EP3365119A1

EP3365119A1 - Multi-stand rolling mill for rod-shaped bodies comprising three motorized-rollers stands

Info

Publication number: EP3365119A1
Application number: EP16810026.1A
Authority: EP
Inventors: Ettore Cernuschi; Aristide Giacomo Bertelli; Veronica Giulia Lilli SANDRINI
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 2015-10-23
Filing date: 2016-10-21
Publication date: 2018-08-29
Anticipated expiration: 2036-10-21
Also published as: RU2687522C9; ITUB20155314A1; EP3365119B1; US20180304327A1; JP2018531154A; PL3365119T3; CN108367322A; RU2687522C1; WO2017068533A1

Abstract

The present invention relates to a multi-stand rolling mill (1 ) for tubular bodies. The rolling mill comprises a first section (10) for rolling on mandrel defined by a first plurality of rolling stands (15', 15, 15") arranged in sequence along a rolling axis (100). According to the invention, the rolling mill also comprises a second rolling section without mandrel, arranged downstream of said first section, which comprises a second plurality of stands (25', 25, 26, 27, 26', 27') arranged in sequence along said rolling axis (100). Each stand (25', 25, 26, 27, 26', 27') of said second section (20) comprises three rollers having rotation axes which are arranged at 120 ° from one another. The rotation axes for each stand (25', 25, 26, 27, 26', 27') are rotated by 180 ° with respect to corresponding rotation axes of an adjacent stand. According to the invention, at least one stand of said second section (20) comprises a motorized roller having a vertical rotation axis.

Description

"MULTI-STAND ROLLING MILL FOR ROD-SHAPED BODIES COMPRISING THREE MOTORIZED-ROLLERS STANDS"

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DESCRIPTION FIELD OF THE INVENTION

The present invention falls within the scope of achieving rolling systems of tubular bodies. Namely, the invention relates to a multi-stand rolling mill comprising stands having three motorized rollers. In particular, the rolling mill is configured to perform a rolling on mandrel and a successive rolling without mandrel of the tubular bodies along a same line.

BACKGROUND ART

Plants are known for the production of hollow bodies (or tubular bodies) such as e.g. seamless tubes. In particular, such a production includes three basic deformation steps, the first of which being identified in the longitudinal drilling of the bodies. The bodies then undergo a first rolling on mandrel, along a first line, in order to define the thickness of the tube. At the end of the first rolling and following the extraction of the mandrel, the tubes are processed in a heating furnace in which they are kept at a predetermined temperature before undergoing, on a second line, a further rolling without mandrel, that is in the absence of a mandrel, aimed to calibrate the diameter of the tubes themselves.

An example of this production process is described and disclosed in Patent Application EP2008732. In particular, in this known solution, the rolling on mandrel is performed through two-rollers rolling stands, while the rolling without mandrel is performed through three-rollers stands. A heating furnace is provided between the two rolling lines. Patent Application EP2878390 instead describes a line in which the rolling on mandrel occurs through three-rollers stands.

Patent applications PCT/EP2013/071021 and PCT/EP2009/056201 describe and show other rolling mills in which the rolling without mandrel occurs through three- rollers stands. In particular, the stands in Application PCT/EP2009/056201 have rollers having a position which is adjustable with respect to the rolling axis.

The calibration rolling typically is performed through three motorized-rollers rolling stands, each rotating about a rotation axis which is inclined by 120 ° with respect to the axes of the other rollers. Typically, one of the rollers has a horizontal rotation axis actuated by a horizontal axis drive shaft. The other two rollers instead are actuated by corresponding drive shafts, one of which is operatively installed below the support surface of the rolling stands. Examples of such rolling stands are described e.g. in Applications US 2001 /0027674, DE 100 15285 and US7424816. Rolling stands with three rollers are also known in the art, typically one of which rollers having a horizontal rotation axis actuated by a horizontal axis drive shaft, while the other two rollers instead are actuated by means of inner conical gears which connect the horizontal rotation axis of the first roller with each of the two inclined rotation axes of the other two rollers. A solution of this type is described in Application EP 1449597, for example.

The rolling plants described above have various drawbacks, the first one of which being the overall dimensions which are decisively affected by the presence of the heating furnace. In general, the presence of the heating furnace is critical for various other reasons, among which the complicated management of tube accumulations, the problem of excessive decarburization and/or oxidation in the event of a prolonged stop inside the furnace, the loss of weight generated by the formation of scale inside the furnace. Overall, all these aspects affect the manufacturing/management costs of the plant and accordingly the production costs. Other drawbacks of the systems described above are associated with the technical solutions currently used for the calibration rolling. In particular, it has been shown that the operation for replacing the stands, also referred to as stand-replacement, is particularly complex due to the configuration of the three-rollers stands typically used. Indeed, the use of a horizontal axis roller motorized by means of a horizontal drive shaft does not make the replacement of the stand of the rolling line very convenient. At the same time, the arrangement of the other rollers and of the related actuation drive shafts requires a complex support structure and just as complex a foundation system below the support surface of the stands, which is required to accommodate the motorization means of one of the drive shafts in the case of individually controlled rollers.

The considerations above reveal the need to provide a new rolling system which allows the drawbacks mentioned above to be overcome. SUMMARY

The present invention relates to a rolling mill for tubular bodies comprising a first section for rolling on mandrel defined by a first plurality of rolling stands arranged in sequence along a rolling axis. The rolling mill according to the invention further comprises a second section for the extraction of the mandrel and the calibration of the tubular bodies. Such second section is arranged downstream of the first section whereby the tubular bodies exiting from said first section (10) directly enter said second section (20). Such a second section comprises a second plurality of rolling stands without mandrel, arranged in sequence along said rolling axis. Each stand of the second section comprises three rollers having rotation axes which are arranged at 120 ° with respect to one another and wherein the rotation axes for each stand are rotated by 180 ° with respect to corresponding rotation axes of an adjacent stand, said position of said rotation axes being assessed with respect to a vertical reference direction. Moreover, according to the invention, at least one stand of the second section comprises a motorized roller having a vertical rotation axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will become apparent from the detailed description provided below of an embodiment thereof and from the accompanying drawings merely given by way of a non-limiting example, in which: - figures 1 to 4 are schematizations related to possible embodiments of a rolling mill according to the invention, comprising a first rolling section and a second rolling section;

- figure 5 is a side view of the second section of the rolling mill schematized in figure 1 ;

- figure 6 is a side view of the second section of the rolling mill schematized in figure 2;

- figure 7 is a plan view of the rolling mill in figure 5;

- figure 8 is a view according to the sectional plane VIII-VIII in figure 5;

- figure 9 is a perspective view of a fixed rollers stand of a second section of a rolling mill according to the present invention;

- figure 10 is a view according to the sectional plane X-X in figure 9; - figure 1 1 is a perspective view of a group of adjustable rollers stands of a second section of a rolling mill according to the present invention;

- figure 12 is a first sectional view according to plane XII-XII in figure 1 1 ;

- figure 13 is a second sectional view according to plane XIII-XIII in figure 1 1 ;

- figure 14 is a plan view of the group of stands in figure 1 1 ;

- figure 15 is a sectional view according to line XV-XV in figure 13;

- figure 16 is a view according to the sectional plane XVI-XVI in figure 5;

- figure 17 is a view according to the sectional plane XVII-XVII in figure 7;

- figure 18 is a sectional view according to the plane XVI I l-XVI 11 in figure 7.

The same numbers and the same reference letters in the figures identify the same elements or components.

DETAILED DESCRIPTION

With reference to the figures mentioned, the present invention relates to a multi- stand rolling mill 1 for hollow bodies (hereinafter also indicated as tubular bodies). The rolling mill 1 according to the invention comprises a first rolling section 10 on tool, or on mandrel, previously inserted inside the hollow body according to a principle which is in itself known. The first section 10 serves the function of defining the thickness of the hollow body and comprises a first plurality of rolling stands 15', 15, 15" arranged in sequence according to a rolling axis 100 (or rolling direction 100). In particular, the first section 10 comprises at least one inlet stand 15' arranged on an inlet side 10' and at least one outlet stand 15" arranged on an outlet side 10" of the first section. Therefore, a feeding direction 200 of the hollow body is defined along the rolling axis 100 so that the inlet stand 15' is the first which intervenes on the hollow body, while the outlet stand 15" is the last which intervenes by completing the definition of the thickness.

The rolling mill 1 according to the invention further comprises a second rolling section 20 without mandrel, arranged downstream of the first section 10 with respect to said feeding direction 200. Such a second section 20 serves the function of performing the extraction of the mandrel from the hollow body and of calibrating the diameter of the hollow body. The term "without mandrel" means rolling which is performed in the absence of a mandrel, i.e. following the extraction thereof. According to the invention, the second section 20 defines a rolling axis which coincides with the rolling direction 100 defined by the first section 10. Therefore, the rolling on mandrel and the rolling without mandrel are performed on the same line (rolling direction 100). In essence, the hollow bodies exiting from the first section 10 directly enter the second section 20 for the extraction of the mandrel from the hollow body and for the calibration of the diameter. This solution advantageously avoids the installation of an intermediate heating furnace, thus obtaining a reduction in the length of the system by at least 70 meters (length of a traditional heating furnace and a outlet roller way before the inlet of the intermediate furnace with a possible intermediate cooling surface) with respect to traditional solutions. Moreover, all the above-described problems associated with installing and managing the furnace itself (decarburization and/or oxidation, formation of scale) are eliminated. Advantageously, the production process is in fact limited to two deformation steps only: drilling and rolling (thickness/calibration). The first section 10 and the second section 20 in fact form a single in line mill which integrates thickness rolling and diameter calibration. Therefore, a drastic simplification is obtained of the tracking of the hollow bodies, since there are no intermediate accumulations caused by the intermediate furnace.

According to the present invention, the second section 20 comprises a second plurality of rolling stands 25, 26, 27, 26' 27' arranged in sequence along said rolling axis 100 starting from an inlet side 20'. Thus, an inlet stand 25' is identified, which intervenes on the hollow body coming from the first section 10. Moreover, an outlet stand is identified, which is the last stand crossed by the hollow body before leaving the second section 20. Said stands 25', 25, 26, 27, 26', 27' are arranged on a substantially horizontal support surface 300.

Each stand 25, 26, 27, 26', 27' of the second section 20 comprises three rolling rollers having rotation axes which are arranged at 120 ° from one another. Moreover, the rotation axes of the rollers for each stand 25, 26, 27, 26', 27' of the second section 20 are rotated by 180 ° with respect to the rotation axes of an adjacent stand. More in details, the position of the axes of any one stand with respect to those of an adjacent stand, is assessed with respect to a vertical direction 150 which is orthogonal to the support surface 300. In this regard, figures 1 a and 1 b are schematized for the purposes of showing such an arrangement. Specifically, figure 1 a schematizes the arrangement of the axes of rollers A, B, C in a stand taken as a reference, while figure 1 b schematizes the arrangement of rollers A', B', C of an adjacent stand. The term "adjacenf means a stand which may be upstream or downstream with respect to the stand taken as a reference with respect to the feeding direction 200.

According to the present invention, at least one rolling stand of the second section 20 comprises a motorized roller having a vertical rotation axis. Preferably, such a roller is motorized through a drive shaft, which also has a vertical axis. As specified better below, the use of one or more stands with a vertical axis motorized roller advantageously simplifies the replacement of the stands of the second section 20, thus drastically decreasing the times related to this operation.

According to another aspect of the present invention, the second section 20 of rolling mill 1 comprises at least one fixed rollers stand, this expression meaning a stand in which the position of the rollers (i.e. of their rotation axes) is not adjustable/modifiable with respect to the rolling axis 100. Said at least one fixed rollers stand comprises mechanical transmission means configured to transmit the motion from one of said rollers, preferably from the vertical axis motorized roller, to the other two rollers of the stand. Figures 9 and 10 commented on below show a possible embodiment of a fixed rollers stand of a rolling mill according to the invention.

According to a preferred embodiment, the rolling mill 1 according to the invention comprises a first series of fixed rollers stands 25', 25 (hereinafter also indicated with the expression first stands 25' 25) arranged in sequence along said rolling axis 100 starting from the inlet side 20' of the second section 20. Therefore, the inlet stand 25' is a fixed rollers stand.

According to a further aspect, also the rolling stands 15', 15, 15" of the first section 10 of the rolling mill 1 have three rolling rollers having rotation axes which are arranged at 120 ° from one another. According to the invention, the rotation axes of the inlet stand 25' of the second section 20 are rotated by 180 ° with respect to the rotation axes of the rollers of the outlet stand 15" of the first section 10. The position of the axes is always assessed with respect to the vertical reference direction 150. In essence, the position of the rollers of the outlet stand 15" of the first section 10 with respect to the rollers of the inlet stand 25' of the second section 20 follows what is shown in the schematizations in figures 1 a and 1 b. Through this contrivance, the rollers of the rolling stands 15', 15, 15" of the first section 10 advantageously are aligned with the rollers of the rolling stands 25', 25, 26, 27, 26', 27' of the second section 20. Thereby, the thickness tolerances may be improved to the benefit of the improved quality of the final product.

Preferably, each fixed rollers stand 25', 25 comprises a vertical axis motorized roller 31 and mechanical transmission means configured to transmit the motion from such a motorized roller to the other two rollers of the stand. Preferably, said vertical axis roller is motorized through a vertical axis drive shaft for each fixed rollers stand 25',

25. This solution is also advantageous because it allows the foundations of the second section 20 to be simplified, as described below in the comments on figure 17.

The second section 20 of the rolling mill 1 preferably comprises at least one adjustable rollers stand operatively positioned downstream of the fixed rollers stand or stands 25', 25. The expression "adjustable rollers stand" means a stand in which the distance of the rollers from the rolling axis 100 can be adjusted in order to vary the rolling conditions and implement a corresponding variation in diameter. Preferably, said at least one adjustable rollers stand also comprises a vertical axis motorized roller.

According to a preferred embodiment shown in the drawings, the rolling mill 1 comprises a series of adjustable rollers stands 26, 27, 26', 27' (or second stands

26, 27, 26', 27') arranged in sequence along the rolling axis 100 downstream of the fixed stands 25', 25, again with respect to the feeding direction 200. Preferably, each of the second stands 26, 27, 26', 27' comprises a first motorized vertical axis roller 34, 34'.

According to a possible embodiment, the second section 20 also comprises a dummy stand 28, this expression meaning a stand in which no thickness reduction or deformation of the hollow body is performed, and in which the roller or rollers present have the only function of carrying and guiding the piece along the rolling direction 100. Such a dummy stand 28 can be arranged for example, between a fixed rollers stand and an adjustable rollers stand or alternatively downstream of the adjustable rollers stand according to the plant engineering needs.

Figures 1 to 4 are diagrams related to the possible configuration of a rolling mill 1 according to the present invention. In such diagrams, the first section 10 of the rolling mill 1 has the same configuration substantially defined by six rolling stands 15', 15, 15", each having three rollers as indicated above. The second section 20 overall defines sixteen positions, each of which is destined to be occupied by a rolling stand (with fixed or adjustable rollers) or alternatively by a dummy stand. In all diagrams, thirteen of the sixteen positions are configured so as to accommodate a fixed rollers stand or alternatively a dummy stand, while the last three positions are instead configured to accommodate any type of stand (fixed rollers - adjustable rollers - dummy stand).

In general, according to the present invention, the second section 20 comprises a first stretch 21 defining a first series of lodging positions which may be occupied by a fixed stand 25', 25 or alternatively by a dummy stand 28. The second section 20 also comprises a second stretch 22 defining a second series of positions which may be occupied by fixed stands, adjustable stands or dummy stands, wherein the adjustable stands also may be operatively connected in a group (60, 62).

According to the configuration shown in the diagram in figure 1 , the second section 20 provides an equal number of fixed stands and more in details provides fourteen fixed stands 25', 25 arranged in sequence starting from the inlet side 20'. The last two positions of the second section 20 are instead occupied by two adjustable rollers stands 26, 27. Preferably, the latter are connected to each other so as to form a single group 60 of two adjustable rollers stands wherein at least one motorized roller of one of the stands is operatively connected to a roller of the other stand. In the continuation of the present invention, such a group 60 is also indicated with the expression "even bi-stand 60" where "even" means that the two stands 26, 27 defining such a bi-stand are used when the overall number of rolling stands is even. In the diagram in figure 2, the second section 20 provides thirteen fixed stands 25', 25 which occupy thirteen positions starting from the inlet side 20'. Here, the first two positions of the second stretch 22 (corresponding to the 14^th and 15^th positions of the second section 20) are occupied by another group 62 of adjustable stands 26', 27' indicated hereinbelow with the expression "odd bi-stand 62", where the term "odd" means that the two stands 26' and 27' which define such a bi-stand are used when the overall number of rolling stands is odd. The last position of the second stretch 22 instead is occupied by a dummy stand 28.

The even bi-stand 62 is conceptually and functionally similar to the odd bi-stand 60 because a motorized roller of one of the stands 26' or 27' is operatively connected to a roller of the other stand. Indeed, the same technical solutions in terms of motion definition and transmission between the various parts preferably are provided for the bi-stands (even 60 and odd 62). It can be noted that both the bi-stands (even 60 and odd 62) are actuated through actuation means, typically drive shafts, installed in predetermined positions along the second stretch 22 of the second section 20. Therefore, in order to adapt to the actuation means installed at the positions the furthest left to the second stretch 22, the odd bi-stand 62 has a configuration which in fact mirrors that of the even bi-stand 60 with respect to a vertical plane containing the rolling axis 100.

In the diagram in figure 3, there are instead provided eight fixed stands 25', 25 and six dummy stands 28 arranged in sequence downstream of the fixed stands 25', 25. The last two positions (15^th and 16^th) of the second section 20 are occupied by the adjustable stands 26, 27 of the even bi-stand 60 similarly to the diagram in figure 1 . Finally, in the diagram in figure 4, there are provided seven fixed stands 25', 25 downstream of which are arranged six dummy stands 28 in sequence. The last three positions instead are occupied by adjustable stands 26', 27' of the odd bi-stand 62 and by a false stand 28 in a similar manner to the diagram in figure 2.

In general, the configuration of the second section 20 in terms of the number and position of fixed stands 25', 25 and of dummy stands 28 in the first stretch 21 and in terms of the position of the adjustable/fixed/dummy stands in the second stretch 22, may vary according to process needs. In particular, the selection of the number of stands used and the related arrangement in the rolling mill 1 substantially depend on the reduction of the diameter which occurs in the calibration step (second section 20). In this regard, it is preferable to limit the number of diameters exiting from the first section 10 with respect to the number of diameters which may be obtained at the outlet of the second section 20. With reference to the sectional views in figures 17 and 18 commented on below, it can be noted how the first stretch 21 of section 20 in fact does not require any foundation below the support surface 300. Such foundations are always limited to the second stretch 22 which defines a significantly lower number of positions than the number of positions defined by the first stretch 21 . Indeed, according to the invention and contrary to known solutions, the rolling without mandrel is mainly performed through fixed rollers stands.

With reference again to figures 1 to 4, it can be noted that in the rolling mill according to the invention, there is provided a first speed meter 166 for measuring the feeding speed of the hollow body between the two sections 10, 20 of the rolling mill 1 in order to control the speed along the second section 20. In this regard, the rolling mill 1 further comprises a second speed meter 167 operatively arranged at the outlet of the second section 20.

The rolling mill 1 further comprises a thickness gauge 178 also arranged at the outlet of the second section 20. It can be noted that the in line configuration of the rolling mill 1 according to the invention advantageously allows at least one of the thickness gauges required in traditional plants comprising two independent rolling lines, one upstream of the heating furnace and the other downstream of the final calibrator, to be eliminated.

Figure 5 and figure 6 are a side view of the second section 20 of a rolling mill 1 according to the diagram in figure 1 and according to the diagram in figure 2, respectively. In particular, the arrangement of the fixed stands 25', 25 and of the even bi-stand 60 forming the second section 20 can be noted in figure 5. The arrangement of the fixed stands 25', 25, the odd bi-stand 62, the dummy stand 28 forming the second section 20 instead can be noted in figure 6. It can be noted how the second stretch 22 of the second section 20 allows the position of the adjustable stands to be varied using an even bi-stand 60 or alternatively an odd bi-stand 62 according to operating needs.

Figure 7 is a plan view of the second section 20 of the rolling mill shown in figure 5. Figure 7 shows the even bi-stand 60 and the actuation means (drive shafts 30A, 30B, 30C) installed in the second stretch 22. It can be noted that the bi-stand 60 is configured to interact with two drive shafts 30A, 30B (hereinafter indicated with "right-hand drive shaft 30A" and "left-hand drive shaft 30B") arranged on opposite sides with respect to the rolling axis 100. The right-hand drive shaft is operatively associated with the second-last position of the second stretch 22, while the left-hand drive shaft is associated with the last position of the same stretch. It can be noted from the comparison between figures 5, 6 and 7 how an odd bi-stand 62 (shown in figure 6), due to the different position which it should take on in the second stretch 22, is configured to interact on the one side with the right-hand drive shaft 30A and on the other with drive shaft 30C arranged on the same side as the left-hand drive shaft 30B but associated with the first position of the second stretch 22 immediately downstream of the first stretch 21 . As indicated above, this condition precisely requires for stand 62 to operatively and constructively mirror stand 60 with respect to a vertical plane containing the rolling axis 100.

With reference to figures 5 and 6, the second section 20 comprises first releasing thrust cylinders 290 positioned on the inlet side 20' and second locking thrust cylinders 291 positioned on the outlet side 20" of the second section 20. The second cylinders 291 exert an axial thrust on the stands 25', 25, 26, 27, 26', 27' and dummy stands 28 in a direction opposite to direction 200 in order to compact them along the rolling direction and lock them axially. Vice versa, the first cylinders 290 exert an axial thrust on the stands 25', 25, 26, 27, 26', 27 and dummy stands 28 in a direction concordant to direction 200 in order to release them once they have been axially locked, in order to allow the stand-replacement operations.

Figure 8 is a view according to the sectional plane VI 11- VI 11 in figure 5. Figure 8 shows the fixed inlet stand 25' frontally, i.e. from an observation point on the rolling axis 100 downstream of the first section 10. As shown in such a drawing, stand 25' is accommodated in a first lodging space 81 defined by a fixed structure 8 which extends vertically (vertical direction 150), simultaneously defining a horizontal plane 300 on which the stand itself lies. Structure 8 further comprises a support plane 82 which extends parallel to the support surface 300. An actuation device 130 of a vertical axis drive shaft 30 is installed above the support plane 82. The vertical axis drive shaft is configured to be removably connected to a first vertical axis roller 31 of stand 25'. In this regard, there is prepared a coupling/releasing device 45 of the vertical control drive shaft 30 which is substantially installed in a second lodging space 83 defined between the first space 81 and the support plane 82. The coupling/releasing device is configured to move the vertical drive shaft 30 between a coupled position, in which the drive shaft is operatively connected to the first roller 31 , and a released position, in which the drive shaft instead is disconnected from the roller to allow for example, the replacement of stand 25'.

Again with reference to figure 8, the actuation device 130 of drive shaft 30 comprises a motor 131 and a mechanical reducer 132. The latter is interposed above the support plane 82, between motor 131 and the vertical drive shaft 30. Preferably, motor 131 is installed so as to have a vertical axis, i.e. so as not to emerge laterally from structure 8. Thereby, the space adjacent to the sides 8', 8" of the structure advantageously remains free to be exploited within the scope of the stand- replacement operation, as described below (with reference to figures 17 and 18). The plan view in figure 7 allows to note how each stand of the section itself is rotated by 180 ° with respect to an adjacent stand, according to the above-described principle. In particular, it can be noted the coupled position 125 of the vertical drive shaft related to the fixed rollers inlet stand 25' which is rotated by 180 ° with respect to the coupled position 125' of the vertical drive shaft of a second stand 25 immediately adjacent to the inlet one. The same principle applies to the coupled position 125" of a third stand adjacent to the second one 25, and so on. It can be noted that such a relationship is kept for all the positions defined by the second section 20, therefore also for the second stretch 22 of the section itself.

It can be noted that the above-indicated technical solutions described in the comments to figures 6, 7 and 8 are valid for all the fixed stands 25', 25 installed in the second section 20 and in fact, also for the adjustable stands 26, 27, 26', 27' of it. For example, for each stand (fixed or adjustable), there is thus provided a corresponding actuation installed above the support plane 82 of structure 8 so as to keep free the space adjacent to the sides 8', 8" of the structure along the whole drive shaft thereof along the rolling axis 100.

Figures 9 and 10 are views related to the embodiment of a fixed stand 25 according to the invention, which may be positioned in any position of the first stretch 21 of the second section 20 or also in a position of the second stretch 22. With reference to figure 9, stand 25 comprises a body 70 which extends between two plates 70' and which carries the rollers 31 , 32, 33. The latter have a configuration which in itself is known and they keep a fixed position, that is not adjustable with respect to the rolling axis 100. Therefore, stand 25 always achieves the same rolling condition, i.e. the same reduction in diameter. Overall, body 70 and the two plates 70' are configured so as to define an operating recess 70" in which there are accommodated three rolling rollers 31 , 32, 33, the mutual position of which in fact defines the rolling axis 100.

With reference to figure 10, the first roller 31 has a vertical axis 101 (or first axis 101 ) defined by a central element 71 onto which the roller itself is keyed. The central element 71 is connected on one side to a first lateral element 71 ', and on the other side to a second lateral element 71 ", which are opposite to each other with respect to the first roller 31 . More in details, the central element 71 is connected to each of the two lateral elements 71 ', 71 " through an axial connection (e.g. axial teeth or grooved profiles) so that the three elements 71 , 71 ', 71 " rotate in a synchronous manner. The first lateral element 71 ' comprises a free end 72 which may be connected to a vertical drive shaft 30, as shown in figure 8, or to another functionally equivalent actuating means.

The three elements 71 , 71 ', 71 " overall define a first set of elements 71 -71 '-71 " which carries and allows the rotation of the first roller 31 . In this regard, there is provided the use of a connector pin 74 arranged longitudinally inside the three hollow elements 71 , 71 ', 71 " to avoid the removal thereof. There are also provided first supports 75 arranged in various positions along the first axis 101 to allow the rotation of the elements of the set of elements 71 , 71 ', 71 ". It is worth noting that the axial connection between the central element 71 and the two lateral elements 71 ', 71 " is removable in order to allow an easy extraction of the first roller 31 from the operating recess defined by the body 70 of stand 25.

Similarly, for the rotation of the second roller 32, there is provided the use of a second set of elements 76-77 defined by an axially connected central element 76 (again through an axial coupling) and two lateral elements 77 rotating on second supports 75'. The second set of elements defines a second rotation axis 102 for the second roller 32, inclined by 120 ° with respect to the first rotation axis 101 . A third set of elements (indicated with numerals 76', 77'), which is constructively equivalent to the second set of elements 76-77, carries the third roller 33 thus defining a third rotation axis 103 inclined by 120 ° with respect to the vertical axis 101 and with respect to the second axis 102.

Again with reference to figure 10, as indicated above, the first roller 31 is also operatively connected to the second roller 32 and to the third roller 33 through drive means configured so that all the rollers are actuated by the control drive shaft 30 connected to the first set of elements 71 , 71 ', 71 " related to the first roller 31 . In the case in point illustrated, the transmission means comprise two conical driving gears 79, 79', each keyed onto one of the lateral elements 71 ', 71 " of the first set of elements 71 -71 '-71 ". A first conical driving gear 79 meshes with a first driven gear 78 keyed onto the lateral element 77 of the second set of elements 76-77 closest to the vertical rotation axis 101 of the first roller 31 . Similarly, the second conical driving gear 79 meshes with a second driven gear 78' keyed onto the lateral element 77' of the third set of elements 76'-77' closest to the vertical rotation axis 101 of the first roller 31 . The transmission means are therefore configured to achieve a synchronous rotation of the three rollers 31 , 32, 33. Therefore, the conical driving gears 79, 79' mesh with the corresponding driven gears 78, 78' with a transmission ratio equal to 1 .

With reference to figure 9, it can also be noted that stand 25 is provided with a cooling system of roller 31 , 32, 33 comprising an intake 174, which may be connected to an external circuit, and a cooling circuit 170 comprising three end nozzles 177, each of which being configured to eject coolant close to one of the three rolling rollers 31 , 32, 33. With reference to figure 8, it can be noted that structure 8 of the second section 20 also comprises a connection device 145 for connecting/disconnecting the above intake 174 of stand 25 to/from an external supply circuit. Such a connection device 145 is installed on the side of the coupling/releasing device 45 of the vertical drive shaft 30.

Figures 1 1 to 16 are related to a group of adjustable rollers stands. In particular, such drawings show an even bi-stand 60 which may be installed in the second stretch 22 of the second section 20, for example in the configuration shown in figures 1 and 3. The technical solutions for the even stand 60 described below are to be considered valid, mutatis mutandis, also for the odd stand 62. In this regard, with reference to diagrams 1 -4 described above, it is underlined that the technical solutions described below for the first stand 26 and for the second stand 27 of the even bi-stand 60 correspond to that provided for the second stand 27' and for the first stand 26' of the odd bi-stand 62, respectively, from a constructional viewpoint (in terms of components, definition of the motion, position of the rollers, etc.).

With reference to figure 1 1 , the even bi-stand 60 comprises a first stand 26 and a second stand 27 adjacent to the first stand 26. As already indicated above, the first stand 26 comprises at least one drive roller, that is a roller which is motorized directly through an actuating means, preferably through a control drive shaft. According to the invention, bi-stand 60 comprises a transmission device which operatively connects said at least one drive roller of the first stand 26 with a driven roller 34' of the second stand 27 so that such a driven roller 34' is motorized, even though in an indirect manner, by the same actuating means which motorizes the drive roller. According to a preferred embodiment, bi-stand 60 preferably comprises three transmission devices, each of which operatively connects a motorized roller of one of the two stands 26 or 27, which acts as a "drive roller", to a roller of the other stand 27 or 26 which becomes a "driven roller". Thereby, the actuation of the six rollers of the bi-stand (three rollers for each stand) overall is achieved only through three control drive shafts, each of which connected to the rollers of the stands 26, 27 which act as "drive rollers".

Figure 1 1 is a perspective view of bi-stand 60 according to the invention. Preferably, the two stands 26, 27 which form bi-stand 60 are integrated in a single structure defined by a body 60' which is axially closed by two plates 60". Body 60' and the plates 60" define an operating recess 61 in which there are arranged the rollers 34, 35, 36 of the first stand 26 and the rollers 34', 35', 36' of the second stand 27. Body 60' also defines the seats for the elements which allow the rotation of the rollers and the position adjustment thereof. In this regard, figures 12 and 13 are sectional views which allow the spatial arrangement of the rollers 34, 35, 36, 34', 35', 36' of the two stands 26, 27, respectively, to be noted.

With reference to figure 12, the first roller 34 in the first stand 26 has a vertical rotation axis 1 1 1 (or first axis 1 1 1 ), while the second roller 35 rotates about a second axis 1 12 inclined by 120 ° with respect to the first axis 1 1 1 . In particular, the second roller 35 is operatively positioned above a reference plane 105 passing through the rolling axis 100 and parallel to the support surface 300. The third roller 36 rotates about a third axis 1 13 inclined by 120 ° with respect to the first axis 1 1 1 . The third roller 36 is operatively positioned below said reference plane 105.

With reference to figure 13 and according to the principles of the present invention, the three rollers 34', 35', 36' in the second stand 27 have a position which is rotated by 180 ° with respect to the position of the rollers 34, 35, 36 of the first stand 26. In this regard, it can be noted from the comparison between figures 12 and 13 that also the second roller 35' of the second stand 27 is operatively positioned above the reference plane 105, but the rotation axis 1 12' thereof is parallel to the rotation axis 1 13 of the third roller 36 of the first stand 26. The third roller 36' of the second stand 27 is operatively positioned below the reference plane 105 and the rotation axis 1 13' thereof is parallel to the rotation axis 1 12 of the second roller 35 of the first stand 26. The rotation axis 1 1 1 of the first roller 34 of the first stand 26 instead has a position which mirrors the rotation axis 1 1 1 ' of the first stand 27 with respect to a vertical plane containing the rolling axis 100.

With reference to figure 13, there is described hereinbelow the method with which the vertical rotation axis 1 1 1 ' of the first roller 34' of the second stand 27 is defined. The technical solutions hereinbelow described also may be applicable to the other rollers 35', 36' of the second stand 27, as well as to the rollers 34, 35, 36 of the first stand 26.

The first roller 34' is keyed onto a central bush 1 34 axially connected (for example, through a cogged coupling) to a first sleeve 135 and to a second sleeve 136. A longitudinal pin 137 is arranged inside the central bush 134 and the sleeves 135, 136 to avoid the removal of the set of elements 134-135-136 thus formed, according to a principle already described above.

The second stand 27 comprises a transmission element 191 which may be connected to an external actuating means such as e.g. a vertical axis drive shaft. The transmission element 191 rotates with respect to the body 60' of stand 60 by means of suitable supports 192. It can be noted that the transmission element 191 establishes a fixed connection position of the vertical drive shaft or in any case, of the actuating means used. The second stand 27 further comprises a joint 195 configured to transmit the motion from the transmission element 191 to the set of elements 134-135-136 which carry the first roller 34'. In particular, joint 195 connects an end part 196 of the transmission element 191 with a connection element 197 keyed/screwed onto a portion of the second sleeve 136 of the set of elements 134-135-136. The position of the first roller 34' is adjustable through an adjusting device (described below), while the position of the transmission element 191 is fixed with respect to the body 60' of bi-stand 60. Thus, the rotation axis of the first roller 34' may take on an eccentric position with respect to the rotation axis of the transmission element 191 defined by the supports 192.

Joint 195 therefore has the specific function of keeping the set of elements 134-135- 136, and therefore the first roller 34', connected to the first transmission element 191 also after the variation of the position of the rotation axis 1 1 1 ' of the first roller 34'.

With reference to figures 12 and 13, it can be noted that there are provided technical solutions corresponding to those described above for the other two rollers 35', 36' of the second stand 27, as well as for the rollers 34, 35, 36 of the first stand 26. In particular, there is provided, for all rollers, a set of support elements which defines the rotation axis thereof, a rotating transmission element with respect to body 60' and a joint which operatively connects the transmission element to the set of support elements according to the methods indicated above. It is reiterated again that the same technical solutions hereto described for the stands 26, 27 of the even bi-stand 60 are to be considered valid also for the odd bi-stand 62 defined above, because the latter constructively mirrors the even bi-stand 60 with respect to a vertical plane containing the rolling axis 100.

According to a preferred embodiment of the invention, the even bi-stand 60 comprises a first transmission device 91 which operatively connects the first roller 34 of the first stand 26 to the first roller 34' of the second stand 27. One embodiment of the transmission drive device 91 is shown in the sectional view in figure 15. In particular, the first device 91 comprises a first cogged wheel 95 and a second cogged wheel 95' having parallel axes, which mutually mesh with each other. The first cogged wheel 95 meshes a cogged portion of the transmission element 191 which is connected to the set of elements 134-135-136 by means of the oscillating joint 195, which set of elements is functional to the first roller 34' of the second stand 27. The second cogged wheel 95' instead meshes with a cogged portion of a further transmission element 191 ' related to the first stand 26. With reference to figure 12, such a further transmission element 191 ' may be connected to a set of elements 134'-135'-136' through a corresponding joint 195' according to the same principle described above.

The rotation of the transmission element 191 is transferred through the two cogged wheels 95, 95' to the other transmission element 191 ', with a transmission ratio preferably equal to 1 . Thereby, the two transmission elements 191 , 191 ' and the corresponding set of elements 134-135-136, 134'-135'-136' rotate at the same speed. Obviously, by alternating the number of cogs of the elements 191 and 191 ', various speeds may be obtained.

The plan view in figure 14 shows the transmission element 191 , to which a first vertical control drive shaft 30' is preferably connected, as also shown in figure 16. In this regard, structure 8 of the second section 20 comprises a coupling/releasing device 45' of the first drive shaft 30'. The latter is actuated through a corresponding actuation device 130' arranged above the support plane 82 of structure 8 according to a similar solution to that described in the comments on the fixed stand 25'. Instead it can be noted, again from figure 16, that the transmission element 191 ' which is functional to the first roller 34 of the first stand 26 is not connected to any external actuation due to the effect of the transmission device 191 . According to a further aspect of the present invention, the even bi-stand 60 comprises a second transmission device which operatively connects the second roller 35 of the first stand 26 to the third roller 36' of the second stand 27. The even bi-stand 60 further comprises a third transmission device which operatively connects the third roller 36 of the first stand 26 to the second roller 35' of the second stand 27. The second transmission device and the third drive device have an entirely similar configuration to that of the first device 91 described above. The use of the three transmission devices indicated above allows the number of drive shafts to be reduced to three, and accordingly the number of motors required for moving the six rollers of the even bi-stand 60. This results in a reduction of the plant manufacturing and management costs.

Preferably, the second transmission device is actuated through a second drive shaft 30" which is connected to a second transmission element 198 (indicated in figures 1 1 and 12) which is functional to the third roller 36 of the first stand 26. The third transmission device instead is actuated through a third drive shaft 30"' which is connected to a further transmission element 199 (indicated in figure 13) which is functional to the third roller 36' of the second stand 27. The term "functional" means that one of the transmission elements 198, 199, 191 , 191 ' mentioned is connected by means of a joint to a corresponding set of elements which supports a corresponding roller, according to the principles described above.

In other words, according to this aspect of the invention, the second transmission device and the third transmission device are actuated through a corresponding inclined drive shaft 30", 30"' which meshes in the corresponding transmission element 198, 199 in a position which is very close to the support surface 300 and in any case is below the reference plane 105 indicated above. This arrangement is clearly visible in the sectional view in figure 18 in which, in addition to the two inclined drive shafts 30", 30"', the configuration is shown of the foundations of the rolling mill 1 obtained for the second stretch 22 of the second section 20. In this regard, the inclined drive shafts 30", 30"' are actuated through actuation means 155 in themselves known. It can be noted that due to the effect of the above-indicated arrangement, the foundations of the second stretch 22 have a more contained height with respect to the foundations of a traditional rolling section with three-rollers stands. It can also be noted that the mutual arrangement of the three drive shafts 30', 30", 30"' advantageously allows a bilateral type stand-replacement plant to be made, as described below.

With reference again to figures 12 and 13, bi-stand 60 comprises a first adjusting mechanism of the position of the rollers 34, 35, 36 of the first stand 26 and a second adjusting mechanism of the position of the rollers 34', 35', 36' of the second stand 27. The two adjusting mechanisms advantageously have the same configuration. Therefore, only the second adjusting mechanism related to the second stand 27 is hereinbelow described for simplicity, referring to that shown in figure 13. The second adjusting mechanism comprises, for each of the rollers 34', 35', 36', a pair of lateral bushes each of which keyed onto one of the lateral sleeves which define the set of elements carrying the corresponding roller according to the principles disclosed above. With reference to the second roller 35', a first lateral bush 171 and a second lateral bush 172 are mounted on the first sleeve 135' and on the second sleeve 136', respectively, which sleeves define the set of elements 134', 135', 136' which carries the second roller 35'. In particular, the two lateral bushes 171 , 172 are mounted on the corresponding sleeves 136', 135' through suitable bearings 182. The second adjusting mechanism comprises a substantially arc-shaped connection element 173, which connects the two lateral bushes 171 , 172 so that the latter remain operatively connected.

Each of the two lateral bushes 171 , 172 comprises a cogged portion which meshes a cogged portion of a corresponding lateral bush 171 ', 172' mounted on a lateral sleeve related to a set of elements which carries another roller of the stand. Specifically, a cogged portion of the first bush 171 meshes with a cogged portion of a corresponding lateral bush 171 ' mounted on the second lateral sleeve 136 of the set of elements 134-135-136 which carries the first roller 34. A cogged portion of the second bush 172 instead meshes with a cogged portion of a further lateral bush 172' mounted on a lateral sleeve 135" of the corresponding set of elements 134"- 135"-136" which carries the third roller 36'. Through such cogged connections, the rotation and the movement in space of the two lateral bushes 171 , 172 related to the second roller 35' causes a corresponding rotation and a corresponding movement of the other lateral bushes 171 ', 172' related to the other rollers 34', 36'. Again with reference to figure 13, the adjusting mechanism comprises an adjusting pinion 175 which may be actuated through an external device 166 (indicated in figure 16) mounted on the support structure 8 of the second section 20 of the rolling mill. Preferably, the adjusting pinion 175 rotates about a vertical rotation axis (parallel to the axis of the first roller 34') and is operatively connected to the assembly formed by the two lateral bushes 171 , 172 and by the connection element 173 so that the rotation of pinion 175 causes a rotation of such an assembly 171 - 172-173 about an axis which is eccentric to the rotation axis 1 12' of the second roller 35'. The rotation of the assembly of elements 171 -172-173 causes a corresponding eccentric rotation of the set of elements 134'-135'-136' and accordingly, of the second roller 35' itself, which varies its position with respect to the rolling axis 100. The eccentric rotation of the set of elements 134'-135'-136' is also transferred to the set of elements carrying the other rollers 34', 36' due to the effect of the meshing between the various lateral bushes 171 , 172, 171 ', 172' described above. Therefore, the other rollers 34'. 36' also vary their position with respect to the rolling axis 100 in corresponding manner to the second roller 35'.

With reference again to figure 16, it is worth noting that the external mechanism 166 configured for actuating the adjusting pinion 175 is preferably installed in the second space 83 defined by structure 8. The external mechanism 166 may be removably connected to the corresponding pinion 175, which emerges with respect to the body 60' of bi-stand 60. As indicated above, the first adjusting mechanism of the first stand 26 of bi-stand 60 has a configuration corresponding to that described above for the second adjusting mechanism, as also shown by the comparison between figures 12 and 13. It can be noted that the two adjustments of the radial positions of the rollers of the stands 26, 27 are independent, since they may be actuated by means of independent pinions 175 and 175'.

According to another aspect of the invention, the second section 20 comprises a first platform 51 and a second platform 52 which extend longitudinally on opposite sides 8', 8" of structure 8. Each of such platforms 51 , 52 is configured to carry a replacement stand 25A, an even replacement bi-stand 60A or an odd replacement bi-stand 62A intended to replace a stand or bi-stand of the second section 20. Simultaneously, the two platforms 51 , 52 are also configured to carry stand 25', 25 or bi-stand (even 60 or odd 62) of the second section 20 which is replaced by the replacement stand or bi-stand. In this regard, the second section 20 comprises a shifting device 299 configured to push at least one replacement stand/bi-stand 25A, 60A, 62A arranged on one of the platforms (e.g. first platform 51 ), against a stand/bi- stand 25, 60, 62 to be replaced up to the latter being completely positioned on the opposite platform (second platform 52). More in details, the shifting device 299 pushes the stands along a direction 109 which is substantially orthogonal to said rolling axis 100. Figures 17 and 18 are further sectional views showing the replacement principle of the fixed rollers stands 25', 25 and/or of the adjustable rollers bi-stands 60, 62. In particular, figure 17 shows the replacement of a fixed rollers stand 25, while figure 18 refers to the replacement of an even bi-stand 60. With reference to figure 17, the first platform 51 represents a loading platform in which the replacement stands 25A are loaded, while the second platform 52 represents an unloading platform from which the stands to be replaced are picked once the replacement operation is complete. Preferably, the movement of the fixed stands 25 to and from the platforms 51 , 52 is performed through loading cranes or functionally equivalent means. This "aerial" movement is mainly allowed by the configuration given to the fixed stands whereby all the rollers are actuated through a vertical axis drive shaft. The configuration of the support structure 8, hence the space adjacent to the longitudinal sides 8', 8", is also free and the installation selections described above (for example, "vertical" actuations above the support plane 82 of structure 8) allow the aerial movement of the fixed stands and therefore allow the reduction of the stand replacement times to just a few minutes.

Again with reference to figure 17, the replacement of one fixed rollers stand 25 includes a first step in which a replacement stand 25A is keyed onto the first platform 51 (arrow 401 ) through a crane. The replacement stand 25A is pushed by the shifting device 299 against the stand to be replaced 25 up to it occupying the position on the second platform 52. At this point, the stand 25 to be replaced is raised, always through a crane, and moved away from the second section 20 (arrow 402). It can be noted how the replacement principle of the stand replacement combined with the possibility of using a hoisting crane in fact avoids designing and manufacturing traditional replacement carriages and/or traditional movable tables used to replace the stands in traditional rolling mills characterized by having horizontal drive shafts. Figure 18 shows how the above-described replacement principle of the fixed stands advantageously also may be used for movable stands and in particular, for replacing the even bi-stand 60 described above. It is understood that the same principle may be applied to an odd bi-stand 62. Indeed, a replacement bi-stand (even 60A or odd 62A) may be easily lowered onto the first platform 51 (arrow 401 ), pushed by the shifting device 299 against a corresponding bi-stand (even 60 or odd 62) to be replaced positioned in the second section 20. Once the bi-stand (even 60 or odd 62) to be replaced occupies the second platform 52, it may be picked and moved away from the second section (arrow 402).

Again with reference to figure 18, it can be noted that in the case of a bi-stand (even 60 or odd 62), the replacement principle may be applied due to the effect of the configuration of the bi-stand itself and due to the fact that the drive shafts 30', 30" inclined with respect to the vertical axis are operatively positioned below the horizontal reference plane 105 (indicated in figure 13) and in position close to the support surface 300 of the stands 25, 26, 27 of the second section 20. In this regard, it can be noted that the actuation means 155 of the inclined drive shafts 30", 30"' are configured so as to move the same between an operating position, in which they are operatively connected to the bi-stand, and a withdrawn position in which the drive shafts 30", 30"' are completely below the support surface 300, thus allowing the movement of the stands along the shifting direction 109.

The rolling mill according to the invention allows the above tasks and objects to be completely achieved. In particular, the configuration of the rolling mill allows the dimensions and costs of the system to be contained, and also all the problems of traditional systems generated by the presence of intermediate heating furnaces to be eliminated. The configuration provided for the second section of the rolling mill and the structure provided for the fixed rollers stands and for the adjustable rollers stands allow the manufacturing costs of the foundations to be minimized while simultaneously greatly reducing the costs related to the actuations of the stands.

Claims

1 . A rolling mill (1 ) for tubular bodies comprising a first section (10) for rolling on mandrel defined by a first plurality of rolling stands (15', 15, 15") arranged in sequence along a rolling axis (100), characterized in that it comprises a second section (20) for extracting said mandrel and calibrating the diameter of said tubular bodies, said second section being downstream of said first section (10), whereby said tubular bodies exiting from said first section (10) directly enter said second section (20), said second section (20) comprising a second plurality of rolling stands (25', 25, 26, 27, 26', 27') without mandrel, arranged in sequence along said rolling axis (100), wherein each stand (25', 25, 26, 27, 26', 27') of said second section (20) comprises three rollers, the rotation axes of which are arranged at 120 ° relative to one another and wherein, for each stand (25', 25, 26, 27, 26', 27'), said rotation axes are rotated by 180 ° relative to corresponding rotation axes of an adjacent stand, said position of said rotation axes being assessed with respect to a vertical reference direction, and wherein at least one stand of said second section (20) comprises a motorized roller having a vertical rotation axis.

2. A rolling mill (1 ) according to claim 1 , wherein said second section (20) comprises at least one fixed rollers stand (25', 25).

3. A rolling mill (1 ) according to claim 1 , wherein said second section (20) comprises at least one adjustable rollers stand (26, 27, 26', 27').

4. A rolling mill (1 ) according to claim 1 or 2, wherein said second section (20) comprises a first series of fixed rollers stands (25', 25) arranged in sequence along said rolling axis (100) starting from an inlet side (20') of said second section (20), at least one of said fixed rollers stands (25', 25) comprising mechanical drive means configured to transmit the motion from said motorized roller having vertical rotation axis to the other rollers of the same stand.

5. A rolling mill (1 ) according to claim 1 , wherein said second section (20) comprises at least one dummy stand (28) comprising at least one guide roller.

6. A rolling mill (1 ) according to any one of claims from 1 to 5, wherein each stand (15', 15, 15") of said first section (10) comprises three rollers, the rotation axes of which are arranged at 120 ° relative to one another and wherein the rotation axes of the rollers of an outlet stand (15") of said first section (10) are rotated by 180 ° with respect to the rotation axes of the rollers of an inlet stand (25') of said second section (20).

7. A rolling mill (1 ) according to any one of claims from 1 to 6, wherein said second section (20) comprises a first stretch (21 ) which defines a first plurality of lodging positions each of which configured for accommodating a fixed rollers stand or a dummy stand, said second section (20) comprising a second stretch (22), downstream of said first stretch (21 ), which defines a second plurality of lodging positions each of which configured for accommodating a fixed rollers stand or a dummy stand or an adjustable rollers stand.

8. A rolling mill (1 ) according to any one of claims from 3 to 7, wherein said second section (20) comprises a group (60, 62) of adjustable rollers stands, said group (60, 62) comprising:

- a first stand (26, 26') and a second stand (27, 27') adjacent to said first stand (26, 26'), wherein said first stand (26, 26') comprises at least one roller motorized by an actuating means;

- a transmission device (91 ) which operatively connects said at least one roller (34, 35, 36) of said first stand (26, 26') to at least one roller (34', 35', 36') of said second stand (27, 27') so that both the rollers are actuated by said actuating means.

9. A rolling mill (1 ) according to claim 8 when depending on claim 7, wherein said second stretch (22) of said second section (20) defines three lodging positions and wherein said group (62) of adjustable rollers stands is configured to occupy the first lodging position and the second lodging position downstream of said first stretch (21 ).

10. A rolling mill (1 ) according to claim 8 when depending on claim 7, wherein said second stretch (22) of said second section (20) defines three lodging positions and wherein said group (60) of adjustable rollers stands is configured to occupy the second lodging position and the third lodging position downstream of said first stretch (21 ).

1 1 . A rolling mill (1 ) according to any one of claims from 8 to 10, wherein said group (60, 62) comprises at least a first transmission device (91 ) which operatively connects a first vertical axis roller (34) of said first stand (26, 26') to a first vertical axis roller (34') of said second stand (27, 27').

12. A rolling mill (1 ) according to any one of claims from 8 to 1 1 , wherein said first stand (26, 26') and said second stand (27, 27') of said group (60, 62) are integrated in a single body (60') defining an operating recess inside which the rollers (34, 35, 36) of said first stand (26, 26') and the rollers (34', 35', 36') of said second stand (27, 27') are accommodated.

13. A rolling mill (1 ) according to any one of claims 8 to 12, wherein said first stand (26, 26') and said second stand (27, 27') of said group (60, 62) each comprise: - a first roller (34, 34') having a vertical rotation axis (1 1 1 , 1 1 1 ');

- a second roller (35, 35') having a rotation axis (1 12, 1 12') inclined by 120° with respect to said vertical rotation axis (1 1 1 , 1 1 1 ') of said first roller (34, 34'), said second roller (35, 35') being operatively positioned above a horizontal reference plane (105) on which said rolling axis (100) lies;

- a third roller (36, 36') having a rotation axis (1 13, 1 13') inclined by 120 ° with respect to said rotation axes of said first roller (34, 34') and of said second roller (35, 35'), said third roller (36, 36') being operatively positioned below said horizontal reference plane (105),

and wherein said group (60, 62) comprises a second transmission device which operatively connects said third roller (36) of said first stand (26) to said second roller (35') of said second stand (27, 26'), said third roller (36) of said first stand (26, 27') being actuated by an actuating means.

14. A rolling mill (1 ) according to claim 13, wherein said group (60, 62) comprises a further transmission device which operatively connects said second roller (35) of said first stand (26, 26') to said third roller (36') of said second stand (27, 27'), said third roller (36') of said second stand (27, 27') being actuated by a further actuating means.