Advancements in POM Injection Molding Boost Material Performance

Imagine a car door lock that remains reliable after thousands of cycles, or precision instrument gears that maintain flawless operation under high-speed rotation. These feats of engineering often owe their durability to polyoxymethylene (POM), a remarkable material known as "metal plastic." But how can manufacturers fully harness POM's potential to create high-quality, high-performance products? This article examines POM's material properties and systematically explains key parameter control strategies for POM injection molding processes.

Polyoxymethylene (POM), also called polyacetal, is a linear polymer with a repeating [-CH2-O-] chain structure. This opaque, crystalline thermoplastic resin emerged as a superior material following nylon's development:

• Circa 1955: DuPont pioneered formaldehyde polymerization to create POM homopolymer (POM-H), marketed as Delrin.
• 1960: Celanese developed copolymer formaldehyde (POM-C) by polymerizing trioxane with dioxolane or ethylene oxide, branding it Celcon.

POM's linear structure and high crystallinity grant exceptional physical and mechanical properties. The material exists in two forms:

• POM-H: Superior ductility and fatigue resistance but challenging processability
• POM-C: Enhanced thermal/chemical stability with easier processing

Understanding POM's characteristics is essential for optimizing manufacturing processes:

1. General Properties: Semi-transparent white material (density: 1.41-1.43g/cm³) with rigidity, hardness, elasticity, and low friction.
2. Thermal Performance: High heat deflection temperatures (POM-H: 136°C; POM-C: 110°C) ensure dimensional stability.
3. Electrical Properties: Excellent insulation (volume resistivity: 1×10¹⁴Ω·cm; surface resistivity: 1×10¹⁶Ω·cm).
4. Flammability: LOI of 15% makes POM combustible, often requiring modification for flame-retardant applications.
5. Weather Resistance: UV-stabilized POM-C outperforms POM-H in outdoor applications.
6. Chemical Resistance: POM-C withstands organic oils, synthetic detergents, and various chemicals.
7. Vulnerabilities: Degrades rapidly in strong acids/oxidizers and concentrated nitric acid.
8. Hydrolysis Resistance: Maintains performance in 80°C water long-term.

• Drying: Typically unnecessary; if required, dry at 80-90°C for 2-4 hours.
• Recycling: Maintains properties through 10 reuse cycles (recommended blend: 25-30% recycled with 70-75% virgin material).

• Machine Selection: Standard injection molding machines suffice (clamping force > product projected area × 40-60MPa).
• Barrel Capacity: Optimal product weight = 40-80% of barrel capacity.
• Nozzle System: Locking nozzles prevent drooling.
• Screw Design: Standard screw with 2.8-3.0:1 compression ratio and 18-22:1 L/D ratio.

• Barrel Temperature: 190-210°C (optimal: 200-210°C).
• Mold Temperature: 60-80°C standard.
• Injection Pressure: >98MPa (holding pressure: 49-98MPa).
• Injection Speed: 5-50mm/s (adjust for product geometry).
• Back Pressure: 0.5-1.0MPa stabilizes metering.
• Screw Rotation: 100-150rpm recommended.

• Shrinkage: High mold shrinkage (2-3.5%) requires compensation in design.
• Secondary Operations: Suitable for engraving, tapping, pressing, metal insert molding, and machining.

Door lock springs, wiper system gears, fuel system components, and various mechanisms requiring strength and wear resistance.

Keypads, switches, relay components, camera mechanisms, and precision instrument parts demanding dimensional stability.

Television, washing machine, refrigerator, and dishwasher components needing chemical and hydrolysis resistance.

Gears, bearings, valves, pumps, and structural components requiring durability and low friction.

Implantable devices like pacemakers and prosthetics where biocompatibility and precision are critical.

Through comprehensive understanding of POM's characteristics and processing requirements, manufacturers can unlock this material's full potential across countless applications.