Applied materials: coal, pebble, limestone, dolomite, granite, construction waste, pebbles, glass, cement clinker, basalt, iron ore, quartz stone, coal gangue, etc. Its advantages: high capacity, ability to handle wet, sticky feeds.
Roll crusher, as one of the most economical and practical crushers, is designed to handle the first and second crushing of friable minerals and stones such as coal, clay, coal gangue, limestone, slag, cement clinkers, and shale, etc.
According to the number of rollers, the FTM roll crushers can be divided into three types: single roll crusher, double-roll crusher, and multi-roll crusher. And the most common one is double-roll crusher.
Roll crusher is applied more widely than other crushers because of its small volume and cheap price. With the adjustable discharging system, it can be used flexibly in coarse and fine crushing processes of the industries such as cement, chemical engineering, electricity, mining, metallurgy, building materials, and others.
Roll crushers can adjust the wedge device between rollers to control the feed and discharge size of the machine. Also, it is equipped with a spring device to protect the crushing machine and avoid shutdown caused by overload and iron passing.
When the adjustable bolt pulls the wedge upward, the wedge pushes the movable roller away from the fixed wheel, then the gap between the two rollers becomes larger, and the discharge port becomes larger, and vice versa.
The gasket device adjusts the size of the discharge by increasing or decreasing the thickness of the gasket. When the gasket is added, the gap between the two rollers becomes larger, and vice versa.
The unique structure of rollers makes selective crushing of the roll crushing equipment. Since minerals fed are crushed along its internal friable crack, the finished products are uniform with the cube shape.
The minerals are crushed under the force of rollers and machine body, and ores smaller than the gap between roller and machine frame (of single roll crusher) or roller (of multi-roll crusher) will pass directly without repeated crushing.
With the supporting CPU, operators can control roll crushing machines and monitor gaps between rollers, and clean up the crushing cavity through the central control room, which will help save energy of 30% to 50%.
The main working parts of the roller crusher is the cylindrical rollers. The rollers are supported by the fixed and movable bearings, and they are relatively rotating which are driven by the motor. The materials are crushed by the friction of the rotating rollers, and the finished products are discharged from the gap of the rollers.
The spring is used to balance the pressure generated between the rolls. If there are non-crushed materials falling between the two rollers, the compression spring of bearings can be pushed to make a large gap so that non-crushed materials can be discharged immediately.
The quality of the crushers has a great impact on its price. The high-quality equipment will cost more in terms of workmanship, technology, materials, etc. Meanwhile, it will have a long service life, low failure rate, and better performance, and bring more profit to investors.
In 2019, Fote has exported a total of 39 roll crushers to India, Indonesia, Zimbabwe, Vietnam, South Africa, the United States, Pakistan, the Philippines and other countries, mainly for coal, bentonite, rare earth ore, limestone, aluminum, manganese and others.
Exports of mining machinery have been booming in recent years and Fote has already opened markets in Africa, Southeast Asia, etc. Fote Heavy Machinery has supported foreign customers with low-price and high-quality roll crushing equipment, which has been popular among the majority of customers.
In recent years, the Indonesian government has taken actions to improve its infrastructure and promote economic development. As a result, Indonesia's demand for crushers has increased significantly.
The roll crusher produced by Fote has fine finished products and the best effect on sand making for river pebble. Due to its good finished product size, low powder content and low price, it is widely favored by Indonesian customers.
Firstly, Fote Heavy Machinery is a professional manufacturer of roller crushers. In order to improve the company's comprehensive strength, Fote has introduced international first-class production lines on the basis of original techniques.
Secondly, FTM produces various types of crushing equipment that is suitable for crushing, sand making and milling hundreds of minerals, and ensures excellent quality, good performance and low price.
Thirdly, Fote has provided patient and prudential after-sales service and all-round consideration for customers, and actively created high-tech crushing equipment to take the leading position in the international market.
As a leading mining machinery manufacturer and exporter in China, we are always here to provide you with high quality products and better services. Welcome to contact us through one of the following ways or visit our company and factories.
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.
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Williams is an industry-leading roll crusher manufacturer and designer for high-quality roll crushers with desirable benefits such as high throughput capacity, minimal maintenance requirements, low cost per ton operation, and more. Learn more about our heavy-duty roll crushers below or contact our sales engineers to talk about your application needs.
A combination of impact, shear, and compression are the forces necessary to perform the crushing and size reduction in a Williams roll crusher. The material enters the roll crusher machine and is impacted by the roll as it rotates. Then, as the material is pulled between a crushing plate or rolls, shear and compression forces act upon the material. The rolls act as flywheels, contributing to smooth operation and efficient use of power. Roll crushing surfaces operate at a fixed distance apart, as opposed to the continually changing distances in a jaw or cone crusher. This creates a more consistent product size.Roll crushers are low in profile and relatively easy to install. They can be fed with a minimum of headroom, or even choke fed. Adjustments are simple andinternal parts are readily accessible.
Typical feed materials for Williams Roll Crushers include: bauxite, cement clinker, chalk, cinders, clay, coal, glass, gypsum, limestone, burnt lime, rock salt, sandstone, shale, sulfur ore, sea shells, and sewer sludge clinker. Single Roll Crushers, sometimes called lump breakers, can also be used for breaking frozen or agglomerated materials.
Williams Roll Crushers are used in a variety of industries such as, mining recycling, and power industries. Interested in learning more about the Williams Roll Crushers for your specific industry and application? Contact our sales engineers!
Choosing between a single roll crusher and double roll crusher depends upon the type of feed material, feed size, product size desired, and consistency of both feed and product. Both single and double roll crushers operate most efficiently with dry, friable materials. However, single roll machines have been widely and successfully used for the reduction of moist clays. They also have been long used as primary and secondary coal crushers, both at mine sites and power plants, where a minimum of fines is desired.
Williams single roll crushers reduce via a combination of impact, shear, and compression. The rolls are always toothed in patterns suited to the feed material. Single Roll Crushers generally handle larger feed sizes at higher reduction ratios in higher capacities and are particularly well suited to be used as lump breakers.
Double roll crushers reduce primarily through compression, although some shear is obtained with toothed rolls. Rolls for these crushers come in combinations of smooth, corrugated, and toothed designs. Double Roll Crushers produce a finer product at lower reduction ratios and capacities.
Oversized, heat-treated, alloy steel shafts plus self-aligning, roller-type bearings assure long life and maximum use of power. Jackshafts for control of roller speed are standard on double roll crushers, optional on larger Single Roll Crushers.
Heavy-duty compression springs permit movement of floating roll to pass tramp metal and other uncrushables, avoiding overload and damage. Smaller Single Roll Crushers are equipped with a shear pin release.
Faces Tooth patterns and corrugations to fit feed material; abrasion-resistant alloy; easily replaceable. Ash Crushers have additional features including dust-tight design and sealed cover plates for breaker plate access.
Williams Single Roll Crushers are also available in a 15 inch (381mm) diameter dust-tight version for applications such where it would be expensive to have dust collection air. Already well known for rugged construction, low profile, high reduction ratio, and economical cost, Williams Dust-Tight Ash Single Roll Crushers also have easy access to the rotor for maintenance. These dust-tight roll crushers are perfect for applications such as crushing ash, limestone, coal, or glass.
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.
Roll crusher, also called roller crusher machine, is a kind of traditional crushing mill, mainly used for the middle and fine processing of raw material applied in cement plant, chemical industry, building materials industry, etc. It is usually classified into three types: single-roll crusher, double-roll crusher and four-roll crusher. The double-roll crusher is the most commonly used one in the factory, but there are still many cases where it is not suitable. While the more efficient and reasonably designed four-roll crusher can bring a better crushing effect. AGICO provides a high-quality four-roll crusher with different capacities. They all have the characteristic of high yield, low noise, and long service life.
Four-roll crusher can be divided into two crushing stages from top to bottom. When working, motors will drive the belt pulleys on both sides of the crusher to rotate the two pairs of rollers. Rollers of the same stage run in the opposite direction and mesh with each other. When materials enter the crusher, the material with smaller particle size will directly pass through the middle clearance of the first pair of rollers into the second stage crushing. The clearance is equivalent to the sieve plate so that materials meeting the requirements of clearance (particle size) can fall automatically. Otherwise, they will be crushed by the rollers in the first crushing stage firstly, and then fall into the second crushing stage. The four rollers all move at a certain differential speed so that each pair of rollers can rub against each other, thus ensuring that materials with different moisture content do not stick or block when crushing. And because of the deceleration movement of the roller, materials are constantly turned over on the roller and crushed at the weakest point, so as to achieve the purpose of quickly crushing with the smallest force.
AGICO Group is an integrative enterprise group. It is a Chinese company that specialized in manufacturing and exporting cement plants and cement equipment, providing the turnkey project from project design, equipment installation and equipment commissioning to equipment maintenance.
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.