EP2736660A2

EP2736660A2 - Roll-holder cartridge for a rolling mill

Info

Publication number: EP2736660A2
Application number: EP12759203.8A
Authority: EP
Inventors: Paolo Marin; Marcello Pacher
Original assignee: SMS Innse SpA
Current assignee: SMS Group SpA
Priority date: 2011-07-26
Filing date: 2012-07-16
Publication date: 2014-06-04
Anticipated expiration: 2032-07-16
Also published as: WO2013014572A2; AR088745A1; CN103781564A; EA201490341A1; JP6130832B2; EA025048B1; CN103781564B; EP2736660B1; JP2014523814A; US20140182346A1; ITMI20111391A1; WO2013014572A3

Abstract

The present invention relates to a roll-holder cartridge for a rolling mill 20. The cartridge 24 comprises two side walls 26, a plurality of roll-lever units 30, two adjusting rings 28 and an adjusting actuator 32. Each side wall of the cartridge comprises a plurality of first seats 260; each adjusting ring comprises a plurality of second seats 280; and each one of the roll-lever units is mounted on the cartridge so as to be able to pivot about a pin 300, each end of each pin being housed in the axial direction inside a first seat and a second seat, respectively. Moreover, the first seats allow a displacement of the respective pins in a purely tangential direction t, the second seats allow a displacement of the respective pins in a purely radial direction r, and the two adjusting rings may be rotated about the axis X by means of the adjusting actuator. The invention also relates to a rolling stand 22 comprising the cartridge described above and a rolling mill comprising a plurality of rolling stands 22.

Description

"Roll-holder cartridge for a rolling mill"

DESCRIPTION

The present invention relates to a roll-holder cartridge for a continuous rolling mill, in particular for a continuous rolling mill suitable for the production of long semi-finished articles. The invention also relates to a stand and a rolling mill comprising such a cartridge. In the description below, specific reference will be made, by way of a non-limiting example, to the rolling of seamless tubes, but it is understood that the same inventive ideas may be applied to the rolling of other long articles such as bars, rods, round bars and the like.

It is known to produce seamless metal tubes by means of successive plastic deformation of a blank billet or bar. During a first step, the billet is pierced longitudinally so as to obtain a pierced semifinished blank with a thick wall and a length 1.5 to 4 times greater than the length of the initial billet. Then this semifinished article is passed through proper rolling mills so as to thin gradually the wall and to increase the length of the finished product. These rolling mills, known as continuous rolling mills, comprise in a manner known per se a plurality of stations. Each station comprises a stand on which rolls with profiled grooves are mounted. Usually the grooved rolls are three in number and each one is supported via a pair of arms by a proper roll-support lever mounted on the stand. The three pairs of arms are coplanar with each other, have a radial direction and are arranged at a distance of 120° from each other around the rolling axis. The set of connected profiles of the grooves of the three rolls defines the external circumference of the tube leaving the rolling station.

In each station, the roll-support levers are mounted on a cartridge so as to be able to pivot about an axis parallel to the rolling axis. An actuator, for example of the hydraulic type, acts on each of the rolls and pushes the roll in the radial direction relative to the rolling axis. The actuators thus produce the force required to deform plastically the tube.

Moreover, the rolls are rotated by proper motors so as to provide, by means of friction, the feeding movement to the tube being processed.

The subsequent stations, together with, if required, an internal mandrel, gradually convert the semi-finished article into a tube with the desired configuration in terms of outer diameter, inner diameter, wall thickness and length.

The rolling rolls are subject to wear and, following given working cycles, must be reconditioned by means of turning. In this way it is possible to eliminate the deformation and wear marks and restore the groove profile of the roll. It is in fact necessary to ensure an optimum profile of the groove of each roll so that the individual station may provide the tube being processed with an optimum profile.

Turning may be performed, in a manner known per se, by disassembling each roll from the respective position and transporting it to a suitable conventional turning station. Alternatively, in a manner equally well known per se, it is possible, for each stand, to remove the entire cartridge, while keeping the three rolls mounted therein, and perform the turning operation with a special tool arranged in the centre of the cartridge in place of the tube.

Each turning operation necessarily reduces the diameter of the individual roll. For this reason, it is known to provide on each stand means for keeping the rolls parallel to each other before and after each turning operation.

It is clear that, following a reduction in diameter, the roll could be brought into contact with the tube by means of simple pivoting of the lever about its axis. This configuration of the roll, however, would be asymmetrical with respect to the radial direction and the contact would not be optimal. In other words, after turning, the set of profiles of the grooves of the three rolls would no longer define a circumference; instead they would define a three-lobed figure composed of circle arcs which are not connected together.

In order to overcome this problem two different solutions are known.

The first solution consists in compensating for the reduction in diameter of the roll by means of an identical lengthening of the respective arms. In this way, the movement of the roll between the initial position and the position following turning is a purely translatory movement in the radial direction passing through the groove plane. The roll therefore remains parallel to itself.

The second solution consists in compensating for the reduction in diameter of the roll by means of an identical displacement of the pin about which the roll- support lever rotates, this displacement being obtained by means of a series of eccentrics nested inside each other. In this way, the movement of the entire roll- lever unit between the initial position and the position following turning is a purely translatory movement in a direction parallel to the groove plane. The roll therefore, in this case also, remains parallel to itself.

The two known solutions described above, although widely used, are not without defects.

As regards the first solution, owing to the masses and dimensions involved, the arm lengthening operation is long and complex. Moreover, this lengthening is usually achieved by arranging special calibrated shims along the arm. With this type of solution, therefore, it is required to provide and manage a large stock of shims. In fact, each rolling station requires three complete series of shims; each series must contain a number of shims equal to the number of turning operations which can be performed on the rolls from the time when they are new to when they are completely worn.

As regards the second solution, again owing to the masses and dimensions involved, displacement of the pins is a long and complex operation. This displacement operation must in fact be completed singly for each of the pins. In the fairly common case of a rolling mill with 6-8 stations, this means operating singly on each one of the 18-24 pins for every single reconditioning of the 18-24 rolls. For each one of the pins, the respective eccentrics must be rotated at the same time so as to obtain a purely translatory movement for the pin of the lever. Moreover, these operations require in each case stoppage of the entire rolling mill which remains non-productive for the time required to remove the cartridges to be reconditioned and to replace them with other cartridges in operating order. The object of the present invention is therefore to overcome at least partly the drawbacks mentioned above with reference to the prior art.

In particular, a task of the present invention is to provide a rolling station for a continuous rolling mill which allows compensating for, in a simple and rapid manner, the reduction in the diameter of the roll following reconditioning by means of turning.

The abovementioned object and tasks are achieved by a rolling station in accordance with that claimed in Claim 1.

The characteristic features and further advantages of the invention will emerge from the description, provided hereinbelow, of a number of examples of embodiments, provided by way of non-limiting examples, with reference to the accompanying drawings in which:

- Figure 1 shows a front view of a rolling mill of the known type;

- Figures 2 to 4 show a roll-lever unit during three successive stages of its working life;

- Figure 5 shows a front view of a rolling cartridge according to the invention on which a single roll-lever unit is mounted;

- Figure 6 shows a close-up view of the detail indicated by VI in Figure 5;

- Figure 7 shows a cross-sectional view along the line VII-VII of Figure 6; - Figure 8 shows a schematic front view of a cartridge according to the invention without the roll-lever units;

- Figure 9 shows a schematic side view of the cartridge according to Figure 8;

- Figure 10 shows a schematic perspective view of the side wall of a roll-holder cartridge similar to that of Figure 8;

- Figure 1 1 shows a schematic perspective view of an adjusting ring similar to that of the cartridge according to Figure 8;

- Figure 12 shows a schematic perspective view of the wall according to Figure 10 and of the ring according to Figure 1 1 arranged alongside each other so as to form part of the cartridge according to Figure 8;

- Figure 13 shows a close-up view of a detail according to Figure 12;

- Figure 14 shows a view of the detail indicated by XIV in Figure 8, in a first operating condition.

- Figure 15 shows the detail of Figure 14, in a second operating condition;

- Figure 16 shows a front view of a cartridge similar to that of Figure 5, without the roll-lever units and where the adjusting actuator is shown partially cross- sectioned; and

- Figure 17 shows a close-up view of the detail indicated by XVII in Figure 16. With particular reference to the accompanying Figure 1 , 20 denotes in its entirety a continuous rolling plant, or rolling mill. With reference to the rolling mill 20, it is possible to define specifically a rolling axis X, which is the longitudinal axis of a long article 18 being processed, referred to below for the sake of simplicity with the term "tube". In a manner known per se, a continuous rolling mill 20 comprises, along the axis X, a plurality of rolling stations, each of which comprises a stand 22.

Each stand 22 comprises, in a manner known per se, a plurality of actuators 21 , a plurality of motor-reducer-spindle units 23, and a roll-holder cartridge 24. The roll-holder cartridge 24 according to the invention comprises two side walls 26, a plurality of roll-lever units 30, two adjusting rings 28 and an adjusting actuator 32. Each side wall of the cartridge comprises a plurality of first seats 260; each adjusting ring 28 comprises a plurality of second seats 280; and each of the roll-lever units 30 is mounted on the cartridge 24 so as to be able to pivot about a pin 300, each end of each pin being housed in the axial direction inside a first seat 260 and a second seat 280, respectively. Moreover, the first seats allow a displacement of the respective pins 300 in a purely tangential direction t, the second seats 280 allow a displacement of the respective pins 300 in a purely radial direction r; and the two adjusting rings 28 may be rotated about the axis X by means of the adjusting actuator 32.

The term "axial" is understood as meaning the direction of any straight line a parallel to the rolling axis X. The term "radial" is understood as meaning the direction of any straight half-line r which has its origin on the rolling axis and is perpendicular thereto. The term "circumferential" is understood as meaning the direction of any circumference c centred on the rolling axis X and lying in a plane perpendicular thereto. The term "tangential" is understood as meaning the direction of any straight line t tangential to a circumference c.

The side walls 26 are fixed to the cartridge 24, while the adjusting rings 28 are movable with respect thereto, and in particular they may rotate about the axis X. Moreover, the cartridge 24 is fixed to the rolling stand 22 during rolling of the tube 18 and, potentially, during some of the slight movements of the pins 300 which will be described below. It is however true that, in some embodiments of the rolling mill 20, the cartridge 24 may be extracted from the rolling stand 22, for example for the operations of reconditioning of the rolls 304 and of the consequent displacement of the pins 300.

As already mentioned above and as can be seen from Figures 7 and 9, the cartridge 24 comprises two side walls 26 and two adjusting rings 28. The detailed description which follows, as well as Figures 10 to 14, refers to only one of the two walls 26, to the respective ring 28 and to the seats 260 and 280 formed therein. Obviously the figures and the description are applicable also to the other wall 26 which is substantially symmetrical with respect to the wall considered here.

In each of the roll-lever units 30, a roll 304 is mounted on the cartridge 24 by means of a roll-support lever 302 (or simply lever 302). The lever 302 is mounted on the cartridge 24 so as to be able to pivot about the pin 300. The pin 300 has an axis a parallel to the rolling axis X. The lever 302 supports the roll 304 by means of two arms 306.

There are normally three roll-lever units 30 for each station. With this solution it is possible to obtain a satisfactory compromise between conflicting requirements. On the one hand, in fact, there exists the need to reduce the structural complexity of the individual station. On the other hand, there exists the need to divide up the outer profile of the tube 18 over as many rolls 304 as possible. It is possible, however, in order to satisfy specific requirements, to change the number of rolls 304 for each station .

Each roll 304 comprises, moreover, an actuator 21 (visible in Figure 1 ) suitable for applying to the roll 304 a force in a radial direction r with respect to the axis X. The force applied by the actuator 21 , indicated by the bold arrow F in Figures 2 to 4, is the one which produces the plastic deformation of the tube 18 being processed. In particular, the composition of the three forces F produced by the three actuators 21 of a stand 22 results in a radial reduction in the thickness of the tube 18 and in an axial lengthening of the tube itself. Advantageously, the actuator 21 comprises a hydraulic jack which acts on a thrusting surface 302 integral with the lever 302. The station also comprises motor- reducer-spindle units 23 suitable for causing the rotation of each roll 304. The rotation of the roll 304 performed by these units 23 is the one which provides the feeding movement displacing, by means of friction, the tube 18 along the axis X.

Each roll 304 defines an axis of rotation /. The roll 304 is formed symmetrically with respect to the axis / and has, formed on its periphery, a groove which is able to reproduce an arc of the outer profile of the tube 18. In particular, in the case where each rolling stand 22 comprises three rolls 304, each of them must act on a nominal arc of 120°. For each roll 304 it is also possible to define a groove plane which intersects, perpendicularly with respect to the axis /, the roll 304 along its smaller section.

During the course of their working life, the rolls 304 must be periodically reconditioned in order to be able to ensure an optimum profile of the groove. Reconditioning is performed by means of turning of the roll 304, with the consequent gradual reduction of its diameter.

Figures 2 to 4 shows a roll 304 at the beginning, halfway through and at the end of its working life respectively. As can be seen in Figure 2, the roll 304 starts its working life with a maximum diameter.

In Figure 3 the diameter of the roll 3 has been reduced by the successive turning reconditioning operations which were necessary during the first half of the working life of the roll 304. In accordance with this known solution, the reduction in the diameter of the roll 304 is compensated for by means of displacement of the pin 300 in the tangential direction parallel to the groove plane. The reduction in the diameter of the roll 304 is schematically indicated in Figure 3 by the arrow b, while the displacement of the pin 300 is schematically indicated by the arrow d.

In Figure 4 the diameter of the roll 304 has been further reduced by the successive turning reconditioning operations which were required during the working life of the roll 304. The further reduction in the diameter of the roll 304 is compensated for by means of the further displacement of the pin 300. The reduction in the diameter of the roll 304 is schematically indicated in Figure 4 by the arrow b, while the displacement of the pin 300 is schematically indicated by the arrow d.

The description provided above in general terms may be applied both to a rolling mill of the known type and to a rolling mill according to the invention. In accordance with the known solution, as already indicated above, the displacement of the pin 300 of the lever 302 is obtained by means of reconfiguration of a series of eccentrics nested inside each other. This reconfiguration operation is particularly laborious because it must be completed singly for each of the pins 300.

The solution according to the present invention will instead be described in detail below. For greater clarity of illustration, in the accompanying Figures 8 to 14, the side walls 26 of the cartridge 26 and the adjusting rings 28 are shown with conventional forms different from each other. In particular, the adjusting rings 28 are shown as circular rims with a radial lug 284 (see Figures 8, 11 and 12) or as circular rim segments (see Figures 13 to 15). At the same time the side walls 26 of the cartridge 24 are shown as polygonal rims (see Figures 8, 10 and 12) or as polygonal rim segments (see Figures 13 to 15). It is understood that these forms have been chosen in a conventional manner with the sole aim of distinguishing the adjusting ring 28 from the side wall 26, also when they are not associated together with the rolling stand 22. These forms there could have been chosen in a different manner, for example with opposite forms, subject to the particular technical requirements of the two components, which are well known to the person skilled in the art. As described above, each of the first seats 260, formed in the side walls 26 and therefore integral with the cartridge 24, allows displacement of the pin 300 housed therein in a purely tangential direction t. Similarly, each of the second seats 280, which are formed in the adjusting ring 28 and therefore rotatable about the axis X, allows displacement of the pin 300 housed therein in a purely radial direction r. In accordance with the embodiments shown in the accompanying Figures 7 and 10 to 16, each of the first seats 260 comprises a recess 261 and a slider block 262 sliding inside the recess 261 . A hole 263 formed in the slider block 262 is intended to receive a first portion 360 of the end of the pin 300. The form of the first seat 260 is such that the slider block 262 is able to slide inside the recess 261 only in the tangential direction t. Similarly, each of the second seats 280 comprises a recess 281 and a slider block 282 sliding inside the recess 281 . A hole 283 formed in the slider block 282 is intended to receive a second portion 380 of the end of the pin 300. The form of the second seat 280 is such that the slider block 282 is able to slide inside the recess 281 only in the radial direction r. Each axial end of each pin 300 is therefore housed simultaneously inside a first seat 260 and inside a second seat 280.

The accompanying figures and the description which follows refer to a stand 22 comprising three rolls 304. As already mentioned, this solution is the most common one and may be usefully regarded as being generally valid since the comments made with reference to three rolls may be easily applied to other solutions which make use of a different number of rolls, for example two or four rolls.

The use of three rolls 304 necessarily results in the cartridge having some geometric features which are invariable, apart from the machining and assembly tolerances which are typical of the sector. Each lever 302, by means of a pin 300, is rotatable about an axis a. The three axes a of each cartridge 24 are located on a circumference centred on the axis and are spaced from each other by 120°.

Since the pins 300 are movable, and the axes a are movable with them, it is convenient to define a nominal position for them in relation to which the movements of the pins 300 and therefore the axes a may be more easily described. For the sake of convenience, the nominal position is that shown schematically in Figure 14, where the slider block 262 is situated at the centre of its working stroke inside the recess 261 and the slider block 282 is situated at the centre of its working stroke inside the recess 281 . It is therefore possible to define the nominal radial direction r₀, i.e. the one which passes through the axis a when the latter is in its nominal position. Similarly it is also possible to define the nominal tangential direction t₀, i.e. the one which passes through the axis a when the latter is in its nominal position.

As can be seen in Figure 14, the nominal radial direction r₀ is perpendicular to the contact surfaces of the recess 261 with the slider block 262 of the first seat 260. Moreover, the nominal radial direction r₀ is parallel to the contact surfaces of the recess 281 with the slider block 282 of the second seat 280. Similarly, as can be seen in Figure 14, the nominal tangential direction t₀ is perpendicular to the contact surfaces of the recess 281 with the slider block 282 of the second seat 280. Moreover, the nominal tangential direction t₀ is parallel to the contact surfaces of the recess 261 with the slider block 262 of the first seat 260.

Since, as already mentioned, the first seat 260 allows displacement of the respective pin 300 in a tangential direction t and since the first seat 260 is fixed with respect to the cartridge 24, consequently the tangential direction t along which the pin 300 may be displaced is always the same (relative to the cartridge 24) and coincides with the nominal tangential direction t₀. On the other hand, the second seat 280 allows displacement of the respective pin 300 in a radial direction r and since the second seat 280 is rotatable about the axis X together with the ring 28, consequently the radial direction r along which the pin 300 may be displaced varies continuously about the nominal radial direction r₀.

The operating principle of the invention is described in detail below, with particular reference to the embodiments of the rolling cartridge 24 shown in the accompanying figures.

The adjusting ring 28 may be rotated about the axis by means of operation of the adjusting actuator 32 which acts, for example, on the radial lug 284 integral with the adjusting ring 28.

As the person skilled in the art may easily understand, there is no need for the adjusting ring 28 to assume exactly the form which is shown in the accompanying figures. It could for example not form a complete circle, provided that it accommodates all the second seats 280 of all the pins 300 and provided that it ensures a sufficient rigidity to ensure the same movements for all the seats 280.

The rotation of the adjusting ring 28 results in a movement of the second seats 280 which takes place generally in a purely circumferential direction c. This feature is illustrated schematically in Figure 8 where the angular movements have been amplified for greater clarity. In other words, if the pin 300 were housed inside the second seat 280 without further constraints, the respective axis a (indicated by x in Figures 14 and 15) would describe an arc of a circumference c. Since, however, the pin 300 is housed simultaneously inside the first seat 260 and the second seat 280, its movement is determined by the combination of the constraints imposed by the two seats 260 and 280.

In particular, therefore, with reference to the embodiments shown, the movement of the adjusting ring 28 imparts a thrust in the circumferential direction c to the slider block 282. The surface of contact between the recess 281 and the slider block 282 is in fact perpendicular to the thrust and therefore does not involve in any way the only (radial) degree of freedom permitted by the particular form of the second seat 280. The movement of the slider block 282 causes the movement also of the pin 300 since it is partially housed inside the hole 283.

The pin 300 itself, since it is partially housed inside the hole 263, therefore transmits a thrust in the circumferential direction c to the slider block 262 of the first seat 260 which, it is recalled, is fixed with respect to the cartridge 24 and therefore, potentially, with the entire plant 20.

The particular form of the first seat 260 allows the slider block 262 a single degree of freedom, i.e. that of being able to slide inside the recess 261 in the nominal tangential direction t₀. As the person skilled in the art is well aware and as can be easily seen in Figure 15, the circumferential trajectory c and the nominal tangential trajectory to diverge increasingly the one from the other moving away from the nominal position. In Figure 15 it can therefore be seen how the final position of the axis a (indicated by x) moves away from the circumferential trajectory c.

As the person skilled in the art may easily understand, in order to compensate for the reduction in diameter b of the roll 304 following reconditioning by means of turning, the pin 300 (and the axis a together with it) must be displaced by an identical length d along the nominal tangent t₀. This displacement may be performed owing to the geometric composition of the degrees of freedom permitted by the first seats 260 and by the second seats 280. As can be easily seen from Figure 15, the displacement of the axis a along the nominal tangent to may be obtained in theoretical terms by the combination of a rotation along the direction c (imparted by rotation of the adjusting ring 28) with a displacement along the radial direction r performed at the end of rotation (imposed by the geometric constraints).

In accordance with certain possible embodiments, the total working stroke d of the pin 300 along the nominal tangent to is such as to be able to compensate for the overall reduction in diameter b affecting the roll 304 from the start to the end of its working life. In accordance with certain possible embodiments, the total working stroke of the pin 300 along the nominal tangent to is between about 20 mm and about 30 mm and is preferably about 25 mm. This stroke of is substantially equal to the total working stroke of the slider block 262 inside the respective recess 261 .

In accordance with certain possible embodiments, the total working stroke of the pin 300 is composed of a half stroke of about 12.5 mm to the right of the nominal position and a half stroke of about 12.5 mm to the left of the nominal position. In accordance with these embodiments, at the start of the working life of the roll 304 the pin 300 is positioned at a first end point along its working stroke (Figure 2). During the first half of the working life of the roll 304, compensation of the subsequent reduction in diameter causes displacement of the pin 300 towards the halfway point of its working stroke. The halfway point of the working stroke of the pin, regarded above as being the nominal position, is reached halfway through the working life of the roll 304 (Figure 3). Therefore, during the second half of the working life of the roll 304, compensation of the subsequent reduction in diameter causes displacement of the pin 300 from the halfway point towards the second end point of its working stroke. The second end point of the working stroke is reached at the end of the working life of the roll 304 (Figure 4).

As already described above, the cartridge 24 according to the invention comprises an adjusting actuator 32 suitable for imparting to the adjusting rings 28 a rotation about the axis X. This adjusting actuator 32 may assume different forms, such as that of a mechanical screw jack, a mechanical worm screw and rack jack, a hydraulic jack, etc.

The accompanying Figures 16 and 17 show a particularly advantageous embodiment of the adjusting actuator 32. In accordance with this embodiment, the adjusting actuator 32 comprises a jack 320, for example a hydraulic jack, which is connected to a movable member 321 . The jack 320 is mounted on the cartridge 24 so as to impart to the movable member 321 a displacement along a radial direction r relative to the axis X. The movable member 321 in turn comprises an inclined guide 322 inside which a slide 323 is slidable seated. The slide 323 comprises a hole 324 which receives a pin 325 integral with both the lugs 284 of the adjusting rings 28. This kinematic configuration has the effect that, following a purely radial displacement of the movable element 321 , the inclination of the guide 322 causes a displacement of the slide 323 which has a radial component e_r and a circumferential component e_c (see Figure 17). It should be noted that, for the sole purposes of description of the adjusting actuator 32, it is no longer necessary to distinguish the circumferential direction c from the tangential direction f. Since the slide 323 houses the pin 325, the radial displacement of the movable member 321 causes a circumferential displacement of the pin 325 and therefore a rotation about the axis of the lugs 284 of the adjusting rings 28. In accordance with certain embodiments, the inclination of the slide 323 with respect to the radial direction ranges between 10° and 20°, preferably between 12° and 18°.

In the embodiment shown in Figures 16 and 17, the inclination of the slide 323 with respect to the radial direction is about 15°. This geometric configuration involves a ratio of about 1 :0.267 between the radial component e_r and the circumferential component e_c of the displacement of the slide 323.

This embodiment of the adjusting actuator 32 is particularly advantageous compared to other embodiments where the (for example hydraulic) jack may be oriented so as to act directly in the tangential direction.

The main advantage arising from the arrangement of the inclined guide 322 in the kinematic chain is that, on the one hand, it allows transmission of the force from the actuator 32 to the single pins 300 via the adjusting rings 28, but at the same time substantially prevents transmission of the forces in the reverse direction, i.e. from the pins 300 to the actuator 32.

During rolling, in fact, the forces F generated by the actuators 21 and the consequent reactions generated by the tube 18 and by the mandrel contained inside it result in the generation of notable constraint reactions on the pins 300. In the rolling stands according to the prior art, the pins 300 are fixed with respect to the stand 22 and the constraint reactions are therefore transmitted to the cartridge 24. On the other hand, in the rolling stand 22 according to the invention, the cartridge 24 allows the pins 300 a certain mobility with respect to the stand 22. In other words, while the radial components of the constraint reactions of the pins 300 are still transmitted to the cartridge 24, the tangential and/or circumferential components are transmitted via the adjusting rings 28 to the adjusting actuator 32. If the latter were directed in the tangential direction, the overall rigidity of the system would depend precisely on the rigidity of the jack itself. In the case of a hydraulic jack, the rigidity of the system would therefore not be satisfactory owing to the compressibility of the oil column. On the contrary, the radial orientation of the jack and the presence of the inclined guide 322 result in a drastic reduction in the forces which are transmitted to the jack and which must be opposed by it.

A significant advantage arising from the use of a cartridge 24 according to the invention in a rolling plant 20 is that of allowing rapid, simple and precise adjustment of the position of the pins 300 following reconditioning by means of turning of the rolls 304. As the person skilled in the art will have been able to understand easily from the description provided above, the operation of displacement of the pins 300 involves merely operation of the adjusting actuator 32. The consequent rotation of the adjusting rings 28 causes simultaneous (purely tangential) displacement of of all the pins 300 of the cartridge 24, thus allowing precise and rapid compensation of the reduction in diameter b of the rolls 304. This operation, which must necessarily be performed after reconditioning of the rolls 304, is preferably performed with the cartridge 24 removed from the rolling mill 20.

The solution according to the invention results however in a further advantage. The ease of displacement of the pins 300 and the fact that it may be performed remotely (i.e. without having to adjust directly the pins themselves) gives rise to the - totally novel - possibility of adjusting the position of the pins 300 without removing the cartridge 24, without stopping the mill 20 or even while rolling is in progress. A slight displacement may in fact be advisable in some cases, even though it is not required to compensate for any reduction in the diameter of the rolls 304; for example, in the case where it is required to roll tubes 18 with a diameter slightly different from the nominal diameter of the set of rolls 304 used during rolling. As is known, in each rolling station, the profiles of the grooves in the rolls 304 define the outer profile of the semifinished article or tube 18. Obviously the arc along which the grooves of the rolls 304 are shaped is taken from a circumference having as diameter the nominal diameter which is to be obtained at that given station.

It may be sometimes required to obtain a tube 18 with an anomalous diameter, i.e. a diameter which cannot be obtained by means of the design configurations of the rolling mill 20 and which in any case is different from a nominal diameter envisaged. In order to obtain a tube with an anomalous diameter it is therefore possible to pivot slightly the roll-lever units 30 so as to increase or decrease slightly the diameter obtained. Obviously, such a configuration is, for each roll, asymmetrical with respect to the radial direction and the contact of the roll itself is not optimal. In other words, after pivoting of the levers 302, the set of profiles of the grooves of the three rolls 304 no longer defines a circumference; instead they define a three-lobed figure composed of circle arcs which are not connected together. The possibility of adjusting the position of the pins 300 improves this situation, reintroducing at least the symmetry with respect to the radial direction r of the contact for each roll 304. Following said adjustment of the pins 300, the outer profile of the tube 18 will continue to be a three-lobed figure composed of arcs of a circle which are not connected together, but will have a more regular form and a more uniform thickness compared to those which may be obtained by means of a cartridge of the known type.

The invention also relates to a stand 22 and a rolling mill 20 for performing the rolling of long semi-finished articles, typically seamless tubes 20. The rolling stand 22 according to the invention comprises a plurality of actuators 21 , a plurality of motor-reducer-spindle units 23, and a cartridge 24 in accordance with that described above. The rolling mill 20 according to the invention comprises a plurality of rolling stations and associated stands 22 in accordance with that described above.

With regard to the embodiments of the cartridge 24, the stand 22 and the rolling mill 20 described above, the person skilled in the art may, in order to satisfy specific requirements, make modifications to and/or replace elements described with equivalent elements, without thereby departing from the scope of the accompanying claims.

Claims

1 . A roll-holder cartridge (24) for rolling a long article (18) having an axis X, comprising two side walls (26), a plurality of roll-lever units (30), two adjusting rings (28) and an adjusting actuator (32), wherein:

- each side wall (26) of the cartridge (24) comprises a plurality of first seats (260);

- each adjusting ring (28) comprises a plurality of second seats (280);

- each of the roll-lever units (30) is mounted on the cartridge (24) so as to be able to pivot about a pin (300), each end of each pin being housed in the axial direction inside a first seat (260) and a second seat (280), respectively;

and wherein:

- the first seats (260) allow displacement of the respective pins (300) in a purely tangential direction t,

- the second seats (280) allow displacement of the respective pins (300) in a purely radial direction r, and

- the two adjusting rings (28) may be rotated about the axis X by means of the adjusting actuator (32).

2. The cartridge (24) according to the preceding claim, wherein each of the first seats (260) comprises a recess (261 ) and a slider block (262) sliding inside the recess (261 ), a hole (263) formed in the slider block (262) being intended to receive a first portion (360) of the end of the pin (300).

3. The cartridge (24) according to the preceding claim, wherein the form of the first seat (260) is such that the slider block (262) may slide inside the recess (261 ) only in the tangential direction t.

4. The cartridge (24) according to any one of the preceding claims, wherein each of the second seats (280) comprises a recess (281 ) and a slider block (282) sliding inside the recess (281 ), a hole (283) formed in the slider block (282) being intended to receive a second portion (380) of the end of the pin (300).

5. The cartridge (24) according to the preceding claim, wherein the form of the second seat (280) is such that the slider block (282) may slide inside the recess (281 ) only in the radial direction r.

6. The cartridge (24) according to any one of the preceding claims, wherein each adjusting ring (28) comprises a radial lug (284) and wherein the adjusting actuator (32) acts on the radial lug (284).

7. The cartridge (24) according to any one of the preceding claims, wherein the total working stroke d of the pin (300) along the tangential direction t is between about 20 mm and about 30 mm and is preferably about 25 mm.

8. The cartridge (24) according to any one of the preceding claims, wherein the adjusting actuator (32) comprises a jack (320) connected to a movable member (321 ) and mounted on the cartridge (24) so as to impart to the movable member (321 ) a displacement along a radial direction r, the movable member (321 ) comprising in turn an inclined guide (322) inside which is slidably housed a slide (323) comprising a hole (324) which receives a pin (325) fixed to the adjusting rings (28) such that a radial displacement of the movable member (321 ) causes a circumferential displacement of the pin (325) and therefore a rotation about the axis Xoi the adjusting rings (28).

9. A rolling stand (22) comprising a plurality of actuators (21 ), a plurality of motor- reducer-spindle units (23) and a cartridge (24) in accordance with any one of the preceding claims.

10. A rolling mill (20) for rolling a long article (18), comprising a plurality of rolling stands (22) in accordance with the preceding claim.