POM Plastic Guide: POM-C vs. POM-H, Applications
What Is POM Plastic?
POM stands for polyoxymethylene and is also commonly called acetal. It is a semi-crystalline thermoplastic engineering plastic with good mechanical strength, stiffness, wear resistance, and dimensional stability.
The material is sometimes referred to as “plastic steel” because it is more suitable than many general-purpose plastics for precision mechanical parts. This term does not mean that POM can replace metal in every application. The actual grade must still be selected according to load, friction, operating temperature, chemical exposure, and expected service life.
POM can be injection molded into gears, bearings, sliding components, and other precision mechanical parts.
Main Characteristics of POM
Suitable for components that provide support, positioning, or transmission functions. Actual load capacity depends on the part structure and selected grade.
Commonly used for gears, bushings, sliders, and other repeatedly moving components where lower friction and wear are required.
Compared with moisture-sensitive materials such as many nylon grades, POM is generally less affected by changes in ambient humidity.
Can be used for components exposed to repeated movement or sustained loading, subject to actual temperature, stress, and life-cycle requirements.
POM is resistant to many fuels, lubricants, and common solvents, but it is not suitable for strong acids or strong oxidizing environments.
Molded parts usually have a smooth surface. However, the low surface energy of POM makes conventional bonding and coating more difficult.
What Is the Difference Between POM-C and POM-H?
The two primary POM types are copolymer acetal, known as POM-C, and homopolymer acetal, known as POM-H. Both provide the general characteristics of POM, but they differ in processing stability, chemical resistance, stiffness, and strength.
| Comparison Item | POM-C Copolymer | POM-H Homopolymer |
|---|---|---|
| Main Characteristics | Processing stability and chemical resistance are generally easier to manage | Generally provides higher stiffness, hardness, and mechanical strength |
| Hot Water and Alkaline Environments | Usually provides better resistance | Performance should be confirmed by grade and service conditions |
| Mechanical Performance | Balanced performance for a broad range of mechanical parts | Often selected where stiffness, hardness, or short-term strength is more important |
| Processing | Typically provides a wider thermal processing window | May be more sensitive to melt temperature and residence time |
| Common Application Direction | Pump and valve parts, sanitary fittings, general gears, and moisture-exposed components | High-stiffness gears, bearings, precision transmission parts, and structural components |
Neither POM-C nor POM-H is universally better. Final selection should be based on the supplier’s technical data sheet for the specified grade, including mechanical properties, chemical resistance, molding shrinkage, temperature limits, and processing requirements.
Common POM Application Areas
Possible applications include gears, sliding mechanisms, window-lift parts, fasteners, and selected fuel-system components. Safety-related parts require approved grades and application-specific validation.
POM is used in printer gears, bearings, connector mechanisms, button structures, and insulating components requiring dimensional stability.
Common parts include rollers, sliders, cams, bushings, internal pump and valve components, and low-friction conveyor components.
Applications include locks, curtain transmission components, filter bearings, sanitary fittings, and other repeatedly operated mechanical parts.
Only specified POM grades with the required food-contact documentation should be considered for food-processing or drinking-water-contact components.
Medical devices require an appropriate grade with relevant supporting data. Sterilization method, biocompatibility, and actual use conditions must also be validated.
POM fan mechanism component
POM bearing and sliding component
POM filter cartridge bearing
POM printer mechanism bearing
Polyoxymethylene structure
POM sheet and component machining
POM, “Plastic Steel,” and Material Brands
POM is the technical name of the material family. “Plastic steel” is a general market term that may be used for POM or other high-stiffness engineering plastics, depending on the supplier and local industry practice.
Formosa Plastics acetal and DURACON® are examples of commercial product or brand series. A brand name alone does not define the final material performance. The complete grade designation, flow characteristics, molding shrinkage, heat resistance, additives, and regulatory documentation should all be confirmed.
POM Compared with PA Nylon and ABS
| Material | Main Advantages | Main Considerations | Typical Selection Direction |
|---|---|---|---|
| POM | Low friction, wear resistance, stiffness, and dimensional stability | Limited resistance to strong acids and oxidizers; difficult to bond or coat | Gears, bushings, sliding parts, and precision mechanical fits |
| PA Nylon | Good toughness, fatigue resistance, and impact resistance; available with glass-fiber reinforcement | Moisture absorption can change dimensions and mechanical properties | Load-bearing parts, fasteners, structural parts, and high-toughness components |
| ABS | Good processability and appearance; suitable for painting, printing, and plating | Wear resistance, chemical resistance, and dimensional stability are generally lower than POM | Housings, panels, controllers, and appearance-focused components |
POM is often reviewed first for low-friction or precision mechanical parts. PA may be more suitable when toughness or glass-fiber-reinforced structural performance is required. ABS is generally easier to use for housings, visible surfaces, and cost-sensitive parts.
Four Steps for Selecting a POM Grade
Review load, speed, friction points, operating cycles, and dimensional tolerance.
Check temperature, humidity, oils, chemicals, and outdoor-use conditions.
Compare POM-C, POM-H, supplier TDS data, and regulatory requirements.
Confirm shrinkage, warpage, dimensions, appearance, wear, and assembly performance.
POM Injection Molding Considerations
- Control Barrel Temperature: POM is sensitive to overheating. Excessive melt temperature and long barrel residence time should be avoided.
- Maintain Stable Mold Temperature: Mold temperature affects surface condition, crystallization, dimensions, and shrinkage.
- Allow for Molding Shrinkage: POM has relatively high molding shrinkage. Part thickness, gate location, packing, and mold dimensions should be reviewed together.
- Avoid Excessive Shear: Excessive injection speed, back pressure, or screw speed may increase melt temperature.
- Provide Adequate Venting: Poor venting may cause burns, trapped air, or incomplete local filling.
- Plan Joining and Secondary Operations: Conventional adhesives may not bond well to POM. Suitable surface treatment or joining methods may be required.
POM Machining Considerations
POM sheet and rod stock can be turned, milled, drilled, and processed by CNC machining. Heat generation, chip removal, clamping, and internal stress should be controlled to reduce dimensional changes after machining.
- Use sharp cutting tools: Reduces cutting heat and material pulling.
- Provide chip removal and cooling: Helps prevent local overheating and surface melting.
- Control clamping pressure: Avoids deformation of thin-wall or precision components.
- Use staged machining: Precision parts may be rough-machined first and finished after stress relaxation.
- Review annealing requirements: Thick or high-precision parts may require stress-relief treatment depending on the material and machining process.
POM can be injection molded for volume production or machined from sheet and rod stock for prototypes and lower-volume components.
Further Reading
- ABS Plastic Material Guide
- Thermosetting Plastics: Properties and Applications
- Complete Guide to Insert Molding
- PMMA vs. PC: Selecting a Transparent Plastic
Frequently Asked Questions
POM Material Review and Injection Molding Development
For products requiring low friction, wear resistance, dimensional stability, or precision transmission , our team can review the POM type, material grade, part structure, mold design, and molding conditions before confirming dimensions, appearance, and assembly through mold trials.
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