crusher - an overview | sciencedirect topics
Roll crushers are generally not used as primary crushers for hard ores. Even for softer ores, like 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 are employed. For close circuit the product is screened with a mesh size much less than the set.
Fig. 6.4 is a typical set up where ore crushed in primary and secondary crushers are further reduced in size by a rough roll crusher in open circuit followed by finer size reduction in a closed circuit by roll crusher. Such circuits are chosen as the feed size to standard roll crushers normally do not exceed 50mm.
Cone crushers were originally designed and developed by Symons around 1920 and therefore are often described as Symons cone crushers. As the mechanism of crushing in these crushers are similar to gyratory crushers their designs are similar, but in this case the spindle is supported at the bottom of the gyrating cone instead of being suspended as in larger gyratory crushers. Fig. 5.3 is a schematic diagram of a cone crusher. The breaking head gyrates inside an inverted truncated cone. These crushers are designed so that the head to depth ratio is larger than the standard gyratory crusher and the cone angles are much flatter and the slope of the mantle and the concaves are parallel to each other. The flatter cone angles helps to retain the particles longer between the crushing surfaces and therefore produce much finer particles. To prevent damage to the crushing surfaces, the concave or shell of the crushers are held in place by strong springs or hydraulics which yield to permit uncrushable tramp material to pass through.
The secondary crushers are designated as Standard cone crushers having stepped liners and tertiary Short Head cone crushers, which have smoother crushing faces and steeper cone angles of the breaking head. The approximate distance of the annular space at the discharge end designates the size of the cone crushers. A brief summary of the design characteristics is given in Table 5.4 for crusher operation in open circuit and closed circuit situations.
The Standard cone crushers are for normal use. The Short Head cone crushers are designed for tertiary or quaternary crushing where finer product is required. These crushers are invariably operated in closed circuit. The final product sizes are fine, medium or coarse depending on the closed set spacing, the configuration of the crushing chamber and classifier performance, which is always installed in parallel.
For finer product sizes, i.e. less than 6mm, special cone crushers known as Gyradisc crushers are available. The operation is similar to the standard cone crushers except that the size reduction is caused more by attrition than by impact, . The reduction ratio is around 8:1 and as the product size is relatively small the feed size is limited to less than 50mm with a nip angle between 25 and 30. The Gyradisc crushers have head diameters from around 900-2100mm. These crushers are always operated in choke feed conditions. The feed size is less than 50mm and therefore the product size is usually less than 6-9mm.
Crushing is accomplished by compression of the ore against a rigid surface or by impact against a surface in a rigidly constrained motion path. Crushing is usually a dry process and carried out on ROM ore in succession of two or three stages, namely, by (1) primary, (2) secondary, and (3) tertiary crushers.
Primary crushers are heavy-duty rugged machines used to crush ROM ore of () 1.5m size. These large-sized ores are reduced at the primary crushing stage for an output product dimension of 1020cm. The common primary crushers are of jaw and gyratory types.
The jaw crusher reduces the size of large rocks by dropping them into a V-shaped mouth at the top of the crusher chamber. This is created between one fixed rigid jaw and a pivoting swing jaw set at acute angles to each other. Compression is created by forcing the rock against the stationary plate in the crushing chamber as shown in Fig.13.9. The opening at the bottom of the jaw plates is adjustable to the desired aperture for product size. The rocks remain in between the jaws until they are small enough to be set free through this opening for further size reduction by feeding to the secondary crusher.
The type of jaw crusher depends on input feed and output product size, rock/ore strength, volume of operation, cost, and other related parameters. Heavy-duty primary jaw crushers are installed underground for uniform size reduction before transferring the ore to the main centralized hoisting system. Medium-duty jaw crushers are useful in underground mines with low production (Fig.13.10) and in process plants. Small-sized jaw crushers (refer to Fig.7.32) are installed in laboratories for the preparation of representative samples for chemical analysis.
The gyratory crusher consists of a long, conical, hard steel crushing element suspended from the top. It rotates and sweeps out in a conical path within the round, hard, fixed crushing chamber (Fig.13.11). The maximum crushing action is created by closing the gap between the hard crushing surface attached to the spindle and the concave fixed liners mounted on the main frame of the crusher. The gap opens and closes by an eccentric drive on the bottom of the spindle that causes the central vertical spindle to gyrate.
The secondary crusher is mainly used to reclaim the primary crusher product. The crushed material, which is around 15cm in diameter obtained from the ore storage, is disposed as the final crusher product. The size is usually between 0.5 and 2cm in diameter so that it is suitable for grinding. Secondary crushers are comparatively lighter in weight and smaller in size. They generally operate with dry clean feed devoid of harmful elements like metal splinters, wood, clay, etc. separated during primary crushing. The common secondary crushers are cone, roll, and impact types.
The cone crusher (Fig.13.12) is very similar to the gyratory type, except that it has a much shorter spindle with a larger-diameter crushing surface relative to its vertical dimension. The spindle is not suspended as in the gyratory crusher. The eccentric motion of the inner crushing cone is similar to that of the gyratory crusher.
The roll crusher consists of a pair of horizontal cylindrical manganese steel spring rolls (Fig.13.14), which rotate in opposite directions. The falling feed material is squeezed and crushed between the rollers. The final product passes through the discharge point. This type of crusher is used in secondary or tertiary crushing applications. Advanced roll crushers are designed with one rotating cylinder that rotates toward a fix plate or rollers with differing diameters and speeds. It improves the liberation of minerals in the crushed product. Roll crushers are very often used in limestone, coal, phosphate, chalk, and other friable soft ores.
The impact crusher (Fig.13.15) employs high-speed impact or sharp blows to the free-falling feed rather than compression or abrasion. It utilizes hinged or fixed heavy metal hammers (hammer mill) or bars attached to the edges of horizontal rotating discs. The hammers, bars, and discs are made of manganese steel or cast iron containing chromium carbide. The hammers repeatedly strike the material to be crushed against a rugged solid surface of the crushing chamber breaking the particles to uniform size. The final fine products drop down through the discharge grate, while the oversized particles are swept around for another crushing cycle until they are fine enough to fall through the discharge gate. Impact crushers are widely used in stone quarrying industry for making chips as road and building material. These crushers are normally employed for secondary or tertiary crushing.
If size reduction is not completed after secondary crushing because of extra-hard ore or in special cases where it is important to minimize the production of fines, tertiary recrushing is recommended using secondary crushers in a close circuit. The screen overflow of the secondary crusher is collected in a bin (Fig.13.16) and transferred to the tertiary crusher through a conveyer belt in close circuit.
Primary jaw crushers typically operate in open circuit under dry conditions. Depending on the size reduction required, the primary jaw crushers are followed by secondary and tertiary crushing. The last crusher in the line of operation operates in closed circuit. That is, the crushed product is screened and the oversize returned to the crusher for further size reduction while the undersize is accepted as the product. Flow sheets showing two such set-ups are shown in Figs. 3.1 and 3.2.
Jaw crushers are installed underground in mines as well as on the surface. When used underground, jaw crushers are commonly used in open circuit. This is followed by further size reduction in crushers located on the surface.
When the run of mine product is conveyed directly from the mine to the crusher, the feed to the primary crusher passes under a magnet to remove tramp steel collected during the mining operation. A grizzly screen is placed between the magnet and the receiving hopper of the crusher to scalp (remove) boulders larger than the size of the gape. Some mines deliver product direct to storage bins or stockpiles, which then feed the crushers mechanically by apron feeders, Ross feeders or similar devices to regulate the feed rate to the crusher. Alternately haulage trucks, front-end loaders, bottom discharge railroad cars or tipping wagons are used. In such cases, the feed rate to the crusher is intermittent which is a situation generally avoided. In such cases of intermittent feed, storage areas are installed and the feed rate regulated by bulldozers, front loaders or bin or stockpile hoppers and feeders. It is necessary that the feed to jaw crushers be carefully designed to balance with the throughput rate of the crusher. When the feed rate is regulated to keep the receiving hopper of the crusher full at all times so that the volume rate of rock entering any point in the crusher is greater than the rate of rock leaving, it is referred to as choke feeding. During choke feeding the crushing action takes place between the jaw plates and particles as well as by inter-particle compression. Choke feeding necessarily produces more fines and requires careful feed control. For mineral liberation, choked feeding is desirable.
When installed above ground, the object of the crushing circuit is to crush the ore to achieve the required size for down stream use. In some industries, for example, iron ore or coal, where a specific product size is required (iron ore 30+6mm), careful choice of jaw settings and screen sizes are required to produce the minimum amount of fines (i.e. 6mm) and maximum the amount of lump ore within the specified size range. For hard mineral bearing rocks like gold or nickel ores where liberation of minerals from the host rock is the main objective, further stages of size reduction are required.
A gold ore was crushed in a secondary crusher and screened dry on an 1180micron square aperture screen. The screen was constructed with 0.12mm diameter uniform stainless steel wire. The size analysis of the feed, oversize and undersize streams are given in the following table. The gold content in the feed, undersize and oversize streams were; 5ppm, 1.5ppm and 7ppm respectively. Calculate:
The self tuning control algorithm has been developed and applied on crusher circuits and flotation circuits [22-24] where PID controllers seem to be less effective due to immeasurable change in parameters like the hardness of the ore and wear in crusher linings. STC is applicable to non-linear time varying systems. It however permits the inclusion of feed forward compensation when a disturbance can be measured at different times. The STC control system is therefore attractive. The basis of the system is:
The disadvantage of the set up is that it is not very stable and therefore in the control model a balance has to be selected between stability and performance. A control law is adopted. It includes a cost function CF, and penalty on control action. The control law has been defined as:
A block diagram showing the self tuning set-up is illustrated in Fig. 18.27. The disadvantage of STC controllers is that they are less stable and therefore in its application a balance has to be derived between stability and performance.
Bone recycling is a simple process where useful products can be extracted. Minerals such as calcium powder for animal; feed are extracted from the bone itself. The base material for cosmetics and some detergent manufacturing needs are extracted from the bone marrow.
The bone recycling process passes through seven stages starting from crushing and ending with packing. Figure 13.14 gives a schematic diagram showing the bone recycling process which goes through the following steps:
Following the standard procedures in the Beijing SHRIMP Center, zircons were separated using a jaw crusher, disc mill, panning, and a magnetic separator, followed by handpicking using a binocular microscope. The grains were mounted together with the standard zircon TEM (417Ma, Black etal., 2003) and then polished to expose the internal structure of the zircons. Cathodoluminescence (CL) imaging was conducted using a Hitachi SEM S-3000N equipped with a Gatan Chroma CL detector in the Beijing SHRIMP Center. The zircon analysis was performed using the SHRIMP II also in the Beijing SHRIMP Centre. The analytical procedures and conditions were similar to those described by Williams (1998). Analytical spots with 25m diameter were bombarded by a 3nA, 10kV O2 primary ion beam to sputter secondary ions. Five scans were performed on every analysis, and the mass resolution was 5000 (at 1%). M257 standard zircon (561.3Ma, U=840ppm) was used as the reference value for the U concentration, and TEM standard zircons were used for Pb/U ratio correction (Black etal., 2003). Common Pb was corrected using the measured 204Pb. Data processing was performed using the SQUID/Isoplot programs (Ludwig, 2001a,b). Errors for individual analyses are at 1, but the errors for weighted average ages are at 2.
A stockpile can be used to blend ore from different sources. This is useful for flotation circuits where fluctuations ingrade can change the mass balance and circulating loads around the plant. Blending can also be done on the ROMpad.
The lowest cost alternative is to have no surge at all, but rather to have a crushing plant on line. This is workable for small-scale plant with single-stage jaw crushers as the availability of these simple plant is very high provided control over ROM size is maintained.
The second alternative is to use a small live surge bin after the primary crusher with a secondary reclaim feeder. Crushed ore feeds this bin continuously and the bin overflows to a small conveyor feeding a dead stockpile. In the event of a primary crusher failure, the crusher loader is used to reclaim the stockpile via the surge bin, which doubles as an emergency hopper.
For coarse ore, the next alternative is a coarse ore stockpile. Stockpiles of this type are generally 1525% live and require a tunnel (concrete or Armco) and a number of reclaim feeders to feed the milling circuit.
Multi-stage crushing circuits usually require surge capacity as the availability of each unit process is cumulative. A fine-ore bin is usually required. Smaller bins are usually fabricated from steel as this is cheaper. Live capacity of bins is higher than stockpiles but they also require a reclaim tunnel and feeders.
different types of crushing equipments - constro facilitator
Crushers are mainly used for crushing stones or mineral ores, recycling construction waste, and producing aggregate. This equipment aims to reduce large solid raw material masses into smaller sizes. They also help to change waste material form so that they can be simply disposed of or recycled. They can also be used for secondary and tertiary crushing to produce the finished product and crushing materials between two parallel solid surfaces.
In an ever-changing industry, waste is one of the major issues for companies when it comes to maximising profits and winning tenders. With the proper application of crushing materials can be reused in other areas of industrial applications.
The primary crusher is only for the breaking of large stones into pieces (this means primary crusher is not for the aggregate size material.). Examples of primary crushers are jaw crusher; hammer mill crusher and gyratory crusher. After receiving the primary crusher crush the material and produce a new fresh reduced size of the source material. The primary crusher has only functioned up to that point. A secondary crusher comes into action and further reduces the size. In secondary crushers some sizes of stones may pass directly from sieve number At the end tertiary crusher reduces the size of crushed pieces very much to the required size and it also brings the fineness to the crushed material. Tertiary crushers are at the job site and these are small in size.
A Jaw Crusher is one of the main types of primary crushers in a mine or ore processing plant. The size of a jaw crusher is designated by the rectangular or square opening at the top of the jaws. Primary jaw crushers are typical of the square opening design, and secondary jaw crushers are of the rectangular opening design. A Jaw Crusher reduces large size rocks or ore by placing the rock into compression. A fixed jaw, mounted in a V alignment is the stationary breaking surface, while the movable jaw exerts a force on the rock by forcing it against the stationary plate. Due to their smaller physical size, jaw crushers are also ideal for tight spaces, such as underground mining and mobile crushing applications.
Newer jaw crusher models are more focused on safety and easy maintenance. Hydraulic separation and individual lifting of shells are in a trend that creates a better environment for any workers on-site working with the equipment
An impact crusher is a machine that uses striking as opposed to pressure to reduce the size of a material. Impact crushers are designated as a primary, secondary, tertiary or quaternary rotor crusher depending on which processing stage the equipment is being utilized. Impact Crushers may be used as primary, secondary, or tertiary crushers depending on the Producers final-product-size needs. Impact Crushers are available in stationary, track, and portable configurations meeting any demand for any of these industries. Although Impact Crushers generally have a higher operating cost than other crushers, they tend to produce a more uniform particle shape (cubical) which is desirable and produces more fines for hot asphalt producers. Common types of Impact Crushers are Horizontal Shaft Impactor (HSI) and Vertical Shaft Impactor (VSI).
The new hybrid models of impact crusher are engineered for maximum feed size, target output size, and total capacity. The newer models are capable of producing construction-grade aggregate, artificial sand and stone materials, run of mine material, especially for the secondary and tertiary crushing stages.
Gyratory crushers are principally used in surface-crushing plants. The gyratory crusher consists essentially of a long spindle, carrying a hard steel conical grinding element, the head, seated in an eccentric sleeve. The spindle is suspended from a spider and, as it rotates, normally between 85 and 150 rpm, it sweeps out a conical path within the fixed crushing chamber, or shell, due to the gyratory action of the eccentric. Gyratory crushers provide high throughput and less downtime to bring maximum efficiency to your operation.
The new primary gyratory crushers have new advancements that bring increased speeds, higher installed power and mechanical improvements. All of these combine to bring additional throughput for your primary gyratory crusher.
A Cone Crusher is a compression type of machine that reduces material by squeezing or compressing the feed material between a moving piece of steel and a stationary piece of steel. The crushed material is discharged at the bottom of the machine after they pass through the cavity. Cone crushers are popular rock crushing machines in aggregate production, mining operations, and recycling applications. They are normally used in secondary, tertiary, and quaternary crushing stages.
The new hybrid models of cone crusher come with multi-cylinder hydraulic cone systems suited for the secondary or tertiary stages of crushing plants by changing body liners and adaptors. It comes with the automatic control and fingertip manipulation system and two hydraulic cylinders that have a protective effect that if one overloads, then another one can fast react to clear choke merely by remote control.
Stationary hybrid crushers combine the advantages of different roll crusher systems and are an ideal solution for primary, secondary and tertiary crushing applications. They have specially designed teeth, hydraulic gap adjustment, overload protection, and a scraper system perfect for dealing with sticky materials. These machines can work at capacities of up to 12,000 metric tons per hour, enabling you to keep productivity high whilst producing high-quality output.
The newer models have a compact design and take up minimal space. The crushing rolls are equipped either with crushing rings, segments, or crushing picks, depending on the application and feed material. The drive system for the rolls consists of individual electric motors for each roll, as well as couplings and gears. Standard components are used for cost-effectiveness and simpler maintenance.
The overall range of capacity for mobile impact crushers is roughly about 100 to 500 tons per hour. Todays mobile impact crushers are especially ideal for smaller-scale recycling operations, for on-site recycling, and tight-space urban and roadside applications. These units are transportable by trailer, simply driven off at the location of the material that needs to be processed, and go to work very quickly. With their capability to produce accurately-sized, cubical-shaped end-product, mobile impact crushers work well as stand-alone plants, or they can add significant productivity to any operation, working in tandem with a jaw crusher or screen plant.
The newer models use a direct drive system for optimum fuel efficiency and low operating costs and include several user-friendly features. This ensures that theyre both simple to operate, and easy to maintain.
This is a type of secondary or reduction crusher consisting of a heavy frame on which two rolls are mounted. These are driven so that they rotate toward one another. Rock fed in from above is nipped between the moving rolls, crushed, and discharged at the bottom.
The newer models offer 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.
The newer models of this machine generate high-quality aggregates, cubical in shape, with superior soundness. Available in three sizes, the HammerMaster is known for making excellent asphalt chip material, concrete stone, and general base material and road rock. This mill is also capable of making agricultural lime for pH control in farm fields.
Rod mills run along with the outside gear. Materials spirally and evenly enter the crushing chamber along the input hollow axis by input devices. Steel rods of different specifications are installed in the crushing chamber. When the frame rotates, centrifugal force is produced. At the same time, the steel rods are carried to some height and then fall to grind and strike the material. After grinded in the crushing chamber, the powder is discharged by an output material board.
The newer models of this machine are driven by motor with speed reducer and peripheral large gear, or low-speed synchronous motor with peripheral large gear. The grinding medium steel rod is put into the cylinder which is lifted, and then falls under the action of the centrifugal force and friction force. The materials entering into the cylinder from the feeding inlet are grinded by movable grinding medium and discharged out by overflow and continuously feeding.
A ball mill is a type of grinder used to grind, blend and sometimes for mixing of materials for use in mineral dressing processes, paints, pyrotechnics, ceramics and selective laser sintering. It works on the principle of impact and attrition: size reduction is done by impact as the balls drop from near the top of the shell. The newer models of this machine are widely used in cement, silicate products, new building materials, refractory materials, fertilizer, black and non-ferrous metals and glass ceramics and other production industries of all kinds of ores and other grind-able materials can be dry or wet grinding.
Manufacturers offering crushing equipment have expanded their respective ranges, offering additional capabilities for these segments. Mobility and versatility have been key factors in the development of new models, with many firms also offering new options in the shape of electric and hybrid drive systems.