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Vertical injection molding machine screw slip will cause material degradation, and then affect the quality of products. Most users want to know more about the cause of screw skid? How to "catch" a skid screw? The following by the small make up for you to explain......
When the screw starts to slip, the material may gather in the feed port and cannot be transported to the end of the injection machine. As the screw rotates and recoils in the barrel to transport material and prepare for the next injection, the screw slips at the plasticized section. At this point, the rotation of the screw is still continuing, but the axial movement of the screw is suspended, that is, the attack of skidding. Slip often causes material degradation before injection, product quality will be reduced (such as lack of material), and the molding cycle will be extended.
The cause of screw skid is many, may be related to the back pressure is too high, the end of the cylinder overheating or cooling, cylinder or screw wear, feeding section thread is too shallow, hopper planning is unreasonable and hopper blocked, resin moisture, resin is too smooth, material is too fine or resin and recycled material is unreasonable cut and other factors.
Overcooling at the end of the barrel is one of the main causes of screw skidding. The feeding barrel of the injection machine is divided into three sections. At the end, the feeding section, the granule will form a layer of melt film and stick to the screw in the process of heating and tightening. Without this film, the pellets are not simply transported to the front end.
It is necessary for the material in the feeding section to be heated to a critical temperature to form the critical melt film. However, usually the material in the feeding period of residence time is very short, can not reach the required temperature. This condition usually occurs on a small injection machine. Too short a residence time can result in incomplete melting and mixing of the polymer, which can then cause the screw to slip or stall.
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