What Are The Main Reasons For Screw Abrasion?

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 in plastic forming and blending modification. In the actual process of blending modification, the screw of the extruder is in a harsh environment with high pressure and high temperature and is subjected to tremendous friction and shear forces.

Due to the special working environment, the screw friction is not the common metal-to-metal, but rather metal-to-high-molecular polymer, so the screw surface often gets heavily worn. The abrasion of the screw increases the distance between it and the barrel, which affects the compression and shear of the screw on the material, leading to a decrease in product quality. On the other hand, frequent replacement of worn-out screws increases costs and delays production schedules, resulting in lower productivity.

Screws have to be scrapped is generally due to that the clearance between screw and barrel is so large after a long-term abrasion that the material can’t be normally extruded， and also there’re examples that the machine's working ability goes beyond the limit because of improper design or operation. The following is a brief description of the causes of screw abrasion.

1. Processing temperature

Each plastic has a processing temperature range for ideal plasticization, and the barrel processing temperature should be controlled so that it is close to this temperature range. Plastic pellets are conveyed from the hopper to the barrel, and they will first reach the filling section. In the filling section, materials will inevitably have dry friction. When these plastics are underheated, and unevenly melted, it is easy to increase abrasion between the inner wall of the barrel and the screw surface.

Similarly, in the compression section and homogenization section, if the molten condition of the plastic is disordered and uneven, it will also cause faster wear.

2. Rotational speed

The rotational speed should be properly adjusted. Since some plastics have reinforcing agents, such as glass fiber, minerals or other fillers. These substances often have much greater friction on metal materials than molten plastics.

If use high rotational speed, while increasing the shear force on the plastics, it is also easy to shred the reinforced fibers. The shredded fibers contain sharp ends so that the abrasive force is greatly increased. Inorganic minerals are gliding at a high speed on the metal surface, and the scraping effect is not slight. All in all, the speed should not be adjusted too high.