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Engineering plastics have many kinds and are widely used. Their excellent functions are often used to replace metal materials. Next, we will introduce several varieties of engineering plastics from several aspects.

Polyamide PA: material function: tough, wear-resistant, oil-resistant, water-resistant, enzyme resistant, but with large water absorption. Nylon 6 has good elasticity, high impact strength and large water absorption; Nylon 66 is superior to nylon 6 in function, high strength and good wear resistance; Nylon 610 is similar to nylon 66, but it has small water absorption and low stiffness; Nylon 1010 is translucent, with small water absorption and good cold resistance. Molding characteristics: the melting point of the crystalline material is high, the melting temperature is narrow, and the thermal stability is poor. The decomposition occurs when the material temperature exceeds 300 ℃ and the residence time exceeds 30min. It is easy to absorb moisture and needs to be monotonous. The water content shall not exceed 0.3%; Good fluidity, easy to overflow. Self locking nozzle should be used and heated; The forming shortening plan and shortening rate are large, the directionality is significant, and shrinkage and deformation are easy to occur; The mold temperature is selected according to the plastic part wall thickness within the 20-90 degree plan, the injection pressure is selected according to the injection machine type, material temperature, plastic part shape standard and mold pouring system, and the forming cycle is selected according to the plastic part wall thickness. When the resin viscosity is small, the injection and cooling time shall be longer, and white oil shall be used as the release agent; The way and standard of mold gating system, increasing runner and gate standard can reduce shrinkage water. Applicable planning: making general mechanical parts, wear-resisting parts, transmission parts, as well as chemical, electrical, surface, etc.

Polycarbonate PC: material function: high impact strength, good standard stability, colorless and transparent, good coloring, good electrical insulation, corrosion resistance and wear resistance, but poor self lubrication, stress cracking tendency, easy hydrolysis at high temperature and poor compatibility with other resins. Molding characteristics: amorphous material, good thermal stability, wide molding temperature planning, poor fluidity. Moisture absorption is small, but it can activate collaterals to water, so it must be monotonically treated. The forming shortening rate is small, which is prone to melting cracking and stress concentration, so the forming conditions should be strictly controlled, and the plastic parts must be annealed; With high melting temperature and high viscosity, heated extension nozzle should be used for plastic parts greater than 200g; The cooling speed is fast, and the mold pouring system is based on the principle of coarse and short. It is appropriate to set a cold well, the gate should be large, and the mold should be heated; Too low material temperature will lead to lack of material, plastic parts have no luster, too high material temperature is easy to overflow, and plastic parts blister. When the mold temperature is low, the shortening rate, elongation and impact strength are high, and the bending, compression and tensile strength are low. When the mold temperature exceeds 120 ℃, the plastic part cools slowly and is easy to deform and stick to the mold. Applicable planning: making small surface parts, insulating transparent parts and impact resistant parts.

POM: material function: good induction function, high strength and stiffness, good abrasion resistance, small water absorption, good standard stability, but poor thermal stability, easy to burn, easy to aging in the atmosphere. Molding characteristics: crystallized material, narrow melting plan, fast melting and condensation, and crystallization occurs when the material temperature is slightly lower than the melting temperature. Medium liquidity. Small moisture absorption, without monotonic treatment; Low friction coefficient, good elasticity, surface defects of plastic parts prone to wrinkle patterns; It is easy to decompose, and the decomposition temperature is 240 ℃. There are irritant and corrosive gases during decomposition. Therefore, the mold steel should be made of corrosion-resistant materials. Applicable planning: making wear-resistant parts, transmission parts, chemical and surface parts.

Polyphenylene oxide PPO: material function: white particles. It has excellent inductive function and can be used in 120 ℃ steam. It has good electrical insulation and small water absorption, but has the tendency of stress cracking. Modified polyphenylene oxide can eliminate stress cracking; It has outstanding electrical insulation and water resistance, and good standard stability. Its dielectric function ranks first among plastics; MPPO is a modified material prepared by blending PPO and hips, which is now available in the market; It has high heat resistance, with a glass transition temperature of 211 ° C and a melting point of 268 ° C. it tends to decompose when heated to 330 ° C. The higher the content of PPO, the better its heat resistance. The thermal deformation temperature can reach 190 ° C; Excellent flame retardancy, self-healing, and moderate flammability after mixing with hips. It is light and non-toxic, and can be used in food and drug industries. Poor light resistance, discoloration after long-time use in the sun; It can be blended with ABS, HDPE, PPS, PA, hips, glass fiber, etc. Molding characteristics: non crystalline material, less moisture absorption; It is a Newtonian fluid with poor fluidity. Its viscosity is flexible to temperature. The thickness of the product is generally more than 0.8mm. It is very easy to decompose, and corrosive gas occurs during decomposition. The forming temperature should be strictly controlled, the mold should be heated, and the resistance of the pouring system to the material flow should be small; The water absorption of polyphenylene oxide is very low, about 0.06%, but a small amount of water will cause unsmooth phenomena such as silver wire on the product surface. It is best to do monotonic treatment, and the temperature should not be higher than 150 degrees, otherwise the color will change; The forming temperature of polyphenylene oxide is 280-330 ℃, and that of modified polyphenylene oxide is 260-285 ℃. Applicable planning: making heat-resistant parts, insulating parts, wear-resistant parts, transmission parts, medical and electronic parts; It can be used as gear, fan blade, valve and other parts under high temperature, and can replace stainless steel; Can make screws, fasteners and connectors; Electrical parts of motor, rotor, casing and transformer.

Polyethylene terephthalate PET: material function: colorless transparent or milky translucent solid; It has high tensile strength, stiffness and hardness, but has certain harmony, excellent wear resistance and creep resistance, and can adhere to these excellent mechanical functions within a wide temperature planning; Excellent electrical insulation; It has excellent weather resistance. After six years of outdoor exposure, its mechanical function can still maintain the initial 80%; Resistant to weak acids, excellent chemical stability to organic solvents and oils. Applicable planning: making film and photosensitive film, such as film base and photographic film; As the packaging of food, medicine, textiles, precision instruments, electrical components, etc., the hollow containers made by it have high strength, good transparency, non-toxic and tasteless. They are widely used plastic packaging materials for carbonated drinks, beer, edible oil, etc; Electrical materials; Used for making various electrical insulation materials, such as wires, switches, electrical enclosures, etc.

Source: Jiangmen engineering plastics http://xrtsm.com.cn/