Statistical load characteristics in the primary lines of broad-strip rolling cells

Abstract

The quality of the grooving and the rolling system may also be evaluated by means of v x . For reduction, bar, and pipe mills, the mean variation coefficients of the rolling force and torque and also the spindle torques are stable. However, the operation and state of the equipment in the primary line have not been evaluated using the variation coefficients of the maximum dynamic torque v d and the combined dynamic state v c . In the present work, we consider the three variation coefficients v st , v d , and v c in terms of their information content regarding the technological process and the operation of the equipment. This is particularly important in that continuous mills consist of a sequence of cells in which the strip is rolled as batches of a particular size. Obviously, the variation in these parameters in each cell will provide certain information. Data on the torque of the elastic forces in cells 5‐7 of the 1680 mill in the interval between the motor and the gear will now be subjected to statistical analysis. 1 For each strip within a batch of a single size, the mean (over the length) static torque M st in steady rolling conditions, the maximum torque of the elastic forces M d , and the dynamic coefficient K are calculated. In addition, for the same batch, the mean values of M st , M d , and K are calculated, as well as their mean square deviation and variation coefficients. As a result, we determine v st , v d , and v c . In rolling a single batch of strip, the speed and deformation are practically unchanged. Therefore, 1 Participants in this work include A. P. Danilchuk and V. V. Korennoi. sample M st has the smallest variation coefficient v st1 if the specified technological conditions (supply rate of the billet in the cell, absence of downtime, etc.) are observed. Analysis of v st for batches rolled in a different time period and comparison of the results permits the selection of the batch with the minimum coefficient v st.min , i.e., the batch rolled with the least spread in the technological parameters. The value of v st.min for cell i may be adopted as the comparison sample when evaluating the rolling technology for other batches of the same size. If the satisfaction of the technological conditions is best (or practically the best) in the first finishing cell 5, we may expect smaller v st in the other cells. If that is not the case, we must suspect that some technological perturbation has occurred. In this way, a table of minimum values v st.min may be formulated for the basic steels and slab (strip) sizes. The v st values obtained for subsequent measurements may be compared with the tabular values, for quantitative evaluation of the technological process in the specific cell. Comparison of the v st values for a continuous mill permits the identification of the cells where instability develops or of the range characterized by instability. The maximum dynamic load M d and dynamic coefficient K depend more significantly on the angular gaps in the drive line than on the technological parameters. Hence, v d and v c may be regarded as informative parameters related to the state of the drive line. By comparing their values in rolling strip of the same type in different operating periods, we may evaluate the state of the equipment in the cells. If we characterize the coefficients as large and small (subscripts L and S, respectively), we may write eight combinations of the three coefficients, in the general case. Analysis shows that, of these combinations, the following are seen in practice: small values of v st.S , v d.S , and v c.S , indicating stable (good) technology and a good engineering state of the drive line; small v st.S and large values of v d.L and v c.L , corresponding to good technology and a poor state of the line; large v st.L and small v d.S and v c.S , corresponding to poor technology and a good state of the line; and large values v st.L , v d.L ,