1. When the screw rotates in the barrel, the materials friction causes the working surface of the screw and the barrels to gradually wear: the diameter of the screw gradually decreases, and the diameter of the hole in the barrel gradually increases. as the screw and the barrel gradually wear out, the mating diameter gap between the screw and the barrel gradually increases. However, since the resistance of the head and the splitter plate in front of the barrel is not changed, this increases the leakage flow rate when the extruded material advances, that is, the flow rate of the material from the diameter gap to the feed direction increases. As a result, the output of the extruder is lowered. This phenomenon in turn increases the residence time of the material in the barrel, causing the material to decompose. In the case of polyethylene, the hydrogen chloride gas produced by the decomposition enhances the corrosion of the screw and the barrel.
2. If the material contains fillers such as calcium carbonate and glass fiber, it will accelerate the wear of the screw and the barrel.
3. Due to the uneven plasticization of the material or the incorporation of metal foreign matter, the rotational torque of the screw suddenly increases. This torque exceeds the strength limit of the screw, causing the screw to twist. This is an unconventional accidental injury.
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