PROPORTIONAL NUMBER OF TUBE MILLS TO STAMPS

The number of tube mills necessary to form a combination for economical stage- grinding will depend upon the size at which the feed is delivered to the mills and the required size of the product. If we have heavy stamps crushing a big tonnage to a coarse mesh and this pulp must be slimed, we require more tube- mill area than where light stamps are delivering a 20-mesh product to be reground to a 90-mesh screen; so unless we know the conditions of the metallurgical treatment and the physical nature of the ore, it is possible to make only an approximation of the proportion of tube mills to stamps or to other crushing machines.

Consulting this table it will be seen that with few exceptions the diameter of the tube mill for sliming gold ores is 5 ft. and that the length varies from 16 to 22 ft.; likewise we see that one tube mill may be used in combination with 10 stamps or with 20 stamps.

In a tabulation based on a comparison of results from 75 stamps and one tube mill versus 75 stamps and four tube mills working under South African conditions, C. O. Smidt shows that the total costs of operating the two plants, when based on pulp of equal fineness, are as 35 to 46 in favor of the larger number of tube mills.