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 the core equipment of plastic extruder equipment. It needs direct contact with plastic raw materials and will bear the working environment of high temperature, high pressure and high shear force for a long time. Therefore, our manufacturers will have high standards for the quality of screws. For the production of different plastic products, our requirements for screws are also different, but there are still some basic manufacturing quality requirements for screws. The specific contents are as follows:
1、 The screw of extruder needs to work in high temperature environment, high friction and corrosive environment for a long time, so we need to choose alloy steel with small thermal deformation, wear resistance and corrosion resistance for manufacturing. 38CrMoAlA alloy steel, 40Cr steel or stainless steel and other materials are commonly used for screw manufacturing, but 45# steel is sometimes used for screw maintenance.
2、The extruder screw cannot be simply produced with round steel before manufacturing. In order to ensure the strength of the final screw, we need to use the alloy steel blank formed by forging.
3、After the screw blank is machined, the cylindrical accuracy of the screw needs to meet the requirements of Grade 8 accuracy quality (gb180-79).
4、The extruder screw is a high-precision part that needs to rotate, so there are certain requirements for the concentricity of the outer circle of the screw and the transmission shaft. Generally, we need to ensure that the coaxiality error between the working shaft surface on the screw and the connecting part of the transmission shaft and the outer circle of the screw thread should not be greater than 0.01mm.
5、There are also great requirements for the surface roughness of the screw. The roughness Ra value of the working surface of the threaded part of the screw: the two sides of the thread shall not be greater than 1.6 μ m. The bottom and outer circle of thread shall not be greater than 0.8 μ m。
6、In order to produce different plastic products, sometimes for various reasons, we also use low-carbon alloy steel to manufacture screws, but many properties of screw working face made of low-carbon alloy steel are insufficient. In order to solve this problem, the screw thread surface needs nitriding treatment, which can greatly improve the hardness, corrosion resistance and wear resistance of the threaded working surface. At this time, the nitriding layer depth is 0.3 ~ 0.6mm, and the surface hardness is 700 ~ 840hv. Brittleness shall not be greater than grade 2.
7、In order to do a good job in temperature control, some extruders sometimes make holes in the core of the screw to pass cooling water or heating oil. It is necessary to conduct a 0.3MPa hydrostatic test outside the connection of the inner hole of the screw for 5min, and there shall be no water leakage.
The above is about the basic manufacturing quality requirements of the screw used in the plastic extruder. If you need more, you are welcome to call for detailed inquiry or visit the factory. Ningbo Fangli Technology Co., Ltd. is a manufacturer with a complete set of equipment for extruder production line for 30 years. We have a lot of equipment manufacturing experience and can provide you with professional technical guidance and equipment procurement suggestions.