Acetal is a well known thermoplastic material known chemically as “PolyOxyMethylene” or POM for short. Acetal is available in 2 types of resin formats. Copolymer acetal (POM-C), available in numerous tradenames from several raw material manufacturers and Homopolymer acetal (POM-H), known commonly as Delrin®. So what’s the difference you ask?
For starters, Acetal copolymer is slightly cheaper than Delrin®. Acetal copolymer is also free of the center line porosity that is inherent in Acetal Homopolymer. Due to its lower crystallinity than the homopolymer, Acetal copolymer offers excellent dimensional stability and maximum continuous use temperature up to 180°F (80°C). Copolymer acetal grades are FDA, USDA, NSF, and 3-A Dairy compliant and available in wide variety of colors. A few other advantages acetal copolymer has over the homopolymer variety are the following:
- Due to its higher level of cyrstalinity, copolymer has better dimensional stability.
- Better impact and wear resistance (especially in wet environments)
The main difference in Acetal Homopolymer, or Delrin® is the fact that Delrin® comes with an inherent low density center known commonly as “center line porosity”. The larger the cross section, the larger the center line porosity. Delrin® offers slightly higher mechanical properties than acetal copolymer, but most of its mechancial properties come within 10% of acetal copolymer. Another feature worth mentioning is the fact that Delrin® offers lower chemical resistance than acetal copolymer. Delrin® is availabe in natural and black colors. A few advantages Delrin® offers over acetal copolymer are the following:
- Greater tensile and impact strength at room temperatures and below.
- Greater stiffness, with higher flexural modulus at room temperature and elevated temperatures.
- A bit harder, giving Delrin a better coefficient of friction in applications where water and moist environments don’t come in to play.
So what does all this mean? In most applications, Acetal Copolymer and Delrin® can be used interchangeably due to the fact that most of the material properties fall within 10% of each other. Just keep in mind that when specifying Delrin®, you will always have the center line poroisty issue to deal with which has its pluses and minuses depending on the specific application.
If you need CNC Machined or Stamped Acetal Copolymer or Delrin® parts, give us a call or send us a message on our contact page.