Comprehensive and overall introduction to mining crusher
6 June, 2013 at 10:01 am in Buy & Sell
Mining industry: jaw crusher is usually used as primary crusher in ore mining industry or other mining process such as copper ore mining, limestone mine industry, coal mining etc.
Smelting industry: jaw crusher is applied widely in metal smelting industries such as aluminum smelting industry, silver smelting industry, lead and zinc smelting industry etc.
Rotary Coal Breaker
This breaker reduces the coal size by impact and also screens out the oversize particles. The breaker consists of a cylindrical drum fitted with perforated plates. The drum rotates at speeds of between 12 and 18rpm. All of the large-size rocks and any tramp material pass along the breaker, being harder or otherwise more resilient to breakdown than the coal, and are subsequently discharged. The coal being softer gets broken and due to reduced size passes through the openings and collected as undersize.
A cone crusher is similar in operation to a gyratory crusher, with less steepness in the crushing chamber and more of a parallel zone between crushing zones. The essential difference is in the short spindle, which is not suspended, but instead supported, in a curved universal bearing located below the gyratory head or 'cone'. As rock enters the top of the cone crusher, it becomes wedged and squeezed between the mantle and the bowl liner or concave. Large pieces of ore are broken once, and then fall to a lower position (because they are now smaller) where they are broken again. This process continues until the pieces are small enough to fall through the narrow opening at the bottom of the crusher.
A roll crusher crushes using compression, with two rolls rotating about a shaft, towards the gap between the rolls. The gap between the rolls is set to the size of product desired, with the realization that the largest feed particle can only be 4 times the gap dimension.
The particles are drawn into the gap between the rolls by their rotating motion and a friction angle formed between the rolls and the particle, called the nip angle. Some major advantages of roll crushers are they give a very fine product size distribution and they produce very little dust or fines.
Coal is probably the largest user of roll crushers, currently, though. Coal plants will use roll crushers, either single roll or double roll, as primary crushers, reducing the ROM coal. Usually, these crushers will have teeth or raised forms on the face of the roll.
Impact crushers use impact rather than pressure to crush material. The material is contained within a cage, with openings of the desired size on the bottom, end, or side to allow pulverized material to escape. This type of crusher is usually used with soft material such as coal, seeds, or soft metallic ores.
A hammer mill crushes material that is friable, by impacting it against a rotating hammer. Then the material is forced against a rugged solid plate called a 'breaker plate' which further degrades the particle size. Finally, the material is forced over a discharge grate by the hammers, where crushed finer particles drop through the discharge grate and larger particles travel around for another crushing cycle, until they fall through the discharge grid.
The hammers are made from manganese steel or, more recently, nodular cast iron, containing chromium carbide, which is extremely abrasion resistant. The breaker plates are made of the same material. The hammers can weigh over 100kg and can work on feed up to 20 cm. The speed of the rotor varies between 500 and 3000rev/min.
There are many other different kind of crushers developed depending upon the ore characteristics and energy requirements such as Gyradisc and Rhodax crushers (special form of cone crushers), Rotary impact mill, Tidco Barmac Crusher, reversible hammer mill etc.
Key variables for a crusher is its open and closed side settings, operating gap for roll crushers, particle nipping angle, resident time for a particle in the crushing chamber and feed size of the particle.