Why combine a metallic base and PTFE topcoat
A zinc-nickel base coat can provide sacrificial corrosion protection. A Xylan/PTFE topcoat can add low friction, release behaviour, barrier support and assembly control. Combining them can make sense when the part needs more than corrosion protection alone.
The system must be approved as a stack. The base coat, conversion/passivation, surface preparation, topcoat adhesion, curing and total thickness interact.
Corrosion versus chemical resistance
Zinc-nickel is strong for sacrificial corrosion protection on steel, but it is not automatically a chemical-resistant coating for every fluid. Xylan/PTFE can support chemical resistance depending on grade and exposure condition, but chemical suitability must be checked against actual media, temperature and contact duration.
For water vapour, mild chemicals, intermittent splash or release applications, the stack may be considered. For continuous immersion in aggressive chemicals, validation is essential.
Dimensional stack and masking
A zinc-nickel layer plus Xylan/PTFE adds total build-up. Threads, bores, holes, sliding fits and mating faces must be reviewed. The customer should specify areas to coat, areas to mask and surfaces where DFT must be measured.
If the part must assemble with no change in drag or clearance, sample validation is mandatory.
Curing and adhesion
The topcoat requires curing. The substrate and base coating must tolerate the cure schedule. Adhesion depends on surface preparation, cleanliness, roughness and compatible intermediate layers.
Incorrect handling after coating can damage the film. Coated parts should not be bulk-dumped, dragged or packed under high pressure against abrasive surfaces.
Stack-design checklist
| Control point | Why it matters |
|---|---|
| Base coat thickness | Affects corrosion protection and total dimensional build-up. |
| Topcoat DFT | Affects friction, release, barrier behaviour and fitment. |
| Cure schedule | Affects film integrity and substrate suitability. |
| Masking | Prevents coating on threads, sealing areas or close fits where not allowed. |
| Packaging | Prevents abrasion, sticking, compression marks and contamination. |
Practical conclusion
A zinc-nickel plus Xylan/PTFE system is technically strong when both corrosion and functional surface behaviour are required, but it must be engineered as a combined coating stack.
How buyers should use this guide in an RFQ
For a technically complete coating RFQ, the customer should provide the drawing, material, quantity, current surface condition, required coating system, thickness or coating-mass expectation, salt spray target, masking requirement and packaging expectation. For zinc flake, Xylan/PTFE and phosphating work, route selection cannot be separated from geometry, surface preparation and post-coating handling.
If the part has threads, internal drives, blind holes, seal faces, bores or close-tolerance assembly zones, those areas should be marked before sampling. Coating build-up, retained coating, masking witness marks and post-curing handling must be accepted or corrected during sample approval rather than after bulk production.
Common avoidable rejection causes
- Approving corrosion performance without checking actual assembly, torque, thread fitment or bore clearance.
- Using ordinary cardboard or recycled paper directly against zinc-based coatings during humid storage.
- Bulk-packing Xylan/PTFE or zinc flake parts so that sharp edges and threads abrade the coating during transport.
- Leaving freshly blasted steel exposed before coating, causing flash rust or surface contamination.
- Treating salt spray hours as a universal field-life guarantee without considering storage, handling and exposure conditions.
Documentation and approval discipline
For controlled coating work, approval should include coating route, surface preparation method, number of coats, curing condition, measurement method, visual standard and packaging method. If the customer later changes part geometry, incoming condition, dispatch packing, storage duration or fitment requirement, the approved coating route should be revalidated before production continuation.