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When the alloy screw is difficult to compress the material at the feed port, or when there is not enough adhesion along the length of the barrel to transport the material, the alloy screw will slip. In the pre-forming stage of the alloy screw, when the alloy screw rotates in the barrel to convey the material in the direction of the screw and backs up to accumulate the material for the next injection, the screw will also slip. If the screw starts to slip during the preforming stage, the axial movement of the alloy screw will stop as the alloy screw continues to rotate. Usually the screw slippage will lead to the degradation of the material before injection molding, and there will also be product quality problems such as short injection time and prolonged processing cycle.

The reasons for the slippage of the alloy screw include excessive back pressure, overheating or undercooling of the second half of the barrel, wear of the barrel or screw, shallow spiral groove in the screw feeding section, improper hopper design, material shortage or blockage in the hopper, wet resin, The lubricant content in the resin is too high, the particle size of the material is too fine, and the resin used or the recycled material has a poor cutting shape.

Low temperatures at the rear of the barrel are often the main cause of alloy screw slippage. The barrel of the injection molding machine is divided into three parts. At the rear of the feed section, a thin layer of molten polymer is formed during heating and compression. The molten film layer is attached to the barrel. Without this thin layer, the granular material is difficult to transport forward.

The material in the feed section must be heated to a critical temperature to produce a critical molten film layer. However, usually the residence time of the material in the barrel is too short to allow the polymer to reach this temperature. This situation may be caused by the smaller size of the equipment and the corresponding smaller barrel and screw. If the residence time is too short, the polymer will easily melt or not mix well, which will cause the screw to slip or stall.

Now, introduce two simple ways to deal with this problem. Add a small amount of material from the end of the barrel to wash and check the melting temperature. If the dwell time is short, the melting temperature will be lower than the set value of the barrel temperature. The second method is to observe the molded product. If you see marbling, black dots, or light streaks, it means that the material in the barrel is not well mixed.

One of the ways to solve the slippage of alloy screw is to gradually increase the temperature of the feeding section until the rotation and retreat of the screw are in harmony. Sometimes the barrel temperature must be raised above the recommended setpoint to reach this range.

Setting back pressure that is too high can also cause the screw to stall or slip. Increasing the back pressure setting will also increase the energy entering the material. If the back pressure is set too high, then the screw may not be able to generate enough pressure and the alloy screw will rotate in a certain position without backing up, which will do more work for the melt and raise the melt temperature significantly, which will affect the product Quality and cycle time are adversely affected. The back pressure applied to the melt can be adjusted by a control valve on the syringe barrel.
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