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There are many kinds of plastics, which can be divided into interior parts, exterior parts and functional parts in cars.
According to the use of different types of plastic, plastic is usually divided into general plastic, engineering plastic and special plastic three types.
1. Universal plastics
It is to point to the plastic with large production, good molding, cheap price and extensive use commonly.
General plastic contains five varieties, polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile - butadiene-styrene copolymer (ABS), are thermoplastic plastics.
PP
Polypropylene, commonly known as polypropylene, is similar to white waxy, transparent, light, good fluidity when injection molding, water absorption less than 0.02%.
The PP shrinkage rate is 1.0-3.5%, and the appropriate thickness is 1.5-2.5mm.
There are two main problems in the widespread use of PP in the automotive field: it is easy to burn (it will drop combustible matter) and it is brittle in low temperature environment.
In view of these two problems, in the industrial practical application of adding appropriate additives, do PP modification.
Flammable will add flame retardant;
It is brittle under low temperature environment, and is mainly modified and toughened by adding other ductile materials, rigid particles or elastomers, such as rubber (EPDM), talcum powder (TD), glass fiber (GF), etc.
There are many automotive products made of PP resin, including various instrument panels, door guard panels, column guard panels, bumpers, water tanks and decorative panels. The application of PP in automobiles has more and more trends.
PE
Polyethylene, one of the lightest plastics, translucent white waxy material, good water resistance, acid and alkali resistance, organic solvent resistance, excellent electrical insulation.
Shrink rate 1.5 ~ 4.0%, suitable thickness 1.0-2.5mm.
The biggest drawback of PE as an automotive material is that it is easy to burn. The most simple and common method is to add appropriate flame retardant to improve the combustion performance of PE.
The main automotive products made of PE are fuel tank, air duct, front seat decorative cover, air duct assembly (HDPE), left and right ventilation duct assembly, upper and lower wind blade connecting bar, left and right foot vent assembly, etc.
PVC
PVC, commonly used PVC is a multi-component plastic, because the content of each component is different, the formation of a variety of mechanical properties of different hardness of PVC particles, generally divided into soft PVC and hard PVC two categories.
Shrinkage rate: hard PVC is 1-1.5%, soft PVC is 2-2.3%, suitable thickness 2-3.5mm.
In the automotive plastic products, the most commonly used plastic raw materials should be PVC, PVC plastic manufacturing of automotive plastic products can be seen everywhere, PVC dashboard skin, PVC plastic steering wheel, PVC plastic lining board, PVC plastic car paving materials.
This is not only because the price of PVC resin is economic, but also the processing performance and comprehensive mechanical properties are better.
PS
Polystyrene, commonly known as hard glue, transparent glass like material, good mobility, not water absorption, due to PS brittleness, often with other substances graft copolymerization, such as butadiene graft copolymerization to form HIPS, the composition containing rubber after the impact strength and surface hardness are greatly improved.
Shrinkage rate 0.4-0.7%, suitable thickness 2-3mm.
PS in the main application of the car in the instrument shell, lamp shade, lighting products.
Polystyrene can also be prepared through foaming molding packaging materials and thermal insulation materials, used for the production of ceiling, and is grafted with other materials copolymerization and modification, get a lot of fixed collocation of PS family of alloy plastic varieties, such as SMA used in the manufacture of automobile dashboard skeleton.
ABS
Acrylonitrile - butadiene - styrene copolymer, commonly known as super non - broken glue, the body is white.
Shrinkage rate is 0.4-0.7%, suitable wall thickness 1.8-3mm.
Because ABS has many kinds, good surface treatment effect and low price, it is widely used in the automotive field.
In view of the poor weather resistance of ABS, AES, ASA and other materials with high weather resistance have been widely used in commercial vehicles to supplement ABS.
When the product needs to do surface treatment (such as water transfer film, spraying), use ABS;
ASA and AES are used when surface treatment is not required.
The most typical automotive products are decorative strip, shift handle head, inner opening handle, plate decoration plate, rear spoiler assembly, rearview mirror body, radiator grille body, handrails and so on.
Two, engineering plastics
Engineering plastics are also widely used in the automotive field because of their good comprehensive mechanical properties. In this paper, polyamide (PA), polymethacrylate (PMMA), polyformaldehyde (POM), polyamide (PU), polycarbonate (PC) are mainly introduced.
PA
Polyamide, commonly known as nylon, there are many types of PA in industrial use, and PA6, PA66 and PA610 are commonly used.
Due to the influence of thermal expansion and water absorption, the dimensional stability of the parts is poor, and the shrinkage rate is 1 ~ 2%. It is necessary to pay attention to the dimensional change of moisture absorption after forming.
Water absorption rate of 100%, relative hygroscopic saturation can absorb 8%, suitable wall thickness: 2 ~ 3.5mm.
PA in the automotive field is mainly used in the manufacture of hoses (brake hoses, fuel pipes), combustion oil filters, air filters, oil filters, water pump housing, water pump impeller, fans, brake fluid tank, power steering fluid tank, white shutters, headlight housing, safety belts.
PMMA
Polymethacrylate, commonly known as plexiglass, outdoor aging resistance, excellent light transmittance suitable plastic products: transparent structure with certain strength requirements.
PMMA is widely used in automobile lighting signs, door glass and lamp glass cover because of its good light transmittance.
POM
Poly formaldehyde, commonly known as plastic steel, shrinkage rate 2-3.5% suitable wall thickness: 1.5-2.5mm.
POM is used to manufacture instrument panel, glove box accessories, various valves (drainage valves, air conditioners, etc.), various impellers (water pump impellers, air heater impellers, oil pump wheels, etc.), various electrical switches, pinion gears on electrical instruments, various handles and door pins, etc.
PC
Polycarbonate, with outstanding impact toughness and creep resistance, good heat resistance and cold resistance.
Shrinkage rate is 0.5-0.7%, suitable wall thickness is 2-3.5mm.
PC added glass fiber can improve its shrinkage, mechanical strength and temperature resistance, at about 100℃ long-term use of steel will increase, available annealing to improve the internal stress.
Introduction of PC-ABS:
PC-ABS is a blend material of PC and ABS. It is usually supplied in the shape of granule after blending.
If only the two materials are simply mixed, direct injection, the effect is very poor, there will be stratification phenomenon;
The advantage of PC is just and tough, the disadvantage is stress cracking, viscosity;
The advantage of ABS is good fluidity, but the surface hardness is low;
In this way, PC-ABS retains the advantages of both materials.
PC-ABS has higher surface hardness, higher rigidity and toughness, but also has higher stress cracking resistance ability;
Its mechanical properties fall between the two.
PC in the automotive field is mainly used in the manufacture of lampshade, left and right wheel cover plate, instrument baffle body (PC+ABS), left and right air frame cover, middle air frame cover (PC+ABS), rear bumper cushion.
PU
Polyurethane, according to the different products of the polymerization reaction, commonly divided into hard polyurethane and soft polyurethane.
Polyurethane foam plastics are widely used in automotive interior decoration and vibration absorbing parts, such as coating material, polyurethane rigid plastic sheet, polyurethane elastomer, soft foam materials for seats, decorative parts, sofa leather, roof accessories;
The most widely used are all kinds of soft and hard polyurethane foam materials, which have vibration isolation, sound insulation, noise reduction, thermal insulation;
PU can also be made into automotive polyurethane coatings, binders, sealants, etc.
On the car, PU representative parts include instrument panel, rearview mirror, bumper, seat cushion, headrest, steering wheel, instrument panel vibration pad, pillar decoration, front roof lining, window frame, ceiling and side roof frame decoration, door liner, sun visor, rear roof frame decoration, etc.
Three, special plastics
Glass fiber reinforced plastic is based on the original pure plastic, adding glass fiber and other additives, so as to improve the use of the material range.
Generally speaking, most of the glass fiber reinforced materials are mostly used in the structural parts of the product, which is a kind of structural engineering materials.
Such as: PP, ABS, PA66, PA6, PC, POM.
Advantages:
(1) after the glass fiber reinforced, glass fiber is a high temperature resistant material, so the heat resistance temperature of reinforced plastic is much higher than before without glass fiber, especially nylon plastic;
(2) restrict the mutual movement of the polymer chain of plastic, so the shrinkage rate of reinforced plastic drops a lot, and the rigidity is also greatly improved;
(3) the reinforced plastic will not stress cracking, and the impact resistance of plastic is improved a lot;
(4) glass fiber is a high strength material, which also greatly improves the strength of plastic (tensile strength, compression strength, bending strength are improved a lot);
⑤ Due to the addition of glass fiber and other additives, the combustion performance of reinforced plastics decreases a lot, and most materials can not be ignited.
Disadvantages:
(1) without glass fiber is transparent, will become opaque;
(2) the toughness of plastic decreases, but the brittleness increases;
(3) the melting viscosity of all materials increases, the flow becomes worse, the injection pressure is much higher than that without glass fiber;
(4) poor liquidity, in order to normal injection, injection temperature of all reinforced plastics than without glass fiber before 10℃-30℃;
The hygroscopic performance of enhanced plastic is greatly strengthened, and the original pure plastic will become absorbent without water absorption, therefore, when injection molding is required to enter the drying;
⑥ in the process of injection molding, glass fiber can enter the surface of plastic products, the surface of the products become very rough, spotty spots (in order to obtain a higher surface quality, the best injection molding using mold temperature machine heating mold, the plastic polymer into the surface of the products, but can not achieve the appearance of pure plastic quality);
⑦ glass fiber is a very high hardness of materials, auxiliary after high temperature volatilization is a corrosive gas, the wear and corrosion of the screw and injection mold of injection molding machine is very big, therefore, the production of mold and injection molding machine using this kind of material, we should pay attention to the surface anti-corrosion treatment and surface hardness treatment of equipment.
Commonly used with glass fiber shrinkage rate:
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+ glass fiber: 0.1-0.3%
POM+ glass fiber: 0.9-1.2%
The representative materials of glass fiber reinforced, FRP/composite materials in the automotive industry application:
Body parts: including body shell, roof, skylight, door, radiator grating plate, headlight reflector, front and rear bumpers and car interior accessories.
This is the main application direction of FRP/composite materials in the automobile, mainly in order to meet the needs of streamlined body design and high quality appearance requirements, the development and application potential is huge at present.
The component material is mainly glass fiber reinforced thermosetting plastic, typical molding process: SMC/BMC, RTM and hand/spray, etc.
Structural parts: including front bracket, bumper frame, seat frame, floor, etc., its purpose is to improve the design freedom, versatility and integrity of the parts.
High strength SMC, GMT, LFT and other materials are mainly used.
Function parts: its main characteristics are high temperature resistance, oil corrosion resistance, mainly to the engine and the engine surrounding parts.
For example: engine valve cover, intake manifold, oil pan, air filter cover, gear chamber cover, air guide hood, intake pipe guard plate, fan blade, fan air guide ring, heater cover plate, water tank parts, water outlet shell, water pump turbine, engine sound insulation board, etc.
Main process materials are: SMC/BMC, RTM, GMT and glass fiber reinforced nylon, etc.
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