1. The screw itself is of poor quality.
2. The temperature of the barrel is set low, and the shearing force of the screw rotation is too large.
3. The length-to-diameter ratio of the screw is not suitable and is large.
4. There is a problem with the screw installation
5. There are too hard metal or non-metallic impurities in the raw materials used.
6. The injection molding machine is cold-started, and the viscosity of the raw material in the barrel is too high.