【導讀】present.electroplated,moderatestrength,Telephonehandsets,electronichousings,luggage,autoparts,consumerproducts,engineering.

　　

【正文】 ut sometimes the source information is not always clear. The largest volume sales are of the PA 6 and PA 6/6 variants. The other materials tend to be specialist polymers at specialist prices. In most cases the information refers to these materials. As a general family the PA group is rigid, translucent with good fatigue, creep and wear resistance. Chemical resistance varies with the variant but is generally good. Typical Applications Mechanical: Gear wheels, bearings, rollers, camwheels, screws, control rollers. Consumer goods: Bicycle wheels, hair brushes and bs, per tool housings, Strimmer cable. Automotive: Fans, fuel system pipe work, oil filters, floats, bearings, tachometer drive pinions, speedometer and windshield wiper gears, jets for windscreen washer systems, radiator header tanks. Electrical: Coil formers, card guides, terminal blocks, distribution boxes, vacuum cleaners, hand lamps, abrasionresistant cable ducts. Miscellaneous: Zips, fibres, nuts and bolts, pressure tubing, pump housings, laboratory equipment, furniture fittings, medical instruments. Physical and Mechanical Properties All the properties of PA depend on the moisture content of the plastic and the crystallinity of PA variant being used. PA can be tough when the moisture content is right (2 3% in air at 20oC) but dry products tend to bee brittle. The equilibrium moisture content depends on the time, temperature and wall thickness of the part. Dimensional and physical property changes take place during moisture absorption and injection moulded parts are often annealed or conditioned after processing to optimise the physical properties quickly. PA has good temperature stability, abrasion resistance and fatigue resistance. The crystalline nature of PA also affects the properties significantly and highly crystalline types can be stiff and hard. The use of glass fibre and other reinforcements can improve the mechanical properties (modulus and strength). The density, equilibrium moisture content and shrinkage varies with the PA variant used. Property Approximate Value PA 6 PA6/6 PA 11 PA 12 Tensile strength 55 80 MN/m 55 80 MN/m2 30 55 MN/m2 30 55 MN/m2 Tensile Modulus 1 2 GN/m2 2 3 GN/m2 1 2 GN/m2 1 GN/m2 Elongation at Break 100 500 % 100 500 % 100 500 % 100 500 % Flexural Strength 50 100 MN/m2 50 100 MN/m2 50 100 MN/m2 50 100 MN/m2 Notched Impact Strength 3 10 kJ/m2 3 10 kJ/m2 3 10 kJ/m2 10 20 kJ/m2 Specific Heat kJ/kg/oC kJ/kg/oC kJ/kg/oC kJ/kg/oC Glass Transition Temperature 50oC 66oC approx. 50oC approx 50oC Heat Deflection Temperature 100oC 100 150oC 100oC 100oC Coefficient of Thermal Expansion 10 15 x 105 / oC 10 15 x 105 / oC 10 15 x 105 / oC 10 15 x 105 / oC Long Term Service Temperature 100 oC 100 oC 100 oC 100 oC Specific Gravity Mould Shrinkage m/m m/m m/m m/m Water Absorption 2 % (50% rh) 2 % (50% rh) 2 % (50% rh) % (50% rh) Transparency Opaque Opaque Opaque Opaque Thermal, Electrical and Optical Properties Thermal properties PA has good high temperature performance and depending on the variant can be used between 80 and 120oC, some stabilised variants can be used for short periods at up to 200oC. PA can be used down to about 40oC, at this temperature the copolymers will still fail in a ductile manner but the homopolymers will generally fail in a brittle manner. PA has a low linear coefficient of thermal expansion and is dimensionally stable nearly up to the melt region when unloaded. Reinforcement with glass fibre gives excellent dimensional stability with changes in temperature. Fire behaviour Most PA variants are flammable and start to depose at above 300oC. Above 450 to 500oC the burning bees self sustaining and the PA will continue to burn when the source of ignition is removed. When burning, the material bubbles and drips and threads can be pulled from the molten material. The flame is blue and has the odour of burning horn. Some variants are selfextinguishing. Electrical properties The electrical properties of all PA variants are strongly dependent on moisture content. The polar nature of PA means that the electrical properties are also dependent on the frequency. Specific details relevant to the variants and grade to be used should be obtained before using PA in electrical applications. Optical properties Natural PA is milkyopaque but can be easily coloured in a wide variety of colours. PA has a refractive index which varies with the variant and for most types it is in the region of to . Chemical Resistance Properties PA has good chemical resistance to aliphatic and aromatic hydrocarbons, benzene, oils, fats, certain alcohols, esters, ketones, ether, anic and inanic bases up to medium concentration and to chlorinated hydrocarbons. Some chemicals . chloroform and methylene chloride, produce significant swelling and others are . alcohols, cause similar swelling to water. PA is not resistant to mineral acids, strong caustic solutions, solutions of oxidising agents, formic acid, phenols, cresols and glycols. Weathering resistance PA has good resistance to ageing and weathering and this can be improved with suitable additives (carbon black improves UV and general weathering performance). Reinforced PA suffers from more surface attack at the glass fibre interfaces and significant visible damage can occur in a short time, this does not generally significantly affect the mechanical properties. Stress cracking resistance Low tendency to stress cracking. PA 6 Chemical Resistance Chart PA 6/6 Chemical Resistance Chart PA 11 Chemical Resistance Chart PA 12 Chemic