Polyoxymethylene (POM), also known as acetal, is a high-performance engineering thermoplastic renowned for its excellent mechanical properties and dimensional stability. Used in a wide range of applications from automotive parts to consumer goods, POM offers a unique combination of strength, stiffness, and low friction. This guide will explore the properties, benefits, applications, and processing methods of POM, providing a thorough understanding of its value in various industries.
What is Polyoxymethylene (POM)?
Polyoxymethylene, commonly known as POM or acetal, is a thermoplastic polymer characterised by its repeating oxymethylene (-CH2O-) units. It is produced through the polymerisation of formaldehyde. There are two main types of POM: homopolymer (POM-H) and copolymer (POM-C). POM-H offers higher mechanical strength and rigidity, while POM-C provides better thermal stability and chemical resistance.
Key Properties of POM
High Strength and Stiffness: POM is known for its excellent tensile strength and rigidity, making it ideal for precision parts.
Low Friction and Wear Resistance: POM has a low coefficient of friction and is highly resistant to wear, making it suitable for applications involving sliding and rotating parts.
Dimensional Stability: POM maintains its shape and dimensions under various environmental conditions, offering reliable performance.
Chemical Resistance: POM is resistant to many solvents, fuels, and oils, enhancing its use in chemical-exposed applications.
Good Fatigue Resistance: POM can withstand repetitive stress and strain, making it suitable for components subjected to cyclic loading.
Low Moisture Absorption: POM absorbs very little water, which helps maintain its mechanical properties and dimensional stability.
Thermal Stability: POM has a high melting point (around 175°C or 347°F) and can operate effectively over a wide temperature range.
Applications of POM
Due to its exceptional properties, POM is used in a wide array of applications, including:
Automotive: Gears, bearings, fuel system components, and interior trim due to its strength, low friction, and chemical resistance.
Consumer Goods: Zippers, buckles, and kitchen appliances benefiting from its durability and ease of moulding.
Industrial: Conveyor belts, pump components, and valve parts where wear resistance and dimensional stability are crucial.
Electronics: Connectors, switches, and housings owing to its electrical insulation properties.
Medical Devices: Surgical instruments and drug delivery systems due to its strength and chemical resistance.
Construction: Fasteners, clips, and fittings where durability and precision are required.
Processing Methods for POM
POM can be processed using various methods, depending on the desired end product:
Injection Moulding: The most common method for producing complex shapes and parts with high precision, such as automotive and consumer goods components.
Extrusion: Used for creating rods, sheets, and profiles by forcing molten POM through a shaped die.
Blow Moulding: Suitable for making hollow objects like containers and ducts by expanding the plastic into a mould using air pressure.
Machining: POM can be easily machined into precise components using traditional machining techniques, making it ideal for prototyping and small batch production.
Compression Moulding: Involves moulding POM powder under heat and pressure to produce high-strength parts.
Advantages of Using POM
Excellent Mechanical Properties: Offers high strength, stiffness, and durability.
Low Friction and Wear Resistance: Suitable for moving parts and reducing maintenance.
Dimensional Stability: Maintains shape and size under various conditions.
Chemical and Thermal Resistance: Enhances its use in demanding environments.
Ease of Processing: Can be easily moulded and machined into various forms.
Low Moisture Absorption: Ensures consistent performance in humid conditions.
Challenges and Considerations
While POM offers many advantages, there are some challenges to consider:
Thermal Degradation: POM can degrade at high temperatures, releasing formaldehyde gas, so processing and operating conditions must be controlled.
UV Sensitivity: POM can degrade when exposed to UV light over time, though UV-stabilised grades are available.
Cost: POM can be more expensive than some other engineering plastics, which may impact its suitability for cost-sensitive applications.
Chemical Resistance Limitations: POM is susceptible to attack by strong acids and bases.
Conclusion
Polyoxymethylene (POM), commonly known as acetal, is a highly versatile thermoplastic prized for its exceptional mechanical properties and dimensional stability. Whether in automotive parts or consumer goods, POM offers strength, low friction, and durability. By understanding its properties and processing methods, you can leverage POM's advantages in your projects, ensuring efficiency and reliability. If you're considering plastic injection moulding for your components, schedule a free consultation to explore the possibilities of using POM for your specific needs.