①The screw of the extruder should be made of alloy steel with small thermal deformation, wear resistance and corrosion resistance. Commonly used materials are 38CrMoAlA alloy steel or 40Cr steel, and repair parts can also be made of 45 steel.

②The blank of screw material should be formed by forging method.

③After the screw is machined, the outer circle accuracy should meet the quality requirements of grade 8 (GB 180-79).

④ The coaxiality error between the working shaft surface on the screw and the connecting part of the drive shaft and the outer circle of the screw thread should not be greater than 0.01mm.

⑤The working surface roughness R of the screw thread part. Value: The two sides of the thread should not be greater than 1.69m, and the bottom and outer circle of the thread should not be greater than 0.8/1m.

⑥ If the screw is made of low carbon alloy steel material, in order to improve the hardness, corrosion resistance and wear resistance of the thread working surface, the surface of the thread should be nitrided, the depth of the nitride layer is 0.3~0.6ram, and the surface hardness is 700~840HV. The brittleness is not more than grade 2.

⑦The connection of the inner hole of the screw should be tested by 0.3MPa hydraulic pressure, and there should be no leakage of water for 5 minutes.