Abstract:
The invention relates to a rolling mill for tubes, in which a series of roll-holder containers ( 10 ) is housed in an external structure ( 2 ) extended along a rolling axis (L); the containers can slide inside the structure to be extracted therefrom and each one houses at least three rolls ( 17, 18, 19 ) controlled by respective driving motors ( 41, 42, 43 ). In accordance with the intervention the rolls ( 17, 18, 19 ) can be moved inside the containers ( 10 ) in a guided way along directions radial in relation to the rolling axis, in order to regulate the distance therefrom.

Description:
FIELD OF THE INVENTION 
     The following invention relates generally to seamless tube rolling operated with a mandrel. 
     DESCRIPTION OF THE PRIOR ART 
     For this rolling process it is known to use rolling mills with two-roll stands having an orientation staggered 90° from one to another, or three-roll rolling mills also staggered from one to another, but at an angle of 60°: the present invention relates to this latter type of rolling mill. 
     In accordance with a currently preferred embodiment, the three rolls of each stand are mounted on respective oscillating arms having an end pivoted to a support container, which can be extracted from the structure of the rolling mill by making it slide along slides parallel to the rolling axis. 
     One example of this type of rolling mill is described in EP565772, to which reference should be made for further details on the subject. 
     On the other hand, what should be noted relating to this state of the art, is that the mounting of the rolls on oscillating arms implies numerous drawbacks. 
     For example, one of these is due to the registration of the pivot following the re-turning of the rolls, of which mention is also made in the patent cited previously. 
     In fact this operation entails non-negligible practical drawbacks, due to the fact that the insertion of thicknesses in the pivot support requires the removal of the respective arm, with the problems deriving from the weight thereof as well as the dirt that deposits on the pivot during rolling. 
     Should one not wish to act on the pivot by holding it immobile, it is possible to interpose packings between the seals of the bearings and the coupling beam that constitutes the top part of the lever, but again in this case the operation proves laborious. 
     Furthermore, in order to be able to extract the arms from the container, it is necessary that the latter is open frontally as in the patent cited above, or radially as in the rolling mill illustrated in U.S. Pat. No. 6,276,182; this entails in any case that the container does not have a very rigid structure, especially in an axial direction. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to improve this state of the art. 
     It therefore has the primary aim of providing a rolling mill with stands with three controlled rolls, wherein the position of the latter can be regulated in a simple and effective way also following the variation in diameter thereof caused by periodic re-turning. 
     The radial regulation of the position of the rolls is also used for rolling diverse products. 
     A second aim of the invention is that of arranging containers for the housing of the rolls, which are structurally resistant and make it possible to extract the rolls in an easy way for maintenance. 
     These and other aims of the invention are achieved by a rolling mill the characteristics of which are illustrated in the attached claims which are an integral part of the present description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages of the invention will be further evident in view of the detailed description of a preferred though not exclusive embodiment such as illustrated with the aid of the appended drawings wherein: 
         FIG. 1  shows a front view, partially in section, of a rolling stand according to the present invention: 
         FIG. 2  shows a side view of the rolling stand in  FIG. 1 ; 
         FIG. 3  shows a section of a roll-holder container of the preceding rolling stand. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to such drawings,  1  is used to indicate a rolling mill according to the invention, comprising an external structure  2  constituted by a series of circular crown elements  2   a ,  2   b ,  2   c . . . ,  2   n  arranged transversally to the rolling axis L, interconnected with spacers  3  inside which pass the rods  4  tightened at the ends by bolts  5 . 
     Inside the structure  2  of the rolling mill pairs of tracks  7  and  8  are arranged parallel to the longitudinal axis L; in particular, the pair of tracks  7  is located lower than the latter, whilst the other pair  8  is located higher: this because the first pair serves for the sliding of the roll-holder containers  10 , whilst the second serves for the blocking thereof. 
     To this end each container is provided with wheels  11  for the rolling on the lower tracks  7  and here hydraulic jacks (not shown in drawing) are arranged, pushing upward the containers  10  in order to keep them pressed against the upper tracks  8 ; for this reason, inside the containers contact shoulders  13  are formed against the upper tracks. 
     Each container  10  houses a triad of rolls  17 ,  18  and  19  mounted with their seals (bearings) on a respective yoke support  21 ,  22  and  23 ; above this is arranged an engagement groove  25 ,  26  and  27  for the roll balancing system, which will be described better below. 
     Rotation axes A, B, C of the rolls of each container  10  are arranged at 60° or, preferably, the median planes of the rolls are equidistant by 120° radially in relation to the rolling axis L; said orientation is staggered by 60° with that of the rolls of the adjacent container in the rolling mill. 
     Furthermore, in accordance with this embodiment of the invention the yoke supports  21 ,  22  and  23  slide radially in relation to the rolling axis; to this end, in the containers  10  there are slides  29 ,  30  and  31  that guide the movements of the yoke supports, which can be extracted radially from the containers opened for this purpose at the slides. 
     Furthermore, in the containers  10  blocks  33 ,  34  and  35  are present to stiffen the structure thereof, which is advantageously formed of two half-shells joined along a median join line  40  (visible in  FIG. 2 ). Such blocks are substantially aligned in the case of even and odd stands, as the containers of two consecutive stands are symmetric in relation to a vertical axis: this fact makes it possible to correctly transmit the forces that act axially along axis L from the containers to the structure  2 . 
     The rolls  17 - 19  are controlled in a known way by their respective engines  41 ,  42 ,  43  and adapters  45 ,  46 ,  47 , whereas their distance from the rolling axis is regulated by hydraulic capsules  49 ,  50 ,  51 . 
     The latter are essentially hydraulic actuators with a fixed part mounted rigidly (with bolts or others) on elements  2   a ,  2   b ,  2   c , etc. of the external structure of the rolling mill, and a mobile part constituted by a piston that is joined to a balancing rod  53 ,  54  and  55 . 
     The latter engages in the grooves  25 - 27  present on the yoke supports  21 - 23  of the rolls, in order to balance the weight thereof and maintain the position thereof between the rolling of one tube and another; it is opportune to observe that when the containers  10  slide along the tracks  7 , the ends of the rods  53 ,  54 ,  55  are extracted from the grooves  25 ,  26  and  27  without hindering the movement of the containers. 
     It is also useful to observe that the balancing system coaxial with the hydraulic capsules  49 ,  50  and  51 , is unique for each roll  17 ,  18 ,  19  unlike the known type of two-roll stands where two balancing systems are present for each roll. 
     Lastly it is necessary to note that the containers  10  are blocked inside the structure  2  of the rolling mill by a blocking system (not shown in drawings) that pushes them against the first element  2   a  of the external structure  2 , furthermore, for roll maintenance and changing operations, the containers are made to slide along the tracks  7  and extracted from a removable bottom  59  of the external structure  2 . 
     In the light of the preceding description it is possible to understand how the rolling stand achieves the purpose of the invention mentioned previously. 
     In fact, despite maintaining the advantages of three roll rolling, it does not present the drawbacks of the solution with oscillating arms of the state of the art. 
     In particular, thanks to the possibility of sliding along the slides  29 - 31  of the supports  21 - 23 , no adjustment is necessary after rolls have been re-turned for the routine maintenance thereof. 
     In fact the dimensional reduction due to the removal of the material with turning does not entail any geometric variation to be compensated with the addition of thicknesses or other as occurs in oscillating arm rolling mills: to this end it is sufficient to perform the normal adjustment of rolls  17 - 19  operated by the hydraulic capsules  49 ,  50  and  51 . 
     It should be further highlighted that the rolls with the relative yoke supports  21 - 23  can be easily extracted and reintroduced into the containers  10  thanks to the guides  29 - 31 , which in addition to guiding the movements are also a reference for assembly; it should also be pointed out that the containers  10  are advantageously open at the guides  29 - 31 , in order to consent the radial movement of the yoke supports with the rolls, without necessarily having to disassemble the containers. 
     Along the rolling mill small mandrel-holder stands are provided that serve to prevent contact between mandrel and processing rolls in the rolling mill input and emptying steps. Such small stands are normally of the three opening roll type and are devices in themselves known to those skilled in the art. 
     Similarly means are provided for releasing the adapters  45 ,  46  and  47  from the processing rolls  17 ,  18  and  19  and for supporting and positioning the adapters.