Why does the screw of the injection molding machine slip

For hygroscopic materials such as nylon, high resin moisture content can also cause screw slip. Improper drying will significantly reduce the viscosity of the material and generate water vapor in the barrel, thus reducing the conveying ability of the screw. In this regard, a moisture analyzer can be used to determine the moisture content of the dried material before processing, so that the drying level of the material can reach the recommended value of the supplier.

The slippage of the screw of the injection molding machine will cause the material to degrade, thereby affecting the quality of the product. What are the reasons for screw slippage? How to catch a slipping screw? When the barrel screw slips, the material probably gathers at the feeding port and cannot be conveyed to the end of the injection machine normally. When the screw rotates and retreats in the barrel to transport the material and prepare for the next injection, screw slip occurs in the plasticizing section.

At this time, the conical twin screw barrel for extrusion rotation of the screw is still inherited, but the axial movement of the screw will stop, that is, slippage will occur. Screw slippage often causes material degradation before injection, resulting in reduced product quality (such as material shortages), and longer molding cycles. There are many reasons for screw slippage, which may be related to 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, unreasonable hopper plan and hopper clogged, resin wet, resin too much Lubrication, too fine material, or unfair cutting of resin and recycled material are related factors.

Overcooling at the end of the barrel is one of the main causes of screw slippage. The barrel of the injection machine is divided into 3 sections. At the end, that is, the feeding section, the pellets will form a layer of melt film and stick to the screw during the process of heating and compression. Without this film, the pellets are not easily transported to the front end. The material in the feed section must be heated to the photocritical temperature to form that critical melt film. However, usually the residence time of the material in the feeding section is too short to reach the required temperature. And this kind of environment is generally produced on small injection machines. A residence time that is too short will result in incomplete melting and inclusion of the polymer, resulting in screw slippage or stall.