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Injection Molding Process of PP Raw Material
Time:2016-10-22  From: auhor
PP, commonly known as polypropylene, because of its good anti-breaking performance, also known as "Baijiao plastic." PP is a translucent, semi-crystalline thermoplastic, with high strength, good insulation, low water absorption, heat on the shape of high temperature, low density, high crystallinity, is made of woven bags of the main raw materials. The modified filler is usually glass fiber, mineral filler, thermoplastic rubber. PP of different uses of its large differences in mobility, the general use of the PP flow rate between the ABS and PC.
1, the treatment of plastic pure PP woven bag is a translucent ivory white, can be dyed into various colors. PP dyeing in the general injection molding machine can only use masterbatch. In the Ramada machine to strengthen the role of independent mixing plastic components, can also be used toner coloring. Articles for outdoor use are generally filled with UV stabilizers and carbon black. Do not use more than 15% recycled material, otherwise it will lead to decreased strength and decomposition of color. PP injection molding generally do not need special drying before processing.
2, injection molding machine selection of injection molding machine selection no special requirements. Since PP has a high crystallinity. Need to use injection pressure can be higher and more control of the computer injection molding machine. Clamping force is generally determined by 3800t / m2, injection volume of 20% -85% can be.
3, mold and gate design Mold temperature 50-90 ℃, for the higher size requirements with high mold temperature. The core temperature is 5 ℃ lower than the cavity temperature, flow channel diameter 4-7mm, needle gate length 1-1.5mm, diameter can be as small as 0.7mm. The length of the gate gate is as short as 0.7mm, the depth is half of the wall thickness, the width is twice of the wall thickness, and increases with the length of the melt in the cavity. Mold must have a good exhaust, exhaust hole depth 0.025mm-0.038mm, thickness 1.5mm, to avoid contraction marks, it is necessary to use a large circular nozzle and circular flow channel, the thickness of ribs to small ( Such as 50-60% of the wall thickness). Homogeneous PP manufacturing products, the thickness can not exceed 3mm, otherwise there will be bubbles (thick-walled products can only be used copolymer PP).
4, melting temperature PP woven bag melting point of 160-175 ℃, decomposition temperature of 350 ℃, but the injection processing temperature setting can not exceed 275 ℃. The temperature of the melting stage is preferably 240 ° C.
5, the injection speed To reduce the internal stress and deformation, high-speed injection should be selected, but some grades of PP and mold is not applicable (human mantle is bubbles, air lines). If engraved pattern surface by the gate diffusion of light and dark stripes, then use low-speed injection and higher mold temperature.
6, melt back pressure can be used 5bar melt adhesive back pressure, color powder back pressure may be appropriate to increase.
7, injection and holding pressure using high injection pressure (1500-1800bar) and packing pressure (about 80% of the injection pressure). About 95% of the whole trip turn pressure, with a longer dwell time. 8, post-processing products In order to prevent post-crystallization shrinkage deformation, products generally need to be treated by hot water immersion.
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