Why does the screw of the injection molding machine slip？
1.People often use high-speed injection molding machines to shorten the injection molding cycle and improve production efficiency. However, in the production process of injection molded products, the slippage of injection molding machine screws is a major problem. Especially when dealing with moisture absorbing materials such as nylon, high resin moisture content can cause the screw of the injection molding machine to slip. Inappropriate drying can significantly reduce the viscosity of the material and generate water vapor in the barrel, resulting in a decrease in the conveying capacity of the screw. For this, a humidity analyzer can be used before processing to determine the moisture content of the dried material, so that the drying level of the material reaches the supplier’s recommended value.
2. Sliding of injection molding machine screws can cause material degradation, thereby affecting product quality. What are the reasons for screw slippage? How to ‘catch’ a slipping screw? When the barrel screw slips, the material is likely to gather at the feeding port and cannot be transported to the end of the injection machine normally. When the screw rotates and retreats inside the barrel to transport materials and prepare for the next injection, screw slippage occurs in the plasticizing section.
3.At this point, the rotation of the screw is still inherited, but the axial movement of the screw will stop, resulting in slippage. Screw slippage often leads to material degradation before injection, resulting in a decrease in product quality (such as material shortage) and an extension of the molding cycle. The reasons for screw slippage are multifaceted, probably related to factors such as high back pressure, overheating or undercooling at the end of the material barrel, wear of the material barrel or screw, shallow threads in the feeding section, unfair hopper planning, blockage of the hopper, resin wetting, excessive lubrication of the resin, material being too fine, and unfair cutting of resin and recycled materials.
4. Undercooling at the end of the barrel is one of the main causes of screw slippage. The material cylinder of the injection machine is divided into three sections. At the end, which is the feeding section, a layer of molten film is formed during the heating and compression process of the pellets, which adheres to the screw. Without this layer of film, the granules are not easily transported to the front end.
5. The material in the feeding section of the injection molding machine must be heated to the critical temperature to form the melt film at that critical point. However, the residence time of materials in the feeding section is usually very short, and they cannot reach the required temperature. And this kind of environment usually occurs on small injection machines. A too short residence time can cause incomplete melting and inclusion processes of the polymer, resulting in screw slippage or stall.
