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Crusher Related terms: Pebble, Cone, Conveyor, Comminution View all Topics

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Crushers Barry A. Wills, James A. Finch FRSC, FCIM, P.Eng., in Wills' Mineral Processing Technology (Eighth Edition), 2016

6.2.2 Gyratory Crushers Gyratory crushers are principally used in surface-crushing plants. The gyratory crusher (Figure 6.5) 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. As in the jaw crusher, maximum movement of the head occurs near the discharge. This tends to relieve the choking due to swelling. The gyratory crusher is a good example of arrested crushing. The spindle is free to turn on its axis in the eccentric sleeve, so that during crushing the lumps are compressed between the rotating head and the top shell segments, and abrasive action in a horizontal direction is negligible.

Figure 6.5. Gyratory crusher: (a) functional diagrams, and (b) cross section and overhead view (Courtesy FLSmidth). With a gyratory crusher, at any cross section there are in effect two sets of jaws opening and shutting like jaw crushers. In fact, the gyratory crusher can be regarded as an infinitely large number of jaw crushers each of infinitely small width, and, as consequence, the same terms gape, set, and throw, have identical meaning in the case of the gyratory crusher. Since the gyratory, unlike the jaw crusher, crushes on full cycle, it has a higher capacity than a jaw crusher of the same gape, roughly by a factor of 2.5–3, and is usually favored in plants handling large throughputs: in mines with crushing rates above 900th−1, gyratory crushers are always selected. Gyratory crushers are identified by the size of the gape and the size of the mantle at the discharge. They range in size up to ca. 1,600mm×2,900mm (gape×mantle diameter) with power consumption as high as 1,200kW and capable of crushing up to ca. 10,000th−1 at a discharge open side setting up to 240mm. Large gyratories typically dispense with expensive feeding mechanisms and are often fed direct from trucks (Figure 6.6). They can be operated with the head buried in feed. Although excessive fines may have to be “scalped” from the feed (more common in jaw crushing circuits), the trend in large-capacity plants with gyratory crushers is to dispense with grizzlies. This reduces capital cost of the installation and reduces the height from which the ore must fall into the crusher, thus minimizing damage to

the spider. Choked crushing is encouraged to some extent as rock-to-rock crushing in primary stages reduces the rock-to-steel crushing required in the secondary crushers, thus reducing wear (McQuiston and Shoemaker, 1978). Choke feeding of a gyratory crusher has been claimed beneficial when the crusher is followed by SAG mills, as their throughput is sensitive to the mill feed size (Simkus and Dance, 1998). Operating crushers under choke feeding conditions gives more even wear and longer crusher life.

Figure 6.6. Truck dumping ore into a primary gyratory crusher (Courtesy Sandvik). The last ten years or so have seen advances in increased installed power which, without increasing crusher size, has increased capacity (Erikson, 2014). Other innovations have been in serviceability, and measurement of wear components (Erikson, 2014).

Gyratory Crusher Construction The outer shell of the crusher is constructed from heavy steel casting or welded steel plate, with at least one constructional joint, the bottom part taking the drive shaft for the head, the top, and lower shells providing the crushing chamber. If the spindle is carried on a suspended bearing, as in most primary gyratories, then the spider carrying the bearing forms a joint across the reinforced alloyed white cast-iron (Ni-hard) liners or concaves. In smaller crushers, the concave is one continuous ring bolted to the shell. Large machines use sectionalized concaves, called staves, which are wedge-shaped, and either rest on a ring fitted between the upper and the

lower shell, or are bolted to the shell. The concaves are backed with some soft filler material, such as white metal, zinc, or plastic cement, which ensures even seating against the steel bowl. The head consists of the steel forgings, which make up the spindle. The head is protected by a mantle (usually of manganese steel) fastened to the head by means of nuts on threads which are pitched so as to be self-tightening during operation. The mantle is typically backed with zinc, plastic cement, or epoxy resin. The vertical profile is often bell-shaped to assist the crushing of material that has a tendency to choke. Figure 6.7 shows a gyratory crusher head during installation.

Figure 6.7. Crusher head during installation (Courtesy FLSmidth). Some gyratory crushers have a hydraulic mounting and, when overloading occurs, a valve is tripped which releases the fluid, thus dropping the spindle and allowing the “tramp” material to pass out between the head and the bowl. The mounting is also used to adjust the set of the crusher at regular intervals to compensate for wear on the concaves and mantle. Many crushers use simple mechanical means to control the set, the most common method being by the use of a ring nut on the main shaft suspension.

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Gyratory and Cone Crusher

In Mineral Processing Design and Operations (Second Edition), 2016

5.1 Introduction Gyratory crushers were invented by Charles Brown in 1877 and developed by Gates around 1881 and were referred to as a Gates crusher [1]. The smaller form is described as a cone crusher. The larger crushers are normally known as primary crushers as they are designed to receive run-on-mine (ROM) rocks directly from the mines. The gyratory crushers crush to reduce the size by a maximum of about one-tenth its size. Usually, metallurgical operations require greater size reduction; hence, the products from the primary crushers are conveyed to secondary or cone crushers where further reduction in size takes place. Here, the maximum reduction ratio is about 8:1. In some cases, installation of a tertiary crusher is required where the maximum reduction is about 10:1. The secondary crushers are also designed on the principle of gyratory crushing, but the construction details vary. Similar to jaw crushers, the mechanism of size reduction in gyratory crushers is primarily by the compressive action of two pieces of steel against the rock. As the distance between the two plates decreases continuous size reduction takes place. Gyratory crushers tolerate a variety of shapes of feed particles, including slabby rock, which are not readily accepted in jaw crushers because of the shape of the feed opening.

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Roll Crushers In Mineral Processing Design and Operations (Second Edition), 2016

6.2.3 Roll crusher circuit design 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. Figure6.4 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 50mm.

Figure 6.4. Roll Crusher Design Circuit.

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Jaw Crusher In Mineral Processing Design and Operations (Second Edition), 2016

4.2 Design of Jaw Crushers Jaw crushers are designed to impart an impact on a rock particle placed between a fixed and a moving plate (jaw). The faces of the plates are made of hardened steel. Both plates could be flat or the fixed plate flat and the moving plate convex. The surfaces of both plates could be plain or corrugated. The moving plate applies the force of impact on the particles held against the stationary plate. Both plates are bolted onto a heavy block. The moving plate is pivoted at the top end (Blake crusher) or at the bottom end (Dodge-type crusher) and connected to an eccentric shaft. In universal crushers the plates are pivoted in the middle so that both the top and the bottom ends can move.

The Blake crushers are single or double toggle drives. The function of the toggle(s) is to move the pivoted jaw. The retrieving action of the jaw from its furthest end of travel is by springs for small crushers or by a pitman for larger crushers. As the reciprocating action removes the moving jaw away from the fixed jaw the broken rock particles slip down, but are again caught at the next movement of the swinging jaw and crushed. This process is repeated until the particle sizes are smaller than the smallest opening between the crusher plates at the bottom of the crusher (the closed set). For a smooth reciprocating action of the moving jaws, heavy flywheels are used in both types of crushers. Figure4.1 shows a sketch of a Blake crusher operated by double toggles and controlled by a pitman. These are commonly used as primary crushers in the mineral industry. The size of the feed opening is referred to as the gape. The opening at the discharge end of the jaws is referred to as the set.

Figure 4.1. Double-Toggle Jaw Crusher. Figure4.2 is a sketch of a Dodge type of crusher. They are comparatively lower in capacity than the Blake crushers and are more commonly used in laboratories.

Figure 4.2. Dodge Jaw Crusher. The factors of importance in designing the size of primary crushers, such as a jaw crusher, are: (4.1) (4.2) (4.3) where the crusher gape is in metres. These dimensions vary as individual manufacturers have their own specifications and their catalogues are a good guide to the geometry and design of individual makes.

4.2.1 Crusher Sizes and Power Ratings The size of a jaw crusher is usually described by the gape and the width, expressed as gape × width. The common crusher types, sizes and their performance are summarised in Table4.1. Currently, the dimensions of the largest Blake-type jaw crusher in use are 1600mm × 2514mm with motor ratings of 250–300kW. Crushers of this size are manufactured by Locomo, Nordberg (Metso) and others. The Metso crusher is the C 200 series having dimensions 1600mm × 2000mm driven by 400kW motors. Table 4.1. Jaw crusher performance [1]. Crusher Type Gape (mm)

Size (mm)

Reduction Ratio

Power (kW)

Width (mm)

Toggle Speed (rpm)

Min

Max

Min

Max

Range

Average Min

Max

Min

Max

Blake, double toggle

125

1600

150

2100

4:1/9:1 7:1

2.25

225

100

300

Single toggle

125

1600

150

2100

4:1/9:1 7:1

2.25

400

120

300

Dodge

100

280

150

28

4:1/9:1 7:1

2.25

11

250

300

For sizing a crusher and ancillaries for open circuit operations, Equations (4.1) and (4.3) are helpful as a first approximation. From the equations, it can be seen that once the gape has an assigned value the rest of the dimensions follow. To size the gape the largest particle to be charged is considered and the following relation is applied: (4.4) The largest particle size is generally ascertained by the blast pattern in the pit or the size of shovels and dump-cars used to transport the ore from the mines. Thus, as a general rule, the size of the gape would be 1.1 times the largest size of the lump ores that are to be charged for crushing. These relations are, in turn, helpful to size the opening of the scalping screens that are placed in the ore stream before the crusher. The purpose of scalping screens, also called grizzly screens, is to reject lumps of ore greater than the size of the gape. Placement of scalping screens results in smooth and uninterrupted operation of the circuit and also prevents any damage to the crusher by extra large lumps.

4.2.2 Jaw Crusher Circuits 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 a closed circuit. That is, the crushed product is screened and the oversize is 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3.212. 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 is 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 downstream use. In some industries, for example, iron ore or coal, where a specific product size is required (iron ore –30+6mm), a careful choice of jaw settings and screen sizes is required to produce the minimum amount of fines (i.e. – 6mm) and the maximum amount of lump ore within the specified size range. For hard mineral bearing rocks such as gold or nickel ores where liberation of minerals from the host rock is the main objective, further stages of size reduction are required.

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Mineral Processing Swapan Kumar Haldar, in Mineral Exploration (Second Edition), 2018

13.3.1.1 Primary Crusher Primary crushers are heavy-duty rugged machines used to crush ROM ore of (−) 1.5m size. These large-sized ores are reduced at the primary crushing stage for an output product dimension of 10–20cm. 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.

Figure13.9. Schematic diagram showing principle of jaw crusher showing the path of lumpy feed ore to fragmented product crushed under high pressure of fixed and moving jaws. 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.

Figure13.10. Medium-sized jaw crusher in operation in underground mine for crushing run-of-mine (ROM) ore before transferring to the surface.

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.

Figure13.11. Working principle of gyratory crusher for breaking lumpy ore pressed between a fixed jaw and rotating conical head.

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Production of High Copper Concentrates – Introduction and Comminution Mark E. Schlesinger, ... William G. Davenport, in Extractive Metallurgy of Copper (Fifth Edition), 2011

3.5.2.1 Autogenous and Semi-autogenous Mills The crusher product is ground in a SAG or AG mill. Autogenous mills crush the ore without the need for iron or steel grinding media. They are used when the ore is

hard enough for the tumbling ore to grind itself. In SAG milling, ~0.15 m3 of 13 cm diameter iron or steel balls are added into the mill per 0.85 m3 of ore (i.e. 15 vol.-% ‘steel’) to assist grinding. SAG mills are much more common. The mill product is usually passed over a large vibrating screen to separate oversize pebbles from ore particles of the correct size. The correct-size material is sent forward to a ball mill for final grinding. The oversize pebbles are recycled through a small eccentric (cone) crusher, then back to the SAG or AG mill (Jones & Pena, 1999; Markkola, Soto, Yañez, & Jimenez, 2007). This procedure maximizes ore throughput and minimizes electrical energy consumption.

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Sensor-based Ore Sorting Barry A. Wills, James A. Finch FRSC, FCIM, P.Eng., in Wills' Mineral Processing Technology (Eighth Edition), 2016

14.4 Example Flowsheet and Economic Drivers SBS installations typically consist of: crusher, screen, sorter, and compressor. Because of the often large particle sizes and low concentrations of valuables, it is advised to install mechanical sampling, size reduction and splitting equipment to enable determination of plant performance. Figure 14.6 shows an example flowsheet for a multi-stage, multi-machine stage operation. Machines are commonly operated in parallel for high throughput operations. Cascading circuit arrangements enhance separation...