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POM Plastic | Material Series for Product Design

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Polyoxymethylene, commonly known as POM or acetal plastic, is a high-performance thermoplastic known for its exceptional mechanical properties, dimensional stability, and ease of fabrication. With characteristics like high strength, stiffness, and durability, POM plastic has become widely used for precision machined parts and components across industries.

Abrasion-resistant engineering plastic POM injection molded parts

This guide provides a comprehensive overview of POM, discussing its properties, applications, and processing capabilities to help designers and manufacturers effectively utilize this material.

What is POM Plastic?

Technical Definition

POM, or polyoxymethylene, is a crystalline thermoplastic polymer resulting from the polymerization of formaldehyde. The ASTM D1600 standard defines POM as having high crystallinity, molding and extrusion properties, high mechanical strength, dimensional stability, and wear and fatigue resistance.

Essentially, the production of POM plastic involves polymerizing formaldehyde molecules into long-chained polymers, resulting in a material with exceptional performance properties.

POM plastic pellets

Types of POM

POM exists in two main forms:

  • Homopolymer POM: Made solely from the polymerization of formaldehyde monomers, this form offers excellent mechanical properties, high stiffness, and exceptional dimensional stability.
  • Copolymer POM: Produced by copolymerizing formaldehyde with a small amount of comonomer, typically an acetaldehyde derivative. This form has improved resistance to thermal degradation, enhanced chemical resistance, and better resistance to hydrolysis compared to homopolymer POM.

Key Characteristics and Properties of POM

Physical Properties of Polyoxymethylene (POM)

Physical PropertyDetails
DensityDensity is 1400 kg/m³, contributing to its strength and durability while being lightweight.

Chemical Properties of Polyoxymethylene (POM)

Chemical PropertyDetails
CategoryThermoplastic, offering versatility in various applications.
Water AbsorptionAbsorbs 0.2% of water by weight per day, ensuring dimensional stability in moist environments.

Thermal Properties of Polyoxymethylene (POM)

Thermal PropertyDetails
Melting PointMelts at 175°C, allowing for applications involving moderate heat.
Thermal ConductivityConducts heat at 0.37 W/m·K, indicating moderate thermal conduction.
Specific Heat Capacity (Cp)Specific heat capacity is 1464 J/kg·K, useful in thermal management applications.
Coefficient of Thermal Expansion (αL)Has a coefficient of thermal expansion of 8.5×10^-5 1/°C, indicating how it expands with temperature.

Electrical Properties of Polyoxymethylene (POM)

Electrical PropertyDetails
Relative Permittivity (@1 MHz)Exhibits a relative permittivity of 3.8, indicating good insulating properties.
Electrical ResistivityShows high electrical resistivity of 10^15 Ω·cm, making it an excellent insulator.
Dielectric Field Strength (Ed)Has a dielectric field strength of 200 kV/cm, providing strong electrical insulation.

Mechanical Properties of Polyoxymethylene (POM)

Mechanical PropertyDetails
Ultimate Tensile StrengthCan withstand tensile stress between 69 and 83 MPa, suitable for high-stress applications.
Yield Tensile StrengthYield strength ranges from 65 to 69 MPa, indicating when plastic deformation begins.
Ultimate Compressive StrengthCan endure compressive stress up to 110 MPa, ideal for structural applications.
Young’s Modulus (E)Modulus of elasticity ranges from 2.9 to 3.2 GPa, showcasing rigidity and stiffness.
Flexural ModulusFlexural modulus lies between 2.41 and 3.10 GPa, indicating resistance to bending.
Elongation at BreakExhibits elongation at break from 40% to 75%, demonstrating flexibility before breaking.
Rockwell Hardness (R)Rockwell hardness of 120, providing a measure of surface resistance to indentation.

Advantages and Limitations of Polyoxymethylene (POM)

Advantages of Polyoxymethylene (POM)

Polyoxymethylene (POM) offers a range of benefits that make it a preferred material in numerous industries. Here are the key advantages:

  • POM boasts high strength, rigidity, and toughness, making it ideal for load-bearing applications.
  • With a low coefficient of friction and high wear resistance, POM is perfect for parts involved in sliding or rotational motion.
  • It retains shape and size across various temperatures and humidity levels, ensuring consistent performance.
  • POM withstands exposure to many solvents, fuels, and chemicals without degrading.
  • It maintains mechanical properties over a wide temperature range.
  • POM easily shapes, drills, mills, or turns, allowing for precise and complex part fabrication.
  • It absorbs minimal moisture, maintaining its properties even in humid or wet environments.
  • It provides high dielectric strength and a low dissipation factor, making it an excellent electrical insulator.
  • POM’s inherent self-lubrication reduces friction and maintenance needs.
  • Certain grades meet FDA standards for food contact applications.
POM can withstand immense mechanical pressure

Limitations of Polyoxymethylene (POM)

Despite its numerous benefits, Polyoxymethylene (POM) has some limitations to consider:

  • POM can absorb small amounts of water over time, which may affect its stability and properties.
  • Prolonged exposure to high temperatures can degrade POM, affecting its mechanical properties.
  • It is susceptible to cracking when exposed to certain chemicals or solvents, necessitating careful material selection.
  • While strong, POM may not be ideal for extremely high-load or heavy-impact scenarios.
  • POM can ignite under high heat or flame, and its combustion releases toxic gases, requiring fire safety precautions.
  • Prolonged sunlight exposure can degrade and discolor POM, making it less suitable for outdoor use without UV protection.
  • Extended exposure to strong acids or bases can degrade POM, limiting its use in certain chemical environments.
  • POM can be more expensive than other engineering plastics, especially in specialized grades.

POM Plastic Applications

Automotive Industry

The automotive industry widely uses POM for components such as gears, bearings, fuel system parts, door handles, seat belt parts, and interior trim pieces.

The material withstands high temperatures and pressures while maintaining dimensional accuracy. Compared to metal components, POM gears and other moving parts also minimize noise and vibration.

Electrical and Electronics

The electrical and electronic industries utilize POM due to its excellent electrical insulation properties. Common uses include connectors, switches, relays, circuit breakers, insulating bushings, and coil forms. These components benefit from POM’s mechanical strength and stability.

Electric power equipment instrument panel buckle - POM product
Electric power equipment instrument panel buckle – POM product

Consumer Goods

POM is found in a range of consumer goods, including zippers, buckles, handles, knobs, and buttons. Its durability, dimensional stability, and low friction properties make it suitable for textile, luggage, and furniture applications.

Parts for hair trimmers made of POM material

Industrial Machinery

In industrial machinery, POM serves in components such as conveyor system parts, rollers, sprockets, pulleys, and gears. Its resistance to wear, low friction, and ability to withstand heavy loads make it ideal for these applications. POM components ensure reliable and long-lasting performance in demanding environments.

Medical Devices

POM is used in medical applications such as surgical instruments, orthopedic implants, drug delivery systems, and dental devices. Its biocompatibility, chemical resistance, and dimensional stability make it suitable for medical applications, where precision and reliability are critical.

Plumbing and Fluid Handling

POM’s resistance to chemicals and low moisture absorption make it suitable for plumbing and fluid handling components such as valves, fittings, couplings, and pump impellers. These components benefit from POM’s durability and performance in varying environmental conditions.

Sports and Recreation

POM is used in sports and recreational equipment due to its impact resistance, toughness, and low friction properties. Items such as ski bindings, bicycle components, archery equipment, and fishing reels often use POM, providing durability and reliability in active use.

Food Processing

POM grades approved for food contact applications are used in the food processing industry. Components such as conveyor belts, food handling equipment, and packaging machinery parts benefit from POM’s strength, impact resistance, and non-stick properties, ensuring hygienic and efficient operations.

Aerospace

In the aerospace industry, POM plastic is utilized for components that require high strength, stiffness, and resistance to wear, such as gears, bearings, and structural parts. These components benefit from POM’s ability to maintain performance under high-stress conditions.

Miscellaneous Applications

POM is also used in various other applications, including textile machinery, agricultural equipment, construction hardware, and musical instruments. Its versatility and reliability make it a preferred choice for a wide range of uses.

Modifying Polyoxymethylene

Impact-Modified POM

This type of POM incorporates impact modifiers to improve its toughness and resistance to impact and shock. Impact-modified POM grades commonly serve in applications where resistance to impact or vibration is crucial, such as automotive interior components or sporting goods.

Reinforced POM

Reinforced POM grades are formulated with additives like glass fibers, carbon fibers, or other reinforcing materials to enhance their mechanical properties, such as strength, stiffness, and dimensional stability. These grades are suitable for applications requiring higher mechanical performance, such as structural components in automotive or industrial applications.

Low-Friction POM

Some POM grades are specially formulated to have lower friction coefficients, reducing wear and enabling smooth movement in sliding or rotating applications. Low-friction POM is often used in gears, bearings, and conveyor systems.

Food-Grade POM

POM can be manufactured using materials and additives that comply with food contact regulations. Food-grade POM is suitable for applications in the food and beverage industry, such as food processing equipment, conveyor systems, or packaging components.

UV Stabilized Grades

UV stabilizers and absorbers can be added to POM resins to improve their stability when exposed to UV light. These grades are suitable for outdoor applications where prolonged exposure to sunlight is expected.

Nanocomposites

POM can be enhanced with nanomaterials such as carbon nanotubes (CNTs), polyhedral oligomeric silsesquioxane (POSS), and zinc oxide (ZnO) to produce nanocomposites with improved properties. These enhancements can include better mechanical strength, thermal stability, and electrical conductivity.

modified POM materials

Processing Techniques for POM

Injection Molding

Injection molding is a prevalent method for producing POM parts. The material is heated until molten and injected into a mold where it cools and solidifies into the desired shape. This technique is ideal for high-volume production and creating complex shapes with tight tolerances.

Extrusion

Extrusion is used to produce semi-finished POM products like sheets, rods, and profiles. The molten polymer is forced through a die to create a continuous shape, which is then cut to length. This method is suitable for making parts that require further machining.

Blow Molding

Blow molding is used for producing hollow parts like bottles and containers. The process involves extruding a tube of molten POM, which is then inflated within a mold to form the desired shape.

Compression Molding

Compression molding involves placing POM granules into a heated mold, which is then compressed to form the desired part. This technique is suitable for producing large, flat, or thick-walled parts.

Rotational Casting

Rotational casting, or rotomolding, involves rotating a mold while heating it to coat the interior with POM. This method is ideal for producing large, hollow parts with uniform wall thickness.

3D Printing

POM can be 3D printed using techniques like fused filament fabrication (FFF) and selective laser sintering (SLS). While less common than other materials, 3D printing with POM materials allows for the creation of complex shapes and prototypes with high strength and durability.

Common Issues in POM Plastic Processing and Solutions

Warping and Shrinkage

POM tends to warp and shrink during cooling, leading to dimensional inaccuracies. To minimize this, ensure proper bed adhesion and use a heated bed in 3D printing. For injection molding, optimize cooling rates and use appropriate mold temperatures.

High Printing Temperatures

POM requires relatively high printing temperatures. Ensure that your 3D printer can reach and maintain the necessary temperatures for POM processing. Use compatible filaments and adjust printer settings accordingly.

Post-Processing

While POM can achieve a smooth surface finish when printed, additional post-processing steps like sanding or polishing may be necessary to meet specific surface quality requirements.

Conclusion

Polyoxymethylene (POM) is a versatile and high-performance thermoplastic that offers a unique combination of mechanical strength, dimensional stability, and ease of fabrication. Its properties make it suitable for a wide range of applications across various industries, including automotive, consumer appliances, industrial machinery, medical devices, and food processing equipment.

By understanding the properties, applications, and processing techniques of POM, designers and manufacturers can effectively utilize this material to create innovative and high-performance products.

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