How to prevent the screw of the injection molding machine from slipping?

Update: 2021/07/20
Summary:

  The screw of the injection molding machine is an impo […]

  The screw of the injection molding machine is an important part of the injection molding machine. It is mainly used for conveying, compacting, melting, stirring and pressing plastics.
  The slippage of the screw of the injection molding machine will cause the degradation of the material, which will affect the quality of the product. What are the reasons for the screw slippage? How to "catch" the slipping screw? Let me explain to you below.
   When the screw slips, the material may gather 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 convey the material and prepare for the next injection, the screw slippage will occur in the plasticizing section. At this time, the rotation of the screw is still continuing, but the axial movement of the screw will stop, that is, slipping occurs. The slippage of the screw will often cause the degradation of the material before injection, the product quality will be reduced (such as lack of material), and the molding cycle will be prolonged.
There are many reasons for screw slippage, which may be related to high back pressure, overheating or overcooling of the barrel end, wear of the barrel or screw, too shallow threads in the feeding section, unreasonable hopper design, and blocked hopper, wet resin, and excessive resin Factors such as lubrication, material too fine or unreasonable cutting of resin and recycled materials are related.
   Process settings:
   Too cold 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, the feeding section, the pellets will form a layer of melt film and stick to the screw during the heating and compression process. Without this film, the pellets are not easily transported to the front end.
  The material in the feeding section must be heated to a critical temperature to form that critical melt film. However, usually the residence time of the material in the feeding section is very short and cannot reach the required temperature. This situation generally occurs on small injection machines. If the residence time is too short, the melting and mixing process of the polymer will be incomplete, resulting in screw slippage or stall.

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