POM polyacetal, we sometimes call it “Sai Steel”, sometimes call it “Trane”, so why such a name? Because, the name is often its parents, that is, its inventor.
We know that there are two main types of paraformaldehyde, one is called copolyformaldehyde, and the other is called homopolyformaldehyde. The invention of copolymerization of formaldehyde company (the United States Celanese) registered a trademark name, named “Celcon”, phonetically translated over the called “Sai Steel”, and the invention of homopolymerization of formaldehyde company (the United States DuPont) also registered a trademark name, named “Delrin”, phonetically translated as ‘Delrin’. Paraformaldehyde is a linear polymer with no side chains, high density and high crystallinity. According to the different chemical structures in the 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, the stability of acid and alkali is slightly lower, the United States DuPont invented the homopolymerization of formaldehyde. And copolyformaldehyde density, crystallinity, melting point, strength are lower, but good thermal stability, not easy to decompose, processing temperature range is wide, the stability of acid and alkali 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 race steel, for the third largest general engineering plastics. Suitable for the production of wear parts, transmission parts, and chemical industry, instrumentation and other parts. The United States Celanese invented the copolymerization of formaldehyde.
POM engineering plastics characteristics :
1, POM can be used without drying before processing, it is best to preheat during processing (about 80 ℃), the stability of the product size is good;
2, POM processing temperature is very narrow, in the barrel stay a little longer or the temperature exceeds 220 ℃ will decompose, producing irritating formaldehyde gas;
3, POM material injection molding pressure to be greater (similar to the injection pressure), in order to reduce the pressure drop, the screw speed can not be too high, the melt residual amount to be less.
4, POM products have a large shrinkage rate, easy to produce shrinkage or deformation, POM specific heat, high mold temperature (80 ~ 100 ℃), the product is very hot when demolding, need to be careful.
5, POM should be in the “medium pressure, medium speed, low material temperature, higher mold temperature” under the conditions of molding, precision products need to control the mold temperature when molding;
6, With high mechanical strength and rigidity;
7, Relatively high fatigue strength;
8, Environmental resistance, good resistance to organic solvents;
9, Strong resistance to repeated impact, good electrical properties, good recovery, with self-lubricating, good wear resistance, excellent dimensional stability.
Typical applications of POM plastic: can replace most of the non-ferrous metals, automobiles, machine tools, instrumentation components, bearings, fasteners, gears, spring sheet, piping, transport belt fittings, electric boilers, pump shells, drains, faucets and so on. POM plastic properties: paraformaldehyde is a smooth surface, glossy hard and dense material, white, thin-walled part of the semi-transparent. Combustion characteristics for easy to burn, away from the fire continues to burn, the flame is yellow at the top end, the bottom end of the blue, the occurrence of molten drops, there is a strong irritating formaldehyde flavor, fishy odor. POM opaque, good coloring, specific gravity 1.41-1.43 g / cm3, molding shrinkage rate of 2% or so, molding temperature 170-200 ℃, drying conditions 80-90 ℃ time 2 hours. POM's long-term heat resistance is not high, which homopolymer POM short-term heat than copolymerization of POM is higher than 10 ℃ or more, but the long-term heat aging copolymerization of POM instead of homopolymerization of POM is higher than 10 ℃ or so. About. Can be used for a long time in the temperature range of -40 ° C to 90 ° C. POM is very easy to decompose, decomposition temperature of 240 degrees. Decomposition of irritating and corrosive gas occurs, so the mold steel should be selected corrosion-resistant material production.
1, POM is semi-crystalline plastic, density of 1.42g/cm3, it is very good rigidity, commonly known as “steel.
2, It has fatigue resistance, creep resistance, wear resistance, heat resistance, impact resistance and other excellent performance, and the coefficient of friction is small, self-lubricating.
3, POM is not easy to absorb moisture, water absorption rate of 0.22 ~ 0.25%, good dimensional stability in a humid environment, its shrinkage rate of 2% or so, the size of the injection molding is more difficult to accurately control, heat distortion temperature of 172 ℃.
POM plastic mechanical properties: POM strength, high stiffness, good elasticity, good wear resistance. Its mechanical properties are excellent, than the strength can reach 50.5MPa, than the stiffness of up to 2650MPa, and metal is very close to the mechanical properties of POM with the temperature change of this piece, copolymerization of POM than the homopolymerization of POM, the change is slightly larger.POM impact strength is higher, but the conventional impact is less than the ABS and PC; POM notch-sensitive, there are notches can be made to the impact strength decreased by 90% of the more. POM's fatigue strength is very prominent, fatigue strength up to 35MPa, while PA and PC is only 28MPa. POM's creep is similar to PA, at 20 ℃, 21MPa, 3000h is only 2.3%, and by the temperature is very small. POM's friction factor is small, wear resistance is good, the limit of the PV value is very large, self-lubricating. POM products against grinding, high load is easy to produce similar to the screaming noise.
POM plastic 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; excellent arc resistance, and can be maintained at high temperatures.POM's dielectric strength is related to the thickness, the thickness of 0.127mm is 82.7kV/mm, the thickness of 1.88mm is 23.6kV/mm. POM Plastics Environmental performance: POM is not resistant to strong alkalis and oxidizing agents, and has a certain stability to enoic acid and weak acid.POM has good solvent resistance to hydrocarbons, alcohols, aldehydes, ethers, gasoline, lubricating oils and weak bases, etc., and can maintain considerable chemical stability at high temperatures. Small water absorption, good dimensional stability. POM's weather resistance is not good, long-term in the ultraviolet, mechanical properties decline, surface chalking and cracking. POM plastic molding: crystalline material, narrow melting range, melting and solidification of fast, material temperature is slightly below the melting temperature that occurs crystallization. The fluidity is medium. Moisture absorption is small, can not be dried.
Modified POM:
1, Enhanced POM main enhancement materials for glass fiber, glass ball or carbon fiber, and glass fiber is most commonly used, enhanced mechanical properties can be increased by 2 to 3 times, the heat distortion temperature increased by more than 50 ℃.
2, Wear-resistant modified POM in POM by adding graphite, F4, molybdenum disulfide, lubricants and low molecular weight PE, etc., can improve its lubricating properties. For example, add 5 parts of F4 in POM, can reduce the friction factor of 60%, wear resistance increased 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.
Inventor of homopolymerized POM--DuPont (Delrin)
DuPont's POM is mainly categorized according to its viscosity: the first number of the product approximates its melt index, so there are 100, 300, 500, 900 series according to the classification, and its melt index increases with the number (the higher the melt index, the lower the viscosity), such as the comparison of the viscosity: POM 100NC010＞POM 300CP BK642＞POM 500AF＞POM 900P BK602＞POM 500AF＞POM 500AF. POM 900P BK602.
