SGS toothed roll crushers and screw feed hammer mill crushers are designed and manufactured with the precision engineering and reliability that has made SGS a world leader in mechanical sampling systems for over 35 years.
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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Based on the high quality and complete after-sales service, our products have been exported to more than 120 countries and regions. Fote Machinery has been the choice of more than 200,000 customers.
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.
The Single Roll Crusher, with its 6:1 ratio of reduction, is ideal for reducing large feed lumps to a medium product size while producing a considerably lower percentage of fines. The minimum product sizing of a Single Roll Crusher is generally limited to 2-3. The crushing is carried out between the full width of the extra-long curved crushing plate and the low-speed crushing roll. The curvature of the crushing plate provides an ample throat opening to capture large irregular feed lumps. The replaceable crushing plate tips or liners are slotted to intermesh with the roll teeth to produce a cubical product and effectively reduce slabbing.
Single Roll Crushers are V-belt driven and employ a large diameter flywheel with a gear and pinion set to reduce roll speed. With the assistance of the inertia generated by the flywheel, this crusher is operated with relatively low horsepower and requires lower headroom in comparison to other crushers used for primary reduction. The roll diameter and width of the crusher will ultimately be dictated by the feed size, product size and capacity.
Single Roll Crushers employ a tramp relief mechanism to allow momentary movement of the crushing plate so the uncrushable object can pass. The mechanism then allows the crusher to return to its original setting and remain in operation.
The Single Roll Crusher, which was originally patented by Samuel Calvin McLanahan in 1894, has evolved over the years to include design features to ensure many years of rugged operation. Complete with all safety guards, the Single Roll Crusher features an automatic tramp relief mechanism that allows the crushing plate to hinge open, pass non-crushable tramp material and return to the previous setting for continued operation.
Based on the application data and extensive field experience, McLanahan selects the proper duty class of Single Roll Crusher for each project. A fully-equipped application research laboratory allows for crushing tests to make sure McLanahan can provide the best possible solution.
A Single Roll Crusher is made up of a toothed roll assembly, which crushes the incoming feed material against a crushing plate. The Single Roll Crusher is designed to reduce larger feed sizes to the desired product size at a 6:1 ratio of reduction while producing a considerably lower percentage of fines. When properly fed in the direction of the roll rotation, the crushing action is carried out along the full width of the curved crushing plate, which ensures maximum throughput capacity. A properly sized roll diameter and tooth configuration grabs the incoming feed and pulls it into the crushing zone without hesitation. The crushing plate has reversible and easily replaceable crushing plate tips, which are designed to produce a cubical product while providing the producer with twice the wear life and simplified maintenance. Single Roll Crushers often require less horsepower and lower headroom in comparison to other crushers used in primary and secondary applications.
These units are designed to make crushing simpler and more effective. McLanahan Single Roll Crushers also feature hydraulic product size adjustment to perform relatively simple changes to the crusher setting if required.
When an uncrushable object, such as metal, roof bolts/timbers, etc., enters the crusher and the force necessary to crush this material is greater than the crushing forces of the crusher, the crusher allows the crushing plate to open and pass the tramp material. The crusher then returns to its previous setting and remains in operation.
Cobra Single Roll Crushers are the lightest duty in the McLanahan line of Single Roll Crushers. They are ideal for wet, sticky feeds and for processing materials such as clean coal, petroleum coke, sulfur, rosin, foundry cores, frozen agglomerates and other friable materials.
Rockmaster Single Roll Crushers are the heaviest-duty model in the McLanahan line of Single Roll Crushers. They are ideal for the most severe crushing applications and reduce extremely hard material and typical mine refuse.
Typically designed for primary crushing, McLanahan Single Roll Crushers efficiently crush material at a 6:1 crushing ratio. . They can continually withstand heavy-impact applications. Single Roll Crushers reduce large size particles in the feed to a medium size, while producing a low percentage of fines.
Roll Crushers are designed to handle the primary, secondary and tertiary stage crushing of friable materials such as coal, salt, clay, bauxite, limestone and other minerals of similar characteristics in the mining, power generation and numerous other industries. Roll Crushers are one of the most widely used crushers in the mining industry and have numerous advantages, such as high capacity, low headroom, low horsepower, the ability to handle wet, sticky feeds and the generation of minimum fines while producing a cubical product.
The simplified design gives these units excellent reliability and requires very little maintenance. Roll Crushers are designed with built-in tramp relief that allows for the passing of uncrushable materials while continuing operation and returning to the initial product setting.
Since patenting the first Single Roll Crusher in 1894, McLanahan has become an expert and leader in the industry in the design and manufacture of single and two stage Roll Crushers. The selection process for each application is based on extensive equipment knowledge and a wealth of test data developed in our research lab or through on-site testing.
McLanahan offers belt-driven Roll Crushers in four designs: Single Roll, Double Roll, Triple Roll and Quad Roll Crushers, which provide a substantial return on investment by operating at low cost and maximizing yield by generating minimal fines. The rugged design, which incorporates a fabricated steel base frame lined with replaceable abrasion-resistant steel liners, stands up to the toughest mineral processing applications while providing safe and simple operation, including an automatic tramp relief system to allow uncrushable objects to pass while the crusher remains in operation. These crushers are also versatile, allowing for adjustments in roll speeds and gap settings to meet most any application requirement.
Whether the application requires a single-stage or two-stage crusher, the forces necessary to perform the crushing remain the same: a combination of impact, shear and compression. The impact force occurs as the material enters the crusher and is impacted by the rotating roll. Shear and compression forces occur as the feed material is pulled between the crushing plate and/or crushing rolls.
Depending on the feed size, material is fed into the crushing chamber and encounters a single or a pair of rotating rolls. If a two-stage reduction is required, either a Triple or Quad Roll configuration can be used. In this scenario, the top stage of the crusher performs the primary reduction either by crushing the material between the roll and crushing plate or between a pair of rolls. The material is then fed directly between the two bottom-stage rolls for additional processing.
If a single-stage reduction is required, then depending on the feed-to-product-size ratio of reduction, either a Single or Double Roll Crusher can be selected. Regardless of the crusher type selected, Roll Crushers allow for the material to fracture along naturally occurring cleavage lines, which helps with minimizing fines generation.
Yes, it will. When a wet, sticky feed is fed to a two-stage crusher, you run the risk of plugging the crusher between the top and bottom stages. If a wet, sticky feed is anticipated and the ratio of reduction requires two stages of crushing, it is recommended that two separate single stages be used.
A good rule of thumb is: Single Roll Crushers have a 6:1 ratio of reduction, Double Roll Crushers have a 4:1, Triple Roll Crushers have a 6:1 on the top stage and a 4:1 on the bottom stage, and Quad Roll Crushers have a 4:1 on both the top and bottom stage.
Single Roll Crushers are typically used as primary crushers that provide a crushing ratio of up to 6:1. They crush materials such as ROM coal, mine refuse, shale, slate, gypsum, bauxite, salt, soft shale, etc., while producing minimal fines. Designed with intermeshing roll teeth and a curved crushing plate, they are extremely effective in reducing slabby feeds.
Double Roll Crushers provide a 4:1 reduction ratio. They are typically used as a secondary or tertiary crusher for materials such as ROM coal with refuse, limestone, gypsum, trona, shale, bauxite, oil shale, clean coal, coke, salt, quicklime, burnt lime, glass, kaolin, brick, shale and wet, sticky feeds. Each machine is custom engineered with roll elements and tooth patterns selected depending on theapplication requirements to produce a cubical product with minimal fines.
Triple Roll Crushers are ideal for producers who want to accomplish two stages of reduction in one pass. They can be used in coal, salt, coke, glass, and trona operations, among others. Triple Roll Crushers combine a Single Roll Crusher with a Double Roll Crusher to form a crusher that is capable of achieving a 6:1 reduction ratio in the primary stage and a 4:1 reduction in the secondary stage while producing a cubicle product at high capacity.
Quad Roll Crushers are ideal for producers, including those with preparation plants, who want to accomplish two stages of reduction in one pass. They can be used in coal, salt, lime, pet coke and potash operations, among others. Quad Roll Crushers are capable of achieving a 4:1 reduction ratio before feeding the crushed material to the secondary stage for an additional 4:1 reduction to make the final product.
Double-toothed Roller crusher, also known as 2PGC crusher, belongs to the type of double-roller. The shape of the roller surface can be divided into coarse and fine-toothed rollers. It can be adjusted according to the size of the material and is suitable for brittle and soft materials. The double-tooth roller crusher is suitable for sintering, coal, cement, silicate, glass, ceramics, and other industries. It is suitable for the crushing of brittle materials below medium hardness. It is mainly used for medium and fine ore crushing operations.
The roller crusher is suitable for medium and fine crushing of solid materials, such as coal, coal gangue, coke, limestone, iron ore, quartz stone and sulfur ore in cement, chemical industry, electric power, mining, metallurgy, building materials, refractory materials, coal mines.
The roller crusher is equipped with two crushing rollers. According to the particle size required by the user, roll crusher can be divided into smooth roller crusher and tooth roller crusher. Smooth roller crusher is suitable for fine crushing operations where the feed particle size is less than 80mm and the final size 1-10mm. The gear roller type is suitable for the medium and fine crushing with feed particle size is less than 150mm and the finished product particle size is 5-30mm.
The two rollers have wedge or gasket adjusting device, wedge device with the top adjustment bolt, when the adjustment bolt wedge block upward pull up,the wedge pushes the movable roller away from the fixed roller, two roller gap becomes larger, the discharge size becomes larger, when the wedge block down, activity roller compression spring (or pressing oil cylinder) under the action of two gap becomes smaller, the discharge size becomes smaller. Gasket device is through increase or decrease the number of gasket thickness to adjust the size of the discharge size, when adding gasket will make two roller wheel gap bigger, when reduce gasket will make two roller wheel clearance decrescent, the discharge size becomes smaller.
No matter what sector you work in, we know there is no room for error. A good crusher has to deliver close product size distribution first time, every time. When this is what you need, you cant go wrong with an Essa Rolls Crusher the most uncomplicated and durable mid-range secondary crushers available. They come with contra-rotating rolls to produce material with a tight size envelope containing minimum of fines. This gives you consistent quality, accurate size distribution, and very little dust. You get the option of plain or toothed rolls to suit a range of materials.
As well as giving you fast and accurate results, you need a crusher thats safe and easy to use. Essa Rolls Crushers have fitted feed hoppers, easily accessible aluminium sample draws, simple stop/start buttons, and motor protection.
Large crushed output with minimal cost - we know thats the challenge of any plant or laboratory involved in sample reduction. Rolls crushers have been widely used for years and are the best when it comes to close product size distribution and low maintenance costs. Just a quick look at the practical design features and youll see that productivity, quality, value and usability are all taken care of. They wont let you down.
For laboratory applications, you cant go wrong with this rugged and low maintenance crusher. Essa RC2000 is a proven mid-range secondary rolls crusher designed for fast and controlled size reduction of various sample types. With a tight footprint, its the smaller of the two rolls crushers in our Essa fine crushing range.
Easy to install The standalone configuration of the RC2000 allows for simple and low-cost installation. Its mounted on a sturdy floor stand and fitted with a feed hopper and easily accessible aluminium sample draw. This ergonomic design makes it easy to use and offers your workers greater protection.
If youre looking for a larger feed size, try the Essa RC3000. This rolls crusher is a dependable and sturdy mid-range secondary crusher that has a maximum feed size of 40 mm. Its also packed with considerably more power.
Floor or bench mount Weve made RC3000 versatile, giving you two installation options to choose from: a floor mount standalone version suitable for batch use, or a low-profile bench mount version. If you need continuous use, such as in mechanical sampling plants, automated laboratories or pilot plants, the bench mount version is the ideal configuration for you.
Ergonomics Like the smaller model, RC3000 is fitted with a range of safety and usability features. Your workers will appreciate the contra-rotating rolls, fitted feed hopper, easily accessible aluminium sample draw, mesh guarding, and dust extraction point.
FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.
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.Get in Touch with Mechanic