Acetal is the common name for polyoxymethylene (POM), a white semi-crystalline thermoplastic. It is strong, abrasion and impact resistant, and tolerates many organic chemical compounds. It has a low coefficient of friction and durable stiffness, so it is often used in moving parts. Because it is widely available in sheet and block form, many machined prototypes are made of acetal. Examples of items made from acetal include a variety of large and small plastic parts:
- Mechanical components like gears, fan wheels, valve bodies, nuts, and screws
- Electrical insulators, connectors, and parts for devices such as TVs and phones
- Medical devices like insulin pens
- Food industry parts like beverage dispenser spigots, filter housings, and food conveyor systems
- Furniture components such as handles, hinges, and glides
- Jewelry items like watch bands
- Sporting goods and toy components
Acetal becomes a liquid at its melting point of 347 degrees Fahrenheit, and is categorized as a thermoplastic, meaning that it can be reprocessed after an initial heat cycle if your application allows it. While acetal is naturally white, colorants can be added to it to create virtually any color. Moreover, acetal's properties can be enhanced with PTFE to improve lubricity or fiberglass to boost stiffness.
Like many semi-crystalline materials, acetal is a higher shrink material, shrinking commonly in the range of 0.018" - 0.024" per inch after molding. The shrink rate is comparable to many nylons, but not to amorphous materials such as ABS or polycarbonate. This can make it difficult to explore other material categories after tooling is built, since the sizes would likely be different.
Two Categories of Acetal
Acetal is a synthetic polymer that comes in two forms: homopolymers and copolymers. Synthetic polymers are large molecules made up of repeating subunits (monomers). Repeating monomers of a single molecular substructure form homopolymers, whereas several different monomer types in combination with one another form copolymers.
These molecular differences produce different physical characteristics. For example, homopolymers have a higher room temperature impact strength and tensile strength. They are also harder, stiffer, and more slippery. Copolymers are less porous when extruded, more resistant to chemicals, and have better dimensional stability. All of these are things to keep in mind as you ponder the right plastic for your project.
Other Names for Acetal
Acetal is also frequently referred to by the product names given to it by different manufacturers, including Delrin®, Celcon®, Ultraform®, and Duracon® to name just a few.
Safe for Food Contact
While acetal can be toxic if inhaled or absorbed through the skin or eyes as a vapor or liquid, in solid form, acetal is not a health hazard. In fact, it is often used in food manufacturing and processing equipment. Naturally, you would want to confirm your requirements with the material manufacturer and consider the environment that it will face.