Background and Problem
The client operated a 3-stage pre-treatment line: alkaline degreasing, water rinse, zinc phosphating. Following an expansion to a second production shift, paint shop rejection climbed to 17% — up from below 3% previously. Parts showed paint blistering, adhesion failure, and early corrosion within 24–72 hours of painting.
Phosphating bath chemistry was audited first. Results were normal. Paint material was unchanged. The issue was identified after 3 weeks of investigation: the conveyor gap between water rinse and phosphating was 9–14 minutes. In the ambient humidity of the Faridabad plant on the second shift — when ventilation was reduced — fine flash rust was forming on cleaned steel surfaces before they reached the phosphating stage.
Flash rust disrupts the zinc phosphating crystal growth reaction, producing thin, non-uniform coating with poor paint adhesion. The problem was invisible to the naked eye but detectable under magnification — and manifested visibly only after painting.
The client was spending Rs. 4.2 lakhs per month on rework. The chemical solution cost Rs. 28,000 per month — a 15:1 return on the investment in the correct chemistry.
REFA Solution
REFA replaced the plain water rinse after degreasing with a 0.5% solution of REFA Inter-Process Rust Preventive Rinse Aid. This product deposits a thin, phosphating-compatible corrosion inhibitor film on the cleaned surface, providing 2–4 hours of flash rust protection. No additional equipment or process steps were required.
- Stage 1: REFA Alkaline Spray Degreaser — 3.5%, 58°C, 2 min spray
- Stage 2: Hot water cascade rinse — 60°C, 1 min
- Stage 3: REFA Rust Preventive Rinse Aid — 0.5%, ambient, 45 seconds
- Stage 4: Zinc phosphating — unchanged
Results
Rejection rate fell from 17% to under 1.8% within 3 weeks. OEM corrective action request closed within 6 weeks.
- Monthly rework cost: from Rs. 4.2 lakhs to under Rs. 38,000
- Phosphate coating weight improved from 1.6 g/m² to 2.5 g/m² — within OEM specification
- Salt spray test: extended from 120 hours to 280+ hours on same paint system
- Chemical cost increase: Rs. 28,000/month — ROI in the first month
- REFA adopted as approved pre-treatment chemical supplier across all three production lines
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