Scope of this guide
This senior guide covers the hard cases: combined variables, boundary conditions and the judgement calls that separate consistent lines from lucky ones.
Process: Cold Painting. Figures in this guide are industry-standard starting ranges; confirm against your supplier TDS before locking settings.
Working ranges and control points
The table below is the daily reference for a cold spray bench. Set by the card, verify by the control point column.
| Parameter | Typical range | Control point | Watch out |
|---|---|---|---|
| Thinner ratio | 5–15% by volume | Viscosity cup per batch | Over-thin low build |
| Air pressure | 2.5–4 bar | Regulator locked | High pressure overspray |
| Coat count | 2–3 light coats | Dry-touch between coats | Heavy single coat sags |
| Dry time, ambient | 20–40 min per coat | Finger-drag test | Stacking too early prints |
| Colour check | Standard card under D65 + A light | Metamerism screen | Match fails indoors only |
Push The Boundary: the senior view
Beyond the basic card, this is the layer that matters at your level:
| Hard case | Why it is hard | Method | Data to keep |
|---|---|---|---|
| Mixed-alloy loads | Different windows collide | Split by family or map positions | Per-family thickness trend |
| Seasonal humidity swings | Flash and dry times move | Season-set viscosities | Monthly setting log |
| Recesses at spec limit | Throwing power ceiling | Auxiliary anode trials | Before/after thickness maps |
| Repeat claim from one customer | Use conditions differ | Reproduce their test | Claim-vs-lab correlation |
Standard routine
- Match colour under two light sources before production
- Filter paint through 120 mesh
- Keep bench drafts off while spraying
- Dry-touch between coats, full dry before pack
- Sign the colour standard card per batch
Engineer notes
- Metamerism is the classic cold-paint reject — check under shop and daylight lamps
- Cold booths need warmer thinner ratio in winter
- Small parts on wire stands show shadow lines — rotate stands 180° between coats
- Record batch numbers; colour claims trace to them
- Old paint absorbs moisture — filter twice and test on scrap
Safety: Spray mists carry isocyanates in some 2K paints. Use supplied-air or A2P respirators for 2K products; skin contact needs barrier cream.
FAQ
Why does colour match in the booth but fail at the customer?
Metamerism. Approve colour under both D65 and warm light before production.
Can I speed drying with heat?
Mild warmth 40 °C is fine; hot air skins the coat and traps solvent.
How much thinner should I add?
To viscosity, not volume: target the cup seconds on the paint card, 16–22 s typical.
How do I train juniors on this judgement?
Have them log the variable they changed and the measured result; review the log weekly against line outcomes.