Patent Publication Number: US-2022219213-A1

Title: Guide device for guiding a driving bar of a mandrel or for guiding a mandrel in a rolling process of tubular bodies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT International Application No. PCT/IB2020/057824 filed on Aug. 20, 2020, which application claims priority to Italian Patent Application No. 102019000014925 filed on Aug. 22, 2019, the disclosures of which are expressly incorporated herein by reference. 
    
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention falls within the scope of rolling plants of tubular bodies. More precisely, the invention relates to a device for guiding a mandrel or guiding a driving bar of a mandrel which can be employed for rolling tubular bodies. The invention also relates to a guide unit comprising at least one guide device according to the present invention. 
     Background Art 
     Processes are known for making hollow bodies (or tubular bodies) such as, for example, seamless tubes. A first process which is very well known in the field is the one called push bench, for example described in U.S. Pat. No. 2,083,698. Such a process consists in preforming a cup made of the material to be rolled and then pushing it through a series of rolling stands or matrixes having decreasing sections by means of a mandrel inserted in the cup. A reduction of the thickness with subsequent elongation of the tube itself is obtained due to the effect of the pressure exerted on the material during the passage thereof between the matrixes (or stands) and the mandrel itself. Conventionally, the cup from which the process starts is generally made from a suitably heated bloom. At the end of the rolling, the mandrel is separated from the rolled tube thus obtained. The end of the tube, called a cap, is cut before the tube continues along the successive passages during which the deformation (calibration, finishing) is completed. 
     Another process of the known type, known as the CPE (Cross Piercing and Elongation) process, consists in making a starting hollow body by piercing the bloom, inserting the mandrel into the hollow body and mechanically fastening the hollow body to the mandrel in the end area of the tip by means of local deformation called crimping. With respect to the push bench type of process, this second process allows improving the yield of the material while avoiding discarding the cap. 
     Both the above-indicated processes provide pushing the mandrel along the rolling mill by means of a driving bar placed at the back of the mandrel with respect to the advancement direction thereof. Conventionally, the nominal diameter (or caliber) of the driving bar coincides with the one of the mandrel to be pushed. In use, the diameter of the mandrel may be slightly greater than that of the bar pushing it due to the increased temperature. In any event, the mandrel is pushed by a greater length than the one of the mandrel itself. Considering, for example, the production of blanks having maximum length of 21 to 21.5 meters, the total length of the mandrel plus the driving bar overall exceeds 45 meters. The driving bar and mandrel assembly is subject to compression during the rolling and, due to the length, tends to result in a very narrow rod. Guide and containment systems are provided which keep the elements to be guided (bar and mandrel) aligned along the rolling direction to avoid the bending of bar and/or mandrel. 
       FIG. 1  is a schematization of a guide unit ( 100 ) which comprises a plurality of devices (hereinafter also indicated by the expression modules), each of which being equipped with sliding rules which are suitably shaped so as to minimize the movement/oscillation space of the mandrel and the bar during the operating stroke. In other words, the sliding rules form containment surfaces against which the element to be guided may rest during the movement thereof along the rolling axis. In the system in  FIG. 1 , a first section ( 100 A) is identified in which there is arranged a first series of devices for guiding the driving bar and a second section ( 100 B), which is downstream of the first with respect to the advancement direction of the bar itself, comprising a second series of devices. The devices of the second section ( 100 B) in particular guide both the driving bar and the mandrel until the crossing of the latter in the rolling stand or matrix is complete. The modules of the second section ( 100 B) are provided with means adapted to allow loading the mandrel in the section itself. The part of plant (not shown in  FIG. 1 ) in which the actual rolling process occurs is positioned downstream of the second section ( 100 B) of the unit ( 100 ). The two sections ( 100 A,  100 B) are configured so that the bar and the mandrel advance along a direction coinciding with the rolling direction ( 201 ). 
       FIGS. 2 to 4  are views of a guide device (hereinafter also indicated as guide module) known from the background art. Such a module comprises a support structure ( 110 ) which is anchored to the floor. The structure defines a movement plane ( 200 ) containing the rolling axis ( 201 ), which conventionally is horizontal. The support structure ( 110 ) comprises a first portion ( 111 ) and a second portion ( 112 ), which are arranged on opposite sides with respect to the movement plane ( 200 ). Each of the portions ( 111 ,  112 ) carries a rule ( 113 ,  114 ) in position which is opposite to the rule carried by the other portion with respect to the movement plane ( 200 ). The containment module further comprises an arm ( 150 ) rotating about a rotation axis ( 250 ) which is parallel to the movement plane ( 200 ). Such an arm ( 150 ) carries a third rule ( 115 ) which, in operating position, is arranged at the movement plane ( 200 ) and more precisely, so that the three rules ( 113 ,  114 ,  115 ) are substantially arranged at 120° from one another or in any case are distributed as homogeneously as possible along the perimeter of the body to be guided. The arm ( 150 ) rotates from the operating position to an open position which, when reached, may allow the mandrel ( 161 ) to be inserted. The same arm ( 150 ) is shown in  FIG. 4  in the two positions described above. The guide module comprises hydraulic and/or mechanical locking means (not shown in  FIG. 4 ) in order to keep the arm ( 150 ) in the operating position, and therefore to keep the mandrel forced between the three rules ( 113 ,  114 ,  115 ). With reference again to  FIG. 4 , when it is intended for the second section of the system (mandrel guide), the module comprises a slide ( 162 ) along which the mandrel ( 161 ) may roll to be positioned between the rules ( 113 ,  114 ) when the arm ( 150 ) is in the open position. 
     Again with reference to  FIGS. 2 and 3 , the support structure ( 110 ) defines a space ( 108 ) inside of which a head ( 280 ) to which the driving bar is connected, is free to move. More precisely, the head ( 280 ) moves parallel to the rolling axis by employing moving means ( 109 ), which conventionally are of the pinion-rack type. 
     As indicated above, due to the length of the bar-mandrel unit, the rolling plant comprises a significant number of these modules. Overall, the rules form a guide system which, during rolling, is subjected to considerable forces, impacts and vibrations. For this reason, the hydraulic locking means, and more generally all the fastening systems, are to be configured so as not to allow the disconnection of the rules. However, the rules are subjected to heavy wear due to the forces involved and the sliding on the surfaces thereof. Therefore, with respect to the significant length (also greater than 40 meters) of the guide unit, the costs associated with performing maintenance on and for replacing the worn rules are particularly significant, especially in those plants in which the use of mandrels with different diameter (also called caliber) is provided. 
     In this regard,  FIGS. 2 and 3  show the same guide module equipped in a different manner to guide a mandrel having a predefined diameter. In particular, it is worth noting from the comparison between these two Figures how, as the diameter of the mandrel varies, the rules are necessarily to be replaced with other ones adapted to the purpose. This aspect also strongly affects the times and costs to be sustained for managing the plant, and therefore the final production costs. In fact, each time the diameter of the mandrel is changed or each time the rules are worn beyond a given value, the guide module is to be equipped again and operatively restored. In fact, in the current state, the times for preparing a guide device and operating on a new diameter are in the range of tens of hours. 
     Therefore, the need arises from the above-indicated considerations, to create a new guide system of the driving bar and/or of the mandrel which allows overcoming the above-mentioned drawbacks. 
     SUMMARY OF THE INVENTION 
     The main task of the present invention is the one of providing a guide device of a driving bar and/or of a mandrel which allows overcoming the above-indicated drawbacks. Within the scope of this task, it is an object of the present invention to provide a guide device which allows a reduction of the costs and the maintenance interventions associated with the wear of the guide surfaces. It is another task of the present invention to provide a functionally versatile guide device, i.e. which easily lends itself to guiding driving bars and/or mandrels having different diameter. It is a yet further object of the present invention to provide a guide device which is reliable and easy to manufacture at competitive costs. 
     The present invention is based on the general consideration of achieving the above-indicated objects by employing four abutment surfaces and arranging such surfaces on slides which are movable along a direction orthogonal to the advancement one of the bar or mandrel (hereinafter generically indicated as movable element). In particular, the device according to the invention comprises a support structure which identifies an advancement direction of the movable element to be guided. The support structure carries a first slide and a second slide, which are slidable along a transverse direction substantially orthogonal to the advancement direction. Each of the two slides carries two abutment surfaces for guiding the movable element and is movable along said transverse direction between at least a first operating position, upon reaching which said abutment surfaces are susceptible to coming into contact with a movable element having a first predefined diameter, and at least a second operating position, upon reaching which said abutment surfaces are susceptible to coming into contact with another movable element having a second predefined diameter; the device according to the invention comprises actuating means which move the slides along the transverse direction between the operating positions and then lock the slides themselves when one of said operating positions is reached. 
     The employment of two slides which are transversely movable with respect to the advancement direction of the element to be guided and the employment of four surfaces, on the one hand allows recuperating the wear of the abutment surfaces and on the other, adapting the device to the possible variation of the diameter of the mandrel. The operating position of the abutment surfaces becomes adjustable through the movable slides, and therefore adaptable to the diameter of the movable element to be guided. 
     According to a possible embodiment, the abutment surfaces of the first slide mirror the abutment surfaces of the second slide with respect to a vertical reference plane containing the advancement axis of the movable element. Preferably, the abutment surfaces for at least one of the slides extend over corresponding planes of extension which are tilted with respect to a horizontal reference plane containing the advancement direction (hereinafter also indicated by the expression “advancement axis”). The planes of extension are tilted by a same angle with respect to said reference plane and substantially intersect on the same reference plane so that the abutment surfaces substantially are arranged in a V. It has been see how this solution allows a particularly effective guide of the element, on the one hand because the contact surfaces are uniformly distributed about the advancement direction and on the other, they mirror one another two-by-two with respect to the vertical reference plane containing the same advancement direction. 
     According to a preferred embodiment, the actuating means comprise a first moving unit for the first slide and a second moving unit for the second slide. At least one of said units comprises an articulated mechanism configured to take on at least a first configuration which is characteristic of said first operating position and a second configuration which is characteristic of said second operating position. The actuating means further comprise thrust means for varying the configuration of said articulated mechanism. The employment of articulated mechanisms and corresponding thrust means allows a rapid movement of the two slides between the two operating positions and, therefore, device tooling times are significantly reduced. 
     According to a possible embodiment, the corresponding moving unit for at least one of the slides comprises a mechanical locking element which intervenes on the corresponding articulated mechanism, thus locking it in said second configuration and so that the configuration of said articulated mechanism can be varied only upon the actuation of said thrust means. The employment of a mechanical locking element is particularly advantageous in terms of reliability because the articulated mechanism may operate (i.e. keep the corresponding slide in the operating position) also in the event of failure or breakdown of the thrust means. 
     Preferably, the thrust means are connected to the connecting rod and comprise a hydraulic, pneumatic or electric type actuator. 
     In a possible embodiment, the mechanical locking element comprises an abutment surface against which the second lever of each pair of levers rests when said articulated mechanism takes on said second configuration. 
     According to a possible embodiment, at least one of said slides comprises a movable portion carrying a first abutment surface of said abutment surfaces; such a movable portion is movable between a closed position and an open position; when in said closed position, said first abutment surface is susceptible to contacting the movable element, and in which in said open position, said first surface occupies a position which is distal from the advancement axis such as to allow the positioning of the movable element in a housing space delimited by the other abutment surfaces. 
     In a possible embodiment, the movable portion is rotatable between the closed position and the open position about a rotation axis parallel to the advancement axis; the device comprises at least one rotation unit for rotating the movable portion between the closed position and the open one. 
     In a possible embodiment, the device comprises two rotation units installed on opposite end parts of said at least one of said slides, in which the end parts are assessed along a direction parallel to said advancement axis. 
     According to a possible embodiment, the rotation unit comprises:
         an articulated kinematism configured to take on at least a first configuration which is characteristic of said closed position and a second configuration which is characteristic of said open position of said movable portion;   an operating element for varying the configuration of the kinematism from said first configuration to said second configuration, and vice versa.       

     Preferably, at least one of said rotation units comprises a mechanical locking element which acts on said articulated kinematism, thus locking it in said second configuration and so that the configuration of articulated kinematism can be varied only upon the actuation of said operating element. 
     According to a possible embodiment, the operating element comprises an actuator and said articulated kinematism comprises:
         a body hinged to said at least one slide and hinged to a rod of said actuator so that a translation of said rod corresponds to a rotation of the body;   a lever hinged to said movable portion of the slide and hinged to the body so that upon a rotation of the body with respect to the at least one slide, the lever causes a rotation of the movable portion and therefore, depending on the direction, a passing from the closed position to the open one, or vice versa.       

    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Further objects and advantages of the present invention will become apparent from the following detailed description of an exemplary embodiment thereof and from the accompanying drawings, which are merely illustrative and non-limiting, in which: 
         FIG. 1  is a diagrammatic view of a plant of the known type; 
         FIGS. 2 and 3  are diagrammatic views of a guide device of a driving bar or a mandrel of the known type; 
         FIG. 4  is a diagrammatic view of a known device of the known type, for guiding a mandrel; 
         FIGS. 5 and 6  are front sectional views of a first embodiment and of a second embodiment of a guide device according to the present invention; 
         FIG. 7  is an enlargement of the detail VII indicated in  FIG. 5 ; 
         FIG. 7A  is a view related to an alternative embodiment of the detail VII shown in  FIG. 5 ; 
         FIGS. 8 and 9  are views of the device in  FIG. 5  in a first and second operating configuration, respectively; 
         FIG. 10  is a further view of the device in  FIG. 6 ; 
         FIG. 11  is a view related to a possible operating configuration of an articulated kinematism of the device in  FIG. 6 ; 
         FIG. 11A  is a detailed view of certain components shown in  FIG. 11 ; 
         FIG. 12  is a view related to another possible operating configuration of the articulated kinematism in  FIG. 11 ; 
         FIGS. 13 and 14  are views of an assembly of components of the device in  FIG. 6 , during various operating steps; 
         FIG. 15  is a view of a guide unit of a driving bar and of a mandrel comprising a plurality of guide devices according to the present invention; 
         FIG. 15A  is a diagrammatic view of certain components of the guide unit in  FIG. 15 . 
     
    
    
     The same numerals and reference letters in the Figures identify the same elements or components. 
     DETAILED DESCRIPTION 
     With reference in particular to  FIGS. 4 to 15A , the present invention relates to a device  1 ,  1 A for guiding a driving bar  5  of a mandrel or for guiding a mandrel  6 . Device  1 ,  1 A comprises a support structure  10  defined by a first part  10 A and by second part  10 B, which are opposite with respect to a reference plane  200  on which the advancement axis  201  (hereinafter also indicated by the expression “advancement direction  201 ”) of bar  5  and mandrel  6  acts. In the continuation of the description, bar  5  and mandrel  6  may also be indicated by the generic term “movable element  5 - 6 ”. 
     Device  1  of the invention comprises a first slide  11  and a second slide  12 , which are carried by said first part  10 A and by said second part  10 B of structure  10 , respectively. More precisely, the two slides  11 ,  12  are slidable along a transverse direction  202 , i.e. substantially orthogonal to the vertical reference plane  200  and to the advancement axis  201 . The movement of the slides  11 ,  12  along the transverse direction  202  is defined by guides  4 A,  4 B which are carried by the two parts  10 A,  10 B of structure  10 . In an embodiment shown in the Figures, two guides  4 A,  4 B are provided for each slide  11 ,  12 . 
     According to the present invention, each of the two slides  11 ,  12  comprises two abutment surfaces  51 ,  52 ,  53 ,  54  for bar  5  and/or for mandrel  6 , depending on the function for which device  1  is intended. More precisely, according to a first possible employment, the abutment surfaces  51 ,  52 ,  53 ,  54  serve to guide bar  5  alone, while in a second possible embodiment, the surfaces  51 ,  52 ,  53 ,  54  guide mandrel  6  and bar  5  in sequence. In any event, each abutment surface  51 ,  52 ,  53 ,  54  serves the function of guiding the movable element (bar and/or mandrel) and of countering the bending/deformation to which the element itself is subjected due to the loads weighing thereon. 
     According to the invention, each of the slides  11 ,  12  is movable along the transverse direction  202  between a first operating position, upon reaching which the abutment surfaces  51 ,  52 ,  53 ,  54  are susceptible to coming into contact with a movable element having a first predefined diameter, and a second operating position, upon reaching which the abutment surfaces  51 ,  52 ,  53 ,  54  are able to come into contact with a movable element having a second predefined diameter which is different from said first predefined diameter. In other words, according to the invention, each operating position of the slides  11 ,  12  is characteristic of a predefined diameter of the movable element  5 - 6 . 
     According to the invention, device  1  comprises actuating means of the slides  11 ,  12  which move each slide  11 ,  12  between said operating positions and lock each slide  11 ,  12  when one of said operating positions is reached. Therefore, the actuating means serve the function of obtaining the movement of the slides  11 ,  12  along the transverse direction  202  from said first operating position to said second operating position, and vice versa. At the same time, the actuating means are configured to lock the slides  11 ,  12  when the same reach one of the operating positions so that the abutment surfaces  51 ,  52 ,  53 ,  54  effectively counter the bending loads to which the movable element (bar  5 —mandrel  6 ) is subjected. 
     Due to the effect of the movement of the slides  11 ,  12  along the transverse direction  202 , device  1  advantageously allows movable elements having at least two different diameters to be guided without the need to perform any tooling or modify the configuration of the device. 
     The actuating means could be configured to allow the abutment surfaces  51 ,  52 ,  53 ,  54  to also reach further operating positions, each characteristic of a predefined diameter of the movable element  5 - 6  to be guided. The possibility also falls within the scope of the present invention, of configuring the actuating means so that the same allow the slides  11 ,  12  to be positioned in any position comprised between two limit positions which are characteristic of a maximum diameter and a minimum diameter of a movable element  5 - 6  to be guided. In other words, the possibility falls within the present, of continuously adjusting the position of the two slides  11 ,  12  when such a position is comprised between the two limit positions defined above. 
     According to a preferred embodiment of the invention, the at least two abutment surfaces  51 - 52  of the first slide  11  mirror the abutment surfaces  53 - 54  of the second slide  12  with respect to a vertical reference plane  200  containing the advancement axis  201 . 
     According to a possible embodiment (clearly shown in  FIG. 7 ), the corresponding abutment surfaces  51 ,  52 ,  53 ,  54  for each of the slides  11 ,  12  extend over planes of extension  501 ,  502 ,  503 ,  504  which are tilted with respect to a horizontal reference plane  500  containing the advancement axis  201 . Preferably but not exclusively, the corresponding planes of extension  501 - 502 ,  503 - 504  for each slide  11 ,  12  are tilted by a same angle (α 1 =α 2 ) but are opposite with respect to the horizontal reference plane  500 . The arrangement of the abutment surfaces  51 ,  52 ,  53 ,  54  is such that the planes of extension  501 ,  502 ,  503 ,  504  intersect at the reference plane  500 . Basically, the two surfaces  51 - 52 ,  53 - 54  for each slide  11 ,  12  are substantially arranged in a V with the vertex substantially on the reference plane  500 . It has been shown that also this particular arrangement of the abutment surfaces  51 ,  52 ,  53 ,  54  contributes to the functional versatility of device  1 ,  1 A according to the invention. Indeed, such an arrangement allows the abutment surfaces  51 ,  52 ,  53 ,  54  to adapt to the variation in diameter of mandrel  6  and/or bar  5  in any case so as to provide four abutment/contact points. 
     According to a possible alternative embodiment to the one above, with respect to the horizontal reference plane  500 , the abutment surfaces  51 ,  53  arranged below the horizontal reference plane  500  might not mirror the abutment surfaces  52 ,  54  arranged above the same plane (α 1 ≠α 2 ). The inclination angle α 2  of the planes of extension  501 - 503  of the abutment surfaces  51 ,  53  below the reference plane  500 , for example could be less than the inclination angle α 1  of the planes of extension  502 - 504  of the surfaces above the same reference plane  500 . This arrangement could depend, for example, on the dimensions of head  280 , which carries and pushes bar  5 , as better indicated below. In any case, the possibility falls within the invention for the abutment surfaces  51 - 53 ,  52 - 54  to be arranged in substantially opposite manner to what is indicated above, i.e. angle α 2  is greater than angle α 1 . 
     According to another embodiment, shown in  FIG. 7A , the abutment surfaces  51 ,  52 ,  53 ,  54  could also have a concave shape with a radius of curvature which is greater than or equal to the radius of the guide element  5 - 6 . According to a further embodiment, two abutment surfaces could extend over a plane, while two others could be concave. 
     Therefore, not only do the embodiments described above for the abutment surfaces fall within the scope of the present invention, but so do combinations thereof or again, further alternative embodiments which are functional for the purpose. In this regard, the abutment surfaces arranged above the horizontal reference plane  500  may mirror or not mirror the ones below the same plane. 
     According to a possible embodiment, device  1 , the actuating means comprise, for each of the slides  11 ,  12 , a moving unit  301 ,  302  for moving a corresponding slide  11 ,  12  from the first operating position to the second operating position (or vice versa). In particular, according to the invention, such a moving unit  301 ,  302  comprises an articulated mechanism  21 ,  22  which takes on at least a first configuration which is characteristic of said first operating position and a second configuration which is characteristic of said second operating position of the corresponding slide  11 ,  12 . The moving unit  301 ,  302  further comprises thrust means  88  for varying the configuration of the articulated mechanism  21 ,  22 , in particular between the two configurations (first and second) described above. It is precisely the variation in configuration of the articulated mechanism  21 ,  22 , induced by the thrust means  88 , to translate into the movement of the corresponding slide  11 ,  12  along the transverse direction  202  between the two operating positions. 
     In this regard,  FIGS. 8 to 10  show a possible, and therefore not exclusive, embodiment of the two moving units  301 ,  302  according to the invention. In particular,  FIGS. 8 and 9  are plan views of device  1  in  FIG. 5  and allow the shape of the articulated mechanisms  21 ,  22  of each moving unit  301 ,  302  to be noted in each of the two operating configurations defined above. More precisely,  FIG. 8  shows the articulated mechanism  21 ,  22  of each slide  11 ,  12  in the first operating configuration (slides  11 ,  12  in the first operating position), while  FIG. 9  shows the same articulated mechanism  21 ,  22  in the second operating configuration (slides  11 ,  12  in the second operating position). 
     The articulated mechanism  21  of the first moving unit  301  comprises a first pair of levers  25 ,  26  and a second pair of levers  25 ′,  26 ′. For each pair of levers, a first lever  25 ,  25 ′ is hinged to the first part  10 A of the support structure  10 , while a second lever  26 ,  26 ′ is hinged to the corresponding first lever  25 ,  25 ′ and to the first slide  11 . The articulated mechanism  21  also comprises a connecting rod  27  which connects the first lever  25  of the first pair of levers to the first lever  25 ′ of the second pair of levers. The connecting rod  27  serves the function of synchronizing the rotation of the two levers  25 ,  25 ′. Such a rotation translates into a translation of the first slide  11  along the transverse direction  202  due to the effect of the guide means which restrain the movement of the first slide  11 . In the embodiment shown in the Figures, the thrust means  88  are connected to the connecting rod  27  and comprise an actuator, preferably of the hydraulic type. The body  88 A of actuator  88  is anchored to the first support part  10 A, while the end of the rod  88 B thereof is restrained to the connecting rod  27 . The related movement of rod  88 B with respect to body  88 A of the actuator itself causes a roto-translation of the connecting rod  27  and a subsequent rotation of the two levers  25 ,  25 ′. In an embodiment not shown in the Figures, the thrust means  88  could be connected to another lever of the articulated mechanism. 
     As shown in  FIGS. 8 and 9 , the moving unit  302  selected to move the second slide  12  has a structure substantially corresponding to the one of the moving unit  301  described above. Therefore, what is disclosed above in reference to the moving unit  301  of the first slide  11  is to be considered entirely valid also for the moving unit  302  of the second slide  12 . 
     According to a first possible embodiment, locking the slides  11 ,  12  in the first operating position or in the second operating position could be actuated directly by the thrust means  88 . The hydraulic actuator mentioned above could therefore be configured so as to exert a sufficient force to keep the corresponding slide  11 ,  12  in the operating position reached previously due to the effect of the thrust exerted by the actuator itself. 
     According to a preferred embodiment of the invention, the related moving unit  301 ,  302  for each of the two slides  11 ,  12  comprises a first mechanical locking element  70 A and a second mechanical locking element  70 B which act on the articulated mechanism  21 ,  22 , locking it in a corresponding operating configuration (i.e. locking the slide in the corresponding operating position) and therefore preventing any variation in configuration potentially caused by the forces acting on mandrel  6  or bar  5 . In other words, each mechanical locking element  70 A,  70 B serves the function of preventing the corresponding slide  11 ,  12  from moving from the occupied operating position, unless such a movement is induced by the above-indicated thrust means  88 . 
     In the embodiment shown in  FIGS. 8 and 9 , each mechanical locking element  70 A and  70 B comprises an abutment surface  71 A,  71 B which extends over a plane  205  which is substantially parallel to the transverse direction  202 . With reference to  FIG. 8 , when the articulated mechanism  21 ,  22  occupies the first operating position, the second lever  26  of one of said pairs of levers  25 - 26  rests against the abutment surface  71 A of a first mechanical locking element  70 A. With reference to  FIG. 9 , when the articulated mechanism  21 ,  22  instead occupies the second operating position, the second lever  26  of the other of said pairs of levers rests against the abutment surface  71 B of the second mechanical locking element  70 B. 
     In any case, each abutment surface  71 A,  71 B prevents the rotation of the corresponding second lever  26 ,  26 ′ which would be induced by the forces acting on the movable element  5 - 6 . Such forces indeed would tend to move the corresponding slide  11 ,  12  away from the advancement axis  201 , along the transverse direction  202 , and therefore to vary the configuration of the articulated mechanism  21 ,  22 . Advantageously, these forces are instead discharged onto the abutment surface  71 A and therefore onto the support structure  10 . In fact, due to the effect of the abutment surface  71 A, the articulated mechanism  21   22  is auto-locked in the second operating configuration. This condition increases the reliability of device  1  according to the invention because locking the slides  11 ,  12  in the operating position is of mechanical type and therefore is not designated to the means pushing the slides  11 ,  12  along the transverse direction  202  (i.e. to the thrust means  88 ). The guiding of the movable element  5 - 6  is thus ensured also in the event of the breakdown or failure of the thrust means  88 . This results in the latter being sized only to vary the configuration of the articulated mechanism  21 ,  22 , i.e. to push the corresponding slide  11 ,  12 . 
     With reference again to  FIGS. 8 and 9 , the following is a description of the moving principle of the two slides  11 ,  12  of the device shown. The slides  11 ,  12  in  FIG. 9  occupy the second operating position. It is worth noting that in this configuration, the rod  88 B of actuator  88  is substantially retracted in the body of the actuator itself. Due to the effect of the connecting rod  27 , the levers of each pair of levers  25 - 26  and  25 ′- 26 ′ have the same angular position assessed with respect to the respective rotation axes. In particular, it is worth noting that the rotation axes of the levers  25 - 26  and  25 ′- 26 ′ for each pair of levers are not aligned in the first operating position, rather they identify a first broken line Z 1  passing through the rotation centers of the levers themselves. 
     The actuation of actuator  88 , i.e. the exit of rod  88 B thereof, causes a movement of the connecting rod  27  and therefore a synchronized rotation of each pair of levers  25 - 26  and  25 ′- 26 ′. With reference to  FIG. 8 , the first lever  25 ,  25 ′ for each pair of levers  25 - 26  and  25 ′- 26 ′ rotates in counterclockwise direction (arrow W 1  in  FIG. 8 ) about the rotation axis thereof, thus causing a rotation in clockwise direction (arrow W 2  in  FIG. 8 ) of the corresponding second lever  26 ,  26 ′. The movement of the levers is completed until the corresponding slide  11 ,  12  reaches the second operating position ( FIG. 9 ), in which the second lever  26 ′ comes into contact with the abutment surface  71 B of the second mechanical locking element  70 A, thus locking the articulated mechanism  21 ,  22  in the configuration reached. It is worth noting that the rotation axes of the levers  25 - 26  and  25 ′- 26 ′ for each pair of levers  25 - 26  and  25 ′- 26 ′ are also not aligned in the first operating position, rather they identify a second broken line Z 2 , which is different from the first one (Z 1 ), passing through the rotation centers of the levers themselves. It is also worth noting that the corresponding two levers for each pair of levers  25 - 26  and  25 ′- 26 ′ take on an intermediate position in the passage between the second operating position and the first operating position, whereby said rotation axes are aligned. 
     The variation of the existing distance (from T 1  to T 2 ) between the two slides  11 ,  12  (distance assessed along the transverse direction  201 ) following the movement from the second operating position to the first operating position may be noted from the comparison between  FIGS. 8 and 9 . Distance T 1 , T 2  is assessed with respect to two points of the slides  11 ,  12  which mirror the vertical reference plane  200  containing the advancement axis  201 . In the configuration shown in  FIG. 8 , such a distance T 1  is less than distance T 2  assessed in the second operating position. It is apparent that the value of the distance depends on the configuration of the levers  25 - 26  and  25 ′- 26 ′, and more generally of the articulated mechanism  21 ,  22 . 
       FIGS. 8 and 9  show how device  1  is easily adapted to operate on movable elements  5 - 6  having at least two different nominal diameters. In particular, not only does the above-described embodiment allow a quick passage from one operating configuration to the other, but simultaneously allows the self-locking of the slides  11 ,  12  in each of the two operating positions following the change in configuration of the articulated mechanism  21 ,  22 . 
     Advantageously, in the above-described embodiment shown in the Figures, device  1  according to the invention may be adapted to operate on movable elements  5 - 6  having a diameter which falls in a range (at least in the order of millimeters) around the nominal diameters which are characteristic of the mentioned operating positions. Such an adaptation may be completed by varying the thickness of the abutment surfaces  71 A,  71 B of the locking elements  70 A,  70 B, or more generally, by varying the position of the same abutment surface  71 A,  71 B (i.e. of plane  205  over which such a surface extends) along a direction which is parallel to the advancement axis  201 . In essence, by modifying the position of the abutment surface  71 A,  71 B, the course of the broken line Z 1 -Z 2  identified by the rotation axes of the levers may be varied when a corresponding operating position is reached. 
     It therefore is worth noting that the variation in thickness of the abutment surface  71 A,  71 B, or the variation of the longitudinal position thereof, in fact is the only operation required to adapt device  1 ,  1 A to guide a movable element  5 - 6  having a nominal diameter close to the value of one of the nominal diameters. Therefore, with respect to the background art, device  1 ,  1 A is much more adaptable and therefore easier to manage. Such a versatility results in a significant decrease in the dead times and therefore, in an increase of the plant productivity in which device  1 ,  1 A itself operates. 
     According to a possible embodiment (shown also in  FIG. 6 ), the first slide  11  comprises a portion  13  carrying one of said abutment surfaces (hereinafter indicated as first abutment surface  51 ), which is movable, preferably rotatable, between a closed position and an open position. In this embodiment, the device according to the invention is indicated by  1 A and preferably is used for guiding a mandrel  6 , it in any case being able to be used also for guiding a bar  5 . 
     In the closed position, the first abutment surface  51  (carried by portion  13 ) is positioned in the position adapted to guide the movable element  5 - 6 . Basically, in the closed position, the first abutment surface  51 , with the other abutment surfaces  52 ,  53 ,  54 , delimits the housing space SP (indicated in  FIG. 13 ) in which mandrel  6  is positioned. In the open position, the abutment surface  51  is positioned in distal position from the other abutment surfaces  52 ,  53 ,  54  so as to define an opening which is useful for loading mandrel  6  in the housing space SP. The latter in any case remains defined by the other three abutment surfaces  52 ,  53 ,  54 . Basically, portion  13  is made movable to allow the loading/insertion of mandrel  6  in the housing space. As indicated below, this operation may be carried out through mechanical arms or using a loading slide. 
     According to a preferred embodiment, the movable portion  13  is rotatable between the closed position and the open one about a longitudinal axis  220  which is parallel to the advancement direction  201 . In this regard, device  1  according to the invention comprises at least one rotation unit  401 ,  402  for rotating said first movable portion  13  between the closed position and the open position. 
     According to a possible embodiment shown in  FIG. 10 , device  1  comprises two rotation units  401 ,  402  installed on opposite end parts of the first slide  11 , when such end parts  11 A,  11 B are assessed along the advancement direction  201 . It is worth noting that the device shown in  FIG. 10 —in essence corresponding to the one shown in  FIGS. 8 and 9  minus the rotation units  401 ,  402  of the first portion  13 —apparently is not in the device in  FIGS. 8 and 9 . The device in  FIGS. 8-9  therefore preferably is intended to guide bar  5  which does not need to be loaded in device  1  because it is pushed ahead or pulled back along the advancement direction  201  by the thrust and dragging means, for example of the type known from the background art. 
     Preferably, the two rotation units  401 ,  402  have the same configuration. According to a preferred embodiment shown in  FIGS. 11 and 12 , each rotation unit  401 ,  402  comprises at least one articulated kinematism configured to take on at least a first configuration which is characteristic of said closed position and a second configuration which is characteristic of said open position of said movable portion  13 . The following is a description of the shape of the first rotation unit  401 , but the following considerations are true mutatis mutandi also for the second rotation unit  402 . 
     The first rotation unit  401  also comprises an operating element  410  for varying the configuration of the kinematism from the first configuration to the second configuration, and vice versa. The operating element  410  preferably is an actuator of the hydraulic, pneumatic or electric type operatively connected to one of the members of the kinematism so as to vary the position thereof, thus inducing the configuration change. The operating element  410  is installed on the first slide  11  and remains integral with the slide itself, together with the whole kinematism, obviously during the movement along the transverse direction  202  from the first operating position to the second operating position, and vice versa. 
     With reference again to  FIGS. 11 and 12 , in a preferred embodiment of the first rotation unit  401 , the articulated kinematism comprises a body  61  hinged to the first slide  11 , preferably so as to rotate about a first rotation axis  451  parallel to the rotation axis of the movable portion  13 . The operating element  410  is connected to the body  61  in order to cause the rotation about the first rotation axis  451 . Body  61  preferably is hinged at a second rotation axis  452  at the rod of the actuator forming the operating element  410  so that a rotation of body  61  corresponds to a translation of the rod. 
     The kinematism also comprises a lever  62  hinged to the movable portion  13  of the first slide  11  and hinged to body  61  at a third rotation axis  453  and a fourth rotation axis  454 , respectively. A rotation, through lever  62 , of body  61  about the first rotation axis  451 , induced by the operating element  410 , translates into a rotation of the movable portion  13  about the longitudinal axis  220 , and therefore depending on the direction, into a passage from the closed configuration ( FIG. 11 ) to the open configuration ( FIG. 12 ), or vice versa. 
     With reference to  FIG. 11 , in the closed configuration, lever  62  comes into contact—with a part thereof close to the fourth rotation axis  454 —an abutment surface  87  which is integral with structure  10 . In such a configuration, the fourth rotation axis  454  is not positioned along direction L joining the first rotation axis  451  and the third rotation axis  453 , rather it is in a position which is misaligned with such a joining direction. This condition is clearly shown in the diagrammatic view in  FIG. 11A , in which the contact between lever  62  and the abutment surface  87  is noted. This contact prevents possible rotations (indicated by arrow R 1  in  FIG. 11A ) of the movable portion  13  induced by the forces acting on mandrel  6  during the guiding thereof. Indeed, a possible radial force (indicated by F 1  in  FIG. 11 ) on the abutment surface  51  would result in the movable portion  13  rotating (in counterclockwise direction) about the longitudinal axis  220 . The abutment surface  87  prevents such a rotation because it locks the rotation of the second lever  62  and accordingly, of the same movable portion  13 . In fact, the contact between lever  62  and the abutment surface  87  causes the kinematism to be self-locking in the closed position. The abutment surface  87  forms a mechanical locking element which prevents varying the configuration thereof once the position corresponding to the closed position is reached unless there is an intervention by the operating element  410 . 
     With reference again to  FIGS. 11 and 12 , following the actuation of the operating element  410  (in particular, following the retraction of the rod of the actuator), body  61  rotates in clockwise direction about the first rotation axis  451 , thus causing the roto-translation of lever  62 . The latter drags the movable portion  13  of slide  11 , thus causing the rotation about the longitudinal axis  220 . It is worth noting in the case in  FIG. 11  that lever  62 , dragged in rotation by body  61 , rotates in counterclockwise direction about the third rotation axis  453  and causes the rotation of the movable portion  13  about the longitudinal axis  220 . In particular, due to the effect of the dragging of body  61  and of the position taken on by the fourth rotation axis  454  (misalignment with respect to direction L), the movable portion  13  initially rotates (about axis  220 ) by a few degrees in counterclockwise direction towards the housing space SP and then in clockwise direction (again about axis  220 ) so as to free the access to the housing space SP. 
     As indicated above, the rotation of the movable portion  13  from the closed position to the open one is in order to allow the loading of mandrel  6  in the housing space SP. For this reason, it is carried out in the absence of a mandrel or during the dragging back of bar  5 , i.e. under a condition which in any case also allows the initial rotation in clockwise direction towards the housing space. 
     Again, it is worth noting from  FIGS. 11 and 12  that the components of the articulated kinematism of the rotation unit  401  are installed on a plane P 1  which is substantially tilted with respect to the movement plane P 0  on which slide  11  moves (transverse direction  202 ). In any case, the possibility for the articulated kinematism to be configured in a different manner from the one described, and in any case installed on slide  11  according to a different arrangement from the one shown in the Figures, falls within the scope of the present invention. 
     Again with reference to  FIGS. 11 and 12 , it is worth further noting that the components of the kinematism (the operating element  410  and the abutment surface  87 , in particular) are installed on blocks  701 ,  702  connected to slide  11  through removable connecting elements (not shown). Also this technical solution is only a possible, and therefore not exclusive, embodiment of the invention. 
       FIGS. 13 and 14  show, in sequence, the loading steps of mandrel  6  in the housing space SP defined by the abutment surfaces  51 ,  52 ,  53 ,  54 . For this purpose, these Figures show, with a dashed line, a slide V comprising a tilted surface V 1  along which mandrel  6  may slide or roll up to falling into the housing space SP. These Figures show only the slides  11 ,  12  for simplicity, while the support structure which carries them is omitted. The movable portion  13  is shown in the open position in both  FIGS. 13 and 14 . 
     Mandrel  6  is positioned on slide V (see  FIG. 13 ) through suitable lifting means so that the same may fall into the housing space SP which remains delimited by the abutment surfaces  52 ,  53 ,  54  when the movable portion  13  is in open position (see  FIG. 14 ). 
     In a possible embodiment, slide V may be replaced by one or more mechanical arms which position mandrel  6  in the housing space SP. The employment of mechanical arms simplifies the design of the plant and protects the abutment surfaces  52 ,  53 ,  54  against impacts. Mandrel  6  may be accompanied in the housing space SP, and therefore in contact with the abutment surfaces  52 ,  53 ,  54 , through the employment of mechanical arms. 
     The present invention therefore also relates to a unit  600  for guiding a driving bar  5  and a mandrel  6  for a rolling plant of tubular bodies. With reference to  FIGS. 15 and 15A , unit  600  according to the invention comprises a first section  600 A for guiding a bar  5  and a second section  600 B for guiding a mandrel  6  and the bar  5  itself. The second section  600 B is downstream of the first section  600 A with respect to the advancement direction  201  of the bar and mandrel. The rolling mill is positioned downstream of the second section  600 B, in which rolling mill the hollow tube is processed after the insertion therein of mandrel  6  according to a principle in itself known. In particular,  FIG. 15  indicates the inlet section  700  of the rolling mill in which the hollow tube  7  is positioned. Each of the sections  600 A,  600 B comprises a plurality of devices according to the present invention. 
     According to a preferred embodiment, the devices (indicated by numeral  1 A in  FIG. 15 ) of the second section  600 B are of the type shown in  FIG. 6 , i.e. comprising rotation units  401 ,  402  for moving the movable portion  13  carrying one of the abutment surfaces  51 , between a closed position and an open position. Thereby, mandrel  6  advantageously may be inserted in the housing space according to the above-described principles. 
     The second section  600 B has a length (assessed along the advancement direction  201 ) which is greater than or equal to the length of mandrel  6 . The employment is provided in the case shown, of mechanical arms which position mandrel  6  in the housing space SP defined by each guide device. 
     As indicated above, according to a known principle, the driving bar  5  is restrained to a head  280  moved along the advancement direction  201  through dragging means, preferably of the pinion-rack type (indicated by letters P and C in  FIG. 15A ). Bar  5  is entirely arranged in the first section  600 A during the loading of mandrel  6  in the second section  600 B. Once the loading of mandrel  6  is complete, the dragging means P, C are actuated, which cause the advancement of bar  5  along the movement direction  201 . Bar  5  pushes the mandrel, which may be partly in the hollow body (check) or external thereto, and accordingly along the rolling mill, also in this case according to a process in itself known. Once mandrel  6  is completely in the hollow body, the dragging means bring bar  5  back into the first section  600 A so as to prepare it for the successive thrust. 
     According to a preferred embodiment, the devices (indicated by numeral  1  in  FIG. 15 ) of the first section  600 A are of the type shown in  FIG. 5 , i.e. not comprising rotation units  401 ,  402  for moving a movable portion  13  carrying one of the abutment surfaces. In a different manner from the second section  600 B, there is no need for the first section  600 A to load a movable element at each operating cycle. However, according to a preferred embodiment, also certain devices (indicated by  1 A) of the first section  600 A immediately adjacent to the second section  600 B could also be of the type shown in  FIG. 6 . Through this solution, the modules provided with a movable portion  13  could advantageously be exploited to perform the operation of replacing the driving bar  5  which, as is known, is to be performed at least each time the diameter is varied of mandrel  6  with which the rolling plant operates, in which the guide unit  600  according to the invention is provided. Practically, the replacement of the driving bar  5  is performed first by moving the movable portions  13  of the devices  1 A into the open position and then replacing the bar used with the one to be employed. 
     The guide device according to the invention allows the tasks and preset objects to be wholly absolved. In particular, the configuration of the device according to the invention allows the wear of the abutment surfaces to be recuperated, and therefore the production of the plant to be increased through a significant reduction of the dead times. Simultaneously, the device according to the invention operatively adapts to a possible variation of the diameter of the mandrel, to the benefit of a reduction of the machine setting times. In general, the device according to the invention allows the frequency of the tooling operations to be simplified and highly contained, and therefore the management costs of the rolling plant associated with guiding the bar and/or mandrel to be reduced.