Polyoxymethylene (English: polyformaldehyde) is a thermoplastic crystalline polymer, known as "super steel" or "race steel", also known as polyoxymethylene, and the English abbreviation is POM. POM is also one of the most common materials in the production of prototypes. From the meaning of "super steel" and "race steel", we can know that this material has high strength.We will introduce POM (polyformaldehyde) several characteristics of this material in detail.
General properties of POM (polyoxymethylene)
POM is a hard and dense material with smooth and shiny surface, light yellow or white, and the thin-walled part is translucent. The combustion characteristics are easy to burn, continue to burn after leaving the fire, the upper end of the flame is yellow, the lower end is blue, melting and dripping occurs, and there is a strong irritating formaldehyde smell and fishy odor. POM is white powder, generally opaque, good coloring, specific gravity 1.41-1.43 g/cm3, molding shrinkage 1.2-3.0%, molding temperature 170-200 ℃, drying conditions 80-90 ℃ for 2 hours. The long-term heat resistance of POM is not high, but it can reach 160 °C in the short term. The short-term heat resistance of homopolymeric POM is more than 10 °C higher than that of copolymerized POM, but the long-term heat resistance of copolymerized POM is about 10 °C higher than that of homopolymerized POM. It can be used for a long time in the temperature range of -40℃～100℃. POM is easy to decompose, the decomposition temperature is 280 ℃, and irritating and corrosive gases occur during decomposition. Therefore, the mold steel should be made of corrosion-resistant materials.
Mechanical properties of POM (polyoxymethylene)
POM has high strength, rigidity, good elasticity, and good wear resistance. Its mechanical properties are excellent, the specific strength can reach 50.5MPa, and the specific stiffness can reach 2650MPa, which is very close to metal. The mechanical properties of POM change little with temperature, and the change of copolymerized POM is slightly larger than that of homopolymerized POM. The impact strength of POM is higher, but the conventional impact is not as good as that of ABS and PC; POM is sensitive to notches, and the notches can reduce the impact strength by as much as 90%. The fatigue strength of POM is very outstanding. After 10 alternating loads, the fatigue strength can reach 35MPa, while that of PA and PC is only 28MPa. The creep property of POM is similar to that of PA, only 2.3% at 20℃, 21MPa, and 3000h, and it is little affected by temperature. The friction coefficient of POM is small, the wear resistance is good (POM>PA66>PA6>ABS>HPVC>PS>PC), the limit PV value is large, and the self-lubrication is good. When POM products are ground against each other, a squeal-like noise is likely to be generated when a high load is applied.
Electrical properties of POM (polyoxymethylene)
POM has good electrical insulation and is hardly affected by temperature and humidity; dielectric constant and dielectric loss vary little over a wide range of temperature, humidity and frequency; excellent arc resistance, and can be used at high temperatures Keep. The dielectric strength of POM is related to thickness, 82.7kV/mm when the thickness is 0.127mm, and 23.6kV/mm when the thickness is 1.88mm.
Environmental performance of POM (polyoxymethylene)
POM is not resistant to strong acids and oxidants, and has certain stability to alkenoic acids and weak acids. POM has good solvent resistance, can resist hydrocarbons, alcohols, aldehydes, ethers, gasoline, lubricating oil and weak bases, etc., and can maintain considerable chemical stability at high temperatures. Low water absorption and good dimensional stability. The weather resistance of POM is not good. Under the action of ultraviolet rays for a long time, the mechanical properties will decline, and the surface will be chalked and cracked.
Advantages of POM (Polyoxymethylene)
1. High mechanical strength and rigidity;
2. The highest fatigue strength;
3. Good environmental resistance and organic solvent resistance;
4. Strong resistance to repeated impact;
5. Wide temperature range (-40℃~120℃);
6. Good electrical properties;
7. Good recovery;
8. It has self-lubricity and good wear resistance;
9. Excellent dimensional stability.
Disadvantages of POM (Polyoxymethylene)
Corrosion by strong acid, poor weather resistance, poor adhesion, thermal decomposition and softening temperature close to, small oxygen limit index.
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