Phan Van Hoang- 12/10/2026
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POM is used in a wide range of mechanical components because of its stiffness and sliding properties. Learn about POM homopolymer and copolymer, along with key considerations for material selection and processing.
What Is POM? Distinguishing Homopolymer and Copolymer
POM, or polyoxymethylene, is also known as acetal resin. It is a semi-crystalline thermoplastic widely used in moving mechanisms and precision components. The two important categories are POM homopolymer and POM copolymer, both of which are available in numerous grades.
Homopolymers and copolymers differ in their polymer structures, so they should not be treated as directly interchangeable materials. In addition to general-purpose grades, there are impact-modified, low-friction, reinforced, and other specialty grades. When purchasing, specify the complete grade designation and functional additives rather than referring only to “POM resin.”
Why Is POM Used for Mechanical Components?
Key properties of interest include stiffness, elastic recovery, sliding performance, dimensional stability, and low water absorption. POM is often considered for gears, sliding bearings, rollers, locks, clips, and small mechanisms. However, suitability at the material-family level does not mean that a specific grade can withstand every load or operating speed.
For gears, specify torque, speed, cycle count, temperature, and the mating material. For clips, determine the number of assembly and disassembly cycles and the deformation during engagement. Each mechanism has different failure modes, so the testing program must be tailored accordingly.
Friction and Wear: Consider the Material Pair
A sliding system is affected by load, speed, surface roughness, temperature, and lubrication. Therefore, a single friction coefficient should not be used to predict the entire service life. Some POM grades are modified to reduce friction or noise; these grades must be evaluated against the actual contact surfaces.
Consider testing both at startup and under steady-state operation, recording pulling force or torque, noise, temperature, and wear. If the component is exposed to dust, include that condition in the test. A system that performs well in a clean room may produce different results in equipment under real operating conditions.
Reading TDS Data for Components Under Long-Term Loads
Modulus and tensile strength help with initial screening, but they do not replace creep or fatigue data. Creep is the increase in deformation over time under load, while fatigue involves repeated loading. For components that must maintain precise clearances, consider deformation after many hours and recovery after the load is removed.
When comparing grades, check melt flow rate, test conditions, notched impact strength, and shrinkage. Typical values in a TDS do not automatically become guaranteed limits for every production lot. If certain properties must be controlled upon delivery, clearly agree on the test methods and acceptance criteria.
Chemical and Thermal Limits That Need Verification
POM can perform well in many engineering environments, but the term “chemical resistance” must be evaluated in relation to the chemical agent, concentration, temperature, and exposure duration. Do not extrapolate results obtained with water at room temperature to hot solutions or oxidizing conditions.
For heat-resistant mechanisms, do not consider only the melting temperature or heat deflection temperature (HDT). Determine the simultaneous load, operating duration, thermal cycling, and allowable deformation. If the product contacts drinking water or food, or is used in medical applications, request documentation for the exact grade. The name POM alone does not establish compliance.
POM Processing and Material Control
Control the melt temperature, residence time, and shutdown procedures in accordance with the manufacturer's documentation. Overheating POM or allowing it to remain in the machine for too long can cause decomposition and release formaldehyde. Manufacturers should provide source-capture ventilation and follow the resin supplier's safety instructions when changing materials, cleaning equipment, or restarting production.
Keep the material clean and sealed during storage, and check the drying requirements for the specific grade and packaging condition. Do not assume that all POM grades must be dried in the same way or that drying is never necessary. For regrind, separate material sources, minimize dust, and check the thermal history. Validate the regrind ratio through mechanical properties, dimensions, and functional performance.
Choosing POM to Replace Metal or Polyamide
When replacing metal with POM, review the entire design, including ribs, wall thickness, press-fit areas, clearances, and load-bearing surfaces. Simply copying the dimensions of a metal component and substituting the material is generally insufficient. Cost-effectiveness should account for tooling, cycle time, post-molding machining, and yield.
When comparing POM with PA, evaluate moisture requirements, friction, stiffness, and temperature performance using two specific grades. For small gears, a loaded operating test is often more useful than selecting a material based on a room-temperature mechanical-property table alone.
Checklist Before Selecting a Grade
The specification should identify the POM type, full grade designation, color, additive requirements, load, speed, friction pair, service life, operating environment, and dimensional tolerances. Include the TDS, processing guidelines, and batch traceability information. When replacing an existing grade, retain a set of original samples for comparison.
Frequently Asked Questions About POM
Is POM completely self-lubricating? Good sliding properties do not mean every mechanism can operate without lubrication. Test the load, speed, temperature, noise, and wear of the entire contact pair.
Is POM copolymer always inferior to homopolymer? There is no universal ranking. Compare specific grades based on mechanical properties, environmental conditions, long-term durability, and processing requirements.
Why can a newly molded gear meet dimensional specifications but still produce noise during operation? Check tooth geometry, concentricity, assembly, the material pair, and operating conditions. Functional problems do not necessarily originate solely from the resin.
Finding POM Grades
See the list of POM resin grades below to compare manufacturers, specifications, and documentation for individual grades.
References
This guide covers material selection at the product-family level. When deciding on a specific grade, verify the current TDS, operating conditions, and test results obtained from the actual product.
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