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In designing a closed-circuit crushing stage, the question of how much circulating load should be carried is a very important one. It not only has a direct bearing upon the capacity of the stage; it determines the amount of screening surface, and the elevating capacity necessary to handle the load in the circuit. There is no "blanket" answer to this question.
It must be analyzed for each case, on the basis of the operating characteristics of the particular size and style of crusher that is being considered for the job.
Usually, when we set up a closed circuit crushing stage, we want to get as many tons of finished material from it as possible or, conversely, we want to do the required job with as little outlay for crushers and screens as possible. We know the size of product the stage is to turn out, and we should know, to a fairly close approximation, how many tons of original feed are to be processed, and the size of this feed. Having this information we can, with the aid of the product tables and curves, and the circulating load table-or formula-analyze the problem for any crusher, or battery of crushers.
To illustrate how the analysis is made, as well as to demonstrate why the optimum setting may vary for different types of crushers, or for different sizes of the same type, the following examples have been worked out for two product sizes, using the Type "R" A -C crusher as our exemplar.
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