There are many types of plastics, and their applications in automobiles are divided into internal parts, external parts, and functional parts. According to the different usage characteristics of different plastics, plastics are generally divided into three types: general purpose plastics, engineering plastics, and specialty plastics.
One, plain plastic
Generally refers to plastics with high production volume, good formability, low price and wide application. General purpose plastics include five main varieties: polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene copolymer (ABS), all of which are thermoplastics.
Polypropylene, commonly known as wrinkled adhesive, is similar to white wax, transparent, light in weight, has good fluidity in injection molding, and has a water absorption of less than 0.02%. The shrinkage rate of polypropylene is 1.0-3.5%, and a suitable thickness is 1.5-2.5 mm.
There are two main problems with the widespread use of PP in the automotive industry: it burns easily (burning materials drip off it) and it becomes brittle at low temperatures. To solve these two problems, suitable additives are added in the industry to modify polypropylene. Flame retardants will be added if it ignites; it becomes brittle at low temperature and is generally modified and made more rigid by adding other strong materials, hard particles or elastomers such as rubber (EPDM), talc (TD), fiberglass. (GF) Wait. There are many automotive products made from PP resin, including various dashboards, door guards, pillar guards, bumpers, water tanks, and decorative panels. There are more and more trends in the use of PP in automobiles.
Polyethylene, one of the lightest plastics, translucent white waxy material, good water resistance, resistance to acids and alkalis, resistance to organic solvents, excellent electrical insulation. The shrinkage rate is 1.5-4.0%, and the suitable thickness is 1.0-2.5mm.
The biggest disadvantage of polyethylene as an automotive material is that it is highly flammable. The simplest and most commonly used method is to add a suitable flame retardant to improve the combustion characteristics of the polyethylene. Automotive products made of polyethylene mainly include fuel tanks, air ducts, front seat upholstery, air duct assemblies (HDPE), left and right ventilation pipes assemblies, connecting rods for up and down guide vanes, left and right foot vents etc. .
Polyvinyl chloride, commonly used PVC, is a multi-component plastic. Because the content of each component is different, different PVC particles with different hardness are formed, which are generally divided into soft PVC and hard PVC. Shrink rate: 1-1.5% for hard PVC, 2-2.3% for soft PVC, the corresponding thickness is 2-3.5mm.
The most commonly used plastic raw material in automotive plastic products is polyvinyl chloride, and automotive plasticsPVC plastic products can be seen everywhere, such as PVC dashboard trim, PVC steering wheel, PVC trim, PVC plastic. car floor material This is not only because the price of PVC resin is economical, but also with relatively good processing performance and comprehensive mechanical properties.
Polystyrene, commonly known as a hard adhesive, is a transparent glassy material with good fluidity and no water absorption. Due to the brittleness of polystyrene, it is often grafted and copolymerized with other substances, such as grafted and copolymerized with butadiene. , HIPS, toughness and surface hardness are greatly improved after incorporation into rubber. The shrinkage ratio is 0.4-0.7% and the corresponding thickness is 2-3mm.
The main applications of polystyrene in automobiles are instrument housings, lampshades and lighting fixtures. Polystyrene can also be expanded for packaging materials and thermal insulation materials for ceiling applications, as well as being grafted and modified with other materials to produce many PS family fixed bond plastics such as SMA. car dashboard frame.
Acrylonitrile-butadiene-styrene copolymer, commonly known as a heavy-duty adhesive, white body. The shrinkage rate is 0.4-0.7%, and the suitable wall thickness is 1.8-3mm.
Because of the variety of ABS, good surface treatment effect and low price, it is widely used in the automotive field. Due to the poor weather resistance of ABS, materials such as AES and ASA with high weather resistance are widely used in addition to ABS in commercial vehicles. When the product requires surface treatment (such as water transfer film, spraying), ABS is used, when surface treatment is not required, ASA and AES are used. The most typical automotive products are decorative bright trims, shift knob heads, interior handles, license plate decorative panels, rear spoiler assemblies, rearview mirror housings, grille housings, armrests, etc.
Second, engineering plastics
Technical plastics are also widely used in the automotive industry due to their good complex mechanical properties. This article mainly features polyamide (PA), polymethacrylate (PMMA), polyoxymethylene (POM), polyamide (PU), polycarbonate (PC). .
Polyamide, commonly known as nylon, has many types of polyamide used in the industry, and the most commonly used are polyamide 6, PA66 and PA610. Due to the influence of thermal expansion and water absorption, the dimensional stability of the part is low, and the shrinkage rate is 1-2%. Note the change in moisture absorption dimensions after molding. The water absorption rate is 100%, and it can absorb 8% when the relative moisture absorption reaches saturation. Suitable wall thickness is 2-3.5mm.
PA is mainly used in the automotive industry for the production of hoses (brake hoses, fuel pipes), oil filters, air filters, oil filters, water pump housings, water pump impellers, fans, brake fluid tanks, power steering tanks, white curtains , headlight housings, seat belts.
Polymethacrylate, commonly known as plexiglass, is resistant to outdoor aging and has excellent light transmission. Suitable plastic products: transparent structural parts with certain strength requirements.
Because of its good light transmission, polymethyl methacrylate is widely used in automotive light panels, door glass and glass lamp covers.
Polyoxymethylene, commonly known as plastic steel, shrinkage rate 2-3.5%, suitable wall thickness: 1.5-2.5mm.
POM is used in automobiles to make accessories for dashboard gloves, various valves (drain valves, air conditioning valves, etc.), various impellers (water pump impellers, heater impellers, oil pump wheels, etc.), various electrical switches and small gears, various handles and door pins on electrical appliances.
Polycarbonate has excellent impact strength and creep resistance, good heat resistance and frost resistance. The shrinkage ratio is 0.5-0.7% and the suitable wall thickness is 2-3.5mm. Adding fiberglass to polycarbonate can improve its shrinkage, mechanical strength, and heat resistance. Long-term use at around 100°C will increase stiffness, and annealing can be used to reduce internal stress.
Introduction to the main synthetic plastic PC-ABS:
PC-ABS is a mixture of PC and ABS, which after mixing is usually supplied in the form of granules. If you simply mix the two materials and inject them directly, the effect will be poor and delamination will occur; the advantage of polycarbonate in rigidity and strength,but the disadvantage is stress cracking and high toughness; The advantage of ABS is good fluidity, but the surface is low hardness; PC-ABS mixed material retains the advantages of both; PC-ABS has high surface hardness, high rigidity and toughness, and high resistance to stress cracking; its mechanical properties are in between.
PC is mainly used for lampshades, left and right wheel covers, dashboard shell (PC+ABS), left and right frame covers, middle frame covers (PC+ABS) and rear bumper cushions. in the automotive field.
Polyurethane, according to different polymerization products, is generally divided into rigid polyurethane and soft polyurethane.
Polyurethane foam is widely used in automotive interiors and vibration-absorbing parts, such as coating materials, polyurethane rigid plastic sheets, polyurethane elastomers, seat soft foam materials, decorative parts, leather sofa and car roof accessories. various soft and hard polyurethane foam materials that have vibration, sound, noise, heat insulation properties, as well as polyurethane coatings for cars, adhesives, sealants, etc. Representative parts of polyurethane for cars include dashboards, rear-view mirrors, bumpers, seat cushions, head restraints, steering wheels, dashboard anti-vibration pads, pillar trim, front roof lining, window frames, roofs and side roofs. rear top shelf trim, etc.
Three, special plastic
Fiberglass reinforced plastic
Fiberglass-reinforced plastic is based on the original pure plastic with the addition of fiberglass and other additives to expand the range of use of the material. Generally speaking, most glass fiber reinforced materials are mainly used in the structural parts of the product, which is a kind of structural engineering material, such as: PP, ABS, PA66, PA6, PC, POM.
①After the fiberglass is reinforced, the fiberglass becomes a high temperature resistant material, so the heat resistance temperature of the reinforced plastic is much higher than before without fiberglass, especially nylon plastic; ② Reciprocal motion between polymers Plastic chains are limited, so the shrinkage rate of reinforced plastics is greatly reduced, and the rigidity is also greatly improved; ③Reinforced plastics will not crack under stress, and the impact resistance of plastics will be greatly improved; ④ Fiberglass is a high-strength material, which also greatly enhances the strength of plastics. Tensile strength, compressive strength and bending strength are greatly improved) ⑤ Due to the addition of glass fiber and other additives, the combustion performance of reinforced plastics has been greatly reduced, and most materials cannot be ignited.
①It is transparent until fiberglass is added and it will become opaque;
② The strength of the plastic decreases and the brittleness increases;
③The melt viscosity of all materials increases, the fluidity becomes poor, and the injection pressure is much higher than without fiberglass;
④Poor fluidity. For normal injection molding, the injection temperature of all reinforced plastics must be increased by 10-30 °C than before adding fiberglass;
⑤The hygroscopic performance of reinforced plastics is greatly improved, and even pure plastics that do not absorb water become water absorbent, so they need to be dried during injection molding;
⑥During the injection molding process, glass fiber may get on the surface of the plastic product, which will make the surface of the product rough and mottled (in order to get a better surface quality, it is best to use a mold heating machine). mold by injection molding, so that the plastic polymer hits the surface of the product, but the appearance quality of pure plastic cannot be achieved);
⑦ Glass fiber is a material with high hardness. After the additive evaporates at high temperature, it will be a very corrosive gas, which will cause severe wear and corrosion of the screw of the injection molding machine and injection mold. Therefore, mold making using this material. When using and injection molding machine, attention should be paid to anti-corrosion surface treatmentand and surface hardness treatment of equipment.
Degree of shrinkage of commonly used fiberglass:
PP+glass fiber: 0.2-0.8%
ABS+glass fiber: 0.1-0.2%
PA66+glass fiber: 0.5%
PA6+glass fiber: 0.4%
PC + fiberglass: 0.1-0.3%
POM+glass fiber: 0.9-1.2%
Representative material for fiberglass reinforcement, FRP/composite applications in the automotive industry:
Body parts: including bodyshells, hardtops, sunroofs, doors, grilles, headlight reflectors, front and rear bumpers, and interior parts. This is the main application of FRP/composite materials in automobiles. It is mainly aimed at meeting the requirements of streamlined body structure and high-quality appearance. At present, there is a huge potential for development and application. The material of this part is mainly glass fiber reinforced thermosetting plastic, and the typical molding processes include: SMC/BMC, RTM, and hand lay-up/spraying, etc.
Structural parts: including front brackets, bumper frames, seat frames, floors, etc. that aim to improve design freedom, versatility, and part integrity. Mainly use high strength SMC, GMT, LFT and other materials.
Functional parts: Its main feature is that it requires high temperature resistance and oil corrosion resistance, mainly of the engine and its peripheral parts. For example: engine valve cover, intake manifold, oil pan, air filter cover, gear chamber cover, air duct cover, intake pipe guard, fan blade, fan air duct ring, heater cover, water tank parts, water outlet housing, water pump. turbine, engine soundproofing plate, etc. Main process materials: SMC/BMC, RTM, GMT and fiberglass reinforced nylon, etc.
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Note. This article is from the "Plastic Price Today" public account (ID: jinrisujia). If you want to know the latest prices for materials such as PC, PP, and ABS, you can search for "Plastic Price Today". " follow.
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