The surface quality of cold rolled strip is closely related to rolls with high grinding quality. In the production practice of a cold rolling mill, straight chatter marks often appear during roll grinding. These defects will inevitably transfer to the strip surface in the rolling process, seriously damaging the appearance quality of finished products. This paper deeply analyzes the causes of chatter marks and puts forward targeted solutions. Actual on-site conditions should be taken into consideration for specific troubleshooting.
## 1. Causes and Countermeasures of Chatter Marks
Straight chatter marks can be observed under side lighting when the roll rotates at low speed in grinding. The marks originate from periodic vibration between grinding wheel and roll. The vibration comes from multiple factors: grinder performance, workpiece material, grinding wheel selection and grinding parameters. Since the grinding parameters of this plant have been fixed for a long time, the analysis mainly focuses on grinder, workpiece and grinding wheel.
Chatter marks on cold rolled strip are highly associated with roll grinding chatter. Optimizing grinding parameters and adding polishing procedures are effective ways to solve this defect.
## 2. Influence of Grinding Machine
Grinder stability directly determines chatter generation. As a core component, shoe condition greatly affects grinding results. Defects in shoe design & fabrication, wear or loose installation will reduce machine stability and trigger chatter. Shoe condition is a key inspection item for grinding chatter analysis.
Shoe status and spindle stability are critical. Fastening bolts, repairing shoes and ensuring good contact can greatly reduce chatter risk.
## 3. Influence of Grinding Wheel
Grinding wheel type, dureté, balance and contact condition with spindle exert remarkable impacts on grinding quality. Proper wheel selection and regular condition monitoring are essential to suppress grinding vibration.
After comprehensive inspection, the plant found the lead screw had a 0.5mm concave middle section with severe chattering and amplitude up to 5mm. Obvious wear existed on lead screw surface, and a large amount of metal debris mixed in guide rail oil. Partial wear also occurred on grinding wheel carriage guide rail with partial worn texture. It was confirmed that chatter was mainly caused by worn lead screw and guide rail. Since lead screw replacement and guide rail scraping required major overhaul, the team optimized grinding parameters to eliminate grinding chatter and meet production requirements:
– Reduce grinding current and carriage traverse speed step by step in rough, medium and finish grinding stages.
– Add polishing procedure; dress grinding wheel precisely before polishing with dressing feed of 0.03mm, repeat 8~10 times.
– Periodically adjust the rotating speed of grinding wheel and work roll during grinding, with variation range of 8~10% every 60 seconds to destroy fixed vibration mode.
