Plastic gear molding is a specialised corner of injection moulding where the part is a motion component, and the tolerances that matter are tooth geometry, bore fit and backlash rather than the overall envelope. A plastic gear that runs quietly in a printer carriage or a car window lift has survived a chain of decisions - resin grade, mould construction, shrinkage compensation and process control - that a general-purpose moulder will not automatically get right. This page covers what Chinese gear moulders produce, the material and tooling choices that decide gear life, and the commercial terms that apply to export orders.
What Plastic Gear Molding Covers
Injection moulded gears span a wide range of sizes and duties:
- Spur and helical gears - module 0.3 to 3.0, the standard range for office equipment, small appliances and actuator drives.
- Worm gears and worm wheels - usually PA or POM wheels paired with steel worms, where the wear pair matters more than the wheel material alone.
- Bevel and sector gears - right-angle drives and partial-rotation positioning, common in automation fixtures.
- Gear packs and clusters - multi-gear single-shot parts that eliminate assembly steps and stack-up error.
Material Selection for Gear Life
The resin choice for a plastic gear is a wear and heat decision before it is a cost decision:
- PA6 and PA66 - tough and wear-resistant with good fatigue behaviour, the standard choice for loaded gears; moisture uptake affects dimensions, so dry-as-moulded conditioning matters.
- POM (acetal) - low friction and excellent dimensional stability, the default for gears running dry against each other or against polymer cams.
- PBT - stiff and stable in humid heat, used in automotive and electrical gear applications.
- POM-PTFE and filled grades - internally lubricated compounds that cut friction and wear in higher-duty meshes.
Where two plastic gears mesh, the usual rule is to pair dissimilar materials - a POM wheel against a PA pinion, for example - because identical polymers can gall. The PA6 versus PA66 guide covers the trade-off in detail.
Tooling and Quality Control
Gear moulds are built to tighter standards than envelope moulds: the tooth form is ground or hobbed into the tool where precision matters, and the toolmaker must compensate shrinkage per tooth flank, not just on the pitch diameter. Quality control follows the gear standard rather than general dimensional practice - ISO 1328 grade 8 to 10 covers most moulded gear work, verified by gear checkers or CMM. Ask for first-article inspection on tooth profile, helix and bore tolerance.
Commercial Terms
Gear programmes run on tooling-plus-piece-price economics: tooling for a single gear typically completes in three to five weeks, and piece prices scale with cavity count and material. MOQs usually start around a thousand pieces per gear, lead times two to four weeks after part approval, and repeat orders are priced against the same tool and resin lot to keep backlash stable. The custom molding category indexes related services, and the China plastic factory directory lists moulders by region and specialism.
