Polyoxymethylene(Polyformaldehyde)(Saigang~Terling)
English name:Polyoxymethylene(Polyformaldehyde)
POM (Polyformaldehyde Resin) Definition: Polyformaldehyde is a linear polymer with no side chains, high density and high crystallinity. According to the different chemical structures in its molecular chain, it can be divided into two kinds of homo- and co-polyformaldehyde. The important difference between the two is: homopolymerization of formaldehyde density, crystallinity, melting point are high, but poor thermal stability, processing temperature range is narrow (about 10 ℃), the stability of acids and bases is slightly lower; and copolymerization of formaldehyde density, crystallinity, melting point, strength are lower, but good thermal stability, is not easy to decompose, the processing temperature range is wide (about 50 ℃), the stability of acids and bases is better. It is an engineering plastic with excellent comprehensive performance. It has good physical, mechanical and chemical properties, especially excellent friction resistance. Commonly known as steel or steel, for the third largest general-purpose plastics. It is suitable for the production of wear-reducing and wear-resistant parts, transmission parts, as well as chemical industry, instrumentation and other parts.
General Properties
Paraformaldehyde is a kind of hard and dense material with smooth and glossy surface, light yellow or white, and the thin-walled part is semi-transparent. Combustion characteristics are easy to burn, continue to burn after leaving the fire, the flame is yellow at the upper end, the lower end of the blue, the occurrence of molten drops, there is a strong irritating formaldehyde flavor, fishy odor. Polyformaldehyde is a white powder, generally opaque, good coloring, specific gravity 1.41-1.43 g / cm3, molding shrinkage 1.2-3.0%, molding temperature 170-200 ° C, drying conditions of 80-90 ° C for 2 hours. POM's long-term heat resistance is not high, but short-term up to 160 ° C, of which homopolymerization of POM short-term heat-resistant than the copolymerization of POM is higher than the 10 ° C or more, but the long-term heat-resistant copolymer POM instead of than the long-term heat-resistant POM. Heat-resistant copolymerization POM instead than homopolymerization POM about 10 ℃ higher. Can be used for a long time in the temperature range of -40 ° C to 100 ° C. POM is very easy to decompose, decomposition temperature of 240 degrees. Decomposition of irritating and corrosive gas occurs. Therefore, the mold steel should be selected corrosion-resistant material production.
Mechanical properties
POM strength, high stiffness, good elasticity, good wear resistance. Its mechanical properties are excellent, than the strength of up to 50.5MPa, than the stiffness of up to 2650MPa, and very close to the metal.POM's mechanical properties with the temperature change is small, copolymerization of POM than homopolymerization of POM, the change is slightly larger.POM's impact strength is high, but the regular impact is less than the ABS and
PC; POM notch-sensitive, there are notches can be made to the impact strength drop as much as 90%. POM's fatigue strength is very prominent, 10 alternating load, fatigue strength up to 35MPa, while PA and PC is only 28MPa. POM's creep is similar to that of PA, at 20 ℃, 21MPa, 3000h is only 2.3%, and by the temperature is very small. POM's friction factor is small, good abrasion resistance (POM>
Pa66>
Pa6>ABS>HPVC>PS>PC), ultimate wear resistance is good (POM>PA66>PA6>ABS>HPVC>PS>PC), ultimate wear resistance is good (POM>PA66>PS>PC). POM has small friction factor, good abrasion resistance (POM>PA66>PA6>ABS>HPVC>PC), large PV limit, good self-lubrication, and it is easy to produce noise similar to screech when POM products are used for abrasion and when high loads are applied.
Electrical properties
POM's electrical insulation is good, almost unaffected by temperature and humidity; dielectric constant and dielectric loss in a wide range of temperature, humidity and frequency changes are very small; arc resistance is excellent, and can be maintained at high temperatures.POM's dielectric strength is related to the thickness of the thickness of 0.127mm is 82.7kV/mm, the thickness of 1.88mm is 23.6kV/mm.
Environmental Properties
POM is not resistant to strong alkalis and oxidizers, and has some stability to enoic acid and weak acids.POM has good solvent resistance to hydrocarbons, alcohols, aldehydes, ethers, gasoline, lubricants and weak bases, etc., and maintains considerable chemical stability at high temperatures. Small water absorption, good dimensional stability.
POM's weather resistance is not good, long-term under the action of ultraviolet light, mechanical properties decline, surface chalking and cracking.
Formability
Crystalline material, melting range is narrow, melting and solidification fast, material temperature slightly below the melting temperature crystallization occurs. Flowability is medium. Moisture absorption is small, can not be dried.
Modified POM
Enhanced POM
The main reinforcing materials are glass fibers, glass balls or carbon fibers, etc., and glass fibers are most commonly used, after the enhancement of mechanical properties can be increased by 2 to 3 times, the heat distortion temperature increased by more than 50 ℃.
Peel high lubrication POM
Add graphite, F4, molybdenum disulfide, lubricants and low molecular weight
PE in POM can improve its lubricating properties. For example, adding 5 parts of F4 in POM can reduce the friction factor by 60%, and improve the wear resistance by 1 to 2 times. Another example, adding liquid lubricant to POM can greatly improve the wear resistance and ultimate PV value. In order to improve the dispersion effect by the oil, need to add carbon black, aluminum hydroxide barium sulfate, ethylene propylene rubber and other oil-absorbing carriers. Add 5% oil POM friction increased by 72%, the ultimate PV value of up to 3.9MPa-m/s (pure POM for 0.213MPa-m/s), for other engineering plastics 3 to 20 times.
Application of polyformaldehyde
Polyformaldehyde has excellent overall performance, specific strength and specific stiffness and metal is very close, so it can replace non-ferrous metals to make a variety of structural components. It is especially suitable for the manufacture of friction-resistant, abrasion-resistant and high load-bearing parts, such as gears, pulleys, bearings, etc. It is widely used in automobile industry, precision instruments, mechanical industry, electronic and electrical appliances, construction equipment, etc. In the automobile industry, it can be utilized to produce various structural parts.
In the automobile industry, the advantages of its high specific strength can be used to replace zinc, copper, aluminum and other metals to make water pump impellers, fuel tank covers, carburetor shells, gas pedals, fans, combined switches, steering wheel parts, steering knuckle bearings and so on.
In the machinery industry, due to the polyformaldehyde fatigue resistance, high impact strength, self-lubricating and other characteristics, it is used in large quantities to manufacture a variety of gears, bearings, cams, pump bodies, shells, valves, pulleys and so on.
In electronics, electrical appliances, industry, due to the polyformaldehyde dielectric loss, high dielectric strength, excellent arc resistance, etc., is used to make relays, coil skeleton, computer control components, power tool shells, as well as telephones, tape recorders, video recorders, etc. accessories.
In addition, it can also be used in construction equipment, such as faucets, water tanks, gas meter parts and water
pipe joints, etc.; used in agricultural machinery, such as the connection and linkage parts of the seed insertion machine, irrigation pump shells, sprayer nozzles, etc.; due to the non-toxic, tasteless, but also used in the food industry, such as food processing machines on the parts, gears, bearings, stents.
