Injection molding of polyethylene PE

The processing behavior of polyethylene PEPE for the crystalline materials, moisture absorption is extremely small, not more than 0.01%, so no need to be dried before processing.PE molecules associated chain flexibility is good, key interactions among small, low melt viscosity, excellent activity, so no high pressure molding can be a long process forming a thin-walled products.PE shrinkage range, shrinking the value of large, clear direction, LDPE shrink rate of about 1.22%, HDPE shrinkage of 1.5 percent. So easy deformation warping, mold cooling conditions on the shrinkage of the great impact, it should control the mold temperature, cooling to maintain uniform and stable.PE crystallization capacity, high mold temperature on the plastic parts of the crystalline state has a greater impact. High mold temperature, melt cooled slowly, plastic crystal, high strength also high.The melting point of PE is not high, but larger than the heat capacity, so when the plastics still need to consume more calories, it is required to have a larger plasticizing unit of heating power, in order to advance production efficiency.PE softening temperature range is smaller, and melt easily oxidized, thus forming in the melt should be avoided as much as possible in contact with oxygen, so as not to reduce the quality of plastic parts.PE parts is soft, and easy to mold, so when the plastic parts are shallow groove side ejection can be powerful.PE melt non-Newtonian behavior is not obvious, the change in shear rate has little effect on the viscosity, PE melt viscosity also less affected by temperature.PE melt cooling rate slower, so must be fully cooled. Mold should have a better cooling system.PE melt if used directly in the injection inlet feed, easy to search and produce uneven stress increases and significantly increases the deformation direction, and should pay attention to choose the inlet parameters.Wide temperature molding of PE, in the active state, small fluctuations in temperature has no effect on the injection molding.PE, good thermal stability, generally 300 degrees no obvious decomposition phenomenon, no impact on quality.http://www.prmindustry.com/Abstract...Articles section PE is the main molding conditionsBarrel temperature: barrel temperature is mainly the density and the level of PE activity rate and the size of the melt, also with the type and performance of injection molding machine, an appearance on plastic parts. Because PE is crystalline polymers, the melt when a certain grain to absorb heat, so the cylinder temperature should be higher than its melting point of 10 degrees. Degree in LDPE, the barrel temperature was controlled at 140-200 ℃, HDPE of the barrel temperature was controlled at 220 ℃, the barrel back to take the minimum, maximum front-end to take.Mold temperature: mold temperature on the plastic parts of the crystalline state have a greater impact, high mold temperature, melt high crystallinity, high strength, but the shrinkage will increase. LDPE mold temperature control is usually at 30 ℃ -45 ℃, and then the corresponding high temperature of HDPE 10-20 ℃.Injection pressure: the pressure is conducive to progress injection melt filling, as PE activity is very good, so in addition to thin-walled slender products, it should be well choose a lower injection pressure, injection pressure is generally 50-100MPa. Simple shape. Wall after the larger plastic parts, injection pressure can be lower, and vice versa high.

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            Peter  Huang