Delrin Material — Rod, Sheet & Tube in POM-H Acetal
Delrin is DuPont's trade name for acetal homopolymer (POM-H), the higher-performance variant of polyoxymethylene. Introduced commercially in 1960 after DuPont patented the stabilized homopolymer in 1956, Delrin delivers higher tensile strength, greater stiffness, and a better fatigue endurance limit than acetal copolymer — making it the default specification for precision mechanical parts, gears, bushings, and wear strips that run at moderate temperatures and require tight dimensional tolerance.
At a glance:
- Chemistry: acetal homopolymer (POM-H); repeating unit -[OCH₂]-; higher crystallinity than copolymer
- Tensile strength: 10,000–11,000 psi (Delrin 500); up to 14,000 psi in glass-filled grades
- Continuous use temperature: 185°F (85°C); short-term to 220°F (104°C)
- Specific grades: Delrin 100, 150, 500, 507, 570, 100AF, 150SA, 500SA
- Key differentiation from acetal copolymer: higher tensile/fatigue, but centerline porosity in large rod diameters
- Forms stocked: rod (.125"–12" dia), sheet (0.062"–4.0" thick), tube
- FDA-compliant grades: Delrin 150SA, 500SA (for direct food contact)
What Is Delrin? Brand History and Chemistry
Delrin is not simply "acetal" — it is specifically acetal homopolymer manufactured from DuPont's stabilized formaldehyde polymerization process. The critical distinction matters in procurement: specifying "Delrin" and accepting "acetal" as equivalent can mean receiving acetal copolymer (Celcon, Hostaform, Ultraform), which has different properties.
POM-H Polymer Chemistry
Polyoxymethylene homopolymer consists of an unbranched chain of oxymethylene units: -[O-CH₂]-. The chain ends are capped with ester groups to prevent unzipping (thermal depolymerization), which was the key technical challenge DuPont solved in the 1950s. This highly regular, linear structure enables crystallinity levels of 75–85% in properly processed stock — significantly higher than most engineering thermoplastics. High crystallinity is what drives Delrin's exceptional fatigue life, stiffness, and resistance to creep at room temperature.
Acetal copolymer, by contrast, incorporates periodic dioxolane or trioxane comonomer units that interrupt chain regularity. This reduces crystallinity slightly, eliminates centerline porosity in large-diameter rod, and improves hot water and hydrolysis resistance — but sacrifices some tensile strength and fatigue performance. For a detailed head-to-head, see the Delrin vs. acetal copolymer comparison.
DuPont History and Current Branding
DuPont introduced Delrin to the market in 1960. The material's combination of metal-like stiffness at low cost — in a machinable, injection-moldable polymer — made it a rapid success in automotive, consumer products, and industrial applications. Today, Delrin is produced by DuPont (now separated from the Specialty Products division that became Celanese-DuPont M&M) and remains the benchmark POM-H grade. The trademark is DuPont's; competitors cannot legally call their homopolymer "Delrin" even when it meets equivalent specifications.
Delrin Properties
Delrin's mechanical profile is dominated by three characteristics: high crystallinity for stiffness and fatigue life, low friction for bearing and wear applications, and dimensional stability under moderate humidity and temperature variation.
Mechanical Properties (Delrin 500, 73°F)
Thermal Properties
Electrical and Physical
Delrin's coefficient of friction in dry sliding against steel (0.20–0.35) is notably lower than many unreinforced engineering plastics, enabling its use in lightly loaded bearings and wear applications without lubricant additives. For the complete properties datasheet including filled grades, see Delrin properties.
Delrin absorbs moisture more readily than acetal copolymer: 0.25% in 24 hours vs. ~0.20% for POM-C. In applications requiring tight dimensional tolerances over the service life, account for swelling under humid conditions. Delrin's dimensional change per 0.1% moisture uptake is approximately 0.003–0.005 in/in.
Delrin Grades
DuPont offers Delrin in a structured grade series. Each grade designation indicates molecular weight class, filler type, or processing modification:
Delrin 100 — Highest molecular weight. Best impact resistance and toughness in the family. Slower crystallization rate on cooling; used for injection molding where tough, ductile parts are needed. Larger stock shapes in Delrin 100 show better impact performance than 500.
Delrin 150 — Medium-high molecular weight, optimized for extrusion. The dominant grade in stock shapes (rod, sheet, tube). Higher surface quality than Delrin 100 in extruded form; preferred by precision machinists. Delrin 150 targets are the keywords "delrin 150" (vol 300) and is the most commonly quoted grade in machining applications.
Delrin 500 — General-purpose injection molding grade, medium molecular weight. Most widely used in injection molded components. Good balance of flow, strength, and surface finish. Also available in stock shapes.
Delrin 507 — Lubricated grade; internally compounded with lubricant additives for even lower coefficient of friction. Used in high-cycle wear applications where additional lubrication is impractical.
Delrin 570 — 20% glass fiber reinforced. Raises tensile strength to approximately 14,000 psi and improves creep resistance significantly. Trade-off: higher tool wear in machining, and glass fiber eliminates some tribological advantage.
Delrin 100AF — PTFE-fiber filled (AF = aramid/PTFE fiber blend). Dramatically improves wear resistance and lowers PV-limit operating temperature; CoF against dry steel drops to ~0.10–0.15. Used in bushings, thrust washers, and sliding components in demanding duty cycles.
Delrin 150SA / 500SA — FDA-compliant natural (white) grades meeting 21 CFR 177.2480. These grades use approved colorants and additives; see Delrin FDA and food-grade compliance.
For the full grade-by-grade comparison and selection guide, see Delrin grades.
Delrin Stock Shapes: Rod, Sheet, and Tube
Delrin Rod
Delrin rod is the highest-volume stock shape, used wherever round stock is turned on a lathe to produce precision components. Standard diameters run from 0.125" through 12.0" in natural (white/ivory) and black. Available in standard 4-foot lengths; some sizes in 6-foot lengths for longer turned parts.
Centerline porosity caution: In Delrin rod diameters above approximately 3.0 inches, POM-H homopolymer can develop a porous centerline zone during extrusion solidification. This is a known characteristic of all acetal homopolymer, not a defect in manufacturing quality. Parts machined from large Delrin rod that must use the center of the rod (e.g., parts with through-bores concentric to the rod axis) should be evaluated for porosity impact on structural performance. Acetal copolymer rod avoids this issue due to the comonomer structure.
See the Delrin rod page for stocked sizes, tolerances, and ordering details.
Delrin Sheet
Delrin sheet is extruded in thicknesses from 0.062" through 4.0". Standard sheet sizes: 24"×48" and 48"×96". Tolerance on thickness: ±10% ASTM standard; tighter tolerances to special order. Sheet is cut by waterjet, bandsaw, or router; laser cutting is generally not recommended due to formaldehyde fume generation.
See Delrin sheet for stocked thicknesses, sheet sizes, and cut-to-size options.
Delrin Tube
Delrin tube (extruded round tube) is stocked in OD ranges from 0.5" through 8.0" with standard wall thicknesses. Tube is practical when a hollow geometry is needed and boring the ID from solid rod is not cost-effective. See Delrin tube for stocked OD/ID combinations.
Key Applications
Delrin's combination of stiffness, dimensional stability, low friction, and machinability drives its use across a wide range of precision mechanical applications:
Gears and Gear Trains
Delrin is one of the two most common plastics for small-pitch gears (the other being nylon 66). Its superior fatigue endurance limit (5,000 psi at 10⁷ cycles, compared to ~4,000 psi for acetal copolymer) directly translates to longer gear life in cyclic-load applications. Used in automotive HVAC actuators, power-window mechanisms, consumer appliances, office machines, and medical devices where quiet, low-lube gear operation is needed.
Precision Machined Components
Delrin is the workhorse for CNC-machined plastic parts: housings, spacers, valve bodies, manifold blocks, clips, and fasteners. It holds tolerances of ±0.001–0.002" in turning and milling, machines without burrs or melt-smearing, and produces smooth surface finishes with standard carbide tooling.
Bearings, Bushings, and Wear Strips
Self-lubricating character and good compressive strength make Delrin a practical bushing and wear-strip material in dry or lightly lubricated service at loads below the PV limit. For heavy-duty or high-speed bearing applications, Delrin 100AF (PTFE-filled) is preferred.
Fluid Handling and Valve Components
Delrin resists most common industrial chemicals, fuels, oils, and hydraulic fluids. It is widely used in fluid couplings, check valves, metering components, and pump impellers in environments where mild chemical exposure and good dimensional stability are required.
For a full application breakdown by industry, see Delrin applications.
Machining Delrin
Delrin is among the easiest engineering plastics to machine. It cuts cleanly, produces short-breaking chips, and holds tight tolerances without the tendency to smear or melt under the tool that plagues softer polymers. Key parameters for machining Delrin:
- Turning: 400–800 SFM surface speed; 0.004–0.012 IPR feed; sharp uncoated carbide
- Milling: 300–600 SFM; 0.003–0.006 IPT chip load; 2–3 flute end mills
- Drilling: 100–200 SFM; parabolic flute carbide drills; peck drilling for deep holes
- Delrin may be machined dry for most operations; coolant helps with thin walls and deep holes
- Avoid laser cutting — formaldehyde gas is generated; waterjet preferred for sheet blanking
Residual stress in extruded stock is generally lower than in PEEK or polycarbonate. Pre-annealing is not routinely required for Delrin unless very tight tolerances (±0.0005") are needed in large cross-sections.
Compliance: FDA, NSF, and RoHS
Delrin 150SA and 500SA are DuPont's FDA-compliant grades, meeting 21 CFR 177.2480 for repeated-use food-contact applications. These are natural (off-white) color grades that use only FDA-listed additives. Unfilled, unpigmented Delrin 500 may also meet 21 CFR in many formulations — verify with the current lot documentation.
| Certification | Delrin 150/500 | Delrin 150SA/500SA | Delrin 570 (GF) | Delrin 100AF |
|---|---|---|---|---|
| FDA 21 CFR 177.2480 | Check lot | Yes | No | Check lot |
| NSF 51 / 61 | Check | Check | No | No |
| RoHS | Yes | Yes | Yes | Yes |
| REACH | Compliant | Compliant | Compliant | Compliant |
| UL 94 | HB | HB | HB | HB |
Full compliance guidance is in the Delrin FDA food-grade page.
Delrin vs. Acetal Copolymer: When to Choose Which
The most common specification decision in this material family is Delrin (POM-H) vs. acetal copolymer (POM-C, e.g., Celcon or Hostaform):
| Property | Delrin (POM-H) | Acetal Copolymer (POM-C) |
|---|---|---|
| Tensile strength | ~10,000 psi | ~9,500 psi |
| Fatigue endurance (10⁷ cyc) | ~5,000 psi | ~4,000–4,500 psi |
| Centerline porosity (large rod) | Present above ~3" dia | Essentially absent |
| Hot water resistance (>60°C) | Fair — degrades over time | Better — POM-C copolymer structure resists |
| Hydrolysis resistance | Moderate | Better |
| Creep resistance | Slightly better | Comparable |
| Relative cost | Slightly higher | Slightly lower |
Choose Delrin for: gears, high-cycle fatigue parts, precision machined components where maximum stiffness and fatigue life matter.
Choose acetal copolymer for: hot-water or steam-exposed components, large-diameter rod applications, and applications sensitive to centerline porosity.
For the detailed comparison, see Delrin vs. acetal copolymer.
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