Manufacturing Process
Surface Treatment
表面处理
Protective or cosmetic finishing such as plating, passivation, anodizing, powder coating or painting.
Process Steps
- Surface cleaned
- Treatment applied
- Cure/dry
- Appearance and adhesion check
What surface treatment is for
Direct answer: surface treatment changes the surface of a part without changing its shape — to resist corrosion, to look right, to resist wear, to conduct or insulate, or to be solderable or paintable. On a stamped part it is usually the last operation before inspection.
The finishes we quote most
| Finish | What it gives | Typical thickness |
|---|---|---|
| Zinc plating (barrel or rack) | Cost-effective corrosion protection; clear, blue, yellow or black passivate | 5–12 µm |
| Zinc-nickel | Much higher corrosion resistance, good for under-bonnet parts | 5–10 µm |
| Nickel plating | Hard, decorative, solderable, good wear resistance | 5–25 µm |
| Phosphating | Absorbs oil, aids break-in and paint adhesion | 2–10 µm |
| Passivation (stainless) | Removes free iron and restores the passive layer | Chemical, no build-up |
| Anodising (aluminium) | Hard, insulating, dyeable | 5–25 µm |
| Powder coat / paint | Appearance and outdoor durability | 60–120 µm |
Barrel or rack plating — the decision that changes the price
Barrel plating tumbles the parts in a rotating drum and is by far the cheapest way to coat small parts. The trade is contact marks: parts that touch each other in the barrel can be dented or left with bare patches, and thin cosmetic parts show it.
Rack plating fixes each part on a jig, so every surface is exposed and the finish is even. It costs more per piece, and on cosmetic parts it is usually paired with packaging that protects the finish in transit.
The practical question is not which process is better but what the part has to look like when the customer opens the box. See quality & certifications for how this is controlled.
Tolerance effects to plan for
- Plating adds thickness on every surface. A thread that gauges before plating may fail after it, and a press fit grows. Specify whether the dimension applies before or after coating.
- Sharp edges plate thicker. Burrs form nodules and later flake, which is why deburring comes before plating, not after.
- Hydrogen embrittlement. High-strength steel that has been pickled or electroplated needs a documented bake; it is a real requirement, not a formality.
- Not every finish suits every substrate. Aluminium does not take zinc plating; stainless is normally passivated rather than plated.
Corrosion performance in numbers
Salt-spray hours are the usual shorthand: a clear trivalent zinc passivate is typically specified around 96 hours, a yellow or black passivate more, and zinc-nickel runs into several hundred hours and beyond. The number is meaningless without the layer thickness and the test standard, so the drawing should quote both. Balford runs salt-spray testing in-house for ongoing verification.
Frequently asked
Which plating should I specify for a stamped steel part?
Trivalent zinc with a clear or coloured passivate covers most indoor and moderate outdoor use. For under-bonnet, marine or long-life applications, zinc-nickel is the usual step up. The right answer depends on the corrosion hours the customer requires.
Will plating change my dimensions?
Yes, by the coating thickness on every surface. Two platings of 8 µm put 16 µm on a diameter. Threads and press fits are where this actually causes a problem, so state whether the tolerance applies before or after plating.
Why are there marks on my barrel-plated parts?
Parts touch each other in the barrel. Where the appearance matters, rack plating is the answer; where it does not, barrel plating saves money.
Is your plating RoHS compliant?
Yes — trivalent chromium passivates, no hexavalent chromium. Material compliance documentation including RoHS and REACH declarations, and IMDS data for automotive part numbers, is available with the delivery.
Related: deburring · heat treatment · quality & certifications · CNC turning · deep drawing