STRIP PROFILE CONTROL

Abstract: In a hot or warm mill for rolling metal strip, a profile control system (G) detects the profile of strip exiting the mill, compares it with a desired profile to provide an error profile and the stand or stands of the mill (S1-S3) have their gap profiles adjusted in the sense to reduce the error substantially to zero.

Description: STRIP PROFILE CONTROL This invention relates to the rolling of metal strip, particularly the hot rolling of steel and the hot and warm rolling of aluminium strip. Cold strip mills have sophisticated gauge and shape control systems giving excellent performance but strip profile is essentially fixed during the preceding hot rolling of the strip. As there is now an increasing demand for metal strip having a satisfactory transverse thickness profile, action has to be taken during the hot rolling of steel and the hot and warm rolling of aluminium strip. According to a first aspect of the present invention a tandem hot rolling mill for metal strip is provided with a profile control system whereby the strip profile exiting the mill is detected, is compared with a desired profile to provide an error, and the individual mill stand roll gap profiles are adjusted in the sense to reduce the error substantially to zero. According to a second aspect of the present invention a hot rolling reversing mill for strip material is provided with a profile control system whereby the profile of the strip exiting the mill on each pass is detected, is compared with a desired profile for that pass to provide an error and the profile of the mill roll gap is adjusted in the sense to reduce the error substantially to zero prior to the next pass. The roll gap profile of the mill stand of the reversing mill and the individual mill stand roll gap - -> - profiles in the tandem mill are adjusted for example by means of work roll bending, spray control, axial work roll shifting and by using Dynamic Shape Rolls. The exiting strip profile is determined by a profile gauge located at the mill exit. The gauge is conveniently a nucleonic or X-ray profile gauge which with its associated circuitry produces both a numerical value of, and tffe form of, the profile of the exiting strip. " * The profile control system always acts to control the roll bending, spray control and any other actuators on each stand in the sense to reduce the numerical value of the profile error to zero. Conveniently it also actuates a special spray control or other actuator on each stand or pass when the profile is found to be one of an undesirable form which requires special action with respect to the thermal camber or other roll properties to correct the profile. In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a profile control system applied to a tandem mill. Figure 2 shows various alternative strip profile forms. Figure 3 shows alternative spray patterns. Three four-high stands S^, S 2 and S 3 of a warm rolling mill for rolling aluminium strip are arranged in tandem. Downstream of stand S 3 the strip is coiled in a coiler (not shown) and between the stand S 3 and the coiler there is a profile gauge G. Conveniently the gauge G is a nucleonic or X-ray profile gauge which measures the gauge of the strip, at a plurality of regions spaced apart across the width of the strip, and at regular time intervals. The gauge forms part of a closed loop profile control system which functions to keep the exit strip profile as measured by the gauge at a selected target profile. This system measures the profile of the strip exiting from the tandem mill, subtracts the measured profile from a target profile to generate a profile error and employs the error to change the rolling conditions in each stand of the tandem mill in the sense to reduce the error. The conditions which can be changed in each stand are work roll bending and the coolant spray pattern. Work roll bending brings about a fast acting response and coolant spray pattern is a slower response because it depends on the build up or decay of the work roll thermal camber. Signals from the gauge G are processed in its own signal processor and processed further within the closed loop system signal processor H and the profile and form of the strip are passed to a profile strategist K. A signal representing the target profile is also supplied to the profile strategist K. In the strategist K, the measured profile is subtracted from the profile target to produce the profile error and the numerical profile error is supplied to the Stand Target Determination Device L. In this device, the profile error is converted into three roll gap corrections, one for each mill stand, and these are supplied to respective Roll Gap Controllers RGC/S1 - RGC/S3 _ _ associated with the mill stands. Each Roll Gap Controller comprises a supervisory controller and subsidiary controllers for roll bending and for spray control. In use, the gauge G sends a vector of the thickness profile to the processing device H where a numerical profile value is obtained from the following equation:- k = (h c - h e ) . 100% h c where k is the actual measured exit strip profile, h c is the centreline thickness and h e is the strip thickness at a nominal distance from the strip edge. The form of the profile is also detected and is classified into one or other of the two groups of profile forms shown in Figure 2. The "acceptable" profile forms shown on the lefthand side of figure 2 are parabolic parabolic edge drop edge drop flat. The "undesirable" profile forms shown on the righthand side of figure 2 are thick edge M shape inverse parabolic inverse edge drop. The profile strategist, in addition to determining the profile error, determines the kind of spray control - _ - which is required. If the form of the profile is one of the "acceptable" types then instructions are sent to the Roll Gap controllers RGC to employ nominal spray control. This selects a spray pattern within the range of specified maximum and minimum spray patterns as shown in figure 3 (a) and 3(c). If the profile is one of the undesirable types the Roll Gap controllers are instructed direct by v/ay of the routes shown by broken lines to take exceptional spray action. For example, if the inverse parabolic or inverse edge drop forms are detected then it is necessary to decrease the roll thermal cambers. In this case the spray patterns would be set immediately to their maximum patterns. If incremental spray patterns are required these can be provided. For example, with an edge drop profile the sprays can be increased near the edge of the strip to reduce the load locally and hence the edge drop effect. Similarly, particular spray patterns may be selected to counter asymmetric profile forms. Referring again to figure 1, it is desirable, but not essential, for Shape measuring devices R to be provided at the exit of each mill stand. Changes to the rolling conditions in each stand can lead to undesirable changes in the shape of the strip. Consequently the purpose of the shape measuring devices R is to monitor the strip for bad shape and to control the stands to improve the profile only to an extent which does not bring about unacceptably bad shape. The outputs from the devices R are supplied to the Profile Strategist K and in the event of bad shape being detected the Profile Strategist instructs the stand or stands concerned on what action is required. The profile error determined by the strategist K is supplied to the Stand target determinator L where the individual roll gap corrections for each of the stands S-_ S 3 are determined. Since profile change in a stand is a function of H/b where H is the strip entry gauge and b is the strip width, then more profile change can be made on stand S- ^ than on stand S 2 and more on stand S 2 than on stand S 3 so the stand target determinator L functions to keep the roll gap changes on each stand in the ratio of the stand's ability to make profile changes, i.e. most profile change on stand 1 and least on stand 3 and the appropriate corrections are passed to the roll gap controllers. If the change in strip profile across one of the stands (i) is _ i where k^ is the nominal exit profile from stand i and K^* is the equivalent entry profile to stand i, The X ratio of stand i is defined as X-: = A l ' - St where f^ is the shape change coefficient for stand i and is a function of the strip width b) and strip thickness H in the stand The Stand Target Determination (L) operates to satisfy the following two constraints - - total profile change applied determined by the profile error X^ is constant for all stands. The Roll Gap Controllers RGC are responsible for converting the corrections from the determinator L into a bend correction and a spray pattern correction. They take into account the composition of the material being rolled and determine a roll bend correction which will produce the required change in the roll gap profile and a correction in the thermal camber of the rolls which will change the roll gap profile. The controller tries to achieve the full correction required on both roll bending and spray control. The response times for the two corrections are very different. The roll bend system acts very quickly, while the thermal camber can only be changed slowly. The instructions to the roll spray controllers are overruled if the form of. the profile of the strip is of the undesirable type. In this case the calculated change in thermal camber is ignored and special spray action is taken. Given a desired roll gap correction each roll gap controller first calculates the required bend correction to reduce the error, it outputs this correction to the roll bending system via the roll gap bend controller. Changes to individual stand bend settings are sequenced according to the current transport delay from stand 1. The roll gap spray controller then compares the actual roll bending value with a preferred roll bending value which is a value which permits both positive and negative bend changes to be made as and when necessary. If the actual bend value is greater than the preferred bend value then the roll gap spray controller tries to increase the thermal camber (by decreasing the spray pattern) with the aim of allowing lower bend values to be used. On the other hand, if the actual bend value is less than the preferred bend value then the roll gap spray controller will try to decrease the thermal camber with the aim of allowing higher bend values to be used. To avoid "hunting" of the sprays, each time the controller outputs a new spray pattern that pattern is retained for a predetermined time before it is changed. Although the invention has been described in relation to its use on a tandem mill it can be applied to a single stand reversing mill.

Claims: Cla ims : 1. A tandem hot rolling mill for metal strip having a profile control system comprising a strip profile detector arranged to detect the profile of strip exiting the mill, means for comparing the output of the detector with a target profile to produce an error, and means for adjusting the individual mill stand roll gap profiles in the sense to reduce the error substantially to zero. 2. A hot reversing rolling mill for metal strip having a profile control system comprising a strip profile detector arranged to detect the profile of the strip exiting the mill on each pass, means for comparing the output of the detector with a target profile for that pass to provide an error and means for adjusting the profile of the mill roll gap in the sense to reduce the error substantially to zero prior to the next pass. 3. A rolling mill as claimed in claim 1 or 2 in which the profile of the roll gap of the reversing mill or the profile of the roll gap of the individual mill stands are adjusting by the combination of work roll bending and coolant spray control. 4. A rolling mill as claimed in any preceding claim wherein the strip profile detector is a nucleonic or X-ray gauge arranged to produce both a numerical value of and the form of the profile of the strip. 5. A rolling mill as claimed in any preceding claim wherein said comparing means subtracts the actual measured profile from the target profile to produce the error and determines whether the strip profile is of a desirable or an undesirable form, the undesirable form of strip profile requiring particular action with respect to the thermal camber to correct the profile. 6. A rolling mill as claimed in claim 5 in which the undesirable forms of strip profile are thick edge, M shape, inverse parabolic and inverse edge drop. 7. A rolling mill as claimed in claim 1 in which the individual mill stand roll gap profiles are changed in the relationship Profile change on stand 1> Profile change on stand 2> Profile change on stand 3. 8. A rolling mill as claimed in claim 7 in which the total profile change is determined by the profile error and the profile change on each stand is determined by the constraint that X^ is constant for all stands where X,- = *ι iR i - Η " κ i* ; and r ^ is the nominal exit profile from stand i , K^* is the equivalent entry profile to stand i, S^ is the shape change coefficient = / (b^ H^ ) where b is the strip width and H is the strip thickness at stand i. 9. A rolling mill as claimed in claim 1 in which each mill stand has a strip shape measuring device associated therewith, the outputs from said devices being used to limit the profile changes on the stands to prevent strip with unacceptably bad shape from being rolled.

Inventors: ROBERT JOHN BEATTIE, ROBERT, JOHN, BEATTIE
Applicants: DAVY MCKEE POOLE, ROBERT JOHN BEATTIE, DAVY MCKEE (POOLE) LIMITED, ROBERT, JOHN, BEATTIE
Application year: 1995
Main classification: B21B37
IPC codes: B21B27, B21B37