People often use high-speed injection molding machines to shorten the injection molding cycle and improve production efficiency. However, during the production process of injection molded products, the slippage of the screw of the injection molding machine is a major problem. Especially when dealing with hygroscopic 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 ability of the screw.
In this regard, 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 recommended value of the supplier.
Slipping 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 screw of the barrel slips, the material tends 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.
At this point, the rotation of the screw is still being inherited, but the axial movement of the screw will stop, resulting in slipping. 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 barrel, wear of the barrel or screw, shallow threads in the feeding section, unfair hopper planning, clogging of the hopper, resin wetting, excessive lubrication of the resin, fine material, and unfair cutting of resin and recycled materials.
The supercooling at the end of the barrel is one of the main causes of screw slippage. The material barrel of the injection machine is divided into three sections, at the end, which is the feeding section. During the heating and compression process, the pellets will form a layer of molten film and stick to the screw. Without this thin film, the granular material would not be easily transported to the front end.
The material in the feeding section of the injection molding machine must be heated to the critical temperature to form the critical layer of molten film. 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 dwell time can cause incomplete melting and inclusion processes of the polymer, leading to screw slippage or stalling.
