In the world of precision machining, Acetal (Polyoxymethylene or POM) is the “go-to” material for gears, bearings, and structural components. However, engineers often face a critical choice: should they use Acetal Homopolymer (POM-H) or Acetal Copolymer (POM-C)?
While they belong to the same family, their performance characteristics differ significantly under stress, heat, and chemical exposure. At Cylex Plastics, we provide both high-grade POM-H+PTFE and versatile Acetal POM-C to meet diverse engineering needs. Let’s dive into the ultimate comparison.
I. What is the Difference? (Homopolymer vs. Copolymer)
The primary difference lies in their molecular structure. POM-H (Homopolymer) consists of a single, continuous chain of monomer units, whereas POM-C (Copolymer) introduces a second monomer to create a more stable molecular lattice.
| Property | POM-H (Homopolymer) | POM-C (Copolymer) |
|---|---|---|
| Mechanical Strength | Higher (Stiffer and stronger) | Slightly Lower |
| Centerline Porosity | Prone to “pith” or voids in the center | Virtually porosity-free |
| Chemical Resistance | Lower (Sensitive to strong bases) | Superior (Better resistance to hot water/bases) |
| Machining Ease | Excellent, but center voids can be tricky | Best for high-precision, void-free parts |
II. When to Choose POM-H (Delrin® Grade)
POM-H is the preferred choice when raw strength is the number one priority. Because it has a higher degree of crystallinity, it offers:
- Higher Fatigue Resistance: Ideal for parts subjected to repeated cyclic loading.
- Greater Hardness: Better wear resistance in dry environments.
- Enhanced Performance with Additives: Our POM-H+PTFE blend adds Teflon fibers, creating a self-lubricating surface with an extremely low coefficient of friction.
Common Uses: High-load gears, small-diameter bushings, and fasteners.
III. When to Choose Acetal POM-C
POM-C is the most widely used industrial Acetal because of its stability. Its main advantages include:
- No Centerline Porosity: When machining large-diameter rods, POM-C is consistent throughout. This is critical for parts that must be leak-proof or aesthetically perfect.
- Hydrolysis Resistance: Acetal POM-C performs much better when exposed to hot water (Above 60℃) or steam.
- Better Chemical Stability: It resists strong alkalis much better than POM-H.
Common Uses: Food processing equipment, manifolds, valves, and medical components.
IV. The Verdict: How to Decide?
The choice usually comes down to the environment and the machining process:
- High Load/Dry Wear? Choose POM-H (especially PTFE-filled grades).
- Chemical Exposure/Moisture? Choose POM-C.
- Deep Machining/Thin Walls? Choose POM-C to avoid issues with centerline porosity.
