Injection molding characteristics of the hottest P

2022-08-16
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Injection molding characteristics of PP polypropylene

typical application range:

automotive industry (mainly PP containing metal additives: fender, ventilation pipe, fan, etc.), equipment (dishwasher door gasket, dryer ventilation pipe, washer frame and cover, refrigerator door gasket, etc.), daily consumer goods (lawn and gardening equipment such as lawn mower and sprinkler, etc.)

injection molding process conditions:

drying treatment: if it is stored properly, it does not need drying treatment

melting temperature: 220~275c, be careful not to exceed 275c

mold temperature: 40~80c, 50c is recommended. The crystallinity is mainly determined by the mold temperature

injection pressure: up to 1800bar

injection speed: generally, the internal pressure can be minimized by using high-speed injection molding. If there are defects on the surface of the product,

low speed injection molding at higher temperature should be used

runner and gate: for cold runner, the typical runner diameter range is 4~7mm. It is recommended to use round injection ports and flow channels. All types of gates can be used. The typical gate diameter range is 1. Fluoroplastics are paraffinic polymers with some or all hydrogen substituted by fluorine ~1.5mm, but Gates as small as 0.7mm can also be used. For edge gate, the minimum gate depth should be half of the wall thickness; The minimum gate width should be at least twice the wall thickness. PP material can use hot runner system

chemical and physical properties:

pp is a semi crystalline material. It is harder than PE and has a higher melting point

because homopolymer PP is very brittle when the temperature is above 0C, many commercial PP materials are irregular copolymers with 1~4% ethylene or clamped copolymers with higher ethylene content. Copolymer PP material has lower heat distortion temperature (100C), low transparency, low gloss and low rigidity, but it has stronger impact strength. The strength of PP increases with the increase of ethylene content

The Vicat softening temperature of

pp is 150C. Due to its high crystallinity, this material has good surface stiffness and scratch resistance

pp has no environmental stress cracking problem. Usually, PP is modified by adding glass fiber, metal additives or thermoplastic rubber. The flow rate MFR of PP ranges from 1 to 40. PP material with low MFR has good impact resistance but low tensile strength. For materials with the same MFR, the strength of copolymer type is higher than that of homopolymer type

due to crystallization, the shrinkage of PP is quite high, generally 1.8~2.5%. And the directional uniformity of shrinkage is much better than that of PE-HD and other materials. Adding 30% glass additive can reduce the shrinkage to 0.7%. Homopolymer and copolymer PP materials have excellent moisture absorption resistance, acid-base corrosion resistance and solubility resistance. However, it has no resistance to aromatic hydrocarbon (such as benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, etc. PP is also different from P reciprocating single screw extruder, whose biggest feature is to realize high filling processing of different materials. E still has oxidation resistance at high temperature

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