|
BEFORE GOING into a discussion of the stages following the primary crusher or crushers we should like to interject a few comments regarding the titles which are applied some of them more or less loosely - crushers and crushing stages.
The term "secondary" has become well established and familiar through long usage; it applies to the crushing stage, either single or multiple, which follows immediately after the primary crusher, taking all or a portion of the product of the primary crushing stage as its feed. The term should not be used, as it sometimes is, to designate a particular type or size of crusher because any type and size might conceivably be used for secondary crushing. A very large number' of secondary crushers in our present-day plants were originally primary crushers in those same plants. "Secondary" and "second-stage" are synonymous, and are equally good and descriptive definitions.
The word "tertiary" has been used rather extensively in recent years to cover not only third-stage crushers, but in a more general sense to delineate any and all crushers in the reduction and fine-reduction classes a use which certainly takes liberties with the intent of the word. It is a legitimate term as applied strictly to a third stage of reduction, just as "quaternary" may be used to designate a fourth stage. Our own preference is to designate these successive reductions as "third-stage," "fourth-stage," and so on, and to identify the crushers themselves by the titles which usage has conferred upon them.
"Reduction-crushers" and "reduction-crushing," through the same authority of common usage, have been narrowed from the broad scope of their definitions to delineate reductions in the intermediate sizes of product, loosely in the range between 3-in. and 1-in. screen sizes. "Fine-reduction," in the same fashion, has come to cover the production of sizes in the range below 1 in., or there abouts.
More recently still, the "fine crusher" has been introduced to extend the application of the gyratory type down into that borderland between crushing and grinding formerly monopolized by the crushing rolls and the hammermill.
|
