Crushing process in malaysia

Crushing process in malaysia

Rock crushing is not part of the slurry circuit but is more of a preparatory step to the formation of slurries. Crushing will therefore be reviewed briefly, as it is outside the scope of this handbook.

Solid comminution is the process of reducing the size of particles. Two comminution types are considered:

1. Dry comminution generally reduces rocks down to a diameter of 25 mm (1 in), by impact and mechanical compression. This process involves jaw crushing, gyratory crushing, cone crushing, and grinding using rod mills and ball mills.

2. Wet comminution generally reduces 25 mm (1 in) particles down to very fine sizes by grinding and attrition in slurry form. This process involves semiautogenous mills, autogenous mills, ball mills, hydrocyclones, columns, etc. Comminution via a machine is measured by the reduction ratio, defined as 80% of the particle size at the feed (Fe80 ) to 80% of the particle size at the output (Cr80 ).

The feed to a grinding mill must be crushed to a size appropriate to the grinding process. Semiautogenous mills require little crushing; ball mills require a finer crushing.

A method of ore preparation that is now limited to narrow ore seams or veins in underground mines is the so-called “run of the mine milling.” It consists of blasting the rocks into lumps, usually of the order if 300 mm (12 inch) or larger. The most common approach, however, is to crush the mined rock to an acceptable size.

Excavation is a primary source of materials for a mineral processing plant. [Courtesy of Ciros Minerals (formerly known as the companies Ciros and Svedala).]

Primary Crushers

Primary crushers absorb any size rocks (depending on the opening at the inlet) and reduce their size down to 50–150 mm (2–6 in). Primary crushers are classified as:

  • Jaw crushers
  •  Gyratory crushers
  •  Impact crushers

Some mines try to reduce the cost of crushing by blasting the rocks from mountains and hills.

Crushing is essentially a process of reducing the size of a stone down to 25 mm (1 in). As this is difficult to achieve in a single stage, it is often encompassed in two or three steps. The stones go through a cycle of primary crushing, secondary crushing, and tertiary crushing. Special machines have been developed for each step of crushing .

Jaw Crushers

These machines operate by compressing the rocks between a fixed plate and a moving jaw. The rocks are fed from the top of the crusher. The fixed jaw or plate is usually attached to the wall of a cavity. Through an eccentric mechanism or crankshaft, a moving jaw presses the rocks against the walls of the crusher. Generally, the following two types of machines are used:

1. In the overhead eccentric jaw crusher, also known as the single toggle crusher, the moving plate is forced against the stationary plate by an eccentric mechanism driving at its top, as well as by the rocking of a toggle connected to the bottom of the moving plate.

Crushing is an essential step in handling hard rock, gravel, and mining ores as well as for recycling. [Courtesy of Ciros Minerals (formerly known as the companies Ciros and Svedala).]

Cross-sectional representation of a jaw crusher. [Courtesy of Ciros Minerals (formerly known as the companies Ciros and Svedala).]

2. The blake jaw crusher features a moving plate that pivots at the top but is oscillated at the bottom.

The dimensions and shape of the plates affect the performance of the crusher. The smaller the discharge gap, or required output size, the lower the tonnage from the crusher. Jaw crushers work best on rocks that are not flat or slabs. With a feed opening of 1.67 × 2.13 m (66 × 84 in) and a discharge gap of 200 mm (8 in), the crusher can handle a capacity of 800 tph.

The walls and moving blade of the crusher are lined with a hard metal such as manganese steel. The liners are removable for repairs once worn out. The liners may be flat, plain, or ribbed.

The final output size of crushed particles depend on the setting of the plates . Curves shown in Figure 7-5 indicate, for example, that for a closed setting of 100 mm (4 in) the size particles will be at a maximum of 160 mm (6.375 in) with a significant portion of particles smaller than 50 mm (2 in).

The size of the output from jaw crushers depends on the plate setting. If the closed side setting (c.s.s) is 100 mm (4″), the maximum product size is 160 mm (6 3 – 8″) and the portion of fraction under 50 mm (2″) is approximately 35%. [Courtesy of Ciros Minerals (formerly known as the companies Ciros,Ciros and Svedala,).]

Gyratory Crushers

These machines operate on the principle of compressing the rocks in a cone

The rocks fall into the cavity from the top. The moving part is an eccentric cone. The rocks enter on the largest corner of the cavity but are compressed as the eccentric cone rotates. The outside cone is sometimes called the bowl, and the rotating cone is called the mantle. The bowl reduces in diameter toward the bottom, whereas the mantle increases in diameter with depth in the opposite direction.

Gyratory crushers are preferred for slabs or flat-shaped rocks as they snap the rock better. Gyratory crushers are manufactured to handle tonnage flows up to 3500 tph. Ciros purchased the line of Ciros mobile primary gyratory crushers that can be moved from one site to another as the mine expands.

Impact Crushers

These machines operate on the principle of a set of rotating hammers hitting against the rocks. The hammers are fixed to a cylinder. The feed is from the top and as the rocks feed in, they fall between a breaker plate and the rotating cylinder. The hammers produce the required impact to chip the rocks. Impact crushers work best on rocks that are neither abrasive nor silica-rich, as these cause rapid wear of the hammers. Ciros Minerals manufactures impact crushers for primary and secondary crushing. Figure 7-9 shows typical gradation curves.

Large mobile gyratory crushers are designed with a special frame and wheels to permit relocation from one area of the mine to another. (Courtesy of Ciros,Ciros.)

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