Full definition
Acetal, also known as Polyoxymethylene (POM) or Delrin, is a high-performance engineering thermoplastic characterized by its low friction coefficient, ranging from 0.1 to 0.3 against steel. This property makes it ideal for applications requiring smooth movement and reduced wear. With an elastic modulus between 2.8 and 3.5 GPa, acetal exhibits high stiffness, contributing to its structural integrity under load. The material's dimensional stability is particularly noteworthy, allowing it to maintain its shape and size even in varying temperature and humidity conditions, which is crucial for precision components. Acetal is available in two primary forms: homopolymer, known as Delrin, produced by DuPont, which is slightly harder and stronger, and copolymer varieties like Celcon or Hostaform, which offer enhanced chemical and thermal resistance.
From a mechanical perspective, acetal features a tensile strength of 60-70 MPa and can operate continuously at temperatures ranging from -40 to +100°C. Its moisture absorption rate is extremely low, at less than 0.2%, making it suitable for humid environments where other plastics may fail. Acetal's excellent machinability allows for precise fabrication of complex geometries, which is essential in manufacturing components such as precision gears, bearings, bushings, cams, rollers, and connector housings.
However, acetal does have limitations. Its poor UV resistance necessitates the use of stabilizers or protective coatings when outdoor applications are considered. It is also classified as flammable (V-2 rating per UL 94) unless flame-retardant additives are incorporated. Additionally, acetal can be chemically attacked by strong acids, which requires careful consideration in selecting materials for specific environments. Despite competing with nylon (PA), acetal often provides superior dimensional stability in humid conditions, making it a preferred choice in various engineering applications.