Spec sheets list POM-H, POM-C, Delrin, Celcon, Kepital, Duracon — half a dozen names for what is essentially one family of material. This guide clarifies what each name means, which POM grade to specify for your application, and the real differences between Delrin (homopolymer) and generic copolymer acetal.
The confusing terminology:
So "Delrin" and "POM" are sometimes used interchangeably in casual speech, but strictly speaking:
The two have different properties in ways that matter for specific applications.
| Property | POM-H (Delrin) | POM-C (Celcon, Kepital) |
|---|---|---|
| Tensile strength | 76 MPa | 66 MPa |
| Flexural modulus | 2,900 MPa | 2,600 MPa |
| Impact strength (Izod notched) | 53 J/m | 67 J/m |
| Continuous service temp | 100 °C | 100 °C |
| Chemical resistance | Good — attacked by strong acids | Excellent — better hot water, better alkaline |
| Hot-water hydrolysis resistance | Poor (>70 °C degrades) | Good — stable to 90 °C water |
| Centerline porosity (risk) | Yes — cast rod has porous center | No — tighter, more uniform |
| Machinability | Excellent | Excellent (slightly better surface finish) |
| Cost (per kg) | ~$28 | ~$24 |
| Best for | Precision mechanical parts, high stiffness | Chemical service, hot water, food contact |
Key takeaway: Delrin (POM-H) is slightly stronger and stiffer; POM-C is more chemically resistant and free of centerline porosity. For most mechanical parts either works; for parts in hot water or mild acid/base, specify POM-C.
POM-H rod stock (Delrin) can have a porous core. During cooling of extruded rod, the outer surface solidifies first, creating shrinkage voids toward the center. These voids may not show on the surface but can be exposed during machining.
For parts where the centerline gets machined (turned parts with axial bores, for example), porosity shows up as:
POM-C is manufactured differently and typically has no centerline porosity. For axially-machined parts, specify POM-C unless there's a specific reason for POM-H.
Alternatively, Delrin AF (acetal with PTFE fibers) and Delrin 100/500 production grades are less porous than standard cast rod. For tight-tolerance Delrin parts, confirm the grade with your supplier.
Mechanical properties close. Chemical environment benign. Pick the cheaper or more available grade.
Delrin hydrolyzes above 70 °C in water. POM-C stable to 90 °C. For water-contact parts in warm environments, POM-C only.
Both have FDA-approved grades, but POM-C more commonly specified for food service equipment.
Eliminates centerline porosity risk. For parts that must be gas/liquid tight or have critical tolerances through the centerline.
10-15% stronger and stiffer. For highly loaded structural plastic parts.
Email [email protected] with your drawing. We'll recommend POM-H or POM-C based on your application and stock the appropriate grade for each order.
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