POM Guide

Introduction

Polyoxymethylene (POM), also known as Acetal, is a high-performance engineering plastic widely used for precision injection molded components requiring excellent dimensional stability, low friction, and superior wear resistance.

Compared with general-purpose plastics, POM offers outstanding mechanical performance and consistent accuracy, making it an ideal material for gears, bearings, bushings, connectors, and other precision components.

Common POM grades include:

• Homopolymer POM (POM-H) – Higher strength, stiffness, and creep resistance
• Copolymer POM (POM-C) – Better chemical resistance and improved processing stability
• Glass-Filled POM – Enhanced stiffness and dimensional stability
• Lubricated POM Grades – Improved friction and wear performance

Selecting the correct POM grade is essential for achieving reliable performance, long service life, and cost-effective manufacturing.

Key Properties of POM (Acetal)

1. Excellent Dimensional Stability

One of POM’s greatest advantages is its ability to maintain precise dimensions under changing environmental conditions.

Compared with many engineering plastics, POM provides:

• Low moisture absorption
• Minimal dimensional variation
• Excellent tolerance retention
• Reliable precision performance

This makes POM suitable for components requiring tight tolerances and consistent operation.

Common applications include:

• Precision gears
• Mechanical assemblies
• Sliding components
• Valve components

2. Low Friction and Excellent Wear Resistance

POM has naturally low friction characteristics and excellent abrasion resistance.

Its self-lubricating properties make it ideal for moving components where reduced maintenance and long service life are required.

Typical applications include:

• Bearings
• Bushings
• Rollers
• Gear systems
• Guide rails

POM components can maintain smooth movement even under repeated mechanical cycles.

3. High Mechanical Strength and Fatigue Resistance

POM combines high stiffness with excellent fatigue resistance.

Key mechanical advantages include:

• High tensile strength
• Good impact resistance
• Excellent creep resistance
• Long-term dimensional performance

These properties allow POM parts to replace metal components in many lightweight engineering applications.

4. Good Chemical Resistance

POM provides resistance against many commonly used chemicals, fuels, and solvents.

It performs well in environments involving:

• Oils and lubricants
• Fuels
• Cleaning agents
• Industrial fluids

However, POM should be evaluated carefully when exposed to strong acids, oxidizing agents, or extreme chemical conditions.

POM Injection Molding Considerations

1. Material Drying and Processing

Compared with Nylon, POM has lower moisture absorption, but proper material handling is still important.

Injection molding considerations include:

• Maintaining stable processing temperatures
• Avoiding excessive residence time
• Preventing material degradation

Proper processing control helps achieve consistent mechanical properties and surface quality.

2. Wall Thickness Design

Uniform wall thickness is critical for POM injection molded parts.

Poor wall design may result in:

• Sink marks
• Internal stress
• Warpage
• Dimensional instability

Recommended design practices:

• Maintain consistent wall thickness
• Avoid unnecessary thick sections
• Use ribs instead of increasing wall thickness for reinforcement

3. Draft Angle Requirements

Proper draft angles help ensure smooth ejection and protect part surfaces.

Recommended considerations:

• Minimum draft: approximately 0.5°–1°
• Additional draft for textured surfaces

The final draft requirement depends on:

• Part geometry
• Surface finish
• Mold texture
• Ejection method

4. Gate Location and Mold Design

Gate placement directly affects:

• Material flow
• Weld lines
• Shrinkage behavior
• Part appearance

For precision POM components, optimized gate location and balanced filling are important for maintaining dimensional accuracy.

Common Applications of POM Injection Molded Parts

Automotive Components

POM is widely used in automotive systems requiring precision and durability.

Examples include:

• Fuel system components
• Gear mechanisms
• Door hardware
• Clips and fasteners
• Adjustment components

Industrial Equipment

POM is commonly selected for mechanical parts requiring low friction and wear resistance.

Applications include:

• Gears
• Bearings
• Rollers
• Conveyor components
• Machine guides

Electrical and Electronics

POM provides reliable mechanical performance for precision electrical components.

Applications include:

• Connectors
• Switch components
• Insulating parts
• Cable management components

Consumer Products

POM is used where smooth operation and durability are required.

Examples:

• Zippers
• Mechanical controls
• Precision housings
• Functional assemblies

POM vs Other Engineering Plastics

Material	Advantages	Typical Applications
POM	Low friction, precision, dimensional stability	Gears, bearings, mechanical parts
Nylon (PA)	High strength, wear resistance	Structural components
ABS	Easy processing, good appearance	Housings and consumer products
PC	High impact resistance	Safety and transparent parts
PEEK	Extreme temperature resistance	Aerospace and advanced applications

POM is often the preferred choice when precision, low friction, and dimensional accuracy are more important than extreme temperature performance.

How to Select the Right POM Grade

Material selection should consider:

Mechanical Requirements

Evaluate:

• Load conditions
• Wear requirements
• Fatigue performance
• Required stiffness

Operating Environment

Consider:

• Temperature range
• Chemical exposure
• Humidity conditions
• Lubrication requirements

Manufacturing Requirements

Review:

• Part geometry
• Required tolerances
• Mold design
• Production volume

Working with an experienced injection molding partner helps ensure the selected POM grade meets both engineering and manufacturing requirements.

Conclusion

POM (Acetal) is one of the most important engineering plastics for precision injection molding applications. Its excellent dimensional stability, low friction, wear resistance, and mechanical performance make it ideal for demanding components across automotive, industrial, electronics, and consumer industries.

By selecting the appropriate POM grade and optimizing mold design, manufacturers can achieve high-quality parts with reliable long-term performance.

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