Camber measurement at hot strip mill at voestalpine by using image processing method

The environmental conditions at hot strip mills are characterized by hot objects (up to 1100°C), dust and dense steam. Conventional methods for characterizing product parameters fail in these unfavorable measurement conditions. An alternative is optical measurement technique. It is non-contact and can be positioned in a safe location in the plant. One parameter of interest at hot strip mills that is to be observed is the geometry of the transfer bar. During the reduction of thickness of the stock in several reversing passes a deviation of the straightness, a so-called camber, can occur. This distortion can cause disturbances at the following steps of production, e.g. at the finishing mill. The value and direction of the camber is determined by means of a CCD-matrix camera and a segmented capture of the shape. The unique character of the measuring system discussed in this paper lies in the use of a single camera system to meet the requirements in contrast to other systems using two or more cameras. In the rolling process of the roughing mill with varying speed additional phenomena like lateral shift and rarely twist can occur, which make the measurement more difficult. Lateral movements of the strip are taken into consideration by checking single edges twice, the twist can be neglected. Finally the results of the camber values are statistically evaluated. One significant result shows the influence of the arrangement of stocks in the pusher-type furnaces on the camber. The results of the measurement are helpful for understanding the rolling process in more detail and even to take measures to avoid cambers and improve quality and process stability.