How much do you know about POM materials?

POM (Polyoxymethylene Resin) Definition: Polyoxymethylene 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 types: homopolymer formaldehyde and copolymer formaldehyde.
The important difference between the two is that homopolymer formaldehyde has high density, crystallinity, and melting point, but poor thermal stability, a narrow processing temperature range (about 10 ℃), and slightly lower acid-base stability; However, the density, crystallinity, melting point, and strength of formaldehyde copolymer are relatively low, but it has good thermal stability, is not easily decomposed, has a wide processing temperature range (about 50 ℃), and has good acid-base stability. It is an engineering plastic with excellent comprehensive performance.
Has good physical, mechanical, and chemical properties, especially excellent friction resistance. Commonly known as Sai Gang or Duogang, it is the third largest general-purpose plastic. Suitable for producing wear-resistant parts, transmission parts, as well as chemical and instrumentation components.
General performance
Polyoxymethylene is a hard and dense material with a smooth and glossy surface, light yellow or white in color, and semi transparent in the thin-walled part. The combustion characteristics are easy to burn, continuing to burn after leaving the flame. The upper end of the flame is yellow and the lower end is blue, with melting and dripping, and a strong irritating formaldehyde odor and fishy smell.
Polyoxymethylene is a white powder, generally opaque, with good coloring properties, a specific gravity of 1.41-1.43 grams per cubic centimeter, a molding shrinkage rate of 1.2-3.0%, a molding temperature of 170-200 ℃, and a drying condition of 80-90 ℃ for 2 hours. The long-term heat resistance of POM is not high, but it can reach 160 ℃ in the short term. Among them, the short-term heat resistance of homopolymer POM is more than 10 ℃ higher than that of copolymer POM, but the long-term heat resistance of copolymer POM is about 10 ℃ higher than that of homopolymer POM.
Can be used for a long time within the temperature range of -40 ℃ to 100 ℃. POM is highly prone to decomposition, with a decomposition temperature of 240 degrees. Stimulating and corrosive gases occur during decomposition. Therefore, mold steel should be made of corrosion-resistant materials.
mechanical property
POM has high strength, rigidity, good elasticity, and good wear resistance. Its mechanical properties are excellent, with a specific strength of up to 50.5MPa and a specific stiffness of up to 2650MPa, which is very close to metals. The mechanical properties of POM change little with temperature, while the variation of copolymer POM is slightly greater than that of homopolymer POM.
POM has a high impact strength, but its conventional impact strength is inferior to ABS and PC; POM is sensitive to notches, and notches can reduce impact strength by up to 90%. The fatigue strength of POM is very outstanding. After 10 alternating loads, the fatigue strength can reach 35MPa, while PA and PC are only 28MPa. The creep deformation of POM is similar to that of PA, only 2.3% at 20 ℃, 21MPa, and 3000h, and is minimally affected by temperature.
POM has a low friction coefficient, good wear resistance (POM>PA66>PA6>ABS>HPVC>PS>PC), a high ultimate PV value, and good self-lubricating properties. POM products are prone to produce screaming noise when subjected to high loads during grinding.
Electrical performance
POM has good electrical insulation and is almost unaffected by temperature and humidity; The dielectric constant and dielectric loss vary very little over a wide range of temperature, humidity, and frequency; Excellent arc resistance and can be maintained at high temperatures. The dielectric strength of POM is related to its thickness, with 82.7kV/mm at a thickness of 0.127mm and 23.6 kV/mm at a thickness of 1.88mm.
Environmental performance
POM is not resistant to strong acids and oxidants, but has a certain degree of stability towards oleic acid and weak acids. POM has good solvent resistance and can withstand hydrocarbons, alcohols, aldehydes, ethers, gasoline, lubricants, and weak bases, and can maintain considerable chemical stability at high temperatures. Low water absorption and good dimensional stability.
POM has poor weather resistance, and its mechanical properties decrease under long-term exposure to ultraviolet radiation, resulting in surface pulverization and cracking.
Formability
Crystalline materials have a narrow melting range, fast melting and solidification, and crystallization occurs when the material temperature is slightly lower than the melting temperature. Medium liquidity. Low moisture absorption, can not be dried.