01How the process works
Steel is degreased, pickled in acid, fluxed and dipped in zinc at about 450 °C. Zinc reacts with the steel to form zinc-iron alloy layers topped by pure zinc. Coating thickness depends on steel thickness and chemistry, especially silicon and phosphorus.
Coating thickness to ISO 1461, uncoated areas, ash and dross inclusions, and distortion of thin parts are the typical checks. Venting and drainage holes must be designed in, or hollow sections can trap air or even explode in the bath.
- Degreasing and pickling. Oil and mill scale removed.
- Fluxing. Flux applied to prevent oxidation.
- Dipping. Immersion in molten zinc.
- Cooling. Air or water quench.
- Inspection. Thickness, appearance, repairs.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Low coating thickness | Steel chemistry, immersion time | Magnetic thickness gauge |
| Bare spots | Poor cleaning, trapped air | Visual |
| Ash and dross inclusions | Bath practice | Visual |
| Excess thickness and brittleness | Reactive steel (Sandelin) | Thickness, adhesion |
| Distortion | Thermal stress | Dimensional check |
| Unauthorised repairs | Large uncoated areas | Visual, records |
03Where an inspector should look
01
Before production
- Venting and drainage design
- Steel chemistry
- Required thickness and repair method
02
During production
- Pickling and flux control
- Bath temperature
03
After production
- Thickness per ISO 1461 sampling
- Visual and repair areas
- Adhesion where required
04Standards and references
ISO 14713 (design for galvanizing), ISO 10684 (galvanized fasteners), ISO 1461 repair limits.
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.
05How we support buyers of galvanizing parts
Coating, Painting and Galvanizing InspectionSurface preparation, paint application, DFT, adhesion and hot-dip galvanizing inspection against the coating specification.
Pre-Shipment InspectionFinal random or complete inspection of finished goods before shipment: quantity, conformity, workmanship, packing and marking.