Patent GB-1383160-A (GB)
Title: Method and apparatus for measurement of thickness of moving metal strip
IPC: G01B15/02
Filed: 1973-04-10
Abstract: 1383160 Measuring metal sheet thickness ALCAN RESEARCH & DEVELOPMENT Ltd 10 April 1973 17254/73 Heading G1A In a system for measuring and controlling the thickness of a moving rolled metal sheet, a first beam of radiation is scanned across the sheet along a path at right angles to the direction of movement so that the sheet thickness may be determined along this transverse path by measuring the radiation passing through the sheet, and a second beam of radiation passes through a fixed point on this path to measure the thickness at that one point. If there are longitudinal variations in sheet thickness these are detected by the second beam as the sheet moves past the fixed point, so that by subtracting the second beam measurement from the first beam measurement a true transverse thickness measurement is obtained from which the effects of any longitudinal variations occurring during the transverse scan have been removed. The radiation is preferably X-rays, and Fig. 2 shows the apparatus for producing and measuring the first beam. In Fig. 2 the apparatus comprises two horizontal arms 30, 32, joined at one end by upright 31. An X-ray generator and detector are housed in the respective ends 34, 35 of these arms, with windows 47 (only one is visible) allowing radiation to pass from one to the other via the metal sheet under test which in use lies between the arms. The apparatus may be moved along rails 50, 51, 52, and has rollers such as 36 and 37 to allow this; this movement scans the sheet under test. The arms 30, 32 are offset so that a further basically similar apparatus may slide on the same rails beside the Fig. 2 assembly, as in Fig. 3 (not shown). The motion of the further apparatus, which produces the second beam, allows the second beam to be positioned at the centre of the sheet under test. The apparatus is motor driven, Fig. 4 (not shown), and as well as giving the X-ray measuring signals it produces signals indicating the position of the scanned beam and the direction of scan. By subtracting the two X-ray measurements a signal is produced which represents the difference between the thickness of the sheet at its centre and at any point on the scan. This signal is combined with the other signals in Fig. 9. Here the scan across the sheet in the forward direction is compared with the average of the previous scan in the reverse direction across the sheet. Any difference is passed on line 107 to gates Gl to GN, which also receive scan position signals from 108. Thus if at a given point on the scan there is a thickness variation from the average of the previous scan the gate corresponding to that point is operated, and the appropriate valve 116 controls cooling fluid to a given point on the roll of the mill to correct the thickness variation. The system thus maintains the thickness at the average value measured in the first scan of the process. Other corrections are possible, e.g. by adjusting roll bending devices, and a visual indication or record may be provided so that the mill operator can adjust the rolls.