EN 
简体中文Feed screw wear in extrusion and injection molding is similar, with the majority of wear occurring in the high-pressure region, especially in the transition and last few metering turns. It is widely believed by processors and suppliers that wear in these areas is caused by metal-to-metal contact between the outer diameter of the thread and the inner diameter of the barrel due to the bending of the screw under these high pressures. This theory is not possible because the internal pressure around the screw is usually the same.
Differential pressure is required to generate the force that deflects the screw, not the usual high pressure. Metal-to-metal contact can occur, but it is a result of mechanical conditions and is a symptom of a potentially larger problem: misalignment, gearbox damage, screw bending, barrel bending, insufficient foundation, etc. Wear testing in many industries has shown that increased pressure and temperature lead to increased friction.
Much like blade OD wear, root wear is usually most severe in these high-pressure areas. Wear is most extreme on the forward and trailing sides of flight. The severity of root wear is greatly affected by the resin or processing resin. When machining abrasive fillers, severe wear can occur in the feed section due to the pressure developed at the front of the blade, and the unmelted particles provide limited lubrication. The amount of filler present and the shape of the particles strongly influence the wear strength. Larger particles with sharper corners tend to wear more than smaller, rounder particles. Unfortunately, the desired physical properties of the molded part dictate the filler to be used.
Mixing sections and baffles are also prone to wear because their function requires resin to flow through their geometry. Dispersion mix designs incorporate some form of undercut geometry that applies high shear forces on the resin to promote a more isothermal melt and uniform color. Sufficient dispersibility is lost as the hybrid design wears out. Much like the dispersive mixing design, the barrier is undercut to help separate the molten pool from the solids bed. Barrier designs may lose their melting ability and efficiency as undercut threads wear.
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