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primary roll crusher

primary crusher - an overview | sciencedirect topics

primary crusher - an overview | sciencedirect topics

The primary crusher is located in the quarry and consists of a McLanahan 48x72 Shale King Crusher rated at 1,000 TPH (Tons Per Hour). The driving flywheel has a diameter of 2.5 meters and is motor driven through six v-belts. The capacity of the primary crusher had to be increased to 1,250 TPH to produce enough material to serve the wet and both dry lines in the plant. To enable the crusher to operate at the higher capacity, the manufacturer recommended grooving the flywheel for two additional v-belts. To avoid the costs of disassembling, shipping and reassembling, Nesher performed the machining in-place. The operation was performed using portable tools and an auxiliary motor that turned the flywheel for machining the new grooves.

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.

Secondary coal crusher: Used when the coal coming from the supplier is large enough to be handled by a single crusher. The primary crusher converts the feed size to one that is acceptable to the secondary crusher.

Detail descriptions of designs are given of large gyratory crushers that are used as primary crushers to reduce the size of large run-of-mine ore pieces to acceptable sizes. Descriptions of secondary and tertiary cone crushers that usually follow gyratory crushers are also given in detail. The practical method of operation of each type of gyratory crusher is indicated and the various methods of computing operating variables such as speed of gyration, capacities and power consumption given are prescribed by different authors. The methods of calculations are illustrated to obtain optimum operating conditions of different variables of each type using practical examples.

Shale, a low-moisture content soft rock, is quarried, transferred to blending stockpiles before it is reduced by primary crushers and dry-milled to a powder of less than 250m. This powder is homogenized and stored ready for pelletization in manner similar to that used for making aggregate from PFA except that no fuel is added. However, after the pellets have been produced to the appropriate size, which depends on the expansion required, they are compacted and coated with finely powdered limestone. The resulting pellets are spherical with a green strength sufficient for conveying to a three-stage kiln consisting of a pre-heater, expander and cooler. Unlike other aggregates produced from argillaceous materials, the feedstock is reduced to a powder and then reconstituted to form a pellet of predetermined size. The expansion (bloating) is controlled during kilning to produce an aggregate of the required particle density. Different particle densities are produced by controlling the firing temperature and the rotational speed of the kiln. The coating of limestone applied to the green pellet increases the degree of surface vitrification which results in a particle of low permeability. This product gives versatility to the designer for pre-selecting an appropriate concrete density. As Figure7.6 shows, while the particle shape and surface texture of the aggregate remain essentially the same, the internal porosity can be varied according to the bloating required for the specified density.

Mined crushed stone is loaded into trucks or onto conveyors and transported to the processing facility. The broken stone is dumped into a primary crusher where the large rock fragments are broken into smaller sizes. Crushing to the proper size usually occurs in stages because rapid size reduction, accomplished by applying large forces, commonly results in the production of excessive fines (Rollings and Rollings 1996). After primary crushing, the material is run through one or more secondary crushers. These crushers use compression, impact, or shear to break the rock into smaller pieces. The material is screened after each crushing cycle to separate properly sized particles (throughs) from those needing additional crushing (overs). Additional washing, screening, or other processing may be required to remove undesirable material. The material is then stockpiled awaiting shipment.

After mining, sand and gravel may be used as is, which is called bank-run or pit-run gravel, or it may be further processed. The procedures for processing sand and gravel are similar to those for processing crushed stone. The amount of processing depends on the characteristics of the sand and gravel deposit and the intended use. If the gravel deposits contain very large cobbles or boulders, that material may be run through a primary crusher. The material may be run through one or more secondary crushers, then washed, screened, or further processed to remove undesirable material. The material is then stockpiled awaiting shipment.

The design of belt and apron feeders is fairly standardized, and most of the producing companies use pre-defined models and calculation methods to get short delivery times with a low-cost approach. The main features of the apron and belt feeders are:

Although the conveying devices are reasonably well defined and standardized, there is still room for improvement of the overall plant layout and construction, e.g. crushing plant, silo discharge system, train unloading system, etc. One of the most obvious ways to improve the overall design of such systems is to develop a better understanding of the equipment itself. Today, most OEMs want to be involved in the process of seeking the solution rather than only the supply of the equipment. This will enable the market to make use of the expertise of the equipment supplier and, at the same time, use their knowledge base for developing a wider scope, including other aspects such as silo design, hopper design, electrical and hydraulic issues, etc.

Highland Valley copper mine experienced a decline in mill throughput after implementing larger holes for blasting, which resulted in coarser fragmentation and a coarser product from the primary crushers [24]. In the quarry at Vrsi, as drilling geometry decreased from 3.0m4.5m to 2.9m3.0m while other parameters such as borehole sizes were constant, a significant savings of 14% was achieved for the quarry [25]. Due to a mine-to-mill implementation at the Red Dog Mine, the mine achieved savings exceeding $30 million per year [26]. This indicates that, at least in some ores, improved internal fragmentation carries through the crushing and grinding circuits. The mine-to-mill project in the same mine identified further benefit, specifically the marked reduction in SAG feed size and throughput variability [5]. A second but important benefit was the reduced wear in the gyratory crusher, resulting in a significantly longer period between relines. When electronic detonators with very short delay time were applied in the Chuquicamata open pit copper mine, the fragmentation was markedly improved [27]. In the Aitik copper mine a raised specific charge from 0.9 to 1.3kg/m3 gave rise to an increase in the throughput by nearly 7% due to more fines produced and shorter grinding time achieved [28].

Jaw crushers are mainly used as primary crushers to produce material that can be transported by belt conveyors to the next crushing stages. The crushing process takes place between a fixed jaw and a moving jaw. The moving jaw dies are mounted on a pitman that has a reciprocating motion. The jaw dies must be replaced regularly due to wear. Figure 8.1 shows two basic types of jaw crushers: single toggle and double toggle. In the single toggle jaw crusher, an eccentric shaft is installed on the top of the crusher. Shaft rotation causes, along with the toggle plate, a compressive action of the moving jaw. A double toggle crusher has, basically, two shafts and two toggle plates. The first shaft is a pivoting shaft on the top of the crusher, while the other is an eccentric shaft that drives both toggle plates. The moving jaw has a pure reciprocating motion toward the fixed jaw. The crushing force is doubled compared to single toggle crushers and it can crush very hard ores. The jaw crusher is reliable and robust and therefore quite popular in primary crushing plants. The capacity of jaw crushers is limited, so they are typically used for small or medium projects up to approximately 1600t/h. Vibrating screens are often placed ahead of the jaw crushers to remove undersize material, or scalp the feed, and thereby increase the capacity of the primary crushing operation.

Both cone and gyratory crushers, as shown in Figure 8.2, have an oscillating shaft. The material is crushed in a crushing cavity, between an external fixed element (bowl liner) and an internal moving element (mantle) mounted on the oscillating shaft assembly. An eccentric shaft rotated by a gear and pinion produces the oscillating movement of the main shaft. The eccentricity causes the cone head to oscillate between the open side setting (o.s.s.) and closed side setting (c.s.s.). In addition to c.s.s., eccentricity is one of the major factors that determine the capacity of gyratory and cone crushers. The fragmentation of the material results from the continuous compression that takes place between the mantle and bowl liners. An additional crushing effect occurs between the compressed particles, resulting in less wear of the liners. This is also called interparticle crushing. The gyratory crushers are equipped with a hydraulic setting adjustment system, which adjusts c.s.s. and thus affects product size distribution. Depending on cone type, the c.s.s. setting can be adjusted in two ways. The first way is by rotating the bowl against the threads so that the vertical position of the outer wear part (concave) is changed. One advantage of this adjustment type is that the liners wear more evenly. Another principle of setting adjustment is by lifting/lowering the main shaft. An advantage of this is that adjustment can be done continuously under load. To optimize operating costs and improve the product shape, as a rule of thumb, it is recommended that cones always be choke-fed, meaning that the cavity should be as full of rock material as possible. This can be easily achieved by using a stockpile or a silo to regulate the inevitable fluctuation of feed material flow. Level monitoring devices that detect the maximum and minimum levels of the material are used to start and stop the feed of material to the crusher as needed.

Primary gyratory crushers are used in the primary crushing stage. Compared to the cone type crusher, a gyratory crusher has a crushing chamber designed to accept feed material of a relatively large size in relation to the mantle diameter. The primary gyratory crusher offers high capacity thanks to its generously dimensioned circular discharge opening (which provides a much larger area than that of the jaw crusher) and the continuous operation principle (while the reciprocating motion of the jaw crusher produces a batch crushing action). The gyratory crusher has capacities starting from 1200 to above 5000t/h. To have a feed opening corresponding to that of a jaw crusher, the primary gyratory crusher must be much taller and heavier. Therefore, primary gyratories require quite a massive foundation.

The cone crusher is a modified gyratory crusher. The essential difference is that the shorter spindle of the cone crusher is not suspended, as in the gyratory, but is supported in a curved, universal bearing below the gyratory head or cone (Figure 8.2). Power is transmitted from the source to the countershaft to a V-belt or direct drive. The countershaft has a bevel pinion pressed and keyed to it and drives the gear on the eccentric assembly. The eccentric assembly has a tapered, offset bore and provides the means whereby the head and main shaft follow an eccentric path during each cycle of rotation. Cone crushers are used for intermediate and fine crushing after primary crushing. The key factor for the performance of a cone type secondary crusher is the profile of the crushing chamber or cavity. Therefore, there is normally a range of standard cavities available for each crusher, to allow selection of the appropriate cavity for the feed material in question.

Crushers are widely used as a primary stage to produce the particulate product finer than about 50100 mm in size. They are classified as jaw, gyratory and cone crushers based on compression, cutter mill based on shear and hammer crusher based on impact.

A jaw crusher consists essentially of two crushing plates, inclined to each other forming a horizontal opening by their lower borders. Material is crushed between a fixed and a movable plate by reciprocating pressure until the crushed product becomes small enough to pass through the gap between the crushing plates. Jaw crushers find a wide application for brittle materials. For example, they are used for comminution of porous copper cake.

A gyratory crusher includes a solid cone set on a revolving shaft and placed within a hollow body, which has conical or vertical sloping sides. Material is crushed when the crushing surfaces approach each other and the crushed products fall through the discharging opening.

Hammer crushers are used either as a one-step primary crusher or as a secondary crusher for products from a primary crusher. They are widely used for crushing of hard metal scrap for different hard metal recycling processes.

Pivoted hammers are pendulous, mounted on the horizontal axes symmetrically located along the perimeter of a rotor and crushing takes place by the impact of material pieces with the high speed moving hammers and by contact with breaker plates. A cylindrical grating or screen is placed beneath the rotor. Materials are reduced to a size small enough pass through the openings of the grating or screen. The size of product can be regulated by changing the spacing of the grate bars or the opening of the screen.

The feature of the hammer crushers is the appearance of elevated pressure of air in the discharging unit of the crusher and underpressure in the zone around of the shaft close to the inside surface of the body side walls. Thus, the hammer crushers also act as high-pressure forced-draught fans. This may lead to environmental pollution and product losses in fine powder fractions.

A design for a hammer crusher (Figure 2.6) allows essentially a decrease of the elevated pressure of air in the crusher discharging unit [5]. The A-zone beneath the screen is communicated through the hollow ribs and openings in the body side walls with the B-zone around the shaft close to the inside surface of body side walls. As a result, circulation of suspended matter in the gas between A- and B-zones is established and high pressure of air in the discharging unit of crusher is reduced.

roll crusher - an overview | sciencedirect topics

roll crusher - an overview | sciencedirect topics

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.

roll crushers | mclanahan

roll crushers | mclanahan

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.

primary crushing

primary crushing

The term primary crusher, by definition, might embrace any type and size of crushing machine. The term implies that at least two stages of crushing are involved, but in many cases the machine which performs the function of initial crusher is the only crusher in the plant. The factors influencing the selection of a crusher for this service are much the same, regardless of how many crushing stages there are in the flowsheet; therefore, the term primary crusher, by common usage, is applied to the crusher which takes up the job of reduction where the blasting operations leave off. Selecting the right type and size of primary crusher is a problem of prime importance in the designing of a crushing plant of any nature and size. Usually this machine is the largest and most expensive single item of equipment in the plant; a mistake in the choice can only be remedied fully by replacement; and, because the entire primary crusher-house arrangement is generally tailored.to fit the crusher, such .replacement is almost always a costly procedure. While personal favouritism toward some particular type of crusher may safely be allowed to swing a close decision, it should never blind the engineer or operator to the merits of other types, nor to the limitations of his favorite. The following factors all have a more or less important bearing upon the choice of the primary crusher.

The first three of these factors will almost always be ascertainable at least to a close approximation before the matter of crusher choice is taken up. Sometimes, as when a new crushing plant, or a new primary crusher set-up, is to be installed at an existing operation the last three factors will be pre-established. Otherwise, it is sound practice to consider them as a part of the problem of crusher selection. The primary crushing setup is closely linked to the quarrying or mining operation, and it is only by careful adjustment of all equipment selections to the general plan of operation that optimum operating results may be realized.

While it is convenient to discuss the influence of these several factors separately, it is well to keep in mind that they are more or less closely interlocked, and that a change in one of them may necessitate altering one or more of the others.In addition to the factors listed there are usually a few which are peculiar to each individual problem such as labor costs and so on. Any plant design problem is an economic as well as an engineering one. We are concerned here ,chiefly with the engineering phases.

Characteristics of the material to be crushed include the geological classification of the rock, its physical structure, its chemical analysis (at least so far as abrasive constituents are concerned), and at least a qualitative evaluation of its resistance to crushing that is, whether soft, medium, hard, or very hard and tough. Frequently such information may be obtained from contiguous deposits which are being operated; sometimes the values must be arrived at by laboratory tests. It is never safe to make blanket assumptions, even on such a material as limestone, which can sometimes prove to be quite tough, as well as to contain significant amounts of abrasive silica.

Physical, or geological, structure of the deposit often has an important bearing upon selection of size or type, or both. If the deposit is thinly stratified, as, for example, many deposits of limestone are, it is safe to assume that the rock can be blasted economically into a condition for feeding a gyratory crusher of medium proportions, or, if other characteristics are suitable, a sledging roll crusher, such as the Fairmount machine. If, on the other hand, the formation is of massive character, again, some limestones are, the gyratory crusher might be ruled out in favour of the jaw crusher, unless the operation is of sufficient magnitude to warrant installation of a large size of gyratory. The proposed quarrying or mining procedure will of course have some bearing upon the size of rock to go to the crusher, regardless of its physical structure, as will be pointed out in further detail later on. If the chemical analysis of the rock discloses that substantial amounts of free silica or any other abrasive are present, crushers of the sledging roll or hammermill types are usually ruled out unless the material is extremely soft and friable. There are occasional speciality applications where such machines may be indicated for crushing abrasive materials, but from the standpoint of, economical operation their use for such service is rarely justifiable. The same restriction holds true for hard and tough materials. For such rock or ore our choice of a primary crusher is restricted to the gyratory and jaw types except, again, for the occasional specialty application where economy in maintenance may be sacrificed for other considerations such as lower first cost, or space restrictions.

The significance of this factor is so obvious that it sometimes does not receive quite as much thought as it should. From the standpoint of minimum requirement, it is of course closely tied up with product size, or crusher setting. But the primary crusher can seldom be chosen solely on the basis of capacity; it should never be selected with a view to just meeting the average capacity required to feed the rest of the crushing plant. Just how much the rated capacity of the primary crusher (at the required discharge setting) should exceed the average capacity of the plant depends upon how uniformly the crusher will be fed; or to put it more definitely, what percentage of the total operating period the crusher will operate at full rated capacity. The answer to this is not always an easy one to predetermine, as it may depend upon several details of plant design and quarry operation.

In the average quarry operation, the only surge capacity between the quarry and the primary crusher consists of whatever quantity of rock may be, at the moment, loaded in cars or trucks, and usually this is not large. For that reason, any operating delays occurring in loading, transportation or primary crushing quickly affect all three of them, with the result that the feed to the balance of the crushing plant is cut-off until the trouble is rectified. If the plant as a whole is to maintain its rated average output, these departments must be capable of making up for such interruptions, and they can only do this if they have reserve capacity over and above the average requirement.

Such interruptions to continuous production are not uncommon in the primary crusher house; they may assume serious proportions if the crusher receiving opening is not large enough for the material it is expected to handle, and the largest crushers of any type will occasionally bridge or block. Crusher capacity tables are predicated upon a continuous feed of rock of a size that will readily enter the crushing chamber; it is obvious therefore that a crusher whose rating just equals the average plant requirement would have no reserve to compensate for the conditions we have outlined. For the average quarry operation this reserve should be not less than 25 percent, and preferably about 50 percent.

Since the minimum dimension of the feed opening of a crusher determines the maximum size of lump that it can take, the choice of a primary breaker is dependent as much on the size of the feed as on the hourly tonnage. Thus a 15 in. by 24 in. jaw crusher would be suitable for a small mine hoisting 300 tons in eight hours from underground workings from which lumps larger than 14 in. are not likely to be received. A crusher of these dimensions will break 40 tons per hour to 2-in. size with a power consumption of 30 h.p. On the other hand, a 14-in. gyratory crusher, working as it should at full capacity, will crush 100 tons per hour to the same size with a power consumption of 70 h.p. ; at 40 tons per hour, it would still require about 50 h.p. The jaw crusher is evidently the more economical machine in this case, and its first cost is only about half that of the gyratory crusher.

If the capacity of the primary breaker is required to be 100 tons per hour or over, a gyratory crusher is likely to be more economical than the other type, since it costs no more than a jaw crusher of similar capacity and consumes less power. Moreover, the difference in power consumption between the two types of machine is greater in practice than in theory; this is due to the fact that, since the gyratory crusher can be choke-fed, it is easier to keep it running at maximum efficiency.

The position is different when mining is done by power-shovel. The maximum size of lump delivered to the crushing plant is much larger than from underground workings, and it is not advisable to use a bin for the storage of the ore on account of the difficulty of handling very large lumps through a bin gate. Consequently the ore is generally sent direct to a preliminary breaker which reduces it to a size suitable for feeding the normal primary breaker. The first machine is often of the jaw type, although this depends on the circumstances. Suppose, to take an instance, that the shovels were equipped with 3-yd. dippers and that 2,000 tons were being mined per day. A 48 in. by 60 in. jaw crusher is more than large enough to take the maximum size of lump that could get through the jaws of the dipper, and it would break the whole days output to 6-in. size in eight hours with a power consumption of under 200 h.p. On the other hand, a 42-in. gyratory crusher, which is the smallest that could be installed with safety, has a maximum capacity of over 5,000 tons in eight hours with a power consumption of about 275 h.p. The jaw breaker would therefore be the more economical machine. It could, if necessary, be installed near the scene of mining operations, and would be set to deliver a 6- or 8-in. product, which could be conveniently transported to the crushing section of the flotation plant where it would be fed through the coarse ore bin to the primary breaker in the ordinary way.

The choice of a primary breaker is an individual problem for every installation. The type of mining and the regularity, size, and rate atwhich the ore is delivered, are the main determining factors, but all local conditions should be taken into consideration before a decision is made.

comminution | henan deya machinery co., ltd

comminution | henan deya machinery co., ltd

In order to separate the minerals from gangue (the waste minerals), it is necessary to crush and grind the rock to unlock, or liberate, valuable minerals so that they are partially or fully exposed.This process of size reduction is called comminution.The crushing and grinding process will produce a range of particles with varying degrees of liberation.Any particles that exceed a target size required for physical separation or chemical extraction are returned to the crushing or the grinding circuit.

ii. Secondary Crushing (intermediate crushing): In this case, ore is crushed from 10 cm to less than 1 2 cm size; for this purpose jaw, cone or roll crushers are used. These secondary crushers consume more power than primary crushers.

ii. Fine Grinding: Fine grinding, which is the final stage of comminution, is performed in ball mills using steel balls as the grinding medium. The ball mill, after feeding 0.5 mm material may give a product that is less than 100 microns.

The first process most ores undergo after they leave the mine is mineral dressing(processing), also called ore preparation, milling, and ore dressing or ore beneficiation. Ore dressing is a process of mechanically separating the grains of ore minerals from the gangueminerals, to produce a concentrate (enriched portion) containing most of the ore minerals anda tailing (discard) containing the bulk of the gangue minerals.

Since most ore minerals are usually finely disseminated and intimately associated withgangue minerals, the various minerals must be broken apart (freed) or liberated before theycan be collected in separate products. Therefore, the first part in any ore dressing process willinvolve the crushing and grinding (which is also known by a common name calledcomminution) of the ore to a point where each mineral grain is practically free.

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