PP commonly known as polypropylene, because of its anti-break performance, also known as "plastic." PP is a translucent, semi-crystalline thermoplastics, with a high intensity, good insulation, low water absorption, hot on the shape of high temperature, density, and high crystallinity. Modified filler usually glass fiber, mineral filler, thermoplastic rubber.
PP its different uses different mobility, the general use of the PP between flow rate between the ABS and PC.
Pure PP is translucent ivory white, can be dyed a variety of colors. PP dyeing in general can only be used on injection molding machine masterbatch. Tatsu machines in China and the United States to strengthen the role of independent mixing plastics components, can also use color dye staining. Outdoor use products, the general use of UV stabilizers and carbon black filled. The use of renewable materials ratio should not exceed 15 percent, or else they will drop in intensity caused discoloration and decomposition. PP injection molding former general without special drying.
2, injection molding machine selection
The selection of injection molding machine there are no special requirements. As the PP has a high crystallinity. The need to adopt a higher injection pressure and multi-stage computer-controlled injection molding machine. Clamping force to determine the general by 3800t/m2, injection volume of 20% -85% can be.
Mold temperature 50-90 ℃, the size requirements of high temperature with high modulus. Core temperature lower than the cavity temperature above 5 ℃, flow channel diameter of 4-7mm, needle-shaped gate length of 1-1.5mm, the diameter can be as small as 0.7mm. Edge-shaped gate length as short as possible, about 0.7mm, a depth of half the thickness, width of wall twice, and with the mold cavity melt flow is willing to increase the length of each. Mold must have good exhaust and vent deep-0.025mm-0.038mm, thick 1.5mm, to avoid contraction of scar, it is necessary to use large and round and round nozzle flow, strengthen tendons thickness smaller (eg is the wall thickness of 50-60%). PP homopolymerization manufactured products, the thickness of no more than 3mm, or it will bubble (thick-walled products can only be used copolymerization PP).
PP's melting point of 160-175 ℃, decomposition temperature of 350 ℃, but the injection processing temperature should not exceed 275 ℃. Melting temperature of the best in the 240 ℃.
In order to reduce internal stress and deformation, should be selected high-speed injection, but some grades of PP and die not applicable (person mantle are bubbles, gas stria). Engraved with patterns such as the surface of the proliferation of light and shade by the gate and white stripes, it will need to low-speed injection and higher mold temperature.
Melt glue can be used 5bar backpressure color powder backpressure can be properly raised.
Higher injection pressure (1500-1800bar) and packing pressure (injection pressure is about 80%). Probably in the whole journey to 95% when the pressure, the pressure to spend more time.
In order to prevent crystallization generated after contraction deformation, products in general is subject to deal with hot water immersion.
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