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There is a specific operating speed for most efficient grinding. At a certain point, controlled by the Mill speed, the load nearest the wall of the cylinder breaks free and it is so quickly followed by other sections in the top curves as to form a cascading, sliding stream containing several layers of balls separated by material of varying thickness. The top layers in the stream travel at a faster speed than the lower layers thus causing a grinding action between them.
There is also some action caused by the gyration of individual balls or pebbles and secondary movements having the nature of rubbing or rolling contacts occur inside the main contact line. A ball mill, a type of grinder, is a cylindrical device used in grinding (or mixing) materials like ores, chemicals, ceramic raw materials and paints. For the most efficient results, the Mill should be at least half filled with grinding media. Some operators prefer to go a little beyond the halfway mark to compensate for wear. There is no objection to this and we have been suggesting a limit of about 5 percent.
Cement ball mill rotate around a horizontal axis, partially filled with the material to be ground plus the grinding medium. Different materials are used as media, including ceramic balls, flint pebbles and stainless steel balls. An internal cascading effect reduces the material to a fine powder. Industrial ball mills can operate continuously, fed at one end and discharged at the other end. Large to medium-sized ball mills are mechanically rotated on their axis, but small ones normally consist of a cylindrical capped container that sits on two drive shafts (pulleys and belts are used to transmit rotary motion).
A rock tumbler functions on the same principle. Ball mill manufacturers are also used in pyrotechnics and the manufacture of black powder, but cannot be used in the preparation of some pyrotechnic mixtures such as flash powder because of their sensitivity to impact. High-quality ball mills are potentially expensive and can grind mixture particles to as small as 5 nm, enormously increasing surface area and reaction rates. The grinding works on the principle of critical speed.
The critical speed can be understood as that speed after which the steel balls (which are responsible for the grinding of particles) start rotating along the direction of the cylindrical device; thus causing no further grinding. The grinding efficiency of the one-half charge is considerably greater than for the one-third and, therefore it ca be expected that power consumption per gallon output will actually be less than with the smaller charge. Grinding media should be periodically checked.
Reduction in the quantity and size of the grinding media will result in poor grinding. We suggest a maximum schedule of once every six months, but any established procedure should be decided by individual experience. In some cases, where abrasive materials are involved, once a month is not too often and, in a few cases, even shorter intervals are indicated. The ball mill is a key piece of equipment for grinding crushed materials, and it is widely used in production lines for powders such as cement, silicates, refractory material, fertilizer, glass ceramics, etc. s well as for ore dressing of both ferrous non-ferrous metals. The ball mill can grind various ores and other materials either wet or dry. There are two kinds of ball mill, grate type and overfall type due to different ways of discharging material. There are many wet ball mill suitable for use in a ball mill, each material having its own specific properties and advantages. Key properties of grinding media are size, density, hardness, and composition. Aside from common ball mills there is a second type of ball mill called Planetary Ball Mill.
Planetary ball mills are smaller than common ball mills and mainly used in laboratories for grinding sample material down to very small sizes. A used ball mills consists of at least one grinding jar which is arranged eccentrically on a so-called sun wheel. The direction of movement of the sun wheel is opposite to that of the grinding jars (ratio: 1:-2 or 1:-1 or else). The grinding balls in the grinding jars are subjected to superimposed rotational movements, the so-called Coriolis forces.
The difference in speeds between the balls and grinding jars produces an interaction between frictional and impact forces, which releases high dynamic energies. The interplay between these forces produces the high and very effective degree of size reduction of the planetary ball mill. ball mill: http://www. crusher-machine. com/21. html ball mills: http://www. hxjq-crusher. com/20. html sand maker: http://www. hxjqchina. com/product-list_57. html Sand making machine: http://www. hxjq-crusher. com/58. html jaw breaker: http://www. hxjqchina. com/product-list_11. html