What are the reasons for the screw slip? How to catch the slippery screw?
When the barrel screw slips, the material collects at the feed port and cannot be normally delivered to the end of the injection machine. When the screw rotates and retreats in the barrel to transport the material and prepare for the next injection, the screw slip occurs in the plasticizing section. At this point, the rotation of the screw is still inherited, but the axial movement of the screw will stop, ie, slippage will occur. Screw slippage often causes the material before injection to degrade, the quality of the product is reduced (such as lack of material), and the molding cycle is prolonged.
The reasons for screw slip are various, probably with too high back pressure, overheating or undercooling at the end of the barrel, wear of the barrel or screw, too shallow thread in the feeding section, unfair hopper planning, intrusion of the hopper, wetting of the resin, excessive resin Lubrication, too small material is probably related to factors such as unreasonable cutting of resin and recycled materials.
Subcooling at the end of the barrel is one of the main causes of screw slippage. The barrel of the injection machine is divided into three sections. At the end, that is, the feeding section, during the heating and compression process, a layer of melt film is formed on the screw. Without this film, the pellets are not easily transported to the front end.
The material of the feed section must be heated to the critical temperature of the light to form the melt film of that layer. However, usually the residence time of the material in the feed section is very short and the required temperature cannot be reached. This environment is usually produced on small injection machines. Too short a residence time can result in incomplete melting and inclusion of the polymer, causing the screw to slip or stall.