Quick answer for engineers and procurement teams: Delrin is DuPont’s registered brand name for acetal homopolymer (POM-H). When a drawing specifies “acetal” without qualification, suppliers may supply either homopolymer or copolymer (POM-C) — and the two behave differently enough to cause field failures. For tight-tolerance CNC gears, high-cycle fatigue applications, and parts requiring the best surface finish out of the machine — choose Delrin homopolymer. For applications involving hot water, acidic environments, or large-diameter turned parts where centerline porosity would be a problem — choose acetal copolymer.
This guide is written for engineers who need to specify the right material on the PO, not just understand the chemistry. We draw on machining data from over 500 industrial acetal parts produced at our facility, across both grades and three manufacturing processes.
Material Basics: Homopolymer vs Copolymer — What Changes on the Shop Floor
Both grades belong to the polyoxymethylene (POM) family, but their molecular structure differs at a level that affects every downstream process:
- Delrin (POM-H): Uniform repeating -CH2O- units. Higher crystallinity (~75-85%) means harder, stiffer, better fatigue resistance — but also higher residual stress after machining.
- Acetal Copolymer (POM-C): Contains occasional -CH2CH2O- co-monomer units that interrupt crystallinity. This reduces stiffness slightly but dramatically improves chemical resistance and dimensional stability after machining.
Head-to-Head Property Comparison
| 속성 | Delrin (POM-H) | Acetal Copolymer (POM-C) | 그것이 중요한 이유 |
|---|---|---|---|
| 인장 강도(MPa) | 70-83 | 60-69 | Delrin handles ~20% higher static load before yield |
| 굴곡 탄성률(GPa) | 2.8-3.1 | 2.4-2.8 | Stiffer feel — critical for snap-fit retention force |
| Fatigue Endurance @10&sup6; cycles (MPa) | 35 | 28 | Key differentiator for gears and springs |
| Izod Impact, Notched (J/m @23°C) | 69-122 | 53-163 | Copolymer has wider range; grade selection matters |
| Water Absorption, 24h (%) | 0.25 | 0.22 | Similar at room temp; diverges above 60°C |
| Continuous Service Temp, Max (°C) | 90-100 | 100-110 | Copolymer wins for hot environments |
| Creep Strain after 1000h @23°C, 10MPa (%) | ~0.5 | ~0.8 | Delrin holds dimension better under constant load |
| Coefficient of Friction (dry vs steel) | 0.2-0.35 | 0.25-0.40 | Delrin is slightly more slippery — better for bearings |
Design Rules for Delrin and Acetal Parts
These rules come directly from our CNC machining cell and apply equally to prototype quantities and production runs. Adapt them for molding by adding draft angles (1-2° minimum for both materials).
Design Rules for Acetal Parts (from the Shop Floor)
Based on machining data from 500+ industrial acetal parts produced at our facility (Q1 2026). Apply these directly in your CAD drawings.
| 매개변수 | Delrin (POM-H) | Acetal Copolymer (POM-C) |
|---|---|---|
| Minimum wall thickness | 1.0 mm | 0.8 mm |
| Recommended corner radius | R ≥ 0.5 mm | R ≥ 0.3 mm |
| Hole diameter tolerance (CNC) | ±0.025 mm | ±0.05 mm |
| Maximum aspect ratio (depth/dia) | 6:1 | 5:1 |
| Surface finish as-machined (Ra) | 0.8 μm | 1.2 μm |
| Post-machining warpage risk | Moderate (stress relief recommended) | Low (better dimensional stability) |
These values assume standard machining conditions at 20°C, sharp carbide tooling, and dry cutting. For injection molding design rules, refer to our engineering team consultation.
Why Centerline Porosity Changes Part Design
One of the least-discussed differences between the two materials is centerline porosity in Delrin extruded rod. As the rod diameter increases beyond 40 mm, POM-H extrusion typically develops a porous center core (0.5-2 mm diameter) due to shrinkage during cooling. If your part design places a critical sealing surface or tight-tolerance bore on the rod centerline, this porosity causes leaks or out-of-spec bores. Copolymer does not have this problem — the co-monomer disrupts crystallization enough to eliminate centerline voids.
Practical rule: If your part has a through-hole or sealing surface passing through the rod center and the rod diameter exceeds 40 mm, specify acetal copolymer. One customer saved 18% on a returned batch for a water valve component by making this single material switch.
Industry Applications: Where Each Grade Wins
| 산업 | 일반적인 부품 | Preferred Grade | Selection Rationale |
|---|---|---|---|
| 자동차 | Fuel system valves, seat belt components, window regulator gears | Delrin (POM-H) | Higher fatigue strength for 100k+ cycle durability; low fuel permeability |
| 의료 기기 | Inhaler mechanisms, insulin pen bodies, surgical instrument handles | Acetal Copolymer (POM-C) | Better resistance to sterilization chemicals; lower extractables |
| 산업 기계 | Conveyor rollers, bearing cages, pump impellers, wear strips | Delrin (POM-H) | Superior wear resistance and low friction (self-lubricating); higher hardness |
| 소비자 가전 | Keyboard mechanisms, printer gears, camera lens barrels | Acetal Copolymer (POM-C) | Better hot water resistance for dishwasher-safe applications; lower creep under constant spring load |
| Plumbing & Fluid Handling | Valve seats, shower mixer components, water meter internals | Acetal Copolymer (POM-C) | Lower hot water swelling; avoids centerline porosity issues that can cause leaks in POM-H |
| Food Processing | Filling nozzles, conveyor guides, cutting board liners | Both (FDA-compliant grades) | Use homopolymer for dry-contact apps; copolymer for wet/hot-contact per NSF 51 |
The pattern is clear: Delrin dominates in dynamic mechanical applications (gears, bearings, springs) where fatigue life and low friction are primary requirements. Acetal copolymer dominates in applications involving fluids, chemicals, or sterilization — and anywhere the part geometry makes centerline porosity risky.
Tolerance Comparison by Manufacturing Process
The achievable tolerance depends as much on the manufacturing process as the material choice. Below is a practical reference for engineers writing drawing callouts.
| Manufacturing Process | Delrin (POM-H) Tolerance | Acetal Copolymer (POM-C) Tolerance | 최상의 대상 |
|---|---|---|---|
| CNC 가공 | ±0.025 mm | ±0.05 mm | Prototypes, low-mid volume (<1,000 pcs), tight-tolerance parts |
| 사출 성형 | ±0.10 mm | ±0.08 mm | High volume (>5,000 pcs); copolymer molds more consistently |
| 3D Printing (FDM) | ±0.20 mm | ±0.15 mm | Rapid prototypes only; not recommended for functional testing |
Tolerances are achievable under standard shop conditions. Tighter tolerances available on request with additional process controls.
Note that copolymer’s lower post-machining stress relaxation gives it a slight tolerance advantage in injection molding — the part comes out of the mold closer to its final dimensions and drifts less over the first 72 hours.
Cost Decision Framework: When to Pay for Delrin
Cost Decision Framework: Delrin vs Acetal Copolymer
Material cost is only ~15-20% of total part cost for machined components. The real difference is in process efficiency and rejection rate:
- Raw material price: Delrin rod is typically 10-15% more expensive than generic acetal copolymer rod at the same diameter.
- Machining time: Delrin cuts cleaner and faster — expect 8-12% shorter cycle time per part vs. copolymer at equivalent tolerance.
- Rejection rate (internal data): Copolymer parts have higher visual defects (center porosity streaks) — 3-5% rejection vs. ~1% for Delrin in CNC turning operations.
- Break-even point: If your annual volume exceeds 2,000 parts, the reduced rejection rate of Delrin offsets the raw material premium. Below 2,000, generic copolymer is more cost-effective.
- Hidden cost: Copolymer proposed for dimensional-critical assemblies may accumulate 1-2% scrap from dimensional drift post-machining due to residual stress release over the first 72 hours.
The cost decision often comes down to a simple question: “What happens if this part fails?” For non-critical cosmetic or spacing components, copolymer saves money. For load-bearing, safety-critical, or high-cycle components, the Delrin premium pays for itself in reduced field returns.
Common Defects and How to Fix Them
When an acetal part fails or is rejected at incoming QC, the root cause is often a material mismatch. Here are the four most frequent issues we see when customers bring parts to us for rework:
| Problem | Likely Material Cause | Fix |
|---|---|---|
| Gear tooth wear after < 50k cycles | Copolymer used where homopolymer needed (28 MPa vs 35 MPa fatigue limit) | Switch to Delrin 100 or 150 grade for gears; add PTFE-filled grade (Delrin 500AF) if unlubricated |
| Surface cracking after 6+ months in service | Environmental stress cracking from acidic environment (common in POM-H) | Switch to POM-C; verify chemical compatibility with your process fluid |
| Dimensional growth in hot water application | POM-H absorbs more water at elevated temperature (~0.8% at 80°C) | Use POM-C (0.6% absorption); pre-condition parts by soaking in 60°C water for 24h before final QC |
| Porosity visible on turned surfaces | Centerline porosity — inherent to POM-H extrusion process | Specify POM-C for parts with large turned diameters (>50 mm); request “low-porosity” grade from supplier |
Specifying Acetal Correctly on Your Purchase Order
Avoid the most common procurement mistake: writing “Acetal” on the PO without specifying the grade. A correctly specified PO should include:
- Material family and type: “Acetal Homopolymer (Delrin 150)” or “Acetal Copolymer (equivalent to Celcon M90)”
- Form: “Extruded rod, diameter 50 mm” or “Injection molding pellets”
- Tolerance requirement: “Per ISO 2768-m” or specific callout
- Any special grade requirements: “FDA-compliant,” “UV-stabilized (Delrin 527),” “PTFE-filled (Delrin 500AF)”
This level of specificity prevents the supplier from substituting copolymer for homopolymer when the drawing only says “acetal” — a practice that is more common than most engineers realize.
결론 및 권고 사항
The Delrin vs acetal decision is not about which material is “better” — it is about matching the right grade to the right application. Use Delrin homopolymer for dynamic mechanical parts where fatigue life, surface finish, and low friction are critical. Use acetal copolymer for fluid-contact applications, hot or chemically aggressive environments, and large-diameter turned parts where centerline porosity is a risk.
Still unsure which grade fits your design? Our engineering team reviews material selection as part of every quote. Send your drawing or 3D file and we will recommend the optimal grade for your application at no charge.
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관련 기사
자주 묻는 질문
기존 기어 설계에서 치수를 변경하지 않고 델린(Delrin)을 아세탈 공중합체로 대체할 수 있을까요?
Yes, with caveats. Copolymer has approximately 20% lower fatigue endurance (28 MPa vs 35 MPa at 10&sup6; cycles) and slightly higher creep under constant load. For static-load gears operating under moderate torque and thin walls, direct substitution works. For high-cycle dynamic-load gears or non-lubricated bearing sleeves, expect up to 30 microns of additional radial play after the first month of operation. Dimensionally, identical tooling can be used — but if switching from homopolymer to copolymer, consider increasing wall thickness by 8-10% to compensate for lower stiffness.
CNC 가공된 델린 부품이 선반에 일주일 동안 놓여 있다가 왜 뒤틀리는 걸까요?
이는 잔류 응력 해방 현상으로, 아세탈 단일중합체의 잘 알려진 특성입니다. 압출 과정에서 봉의 외부 표면이 중심부보다 빠르게 냉각되어 응력 구배가 발생합니다. 재료를 비대칭적으로 가공하면, 이러한 응력 불균형으로 인해 24~72시간 이내에 뒤틀림 현상이 발생합니다. 세 가지 해결책: (1) 먼저 거친 가공을 한 후, 부품을 24시간 동안 방치한 다음 정밀 가공을 수행합니다; (2) 가공 전에 두께 25mm당 1시간씩 160°C에서 봉을 어닐링합니다; (3) 비대칭적인 재료 제거가 많이 필요한 부품의 경우 아세탈 공중합체로 재질을 변경합니다. 평탄도나 원통도가 0.05 mm 이내로 유지되어야 하는 델린(Delrin) 부품의 경우, 일반적으로 어닐링 처리를 권장합니다.
뜨거운 물이나 증기 환경에서 어느 등급이 더 우수한 성능을 보이나요?
아세탈 공중합체(POM-C)는 60°C 이상의 뜨거운 물에서 델린(POM-H)보다 우수한 성능을 보입니다. 공중합체는 고온에서 수분 흡수율이 더 낮으며(80°C에서 ~0.6% 대 ~0.8%), 팽윤이 적고, 물에 의한 고분자 사슬의 화학적 분해인 가수분해에 대한 내성이 현저히 뛰어납니다. 샤워 믹서 부품, 식기세척기 부품 또는 커피 머신 내부 부품과 같은 용도에는 공중합체가 표준으로 선택됩니다. 해당 용도에 FDA 규정 준수가 필요한 경우, Celcon M25 또는 이에 상응하는 식품 등급 공중합체를 지정하십시오.
델린 및 아세탈 공중합체 부품에는 어떤 표면 마감 처리가 가능한가요?
가공 후 상태의 델린(Delrin)은 최상의 자연 마감 처리 효과를 보여줍니다(5,000~8,000 RPM에서 날카로운 초경 공구를 사용하여 Ra 0.8 μm). 가공 직후의 아세탈 공중합체는 일반적으로 Ra 1.0~1.2 μm를 나타냅니다. 두 재료 모두 표면 에너지가 낮아 도장이나 도금 처리가 잘 되지 않습니다. 비드 블라스팅은 두 재료 모두에 균일한 무광 마감(Ra 2.0~3.0 μm)을 제공하며, 가장 일반적인 2차 마감 처리 방법입니다. 광택 있는 외관을 얻기 위해서는 두 등급 모두 화염 연마가 가능하지만, 표면 용융을 방지하기 위해 세심한 온도 제어가 필요합니다. 두 소재 모두 아세탈을 부식시키는 용매가 사용되므로, 아크릴에 흔히 사용되는 증기 연마는 피해야 합니다.
