Key Takeaways
- Precise Process Control is Essential – Managing zinc bath chemistry, cooling rates, and substrate standards helped achieve consistent spangle formation.
- Optimised Temperature Management – Adjusting burners to maintain a minimum strip temperature of 500°C improved spangle consistency.
- Unnecessary Additives Eliminated – Removing 53 metric tonnes of tin annually saved £700K per year without extra investment, thanks to sufficient lead and antimony levels.
- Enhanced Quality Control – Improved strip handling and tracking ensured even spangle formation, reducing defects and customer complaints.
Galvanized steel coil showcasing its distinctive spangle pattern formed during the zinc coating process.
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Saved annually by eliminating 53 tonnes of unnecessary tin additions – no capex needed.
Overview
Our client in Bangladesh produced galvanised coils with inconsistent spangle formation leading to high operating costs and customer complaints.
Challenge
The challenge was to maintain the desired spangle size, appearance, and brightness while reducing dependency on costly bath additives such as tin and antinomy. This required precise control over the galvanising process parameters, including bath chemistry, cooling rates and substrate standards. The additional cost of tin as an additive further compounded operational expenses.
Solution
- The expert team analysed the zinc bath chemistry to identify factors affecting spangle formation, including the concentrations of alloying elements such as lead, tin and antimony.
- Modifications were made to the cooling rate by increasing the strip temperature and line speed from the zinc bath help promote uniform spangle formation.
- Reviewed cold rolled substrate standards such as surface roughness and cleanliness.
Results
- Improved Quality Control: Developed a quality tracker and improved strip handling procedures to reduce surface residues, ensuring consistent and even spangle formation across products.
- Optimised Temperature Management: Adjusted burners in the DFF exit to maintain a minimum strip temperature of 500°C, a critical factor in controlling spangle formation during the zinc coating process.
- Elimination of Unnecessary Tin Additions: Identified that over 53 metric tons of tin added annually to seven galvanising lines were unnecessary due to sufficient levels of lead and antimony in the zinc bath. This adjustment saved the client approximately USD 700,000 per year without requiring any capital investment.
