FIELD OF THE INVENTION 0001 Our present invention relates to a strip treating line for leveling of metal strip and, more particularly, high quality steel strip and especially stainless steel strip.

BACKGROUND OF THE INVENTION 0002 In the processing of high quality steel strip and especially stainless steel strip, it is common to subject a cold-rolled, annealed and pickled or bright annealed strip to leveling during the processing. 0003 The strip processing line thus can include a dressing mill stand, i.e. a mill stand which subjects the strip to only a minimum of thickness reduction, followed by one or more zones in which tension or stretch leveling occurs. For example, between the dressing mill stand and a pair of rolls looped by the workpiece steel strip, e.g. a bridle, a stretching zone is formed in which the strip tension is raised from the level of the strip tension as the strip is drawn through the dressing mill stand to a level at which the stretch leveling occurs. 0004 This has been found to be successful in practice. However, basic to the use of bridles and rolls to increase the strip tension or to bring the strip tension from one level to another, is the problem of damage to the surface of the strip since each roll encountered by the strip introduces the possibility of such damage to the surface.

OBJECT OF THE INVENTION 0005 It is, therefore, the principal object of the present invention to provide an improved stretch leveler system in a strip treatment line of the aforedescribed type whereby the danger of surface damage to the treated strip can be reduced. More specifically it is an object of the invention to provide a strip treatment line for metal strip of the aforedescribed type which can assure a high degree of planarity of the strip to be leveled while minimizing the risk of damage to the strip surface.

SUMMARY OF THE INVENTION 0006 These objects are achieved, in accordance with the invention in a strip treatment line for leveling metal strip, especially high quality steel strip and most importantly stainless steel strip which comprises the steps of: 0007 a dressing mill stand having a pair of dressing rolls between which a workpiece metal strip passes for reduction to a dressed thickness; and 0008 a first roll directly downstream of the dressing mill stand and looped by the workpiece metal strip immediately upon traversing the dressing mill stand and applying tension to the workpiece metal strip, and a second roll spaced downstream of the first roll and looped by the workpiece metal strip immediately upon passing around the first roll and applying tension to the workpiece metal strip, whereby the first and second rolls form a tension-producing stretching roll pair forming a strip prestretching zone between the dressing mill stand and the first roll and a strip afterstretching zone between the first and second rolls. 0009 With the system of the invention the dressing mill stand is followed by two rolls applying tension to the strip and referred to above as the first and second rolls without an intermediate bridle for increasing the tension as has hitherto been necessary. Between the dressing mill stand and the first roll of the stretching roll pair, a prestretching zone is created and between the first and second rolls of the stretching roll pair a first afterstretching zone is provided. 0010 The prestretching zone can be operated either as an elastic stretching zone for the strip close to the elastic limit or as a plastic or elastoplastic or semiplastic stretching zone. 0011 In the afterstretching zone, a plastic or elastoplastic stretching of the strip is effected. 0012 To the extent that the strip tension must be increased from that at the outlet side of the dressing mill stand, the prestretching zone can serve directly for that purpose and can use the first tension applying roll of the stretching roll pair. Since the separate bridle or roll set for raising the strip tension from the level of the dressing mill stand to the level at which the stretching is to take place is thereby completely eliminated, the number of tension-applying rolls is reduced and therewith also the risk of damage to the strip surface. Naturally there is a concomitant reduction in cost corresponding to the number of tension rolls or bridles which can be eliminated. 0013 Surprisingly, the elimination of a bridle or tension roll set between the dressing mill stand and the stretch-producing roll set does not adversely affect planarity. In fact it has been found that with the system of the invention excellent planarity results are obtainable utilizing the prestretching in combination with at least one afterstretching zone whereby the prestretching with the invention occurs directly downstream of the dressing roll stand and up to the first tension roll of the stretching roll depth. 0014 Preferably ahead of the dressing mill stand, there is provided a first set of rolls (at least one bridle and preferably two bridles) capable of maintaining tension in the strip. This set of rolls can be, therefore, a braking roll set. Upstream of the stretching roll pair, we can provide a tensioning roll set, again at least one (and preferably two bridles) around which the strip is looped. The sets of braking and tensioning rolls further improve planarity and permit an optimum planarity to be obtained, especially when between the stretching roll pair and the tensioning roll set a second afterstretching zone is provided in which a plastic or elastoplastic or semiplastic stretching is effected as in the first afterstretching zone. In this case a plurality of elastoplastic or semiplastic afterstretching zones will follow an elastic or elastoplastic prestretching. 0015 At least one of the rolls of the stretching roll pair can have a concave or convex contour and, indeed it has been found that it is possible to provide concave or convex contours for a multiplicity of the rolls following the dressing roll stand or to provide each of these rolls with an adjustable camber, i.e. a convex or concave profile which can be adjusted online. 0016 Downstream of the dressing rolls and one or more planarity measuring devices can be provided. For example, one planarity measuring device can be provided between the dressing roll stand and the first tension roll and a second planarity measuring device can be provided between the stretching roll pair and the downstream set of tensioning rolls. The measured values can be supplied on an online basis to the controller which regulates the prestretching and leveling process.

BRIEF DESCRIPTION OF THE DRAWING 0017 The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which: 0018 FIG. 1 is a diagrammatic side elevational view of a leveling line according to the invention; 0019 FIG. 2 is an elevational view of one of the tension rolls of the prestretching roll pair showing a convex camber; 0020 FIG. 3 is an elevational view of one of the tension rolls of the prestretching roll pair showing a concave camber; and 0021 FIG. 4 is an elevational view of one of the tension rolls of the prestretching roll pair showing a variable camber.

SPECIFIC DESCRIPTION 0022 FIG. 1 shows a strip processing line for processing a stainless steel strip 11 which derives from cold rolling of stainless steel following annealing and pickling or bright annealing. The strip is passed through a dressing mill stand 12 and which is slightly reduced in thickness between the rolls 12a and 12b and can pass under and over rolls 13a and 13b at the entrance to the mill stand and over and under rolls 14a and 14b upon exiting the mill stand. 0023 After traversing the mill stand 12 the strip is looped around two tension rolls 5, 6 which form a bridle and which are driven at successively higher speeds. Thus the strip is directly passed first into a prestretching zone A between the dressing mill stand 12 and the first tension roll 5 and a second or afterstretching zone B between the first tension roll 5 and the second tension roll 6. 0024 In the prestretching zone A, an elastic stretching of the strip 11 is effected up to or just below the elastic limit. An elastoplastic stretching is also possible in zone A. In the afterstretching zone B an elastoplastic stretching is carried out. 0025 Upstream of the dressing mill stand 12, we provide a braking roll set 1, 2, 3, 4, in the form of rolls 1 and 2 forming a first bridle and rolls 3 and 4 forming a second bridle. 0026 Downstream of the stretching roll pair 5, 6 is a second tension roll set 7, 8, 9, 10, operating at a speed greater than the roll 6 so that a further afterstretching zone C is provided between roll 6 and 7. The rolls 7, 8 and the rolls 9, 10 can form respective bridles. 0027 As shown in FIGS. 2, 3 and 4, the rolls 5 an 6 can be either of a convex pair as shown at 15, a concave pair as shown at 16 or of a variable camber as shown at 17, regulated by an online camber control 18. 0028 In the prestretching zone A and the second afterstretching zone C, respective planarity measurement devices 13 and 14 can be provided to provide inputs to a controller 19 which has outputs 20 to the individual roll motors and at 21 to online camber controllers. Other planarity sensors may be provided as shown at 22 to afford inputs to the controller for the overall control of the stretching process.