EP0112969A2 - Method for rolling metal strip - Google Patents

Abstract

In a method for rolling metal strips in a four-roll stand using axially displaceable workpieces that can be subjected to bending moment, the possibilities of acting on the strip profile are to be increased while reducing the construction and operating costs to be carried out for the stand. For this purpose, it is proposed that in the course of a roller journey with increasing service life of the work rolls, they are progressively shifted axially against the rolling stock, with bending devices acting on the work rolls attacking both positive and negative bending moments on their for the present bandwidth and to achieve a predetermined profile of the rolling stock the profile is set to the optimum value and the back-up rollers are axially displaced into an optimal position in the present range in order to achieve the profile.

Description

The invention relates to a method for rolling metal strips in a four-roll stand using axially displaceable and bending moment loadable work rolls and a four-roll stand for performing the method.

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 between the stands Standing in the middle. In order to meet the increased demands with regard to the flatness of the rolled strip and its absence of tension, six-roll stands were built in which the contact forces are transferred 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 jacket lines the work rolls can be specified. 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 arise during operation, because now two more rollers have to be changed and then refurbished when changing the rollers. Although through the use of intermediate rolls the service life of the backup rolls increases slightly, but the wear on the work rolls increases, and the disadvantage is 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 them and the backup rolls fall below those that occur with an equally loaded four-roll stand between the work rolls and the backup rolls, the between the work rolls and the pressures caused by the intermediate rolls increase and accordingly also increase the material stress. Despite the high expenditure, 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 increasing wear and increase the service life of the work rolls, it is advisable to roll wider and then narrower belts within one roll travel. However, this requires a further organization of the rolling program and fails if essentially strips of the same width are to be rolled.

In DE-PS 22 60 256 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, to keep one end of the working surface of a work roll between an edge of the rolling stock and the end of the associated backup roll. 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.

The invention is therefore based on the object, the possibilities of acting on the band profile while lowering the to increase the scaffolding to be driven construction and operating expenses.

This problem is solved when rolling in a four-roll stand according to the type specified, by progressively shifting the work rolls axially against the rolling stock in the course of a roll trip with increasing service life, with bending devices acting on the work rolls acting on the work rolls for both positive and in order to achieve a predetermined profile of the rolling stock negative bending moments are also set to their optimum value for the belt width and the profile, and the back-up rolls are axially shifted to an optimal position in the present belt width to achieve the profile. The object is further achieved in a method of the type corresponding to the rolling of metal strips, in which the work rolls are shifted in opposite directions until a bale end of one of the work rolls is flush with each of the two strip edges, in order to achieve a predetermined profile of the rolling stock the bending devices attacking the work rolls for both positive and negative bending moments are set to their optimum value for the strip width and the profile, and the back-up rolls are axially displaced into an optimal position in the present strip width in order to achieve the profile. In both cases, the possibilities that result from the application of torque to the work rolls are increased by the fact that either positive or negative bending moments can be specified, and the possibilities that result are considerably increased by the support rolls also being designed to be axially displaceable. DE-PS 22 60 256 has already addressed the possibility of axial displacement of back-up rolls, but their considerable effect on the shape of the roll gap was not recognized, otherwise the application would not have been dispensed with due to alleged difficulties in practical implementation. As However, it has also been shown that, with such an arrangement, work roll bending and back-up roll shift already have a considerable influence on the shape of the roll gap, so that in general the retained axial displaceability of the work rolls can be used to shift the given essential wear areas and thus to prevent areas of maximum erosion of the roller surface. If, on the other hand, the highest demands are placed on the flatness of the strip, it is possible to meet this by also using the displaceability of the work rolls for flatness adjustment or flatness control. With a four-roll stand that is much simpler than a six-roll stand, you can take over the possibilities of influencing the roll gap with reduced effort and, in addition, by distributing the wear, longer service lives of the rolls and thus further reduced operating expenses as well as, if necessary, a significant increase in the influence on the roll form.

'It has proven useful to shift the back-up rollers in opposite directions until each end of the bale is flush with the edge of the rolling stock, or else the back-up rollers also move beyond this dimension in such a way that the end of the bale is already led over the edge of the strip.

In the construction of the four-roll stand suitable for carrying out the method according to the invention, the chocks of both the backup rolls and the work rolls are designed to be axially displaceable, and their actuating devices which control them are assigned to them, and furthermore the bending cylinders provided for bending the work rolls are arranged and designed such that they can cause both positive and negative bending moments.

In practical construction, it has proven useful to have the windows of the uprights gripped by two crossbeams, on which the chocks of the support rollers are slidably supported, slides being provided between one of the crossbeams and the upright yoke facing it, while the other is expedient supported directly on the stand yokes facing you. The stability of the work rolls and any horizontal deflection of the work rolls which can occur can be avoided if the chocks are assigned to at least one of the work rolls, their horizontal adjustment adjusting devices. The flatness of the rolled strips or the shape of the roll gap can also be influenced if the chocks of the work rolls can be displaced horizontally in opposite directions by means of the adjusting devices, if necessary, so that the work rolls can be set.

• 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 schematisch das Walzen eines Metallbandes, bei dem die Ballenenden der Arbeitswalzen jeweils mit Walzgutkanten bündig stehen und die im gleichen Maße verschobenen Stützwalzen durch kürzere Ballenlängen über die Bandkanten hinaus vorgeschoben sind,
• Figur 7 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,
• Figur 8 eine ähnliche Einstellung, bei der die Ballenenden der Stützwalzen jeweils über die Bandkanten hinaus vorgeschoben sind, und
• Figuren 9 Band- und Randwölbungen sowie eine aus diesen resultierende Gesamtwölbung beispielhaft darstellendé Diagramme.

The features of the invention are explained in more detail with reference to the following description of an exemplary embodiment with working examples in conjunction with this and the drawings which illustrate the same. They show:

• FIG. 1 shows a section through a four-roll stand,
• FIG. 2 shows schematically the rolls of a conventional four-roll stand,
• FIG. 3 shows the work rolls of a four-roll stand with the wear that usually occurs,
• FIG. 4 the work rolls of a four-roll stand with distributed wear,
• FIG. 5 shows the rolls of a four-roll stand with symmetrical displacement of the work rolls and the same displacements of the respectively associated backup roll,
• FIG. 6 shows schematically the rolling of a metal strip, in which the bale ends of the work rolls are each flush with the edges of the rolling stock and the supporting rollers, which are displaced to the same extent, are advanced beyond the strip edges by shorter bale lengths,
• 7 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,
• FIG. 8 shows a similar setting, in which the bale ends of the support rollers are each advanced beyond the belt edges, and
• Figures 9 band and edge curvatures as well as a diagram resulting from these resulting total curvature.

1 shows a section through the stands 1 and 2 of a four-roll stand, in the stand window 3 of which a cross member 4 is placed on the lower stand yokes, on which in the area of the stand rest slides 5, on which the chocks 6 of the lower support rolls 7 are supported. On the top of the chocks 6 provided sliding surfaces - rest of chocks 8 of the lower work roll, above which the chocks 9 of the upper work roll 11 are provided, which abut on sliding surfaces of chocks 12 for the upper support roll. 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 means of spindles; push rods 14 and 15 continue to engage on the chocks shown lengthwise, and the chocks of the upper work roll can be displaced 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 stator window 3, which in turn is supported against the upper yokes of the stator 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. Is rolled with such an arrangement essentially rolled material of the same width, there is increased erosion of the work rolls in the area of the strip edges, as is shown exaggerated in Fig. 2: In those surface areas of the work rolls 8, 9, in which mainly during rolling Strip edges of the rolling stock have run, zones 21 of increased erosion can be determined, the depth of which is decisive for changing the work rolls and reworking them, while in the intermediate zones 22 only a significantly lower erosion can be found. 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 over a longer jacket zone than was the case with operation only with the position of the work rolls shown in FIG. 3, due to the rolling with work rolls shifted against one another by different amounts, and the rolls achieve a much longer time with the controlled mutual displacements Service life than when operating without axial displacements can be allowed. 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 a corresponding displacement of the support rolls in connection ... with a pre-bending of the work rolls. A further correction of the crowning can be brought about in that the work rolls are additionally positioned horizontally in opposite directions from the horizontal plane having the support roll axes, both the mutually opposite chocks of a work roll and the two chocks of the work rolls held within a stand being set in opposite directions, so that there is a set effect. Through additional coincident adjustments of the chocks of a work roll, the effective crossover point can be kept within the plane of symmetry of the stand even when the work rolls are axially displaced, or can be shifted against them if required.

The possibilities for the displacements of the support rollers can be seen from FIGS. 2 and 5 to 8. 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 rollers are flush with the left edge of the belt, and accordingly the upper work roller 10 and the upper support roller 17 shifted to the left until its 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 an arrangement according to FIG. 2 the line loads when loading the rollers 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.

Another possible operation is shown in FIG. 6. Here, too, the work rolls 10 and 11 are moved axially against one another in such a way that their bale ends are aligned with the edges of the rolling stock. The support rollers 7 and 17, however, are either shifted to a lesser length of their bale or by a greater displacement so far that their bale ends are still displaced beyond the edges of the rolling stock 20, so that a short root piece of the bale of the work rolls runs without support. Here, too, there is a relatively small basic deformation of the roll gap profile, and the roll deflection allows corrections even at relatively low moments. This makes it entirely possible to form the rolls with cylindrical bales, and the only disadvantage that becomes noticeable is that, because of the negative overhang of the bales of the rolls, there is a risk of markings on the surface of the rolling stock: the bale edges delimiting the bales of the rolls run in the region of the Rolled good.

7 and 8 two further possibilities of rolling are designated. Here they are on one side of the rolling stock 5 and 6, in the same direction and preferably shifted by the same amounts, according to FIGS. 7 and 8, however, the rolls running on one side of the rolling stock are each shifted in opposite directions so that one end of the bale is in each case the work rolls are flush with one belt edge and the associated work rolls are each flush with the other belt edge or have a negative projection against it. In both cases there is extensive compensation, in the case of FIG. 8 even overcompensation, of the roll gap, so that the roll bending can be reduced or even used in a negative sense. This makes it possible to use cylindrical rollers in both cases, but in the case of FIG. 8 there is again the risk of markings occurring due to the negative projection.

This shows that a scaffold designed according to FIG. 1 gives almost the same possibilities as are praised for the six-roll stand, with the possibility of distributing the wear occurring during rolling by shifting 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 of FIGS. 7 and 8 in opposite directions, since here the smallest deformations of the roll gap profile occur and the maximum effect of the work roll deflection is achieved, so that even overcompensation can be easily achieved. Such overcompensation or a limitation of the required bending moments to small values can be achieved if a position of the 8 is taken in which the back-up rolls run with a negative overhang.

When compensating profile errors of the strip, use is made of a further finding: Usual overall deformations of a rolled strip, such as that shown in FIG. 9a, can be divided into essentially two categories. When _B andwölbung a square parabolic camber is referred to, which can be represented mathematically by substantially quadratic terms. An example of a positive band curvature is given in FIG. 9b, 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 an edge curvature, as is shown, for example, in FIG. 9c. In practice, both usually occur simultaneously, as can be seen from FIG. 9a, which represents an additive superimposition of the curves according to 9b and 9c. These strip curvatures are brought about by the prevailing roll gap profile, and, as shown in FIG. 9, 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 a finding of the present invention, in the correction of the roll gap profile and thus the total curvature resulting on the rolling stock, to substantially compensate for edge curvature 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. For example, the work rolls can be shifted or set horizontally at an angle, and such an inclination or setting can also be effected asymmetrically to the center of the stand or rolling stock. However, it is also possible to dispense with the axial adjustment of the work rolls as a means of distributing the wear or for further correction of the roll gap and to equip the work rolls as bottle rolls with contours which allow the strip curvature to be adjusted. Furthermore, the displacement of the support rollers already gives rise to correction possibilities which can still be adjusted by using support rollers with a diameter which is not too large and the bending devices assigned to them. This results in the possibility of targeted and easily programmable change or correction of roll gap profiles. In essence, it is desired to maintain the profile shape already removed from the rolling stock relatively, so that largely tension-free rolled strip is obtained. As a result of the relationships which are recognized as being relatively simple, there is the possibility here of determining deviations from the profile shape by regions of deviating strip tension, without the need for deformation of the rolled strip. It has therefore proven 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 bend 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 (17)

1. A method for rolling metal strips in a four-roll stand using axially displaceable work rolls that can be subjected to bending moment,
characterized,
that in the course of a roller journey with increasing service life of the work rolls (10, 11), these are progressively shifted axially against the rolling stock (20), with bending devices acting on the working rolls acting on both for positive and negative bending moments on their for achieving a predetermined profile of the rolling stock the present bandwidth and the profile are set to the optimum value, and the support rollers (7, 17) are axially displaced into an optimal position in the present range to achieve the profile. 2. A method for rolling metal strips in a four-roll stand using axially displaceable and bendable work rolls, which are shifted against each other until a bale end of one of the work rolls is flush with each of the two strip edges, characterized in that
that to achieve a given profile of the rolling stock, the bending devices acting on the work rolls for both positive and negative bending moments are set to their optimum value for the present strip width and the profile, and the back-up rolls (7, 17) in one with the available bandwidth to reach the optimal position to reach the profile. 3. A method for rolling metal strips according to one of claims 1 or 2,
characterized,
that the support rollers (7, 17) are displaced in opposite directions so far that one bale end of one of the support rollers is flush with each of the two belt edges. 4. Process for rolling metal strips according to
Claim 1 or 2,
characterized in that the support rollers are displaced in opposite directions to such an extent that the ends of their bales, which essentially overlap the rolling stock, are each advanced a predetermined distance beyond the respective strip edge. 5. Four-roll stand for carrying out the method according to one of claims 1 to 4 with bending cylinders provided for bending the work roll and devices for displacing the work rolls in the axial direction,
characterized ,
that the chocks (6, 8, 9, 12) of both the support rolls (7, 17) and the work rolls (10, 11) are designed to be axially displaceable and their displacement-causing adjusting devices are assigned to them, and that the bending cylinders are arranged and are trained to be able to cause both positive and negative bending moments. 6. four-roll stand according to claims 1 to 5,
characterized , that the windows (3) of the stand (1, 2) are penetrated by two crossbeams (4, 18), on which the chocks (6, 12) of the support rollers (7, 19) are displaceably supported by slides (5), and that adjusting devices (19) are provided between one of the crossbeams and the stator yokes facing it. 7. Four-roll stand according to one of claims 1 to 6, characterized in that
that the chocks (8, 9) of at least one of the work rolls (10, 11) are associated with their horizontal adjustment adjusting devices. 8. Four-roll stand according to claim 7, characterized in that
that the chocks (8, 9) of the work rolls (10, 11) can be displaced horizontally in opposite directions by means of the adjusting devices. 9. Four-roll stand according to one of claims 1 to 8, characterized in that
that the chocks (6, 12) of the support roller (7, 17) support the (8, 9) of the work rollers (10, 11) by means of sliding surfaces. 10. Four-roll stand according to one of claims 1 to 9, characterized by
the use of work rolls (10, 11) designed as bottle rolls. 11. Four-roll stand according to one of claims 1 to 10, characterized in that
that the chocks (6, 8, 9, 12) axially displaceable and stressable with bending forces rollers (7, 10, 11, 17) in horizontal guides of spacers are, which in turn are displaceable in vertical guides fixed to the stand, which can be acted upon by the bending forces. 12. Four-roll stand according to one of claims 1 to 11, characterized in that
that the movable support rollers (7, 17) are assigned to roller bending devices. 13. Four-roll stand according to one of claims 1 to 12, characterized in that
that the application of bending forces to axially displaceable rollers is effected in each case by two hydraulic cylinders assigned to the installation or intermediate pieces at a distance from the axial roller stroke, and a control device arranged upstream of them pressurizes them differently, so that the sum of their forces results in the predetermined actuating force and the ratio of the forces is continuously adjusted so that the line of action of the common forces shifts with the axial adjustment of the roller. 14. Four-roll stand according to one of claims 1 to 12, characterized by
a control device which corrects edge warping errors of the rolling stock (20) by changing the work roll bend, and the band warping errors by setting the work rolls when they are horizontally adjusted, by axially displacing bottle rolls and / or by the bending and / or lateral displacement of the support rolls (7, 17) compensates. 15. Four-roll stand according to claim 14, characterized in that
that the control device when leveling a strip crown error, the _A rbeitswalzenbiegung slightly in opposite directions and when compensating an edge warping error, the adjustment option to be used to compensate for belt warping errors is actuated in the opposite direction to the work roll bending. 16. Four-roll stand according to one of claims 1 to 15, characterized in
that it is followed by a belt tension meter, which communicates the belt tension determined in different width ranges of the rolled strip (20) to the control device, which compensates for tension differences by roller displacements, roller bends and offsets. 17. Four-roll stand according to claim 16, characterized in
that the belt tension meter is a tension measuring roller.

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