Polyoxymethylene (POM)

Polyoxymethylene (POM), a high-strength thermoplastic known as acetal or Delrin, is valued in aviation for its precision and low-friction properties.

Background and Evolution

POM was first synthesized by Hermann Staudinger in the 1920s, with commercial production starting in the 1950s by DuPont (as Delrin) and Celanese (as Celcon). Its aviation use began in the 1960s with aircraft like the Boeing 727, replacing metal in gears and fittings due to its durability. It remains critical in modern planes like the Airbus A350, prized for its mechanical reliability.

How Polyoxymethylene is Used

POM, a smooth white or black plastic, is machined into:

• Gears and Bearings: Forms components in flap actuators and landing gear, reducing friction and wear.
• Fasteners: Shapes clips, snaps, and fuel line connectors, offering strength and stability.
• Fuel System Parts: Constructs fuel pump housings and check valves, resisting corrosion.
• Interior Fittings: Used in seat recliners and overhead bin latches, ensuring smooth operation.

Why Polyoxymethylene is Used

• High Strength: Delivers tensile strength (~60–70 MPa), supporting precise mechanical loads.
• Low Friction: Self-lubricating surface (coefficient ~0.2–0.3) minimizes wear in moving parts.
• Lightweight: At 1.41 g/cm³, lighter than metals, enhancing efficiency.
• Dimensional Stability: Resists creep and moisture (<0.5%), maintaining tight tolerances at altitude.

• Chemical Resistance: Withstands fuels, oils, and vibration in flight, meets FAA flammability standards (e.g., FAR 25.853), ideal for harsh conditions.

Technical Specifications

• Density: 1.41 g/cm³, slightly heavier than nylon.
• Melting Point: ~165–175°C, limiting high-heat use.
• Hardness: 80–90 Rockwell R, durable for mechanical roles.
• Fatigue Resistance: Excellent endurance under cyclic stress.

Comparison to Alternative Materials

• Nylon: More flexible and wear-resistant, but absorbs more moisture.
• PTFE: Lower friction and heat-tolerant, but softer and costlier.
• ABS: Cheaper and moldable, but less strong and precise.
• Steel: Stronger and durable, but heavier (7.8 g/cm³) and corrosive.

POM excels in precision and friction reduction.

Role in Modern Aviation

In aircraft like the Boeing 737 and Airbus A320, POM supports gears, fasteners, and fuel system parts, ensuring reliable performance. It complements nylon in wear-heavy roles and PTFE in high-heat zones, as seen in the Boeing 787 Dreamliner.

Environmental and Economic Considerations

• Production: Moderate energy use, with cost-effective molding.
• Cost: More expensive than ABS, balanced by longevity.
• Recycling: Reprocessable, though aviation-grade additives may limit reuse.

Future Trends

Reinforced POM blends or 3D-printed parts could broaden its use, though advanced thermoplastics like PEEK may challenge it in high-performance roles.

Summary

POM’s strength, low friction, and stability make it a key plastic in aviation’s mechanical and fuel systems. Since the 1960s, it has ensured precision and durability, maintaining a vital niche among materials.