Plastic Material - POM (Polyoxymethylene)

POM -- POLYOXYMETHYLENE --  ACETAL --  POLYACETAL  -- POLYFORMALDEHYDE 

An engineering  thermoplastic used in precision parts that require high stiffness, low friction and excellent dimensional stability.

POM  is a high crystalline thermoplastic with a high level of stability and rigidity as well as good sliding properties and wear resistance with a low level of moisture absorption. Its good dimensional stability, exceptional fatigue resistance and excellent machining properties make Polyacetal a versatile design material also for complex components. It satisfies high surface finish requirements and offer better surface hardness, toughness and excellent solvent and gasoline resistance.

A High Degree of crystallinity makes acetals stiffer and stronger than most thermoplastics, yet they are tough at ambient and low temprature, good dimensional stability is a key property. Acetals absorb little water, minimizing its effect on their physical properties.

Properties:

Creep resistance, strength, stiffness, hardness, dimensional stability, toughness, fatigue resistance, solvent and fuel resistance, abrasion resistance, low wear and low friction.

Applications:

Gears, bearings, conveyors, window guides, speaker grilles, ski-bindings, zippers, lighters, aerosol valves, medical devices, snap-fits, fasteners, furniture components.

Physical Properties and characteristics

·         Unreinforced grades offer exceptionally high mechanical strength and rigidity

·         High resistance to repeated impacts

·         Toughness at low temperature (down to -40 Degrees Centigrade)

·         Outstanding long-term fatigue endurance

·         Excellent resistance to moisture, gasoline, solvents and many other chemicals of neutral pH

·         Excellent dimensional stability

·         Natural lubricity

·         Wide useful temperature range (in air -50 to +90 degree centigrade with intermittent use up to 160 degree centigrade)

·         Good electrical insulation characteristics

POM is characterized by its high strength, hardness and rigidity to -40°C. POM is intrinsically opaque white, due to its high crystalline composition, but it is available in all colors. POM has a density of ρ = 1.410 - 1.420 g / cm^3. 

POM homopolymer is a semi-crystalline polymer (75-85% crystalline) with a melting point of 175° Celsius. The POM copolymer has a slightly lower melting point of 162 – 173° Celsius.

Properties	Homo-Polymer Acetal	Co-Polymer Acetal
Tensile Modulus of Elasticity	450,000	400,000
Flexural Modulus of Elasticity	470,000	366,000
Heat Deflection Temp @ 264 psi – degress F	257	220
Melting Point – degress F	347	335
Coef. of Linear Thermal Expansion	6.8 x 10-5	5.4 x 10-5
Water Absorption @ Saturation	0.90	0.80

The homoplymers’ strength properties tend to be slightly higher than those of the copolymers. Delrin® is a homopolymer Polyacetal. Delrin® has higher (short term) heat deflection temperatures than copolymers, but their continuous use  temprature is 85°C (185°F) compared to 100°C (212°F) for copolymers. The homopolymers, tend to have somewhat greater surface hardness, higher degree of density and a slightly lower coefficient of friction.

The copolymers, compared to homopolymers, tend to absorb less water, are more resistant to hydrolysis and have superior processing characteristics. Copolymers, however, have higher impact toughness, greater wear resistance and thermal / chemical resistance.