Effect of Steady Rest Changes (2/3)
- fc8635
- Dec 4, 2024
- 2 min read
Updated: 8 hours ago
Background
Following reports of chatter marks on output aluminium strip from a 6-high cold rolling mill, we initiated a targeted investigation to find the root cause of the problem. Our initial measurements on the rolling mill, described in this article, revealed that the intermediate rolls were marked.
The next step was to find out where the rolls were being marked. Was it in the mill during rolling, or during the grinding process? To answer this question, we focused our analysis on the intermediate roll grinder, the subject of this second investigation.
Initial Measurements
Initial measurements taken during grinding identified a vibration within a specific frequency range. The characteristics of this vibration – when correlated with roll speed and diameter – allowed us to calculate a marking pitch identical to the one seen on the output strip. This confirmed that the vibration source was indeed the grinder and that it was responsible for marking the intermediate rolls.
The instability and amplitude of the vibration suggested a potential structural weakness, which was confirmed through resonance testing. This testing revealed a significant resonance in the roll steadies, matching the marking frequency observed during operational measurements.
Solution
We worked with the clients’ maintenance team onsite to make structural changes to the steadies. The steady rests were changed, switching from the existing curved rests to new flat ones, resulting in line contacts with the roll.
Resonance testing was carried out again after the modification, showing that the resonance observed with the curved steady rests split into two separate resonances with significantly lower amplitudes after switching to flat steady rests.
Outcome
During grinding, it was found that the modifications to the steady rests completely eliminated the resonance issue. The vibration levels were significantly lower at the resonant frequency when using the same grinding conditions and the grinding machine was able to produce chatter free rolls!
Vibremo recommended that the client maintain flat steady rests, either by replacing the steady rests when they lose their flateness, or scraping the existing rests regularly.
"It can be surprising how seemingly small changes to a much larger system can affect overall machine performance. Examples like this show that with the right measurement tools and knowledgeable engineers, small changes can make a significant improvement to the quality of output material."
Jacob McCormick – Vibration Consultant – Vibremo
The results presented here demonstrate that the modifications to the roll grinder's steadies were successful in addressing the vibration issues. The reduction in unstable vibration during grinding, shown after the structural modification, strongly indicates that the rolls are no longer being marked.
The validation of this outcome, with data from the rolling mill itself, can be seen in our third case study: Chatter Marks – Solution Confirmed!, as the measurements taken show the absence of the marking pitch frequency that had been causing quality issues.
To find out how Vibremo can do the same for you, contact us here.
