Abstract:
Method and device to control the axial position of slabs emerging from a continuous casting machine, providing to control the axial position of the slab ( 24 ) in correspondence with the inlet to the first rolling stand and to act in feedback on means to modify the correct position of the axis ( 32 ) of the slab ( 24 ) in a position located between the first rolling stand and the foot rolls ( 26 ) of the ingot mold ( 13 ) from which the slab ( 24 ) emerges, wherein alignment means operating inside the furnace ( 15 ) are employed to induce a controlled lateral displacement governed by the control of the axial position of the slab ( 24 ).

Description:
FIELD OF THE INVENTION 
     This invention concerns a method to control the axial position of slabs emerging from continuous casting and the relative device as set forth in the respective main claims. 
     The invention is applied in rolling mills which have the rolling train located in line with the continuous casting machine, and is employed to obviate the problems of the slab emerging from the casting machine with its axis misaligned with respect to the axis of the first rolling stands. 
     The invention is employed both when the slab is less than 100-120 mm thick and is sheared to size in segments, and also when the slab is obtained with a whole cast of molten metal, and also when the slab is worked with continuity between the casting machine and the rolling train. 
     BACKGROUND OF THE INVENTION 
     One of the main problems which rolling mill operators complain about is how to control the axial position of the slab with respect to the axis of the first rolling stands located downstream of the heating furnace. 
     It is well-known that the slab as it emerges from the continuous casting machine, since it must be subjected to the processes of extraction, pre-rolling and straightening, rarely remains correctly aligned with the axis of feed; this causes considerable problems when the slab enters the rolling stands and during the rolling steps. 
     Moreover, as it travels inside the tunnel furnaces, either the heating furnace or the temperature maintenance furnace, the slab may be subject to lateral displacements which send it out of line. 
     If the slab arrives misaligned with respect to the axis of the first stand, rolling becomes difficult, particularly when thin diameters are being rolled. 
     In fact, in order to compensate for this misalignment after the slab has entered the stand, and to ensure that it enters the downstream stand correctly, it is necessary to act on the horizontal positioning of the first stand, which may have negative effects on the symmetry of the profile in the cross section of the slab itself. 
     While this does not create particular problems when the partly rolled product has a greater thickness, for example above 2 mm, in the case of thinner products there are considerable problems of quality, inasmuch as it becomes extremely difficult, if not impossible, to recover the difference in thickness between one side and the other, when the product is 0.6-0.8 mm thick. 
     In the case of thin products the transverse sliding of the material is very difficult to obtain and in any case it causes errors in planarity deriving from a differentiated stretching of the material. 
     In order to solve these problems, at least partly, solutions known to the art employ the action, either individually or in combination, of lateral guides, of the descaling assembly or the rolls or assemblies to finish the edges, which are arranged between the outlet of the heating furnace and the inlet to the stand, in order to obtain the progressive axial alignment of the slab and the rolling axis. 
     These solutions have shown themselves to be only partly efficacious, for a variety of reasons. 
     First of all, there is a technological requirement whereby the entrance to the stand cannot be too distant from the outlet of the furnace (the typical maximum value is around 14-20 meters), to prevent the excessive cooling of the slab to below the optimum rolling temperature. 
     For this reason it is necessary to obtain a great displacement of the slab per unit of length of the plant, in order to obtain the desired alignment in correspondence with the inlet to the stand. 
     Guide systems as are known to the art, however, are not able to obtain such values of displacement, and therefore they do not enable the desired alignment to be reached in the little space available between the furnace and the stands, which is imposed by technological constraints. 
     Lateral guides as are known to the art, moreover, occupy about 10 meters in length of the segment between the furnace and the stand, and define a transit width which is greater than the width of the slab, on both sides, by at least 25 mm per side, up to as much as 50 mm per side. Therefore, the alignment of the slab is imprecise by values of ±25-50 mm. 
     Moreover, the rollers which refine the edges, or edgers, cannot act upon the edges of the slab for more than about 10 mm per side. 
     All these factors make it impossible to centre the slab if the slab arrives misaligned with respect to the rolling axis beyond a minimum value which can be compensated, and which can be estimated in the region of ±10 mm. 
     There is also the further problem concerning the transport rollers inside the heating furnace. 
     In order to withstand the extremely high temperatures of up to 1110-1200° C. inside the furnace, these rollers are structured with cooled rolls which support disks made of refractory material which is mechanically very delicate, so that even a slight transverse displacement of the advancing slab causes considerable damage and puts the disks out of action very quickly. 
     It is therefore highly inadvisable to make the slab translate laterally when it is inside the furnace. 
     JP-A-62235429 teaches to provide nozzles arranged above and below the rolled stock passing through, which deliver a jet of gas in the opposite direction to the direction of feed of the rolled stock. 
     The nozzles are arranged in a zig-zag conformation and exert an action of mechanical displacement on the rolled stock if it is not centered with respect to the relative feeding means. 
     This device makes possible to obtain only limited adjustments in the position of the rolled stock, and moreover it may cause unacceptable modifications in the surface temperature conditions thereof. 
     EP-A-416356 describes an alignment station for rolled products arranged between the drawing-straightening assembly which acts on the rolled stock emerging from the continuous caster and the shears which shear the rolled stock into segments which are then sent to the temperature equalisation furnace. 
     The alignment station consists of a supporting roller, positioned under the plane on which the rolled stock is fed, with bearings which are connected to a relative vertical piston suitable to incline the roller to one side or the other so as to correct any possible lateral displacement of the rolled stock. 
     Alternatively, the alignment station comprises at least a burner, or at least a sprayer nozzle, cooperating with at least one edge of the rolled stock in order to align the rolled stock, either by exploiting the dilation caused by heating, or by exploiting the shrinkage caused by cooling. 
     The fact that the alignment station is positioned upstream of the shears assembly and of the furnace creates the problem that, precisely during the shearing cycle or during the heat treatment in the furnace, the segment of rolled stock becomes misaligned and arrives in correspondence with the first stands of the rolling train in an out-of-center condition. 
     Moreover, the inclusion of a single alignment roller can make it impossible to correct misalignments of the rolled stock of a certain entity, inasmuch as the lowering or raising of one side of the roller with respect to the other is limited by the overall height of the plane of feed. 
     Furthermore, EP&#39;356 does not mention any systems to control the position of the slab with respect to the axis of the rolling stands, nor any feedback systems which govern the alignment means and condition the functioning thereof in the event of misalignments being found downstream. 
     The present applicant has designed and tested this invention to overcome these shortcomings which cause serious operating and technological problems, and problems of quality, in the rolling of flat products, particularly thin flat products of less than 2 mm and down to 0.8-0.5 mm. 
     SUMMARY OF THE INVENTION 
     The invention is set forth and characterised in the respective main claims, while the dependent claims describe other characteristics of the main embodiment. 
     The purpose of the invention is to centre and axially align the slab as it emerges from the continuous casting machine so that, when it arrives at the entrance to the first stands, whether they be roughing stands, pre-finishing or finishing stands, it is perfectly aligned with the axis of these stands. 
     The invention obtains the aforesaid result without causing any deterioration on the surface or edges of the slab, without any risk of damaging the disks of the transport rollers inside the furnace, without any substantial modifications to the structure of the lateral guides, the edgers or the descaling assembly located at the outlet of the furnace, nor of the channels used to guide the rolled stock which are located at the entrance to the stands. 
     The invention allows to reduce the extension of the lateral guides, or even to eliminate them, with consequent advantages in terms of lay-out; thus the slabs are hotter as they enter the rolling stands and the length of the plant is reduced. 
     The invention uses the individual or combined action of a plurality of assemblies and devices located between the outlet of the ingot mold, in the zone of the foot rolls which contain and extract the slab, and the inlet of the first rolling stand. 
     According to the invention, the slab emerging from the ingot mold is subjected to a controlled cooling process cooperating with the sides of the slab, in order to obtain a desired lateral displacement achieved by the different thermal expansion of the two sides of the slab. 
     In other words, if it is discovered that the slab leaves the continuous casting machine already misaligned with respect to the nominal rolling axis, the secondary cooling assemblies are made to act in a controlled manner so as to achieve a differentiated thermal expansion on the two sides to compensate, at least partly, the extent of this misalignment. 
     According to a variant, downstream of the secondary cooling assemblies and/or in an intermediate position between them there are elements to measure and control the axial position. 
     The measurement and control elements verify, either continuously or periodically, that the misalignment is corrected and condition the secondary cooling assemblies in feedback in order to vary the intensity and action of the cooling in a desired manner. 
     According to another variant, in the event that the measurement and control elements verify that there is an excessive displacement which can no longer be compensated downstream, they order shearing means to be activated which intervene and form short slabs which can easily be manipulated inside the furnace even if they are progressively misaligned. 
     According to the invention, the rollers inside the heating furnace are driven independently, individually or in groups, in such a way as to determine the progressive re-alignment of the advancing slab. 
     In one embodiment, the rollers are arranged at an angle with respect to the nominal horizontal plane on which the slab lies, and the even rollers and the odd rollers are driven in an autonomous and separate manner. 
     The motors of the odd and even rollers are governed, according to a variant, by means to control the axial position of the slab, which order the rollers to be activated according to the extent of the misalignment found, possibly correcting the working parameters in feedback. 
     The different and controlled speed of rotation of the odd and even rollers inside the furnace, together with their angled position with respect to the plane of the slab, causes a progressive re-alignment of the slab with respect to the rolling axis of the stand located downstream, without causing any deterioration of the slab itself, and without intervening on the guide devices located between the furnace and the stand. 
     In another embodiment of the invention, the rollers of the furnace, either individually or in groups, are associated with means which regulate the inclination of the rollers on the horizontal plane with respect to the nominal position which corresponds to the orthogonal to the axis of feed of the rolled stock. 
     The said inclination regulation means are governed by means which control the axial position of the slab at the outlet of the furnace, and intervene by varying the inclination of the rollers, on one side and/or the other thereof and by defined angles, until the axial position of the rolled stock has been restored with respect to the axis of the first rolling stands. 
     In a further embodiment of the invention, there is a trolley used as an element to transport the slab, with an insulated cover and with heating means, which functions at least partly as a heating and/or temperature maintenance furnace. 
     The trolley can be translated sideways in a controlled manner. 
     In this embodiment, there is a device to control and measure the axial position of the slab, located at the outlet of the trolley, which verifies the alignment with respect to the axis of the first stand, and commands the lateral displacement of the trolley in such a manner as to take the slab progressively into alignment with the rolling axis. These verifications and consequent lateral displacements may take place either continuously or periodically at pre-determined intervals. 
     According to a variant, the device to control and measure the axial position is included, or also included, inside the trolley. 
     According to another variant, the two supporting girders lengthwise to the furnace, on which the rollers which extend inside the furnace are mounted, are sub-divided into several coherent segments which are equipped with lateral movement independent from each other. 
     These independent lateral movements, commanded by means to control and measure the axial position of the slab, make it possible to correct any possible misalignment of the slab and reduce its misalignment with respect to the nominal rolling axis. This embodiment is particularly indicated for long slabs, up to 200-300 meters long, that is, slabs which occupy substantially the whole length of the tunnel furnace. 
     According to a further variant, the rollers of the furnace are associated, on the opposite side with respect to the side of the motor, with a support which can be raised and lowered to modify the lateral position of the slab travelling through the said furnace. 
     The rollers, according to a further variant, are in groups and are raised/lowered in a coordinated and progressive manner by means of actuators associated with the monitoring of any misalignment between the axis of the slab and the rolling axis. 
     According to another embodiment, the respective disks of the rollers are arranged alternately between one roller and the subsequent roller, that is to say, the disks are grouped together on one half of one roller and on the other half of the following roller. 
     This configuration gives an undulated progress of the slab inside the furnace, which regularises the position and substantially aligns the slab with the rolling axis. 
     According to another embodiment, outside the furnace in a lateral position thereto, there are cone-shaped rollers distributed along the length of the furnace and on both sides thereof, to a desired number at intermediate positions between the usual transport rollers. 
     One and/or the other of the conical rollers are inserted inside the furnace when a misalignment of the slab is monitored, so that a controlled axial displacement is determined due to the conical shape of the rollers. 
     When the conical rollers are inserted the slab is lifted and loses contact with the usual transport rollers and can therefore be laterally displaced in the desired direction. 
     According to a variant, two conical rollers arranged coaxial on one side of the furnace and the other are inserted simultaneously inside the furnace so as to completely lift the slab and translate it sideways in the desired direction. 
     According to another variant, the conical rollers have a raised edge on the base which is used as an element to physically displace the slab. 
     According to a further variant, the conical rollers with the raised edge are maintained constantly inside the furnace on the two sides thereof so as to function as an element to constantly control the axial position of the slab and to limit the lateral displacement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The attached Figures are given as a non-restrictive example and show some preferential embodiments of the invention as follows: 
     FIG. 1 is a diagram of a rolling line, seen from the side, directly connected to the continuous casting machine to which the invention is applied; 
     FIG. 2 is a diagram of a segment of the line shown in FIG. 1, as seen from above; 
     FIG. 3 shows a first embodiment of the invention applied at the outlet of the continuous casting machine; 
     FIG. 4 shows another embodiment of the invention as applied to the heating furnace located upstream of the first rolling stand; 
     FIGS. 5 a  and  5   b  show, respectively from the front and from above, another embodiment of the invention; 
     FIGS. 6 and 7 a  show further embodiments of the invention; 
     FIG. 7 b  shows a part front view of FIG. 7 a;    
     FIG. 8 shows a cross section of another embodiment of the invention; 
     FIGS. 9 a  and  9   b  show two working arrangements of the embodiment shown in FIG. 8; 
     FIG. 10 shows a further embodiment of the invention; 
     FIG. 11 shows a working arrangement of the embodiment shown in FIG. 10; 
     FIG. 12 shows a variant of FIG. 11; 
     FIG. 13 shows a variant of the previous embodiments; 
     FIG. 14 shows a further embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The rolling line  10  shown diagrammatically in FIG. 1 comprises a rolling train  19  arranged in line with a continuous casting machine  11  including an ingot mold  13  and an extraction and straightening assembly including rollers  12 . 
     Downstream of the assembly  12  there is a shears for shearing to size  14  and a heating and/or temperature maintenance furnace  15  which feeds the slabs at temperature to a rolling train  16 , in this case with two stands  17 , which can be a roughing train or a pre-finishing train according to the case. 
     Between the train  16  and the finishing train  19 , in this case, there is a system to equalise and restore the temperature  18 , while downstream of the finishing train  19  there is the coiling assembly  21  to coil the strip produced. 
     In this case, between the heating furnace  15  and the train  16  there are conventional systems including lateral guides  20 , a descaling assembly  22  and an assembly to finish the edges  23 , of the type including rollers. 
     According to the invention, the rolling line  10  includes means to align the axial position of the slab  24  as it emerges from the continuous casting machine  11  to the rolling axis  25  of the rolling stands  17  and particularly to the axis  25  of the first stand  17  of the train  16 . 
     FIG. 3 shows a first embodiment of the invention. In this case, the slab  24  emerging from the ingot mold  13  and from the foot rolls  26 , and engaged by the rollers  27  of the extraction and straightening assembly  12 , is made to cooperate with cooling means  28  comprising delivery nozzles  29  cooperating with the sides of the slab  24 . 
     The delivery of the cooling fluid by the delivery nozzles  29  is governed by command units  30  which receive position signals from detectors  31  arranged in cooperation with the sides of the slab  24  being extracted. 
     The detectors  31  are pre-set to detect the position of the axis  32  of the slab  24  and to verify any difference in the axial position with respect to the rolling axis  25 . 
     There may also be a detector  36  suitable to detect the position of the edges, which does not need re-positioning as the width of the slab  24  varies. 
     When a misalignment is detected, there is a variation in the delivery of the cooling fluid, possibly differentiated on the two sides of the slab, by means of a controlled activation of the nozzles  29 . 
     By means of this control, which is carried out directly during the step of secondary cooling, the axis  32  of the slab  24  can be aligned with the rolling axis by laterally displacing the slab  24  itself due to thermal expansion. 
     In the event that the displacement is excessive, and cannot be compensated downstream, the invention provides to activate the shears  14  as an emergency shears, in order to obtain short slabs of such a size that the front edges do not damage the inner refractory surfaces of the furnace  15 , even if the slab is misaligned. 
     In the embodiment shown in FIG. 4, the heating and temperature maintenance furnace  15  consists of a trolley  34 , which can be moved sideways on rails  35 , inside which the supporting rollers identified by the axes  37  are mounted. 
     The trolley  34  cooperates with an insulated hood  38  associated with heating means and intake means which are not shown here. 
     The trolley  34  can receive slabs  24  from one or more casting lines and can be employed to feed a single rolling train with slabs  24  arriving from several casting lines or from stores of cold slabs or of special products. 
     According to the invention, the lateral movement of the trolley  34  is used to axially align slabs  24  which are misaligned with respect to the rolling axis  25 . 
     To be more exact, the axial position of the slabs  24  is monitored by detector means  36  arranged stationary at the outlet of the furnace  15  and upstream of the train  16 , or inside the trolley  34  itself, which are connected in feedback with a control unit  30 . 
     The control unit  30 , according to the position signals arriving from the detector means  36 , activates the actuator  33  which laterally displaces the trolley  34 , progressively aligning the axis  32  of the slab  24  to the rolling axis  25 . 
     In the case shown here, the trolley  34 , with an axis  34   a,  has been displaced by a value Δ so as to align the rolling axis  25  to the axis  32  of the slab  24 , the slab  24  having entered the trolley  24  misaligned with respect to the axis  25 . 
     Once the slab  24  has emerged, the trolley  34  can be progressively taken back to its original position, that is to say, with its axis  34   a  aligned with the rolling axis  25 . 
     In the embodiment shown in FIGS. 5 a  and  5   b,  the supporting rollers  39  inside the furnace  15  are associated, individually or in groups, with piston means  57 , respectively  57   a  on one side and  57   b  on the opposite side, suitable to displace the inclination of the rollers  39  with respect to the horizontal plane on which the said rollers  39  lie. 
     To be more exact, the supporting rollers  39 , which have a nominal position “0” wherein their axis  37  is substantially orthogonal to the axis of feed of the slab  24 , are inclined on the horizontal plane by an angle α, in one direction or the other, by activating the piston  57   a  or  57   b.    
     The entity of the inclination α and the direction of the inclination are determined according to the signals supplied by the detector means  36 , which measure the entity of the misalignment of the slab  24  at the outlet of the furnace  15 , and send the signals to the control unit  30 . 
     The control unit  30  processes the data and sends command signals to the piston means  57   a  and  57   b  to restore the correct alignment of the slab  24  with respect to the axis of the first rolling stands. 
     The rollers  39  are assembled individually on trolleys  58  equipped with wheels  59  and each can be equipped with its own piston means  57 . 
     In the embodiment shown in FIG. 5 b,  several rollers  39  are connected together by means of respective connection means  60 , which allows the rollers  39  to be driven simultaneously; this can affect groups of rollers  39  or even the whole totality of rollers  39  inside the furnace  15 . 
     In the further embodiment as shown in FIG. 6, the supporting rollers  39  inside the furnace  15  can be displaced laterally in a controlled manner, parallel to their axis  37 , with respect to the stationary structure  38  of the furnace  15 , which does not move. 
     In a first embodiment, all the rollers  39  can be laterally displaced independently of each other. 
     According to a variant, the rollers  39  can be displaced in groups, for example two by two or three by three. 
     The lateral displacement can be commanded by position detectors of the same type as the detectors  36  as shown in FIG. 4; it allows to displace the slab  24  laterally as it rests on the disks  40  without the slab  24  sliding laterally on the disks  40 , that is to say, without damaging them and wearing them out. 
     The position detectors  36 , which are not shown in FIG. 5, are connected in feedback with the displacement actuators  41  which act on the sliders  42  on which the bench supports  43  rest; the bench supports  43  support the rotation bearings  44  of the rollers  39 . 
     The rollers  39  are made to rotate by a motor  47 . The sliders  42  slide on guides  45  made on displacement planes  46 . 
     Once the trailing end of the slab  24  has left each individual roller  39  or group of rollers  39 , the rollers are re-aligned to receive a new slab  24 . 
     In the embodiment shown in FIG. 7 a,  the axial alignment of the slab  24  with respect to the rolling axis  25  is obtained by modulating the speed of rotation of the rollers  39  in a differentiated manner. 
     In this specific case, the rollers  39  are angled with respect to the plane on which the slab  24  lies. 
     The odd rollers  39   a  are commanded by one command unit while the even rollers  39   b  are commanded by their own autonomous command unit. 
     The command units are connected in feedback with detectors  36  of the type shown in FIG. 4, suitable to detect any axial misalignment between the axis of the slab  32  and the rolling axis  25 . 
     If any misalignment is detected, and according to the extent of the misalignment, the rollers  39   a  and  39   b  are commanded to obtain the controlled lateral displacement of the slab  24  by acting on their differentiated and variable speeds. 
     By inclining the rollers  39  with respect to the plane of the slab  24 , the contact points of the relative disks  40  rotate at different speeds on one side of the slab  24  and the other (FIG. 7 b ) and therefore the slab  24  can be displaced laterally in a controlled manner. 
     According to a variant, each roller  39  can be controlled individually and independently of the other rollers  39 . 
     In the embodiment shown in FIG. 8, the rollers  39  are supported at the side, on the side of the motor, by a stationary support  48 , while on the opposite side they are supported by a support  49  which is vertically movable. 
     In the embodiment shown here, the support  49  consists of a plane inclined towards the furnace  15  and cooperating with an actuator  50  which displaces the support  49  on the horizontal plane. 
     When the actuator  50  is activated in one direction or the other, there is a correlated lifting or lowering of the movable support  49 , and therefore one side of the relative roller  39  is consequently inclined in one direction or the other. 
     FIGS. 9 a  and  9   b  show two possible conditions which may occur: 
     in FIG. 9 a,  where the slab  24  tends to become misaligned towards the right with respect to the rolling axis  25 , the movable supports  49  are raised so as to incline the rollers  39  downwards and towards the left; 
     in FIG. 9 b,  where the slab  24  tends to become misaligned towards the left with respect to the rolling axis  25 , the movable supports  49  are lowered so as to incline the rollers  39  downwards and towards the right. 
     The actuator  50  is connected, advantageously by means of a control system in feedback, to a command unit which receives signals relative to the misalignment of the slab  24  from detectors  36  arranged inside the furnace  15  and correlates the extent and the direction of movement of the movable supports  49  to the extent of the misalignment. 
     In the embodiment shown in FIG. 10, in a lateral position outside the furnace  15 , advantageously on both sides of the furnace  15 , there are conical rollers  51 , cooled and mounted as cantilevers on a relative support  52 ; their axis is parallel to the axis  37  of the usual feeder rollers  39 . 
     The support  52  is associated with a slider  53 , which slides on a guide  54 , so as to take the roller  51  from a stand-by position outside the furnace  15  to an active position wherein it is inserted inside the furnace  15 ; as it enters into cooperation with the slab  24 , it raises the slab  24  at least on one side from the usual feeder rollers  39  and causes it to be displaced sideways in the desired manner. 
     In the event that the lateral displacement caused only by the conical shape of the working surface of the roller  51  is not sufficient, or in any case difficult to achieve, a raised edge  55  cooperating with the base of the roller  51  is brought into contact with an edge  24   a  of the slab  24  so as to physically displace the slab  24 . 
     The conical rollers  51  can be arranged alternate and off-set, on one side of the furnace  15  and the other, along the whole length of the furnace  15  itself, for example every 4-6 of the usual rollers  39 . 
     According to the variant as shown in FIG. 12, the conical rollers  51  are in pairs, arranged axially on one side of the furnace  15  and the other, and are made to act simultaneously so as to raise the slab  24  from the supporting plane  56  defined by the usual rollers  39 , and to displace it laterally, in one direction or the other according to the misalignment Δ detected between the rolling axis  25  and the axis  32  of the slab  24 , by introducing the conical rollers  51  inside the furnace  15  to a greater or lesser extent. 
     Once the slab  24  has been repositioned axially, the conical rollers  51  are returned to their stand-by position outside the furnace  15 . 
     According to the variant as shown in FIG. 13, which is valid for every embodiment described hereinbefore, the conical rollers  51  are maintained constantly inside the furnace  15 , arranged on both sides thereof, and function as elements to control and limit the maximum difference between the axial position of the slab  24  and the rolling axis  25 . 
     The conical rollers  51 , arranged coaxially in pairs at an intermediate position, for example every four usual rollers  39 , with their raised edges  55  define the position of maximum lateral displacement of the slab  24 ; at the same time, with their inclined work planes, they act as elements to constantly and continuously control the axial position of the slab  24 . 
     According to the further variant as shown in FIG. 14, the disks  40  mounted on the rollers  39  are arranged in groups on one half of one roller  39  and on the other half of the roller  39  immediately after. 
     This arrangement of the disks  40 , together with the individual control of the speed of rotation of the individual rollers  39 , makes it possible to give an undulated development to the slab  24  as it passes through the furnace  15 , to control the lateral position thereof and to correct any possible misalignment of the slab  24  with respect to the rolling axis  32 .