Polyoxymethylene is divided into two types: homopolymerization and copolymerization. Copolymer has good short-term strength while homopolymer has good flexibility. The copolymer has a softening point 10°C higher than that of homopolymer, has a high thermal deformation temperature under load, good thermal stability, and a wide molding temperature range. Commonly used in industry is acetal copolymer. Homopolymer is mostly used in luggage products and making zippers. There are differences in the molding process. What we are talking about here is acetal copolymer.
Although POM RAW MATERIAL is less hygroscopic than PA, it still needs to be dried before processing due to size and surface quality considerations. Gears and other precision gear parts: 100~120℃, 4~8 hours; general parts: 80~90℃, 3~4 hours.
The melting point of POM is 163°C, and it melts above this temperature. Generally speaking, the processing range of most POM is 170~230℃, and the commonly used temperature is divided into 170~200℃. POM is a heat-sensitive plastic part that will decompose when heated for a long time. The decomposed formaldehyde is easily oxidized into formic acid, which further accelerates the decomposition of polyformaldehyde. If this situation is discovered, it should be cleaned in time to eliminate decomposition products. PE can be used for cleaning.
Since formaldehyde is easily soluble in water, the cleared POM material can be poured into a bucket of water to reduce smoke. Therefore the following points should be made:
- Do not heat POM above 250℃ to avoid pyrolysis;
- When the temperature of the barrel exceeds 210°C, the POM melt should not stay in the barrel for more than 30 minutes. The higher the barrel temperature, the shorter the residence time.
- As long as the machine is turned on, the nozzle temperature must be maintained above the melting point of POM (163°C). This way the nozzle won’t get clogged when overheating occurs.
- If the machine has just processed PVC, the barrel must be cleaned strictly, and PVC particles must not be mixed into POM particles, otherwise a strong reaction will occur.
- If it is necessary to stop the machine: Stop the machine for a short time, adjust the material temperature to close to the melting point, remove the plastic in the barrel, the screw should always be in the forward position, and turn off the heater. If the machine needs to be shut down for a long time, PE should be used to clean it according to normal procedures.