Rolling Mill 3rd Octave Resonance Investigation

Background

4-high rolling mills have 2 main resonances, known as 3^rd and 5^th Octave resonance. 3^rd Octave resonance is the most severe and is usually a result of structural issues. When this mode is excited, it can cause gauge variation, and in the worst cases, strip break.

Fig. 1 - Vibremo engineer placing sensors

Earlier this year, Vibremo engineers carried out an investigation for a steel producer on a 5-stand cold rolling mill that was experiencing severe 3^rd Octave resonant excitation.

Using advanced vibration analysis techniques - including Operational Deflection Shape (ODS) analysis - and our practical expertise, we confirmed the presence of the 3^rd Octave issue and identified the area for improvement that would have the most significant positive effect on performance.

Findings

Simultaneous measurements taken on the last 3 mill stands allowed us to identify the stand at which the 3^rd Octave issue originated. This meant that more precise analysis could then be carried out on the specific mill stand of interest.

Fig. 2 - Multi-stand simultaneous measurements

ODS analysis was performed on the mill stand, which confirmed the 3^rd Octave mode shape: the top and bottom roll sets were moving in anti-phase, each oscillating in opposite directions at the same frequency. This movement is what leads to gauge variation and, in severe cases, strip break.

Fig. 3 - Mill ODS chock positions

Fig. 4 - Operational Deflection Shape animation - Roll stack

ODS analysis was also carried out on the mill housing and the roll chocks. This identified the main structural weakness by showing clearly where the maximum amplitude vibration was occurring on the roll stack relative to the mill housing.

Fig. 5 - Mill ODS mill housing positions

Fig. 6 - Operational Deflection Shape animation - Mill housing & roll stack

Outcome

Through our investigation and detailed vibration measurements, we were able to confirm that 3^rd Octave resonant excitation was occuring, identify the exact stand where the issue originated, and determine the main structural weaknesses. Based on these results, we provided targeted recommendations for structural improvements to the roll stack to prevent the issue from recurring.

Fig. 7 - Mill stack component diagram

Identifying the mode shape of severe resonant excitation is vital in order to be able to prevent unwanted vibration. Using advanced vibration measurement techniques like Operational Deflection Shape analysis allows our engineers to give specific, precise and practical recommendations to resolve complex issues like 3^rd Octave resonant excitation.

Vibremo helps to take the guesswork out of quality issue resolution in the sheet metal production process.