Chatter Marks – Solution Confirmed! (3/3)

The Story So Far

Chatter marks on output strip

Our engineers were called onsite to help an aluminium producer who was experiencing chatter marks on output aluminium strip produced by a 6-high cold rolling mill. The earlier phases of this investigation involved:

• Part 1: Marked Rolls in Cold Rolling Mill:

  We identified the intermediate roll grinder as the source of the issue. The intermediate rolls were already marked before being loaded into the mill.

  
  

• Part 2: Effect of Steady Rest Changes:

  We implemented modifications on the grinder to address the structural weakness that was causing the issue. At our request, the client replaced the curved steady rests with flat ones to prevent the rolls being excited at the problem frequency.

Now, the crucial question: Did these changes eliminate the chatter marks for good?

Validating the Fix: Rolling Mill Results

To confirm the effectiveness of the grinder modifications, we returned to the mill to take measurements after a full roll stack change, including intermediate rolls ground after the grinder modifications. We found clear evidence that the fix worked! Unlike previous measurements, the spectra showed no evidence of the intermediate rolls being marked. The marking pitch frequency was gone, and overall vibration levels were significantly lower across all rolling speeds.

The figures below compare the frequency spectra taken at the same point in the roll lifecycle. The first plot shows the mill vibration immediately after a full roll stack change, before the modifications to the intermediate roll grinder. The second one shows the mill vibration right after the roll stack change, following the adjustments to the grinder. The material, rolling speed, and all other mill conditions remained the same.

Vibration measured on the mill before and after modifications to the grinder

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"Thanks to your help there are now no issues with the output strip quality."

Mechanical Maintenance Senior Engineer

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Conclusion

As evidenced by the elimination of chatter marks following our intervention, Vibremo's comprehensive investigation methodology can successfully address complex vibration-related challenges in rolling mills. By thoroughly examining the entire system – from the roll grinders to the mill itself – we identified and rectified the root cause of the problem. This targeted approach resulted in a significant improvement in the quality of the output strip.

Are you facing similar challenges with your rolling mill or grinders? Learn how Vibremo's specialised investigation services can help you achieve optimal performance and product quality. Click here to find out more about chatter mark root cause investigations in rolling mills and roll grinders.