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Rock processing introduction, rock process equipment

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Rock processing introduction, rock process equipment

May 3, 2023 nflg 0 Comments

Blasted material within a hard rock quarry must be crushed several times before it is at a size that is suitable for use by industry. Several stages of crushing and screening of mineral are employed to produce the final aggregate product.

Primary crushing

Crushing (the act of breaking a large rock into smaller pieces) is the most energy intensive part of aggregate processing and is often expensive, requiring special care in the selection of crushing equipment.

The final aggregate product should have the particle size distribution suitable for the desired market. Crushing starts with primary crushing; usually using jaw crusher , gyratory crusher , roller or impactor-type crushers depending on the characteristics of the rock.

Jaw and gyratory crushers can both handle hard, abrasive rocks, cone crusher are restricted to non-siliceous rocks e.g. limestones, although they can handle high throughputs (up to 1000 tonnes per hour) and lump sizes in excess of 1 m. Roller crushers are rarely installed in new quarries but may still be found in some of the older limestone quarries. Material is loaded into the primary crusher by dump trucks, and the crushed material is then transported to the processing plant by conveyor .

Scalping screen

Scalping screens are used to allow rock fragments and fines that do not require crushing to bypass further crushing stages. Most quarries will install a scalping screen after the primary crusher. Material is passed over a vibrating mesh that allows particles less than 20 mm in diameter to pass through. This material bypasses the remaining crusher stages and is fed directly to the sizing screens.
A scalping screen is often used to remove excessive amounts of clay before the mineral is fed into the primary crusher. However the material removed at this stage will usually still contain some useable rock and is therefore washed to recover the maximum amount of mineral before being fed into the sizing screens.

Secondary crushers

The secondary crusher breaks rock fragments down into sizes that are suitable for the market. A variety of crushers can be used depending on the rock type.Material bounces round within the crushing chamber until it is small enough to escape. The size of the final product can be adjusted by adjusting the gap between the rotor blades and breaker bars attached to the chamber edge.

The cone crusher is favoured in igneous rock quarries. Material is fed into the top of the cone and moves along the gap between the cone and the fixed outer wall. As the cone is rotated on an off-centre axis the size of the gap gets bigger and smaller, resulting in the crushing action. Sizes from 50 mm down can be created and the size range can be adjusted by adjusting the height of the cone within the concaves. However, the requirement for smaller final products will result in the production of greater quantities of fines.

It is normal in some hard rock quarries to crush the rock a third time before sizing (tertiary crushing). Each stage of crushing (primary and secondary) can be expected to reduce the size of the material feeding through it by between 60% and 80%. This reduction ratio can be increased by demanding more of each crusher, however this increases the quantity of fines produced, decreases the throughput and increases the power requirements and costs of crushing. Tertiary crushing is therefore used to produce the final aggregate size and shape.

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