Automotive plastics have many advantages that traditional materials do not have. They are mainly characterized by light weight, good decorative appearance, various practical application functions, good physical and chemical properties, easy processing and molding, energy conservation, sustainable use, etc. aspect.
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Engineering plastics
Engineering plastics are widely used in the automotive field due to their good comprehensive mechanical properties. In this paper, polyamide (PA), polymethacrylate (PMMA), polyoxymethylene (POM), polyamide (PU) are mainly introduced. ), polycarbonate (PC).
PA
Polyamide, commonly known as nylon, is widely used in industrial applications. PA6, PA66 and PA610 are commonly used. PA is easy to print, easy to dye, excellent in electrical properties; resistant to chemicals and oil. The mechanical commonality is tough, both have high surface hardness, good tensile strength, good impact resistance, fatigue resistance, folding resistance and stress crack resistance. The tensile strength of PA changes with temperature and moisture absorption, so water is a plasticizer for PA. After adding glass fiber, its tensile and compressive strength can be increased by about 2 times, and the temperature resistance is also improved. PA itself The wear resistance is very high, so it can work without lubrication.
The disadvantages of PA are poor acid resistance, poor light resistance, and poor stain resistance. Due to the influence of thermal expansion and water absorption, the dimensional stability of the workpiece is poor, and the shrinkage rate is 1-2%. It is necessary to pay attention to the dimensional change of moisture absorption after molding. The water absorption rate is 100%, and it can absorb 8% when it is saturated with moisture absorption. The suitable wall thickness is 2 to 3.5 mm.
Injection molding performance: PA has strong water absorption and strong water absorption due to the presence of amide group. Therefore, it should be fully dried during injection molding, generally drying at 120 ° C for 3-4 hours; PA viscosity is small, flow speed is fast, to prevent shot If the mouth is flowing, a self-locking nozzle or a nylon-specific nozzle should be used. At the same time, pay attention to the accuracy of the mold.
Applications: PA is mainly used in the automotive field to manufacture hoses (brake hoses, fuel pipes), combustion oil filters, air filters, oil filters, water pump housings, water pump impellers, fans, brake fluid tanks, power Steering tank, white leaf window, headlight shell, seat belt.
PMMA
Polymethacrylate, commonly known as plexiglass, is resistant to outdoor aging, has excellent light transmission, and does not affect its transparency. It can still pass 92% of sunlight after 240 hours of accelerated aging of light, outdoor There are still 89% in the decade and 78.5% in the ultraviolet. High mechanical strength, certain cold resistance, corrosion resistance, good insulation performance, stable size, easy to form, brittle, easy to melt in organic solvents, insufficient surface hardness, easy to scratch and fluff. Suitable plastic products: transparent structural parts with a certain strength requirement.
Injection performance: PMMA has a moisture absorption rate of 0.3%. It must be dried before injection. It is usually dried at 80 °C for 2 to 4 hours. At injection temperature, the melt temperature is 240 to 270 °C, and the mold temperature is controlled at 35 to 70 °C.
PMMA is widely used in automotive lighting signs, door glass and lamp glass covers due to its good light transmission properties.
POM
POM, commonly known as plastic steel, tensile strength, impact toughness, rigidity and fatigue strength, high creep resistance, good dimensional stability, low water absorption, small friction, excellent friction and wear resistance, high temperature and The water is still very rigid and has the same chemical resistance as PA, but it is cheaper, resistant to repeated twisting and has outstanding resilience. It can be used for a long time between -40 degrees Celsius and 100 degrees Celsius. The shortcomings of POM are: it is susceptible to strong acid corrosion, high temperature resistance and poor thermal stability. Shrinkage rate 2-3.5% Suitable wall thickness: 1.5-2.5mm.
Injection molding performance: POM has obvious melting point, melting at 175 °C, decomposition at 240 °C, general processing temperature is 190 °C ~ 220 °C, its processing range is very narrow; POM does not absorb water, generally does not need to be dried during injection molding However, the product with high quality requirements can be dried at 60 ° C for 1 to 2 hours; the temperature should not be too high, otherwise the dyed product will be discolored; its acid resistance is poor, and it can not be dyed with acid dye.
Applications: POM uses and manufactures instrument panel glove box accessories, various valves (drain valves, air conditioner valves, etc.), various impellers (water pump impellers, heater blades, oil pump wheels, etc.), various electrical switches And small gears on the electrical instrument, various handles and door pins.
PC
Polycarbonate, with outstanding impact toughness and creep resistance, good heat resistance, good cold resistance, embrittlement temperature of -100 ° C, bending strength equivalent to nylon, and high elongation and elasticity Modulus, but fatigue strength is less than nylon 66. Low water absorption, low shrinkage and good dimensional stability. The wear resistance is comparable to that of nylon and has a certain corrosion resistance, but the molding conditions are high. Good weather resistance, long-term application under high temperature and high load conditions, but can not be used under wet temperature, poor solvent resistance, stress cracking, and poor fatigue strength. The shrinkage is 0.5-0.7%, and the suitable wall thickness is 2-3.5 mm. The addition of PC to glass fiber can improve its shrinkage, mechanical strength and temperature resistance. The long-term use of steel at 100 °C will increase, and the internal stress can be improved by annealing.
Injection performance: PC has obvious melting point, melt at 220 ° C, decompose at 350 ° C, the general processing temperature is 250 ° C ~ 320 ° C; it absorbs water, a small amount of water can cause it to decompose at high temperatures, must be baked during injection molding Dry, drying temperature can be dried at 120 °C for 4 to 5 hours; PC material has a high melt viscosity, which requires a large pressure during injection; PC can be used to improve the mold with mold temperature if the conditions permit. Temperature to reduce the residual stress of the product; PC shrinkage rate is independent of the processing conditions and the wall thickness of the product, and its longitudinal and transverse shrinkage ratio is relatively close, so it can be processed into a highly accurate product; its shrinkage rate is 0.5%. .
The main synthetic PC-abs: PC-ABS is a blending material of PC and ABS, which is usually supplied in the form of pellets after blending. If only two materials are simply mixed, direct injection molding, the effect is very poor, there will be stratification; PC has the advantage of being rigid and tough, the disadvantage is stress cracking, high viscosity; ABS has the advantage of good fluidity, but the surface The hardness is low; the blended material PC-ABS retains the advantages of both; PC-ABS has high surface hardness, high rigidity and toughness, and high resistance to stress cracking; its mechanical properties Between the two.
Scope of application: PC is mainly used in the automotive field to manufacture lampshades, left and right wheel cover guards, instrument baffle body (PC+ABS), left and right wind frame cover, middle wind frame cover (PC+ABS), rear bumper cushion.
PU
Polyurethane is generally classified into a rigid polyurethane and a flexible polyurethane depending on the polymerization product. The rigid polyurethane has high strength, good toughness, good heat insulation, good waterproof effect, simple molding process and high production efficiency; flexible polyurethane has good elasticity, good sound absorption effect, aging resistance and chemical resistance, etc. The mechanical properties far exceed the materials such as pvc. The polymerization of polyurethane is very convenient, not only can be carried out under normal temperature and normal pressure conditions, but also can be directly foamed or sprayed, repaired, etc. after on-site polymerization.
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, sofa leather, roof accessories; It is a variety of soft and rigid polyurethane foam materials, it has vibration isolation, sound insulation, noise reduction, thermal insulation; PU can also be made into automotive polyurethane coatings, adhesives, sealants and so on. The PU on the car represents the instrument panel, rear view mirror, bumper, seat cushion, headrest, steering wheel, instrument panel anti-vibration pad, pillar trim, front roof lining, window frame, ceiling and side top Frame decoration, door lining, sun visor, rear top frame decoration, etc.
