01How the process works
Coating material in powder or wire form is melted by flame, arc, plasma or a high velocity oxy-fuel (HVOF) jet and sprayed onto a blasted surface, building up layer by layer. Thermally sprayed zinc and aluminium protect structures; carbides protect against wear.
Bond strength, porosity, oxide content and thickness define coating quality and are verified on coupons sprayed alongside parts, plus thickness and visual checks on the parts themselves.
- Masking and blasting. Surface roughened, masked.
- Preheat. Substrate brought to temperature.
- Spraying. Passes deposit the coating.
- Finishing. Grinding or sealing.
- Testing. Coupons, thickness, visual.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Low bond strength | Surface preparation | Tensile bond test on coupons |
| High porosity | Parameters, spray distance | Metallography |
| Cracking and spalling | Thickness, thermal stress | Visual, PT |
| Thickness variation | Manipulation | Gauge, micrometer |
| Oxide inclusions | Process gas | Metallography |
| Overspray on masked areas | Masking | Visual |
03Where an inspector should look
01
Before production
- Coating specification and process qualification
- Coupon plan
02
During production
- Parameters and pass count
- Surface roughness before spray
03
After production
- Coupon metallography and bond test
- Thickness and finish
04Standards and references
ISO 14916 (adhesive strength), ISO 2063 (thermal spray zinc and aluminium), EN ISO 14922 (quality requirements).
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.
05How we support buyers of thermal spray parts
Coating, Painting and Galvanizing InspectionSurface preparation, paint application, DFT, adhesion and hot-dip galvanizing inspection against the coating specification.
Manufacturing and Special Process AuditsProcess audits of casting, machining, welding, heat treatment, plating and moulding, with VDA 6.3 style evaluation.