Adhesion starts before coating

Coating performance depends heavily on surface preparation. Degreasing, blasting, activation, dust removal and timing decide whether the coating bonds properly. A premium coating applied over oil, rust, scale or shop contamination will not perform correctly.

For zinc flake, Xylan/PTFE and phosphating, pretreatment is not a cosmetic step. It directly affects corrosion, adhesion and wear behaviour.

Blasting profile and cleanliness

Shot blasting can create profile for adhesion. Glass bead blasting can clean and satin-finish surfaces with lower aggression. The correct process depends on the coating system and substrate.

Too little profile may reduce adhesion. Too much profile can increase coating consumption, roughen the finish or damage dimensions.

Timing after preparation

Freshly blasted steel can flash-rust quickly in humid conditions. Prepared parts should not be left in open humid air for extended periods before coating. Handling should prevent fingerprints, oil transfer and dust pickup.

If parts arrive blasted by the customer, the time gap, storage condition and contamination risk should be disclosed.

Incoming condition matters

Heavy oil, paint, silicone, rubber residue, weld scale, heat tint or old coating may need additional processing. Customers should not assume the standard coating price includes removal of every unknown contaminant.

For repeat jobs, defining incoming condition improves quality and quotation accuracy.

Practical conclusion

Surface preparation is the foundation of coating performance. The coating is only as good as the surface it bonds to.

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.