Delrin Properties — Mechanical, Thermal & Chemical Datasheet
Delrin (acetal homopolymer, POM-H) properties are defined by its highly crystalline, linear oxymethylene chain: tensile strength of 10,000–11,000 psi in the standard 500 grade, a fatigue endurance limit near 5,000 psi at 10⁷ cycles, and a coefficient of friction in dry sliding that rivals lubricated metals. This datasheet covers mechanical, thermal, electrical, chemical, and wear data for the primary Delrin grades in stock-shape rod, sheet, and tube.
At a glance:
- Tensile strength (Delrin 500): 10,000 psi; Delrin 570 (GF): ~14,000 psi
- Fatigue endurance limit (~10⁷ cycles): ~5,000 psi — best in class for unfilled acetals
- Continuous use temperature: 185°F (85°C); melt point 347°F (175°C)
- Coefficient of friction (dry vs. steel): 0.20–0.35 unfilled; ~0.10–0.15 for Delrin 100AF
- Water absorption (24 hr): 0.25%; dimensional stability generally good below 120°F
- POM-H crystallinity: 75–85%; drives stiffness and fatigue advantage over POM-C
Mechanical Properties
Tensile, Compressive, and Flexural Data
Impact and Hardness
Delrin 100 (highest molecular weight) shows 20–30% higher notched Izod impact than Delrin 500 at room temperature. For applications prone to shock loading, Delrin 100 is the preferred grade.
Fatigue Performance
Delrin's fatigue endurance limit is one of its strongest differentiators. At 10⁷ cycles of fully reversed bending stress at 73°F, the endurance limit is approximately 5,000 psi (34 MPa) for Delrin 500. Acetal copolymer grades (Celcon, Hostaform) typically test at 4,000–4,500 psi under the same conditions.
This ~10–25% fatigue advantage is the primary reason gear designers specify Delrin (POM-H) over generic acetal: gear teeth undergo cyclic flexural loading, and the endurance limit directly bounds allowable tooth stress in the AGMA/ISO gear design framework.
Creep and Stress Relaxation
Delrin exhibits modest creep under sustained load at room temperature. At 23°C and 5,000 psi applied stress, typical creep strain over 1,000 hours is 1.5–2.0% for Delrin 500. At 75°C and 3,000 psi, creep over 1,000 hours can reach 3–5%. For sustained-load applications (bolted joints, snap-fits under compression), design with creep relaxation allowances of 15–30% over the service life, depending on temperature.
Grade-to-Grade Comparison
Thermal Properties
Delrin's CTE of 122 ppm/°C is significantly higher than metals (steel: ~12 ppm/°C; aluminum: ~23 ppm/°C). In assemblies with metal hardware, account for differential thermal expansion, especially in temperature-cycling environments. A 1-inch Delrin rod in an aluminum housing will expand approximately 0.001" more than the housing for every 10°F temperature rise.
Electrical Properties
Delrin is an electrical insulator in all standard grades. No static-dissipative or conductive Delrin grades are commonly stocked in rod and sheet form; applications requiring ESD control should consider conductive acetal copolymer compounds or alternative materials.
Chemical Resistance
Delrin's chemical resistance is good to excellent for aliphatic hydrocarbons, most organic solvents, weak acids, and dilute bases. Its limitations are: strong inorganic acids, oxidizing agents, and prolonged exposure to hot water above 80°C.
| Reagent / Environment | Resistance at 73°F | Notes |
|---|---|---|
| Water (ambient) | Excellent | 0.25% absorption in 24 hr; dimensional impact minimal |
| Hot water / steam (>80°C) | Fair–Poor | POM-H is susceptible to hydrolysis under prolonged exposure; use POM-C for hot water service |
| Aliphatic hydrocarbons (fuels, oils) | Excellent | Gasoline, diesel, mineral oil, hydraulic fluids |
| Aromatic hydrocarbons | Good | Some surface swelling at prolonged exposure |
| Alcohols (IPA, methanol, ethanol) | Excellent | Common industrial cleaning solvents acceptable |
| Ketones (acetone, MEK) | Good | Minor surface softening at extended exposure |
| Dilute acids (pH > 4) | Good | HCl, acetic acid at low concentration |
| Strong mineral acids (pH < 2) | Poor | Attacks polymer chain |
| Dilute bases (NaOH < 10%) | Good | |
| Strong oxidizing agents | Poor | Bleach, concentrated H₂O₂ |
| Gasoline / diesel | Excellent | Widely used in fuel system components |
Hot water service above 60°C (140°F) is Delrin's key weakness versus acetal copolymer. POM-H hydrolyzes under sustained hot-water exposure, causing surface degradation and dimensional change over months to years. For hot-water-contact parts — dishwasher components, hot water valves, steam applications — specify acetal copolymer (POM-C) instead. See the acetal copolymer material hub.
Tribological Properties (Wear and Friction)
Delrin is inherently self-lubricating due to the low surface energy of the POM backbone. Wear performance depends heavily on the counterface material, surface roughness, and operating PV (pressure × velocity).
For high-duty bearing and wear applications, Delrin 100AF provides substantially better tribological performance by incorporating PTFE fiber reinforcement that deposits a transfer film on the counterface and reduces adhesive wear. Compare with acetal copolymer properties for grade-selection guidance in lubricated vs. dry sliding.
Physical Properties
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Acetal family
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