Six solutions to screw slippage in twin-screw granulators
1、High back pressure: If the back pressure is set too high, the screw may not be able to deliver enough melt pressure forward to overcome the back pressure. The screw will rotate in a certain direction and will not retreat, which will do more work on the melt and significantly increase the melt temperature, thereby having a negative impact on the quality of the finished product and cycle cycle.
2、Overheating or undercooling in the latter half of the barrel: In the rear of the feeding section, a thin layer of molten polymer is formed during the heating and compression process of the material. The molten film layer is attached to the barrel. If it weren't for this thin layer, it would be difficult to transport the pellets forward. The material in the feeding section needs to be heated to the critical temperature in order to produce a critical molten film layer. But often the material stays in the barrel for too short a time to reach the temperature of the polymer. The occurrence of this situation may be due to the small scale of the equipment, resulting in smaller machine barrels and screws. A short dwell time can easily lead to polymer melting or insufficient mixing, which can cause the screw to slip or stop rotating.
3、Wear of machine barrel or screw: Similar to the feeding section, when the resin melts in the screw tightening section, it adheres to the wall of the machine barrel. When the screw of the twin-screw granulator rotates, the material is subjected to shear force and detached from the barrel wall before being transported forward. If there are wear areas on the screw and barrel, the screw cannot effectively transport materials forward.
4、Improper hopper planning: Correct hopper planning is crucial to ensuring the safe and stable transportation of materials. Generally speaking, uniformly sized new pellets operate well in square hoppers with abrupt contraction zones. However, this is not the case when participating in recycled materials. By disrupting the shape and size of the particles again, it can affect the uniformity of the feed. Incoherent feeding means that the screw cannot adhere to the uniform transport pressure on the melt, resulting in slipping.
5、When processing moisture absorption data: Incorrect material drying can significantly reduce the viscosity of the data in the barrel and cause water vapor, making it difficult for the screw to transport the material forward.
6、Failure of the check ring: When the screw is rotating and plasticizing the material, the check ring should be in the front position, in contact with the fixed ring seat. If the check ring is in a backward state, or in a state between forward and backward, the molten polymer will have resistance when passing through the gap between the check ring and the ring seat. If there is suspicion of a problem with the check ring, it should be replaced immediately.
