The PP or polypropylene, because of its good anti breaking performance, also known as the "folding glue". PP is a translucent, semi crystalline thermoplastic plastics, has high strength, good insulating property, low water absorption, low density, high crystallinity. Modified filler are usually divided into glass fiber, mineral filler, thermoplastic rubber etc.
The different uses of PP makes different liquidity, general PP flow rate between ABS and PC use.
1. Plastics processing
Pure PP is translucent and ivory white, can be dyed various colors. PP staining in the general injection molding machine can only use color master batch. Ramada machine with independent plasticizing component mixing effect, also can use toner staining. Products for outdoor use, generally use of UV stabilizer and filled with carbon black. Using the ratio of renewable materials should not exceed 15%, otherwise it will cause the strength decrease and discoloration decomposition. PP injection processing does not need special pre-drying treatment
Injection molding machine selection
The selection of injection molding machine has no special requirements. Because PP has a high crystallinity. Need to adopt computer injection molding machinc with high pressure and multi segment control function. Clamping force is generally set as 3800t/m2, the injection amount is 20%-85%.
3、Mold and spur design
Mold temperature 50-90 ℃, If need higher requirements it will set to high mold temperature. Core temperature is 5 ℃ higher than the cavity temperature, channel diameter 4-7mm, needle shaped spur length 1-1.5mm, diameter is 0.7mm. Make the Edge spur length as short as possible, like 0.7mm, the depth is half of the wall thickness, width is two times of the wall thickness, and with the mold cavity melt flow length would increase by. The mold must be of air exhaust hole, deep 0.025mm-0.038mm, thickness of 1.5mm. If you need to avoid shrinkage marks, you should use the big and round injection port and a circular runner, the thickness of the stiffener need to be small (such as 50-60% of wall thickness). The product that made by homopolymerization PP, thickness of it cannot more than 3mm, otherwise it will bubble (thick wall products can only be used in the PP copolymer material)
4、Melt temperature
The melting point of PP is 160-175 ℃, decomposition temperature 350 ℃, but in the injection processing temperature should not exceed 275 ℃. The melting temperature is best at 240 ℃.
5、Injection speed
In order to reduce the internal force and deformation, we should choose high speed injection, but some grade PP and die are not applicable (mantle, the bubble gas lines). Such as surface carved by the advent of the gate diffusion light stripes, should use low speed injection and high mold temperature.
6、Melt pressure
Available to udr 5 bar melt pressure, the toner discharge pressure can be adjusted high
7、The injection and holding pressure
Using higher injection pressure (1500-1800bar) and pressure (about 80% of injection pressure). About 95% of the whole trip to holding pressure, pressure time longer.
8、Products after processing
To prevent crystallization contraction deformation, products generally need hot water immersion.
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