Size reduction work required

Bond terms Ei the work index, and expresses it as the amount of energy required to reduce unit mass of material from an infinite particle size to a size L2 of 100. im, that is q = 00. The size of material is taken as the size of the square hole through which 80 per cent of the material will pass. Expressions for the work index are given in the original papers 8,9) for various types of materials and various forms of size reduction equipment. 

Secondary Crushing.— After the work of the primary breakers has been done, the rock is in pieces varying according to the size of the original breaker, from 2 or 2 K up to 6 in. in diameter. In industrial use, the rock, unless it be limestone flux or ore for furnace use, requires further reduction therefore a second stage in reduction is required— this stage we classify as crushing. It may be performed in machines of a number of different kinds. 

Kick s law essentially states that the work required to obtain a given reduction ratio is the same irrespective of starting size. According to Rittinger s law work is proportional to surface created. Rittinger s and Kick s laws are only useful over a limited particle size range and are not utilized today. 

In 1885 Kick proposed another law, based on stress analysis of plastic deformation within the elastic limit, which states that the work required for crushing a given mass of material is constant for the same reduction ratio, that is, the ratio of the initial particle size to the final particle size. This leads to the relation... 

In some size-reduction problems the feed stoeks are too tenacious or too resilient to be broken by compression, impact, or attrition, In other problems the feed must be reduced to particles of fixed dimensions. These requirements are met by devices that cut, chop, or tear the feed into a product with the desired characteristics. The sawtoothed crushers mentioned above do much of their work in this way. True cutting machines include rotary knife cutters and granulators. These devices find application in a variety of processes but are especially well adapted to size-reduction problems in the manufacture of rubber and plastics. They are finding important applications in recycling paper and plastic materials. ... 

Formation Require input of mechanical work for size reduction of the phase to be dispersed (homogenization) Form spontaneously... 

The chemical engineer should know the particle size of the feed, especially the maximum value, the tonnage per hour required, and the particle size and other characteristics desired in the product. He should then look for the size-reduction machine that produces a maximum amount of that product with a minimum of power and a minimum of wear on the working parts. 

GrindabiUty is normally measured by determining the number of revolutions in a pulverizer that are required to achieve a given size reduction. This is an indirect measure of the amormt of work required for that size reduction. GrindabiUty increases slowly to a maximum at 90% carbon and decreases rapidly beyond this point. Hardness is ascertained by meastrring the size of the indentation left by a penetrator of specified shape pressed onto the coal with a specified force for a specified time. It changes only slightly between 70 and 90% carbon and increases rapidly beyond 90% carbon. 

When Xi and X2 are measured in micrometers and E in kWh/ton, K = 5Ei, where E is the Bond Work Index, defined as the energy required to reduce a unit mass of material from an infinite particle size to a size such that 80% passes a 100 pm sieve. The Bond s work index is obtained from laboratory crushing tests on the feed material. Bond s law holds reasonably well for a variety of materials undergoing coarse, medium, and fine size reduction. 

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