Background
Vibremo recently conducted an in-depth vibration investigation to identify the origin of persistent chatter marks on aluminum strips produced by a 6-high cold rolling mill.
Although operators initially managed to control the problem by optimising operational conditions, the situation has worsened significantly in recent times, with the marks appearing more frequently. This has not only impacted the quality of the final product but also reduced the overall productivity of the mill.
To mitigate the short-term negative effects, frequent grinding of the intermediate and backup rolls became necessary, leading to increased downtime for the mill higher energy consumption for the grinders, further increasing operating costs.
Investigation
A detailed vibration analysis was performed over several days to identify the root cause of the chatter marks. The investigation revealed high vibration levels in the marking pitch frequency range across all measured speeds (400–1110 m/min).
The following plot shows a significant peak at the marking frequency. Through detailed analysis of the measured vibrations, we identified evidence pointing to the intermediate rolls as the source of the issue. The observed patterns clearly indicated that the intermediate rolls were marked with the problem pitch.
The next step after this was to determine whether the intermediate rolls were already marked when they entered the mill or if the problem was developing inside the mill.
To answer this question, Vibremo worked collaboratively with the client to replace the entire roll stack, and took vibration measurements right after the change. The data collected clearly showed that the marking frequency was present from the first coil rolled with the freshly ground rolls, with similar evidence that the intermediate rolls were marked, indicating that the intermediate rolls were already marked before entering the mill!
Solution
Based on these findings, our team made the decision to shift the focus of the investigation from the rolling mill to the intermediate roll grinder. A thorough inspection of the machine is described in this case study, presenting why and how the structural modifications applied to the grinder proved beneficial to the quality of the rolls ground.
With the corrective actions applied by Vibremo engineers, the grinder issues have been solved and the mill achieved a significant improvement in strip quality. These changes minimised machine downtime, restored productivity, and eliminated the marking on output strip caused by this issue.
This case of marked rolls in the 6-high cold rolling mill demonstrates the importance of thorough on-site vibration investigations in resolving complex operational challenges. By identifying the intermediate roll grinder as the source of the problem, Vibremo helped the client to successfully eliminate persistent chatter marks and enhance mill performance. This highlights the critical role of vibration analysis and precision maintenance in sustaining high-quality output in the rolled metals industry.
