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POM
Material Type
Engineering Plastics
Material Full Name
Polyoxymethylene
Process Compatibility
Injection Molding, CNC Machining
Basic Properties
Property |
Parameter/Performance |
Remarks |
|---|---|---|
| Chemical Name | Polyoxymethylene | Commonly called “Acetal” or “Delrin®” (CH₂O repeating units) |
| Molecular Structure | Highly crystalline thermoplastic (60-80% crystallinity) | Homopolymer (e.g., DuPont Delrin®) vs. Copolymer (e.g., BASF Ultraform®) |
| Density | 1.41~1.42 g/cm³ | Heavier than PA66/PC |
| Color | Naturally off-white (dyeable) | Opaque, self-lubricating surface gloss |
| Mechanical Properties | ||
| – Tensile Strength | 60-70 MPa (dry) | Superior rigidity among engineering plastics |
| – Impact Strength | 6-10 kJ/m² (notched Izod) | Good low-temperature toughness (-40℃) |
| – Wear Resistance | Coefficient of friction: 0.1-0.3 (unlubricated) | Second only to PTFE, ideal for gears/bearings |
| Thermal Properties | ||
| – HDT (1.82MPa) | 110-136℃ | Homopolymer has higher heat resistance |
| – Service Temperature | -40℃~100℃ (short-term 120℃) | Rapid mechanical decline >100℃ |
| Chemical Properties | ||
| – Solvent Resistance | Resists hydrocarbons/alcohols; degrades in strong acids/bases | Nitric/concentrated sulfuric acid attack |
| – Water Absorption | 0.2-0.3% (24hr) | Exceptional dimensional stability (no drying needed) |
Processing Characteristics
Thermal Stability:
- Melting Temperature: 190-220°C (releases formaldehyde gas above 240°C)
- Requires thermal stabilizers (e.g., melamine) to delay decomposition
Flowability:
- Melt Flow Index: 8-25 g/10min (190°C/2.16 kg)
- High flowability suitable for thin-walled parts (e.g., 0.5 mm thick gears)
Mold Design:
- Shrinkage Rate: 1.5-2.5% (requires enlarged gates for compensation)
- Mold Temperature: 80-120°C (reduces crystalline stress)
Common Application Areas
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Precision Machinery: Watch gears, 3D printer nozzles
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Automotive: Door lock mechanisms, fuel pump gears
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Medical: Insulin pen transmission components
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Consumer Goods: Zipper teeth, sprayer valves
POM Modified Types
Type |
Characteristics |
Typical Applications |
|---|---|---|
| Homopolymer POM | Higher strength/heat resistance, narrower processing window | Precision gears, firearm components |
| Copolymer POM | Better thermal stability, improved alkali resistance | Automotive fuel system parts |
| Lubricated POM | Added PTFE/silicone (50% lower friction coefficient) | Oil-free bearings, guide rails |
| UV-Resistant POM | Contains carbon black/UV absorbers (5x longer outdoor lifespan) | Garden equipment parts |
| Conductive POM | Added carbon fiber (volume resistivity 10³-10⁶ Ω·cm) | Anti-static conveyor belt rollers |
Advantages & Disadvantages
Advantages |
Disadvantages |
|---|---|
| Top-tier rigidity/fatigue resistance (no creep under repeated load) | Releases toxic formaldehyde gas when burned |
| Self-lubricating (ideal for replacing metal gears) | Poor weather resistance (UV causes chalking) |
| Excellent dimensional stability (water absorption <0.3%) | Difficult to bond (requires special adhesives) |
Other Engineering Plastics Selection
PES Materials
PA Materials
PC Materials
PET Materials
PEEK Materials
FAQ Of POM Materials
Visit our FAQ center for more questions.
What should be considered when processing POM plastic?
- Drying: Low hygroscopicity but pre-dry at 80-90°C for 2-3 hours to avoid bubbles.
- Injection temperature: 190-210°C; excess heat causes decomposition (formaldehyde release).
- Mold design: Account for high shrinkage (~2-3%); use high mold temps (80-120°C) to minimize warpage.
How to solve post-mold shrinkage in POM parts?
Root Cause: High crystallinity causes delayed shrinkage (continues 24h post-mold).
Solutions:
Process Optimization:
- Mold temp >100℃ (promotes full crystallization)
- Extend packing time (≥1.5× gate freeze time)
Mold Design:
- Design cavities for 2.2-2.5% shrinkage
- Use compensation gates (e.g., fan gates)
How to choose between POM and nylon (PA)?
| Property | POM | Nylon (PA) |
|---|---|---|
| Wear Resistance | Superior (self-lubricating) | Good, but reduced when wet |
| Heat Resistance | Lower (80-100°C long-term) | Higher (PA66 up to 150°C) |
| Water Absorption | Very low (stable) | High (requires drying) |
| Cost | Moderate | PA6: low; PA66: high |
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POM: Precision gears, sliding parts (zippers, printer components).
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PA: High-load/high-temperature uses (e.g., automotive engine parts).