The best general-purpose precision machining plastic. Delrin — DuPont's trade name for acetal homopolymer (POM-H) — delivers excellent dimensional stability, low friction, good toughness, and predictable machinability at a fraction of the cost of higher-performance thermoplastics. The go-to choice for small precision mechanical parts: gears, bushings, slides, valve components, fluid handling.
Delrin occupies the "precision mechanical plastic" sweet spot. It's stiffer than nylon (2.9 vs. 2.1 GPa flex modulus), absorbs far less moisture (0.25% vs. 2–3% for nylon 6/6), and holds tolerance far better than any inexpensive thermoplastic. It's cheap enough to use without second-guessing ($6–12/kg for standard stock), machines like warm butter, and is FDA-compliant in natural grade for food-contact applications. For any application where you need a plastic part with engineering-grade dimensional stability under $30 in material cost, Delrin is probably the right answer.
Its limits: continuous service temperature tops out around 90°C (105°C intermittent); it's vulnerable to strong acids and oxidizers; it cannot be ultrasonically welded; and it accumulates static charge (ESD-safe variants exist). For most industrial mechanical applications, none of these matter — which is why Delrin has been a workshop staple since DuPont introduced it in 1960.
Delrin = DuPont's trade name for the homopolymer grade (POM-H). Celcon / Hostaform / Ultraform = various manufacturers' names for copolymer (POM-C). Both are "acetal." Delrin is slightly stronger and stiffer, POM-C is slightly more chemically resistant and less prone to centerline porosity. For machining, either works — specify "Delrin or equivalent POM-H" unless you have a specific reason to insist on one brand.
| Property | POM-H (Delrin) | POM-C (Celcon, etc.) | Notes |
|---|---|---|---|
| Structure | Homopolymer — single repeat unit | Copolymer — with ethylene oxide comonomer | — |
| Tensile strength | 70 MPa | 62 MPa | POM-H ~12% stronger |
| Flexural modulus | 2.9 GPa | 2.6 GPa | POM-H stiffer |
| Centerline porosity | Possible in thick rod stock | Negligible | POM-C better for hollow or thin-wall parts from solid rod |
| Chemical resistance | Good to most, attacked by strong acids | Slightly better to bases and hot water | — |
| Long-term thermal stability | Gradual strength loss >80°C | Better retention at 80–100°C | POM-C preferred for sustained heat |
| Cost | Baseline | ~0.9× POM-H | POM-C slightly cheaper |
| Property | Value | Test method |
|---|---|---|
| Tensile strength at yield | 70 MPa | ASTM D638 |
| Tensile modulus | 3.1 GPa | ASTM D638 |
| Elongation at break | 30–40% | ASTM D638 |
| Flexural strength | 97 MPa | ASTM D790 |
| Rockwell hardness | M94 / R120 | ASTM D785 |
| Izod impact (notched) | 73 J/m | ASTM D256 |
| Coefficient of friction (static, on steel) | 0.20 | ASTM D1894 |
| Coefficient of thermal expansion | 1.1 × 10⁻⁴/K | — |
| HDT (1.8 MPa) | 100°C | ASTM D648 |
| Max continuous service temp | 90°C | UL 746B |
| Water absorption (24 h) | 0.25% | ASTM D570 |
| Density | 1.42 g/cm³ | ASTM D792 |
| Dielectric strength | 20 kV/mm | ASTM D149 |
| Food-contact compliance | FDA 21 CFR 177.2470 (natural grade) | |
Delrin is among the easiest engineering plastics to machine. Sharp tools, high speeds, moderate feeds, and light chip loads. Use compressed air or water-soluble coolant — never petroleum-based oils for food-contact parts. Chips peel off in long ribbons; plan chip evacuation accordingly.
| Operation | Surface speed (m/min) | Feed per tooth (mm) | Notes |
|---|---|---|---|
| Face milling | 300–600 | 0.10–0.30 | Sharp carbide, positive rake, 2–3 flute |
| End milling (rough) | 200–400 | 0.05–0.15 | High helix, polished flute |
| End milling (finish) | 300–500 | 0.02–0.08 | Single-flute for best finish |
| Drilling | 60–120 | 0.10–0.25/rev | Parabolic flute, peck cycle for depth |
| Tapping | 6–15 | — | Form tap, Delrin compresses well |
| Turning | 250–500 | 0.10–0.30/rev | Sharp positive-rake insert |
Small-module gears for light-duty applications. Low noise, self-lubricating, stable under moderate load. Common in printers, office machines, timing mechanisms.
Plain bearings under 5 m/s surface velocity. Low friction against steel and aluminum; no external lubrication needed for most applications.
Valve seats, check valves, pump impellers for water and mild chemical service. Dimensional stability over long service life.
Conveyor components, fill nozzles, seal rings in FDA-compliant applications. Natural (unpigmented) stock required.
Clips, fasteners, sliding mechanisms in seats and HVAC. Below 85°C typical automotive interior peak temp.
Fixtures, housings, sterilizable components. Limited autoclave compatibility — specify nylon or PEEK for repeated steam sterilization above 100°C.
| Material | Strength | Max temp | Moisture | Cost ratio |
|---|---|---|---|---|
| Delrin (POM-H) | 70 MPa | 90°C | 0.25% | 1.0× (baseline) |
| POM-C (Celcon) | 62 MPa | 100°C | 0.20% | 0.9× |
| Nylon 6/6 | 85 MPa dry / 55 wet | 85°C | 2.5% | 0.7× |
| Nylon 6 | 80 MPa dry / 50 wet | 80°C | 3.0% | 0.6× |
| UHMW-PE | 21 MPa | 80°C | <0.01% | 0.5× |
| Polycarbonate | 65 MPa | 120°C | 0.15% | 1.1× |
| PEEK | 100 MPa | 260°C | 0.1% | 20–30× |
Extruded POM-H rods over ~75 mm diameter can have a small void along the centerline. If your part uses the center of a thick rod, specify POM-C (Celcon) instead, or order cast/compression-molded stock. Most commodity Delrin suppliers won't disclose this unless asked.
CTE of 1.1×10⁻⁴/K is 4× steel, 2× aluminum. A 100 mm Delrin part changes ~0.11 mm over 10°C. Don't design steel-pin-in-Delrin-hole fits without accounting for this, especially in outdoor or high-temperature applications.
Concentrated acids (HCl, HNO₃) degrade POM rapidly. Chlorinated water above 60°C causes slow chain scission — a known failure mode in hot-water plumbing applications. Chemical service: double-check compatibility chart.
Delrin's low surface energy resists adhesives and printing ink. For bonding: flame treatment, chromic acid etch, or PlasmaPen. For printing: same. Design for mechanical fastening rather than adhesive if possible.
For tight-tolerance parts, ask for stock that has been annealed (typically 150°C, 24 hours), or request post-machining anneal. Adds $5–15/part but eliminates dimensional drift in service.
DuPont, Mitsubishi, or Ensinger stock with full material certs. FDA-grade natural available. Typical lead: 5–10 days prototype, 10–21 days production.