Description
In the automotive industry in recent years, the use of plastic materials to replace expensive and heavy metal materials has gradually expanded. Some engineering plastic injection molded parts have high strength, even higher than metal, but have the advantages of light weight and low price. , which can greatly reduce the cost of parts processing, assembly and maintenance, and can also make the car lightweight and reduce fuel consumption. In today’s cars, there are many parts that use plastic injection molded products. For example, the automotive high-voltage connector produced by Shenzhen Huanke Precision Injection Molding is a good example. For cars, every part is important, especially the qualification of plastic injection molded parts will also affect the safety of the car. Therefore, waterproof testing and air tightness testing of plastic injection molded parts are very important, so automotive high-voltage connectors How are injection molded parts tested for waterproofing and air tightness?
The waterproof level of automobile plastic injection molded parts is generally above IP65, and it is different for different products. So, how to know whether the waterproof level of automobile plastic injection molded parts reaches the corresponding standard? This requires the use of professional automotive plastic injection molded parts waterproof testing equipment to conduct waterproof testing and air tightness testing. Methods for waterproofing and air-tightness testing of automotive plastic injection molded parts: Depending on the product to be tested for waterproofing and air-tightness testing of automotive plastic injection molded parts, see whether a test fixture is needed. If it is an open semi-finished product, use the direct test method. According to For the structure of the product, a fixed fixture is made, and the product is placed on the fixture for direct inflation; if it is a relatively sealed product, indirect testing methods must be used to perform waterproof testing and air tightness testing of automotive plastic injection molded parts. It is necessary to customize a test fixture according to the shape of the product. After the internal cavity is sealed, just put the product down, and then connect it to the test port of the automotive plastic injection molded parts waterproof testing equipment. After setting the parameters, the test can be carried out.
There are many types of raw materials, and their application in automotive plastic injection molded parts is divided into interior parts, exterior parts and functional parts. According to the different usage characteristics of famous plastics, plastics are usually divided into three types: general plastics, engineering plastics and special plastics.
1. General plastics
Generally refers to plastics that have large production volumes, good formability, cheap prices, and are widely used. General plastics include five major varieties, polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), and acrylonitrile-butadiene-styrene copolymer (ABS), all of which are thermoplastics. plastic.
① PP
Polypropylene, commonly known as polypropylene, is white wax-like, transparent, lightweight, has good fluidity during injection molding, and has a water absorption of less than 0.02%. The shrinkage rate of PP is 1.0-3.5%, and the suitable thickness is 1.5-2.5mm.
There are two main problems with the widespread use of PP in the automotive field: it is easy to burn (it will drip burning substances) and it is brittle in low-temperature environments. To address these two problems, appropriate additives are added to modify PP in practical industrial applications. If it is easy to burn, flame retardants will be added; it is brittle in low temperature environments. It is mainly used to add other tough materials, rigid particles or elastomers for various modifications and toughening, such as rubber (EPDM), talc powder (TD), glass fiber (GF). There are many automotive products made of PP resin, including various dashboards, door guards, pillar guards, bumpers, water tanks, and decorative panels. There is an increasing trend of PP being used in automobiles.
②PE
Polyethylene, one of the lightest plastics, is a translucent white waxy material with good water resistance, acid and alkali resistance, resistance to organic solvents, and excellent electrical insulation. The shrinkage rate is 1.5~4.0%, and the suitable thickness is 1.0-2.5mm.
The biggest disadvantage of PE as an automotive material is that it is easy to burn. The simplest and most commonly used method is to add appropriate flame retardants to improve the combustion performance of PE. Automobile products made of PE mainly include fuel tanks, air ducts, front seat decorative covers, air duct assemblies (HDPE), left and right ventilation duct assemblies, upper and lower air direction blade connecting bars, left and right foot vent assemblies, etc.
③PVC
Polyvinyl chloride, commonly used PVC, is a multi-component plastic. Because the content of each component is different, various PVC particles of different hardnesses with widely different mechanical properties are formed. They are generally divided into two categories: soft PVC and hard PVC. Shrinkage: Rigid PVC is 1-1.5%, soft PVC is 2-2.3%, suitable thickness is 2-3.5mm.
The most commonly used plastic raw material in automotive plastic products is polyvinyl chloride. Automotive plastic products made of PVC plastic can be found everywhere, including PVC instrument panel skins, PVC plastic steering wheels, PVC plastic linings, and PVC plastic automotive floor coverings. This is not only because PVC resin is economical in price, but also has better processing performance and comprehensive mechanical properties.
④PS
Polystyrene, commonly known as hard glue, is a transparent glass-like material with good fluidity and does not absorb water. Due to the brittleness of PS, it is often grafted and copolymerized with other substances, such as grafted and copolymerized with butadiene to form HIPS. Ingredients After containing rubber, the impact strength and surface hardness are greatly improved. The shrinkage rate is 0.4-0.7%, and the suitable thickness is 2-3mm.
The main applications of PS in automobiles are instrument casings, lampshades, and lighting products. Polystyrene can also be used to prepare packaging materials and thermal insulation materials through foaming molding for the production of ceilings. Polystyrene can also be grafted, copolymerized and modified with other materials to obtain many fixed-matching alloy plastic varieties of the PS family, such as for SMA In manufacturing car dashboard skeleton.
⑤ABS
Acrylonitrile-butadiene-styrene copolymer, commonly known as super unbreakable glue, has a white body. The shrinkage rate is 0.4-0.7%, and the suitable wall thickness is 1.8-3mm.
Because ABS has many types, good surface treatment effects, and low price, it is widely used in the automotive field. In view of the poor weather resistance of ABS, highly weather-resistant materials such as AES and ASA have been widely used in commercial vehicles to supplement ABS. 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 strips, shift knob heads, inner opening handles, license plate decorative plates, rear spoiler assemblies, rearview mirror bodies, radiator grille bodies, armrests, etc.
2. Engineering plastics
Engineering plastics are also widely used in the automotive field due to their good comprehensive mechanical properties. This article mainly introduces polyamide (PA), polymethacrylate (PMMA), polyoxymethylene (POM), polyamide (PU). ), polycarbonate (PC).
①PA
Polyamide, commonly known as nylon, has many types of PA used in industry, and the commonly used ones are PA6, PA66 and PA610. Due to the influence of thermal expansion and water absorption, the dimensional stability of the parts is poor, with a shrinkage rate of 1 to 2%. Pay attention to the dimensional changes due to moisture absorption after molding. The water absorption rate is 100%, and it can absorb 8% when the relative moisture absorption is saturated. Suitable wall thickness: 2 ~ 3.5mm.
PA is mainly used in the automotive field to manufacture hoses (brake hoses, fuel pipes), combustion oil filters, air filters, oil filters, water pump casings, water pump impellers, fans, brake fluid tanks, and power steering fluid tanks. , white leaf windows, headlight housings, seat belts.
②PMMA
Polymethacrylate, commonly known as plexiglass, is resistant to outdoor aging and has excellent light transmittance. Suitable plastic products: transparent structural parts with certain strength requirements.
Due to its good light transmittance, PMMA is widely used in automotive lighting signs, door glass and lamp glass covers.
③POM
Polyformaldehyde, commonly known as plastic steel, has a shrinkage rate of 2-3.5% and suitable wall thickness: 1.5-2.5mm.
POM is used in automobiles to manufacture dashboard glove box accessories, various valves (drainage valves, air conditioner valves, etc.), various impellers (water pump impellers, heater impellers, oil pump impellers, etc.), various electrical switches and electrical instruments Small gears, various handles and door pins, etc.
④ PC
Polycarbonate has outstanding impact toughness and creep resistance, good heat resistance, and good cold resistance. The shrinkage rate is 0.5-0.7%, and the suitable wall thickness is 2-3.5mm. Adding glass fiber to PC can improve its shrinkage, mechanical strength and temperature resistance. Long-term use at around 100°C will increase its rigidity, and annealing can be used to improve internal stress.
Introduction to the main composite PC-ABS:
PC-ABS is a blend material of PC and ABS. It is usually blended and supplied in the form of pellets. If the two materials are simply mixed and then injected directly, the effect will be very poor and delamination will occur; PC has the advantage of being rigid and tough, but has the disadvantage of stress cracking and high viscosity; ABS has the advantage of good fluidity, but the surface Low hardness; the blended material PC-ABS retains the advantages of both; PC-ABS has higher surface hardness, higher rigidity and toughness, and higher resistance to stress cracking; its mechanical properties between
PC is mainly used in the automotive field to manufacture lampshades, left and right wheel housing guards, instrument bezel bodies (PC+ABS), left and right wind frame covers, middle wind frame covers (PC+ABS), and rear bumper cushions.
⑤ PU
Polyurethane, according to the different polymerization reaction products, is commonly divided into hard polyurethane and soft polyurethane. Polyurethane foam is widely used in automotive interiors and vibration-absorbing parts, such as coating materials, polyurethane hard plastic sheets, polyurethane elastomers, seat soft foam materials, decorative parts, sofa leather, and roof accessories; it is the most widely used It is a variety 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, adhesives, sealants, etc. Representative PU parts in automobiles include dashboards, rearview mirrors, bumpers, seat cushions, headrests, steering wheels, dashboard anti-vibration pads, pillar trims, front roof linings, window frames, ceilings and side roofs. Frame decoration, door lining, sun visor, rear roof rack decoration, etc.
3. Special plastics
Glass fiber reinforced plastic is based on the original pure plastic, adding glass fiber and other additives to improve the use range of the material. Generally speaking, most glass fiber reinforced materials are mostly used in structural parts of products and are structural engineering materials; such as: PP, ABS, PA66, PA6, PC, POM.
Advantage:
① After glass fiber reinforcement, glass fiber is a high-temperature resistant material, so the heat-resistant temperature of the reinforced plastic is much higher than before without adding glass fiber, especially nylon plastics; ② It limits the mutual movement between the polymer chains of the plastic, so it is reinforced The shrinkage rate of plastics is greatly reduced, and the rigidity is also greatly improved; ③ Reinforced plastics will not stress crack, and the impact resistance of plastics is greatly improved; ④ Glass fiber is a high-strength material, which also greatly improves the strength of plastics (tensile strength, The compressive strength and bending strength have increased a lot) ⑤ Due to the addition of glass fiber and other additives, the combustion performance of reinforced plastics has dropped a lot, and most materials cannot ignite
Shortcoming:
① If it is transparent before adding glass fiber, it will become opaque; ② The toughness of the plastic decreases and the brittleness increases; ③ The melt viscosity of all materials increases, the fluidity becomes worse, and the injection pressure is much higher than that without adding glass fiber. ; ④ Poor fluidity. For normal injection molding, the injection molding temperature of all reinforced plastics is 10℃-30℃ higher than before without adding glass fiber; ⑤ The hygroscopic performance of reinforced plastics is greatly enhanced. Pure plastics that do not absorb water will become water-absorbent. Therefore, drying is required during injection molding; ⑥ During the injection molding process, glass fiber can enter the surface of the plastic product, making the surface of the product very rough and speckled (in order to obtain higher surface quality, it is best to use a mold during injection molding) The warm machine heats the mold, causing the plastic polymer to enter the surface of the product, but it cannot achieve the appearance quality of pure plastic); ⑦ Glass fiber is a very hard material, and the additives evaporate at high temperatures and become highly corrosive gases, which are harmful to the injection molding machine. Screws and injection molds are subject to great wear and corrosion. Therefore, when producing molds and injection molding machines using such materials, attention should be paid to the surface anti-corrosion treatment and surface hardness treatment of the equipment.
Commonly used shrinkage rates for adding glass fiber:
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%
Representative materials of glass fiber reinforcement, applications of fiberglass/composite materials in the automotive industry:
Body parts: including body shells, hood hardtops, sunroofs, doors, radiator grilles, headlight reflectors, front and rear bumpers, etc., as well as interior accessories. This is the main direction for the application of FRP/composite materials in automobiles. It is mainly aimed at meeting the needs of streamlined design of the body and high-quality appearance requirements. Currently, there is huge potential for development and application. The material of this part is mainly made of glass fiber reinforced thermosetting plastic. Typical molding processes include: SMC/BMC, RTM and hand lay-up/spraying.
Structural parts: including front-end brackets, bumper frames, seat frames, floors, etc. The purpose is to improve the design freedom, versatility and integrity of the parts. Mainly use high-strength SMC, GMT, LFT and other materials.
Functional parts: Their main features are high temperature resistance and oil corrosion resistance, mainly for engines and engine peripheral parts. Such as: engine valve cover, intake manifold, oil pan, air filter cover, gear chamber cover, air guide cover, intake pipe guard, fan blades, fan air guide ring, heater cover, water tank parts, Water outlet casing, water pump turbine, engine sound insulation board, etc. The main process materials are: SMC/BMC, RTM, GMT and glass fiber reinforced nylon, etc.