Crushing Machine and its Type,Crushing Technology in Cement Industry
The technology of crushing is governed by the laws of physics involving mass, velocity, kinetic energy and gravity. Crusher selection even today is not a science but is still mainly a matter of personnel experience and testing. Field experience and tests conducted in a laboratory are the best method of indicating the reaction of a material to the various forces associated with reduction. From this the selection of the most economical crushing plant to produce the required product is made.
In general the total number of crushing stages in a comminution plant is determined by the overall reduction ratio required. In the cement industry the abrasiveness of the rock to be crushed is the primary determining factor of the number of reduction stages required. The plant feed originating from a quarry usually contains large rocks and boulders. The size of the first or primary crusher is usually specified by the total capacity required or maximum lump size of th e feed. For hard abrasive rocks such as Dolerite, a compression type jaw or gyratory crusher is used for the primary crushing duty.
Product size of this type is normally about 80 % passing 1000 mm to 250 mm. Normally feed to a gyratory is not pre -screened but may be necessary when using a jaw crusher to increase throughput. For softer rocks such as limestone, an impact crusher will give the best results. They are designed for the crushing of non or low abrasive materials and have a high throughput and reduction ratio with a product containing a large percentage of fines. The power consumption of these machines is lower per ton throughput than for an equivalent size jaw or gyratory crusher. Because of their mechanical strength they are also suitable for the crushing of hard materials, but at a very much higher cost than for an equivalent compression crusher. Reduction ratios vary between 3 to 1 and 7 to 1 for compression crushers and up to 50 to 1 for impact crushers. To obtain the maximum reduction ratios from any crusher is not the most economic way of crushing a material as it results in hang-ups and increased power consumption which leads to excessive costs. To achieve the required reduction ratio it is usual to have two or more sets of crushing stages. These are then termed primary, secondary and tertiary stages of crushing.
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