Method for detecting the vibrations of a roll stand

1. A method for detecting the vibrations of a roll stand of the type comprising two pillars which each form a ring and between which are located a set of rolling rolls, formed by at least two working rolls, which enable the thickness of the product to be rolled to be reduced and which are stacked in a substantially vertical plane constituting the adjusting plane and are mounted to rotate in chocks forming bearings, which chocks are mounted to slide vertically between guide surfaces supported by the upright portions of the pillars, the roll stand comprising means for adjusting the rolls by means of hydraulic jacks resting on a horizontal portion of each pillar and exerting the adjusting force on the chocks of the rolls, the hydraulic jacks also comprising a position sensor which gives at each instant a signal representative of the position of the mobile portion of the hydraulic jack, and of the chock, relative to the fixed portion of the hydraulic jack, and to the horizontal portion of each pillar, wherein the measurement signal of the position sensor is memorized in real time and permanently, in that a sample of that signal is compared directly with a spatio-temporal observation window, the size of the sample and the dimensions of the window being chosen as a function of the roll stand and the frequency of the vibrations to be detected, and in that a vibration detection signal is triggered when the signal sample is no longer contained within the window.

2. A method for detecting the vibrations of a roll stand according to claim 1 , wherein the temporal dimension of the observation window has a length of time sufficient for the sample contained to be representative of the vibration phenomenon to be detected.

3. A method for detecting the vibrations of a roll stand according to claim 2 , wherein the temporal dimension of the observation window has a length at least equal to a time equivalent to 2 periods of the signal of the vibration phenomenon to be detected.

4. A method for detecting the vibrations of a roll stand according to claim 2 , wherein the height of the observation window has a spatial dimension representing a size greater than the amplitude of the greatest repetitive variation of the position measurement signal of the hydraulic adjusting jack.

5. A method for detecting the vibrations of a roll stand according to claim 3 , wherein the height of the observation window has a spatial dimension representing a size greater than the amplitude of the greatest repetitive variation of the position measurement signal of the hydraulic adjusting jack.

6. A method for detecting the vibrations of a roll stand according to claim 5 , wherein the height of the observation window has a spatial dimension representing an amplitude of the position measurement signal of the hydraulic adjusting jack greater than 4 micrometers.

7. A method for detecting the vibrations of a roll stand according to claim 1 , wherein the number of times the amplitude of the position measurement signal of the hydraulic adjusting jack has exceeded the height of the observation window is counted.

8. A method for detecting the vibrations of a roll stand according to claim 7 , wherein a vibration detection is signalled when the number of times the amplitude of the position measurement signal of the hydraulic adjusting jack has exceeded the height of the observation window is greater than that normally observed during corrective actions of the greatest amplitude permitted, of the control systems of the roll stand.

9. A method for detecting the vibrations of a roll stand according to claim 7 , wherein a vibration detection is signalled when the number of times the amplitude of the position measurement signal of the hydraulic adjusting jack has exceeded the height of the observation window is greater than two.

10. A method for detecting the vibrations of a roll stand according to claim 7 , wherein the amplitude of each overshoot relative to the dimension of the window is measured for the observation windows that have triggered a vibration detection signal.

11. A method for detecting the vibrations of a roll stand according to claim 10 , wherein the slope of the variation in the amplitude of each overshoot, in the same observation window, is determined for the observation windows that have triggered a vibration detection signal.

12. A method for detecting the vibrations of a roll stand according to claim 10 , wherein the slope of the variation in the amplitude of each overshoot, in different observation windows, is determined for the observation windows that have triggered a vibration detection signal.

13. A method for detecting different vibration modes of a roll stand according to the method of claim 1 , wherein different sample sizes of the position measurement signal of the hydraulic adjusting jack and different dimensionings of the observation window are used, each of them being adapted to the frequencies of the vibrations corresponding to each of the vibration modes to be detected.

14. A method for detecting the vibrations of the stands of a tandem-mill comprising a plurality of stands, using the method of claim 1 , wherein, for each roll stand, a sample size of the position measurement signal of the hydraulic adjusting jack and a dimensioning of the observation window which are adapted to the frequencies of the vibrations to be detected on the roll stand are used.

15. A method for detecting the vibrations of the stands of a tandem mill comprising a plurality of stands using the method according to claim 14 , wherein the slopes of the variation in the amplitude of the overshoots are determined for each stand of the tandem mill.

16. A method for detecting and correcting the vibrations of the stands of a tandem mill according to claim 15 , wherein the corrective actions to be carried out are performed at least on the stand whose slope of the variation in the amplitude of the overshoots is the greatest.