EP0112969B2 - Method for rolling metal strip - Google Patents

Abstract

A roll stand has a frame, a pair of small-diameter and substantially parallel working rolls defining a workpiece nip, and respective journal blocks supporting the working rolls in the frame for rotation about substantially parallel axes flanking the nip. These working-roll journal blocks and the respective working rolls can be axially shifted in the frame and the working rolls can be bent positively and negatively, that is respectively convex and concave toward the workpiece. A pair of large-diameter and substantially parallel backup rolls flank and bear toward the nip on the working rolls. Respective journal blocks support the backup rolls in the frame for rotation about substantially parallel axes flanking and generally coplanar with the working-roll axes. A strip is passed repeatedly in a multipass run through the nip generally perpendicular to the plane while the working rolls are pressed against the workpiece to reduce its thickness. The working rolls are axially displaced relative to the workpiece a plurality of times during the run to change the region of contact between the workpiece edges and the working rolls during the run. The working rolls are also bent at least to maintain the workpiece thickness downstream of the nip generally uniform.

Description

The invention relates to a method for rolling metal strips starting point is DE ― A ― 2 260 256.

The object of the present invention is to provide a method for rolling metal strips which allows metal strips of the same width to be rolled continuously in a four-roll stand, the metal strips produced being to be as flat as possible and the service life of the work rolls being to be as long as possible .

When rolling metal strips in four-roll stands, it has long been known to keep the work and support rolls in chocks vertically translationally displaceable or adjustable, but to guide the rolls axially constant in such a way that the bales of the rolls are symmetrical to the one located between the stands Stand middle level. In order to meet the increased demands regarding the flatness of the rolled strip or its absence of tension, six-roll stands were built in which the contact forces are transmitted from the support rolls to the work rolls via intermediate rolls, which are designed to be axially displaceable, so that the axially supported length of the surface lines of the work rolls. A disadvantage here is the high effort required, which not only consists in increasing the space requirement, lengthening the stands and interposing two additional rollers with chocks and arranging corresponding guide and displacement devices, increased costs and increased idle times also result during operation, since now two more rolls have to be changed and then refurbished when changing the rolls. Although the service life of the back-up rolls is increased slightly by the use of intermediate rolls, the wear on the work rolls increases, and it is disadvantageous that the intermediate rolls are also subject to relatively high wear. Even if the support caused by the diameter of the intermediate rolls, which is higher than that of the work rolls, the surface pressures caused between these and the support rolls fall below those which occur in the case of an equally loaded four-roll stand between the work rolls and the support rolls, nevertheless those between the work rolls and the pressures caused by the intermediate rolls increase and accordingly also increase the material stress. Despite the great effort, however, the problem of the increased wear of the work rolls occurring in the area of the strip edges of the rolling stock also persists with the six-roll stand. In order to reduce the impact of the locally increased wear and increase the service life of the work rolls, it is advisable to roll wider and then narrower belts during a roll trip. However, this requires further organization of the rolling program and fails if essentially strips of the same width have to be rolled.

In DE-A-22 60 256 and DE-C2-23 35 809 it is recommended for four and six-roll stands to reduce the influence of the deflection of the work rolls on the profile of the rolling stock, one end of the work surface of a work roll between each Edge of the rolling stock and the end of the associated backup roller to hold. However, the profile improvements possible with the four-roll stand do not reach the desired extent, and the distribution of the areas of greatest wear that was previously possible through the program selection is no longer possible. In the four-roll stand according to DE-A-22 60 256, the successive rolls of rolling stock of decreasing width are axially displaced from one another in such a way that the contact length of the rolls defined by the working rolls is shortened from time to time in accordance with the plate width of the rolling stock and this contact length is approximately equal to the plate width of the rolling stock. In the four-roll stand according to DE-C2-23 35 809 there is an opposite axial displacement of the support rolls on the edges of the rolling stock to adapt to the rolling of rolling stock with decreasing width. The work rolls cannot be moved axially. The wear of the work rolls is uneven and reduces their service life.

DE-C-200 426 describes a rolling mill with two rolls which are axially displaceable in order to achieve uniform wear of the rolls and thus a longer service life when rolling metal strips. However, the rollers are obviously dimensioned so strong that they cannot be subjected to a bending moment. There are also no back-up rolls. A correction of the flatness of the manufactured metal strips in the sense of the task set out above is excluded.

The object mentioned is solved by the features of the claim

• Figur 1 einen Schnitt durch ein Vierwalzengerüst,
• Figur 2 schematisch die Walzen eines üblichen Vierwalzengerüstes,
• Figur 3 die Arbeitswalzen eines Vierwalzengerüstes mit dem üblicherweise sich einstellenden Verschleiß.
• Figur 4 die Arbeitswalzen eines Vierwalzengerüstes mit verteilt bewirktem Verschleiß,
• Figur 5 die Walzen eines Vierwalzengerüstes mit symmetrischer Verschiebung der Arbeitswalzen und gleichen Verschiebungen der jeweils zugeordneten Stützwalze.
• Figur 6 das Walzen eines Metallbandes, bei dem der Ballen jeweils einer Arbeitswalze mit einer der Bandkanten bündig und das gegenüberliegende Ballenende der zugeordneten Stützwalze mit der gegenüberliegenden Bandkante bündig stehen.
• Figuren 7 Band- und Randwölbungen sowie eine aus diesen resultierende Gesamtwölbung beispielhaft darstellende Diagramme.

The invention is explained in more detail with reference to the following description in conjunction with the drawings. They show:

• FIG. 1 shows a section through a four-roll stand,
• FIG. 2 shows schematically the rolls of a conventional four-roll stand,
• Figure 3 shows the work rolls of a four-roll stand with the wear that usually occurs.
• FIG. 4 shows the work rolls of a four-roll stand with distributed wear,
• Figure 5 shows the rolls of a four-roll stand with symmetrical displacement of the work rolls and the same displacements of the associated backup roll.
• 6 shows the rolling of a metal strip, in which the bale of a work roll is flush with one of the strip edges and the opposite bale end of the associated support roller is flush with the opposite strip edge.
• Figures 7 band and edge curvatures and a diagram resulting from this resulting total curvature exemplary.

In Fig. 1 a section through the stands 1 and 2 of a four-roll stand is shown, in the stand window 3 of which a cross member 4 is placed on the lower stand yokes, on each of which rests in the area of the stand slide 5 on which the chocks 6 of the lower support rolls 7 are supported. On the upper side of the chocks 6, the sliding surfaces of the chocks 8 of the lower work roll, over which the chocks 9 of the upper work roll 11 are provided, are located on the sliding surfaces of the chocks Position 12 for the upper support roller. The carriage 5 carrying the chocks 6 of the lower support roller 7 are coupled to one another by a link and can be axially displaced by a push rod 13. As usual, the axes of the work rolls are overlapped by couplings and driven by spindles; Push rods 14 and 15 continue to engage the chocks shown on the left, the chocks of the upper support roller 17 being displaceable by a push rod 16.

The sliding surfaces provided at the top of the chocks 12 of the upper support roller are supported on a cross member 18 placed transversely through the stand window 3, which in turn is supported against the upper yokes of the stands 1 and 2 via pressure medium cylinders provided as adjusting devices. If necessary, one of the crossbeams 4 or 18 can additionally be supported by pressure measuring elements or the like.

The starting position during rolling can correspond to that of a conventional four-roll stand, in which the work and back-up rolls are symmetrical to the central vertical plane of the stand. If such an arrangement essentially rolls rolled material of the same width, there is increased erosion of the work rolls in the area of the strip edges, as shown in an exaggerated manner in FIG. 3: In those surface areas of the work rolls 10, 11 in which the strip edges are predominantly during rolling zones 21 of increased erosion, the depth of which is decisive for changing the work rolls and reworking them. while in the zones 22 in between there is only a significantly lower erosion. If the work rolls are now axially shifted from time to time during rolling, no such pronounced wear zones occur even when the rolling stock is always of the same width; rather, a wide, flat-running wear area 23 is obtained by superimposing wear areas that are shifted against one another, as shown in FIG. 4 is again shown exaggerated, and is completely free from wear maxima such as zones 21 of increased erosion. Thus, the wear is distributed more evenly by rolling with work rolls shifted by different amounts relative to one another and over a longer jacket zone than was done during operation solely with the position of the work rolls shown in FIG. 3, and the rolls achieve a much longer time with the controlled mutual displacements Service life than can be admitted during operation without axial displacements. The desired corrections of the roll gap are achieved here if the displacement of the work rolls is essentially used to avoid strong local erosions of the work rolls by corresponding displacement of the support rolls in connection with a pre-bending of the work rolls.

The possibilities for the displacements of the support rollers can be seen from FIGS. 2 and 5 and 6. 2 schematically shows the positions of the rolls which they assume in a conventional four-roll stand. Since the effect of the work roll bending is only moderate due to the support of the work rolls over their entire length by the relatively stiff backup rolls, it is common to use cambered rolls to compensate for the roll deflection.

5 shows the same roller arrangement in a working state which can be achieved with a four-roll stand designed according to FIG. 1: the lower support roll 7 and the lower work roll 10 are jointly shifted to the right against the vertical plane of symmetry of the stand until the bale ends of the two rolls are flush with the left edge of the strip, and accordingly the upper work roll 11 and the upper backup roll 17 are shifted to the left until their right bale ends are flush with the right side edge of the rolling stock 20. This results in approximately the same behavior that can be achieved with a six-roll stand when the intermediate rolls are shifted to the strip edges, ie only half the deformation of the profile of the roll gap is achieved under load as in the case of an arrangement according to FIG. 2 the line loads when loading the rolls are the same as those of the six-roll stand, but the pressings are more favorable than with a corresponding six-roll stand because of the changed diameter pairings. The effect of the work roll bending is also significantly improved compared to the arrangement according to FIG. 2, so that the rolls may not be cambered and cylinder rolls may be used.

6 the end position of the rollers according to the invention is shown. Here, the rollers running on one side of the rolling stock are not shifted in the same direction, and preferably by the same amounts, as in the applications shown in FIG. 5; however, according to FIG. 6, the rolls running on one side of the rolling stock are shifted in opposite directions so that one bale end of each of the work rolls is flush with one belt edge and the associated work rolls are each flush with the other belt edge. Here there is extensive compensation of the roll gap so that the roll bending can be reduced. This enables the use of cylindrical rollers.

This shows that a scaffold designed according to FIG. 1 gives almost the same possibilities as are praised for the six-roll stand, it being possible to distribute the wear occurring during rolling by moving the work rolls and thus the wear caused by the roll change and refurbishment Reduce work roll related effort. Since such a shifting of the rolls, which can be designated as arbitrary with regard to the roll gap profile, has repercussions on the roll gap, it is necessary to compensate for these repercussions by means of the work roll bending. If, on the other hand, value is placed on maximum flatness of the strip, it is advisable to shift the rollers 7 and 10 or 11 and 17 running on one side of the rolling stock 20 in opposite directions, since the smallest deformations of the roll gap profile occur here and the maximum effect of the work roll deflection is achieved so that even overcompensation can be easily achieved.

The following knowledge is used to compensate for belt profile errors made: Usual overall deformations of a rolled strip, such as one shown in FIG. 7a, can be divided into essentially two categories. A band-parabolic elevation is referred to as a band curvature, which can be mathematically represented essentially by square terms. 7b shows an example of a positive band curvature in which the band center extends essentially parabolically over the plane containing the two upper band edges. Odd mathematical terms result in a change in the upper cover surface of the rolled strip, referred to here as edge curvature, as is shown, for example, in FIG. 7c. In practice, both usually occur simultaneously, as can be seen from FIG. 7a, which represents an additive superimposition of the curves according to FIGS. 7b and 7c. These strip curvatures are brought about by the prevailing roll gap profile, and, as shown in FIG. 7, they can be positive and protrude beyond the base plane of the rolled strip or they can recede behind the plane as negative values. This representation is essential due to the knowledge that essentially uneven links or an edge bend are caused by work roll bends, which are identified by more than one, usually two, maxima, while strip curvatures or distortion forms similar to these are achieved by other means of influencing the roll gap. It is therefore possible, in the correction of the roll gap profile and thus the total curvature resulting on the rolling stock, to compensate for marginal curvature portions essentially by the bending forces acting on the workers, while different means can be used to compensate for the strip curvature extending over the entire range. Furthermore, the displacement of the support rollers already offers correction options which can still be adjusted by using support rollers with a diameter that is not too large and bending devices assigned to them. This results in the possibility of targeted and easily programmable change or correction of roll gap profiles. Essentially, it is desired to maintain the profile shape already removed from the rolling stock relatively, so that largely tension-free rolled strip is achieved. As a result of the relationships which are recognized as relatively simple, there is the possibility of deviations determined from the profile shape by areas of different strip tension without deformation of the rolled strip having to occur. It has therefore proven to be useful to arrange a strip tension measuring device after the stand and to transmit the values obtained for different width ranges of the rolled strip to the control device which controls the roll stand, so that it can compensate for the tension differences. In practice, however, it has been found that, when compensating for a strip curvature error, the work roll bend is deflected slightly in the opposite direction to the measures taken to correct the strip curvature error, while when compensating for a curvature of the edge, in addition to the work roll bending provided for this purpose, the measures provided for the correction of the strip curvature correction error will.

Belt tension meters designed as tension measuring rollers have proven themselves in practical construction.

Claims (1)

1. Method of rolling metal strips (20) in a 4-high roll stand utilising working rolls (10, 11) loadable by bending moment and axially displaceable backing rolls (7, 17), wherein the backing rolls are displaced in opposite sense in dependence on the width of the respective rolled stock in such a manner that each barrel end of the upper backing roll (17) is flush with a respective one of the flanks of the rolled strip (20) and the oppositely disposed barrel end of the lower backing roll (7) is flush with that flank of the rolled strip (20) which lies opposite the first, wherein the working rolls (10, 11), after the passage of one or more strips during the rolling of metal strips of equal width, are displaced axially relative to these through oppositely directed displacement travels into a working state in which the rolls (7, 10; 11, 17) running on one side of the rolled stock are so displaced respectively in opposite sense that each time one barrel end of the backing rolls is flush with one strip edge and the associated working rolls each time are flush with the other strip edge (Fig. 6).

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