Is the extruder screw often worn? There are these main reasons!

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 extruder is the core equipment of plastic forming and blending modification. In the actual production process of blending modification, the screw of the extruder is in a harsh high pressure and high temperature environment, and bears huge friction and shear force.

Due to the special working environment, the extruder screw is not a common metal to metal friction, but a metal to polymer, so the wear of the screw surface is often serious.

The wear of the screw increases the distance between the screw and the barrel, which affects the compression and shearing of the screw on the material, thus leading to a decline in product quality. On the other hand, the frequent replacement of worn screws not only increases the cost, but also delays the production plan, resulting in lower production efficiency.

The screw is generally scrapped due to long-term wear, and the gap between the screw and the barrel is too large to be extruded normally. However, there are also cases where the working stress caused by improper design or operation exceeds the strength limit and is damaged. The following is a brief introduction to the wear causes of the extrusion screw:

1 Processing temperature

Each kind of plastic has an ideal plasticizing processing temperature range. The barrel processing temperature should be controlled to make it close to this temperature range. When the plastic particles enter the barrel from the hopper, they will first reach the feeding section, where dry friction will inevitably occur. When these plastics are not heated enough and the melting is uneven, it is easy to form the inner wall of the barrel and the surface of the screw to increase wear.

Similarly, in the compression section and homogenization section, if the melting state of the plastic is disordered and uneven, the wear will also be accelerated.

2 Speed

The speed shall be properly adjusted. Some plastics are added with reinforcing agents, such as glass fiber, minerals or other fillers. The friction force of these substances on metal materials is often much greater than that of molten plastics.

If high rotating speed is used, it is easy to tear the reinforcement fiber while improving the plastic shearing force. The torn fiber contains sharp ends, which greatly increases the wear force. When inorganic minerals slide on the metal surface at high speed, their scraping effect is not small. Therefore, the speed should not be too high.