Injection molding is a method of producing shapes for industrial products. Products usually use rubber injection molding and plastic injection molding. Injection molding can also be divided into injection molding compression method and die casting method. Injection molding machine (abbreviated as injection machine or injection molding machine) is the main molding equipment that uses plastic molding molds to make various shapes of plastic products from thermoplastics or thermosets. Injection molding is achieved through injection molding machines and molds.
1. AS styrene-acrylonitrile copolymer
★Typical application range:
Electrics (sockets, housings, etc.), daily commodities (kitchen appliances, refrigerator devices, TV bases, cassette boxes, etc.), automotive industry (headlight boxes, reflectors, dashboards, etc.), household goods (tableware, food knives, etc.) Etc.), cosmetic packaging, etc.
★Injection mold process conditions:
▶Drying treatment: If stored improperly, AS has some hygroscopic properties. The recommended drying conditions are 80°C, 2~4 hours.
▶Melting temperature: 200~270℃. If processing thick-walled products, you can use a melting temperature below the lower limit.
▶Mold temperature: 40~80℃. For reinforced materials, the mold temperature should not exceed 60°C. The cooling system must be well designed, because the mold temperature will directly affect the appearance, shrinkage and bending of the product.
▶Injection pressure: 350~1300bar.
▶Injection speed: High-speed injection is recommended.
▶Runner and gate: All conventional gates can be used. The gate size must be appropriate to avoid streaks, freckles and voids.
★Chemical and physical properties:
AS is a hard, transparent material. The styrene component makes AS hard, transparent and easy to process; the acrylonitrile component makes AS have chemical and thermal stability. AS has strong load bearing capacity, chemical resistance, thermal deformation resistance and geometric stability. Adding glass fiber additives to AS can increase strength and thermal deformation resistance, and reduce thermal expansion coefficient. The Vicat softening temperature of AS is about 110°C. The deflection temperature under load is about 100°C. The shrinkage rate of AS is about 0.3~0.7%.
2. PS, also called polystyrene, is a kind of thermoplastic.
Transparent when uncolored. When the product falls on the ground or knocks, it has a metal-like crisp sound, good gloss and transparency, similar to glass, brittle and easy to break, and can mark the surface of the product with a fingernail. Modified polystyrene is opaque.
★Common products: stationery, cups, food containers, appliance shells, electrical accessories, etc.
3. ABS material is a kind of engineering plastic. ABS resin is composed of copolymer of acrylonitrile (A), butadiene (B) and styrene (S). A material that is mostly used to make small toys, like small alarm clocks, and sometimes used in mobile phone shells.
4. PC is the abbreviation of polycarbonate, the English of polycarbonate is Polycarbonate, PC engineering plastics for short. PC material is actually one of the engineering plastics we call. As a material widely used worldwide, PC has its own The characteristics and advantages and disadvantages of PC is an amorphous thermoplastic resin with excellent comprehensive performance. It has excellent electrical insulation, elongation, dimensional stability and chemical resistance, high strength, heat resistance and cold resistance. ; It also has the advantages of self-extinguishing, flame-retardant, non-toxic, colorable, etc., you can see the shadow of PC plastic in every corner of your life, and the characteristics of large-scale industrial production and easy processing also make the price extremely low. Its strength can meet various needs from mobile phones to bulletproof glass. The disadvantage is that it is not hard enough compared with metal, which makes its appearance easier to scratch, but its strength and toughness are good, whether it is heavy pressure or general beating , As long as you are not trying to hit it with a rock, it will live long enough.
5. PE plastic (polyethylene)
★English name: Polyethylene
★ Specific gravity: 0.94-0.96 g/cm3
★Molding shrinkage: 1.5-3.6%
★Molding temperature: 140-220℃
★Material properties: corrosion resistance, excellent electrical insulation (especially high frequency insulation), can be chlorinated, modified by irradiation, and can be reinforced with glass fiber. Low pressure polyethylene has a melting point, rigidity, hardness and strength, and water absorption It is small, has good electrical properties and radiation resistance; high-pressure polyethylene has good flexibility, elongation, impact strength and permeability; ultra-high molecular weight polyethylene has high impact strength, fatigue resistance, and wear resistance.
Low-pressure polyethylene is suitable for making corrosion-resistant parts and insulating parts; high-pressure polyethylene is suitable for making films, etc.; ultra-high molecular weight polyethylene is suitable for making shock-absorbing, wear-resistant and transmission parts.
▶The crystalline material has low moisture absorption, does not need to be fully dried, and has excellent fluidity. The fluidity is sensitive to pressure. High pressure injection should be used when molding, the material temperature is uniform, the filling speed is fast, and the pressure is adequate. Evenly, the internal stress increases. Pay attention to choosing the gate position to prevent shrinkage and deformation.
▶The shrinkage range and shrinkage value are large, the directionality is obvious, and it is easy to deform and warp. The cooling speed should be slow, and the mold should be equipped with a cold material cavity and a cooling system.
▶The heating time should not be too long, otherwise it will decompose and burn.
▶When soft plastic parts have shallow side grooves, they can be demolded forcibly.
▶Melting fracture may occur, so it is not suitable to contact with organic solvents to prevent cracking.
6. PVC (Polyvinyl Chloride) Chemical and Physical Properties Rigid PVC is one of the most widely used plastic materials. PVC material is a non-crystalline material. In actual use, PVC materials often add stabilizers, lubricants, auxiliary processing agents, pigments, impact agents and other additives.
PVC material has non-flammability, high strength, weather resistance and excellent geometric stability. PVC has strong resistance to oxidants, reducing agents and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid and is not suitable for contact with aromatic hydrocarbons and chlorinated hydrocarbons.
The melting temperature of PVC during processing is a very important process parameter. If this parameter is not appropriate, it will cause material decomposition. The flow characteristics of PVC are quite poor, and its process range is very narrow. Especially the high molecular weight PVC material is more difficult to process (this kind of material usually needs to add lubricant to improve the flow characteristics), so the PVC material with small molecular weight is usually used. The shrinkage rate of PVC is quite low, generally 0.2~0.6%.
★Process conditions of injection mould:
▶Drying treatment: usually no drying treatment is required.
▶Melting temperature: 185~205C Mold temperature: 20~50C
▶Injection pressure: up to 1500bar
▶Holding pressure: up to 1000bar
▶Injection speed: In order to avoid material degradation, it is generally necessary to use a considerable injection speed.
▶Runner and gate: All conventional gates can be used. If processing smaller parts, it is best to use needle-point gates or submerged gates; for thicker parts, it is best to use fan gates. The minimum diameter of the needle-point gate or the submerged gate should be 1mm; the thickness of the sector gate should not be less than 1mm.
▶Typical uses: water supply pipes, household pipes, house wall panels, commercial machine housings, electronic product packaging, medical equipment, food packaging, etc.
1. Easy to process Injection mold parts are mostly made of metal materials, and some structural shapes are still very complex. In order to shorten the production cycle and improve efficiency, the mold materials are required to be easy to process into the shape and accuracy required by the drawings.
2. Good wear resistance. The gloss and accuracy of the surface of the plastic part are directly related to the wear resistance of the mold cavity surface, especially when glass fiber, inorganic fillers and certain pigments are added to some plastics. The melt flows at high speed in the runner and the mold cavity together, and the friction on the surface of the cavity is great. If the material is not wear-resistant, it will wear out quickly, which will damage the quality of the plastic part.
3. High corrosion resistance Many resins and additives have a corrosive effect on the surface of the cavity. This corrosion causes the metal on the surface of the cavity to corrode and peel off, the surface condition becomes worse, and the quality of the plastic parts deteriorates. Therefore, it is best to use corrosion-resistant steel, or chromium plating, cymbal nickel treatment on the cavity surface.
4. Good dimensional stability. During injection molding, the temperature of the injection mold cavity must reach above 300°C. For this reason, it is best to select tool steel (heat-treated steel) that has been properly tempered. Otherwise it will cause changes in the microstructure of the material, resulting in changes in the size of the mold.
5. Less affected by heat treatment In order to improve the hardness and wear resistance, the mold is generally heat treated, but this treatment should make the size change small. Therefore, it is best to use pre-hardened steel that can be cut.
6. Good polishing performance. Plastic parts usually require good gloss and surface condition. Therefore, the roughness of the cavity surface is required to be very small. In this way, the surface of the cavity must be surface processed, such as polishing, grinding, etc. Therefore, the selected steel should not contain rough impurities and pores.
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