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Gap standard between screw and barrel

Update:21 Sep 2019
Summary:

Choose a screw that is more suitable for the plastic us […]

Choose a screw that is more suitable for the plastic used, so that the plastic achieves a better mixed melt state. Appropriate information on the plastic properties can be requested from the plastics supplier. The manufacturer of the screw can design the appropriate number of screw turns to prevent the plastic from overheating and decomposing. The injection volume should generally be maintained at 20~80% of the machine specification. For temperature sensitive materials, a narrower temperature range is used. Inspect the scratches or dents on the surface of the barrel/screw to avoid accumulation of plastic and cause the plastic to overheat or burn. Check if the solid heater or controller has failed to prevent the plastic from overheating. Molding analysis software for plastic injection molding can assist the mold in selecting the appropriate size of the injection machine, thus avoiding the plastic staying in the barrel for too long.

2. Adjust the forming conditions: If the temperature of the barrel and the nozzle is too high, the plastic in the barrel may overheat and cause decomposition, which can lower the barrel temperature and the nozzle temperature. In addition, the back pressure, screw speed, injection speed or injection pressure can be reduced to avoid decomposition due to too high shear heat. In addition, the heating coils of the barrel and nozzle should be inspected and the thermocouple calibrated to determine the temperature of the barrel and nozzle.

The relationship between the dimensional change and the screw barrel.

Dimensional variation means that the dimensions of the resulting plastic part vary between each batch of molded articles or between each cavity molded article of each die under the molding conditions of the same injection molding machine.

The reasons for this are:

1. The wear of the screw unit of the injection unit causes the gap to become larger.

2, the anti-reverse ring (over the rubber ring) and the rubber meson seal is not strict, the anti-reverse effect is not good.