The manufacturer briefly talks about the basic manufacturing quality requirements for screws used in plastic extruders

Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with nearly 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.

Screw is a core component of plastic extruder equipment, which needs to directly contact with plastic raw materials and withstand long-term high temperature, high pressure, and high shear working environment. Therefore, our factory has very high standards for the quality of screws. For the production of different plastic products, we have different requirements for screws. However, there are still basic manufacturing quality requirements for screws, as follows:

I.The screw of the extruder needs to work in a high temperature environment with high friction and certain corrosion, so we need to choose alloy steel with small thermal deformation, wear resistance, and corrosion resistance for manufacturing. The commonly used materials for screw manufacturing are 38CrMoAlA alloy steel, 40Cr steel, or stainless steel. Sometimes, 45# steel is also used as a substitute for screw repair.

II.Before manufacturing, the screw of the extruder cannot be simply produced using round steel. In order to ensure the final strength of the screw, we need to use forged alloy steel blanks.

III.After the screw blank is machined, the minimum outer diameter accuracy of the screw needs to reach level 8 precision quality (GB180-79) requirements.

IV.The screw of the extruder is a high-precision part that requires rotational motion, so there are certain requirements for the concentricity of the outer circle of the screw and the transmission shaft. Generally, the coaxiality error between the working shaft surface at the connection part of the screw and the outer circle of the screw should not be greater than 0.01mm.

V.The surface roughness of the screw is also highly required. The surface roughness Ra value of the working surface of the screw thread is as follows: the roughness of the thread on both sides should not be greater than 1.6μm, and the roughness of the thread bottom and the outer circle should not be greater than 0.8μm.

VI.In order to produce different plastic products, extruders sometimes use low-carbon alloy steel to manufacture screws due to various reasons, but many properties of the working surface of the screw made of low-carbon alloy steel are insufficient. To solve this problem, the thread surface of the screw needs to be nitrided, which can greatly improve the hardness, corrosion resistance, and wear resistance of the thread working surface. At this time, the nitriding layer needs to be 0.30.6mm deep, and the surface hardness is 700840HV. The brittleness is not greater than level 2.

VII.In order to control the temperature of some extruders, sometimes holes are drilled in the core of the screw to pass cooling water or heating oil. The internal hole of the screw needs to undergo a 0.3MPa water pressure test for 5 minutes without leakage.

The above are the basic manufacturing quality requirements for screws used in plastic extruders. If you need more information, please feel free to contact us or visit our factory in person. As a manufacturer with 30 years of experience in extruder production line equipment, Ningbo Fangli Technology Co., Ltd. can provide you with professional technical guidance and equipment procurement advice.