Packaging is part of coating performance
Zinc flake, Xylan/PTFE, phosphated, passivated and blasted parts can be damaged after correct processing if packaging and storage are poor. Coated parts are vulnerable to abrasion, compression, sticking, trapped moisture and chemical contamination. Blasted uncoated surfaces can flash-rust quickly if left exposed in humid conditions.
The coating supplier and job worker can control the process up to dispatch. Customer-side repacking, storage duration, warehouse humidity and line-side handling strongly influence the final condition at assembly.
Cardboard, glue and alkaline residues
Zinc-based coatings are particularly sensitive to unsuitable packaging materials. Ordinary cardboard can trap moisture against the surface. Some boards, recycled paper, adhesive systems or glue residues can be alkaline; alkaline contamination including sodium hydroxide-type residues can attack zinc-based coatings.
Direct cardboard contact should be avoided for zinc flake and zinc-plated/zinc-nickel coated parts where storage is long, humid or quality-critical. Use clean inner poly liners, VCI packaging, neutral interleaving, plastic crates or validated export packaging.
Abrasion and compression damage
Xylan/PTFE and other functional topcoats can be scratched or compressed by hard stacking. Sharp threads, edges and heavy parts can mark the coating during transport. Bulk dumping can destroy a good coated finish even before the customer opens the box.
Parts should be cooled, separated and packed at manageable weights. Delicate coated components should use trays, dividers, sleeves or layer separation.
Moisture and storage duration
Sealing warm or wet parts can cause condensation. Condensation trapped in threaded parts, washers, blind holes or nested clips can create white corrosion, staining or film damage. Long storage during monsoon conditions requires additional controls.
Use desiccants, VCI, moisture barrier liners and elevated pallet storage for long-distance or long-duration storage. Avoid placing parts near acids, alkalis, chemical vapours, wet floors or outdoor doors.
Customer receiving checklist
- Inspect packaging condition at receipt and record any wet, crushed or torn cartons.
- Move finished parts to dry storage immediately; do not keep them in loading areas during monsoon.
- Do not repack coated parts directly into untreated cardboard or used chemical cartons.
- Use gloves for appearance-sensitive and passivated surfaces.
- Avoid mixing finished parts with rusty, oily, wet or unprocessed components.
- Use FIFO and inspect long-stored zinc-based parts before line issue.
Packaging recommendations by finish
| Finish type | Main risk | Recommended care |
|---|---|---|
| Zinc flake | Moisture, alkaline cardboard contact, thread/recess retention, abrasion. | Dry/cool before packing, avoid direct cardboard, use VCI/desiccant, prevent bulk abrasion. |
| Xylan/PTFE | Scratching, compression, sticking, contamination. | Use dividers/trays, avoid hard stacking, pack after cooling, prevent rubbing. |
| Manganese phosphate | Uneven oil marks, moisture corrosion if dry/unsealed. | Drain/dry/oil as specified, avoid wet dense packing. |
| Blasted steel | Flash rust before coating or dispatch. | Minimize delay, keep dry, coat quickly or protect. |
| Passivated stainless | Recontamination from iron, chlorides or dirty packaging. | Use clean handling, separate from carbon steel, dry neutral packing. |
Practical conclusion
A coating that passes inspection can still fail in the box. Packaging material, humidity, cooling, separation and customer storage must match the finish sensitivity.
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.