Simple Repair Process for Surface Cracks and Scratches on Mill Rolls
Step 1: Pre-Treatment and Surface Cleaning
After identifying cracks or scratches on the mill roll surface, start by thoroughly cleaning the damaged area. Use a grinding wheel or angle grinder to remove oxidation layers, oil residues, and loose metal until clean base material is exposed. For cracks deeper than 0.3mm, use a carbon arc gouging tool to create a 60° V-shaped groove to ensure proper welding fusion. Preheat the mill roll to 100–150°C using an oxyacetylene flame to minimize welding stress and prevent cold cracking.
Step 2: Welding and Polishing
Apply manual arc welding or overlay welding with wear-resistant alloy electrodes matching the base material. Control the welding current between 120–200A, using short arc welding with multi-layer and multi-pass cross welding. Each layer should not exceed 3mm in thickness, and interlayer temperatures must stay below 50°C. For shallow scratches, weld 1–2 layers and leave a 2mm machining allowance. After welding, grind the surface smooth and use penetrant testing (e.g., dye penetrant) to confirm complete crack removal.
Step 3: Post-Treatment and Quality Assurance
Wrap the repaired mill roll in thermal insulation blankets to cool slowly to below 80°C, then perform stress-relief annealing at 150–180°C for 6 hours. Grind or lathe the mill roll to restore original dimensions, and verify hardness (HRC 56–60) using a hardness tester. Conduct ultrasonic testing to ensure no internal defects. If qualified, the mill roll can resume production with performance close to new rolls.