What are the reasons for the slippage of the screw barrel of the injection molding machine?

Update:02-04-2021
Summary:

The material pipe will cause material degradation, ther […]

The material pipe will cause material degradation, thereby affecting the quality of the product. What are the reasons for the screw slippage? How to "catch" the slippery screw?

When the screw of the barrel is slipping, the materials probably 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 transport the material and prepare for the next injection, screw slippage will occur in the plasticizing section. At this time, the rotation of the screw is still inherited, 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 quality of the product will be reduced (such as lack of material), and the molding cycle will be prolonged.

There are many reasons for the slippage of the barrel, which may be related to too high back pressure, excessive heat or cold at the end of the barrel, wear of the barrel or screw, too shallow threads in the feeding section, unfair hopper plan, and hopper blocked, resin wetting, resin Excessive lubrication, too fine materials or unfair cutting of resin and recycled materials are related to factors. 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 process of heating and compression. Without this film, the pellets are not easily transported to the front end. The material in the feeding section must be heated to the 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. And this kind of environment is generally produced on a small injection machine. If the residence time is too short, the melting and inclusion process of the polymer will not be complete, which will cause the screw to slip or stall.

The screw speed of the screw barrel of the injection molding machine can be realized as a stepless pressure and speed adjustment configuration. Linear guide injection instead of guide pillar injection reduces friction during injection and improves injection accuracy (optional). The screw and barrel are made of alloy materials, quenched and tempered and desalinated to improve wear resistance. The injection is made of an electronic ruler made by Gefferan, Italy, and the position control accuracy can be controlled within 0.1mm. The independent control of the 4-stage injection pressure and speed, and the 4-stage holding pressure and speed is more conducive to the adjustment of the injection process. The manual back pressure device (optional with CNC back pressure) improves the plasticization, exhaust and density of the plastic by the screw. After feeding, a back pressure elimination device is added to prevent the plastic from flowing into the mold when the back pressure of the feeding is used in the production of the product without loosening and causing cold material.
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