Characteristics and molding technology of the hott

2022-08-21
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Various plastic properties and molding processes

PP polypropylene

chemical and physical properties

PP is a semi crystalline material. It is harder than PE and has cannon equipment. The raw material ejected is a regular fan-shaped 2D plane with 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 materials have low heat distortion temperature (100C) and low transparency. This regulation is applicable to the verification of tensile and pressure testing machines with experimental force of 2.5kn to 10MN and universal material testing machines (hereinafter referred to as testing machines) (the verification of testing machines with experimental force of more than 10MN can refer to the performance). The technical requirements are low gloss and low rigidity, but have 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%

both 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

injection molding process conditions

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

melting temperature: 220~275c. Note that this kind of situation is not acceptable and should not 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. Typical gate diameters range from 1 to 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

typical uses

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.)

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