Tuesday, November 13, 2012
Engineering Plastic POM Polyacetal
Normally, we use steels to make machine components. But in some applications, engineering plastics are also commonly used in machine parts since their unique properties e.g. lighter weight, easy for machining, great quantities can be made quickly by injection, etc.
General properties of engineering plastics:
Light weight - The density of engineering plastics is usually about 1-2 g/cm3. We often use them in the portable machines that we often move them, or use in the parts that the user has to hold by hand.
No rust - We normally use engineering plastics without surface treatment to prevent rust. However, engineering plastics do not withstand the corrosion from oxygen or ultraviolet, so we need to consider this point when using plastic for long time.
Low electrical conductivity - We use plastics to prevent users from direct contact with electrical parts for safety reason.
Low thermal conductivity - Engineering plastics are good for insulation. We can prevent some heat from machine. However, they usually cannot withstand high temperature and they may deform and strength reduced.
POM or Polyoxymethylene , also known as acetal, polyacetal and polyformaldehyde is an engineering thermoplastic used in precision parts that require high stiffness, low friction and excellent dimensional stability. We use POM to make gears, cams, bearings, guides, rollers, etc. It normally has milky color or black color. Its tensile strength is about 60 MPa which is 1/7 of the strength of SS400 steel and the weight is about 1/7 of steel. It can be used for sliding application. Working temperature should be within - 40oC to 105oC.