FR2746680A1 - METHOD FOR ROLLING A SPECIAL STEEL FOIL - Google Patents

Abstract

The present invention relates to a method for rolling special steel strip in continuous strip plants, in which a pre-strip is reduced in at least one rolling stand, to a final thickness, and is temporarily stopped. According to the invention, to stop the strip (B), the grip of the rolls of each rolling stand (A1 to An) is open to at least the thickness of the rolled material detected on the inlet side of this rolling stand. rolling mill, and the sections of strip, located behind each rolling stand, are moved back at least before the respective rolling stand and, after closing the rights-of-way of the rolls to the set thicknesses set before the opening of said rights-of-way, the sections of strip Next, these strip sections again pass through the following rolling stands in the rolling direction.

Description

The present invention relates to a method for rolling a strip

  of special steel in continuous strip installations, in which a pre-beam is reduced, under predetermined tensile forces, in at least one, preferably several, rolling mill stands, in steps, with decreasing target thicknesses, to a

  final thickness, and is stopped temporarily, advantageously-

  for the exchange of cylinders, maintaining the forces

traction.

  The present invention is useful in installations in which a special steel strip is continuously guided under controlled traction through the mill, laminated thereon and machined continuously in adjacent processing facilities. In the case of endless rolling of special steel strips, it is from time to time necessary to stop the installation, for example to change the working rolls of the rolling mill stands. If a strip in the rolling mill is stopped, the contours of the rolls are drawn on the strip in the area of the roll stands and, in the rolling direction, the strip is deformed from cage to cage in different stages, it is ie thicknesses. After the exchange and adjustment of the cylinders exchanged at the target thickness of the cylinder areas, the rolling process is started again, the strip not having, in most cases, in this way, the

  nominal deformation required in the pass area, so that partial areas of the strip do not exhibit the same quality characteristics, surface structure, and tolerances as the remainder of the strip.

  The described partial areas of the strip having a lower quality can often not be sold and must be separated from the strip or coil formed therefrom. Especially for special steel qualities with high sales values, this large waste production means a strongly negative load on the profitability of the plant. From the problems and disadvantages mentioned in continuous steel strip installations, the present invention aims to provide a method for rolling a special steel strip, in which the loss of quality caused by the stoppage of the strip , for example for the exchange of cylinders, is avoided, the proportion of strip waste by the stop is eliminated and, thus, the

  profitability of the installation is increased.

  For this purpose, the method for rolling a strip of special steel in continuous strip installations,

  of the type indicated above, is remarkable, according to the invention.

  in that, in order to stop the strip, the grip of the rolls of each roll stand is open to at least the thickness of the laminated material detected on the entry side

  of this roll stand, in that the sheet sections

  Bacon, lying behind each roll stand, already

  laminated to the nominal thickness are moved backwards by

  the direction of advance of the strip, at least before the respective rolling mill stand and, after further reversing of the direction of advance of the strip and closing of the cylinder areas with respective set-point thicknesses set beforehand

  the opening of the roll areas, the sections of strip following these stretches of strip again through the following roll stands in the direction of rolling.

  The invention thus consists essentially of the recoil of the rolled strip to the target thickness after stopping behind the previous cage and subsequent rolling of the strip to the nominal rolling thickness. With this way of

  the advantage of a larger farm

  the elimination of long, otherwise usual waste parts, a significant cost reduction compared to the usual special steel rolling process should be expected. The exchange of

  cylinders can now be performed, preferably

  During the continuous operation, the strip section in the region of the cylinders to be exchanged also has, after the stoppage of the installation, the same surface structure and the same nominal deformation as the strip as a whole. This is made possible by the

  Renewed lamination of the strip with the last leap of

  thickness of the reduction cage characterized by the exchange

cylinders.

  According to another characteristic of the invention, it is provided that the strip section, located behind the last output-side roll stand, already rolled to the final dimension is moved back before the first roll stand on the die side. and again crosses all the mill stands at the same time as the other sections of strip already reduced to the target thickness, the margins of the rolls of the individual rolling mill stands being returned to the respective setpoint thicknesses set before opening. the grip of the cylinders. With this method, we obtain a new rolling of the

  strip section as a whole stopped inside the rolling mill.

  Preferably, the opening of the grips of the rolls is carried out already during the stoppage of the strip, so that a smooth transition between the strip section already reduced

  and the section of strip still to be reduced must be expected.

  Another variation of the process of the invention is remarkable in that, before stopping the strip, starting with the first inlet side mill stand, the roll right-of-way of each subsequent roll stand in the direction of rolling are opened one after the other and directly before the entrance of the strip section, with the thickness of the prefeuillard, at least the thickness of the prefeuillard, in that, after stopping the strip, the section of the strip, lying behind the last exit-side cage, already rolled to the final dimension, is moved back before the first roll stand on the inlet side, and after having made the exchange of the rolls and

  regulating the grips of cylinders to thicknesses of

  their respective rules before opening the right-of-way of

  cylinders, crosses all the mill stands again.

  In this variant, the stepped transition zone in form

  wedge between the inlet thickness and the thickness of

  The temperature of each rolling step, which necessarily occurs on the rolled material until the roll rim is fully open, can be reduced to a minimum strip length. Whereas, in the first version of the procedure, the length of the stepped strip portion first corresponds essentially to the length of the

  rolling mill, in a second variant, this part of

  Bacon can be reduced to less than the distance between two cages.

  The advantage of this step of the process is that

  only a portion of the wedge-shaped strip must be further deformed and, indeed, in all the rolling mill stands, so that a very good surface quality and maintenance of tolerances of this section of strip

lamination should be expected.

  In this variant of the process, the opening of the cylinder roll of all the mill stands is controlled one after the other and is carried out in the same section of strip, while the tension of the strip is kept constant. before, between, and behind the cages. Thanks to the constant tension of the strip, exact deformation conditions are obtained in the roll grip, so that the quality of the strip at rest, brought before the

  first rolling mill stand, and again started is

  made. Elimination of this critical strip section

no longer necessary.

  Advantageously, the section of strip which is not

  laminated is pushed back before the mill stand

  at least one length of acceleration range, in all process steps, required by the strip to achieve the speed necessary for the reduction. With modern rolling mill drives, this extension will, in practice, be a short length of strip, so that the length of strip to be rolled reaches, at the

  rolling speed, the respective cylinders' grip.

  It is necessary, in a known manner, in strip installations, to pay attention to the fact that the strip enters centrally, that is to say centrally by its central axis, into the cylindrical grip. Lateral movements of the strip towards the cylinder supports are regulated by special devices. These consist, for example, of pairs of rollers arranged on a frame, around which the strip is guided in the shape of S and which direct the strip, by adjusting the frame, transversely to its plane of displacement. By rolling back the strip according to the teaching of the invention, it is possible to achieve, for a strip moved in a manner corresponding to the adjustment algorithm of this strip center regulator, a position of the strip which, after restarting the strip , misses the exact same position in the mill. Thus, during the new start of the rolling process, the rolling conditions are no longer accurate, and the desired quality of the laminated material is no longer maintained. To guarantee the quality of the strip, it is proposed, according to

  another development of the invention, a method of

  strip forming in which the strip, as is known, is oriented, before entering the first roll stand, transversely to the rolling direction, so that the center of the strip extends to the center of the roll body , and that when changing from forward to reverse and from reverse to forward, the direction of adjustment of the center regulator is changed, to

  each time by inverting the tuning algorithm.

  Appropriately, thanks to this proposal of the invention

  The existing strip control device can be used as a combination control device for forward and reverse. For this, the strip control device is equipped with an additional adjustment system consisting of a drive, a guide means and a regulator, which acts only during reverse. When rolling is resumed (forward), the additional adjustment system is brought back from

  controlled way, to a neutral position.

  Thus, it is guaranteed that during the retreat of the material

  When laminated before the first rolling stand, the position of the rolled material with respect to the axis of the laminar stand is retained, so that the rolling process can be restarted with identical rolling conditions.

  The figures of the annexed drawing will make clear how

the invention can be realized.

  Figure 1 is a schematic view of a rolling mill with three

  cages for rolling a special steel strip.

  Figure 2 illustrates the deformation conditions in the

three rolling mill stands.

  FIG. 3 shows the deformation of the rolled material in the three mill stands before the sheet is retracted, under

diagram form.

  FIG. 4 shows the deformation of the rolled material in the three roll stands after the sheet has been retracted, under

form of a diagram.

  In FIG. 1, following the example of a continuous three-stand rolling mill, the rolling mill stands are designated A1, A2, An n, which means that the rolling mill may also consist of more than three roll stands. The roll supports of the rolling mill stands A1 to An are each time designated 1, the working rolls 2 are supported, in known manner, by support rolls 3. The strip B passing through the rolling mill stands A1 In An is reduced in each roll stand between the work rolls 2 by a predetermined value, so that the strip sections 4, 5, 6, 7 have different set-point thicknesses. In the lower half of the drawing of FIG. 1, the strip B is shown, for a better overview, without the rolling mill stands A1 to An, one of the transition zones between two steps with different setpoint thicknesses being shown. enlarged below. The transition between the reduction end points A1 and A12 of the strip sections 4 and 5 extends over a distance n1, when working according to the method of a first variant of the invention. This corresponds, correspondingly, to the transition zones between the strip sections 5 and 6, as well as 6 and 7. In these cases, the working rolls 2 of the individual rolling mill stands A1 to An are open during the shutdown. of the strip, in each case, to the thickness of the laminated material which has been detected on the inlet side of the

  respective rolling mill. In other words, the laminating force

  The rolling mill cage A1 is reduced until the latter reaches the value 0. This means that, for example, the cage A1 opens the working rolls 2 & the nominal thickness of the strip section 4 and , in truth, from the setpoint thickness of the stretch of

  5. In the same way, cage A2 opens the cylinders

  working widths 2 to the nominal thickness of the strip section 5, starting from the set section thickness

  6. The cage An is open, from the thick

  setpoint of the strip section 7, by recoil of the working rolls 2 to the target thickness of the strip section 6. As the opening of the working rolls is performed at the same time as the stopping of the strip B, obtains the transition represented at the bottom in FIG. 1 on the range n1 which presents, in practice, between the sections

  each time neighbors, soft transitions

rounded.

  After the strip B has come to a standstill, the sections of strip 5, 6, 7 already rolled to the target thickness are moved back by reversing the direction of movement of the sheet before the respective rolling mill stands A1, A2. and An.30 After the restart, for example after the change of the cylinders and after the setting of the cage A1 to the target thickness of the strip section 5, the setting of the cage A2 to the setpoint thickness of the section of 6, and after adjusting the cage An to the target thickness (the final thickness) of the strip section 7, these sections are rolled again. The decline of the sections of

  already rolled to the set thickness is

  killed over a span length as necessary to achieve the required rolling speed after start of rolling mill stands A1 to An, which is

  necessary for the reduction of the strip.

  In FIGS. 2 and 4, schematically

  way of proceeding according to another variant of the invention.

  Also in this case, for example, starting from a mill with three cages, which may however also consist of one or more cages. The three rolling mill stands are designated A1, A2 and An. In the diagram, it can be seen that the prefail has been reduced in the cage A1 of point 8 to a target thickness which is indicated in 9. In cage A2, the The pre-beam thickness 9 is further reduced and, indeed, to a target thickness 10. This setpoint thickness is once again reduced in the last cage A and, indeed, in the final strip thickness 11. n The method according to still another variant of the invention, before stopping the strip, all the cages are advanced to the thickness 8 of the prefeuillard of the first cage of the input side, so that the rolling force is zero . The advance is effected each time directly before the entry of the strip portion having the thickness 8 8, so that, after stopping the strip, there remains a section of strip which has a transition between them.

  thicknesses 8 and 11 over a relatively short distance. By retreating the transition of the strip before the cage A1 relative

  To a renewed extent of acceleration and rolling, shown in FIG. 4, of the zone of the strip successively in the cages A1 and An, this section of strip is

  laminate, obtaining the deformed surfaces 12, 13 and 14 corresponding to FIG. 4.

  In FIG. 3, the thickness of the laminated material is again represented in the form of a diagram along the length of the section of strip each time deformed. In this figure, the deformation end points PYX are designated each time, where y represents the number of passes and x, in each case, the location of the point o takes place.

  end of the reduction. Visibly, the individual deformation steps of cages A1 to Anse overlap and, furthermore, it can be seen that the extent constituting the jump between two set steps is relatively short.

  The wedge-shaped transition zone of deformation

  nominal to full discharge and the opening of the respective cage can be reduced to a minimum strip length and, indeed, less than the gap between the cages.

Claims (7)

  l. A method for rolling a special steel strip into continuous strip installations, in which a   prefeuillard is reduced, under predetermined tensile forces   in at least one, preferably more than one roll stand, in steps, with setpoint thicknesses   decreasing, to a final thickness, and is stopped   advantageously for the exchange of the rolls, while maintaining the tensile forces, characterized in that, to stop the strip (B), the roll grip of each roll stand (A1 to An) is open to at least the thickness of the laminated material detected on the inlet side of this roll stand, in that the strip sections, lying behind each roll stand, already rolled to the set thickness, are moved back by reversing the direction in advance of the strip, at least before the respective roll stand and, after   new reversal of the forward direction of the strip and   clearance of the cylinders to respective setpoint thicknesses set before the opening of the cylinder grips, the strip sections following these sections of   straps go through the following rolling mill cages again in the rolling direction.   A method for rolling a special steel strip in continuous strip installations according to claim 1, characterized in that the strip section, lying behind the last output-side roll stand, is already dimensionally rolled. The final end is moved back before the first inlet-side mill stand and again passes through all the mill stands at the same time as the other strip sections already reduced to the set-point thickness, the roll area of the individual roll stands. being brought back to the respective setpoint thicknesses set before opening the cylinder nip. A method for rolling a special steel strip in continuous strip installations according to claim 1 or 2, characterized in that the opening of the roll areas   is performed during the stopping of the strip.   4. A method for rolling a special steel strip in continuous strip installations, wherein a prefire is deformed, under defined tension, in a plurality of rolling mill stands into a corresponding number of rolling passes by reducing it to a thickness final,   and in which the strip is brought to a temporary stop-   advantageously for the exchange of the rolls, while maintaining the tensile forces, characterized in that, before the stoppage of the strip (B), in   starting with the first roll stand on the side of   In the rolling direction, the roll margins of each subsequent roll stand in the rolling direction are opened one after the other and directly before the entry of the strip section, with the thickness wedge up to the thickness of the roll. prefeuillard, at least the thickness of the prefeuillard, in that, after stopping the strip, the strip section, behind the last cage on the outlet side, already rolled to the final dimension is moved back before the first cage of the mill on the entry side and, after having   the exchange of the rolls and setting the roll grips to the respective setpoint thicknesses set before opening of the cylinder roll gap, again crosses all roll stands.   5. A process for rolling a special steel strip in continuous strip installations according to one of the Claims 1 to 4,   characterized in that the strip section which is not   laminated is pushed back before the mill stand   at least one length of acceleration range required by the strip to achieve the speed necessary for the reduction. 6. A method for rolling a special steel strip into continuous strip installations according to one of the claims 1 to 3,   characterized in that, by means of a known center regulator, the strip is oriented prior to entry into the first roll stand transverse to the rolling direction so that the center of the strip extends to the center of the body of the cylinder, and in that, when moving from the forward to the reverse and from the reverse to the forward, the direction of adjustment of the center regulator is changed, each time, by inversion of the tuning algorithm.   7. A method for rolling a special steel strip in continuous strip facilities according to claim 4 or 5, characterized in that, by means of a known center regulator, the strip is oriented before entering the sheet. first roll stand transverse to the rolling direction so that the center of the strip extends to the center of the roll body, and in that, when moving from the forward to the reverse and the step   backward in the forward direction, the setting direction of the center controller is changed, each time, by inverting the setting algorithm.