Impact crusher is a kind of crushing machine that uses the plate hammer of the high speed rotating rotor to crush the materials at a high impacting crushing force. When the materials get into the action area of plate hammer, they are crushed by the hammer at a high speed. The crushed materials are thrown to the impact plate along the tangential direction to crush again. Then they are rebounded from the first impact plate to the action area of the plate hammer and enter into the second impact plate to repeat the above process. During this process, materials also crash with each other. This process will proceed repeatedly until the material are crushed to the required granularity, and then discharged from the clearance between impact plate and plate hammer.