Some molders told me because a “compatible” grade cracked a mold, released formaldehyde, or missed a cycle time target by 4 seconds. The root cause is almost always the same: someone treated POM melting point as one number, when it is actually two very different numbers with very different processing windows.
This guide gives you the hard data — melting points, drying, melt temperature, mold temperature, cycle rules — for every mainstream acetal grade you can buy in 2026. Use it before you sign a PO, not after the first shot short.
1. POM Melting Point in One Sentence
POM (polyoxymethylene, also called acetal) exists in two chemistries with two distinct melting points:
- Homopolymer POM melts at 175°C (347°F) — narrow window, high crystallinity, higher stiffness.
- Copolymer POM melts at 165°C (329°F) — wider window, better thermal stability above the melt, easier to process.
That 10°C gap is not a rounding error. It changes your drying schedule, barrel setpoint, mold temperature, hot runner selection, and — most importantly — your scrap rate.
2. Why the 10°C Gap Matters to Procurement
As a buyer, I care about melting point because it drives five hard cost lines:
- Energy per kg — Every 10°C higher barrel setpoint adds roughly 3–5% to electricity cost per shot.
- Cycle time — Higher melt point = higher mold temperature = longer cooling. A 175°C homopolymer typically adds 1.5–3 seconds per cycle versus a 165°C copolymer on the same wall thickness.
- Scrap rate — Wrong assumption of 5–10°C on melting point pushes scrap above 3% on precision gears and connectors.
- Tool life — Formaldehyde released above the decomposition threshold corrodes tool steel. Homopolymer decomposes near 220°C; copolymer tolerates 230°C.
- Purge frequency — Copolymer allows 20+ minutes of residence at 210°C; homopolymer forces a purge every 6 minutes if the machine stops.
None of this is on the front page of a datasheet. All of it hits your unit cost.
3. Homopolymer vs Copolymer — Side-by-Side Data
- Melting Point — Homopolymer 173–178°C / Copolymer 162–168°C.
- Typical Melt Temperature (Barrel) — Homopolymer 210–230°C / Copolymer 190–220°C.
- Mold Temperature — Homopolymer 80–105°C / Copolymer 60–90°C.
- Crystallinity — Homopolymer 75–80% / Copolymer ~70%.
- Glass Transition (Tg) — Both −60°C (−76°F).
- Decomposition Onset — Homopolymer ~220°C / Copolymer ~230°C.
- Max Residence Time in Barrel — Homopolymer ≤6 min at 220°C / Copolymer ≤20 min at 210°C.
- Shrinkage — Homopolymer 2.0–2.5% / Copolymer 1.8–2.2%.
Read the shrinkage line twice. If a mold was cut for copolymer and you switch to homopolymer, expect a 0.3–0.5% dimensional shift. That is enough to fail a gear tolerance stack.
4. Grade-by-Grade Melting Point Reference Table — Suke Plastics Portfolio
At Suke Plastics we mainly supply three copolymer POM lines: Yuntianhua® / Yuncon® (Yuntianhua), FORMOCON® (Formosa FPC), and DURACON® (Polyplastics). All grades below are copolymer POM with a nominal melting point of 165°C (329°F). Glass-fiber and lubricant-modified grades share the same melting point but shift the recommended melt/mold window and HDT.
| Type | Grade No. | Manufacturer | Brand | Melting Point | Melt Temp (Barrel) | Mold Temp | Grade / Features | Typical Applications |
|---|---|---|---|---|---|---|---|---|
| Copolymer | M25 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | High-impact, high-elongation, increased molecular weight | Extruded rods, extruded sheets, roller conveyor parts |
| Copolymer | M270 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–85 °C | High-flow, minimized mold deposit | Lighters, aerosol bottles, fasteners |
| Copolymer (PTFE-filled) | SF-5 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | ~5% PTFE, improved friction & abrasion coefficient | Gears, rollers, sliders in low/no-oil environments |
| Copolymer (PTFE-filled) | SF-10 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | ~10% PTFE, further improved friction & abrasion | Gears, rollers, sliders in low/no-oil environments |
| Copolymer (Impact-modified) | ST-10 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Elastomer-modified, higher impact & fatigue resistance vs M90 | Spoiler clip, bumper clip, mudguard clip, gear, sleeve, gasket |
| Copolymer (Impact-modified) | ST-20 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Elastomer-modified, higher toughness, wear & chemical resistance | Spoiler clip, bumper clip, mudguard clip, gear, sleeve, gasket |
| Copolymer (GF-reinforced) | GF-10 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 200–220 °C | 80–100 °C | ~10% glass fiber, HDT up to 150 °C, higher stiffness & creep resistance | Oil box cover, radiator cover, valve, gear, bearing, cam, accelerator pedal, impeller |
| Copolymer (GF-reinforced) | GF-20 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 200–220 °C | 80–100 °C | ~20% glass fiber, HDT up to 160 °C | Oil box cover, radiator cover, valve, gear, bearing, cam, accelerator pedal, impeller |
| Copolymer (GF-reinforced) | GF-25 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 200–220 °C | 80–100 °C | ~25% glass fiber, HDT up to 160 °C, top-end stiffness | Oil box cover, radiator cover, valve, gear, bearing, cam, accelerator pedal, impeller |
| Copolymer (Lubricated) | EF | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Special lubricant, low friction & noise, for high-speed/high-load | Gears, rollers, sliders in low/no-oil environments |
| Copolymer (Lubricated) | FP | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Special lubricant, noise-resistant, high-speed/high-load | Gears, rollers, sliders in low/no-oil environments |
| Copolymer (PTFE-filled) | MD-1 | Yuntianhua | Yuntianhua® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | ~10% PTFE, improved friction & abrasion coefficient | Gears, rollers, sliders in low/no-oil environments |
| Copolymer | M90 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, minimized mold deposit | Automotive electronics, fittings, thin-wall parts, gears, valves, wheels, bearings, pump parts |
| Copolymer | GM90 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, minimized mold deposit | Automotive electronics, fittings, gears, valves, wheels, bearings, pump parts |
| Copolymer | CM90 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, high hardness & stiffness | Automotive electronics, gears, valves, wheels, bearings, pump parts |
| Copolymer | M90-01 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, minimized mold deposit | Automotive electronics, fittings, gears, valves, wheels, bearings |
| Copolymer | M120 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–85 °C | Higher flow, minimized mold deposit | Automotive exterior parts, thin-wall parts, gears, wheels |
| Copolymer | M350 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–205 °C | 60–85 °C | Super high-flow, minimized mold deposit | Lighters, aerosol bottles, fasteners |
| Copolymer | M450 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–205 °C | 60–85 °C | Super high-flow, minimized mold deposit | Lighters, aerosol bottles, fasteners |
| Copolymer | CN90 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, high hardness & stiffness | Automotive electronics, gears, valves, wheels, bearings, pump parts |
| Copolymer | N120 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–85 °C | Higher flow, high hardness & stiffness | Automotive exterior parts, thin-wall parts, gears, wheels |
| Copolymer | N25 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | High-impact, high-elongation, increased molecular weight | Extruded rods, extruded sheets, roller conveyor parts |
| Copolymer | N270 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–85 °C | High-flow, minimized mold deposit | Lighters, aerosol bottles, fasteners |
| Copolymer | N350 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–205 °C | 60–85 °C | Super high-flow, minimized mold deposit | Lighters, aerosol bottles, fasteners |
| Copolymer | N450 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–205 °C | 60–85 °C | Super high-flow, minimized mold deposit | Lighters, aerosol bottles, fasteners |
| Copolymer | N90 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, minimized mold deposit | Automotive electronics, fittings, gears, valves, wheels, bearings, pump parts |
| Copolymer | N90-01 | Yuntianhua | Yuncon® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, minimized mold deposit | Automotive electronics, fittings, gears, valves, wheels, bearings |
| Copolymer | FM025 | Formosa (FPC) | FORMOCON® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | High-viscosity, minimal mold deposit, extrusion grade | Extruded rods and sheets, other extrusion parts |
| Copolymer | R6 | Formosa (FPC) | FORMOCON® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, high toughness, minimal mold deposit | Buttons, press-in fasteners, plumbing, gears, electronic & automotive parts, bearings |
| Copolymer | FM090 | Formosa (FPC) | FORMOCON® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, minimal mold deposit | Buttons, press-in fasteners, plumbing, gears, electronic & automotive parts, bearings |
| Copolymer | FM130 | Formosa (FPC) | FORMOCON® | 165 °C / 329 °F | 190–210 °C | 60–85 °C | Medium-flow, minimal mold deposit | Buttons, press-in fasteners, plumbing, gears, electronic & automotive parts, bearings |
| Copolymer | FM270 | Formosa (FPC) | FORMOCON® | 165 °C / 329 °F | 190–210 °C | 60–85 °C | High-flow, minimal mold deposit | Press-in fasteners, zippers, gears, electronic & automotive parts, small mechanical parts |
| Copolymer | FM450 | Formosa (FPC) | FORMOCON® | 165 °C / 329 °F | 190–205 °C | 60–85 °C | Super high-flow, minimal mold deposit | Press-in fasteners, zippers, gears, electronic & automotive parts, small mechanical parts |
| Copolymer (UV-stabilized) | FM090UV | Formosa (FPC) | FORMOCON® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, weather resistant | Outdoor buttons, plumbing hardware, automotive exterior parts |
| Copolymer | FM090LMD | Formosa (FPC) | FORMOCON® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard-flow, low mold deposit (LMD) | Buttons, press-in fasteners, plumbing, gears, electronic & automotive parts, bearings |
| Copolymer | M90-44 | Polyplastics | DURACON® | 165 °C / 329 °F | 190–210 °C | 60–90 °C | Standard copolymer, ideal for wear-resistant parts such as gears | Gears, bearings, precision mechanical parts |
5. Processing Guide — Drying, Melt, Mold, Cycle
5.1 Drying
POM is not strongly hygroscopic, but surface moisture still causes splay and silver streaks.
- Homopolymer — 80°C for 3 hours in a desiccant dryer, target moisture <0.1%.
- Copolymer — 80°C for 3 hours, target moisture <0.2%.
- Never dry POM above 100°C. Above 100°C, surface oxidation begins and formaldehyde release starts before molding.
5.2 Barrel (Melt) Temperature Profile
Set the barrel in three zones, ascending from feed to nozzle:
- Homopolymer 175°C grade — Feed 180°C → Middle 210°C → Front/Nozzle 220°C. Never exceed 230°C.
- Copolymer 165°C grade — Feed 170°C → Middle 195°C → Front/Nozzle 210°C. Never exceed 230°C.
- Screw speed — 60–120 rpm. Higher shear pushes actual melt temperature above the setpoint by 10–20°C.
5.3 Mold Temperature
- Homopolymer — 80–105°C. Below 80°C, crystallization is incomplete and dimensions drift over 24–48 hours.
- Copolymer — 60–90°C. For high-gloss surface parts, run at 90°C.
- For gears and precision parts, run at the upper end of the range. Full crystallinity locks tolerance.
5.4 Cycle Time & Residence
- Homopolymer — Barrel residence must stay under 6 minutes at 220°C. Any stop over 3 minutes: drop barrel to 180°C or purge with PE.
- Copolymer — Tolerates 20 minutes at 210°C without darkening. Still, purge before shift end.
- Never mix homopolymer and copolymer regrind. Different melting points create unmelted particles that cause black specks and gate freeze-off.
6. Common Defects Tied to Melting Point Errors
Every one of these has landed on my desk as a customer complaint. All are traceable to melting-point handling:
- Black specks / brown streaks — Barrel above 230°C, residence too long, formaldehyde carbonizing. Fix: drop 15°C, purge with PE.
- Silver streaks / splay — Moisture above 0.2%. Fix: verify dryer at 80°C for full 3 hours.
- Short shots on thin walls (<1 mm) — Melt too cold on homopolymer. Fix: raise nozzle to 220–225°C, raise mold to 100°C.
- Warpage on flat parts — Mold too cold, crystallization incomplete. Fix: raise mold temperature 15–20°C.
- Dimensional drift 24 h after molding — Under-crystallized copolymer. Fix: raise mold from 60°C to 85°C, or add 30-minute annealing at 120°C.
- Formaldehyde odor at machine — Melt above decomposition threshold. Immediately drop 10–15°C and ventilate.
7. Procurement Decision Checklist
Before you approve a POM PO, verify these six items against the supplier datasheet:
- Melting point stated as a specific number (e.g., 165°C), not a range like “160–170°C” without a test method.
- Test method listed — ISO 3146 or ASTM D3418 (DSC) is the acceptable standard.
- Melt flow rate (MFR) at a defined condition (190°C / 2.16 kg for POM).
- Density — Homopolymer 1.42 g/cm³ / Copolymer 1.41 g/cm³.
- Formaldehyde emission compliance if the part is for automotive interior or medical use.
- Regrind ratio the supplier assumes — some Chinese copolymer grades quote MFR at 30% regrind, which is not comparable to virgin data from BASF or Celanese.
If any of the six is missing, ask for a corrected datasheet before signing.
8. FAQ
Q1. What is the melting point of acetal?
Acetal is the common name for POM. Homopolymer acetal melts at 175°C (347°F); copolymer acetal melts at 165°C (329°F).
Q2. Is POM the same as Delrin?
No. Delrin® is Celanese’s (formerly DuPont’s) brand of homopolymer POM. It melts at 175–178°C. Copolymer POM sold under Celcon®, Hostaform®, Duracon®, or Ultraform® melts at 165–166°C.
Q3. Can I run POM at 250°C?
No. Above 230°C, both homopolymer and copolymer POM decompose and release formaldehyde. This corrodes tool steel and creates a workplace hazard.
Q4. Why does my POM part shrink days after molding?
Under-crystallized copolymer continues to crystallize at room temperature. Raise mold temperature to 85–90°C or anneal at 120°C for 30 minutes.
Q5. Can homopolymer and copolymer POM regrind be mixed?
Never. The 10°C melting point gap creates unmelted particles, gate freeze-off, and inconsistent shrinkage.
9. Bottom Line for Buyers
POM melting point is a two-number decision, not a one-number spec. Homopolymer at 175°C gives you stiffness and fatigue strength — with a narrow processing window and higher energy cost. Copolymer at 165°C gives you a wider window, longer residence tolerance, and better alkaline resistance — at a small trade-off in stiffness.
Match the melting point to your mold, your machine, and your cycle target before you place the PO. The 10°C difference between 165°C and 175°C is where scrap rates live.
