Auto parts mould which plastic applications
2018-4-28 12:33:13 浏览3623次
With the development of automobile lightweight and the increase of automobile output, the amount of plastic used in automobile is increasing. In recent years, the market demand for energy saving and consumption reduction has been exerting pressure on vehicle lightweight design. In order to better adapt to the increasingly stringent market regulation, many automotive parts manufacturers have been looking for environmentally friendly materials to replace traditional plastics. So let's see what kind of plastics are used in auto parts moulds.
Engineering plastics
Engineering plastics are widely used in automotive industry 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, has many kinds of PA used in automotive parts molds, such as PA6, PA66 and PA610. PA is easy to print and dye, and has excellent electrical properties. It is resistant to oil and corrosion. The common mechanical properties are toughness, high surface hardness, good tensile strength, good impact resistance, fatigue resistance, folding resistance, stress cracking resistance. The tensile and compressive strength of PA varies with temperature and moisture absorption, so water is the plasticizer of PA. When glass fiber is added, the tensile and compressive strength of PA can be increased by about two times, and the temperature resistance can be improved accordingly. The wear resistance of PA itself is very high, so it can work continuously without lubrication.
The disadvantages of PA are poor acid resistance, light resistance and pollution resistance. 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 size change of moisture absorption after moulding. Water absorption rate is 100%, relative moisture absorption saturation can absorb 8%, suitable wall thickness: 2-3.5mm.
Injection plasticity: PA has strong water absorption and strong water absorption due to the presence of amide group. Therefore, it should be fully dried during injection moulding, generally drying at 120 C for 3-4 hours; PA has low viscosity and fast flow speed. In order to prevent nozzles from flowing, self-locking nozzles or special nylon nozzles should be used. At the same time, attention should be paid to the accuracy of the die.
Applications: PA is mainly used in the automotive field to manufacture hoses (brake hoses, fuel pipes), combustion oil filters, air filters, oil filters, pump housing, pump impellers, fans, brake tanks, power steering tanks, white-leaf windows, headlights, seat belts.
PMMA
Polymethacrylate, commonly known as plexiglass, is widely used in automotive parts molds. It is resistant to outdoor aging and has excellent transparency. It can penetrate 92% of the sun after 240 hours of accelerated aging. It still has 89% in outdoor ten years and 78.5% in ultraviolet radiation. It has high mechanical strength, cold resistance, corrosion resistance, good insulation, stable size, easy to shape, brittle quality, easy to melt in organic solvents, insufficient surface hardness, easy to scratch and hair. Suitable plastic products: transparent structural parts with certain strength requirements.
Injection plasticity: the moisture absorption rate of PMMA is 0.3%. It must be dried before injection, usually at 80 C for 2-4 hours. The melt temperature is 240-270 C during injection, and the mould temperature should be controlled at 35-70 C.
PMMA is widely used in automobile lighting signs, door glass and lamp glass cover because of its good light transmission performance.
POM
Polyformaldehyde, commonly known as plastic steel, is an indispensable plastic for automobile parts mould. It has high tensile strength, impact toughness, rigidity and fatigue strength, high creep resistance, good dimensional stability, small water absorption, small friction number, excellent friction and wear resistance. It still has great rigidity in high temperature and water, and chemical corrosion resistance is similar to PA, but its price is low and repetitive resistance is good. Distortion, with outstanding resilience. It can be used for a long time between - 40 degrees Celsius and 100 degrees Celsius. POM is vulnerable to strong acid corrosion, high temperature resistance and poor thermal stability. Shrinkage 2-3.5% is suitable for wall thickness: 1.5-2.5mm.
Injection plasticity: POM has obvious melting point, melts at 175 C, decomposes at 240 C, generally processing temperature is 190 ~220 C, its processing range is very narrow; POM does not absorb water, generally does not need to be dried in injection moulding, but products with high quality requirements can be dried at 60 C for 1-2 hours; temperature should not be too high, otherwise the dyed products will change color; its acid resistance is poor, and it can not use acid. Dyeing with sex dyes.
Applications: POM in automobiles and manufacturing instrument panel glove box accessories, various valves (drainage valves, air conditioner valves, etc.), various impellers (pump impellers, heater impellers, oil pump wheels, etc.), various electrical switches and pins on electrical instruments, various handles and door pins, etc.
PC
Polycarbonate has outstanding impact toughness and creep resistance, good heat resistance, good cold resistance, brittle temperature up to - 100 C, bending strength and nylon equivalent, and has higher elongation and modulus of elasticity, but fatigue strength is less than nylon 66. Low water absorption, small shrinkage and good dimensional stability. The wear resistance is comparable to nylon and has a certain corrosion resistance, but the forming conditions are demanding. It has good weather resistance and can be used at high temperature and high load for a long time, but it can not be used at wet temperature. It has poor solvent resistance, stress cracking and poor fatigue strength. The shrinkage rate is 0.5-0.7%, and the suitable wall thickness is 2-3.5 mm. The shrinkage, mechanical strength and temperature resistance of PC can be improved by adding glass fibre. The steel property will increase when PC is used for a long time at about 100 C, and the internal stress can be improved by annealing.
Injection plasticity: PC has obvious melting point, melting at 220 C, decomposing at 350 C, generally processing temperature is 250 320 C; it absorbs water, a small amount of water can cause it to decompose at high temperature, it must be dried when injection moulding, drying temperature can be used to dry PC materials at 120 C for 4 ~ 5 hours;The melting viscosity of PC material is high and the injection pressure is high; the temperature of the mould can be increased by the mould temperature machine to reduce the residual stress of the product if the conditions permit; the shrinkage rate of PC has nothing to do with the processing conditions and the wall thickness of the product, and its longitudinal and transverse shrinkage rate is close, so it can be processed into products with high precision; its shrinkage rate is 0.5%.
PC-abs: PC-ABS is a blend material of PC and ABS. It is usually supplied in granular shape after blending. If the two materials are simply mixed, the effect of direct injection is very poor, and there will be delamination phenomenon; PC has the advantage of rigidity and toughness, but the disadvantage is stress cracking and high viscosity; ABS has the advantage of good fluidity, but low surface hardness; so the blended material PC-ABS retains the advantages of both; PC-ABS has higher surface hardness, higher rigidity and toughness, and also has higher stress resistance. Cracking capacity; its mechanical properties are somewhere between the two.
Scope of application: PC is mainly used in manufacturing lampshade, left and right wheel shield, instrument baffle body (PC + ABS), left and right wind frame cover, middle wind frame cover (PC + ABS), rear bumper cushion in automobile parts mould.
PU
Polyurethane, according to the different products of polymerization, is commonly divided into rigid polyurethane and soft polyurethane. Rigid polyurethane has high strength, good toughness, good thermal insulation, good waterproof effect, simple forming process and high production efficiency; soft polyurethane has good elasticity, sound absorption, aging resistance and chemical medium resistance, and its comprehensive mechanical properties far exceed those of PVC and other materials. Polyurethane polymerization is very convenient. It can not only be polymerized under normal temperature and pressure, but also can be directly foamed, sprayed and repaired after on-site polymerization.
Polyurethane foam is widely used in automotive interior parts and vibration absorbing parts, such as coating materials, polyurethane rigid plastic plates, polyurethane elastomers, seat soft foams, decorative pieces, sofa leather, roof decorations. The most widely used are various soft and rigid polyurethane foam materials, which have vibration isolation, noise insulation, noise reduction, thermal insulation and PU. Ester coatings, binders, sealants, etc. The PU representative parts on automobiles include dashboard, rearview mirror, bumper, seat cushion, headrest, steering wheel, dashboard anti-vibration pad, pillar decoration, front-top lining, window frame, ceiling and side-top frame decoration, door lining, sunshade, rear-top frame decoration, etc.
Special Plastic Glass Fiber Reinforced Plastics
Glass fiber reinforced plastics are based on the original pure plastics, adding glass fiber and other additives, thereby improving the use of materials. Generally speaking, most of the glass fiber reinforced materials are used in the structural parts of the automotive parts die, which is a kind of structural engineering materials, such as: PP, ABS, PA66, PA6, PC, POM.
English
中文