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Method for preventing slippage of injection screw

Update:21-06-2018
Summary:

When the Injection Molding Barrel is difficult to feed […]

When the Injection Molding Barrel is difficult to feed material at the feed port or along the length of the barrel, it can not form enough adhesive force to transport the material, then the screw will have skid. In the screw pre-molding phase, the screw also slips when the screw rotates in the barrel to convey material along the screw and retreat accumulates material for the next injection.

If the screw starts to slip during the pre-molding phase, the axial movement of the screw will stop when the screw continues to rotate. In general, screw slippage will lead to degradation of the material before injection molding, as well as product quality problems such as short shots and prolonged processing cycles.

Reasons why the screw slips include high back pressure, overheating or undercooling in the second half of the barrel, wear of the barrel or screw, shallow screw groove in the screw feed section, improper hopper design, lack of material in the hopper or clogging, resin moisture, resin The lubricant content is too high, the material particle size is too fine, the resin used is cut in poor shape or recycled material.

Now introduce two simple ways to deal with this problem. Add a small amount of material from the end of the barrel for cleaning and check the melting temperature. If the residence time is short, the melting temperature will be lower than the barrel temperature setting. The second method is to observe molded articles. If there are marble markings, black spots or light stripes, it means that the materials are not well mixed in the barrel.

One of the solutions to the occurrence of screw slipping attempts is to gradually increase the temperature of the feed section until the screw rotates and retreats in a coordinated manner. Sometimes the barrel temperature must be raised above the recommended setting to reach this range.
Setting excessive back pressure can also cause the screw to stop or slip. Increasing the back pressure setpoint also increases the energy that goes into the material. If the back pressure is set too high, then the screw may not be able to produce enough forward delivery melt pressure to overcome the back pressure back pressure, the screw will rotate in a certain position will not back, this will do more to the melt The work also significantly increases the melt temperature, which adversely affects the product quality and cycle time. The back pressure exerted on the melt can be adjusted by the control valve on the injection cylinder.