Ball milling residence time

Ultrafine grinding is carried out batchwise in vibratoiy or ball mills, either diy or wet. The purpose of batch operation is to avoid the residence time distribution which would pass less-ground material through a continuous mill. The energy input is 20-30 times greater than for standard grinding, with inputs of 1300-1600 kWh/ton compared to 40-60. Jet milling is also used, followed by air classification, which can reduce top size Below 8 [Lm. 

In the compound mill, the cylinder is divided into a number of compartments by vertical perforated plates. The material flows axially along the mill and can pass from one compartment to the next only when its size has been reduced to less than that of the perforations in the plate. Each compartment is supplied with balls of a different size. The large balls are at the entry end and thus operate on the feed material, whilst the small balls come into contact with the material immediately before it is discharged. This results in economical operation and the formation of a uniform product. It also gives an improved residence time distribution for the material, since a single stage ball mill approximates closely to a completely mixed system. 

The beryl is ground, wet or dry, to about 200 mesh in a ball mill, and then mixed with the sodium ferric fluoride and sodium carbonate in a wet condition. Briquettes are fabricated from the paste, dried and sintered, e.g. by passing continuously through a gas-heated tunnel kiln with a residence time of several hours at 750 C. A rotary kiln would probably not be very satisfactory since the briquettes are somewhat plastic and would tend to adhere to the lining. ... 

Ball mills ara somatimas used for batch processes whan tha product is a solid. Tha feed enters tha ball mill and is concentrated as evaporation occurs and tha vapor is removed. Tha ball mill prevents tha haat transfer surface from becoming fouled. The solid product is periodically removed. Residence times ara... 

The ball mill is insensitive to foreign bodies in the feed material, and the wear of the grinding media can be compensated without any great effort or cost. The relatively long residence time of the coal in the mill has the effect of equalizing any shortterm variations in the quality of the mill feed, thanks to the blending action of the system. Also, harder constituents such as quartz and pyrite are effectively pulverized... 

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