How do you determine if the screw is slipping and what is the solution?
1. Add a small amount of material to the end of the barrel to check the melt temperature. If the residence time is too short, the melt temperature will be lower than the barrel temperature set point
2. Inspection of the product: If there are patterns or light and dark stripes on the product, it means that the material is not evenly mixed in the barrel.
Once screw slippage occurs, one solution is to increase the temperature of the feed section barrel until the screw is rotated and retracted. To achieve this, the barrel temperature may need to be raised above the recommended set point.
High back pressure can also cause the screw to stagnate or slip. Increasing the back pressure setting increases the energy applied to the material. However, if the back pressure setting is too high, the screw will not have enough pressure to overcome the back pressure and will not be able to deliver the material to the front. At this time, when the screw is rotated at a certain position without normal retraction, it will do more work on the material, thereby significantly increasing the melt temperature, resulting in a decrease in the quality of the product and an extension of the molding cycle. The back pressure of the melt can be controlled by adjusting the valve of the injection cylinder.