Impact crushers are commonly applied in intermediate crushing. However, when used in crushing of mixed C&D waste, the wood and fabric materials will be broken and mixed in recycled aggregate materials by the high-speed operating rotors and are difficult to be separated.
Although not widely used in the minerals industry, roll crushers can be effective in handling friable, sticky, frozen, and less abrasive feeds, such as limestone, coal, chalk, gypsum, phosphate, and soft iron ores.
Roll crusher operation is fairly straightforward: the standard spring rolls consist of two horizontal cylinders that revolve toward each other (Figure 6.14(a)). The gap (closest distance between the rolls) is determined by shims which cause the spring-loaded roll to be held back from the fixed roll. Unlike jaw and gyratory crushers, where reduction is progressive by repeated nipping action as the material passes down to the discharge, the crushing process in rolls is one of single pressure.
Roll crushers are also manufactured with only one rotating cylinder (Figure 6.14(b)), which revolves toward a fixed plate. Other roll crushers use three, four, or six cylinders, although machines with more than two rolls are rare today. In some crushers the diameters and speeds of the rolls may differ. The rolls may be gear driven, but this limits the distance adjustment between the rolls. Modern rolls are driven by V-belts from separate motors.
The disadvantage of roll crushers is that, in order for reasonable reduction ratios to be achieved, very large rolls are required in relation to the size of the feed particles. They therefore have the highest capital cost of all crushers for a given throughput and reduction ratio.
The action of a roll crusher, compared to the other crushers, is amenable to a level of analysis. Consider a spherical particle of radius r, being crushed by a pair of rolls of radius R, the gap between the rolls being 2a (Figure 6.15). If is the coefficient of friction between the rolls and the particle, is the angle formed by the tangents to the roll surfaces at their points of contact with the particle (the angle of nip), and C is the compressive force exerted by the rolls acting from the roll centers through the particle center, then for a particle to be just gripped by the rolls, equating vertically, we derive:
The coefficient of friction between steel and most ore particles is in the range 0.20.3, so that the value of the angle of nip should never exceed about 30, or the particle will slip. It should also be noted that the value of the coefficient of friction decreases with speed, so that the speed of the rolls depends on the angle of nip, and the type of material being crushed. The larger the angle of nip (i.e., the coarser the feed), the slower the peripheral speed needs to be to allow the particle to be nipped. For smaller angles of nip (finer feeds), the roll speed can be increased, thereby increasing the capacity. Peripheral speeds vary between about 1ms1 for small rolls, up to about 15ms1 for the largest sizes of 1,800mm diameter upwards.
Equation 6.6 can be used to determine the maximum size of rock gripped in relation to roll diameter and the reduction ratio (r/a) required. Table 6.1 gives example values for 1,000mm roll diameter where the angle of nip should be less than 20 in order for the particles to be gripped (in most practical cases the angle of nip should not exceed about 25).
Unless very large diameter rolls are used, the angle of nip limits the reduction ratio of the crusher, and since reduction ratios greater than 4:1 are rare, a flowsheet may require coarse crushing rolls to be followed by fine rolls.
Smooth-surfaced rolls are usually used for fine crushing, whereas coarse crushing is often performed in rolls having corrugated surfaces, or with stub teeth arranged to present a chequered surface pattern. Sledging or slugger rolls have a series of intermeshing teeth, or slugs, protruding from the roll surfaces. These dig into the rock so that the action is a combination of compression and ripping, and large pieces in relation to the roll diameter can be handled. Toothed crushing rolls (Figure 6.16) are typically used for coarse crushing of soft or sticky iron ores, friable limestone or coal, where rolls of ca. 1m diameter are used to crush material of top size of ca. 400mm.
Wear on the roll surfaces is high and they often have a manganese steel tire, which can be replaced when worn. The feed must be spread uniformly over the whole width of the rolls in order to give even wear. One simple method is to use a flat feed belt of the same width as the rolls.
Since there is no provision for the swelling of broken ore in the crushing chamber, roll crushers must be starvation fed if they are to be prevented from choking. Although the floating roll should only yield to an uncrushable body, choked crushing causes so much pressure that the springs are continually activated during crushing, and some oversize escapes. Rolls should therefore be used in closed circuit with screens. Choked crushing also causes inter-particle comminution, which leads to the production of material finer than the gap of the crusher.
The objective of sample preparation is to prepare test samples from a parent sample or individual primary increments, Fig.5.19 for analysis. Sample preparation includes all procedures that a sample is subjected to in order to produce a reduced mass of sample (analysis sample) that is representative of the parent sample and from which subsamples of relatively small mass can be used directly for analysis. Samples for general analysis (proximate, ultimate, calorific value, total sulphur, etc.) are typically milled samples with 95% passing 0.212mm. Standard AS4264.1 stipulates that the minimum mass required for general analysis is 30g.
However, some laboratory analyses will require larger sample masses. Some examples from AS 4264.1 include Hardgrove grindability index (AS 1038.20) which requires 1kg at 4.75mm top size, and total moisture (AS 1038.1 Method A and B) 300g at 4mm. However, the principles of preparing a representative analysis sample from the original coal sample are the same.
Taking the ash determination as an example: 1g of coal is used in a single ash determination, and that 1g has to be representative of the coal sample. At a top size of 0.212mm the sampling constant, Ks, for most coals will be very small and this constant combined with a 1g mass of coal enables the variance contribution from the IH of the analysis sample to be almost insignificant and therefore a high level of precision can be expected.
Apart from exploration samples, most samples received by laboratories are from mechanical sampling systems at coal handling facilities at mine sites, ports or power stations. In some areas where coal is being sold across land boarders such as the MongolianChinese border, most samples will be extracted directly from haulage trucks. Many samples, such as ship loading samples and some coal preparation plant samples, are produced by multistage mechanical sampling systems. Other samples may be produced from single-stage samplers. As a result, laboratories can receive samples in a wide range of conditions, most importantly sample mass, moisture content and particle size distributions. Sample preparation procedures have to be tailored to suit the samples and the proposed testing and analyses procedures that the sample has been collected for.
In some instances the particle size reduction may be omitted before sample subdivision, for example at the first stage after collection of the primary increment. However, generally before subdivision (subsampling) the particle size should be reduced.
In each case at every stage, the process recognises the relationships between the number of increments, sample mass and particle size to sampling variance, as each stage is a standalone sampling exercise.
Hammers mills comprise a set of swinging hammers attached to a rotating shaft (Fig.5.22). Typically, they are fed a 4mm top size coal to produce analysis samples with >95% passing 0.212mm. They have a device for feeding the coal into the mill. This is often a screw-type feeder. They also usually have a screen on the outlet to ensure that the entire sample achieves a specific top size. Hammer mills tend to generate excessive fines and should not be used in some instances, such as preparation of samples for petrographic analysis and Hardgrove grindability index determination.
Ring mills comprise a cylindrical canister and lid, a steel ring, and a smaller steel cylinder that fits inside the canister (Fig.5.23). The coal is placed in the canister with the ring and the cylinder, and the lid is attached. This is then placed in a jig that moves the canister in a circular motion. The movement of the various metal components within the canister crushes the coal. There is some concern that these mills can become heated and that this may affect the coal quality, particularly CSN values. This type of mill is particularly useful for crushing low mass samples as sample loss is kept to a minimum. Automated ring mills have been in use in laboratories handling large sample volumes to ensure consistent milling and improved productivity.
Roll crushers are comprised of two steel cylinders (Fig.5.24). The coal is crushed as it passes between the cylinders. This type of crusher is useful when preparing samples with a minimum of fines generation.
Incremental division is a manual method of subdivision that can provide precise subsamples. This method requires that the coal is well mixed prior to division. The coal is spread onto a flat surface in the form of a rectangle in a thickness approximately three times the nominal top size of the sample. A grid pattern is marked out on the sample (usually composed of at least 20 rectangles in a 54 grid) and a single increment is obtained from each square. The increment is removed from the sample using a suitable scoop and bump plate to prevent the increment from falling out of the scoop. Incremental division is used almost exclusively in obtaining the final (0.212mm) laboratory sample after the hammer mill operation, because of excessive dust losses by other methods.
Rotary sample division (rsd) is the most common method for subdivision of large samples in coal laboratories. The rotary sample divider (Fig.5.25) comprises a feed hopper, a device for feeding the coal at a constant rate (usually a vibratory feeder) and a number of sector-shaped canisters formed into a cylinder on a rotating platform. The uniform coal stream produces a falling stream of coal that is collected in the rotating canisters, dividing the sample into representative parts.
As the coal particles move through the feed hopper there is a high potential that some segregation and grouping will occur. To counter the effect that this may having on sample preparation variance it is advisable to ensure that each canister cuts the falling stream at least 20 times, i.e. there are at least twenty rotations of the turntable as the coal flows into the canisters. Additionally, it is a good practice to combine material collected in two or more canisters to form the divided increment or subsample. When doing so, canisters that are opposite each other in the rotary sample divider should be selected for recombination. The machine pictured in Fig.5.25 is set to divide a sample into eight divisions. If the requirement was to extract a quarter of the sample for analysis, two of the 1/8th divisions would be recombined.
Riffles (Fig.5.26) are less regularly used in laboratories. Riffles divide the coal into halves by allowing the coal to fall through a set of parallel slots of uniform width. Adjacent slots feed opposite containers. The width of the slots should be at least three times the nominal top size of the coal. There should be at least eight slots for each half of the riffle.
Fractional shovelling may be used for subsampling when a large rotary sample divider is not available. In this process, the coal is formed into a conical heap. Successive shovels of coal are removed from the base of the heap and are placed into daughter heaps. The shovels of coal should be allocated consecutively and systematically to each daughter heap.
Shredding rubber waste reduces the volume of used tires. Generally, the cost of shredding increases with the need to obtain pieces as small as possible. For grinding, rubber wastes are initially processed through mechanical cutters, roll crushers and screw shredders. To obtain finer particles, shear crushers and granulators are used. The final processing of rubber wastes is with high-temperature shredding equipment, such as rotary shredders, where degradation occurs during compression simultaneously with shear and wear (Mikulionok, 2015). In the initial phase, shredding rubber wastes results in dimensions of approximately 7.6210.16cm. These pieces are then placed in cutters that reduce the size to 0.630.63cm (Rafique, 2012).
Granulators are used in the second step of the recycling process, where pieces of waste tyres are grinded in the large-sized granulators to produce a large quantity of granules. The use of pulverises can reduce the rubber granulated material into fine powder. The rubber particles size can range from a few micrometres up to centimetres.
Rotary Breakers (Fig. 1). The rotary breaker serves two functionsnamely, reduction in top size of ROM and rejection of oversize rock. It is an autogenous size-reduction device in which the feed material acts as crushing media.
Roll Crusher. For a given reduction ratio, single-roll crushers are capable of reducing ROM material to a product with a top size in the range of 20018mm in a single pass, depending upon the top size of the feed coal. Double-roll crushers consist of two rolls that rotate in opposite directions. Normally, one roll is fixed while the other roll is movable against spring pressure. This permits the passage of tramp material without damage to the unit. The drive units are normally equipped with shear pins for overload protection.
Process is designed to reduce the size of large pieces with minimum production of dust. Two main types of breakers are used in Great Britain, viz. (a) Pick Breaker and (b) Bradford Breaker. Other crushers commonly used are jaw crushers, roll crushers, disc crushers, cone crushers and hammer crushers.
Pick breakerdesigned to imitate the action of miners' picks. Strong pick blades are mounted rigidly on a solid steel frame moving slowly up and down. Coal passes under the picks on a slowly moving horizontal plate conveyor belt. The amount of breakage is roughly controlled by the height to which picks are raisedupper limit is 0.5 m Typical performances: 450 ton/hr with a 2-m-wide machine. Size reduction from 500 mm to 300 mm. Several machines may be placed in series, with screens in between to remove fines. Main advantageminimum production of fines can be achieved. Fines production is controlled by the diameter and spacing of picks. Reduction in diameter and increase in spacing, decrease the proportion of fines.
Bradford breakerScreens break and removes large pieces of accidental material, e.g. pit props, chains or tramp iron, in one operation. Consists essentially of a massive cylindrical screen or Trommel, with fins fitted longitudinally inside the screen. These raise the lumps of coal as the cylinder rotates, until they fall, break, and are screened. Unbroken material passes out of the end of the cylinder. Production of fines is also small. Capacity of machine: up to 600 ton/hr.
Blake jaw crusher. Consists of a heavy corrugated crushing plate, mounted vertically in a hollow rectangular frame. A similar moving plate (moving jaw) is attached at a suitable angle to a swinging lever, arranged so that the reciprocating movement opens and closes the gap between the plates, the greater movement being at the top. The machine is available with top opening up to 2 2.7 m. Usual capacity up to 300 ton/hr. Horsepower required: up to 150.
Corrugated and toothed roll crushers. Two heavily toothed, or corrugated, cylindrical rollers (Fig. 10.1) are mounted horizontally and revolve in opposite directions. (Towards each other at the top side or nip, one being spring loaded.) Alternatively, a single roll may revolve against a breaker plate. Capacity of a 1.5 m-long machine with a 300 mm opening and roll speed 40 r.p.m. is about 350 ton/hr, with a power consumption of about 200 h.p. Best results are obtained by the use of several rolls in series, with screens between.
Run-of-mine coal produced by mechanized mining operations contains particles as small as fine powder and as large as several hundred millimeters. Particles too large to pass into the plant are crushed to an appropriate upper size or rejected where insufficient recoverable coal is present in the coarse size fractions. Rotary breakers, jaw crushers, roll crushers, or sizers are used to achieve particle size reduction. Crushing may also improve the cleanability of the coal by liberating impurities locked within composite particles (called middlings) containing both organic and inorganic matter. The crushed material is then segregated into groups having well-defined maximum and minimum sizes. The sizing is achieved using various types of equipment including screens, sieves, and classifying cyclones. Screens are typically employed for sizing coarser particles, while various combinations of fine coal sieves and classifying cyclones are used for sizing finer particles. Figure 2 shows the typical sizes of particles that can be produced by common types of industrial sizing equipment.
The sponge masses as produced by vacuum distillation have to be prepared before melting. The nine ton mass of sponge has to be crushed to about 12mm size pieces. The sponge in contact with retort wall and the push plates have a high likelihood of contamination with iron and nickel since these metals are soluble in titanium. The top of the mass may also have some contamination of iron and nickel from reaction with the radiation shield and substoichiometeric chlorides. To remove this contamination the outer skin of the sponge mass is removed by use of powered chisels. This material is downgraded from aerospace use and used in less critical applications. The sponge mass then is sliced radially to one to 5cm sections with a large guillotine or similar blade. The bottom section of the mass is removed first as this likely has the most amount of iron incorporated into the sponge. The sponge mass is removed from the working table, so this material can be segregated from the balance of the mass. At this point the mass is placed back on the table, sliced and then sent to a crushing circuit. Titanium sponge is malleable material, thus traditional mineral processing equipment such as roll or jaw crushers are not as effective as high shear shredding machines such as rotary shears or single rotor/anvil shears in preparing sponge with limited very fine particle generation.
Dust generation in the crushing process is a very important aspect of operation. Control of the dust by collection and washing of equipment on a periodic basis is very important to reduce the risks of fire in the processing of sponge. Care has to be taken to avoid working on equipment when dust present as titanium metal fires are difficult to extinguish; a class D extinguisher or rock salt are used to suppress the first. The high temperature of the fire and the low melting point of iron-titanium eutectic can result in melting of equipment, supports or piping in these plants if a fire does occur.
The core of the sponge mass has the lowest level of metal contamination. To harvest the material for applications that need low iron and low nickel levels, it is necessary to core the mass. This is done in several ways; the mass can be upended and the guillotine blade can be used to remove thick layers of outer skin, or chisels can be used to remove the outer layers. Control of the lot by separation during the crushing campaign is used to separate the high-purity products from the normal grades of sponge. Control of the nickel level in the magnesium used in the reduction is also important. Removal of as much stainless steel in piping, retorts and metal reservoirs is also important, as nickel in the magnesium will be incorporated into the sponge. Small concentrations of nickel in magnesium can take a long time to be purged from the process. Control of the quality of magnesium used for make up in the VDP process is as important, as some magnesium can be contaminated with nickel during production. Iron is not as significant an issue as its solubility in magnesium is low.
A DEM model of a toothed double-roll crusher was established based on bonded particle model.Validation in terms of product size distribution was conducted for three groups of tests.The effects of rotation speed and structure of rolls on the crushing process were investigated.The breakage mechanism of the particle was discussed based on fracture dynamics.
A discrete element method (DEM) model of the crushing process of a toothed double-roll crusher (TDRC) is established using the bonded particle model. DEM results and experimental data are compared quantitatively and a relatively good agreement is observed. The effects of rotation speed and structure of crushing rolls on the performance of TDRC are investigated numerically. The results show that when the rolls' speed is relatively high, the nipping condition would be improved, and more cracks could be created to release the increasing strain energy, generating more fractions of small sizes in the products. But, when rolls' speed exceeds 150rpm, the crushing performance would not be significantly improved. A reasonable working gap and better nipping behaviour are obtained using the spiral-tooth-roll or the staggered-tooth-roll. The validated DEM model could be applied to gain a fundamental understanding of the crushing mechanisms of TDRC.