Polyoxymethylene (POM)

Polyoxymethylene (POM) is an engineering thermoplastic composed of repeating oxymethylene units (–CH₂O–). This linear, crystalline structure gives POM its outstanding rigidity, dimensional stability, and abrasion resistance, making it ideal for precision components.

POM is produced by the polymerization of formaldehyde or trioxane using anionic or acid catalysis processes. This results in two main types:

POM-H (homopolymer) is produced directly by the polymerization of formaldehyde and is characterized by high crystallinity and stiffness.

POM-C (copolymer) is produced by copolymerization of trioxane with small amounts of comonomers, which improves thermal stability and hydrolysis resistance.

These manufacturing processes make it possible to tailor POM to specific areas of application, particularly for components that require high precision and dimensional stability under mechanical stress.

POM is an excellent injection-moldable engineering thermoplastic and is used in particular for the series production of precision components such as gears, plain bearings, housings, and valves. Both POM-H (homopolymer) and POM-C (copolymer) are suitable for injection molding, although POM-C has higher thermal stability against hydrolysis, making it easier to process. The recommended cylinder temperatures are approx. 190–210°C, depending on the type and manufacturer's specifications, this can also be up to 230°C. The mold temperature should be between 60–100°C, with higher mold temperatures promoting improved surface quality and dimensional accuracy. The injection pressure is typically between 800 and 1200 bar. After injection molding, the parts should be cooled in a controlled manner to minimize stress and warping. POM can also be injection molded with glass fibers or PTFE additives to optimize stiffness, abrasion resistance, or sliding properties depending on the application.

POM can be processed using extrusion, particularly for the production of rods, sheets, profiles, and film strips for machining blanks. The extrusion of POM requires precise process control in order to achieve a homogeneous melt and the required crystallinity. The cylinder temperature profiles range between 170–200°C, with moderate shear preferred to avoid thermal decomposition. The mold temperatures are typically between 80–120°C. The extruded semi-finished products are characterized by high strength, rigidity, and excellent dimensional stability and are ideal for further machining. Due to their low water absorption, the dimensional stability of the extruded products is maintained even under changing climatic conditions.

Since POM is extremely easy to machine, machining (turning, milling, drilling) is a widely used manufacturing method, especially for prototypes or small series with tight tolerances. Machining can be carried out with standard HSS or carbide tools. Coolants are usually not essential, but can be used to optimize surface quality and heat dissipation. Due to its low tendency to form burrs and good chip breaking properties, POM is ideal for precision parts such as gears, sliding elements, and valve components. However, when machining POM, the springback effects (dimensional change after machining) should be taken into account, which is why post-tempering is often recommended to reduce stress.

POM is a key material in the automotive industry and is used for precise, resilient components such as fuel caps, window regulator components, door locks, sensor and pump housings, and sliding and guide elements. Thanks to its high strength, rigidity, abrasion resistance, and good chemical resistance, POM is ideal for applications in the interior, powertrain, and fuel and cooling systems. POM also offers low water absorption and excellent dimensional stability, enabling it to function reliably even under changing climatic conditions.

POM is used in many everyday and consumer products where precise fits and long-lasting resilience are important. Typical applications include gears in kitchen appliances, plain bearings in household machines, snap fasteners, writing instruments, zipper parts, and razor components. Due to its high abrasion resistance, low friction, and good surface quality, POM is particularly suitable for moving parts in consumer products that must remain quiet and functional over time.

In industry and mechanical engineering, POM is used for slide guides, gears, bearings, valves, pump parts, and precision technical semi-finished products. POM is ideal for components that need to function with permanent dimensional stability and low friction, even with little lubrication or dry running. Thanks to its chemical resistance to many oils, fuels, and solvents, POM is also used for parts in food technology, medical technology, and automated systems. POM is available in the form of rods, sheets, and profiles for machining and is used there as a material for precise, highly stressed parts.

Polyoxymethylene (POM) is available as a homopolymer (POM-H), copolymer (POM-C), and in glass fiber-reinforced form, and differs in its mechanical and chemical properties. POM-H is characterized by high stiffness and strength, while POM-C offers slightly lower stiffness but better chemical resistance and higher elongation at break. The melting point of POM-H is around 175°C, while that of POM-C is around 165°C. Both types absorb very little moisture, ensuring good dimensional stability even in humid environments.

Glass fiber reinforced POM has significantly higher stiffness and tensile strength, making it attractive for components subject to high loads. However, it is more brittle and has significantly lower elongation at break. The coefficient of sliding friction is slightly higher than that of unreinforced POM, which should be taken into account in sliding applications. In terms of chemical resistance, POM-H and POM-C are highly resistant to many chemicals, while the glass fiber reinforced variant is slightly less resistant but more mechanically resilient.

POM-C is particularly advantageous in processing, as it is easier to injection mold and offers greater dimensional stability. POM-H offers better mechanical properties, but requires more precise processing. Glass fiber-reinforced POM is more demanding to process, but is used when high rigidity and strength are required, for example in heavily loaded gears or precision parts.