POM Acetal Resin Supplier China | Homopolymer & Copolymer

Choosing between acetal homopolymer and copolymer

The two branches share the same oxymethylene backbone but differ in how the chain is terminated, and that shows up in the moulded part. Choose from the media and the section thickness, not from the headline strength on the datasheet.

Decision point	Homopolymer	Copolymer
Stiffness, creep	Higher crystallinity	Slightly lower
Thick sections	Centreline porosity risk	More forgiving
Hot water, alkali	Weaker long-term	Better long-term
Processing window	Narrower	Wider
Special grades	Fewer	Widest

Specifications to put in your RFQ

Branch — homopolymer or copolymer, and the reason for choosing it
Wear duty — speed, load, counterface; ask for the test method behind "lubricated"
Media — fuels, oils, coolants, cleaning agents, hot water, at temperature
Dimensions — which features are fit-critical, and the measurement temperature
Colour and UV — outdoor parts need a stabilised grade and a colour standard
Flammability — UL 94 rating at your thinnest wall, not the generic grade

Documents and compliance to request

Lot Certificate of Analysis with melt flow and moisture at delivery
Technical Data Sheet for the exact grade code, giving drying and melt limits
Food-contact declaration against EU 10/2011 or FDA 21 CFR, as your market requires
Potable-water approval — name the scheme (WRAS, KTW or NSF-type), not "drinking water safe"
REACH SVHC and RoHS statements plus SDS, and an IMDS entry for automotive supply
Toy or electrical declarations where relevant — EN 71-3 limits for toys

Moulding acetal: shrinkage, degradation and the mistakes that cost parts

Overheating the melt. Acetal unzips to formaldehyde when it is overheated or held too long. Agree melt and residence limits, and ask how the moulder purges.
Ignoring post-mould shrinkage. Acetal keeps shrinking after ejection, so measure fit-critical features after conditioning and plan a correction loop — see the tolerance guide.
Assuming it replaces metal one-to-one. Wall sections and ribs carry the load; redesign for polymer stiffness to make the switch pay, and settle who owns the mould before funding tooling.
Finishing away porosity. Centreline voids in thick homopolymer sections are a section-design fault, not a finishing one — core out the mass or move to copolymer.
Overlooking the media. Strong acids, oxidisers and chlorinated cleaners attack acetal; test the real fluid at temperature.
Leaving UV and fire behaviour to chance. Unstabilised acetal chalks outdoors and flame-retardant options are limited, so specify both up front.

Frequently Asked Questions

Homopolymer or copolymer — which should I buy?

Copolymer for hot water, alkaline media and thick sections; homopolymer where you need the last increment of stiffness and can keep sections thin. Confirm against the grade datasheet, not the trade name.

Can acetal really replace a machined brass or steel part?

Often yes — gears, bushings, fasteners and pump parts are exactly what it was developed for — but design for polymer stiffness and creep, and re-check fit after conditioning. The unfilled copolymer guide covers the precision case.

Why do some acetal parts smell of formaldehyde?

Thermal or oxidative degradation, usually from overheating, long residence or dead spots in the tool. Agree melt and residence limits, or specify a low-emission grade.

Is every acetal grade food-contact or drinking-water approved?

No. Only specific grades carry the file; general-purpose acetal is not approved by default. Ask for the declaration against EU 10/2011 or FDA 21 CFR, name your water scheme, and check the checklist in our food-contact acetal guide.

When should I move off acetal altogether?

Sustained high temperature, strong acids or oxidising media, heavy sliding duty, or outdoor UV. Compare acetal versus nylon or acetal versus PTFE for wear, and PPS or PEEK for heat.