Difference between revisions of "Stone Crushers"

In  the industry, crushers are machines which use a metal surface to break  or compress materials. Mining operations use crushers, commonly  classified by the degree to which they fragment the starting material,  with primary and secondary crushers handling coarse materials, and  tertiary and quaternary crushers reducing ore particles to finer gradations. Each crusher is designed to work with a certain maximum size of raw material, and often delivers its output to a screening machine which sorts and directs the product for further processing. Typically, crushing stages are followed by milling stages if the materials need to be further reduced. Crushers are used to reduce particle size enough so that the material can be processed into finer particles in a grinder. A  typical circuit at a mine might consist of a crusher followed by a grinder SAG mill followed by a grinder ball mill. In this context, the SAG mill and ball mill are considered grinders rather than crushers.

For  the purpose of mineral extraction when ore is excavated from earth  the  size of run of-mine ore can vary a lot between fines powders to big  boulders of 1.5 m across. Moreover the feed can also be intermittent  type in the form of dumpers feeding the crushing plant. The crusher at  this stage is called primary crusher  the main purpose of which is to give continuous feed to the plant down  the line in a size convenient for further handling in the process plant. In the next stage further crushing may be required so as to ensure proper releasing of mineral from gangue. The crusher in this stage is called  

secondary crusher.

There  can be also another stage of crushing called tertiary crushing depending on the initial size of the run of mine ore and the final product size requirement.  Different stages are required as total size reduction in one single crusher is not possible efficiently. Moreover smaller sizes of material  tend to jam the flow of ore in the crusher and unless there is  sufficient space for the crushed ore to expand in volume there will be  choking of the crusher. Hence vibrating screens are deployed in between  different stages of the crushers so that only those oversize ore can be  fed to the crusher whose sizes need to be reduced. This also helps in  reducing the capacity requirement of the crusher as total run of mine  ore need not be fed to the crusher. Also there will be closed circuit  operation in case of secondary and tertiary crushers so as to avoid passing of any oversize material to the final stage. Primary crushing is done in open circuit only.  

Some  crushers are mobile and can crush rocks (as large as 60 inches). Primarily used in-pit at the mine face these units are able to move with the large infeed machines (mainly shovels)to increase the tonnage produced.  In a mobile road operation, these crushed rocks are directly combined with concrete and asphalt which are then deposited on to a road surface.  This removes the need for hauling over-sized material to a stationary crusher and then back to the road surface.

For  the most part advances in crusher design have moved slowly. Jaw  crushers have remained virtually unchanged for sixty years. More  reliability and higher production have been added to basic cone crusher   designs that have also remained largely unchanged. Increases in rotating  speed, have provided the largest variation. For instance, a 48 inch  (120 cm) cone crusher manufactured in 1960 may be able to produce 170  tons/h of crushed rock, whereas the same size cone manufactured today  may produce 300 tons/h. These production improvements come from speed  increases and better crushing chamber designs.