Surface Quality Improvement of GI Chromate Coating Product

by Lo Wan-Fu, Lin Cheng-Hua

Publisher - China Steel Corporation, Taiwan

Category - General Novel

Chromate coating is one of the post treatment processes for GI product which are applied to construction material. The main function of chromate coating is anti-rust. The aim of this study was to improve the strip surface defects which were caused by the interaction of the skin pass mill temper solution and chromic acid of the post treatment process in China Steel Corporation (CSC) No.2 CGL. It is necessary to use the temper solution in the skin pass mill (SPM) to eliminate the zinc powder adhered to both work rolls and back up rolls. The concentration of solution is between 3% and 5% in the original design. According to the investigation, we found that higher concentration of temper solution with chromic acid in the post treatment will cause the strip surface defect named striation mark (coating roll mark). A suitable concentration of solution must be controlled to avoid striation mark happened and eliminate the zinc powder adhered to the rolls in the same time. No.2 CGL succeeded to modify the wet temper system to ensure the suitable concentration of temper solution for GI chromate coating product.

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