Impact crusher is a kind of crushing machine which utilizes impact energy to break materials. When the machine works, driven by the electric motor, the rotor rotates at high speed, the material enters action area of hammer bar, crushes with the hammer bar on the rotor, and then it is thrown to impact device to be crushed again, and then bounces back to the hammer bar reaction area to be crushed again from the impact liner. This process repeats itself, and the material enters primary, secondary and tertiary impact cavities from large to small for repeated crushing, until the material is crushed to the required granularity and then discharges from discharge opening. Clearance between the impact rack and the rotor can be adjusted to change material discharge granularity and shape of the material.