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Plastic Injection Molding Process

Plastic Injection Molding Process FAQ Mainly includes high-speed filling, low-speed filling, injection temperature control, pressure-retaining phase of the problem treatment, back pressure screw problems, plastic injection molding mold temperature problems, plastic injection molding process in the previous article also mentioned, followed by plastic injection molding process common problems to do a brief description!

Shan High speed padding. High rate of shear at high speed, because of the effect of shear thinning, the viscosity of plastics decreases, so the overall flow resistance is reduced. In the flow control stage, because of the high speed filling, the shear thinning effect of the melt is often very large, and the cooling effect of the thin wall is not obvious, Custom Injection Molding And Plastic Molding so the effect of the rate has prevailed.

Shan Low Speed padding. The shear rate is lower when the heat conduction is controlled at low speed. The local viscosity is higher and the flow resistance is larger. Because of the slow replenishment rate of thermoplastic materials, the flow is relatively slow, so that the heat transfer effect is more obvious, heat quickly for the cold mold wall away. With a small amount of viscous heating phenomenon, the thickness of the solidified layer is thicker, and further increase the flow resistance of the thinner part of the wall. Therefore, Custom Injection Molding And Plastic Molding it is easier to fill at a low speed when it is filled with a thick wall.

Shan injection temperature must be controlled within a certain range. The temperature is too low, the melt material is not good, it affects the quality of the molding parts, increases the process difficulty, the temperature is too high, the raw material is easy to decompose. In the actual injection molding process, the injection temperature is often higher than the barrel temperature, Custom Injection Molding And Plastic Molding the numerical value is related to the injection rate and material performance, the highest can reach 30c. This is caused by the high heat generated by the shear of the molten material through the feeding mouth. There are two ways to compensate for this difference in the modeling flow analysis: One is to try to measure the temperature when the melt is injected into the air and the other is to include the nozzle when modeling.

Shan holding pressure in the injection process near the end of the screw stop rotation, just forward, at this time injection into the holding stage. During the holding process, the nozzle of the injection molding machine is continuously feeding to the cavity to fill the volume vacated by the shrinkage of the workpiece. If the cavity is filled with no pressure, the workpiece will shrink about 25%, especially because the shrinkage is too large to form contraction traces. Pressure is generally to fill the maximum pressure of about 85%, of course, according to the actual situation, the holding time is too long or too short to the molding unfavorable. Custom Injection Molding And Plastic Molding Too long will make the pressure is uneven evenly, plastic parts internal stress increase, plastic parts easily deformed, serious stress cracking occurs. Too short to keep pressure is not sufficient, workpiece volume shrinkage is serious, surface quality is poor.

The pressure to be overcome when Shan back pressure screw to reverse the storage material. The use of high back pressure is conducive to the dispersion of pigment and plastic melting, but at the same time extend the screw retraction time, reduce the length of the plastic melt segment, increase the pressure of the injection molding machine, so the back pressure should be lower, generally no more than 20% of the injection pressure. Injection foam plastic material, the back pressure should be higher than the gas formation pressure, or the screw will be pushed out of the barrel. Some injection molding can be back-pressure programming to compensate for the reduction in the length of the screw during melting, which will reduce the input heat, causing the temperature to drop.

Shan Cooling and mold temperature control of injection molding mould The mold temperatures have a great influence on the plastic forming process. If the injection molding mold temperature is too low, on the one hand, the plastic melt cooling faster, the thickness of the solidified layer increases, melt viscosity also increases, resulting in a large molding pressure, forming relatively difficult; on the other hand, Custom Injection Molding And Plastic Molding the flow of plastic melts is not smooth, easy to appear flow traces, the product profile is not smooth, while the length of weld-joint traces and clarity of the increase, product appearance quality. Mold temperature on the performance of products also has a certain impact, in particular, crystallization molding, products, mold temperature directly affect the crystallization of the crystallization of the degree of false material and the quality of crystallization.

The above-mentioned problems are more common in plastic injection molding process, and the correct understanding of the factors affecting injection molding process has very good guiding significance for the control of injection molding.

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