Plastic polymers of formaldehyde, correctly called polyoxymethylenes (POM), acetals are about the strongest and stiffest thermoplastics; acetals also are characterized by excellent fatigue life and dimensional stability. Other outstanding properties include low friction coefficients, exceptional solvent resistance, and high heat resistance for extended use. At present there are two basic types of acetal plastic: homopolymer and copolymer. The homopolymers are somewhat tougher and harder than the copolymers but suffer from instability in processing.
Applications: Many involve replacement of metals where the higher strength of metals is not required and costly finished and assembly operations can be eliminated. Typical parts include gears, rollers, and bearings, conveyor chains, auto window lift mechanisms and cranks, door handles, plumbing components, and pump parts.