- Jaw Crushers:
These are the oldest type of and most commonly used crushers in use and have changed little from the original design. In Jaw Crusher the feed is compressed between a stationary and a movable surface. A few of common types of Jaw crushers, in use, are described below.
- Double Toggle Crusher: The Blake jaw crusher has a fixed jaw and a moving jaw pivoted at the top. The crushing faces themselves are formed either of manganese steel or of chilled cast iron. The maximum pressure is exerted on the large material, which is introduced at the top. These crushers are made with jaw widths varying from about 2” to 48” and the running speed varies from about 100 to 400 RPM.
- Single toggle Jaw crusher: The single-toggle crusher is the simplest and the lightest of the jaw crushers but is suitable only for producing low crushing forces and therefore used for soft rocks.
- Impact Jaw Crushers: In this type of crusher the crusher cavity is inclined. As there is larger stroke and higher rotation speed (about 400 rpm) a stronger impact is achieved. As a result, hard, tough materials can be processed.
In Gyratory Crushers the stress to the feed is applied between a stationary and a movable surface. The crushing head is employed in the form of a truncated cone, mounted on a shaft, the upper end of which is held in a flexible bearing, whilst the lower end is driven eccentrically so as to describe a circle. The crushing action takes place around the cone.
- Primary Gyratory Crusher: In the primary gyratory crusher the stress is applied to the feed by pressure as the conical head periodically approaches the bowl. The primary Gyratory Crusher is a large, heavy and expensive machine. It is used only for special materials and high through put. As the crusher is continuously in action, the fluctuation in the stresses is smaller compared to the jaw crusher but the power consumption is lower. It gives a finer and more uniform product compared to the jaw crusher.
- Cone Crusher: Cone crusher have shallower cavity than that of the primary gyratory crusher. This crusher produces higher reduction ratios of up to 18.
A uniform product size and good shape is ensured because of the long parallel gap before aperture. The stroke is large and the speed of rotation is 200 – 300 rpm, which ensures a cubical shape to the product. The shallow cone crushers are mainly used for the fine crushing of hard and moderately hard materials.
The roller crushers operate on the principal that the stress (to the feed) is applied between the rollers or between a roller and a crushing surface.
- Double Roll Crusher: Double roll crusher consists of two rollers, which rotate towards each other and are separated by an adjustable gap. The gap can be adjusted according to the size of the feed and the required size of the product. Rollers with diameters up to 2m can handle feed sizes up to 1m. From soft to moderately hard materials, throughputs as high as 3500T/hr can be achieved.
- Single-Roll Crusher: In the single roll crusher, a crushing roller acts against a crushing plate, which is held either by springs or a hydraulic system. This design helps in coarse crushing of moderately hard to soft materials.
In hammer crushers the hammers are attached to the rotor via pivots so that they are deflected when they hit strong and particularly large stones. In most cases the crushing zone is surrounded by grate bars so that fragments which are larger than the openings of the grating are retained in the crushing zone. Huge hammer crushers with rotor diameters up to 3 m are available which have throughput of even 1500T/hr.
Although hammer crushers wear more quickly than impact crushers, they can process moist materials more efficiently. Only soft to moderately hard materials can be processed because of wear considerations. These crushers are simpler than jaw and cone crushers and units with equivalent throughput are much smaller in size.
The Impact Crusher or double impeller breaker crusher uses the energy contained in falling stone, plus the power imparted by the massive impellers. Rock fed into the breaker falls directly on to the impellers (which weigh up to 6.5 tons) and rotate away from each other, turning up and outward, atspeeds from 250 to 1000 rpm depending on the desired size of finished product. Pieces of rock are sent crashing against steel breaker bars mounted in specific positions around the breaking chamber or crash against other rocks hurtling through the chamber and are further reduced without the use of extra horsepower. The stone falls again onto the impellers to repeat the cycle until reduction is complete. Size is controlled by impeller speeds and the vertical and horizontal spacing of adjustable breaker bars.