Skew-rolling mill for reducing solid and hollow cross-sections
BACKGROUND OF THE INVENTION 
     This application relates to applicant&#39;s copending application Ser. No. 06/375,569, filed May 6, 1982, titled &#34;Apparatus For Changing The Tapered Dolls Of A Skew Rolling Mill&#34;, assigned to the same assignee. 
     FIELD OF THE INVENTION 
     The invention relates to a skew-rolling mill, in which a roll carrier (rotor) and a hollow shaft, which is rotatably disposed in this latter and allows passage of the rolled stock, are rotatably supported independently of each other in a stand (stator). The driven roll carrier (rotor) is provided with three conical working rolls inclined to the rolled stock axis at 120° to each other, each being driven by way of one of three planet pinions which roll on a sun wheel mounted on the hollow shaft, as the roll carrier (rotor) rotates. Such planetary skew-rolling mills have proved satisfactory both for the high deformation of semifinished products, i.e. solid cross-sections, and for the reduction of hollow cross-sections. 
     The working rolls are adjustable relative to the rolled stock in order to give the cross-section the required dimensions, or the hollow cross-section the required outer diameter, the inner diameter being determined by the mandrel rod. 
     The feed motion for the rolled stock is derived from an inclined positioning of the rolls in which the axes of the shafts carrying the working rolls cross the rolled stock axis at short distances apart. In order to be able to adjust these crossing angles, the roll heads in which the working roll shafts are supported are inserted into the roll carrier (rotor) such that they can be swivelled about axes parallel to the rolled stock axis. 
     In order to drive the planet pinion associated with any working roll, an intermediate shaft is supported in the roll heads parallel to the rolled stock axis, and carries an intermediate gear wheel which is engaged with the planet wheel and a bevel pinion which is engaged with a bevel gear mounted on the roll shaft. 
     The inclined positioning of the rolls, by means of which the feed motion of the rolled stock is determined, is conditional upon a determined relationship between the roll rotational speed and the rotor rotational speed if, for a determined roll position and a determined rolled stock diameter as defined thereby, the rolled stock is to be able to pass through the rolling mill without rotating. However, in order to prevent the rolled stock from rotating for other roll positions or inclinations, the hollow shaft is rotatable together with the sun wheel mounted thereon, and thus the relationship between the roll rotational speed and the rotor rotational speed can be controlled. 
     DESCRIPTION OF THE PRIOR ART 
     In known planetary skew-rolling mills constructed in the manner heretofore described, the provision of a stable support and the rotary drive for the two mutually separate rotatable parts, namely the roll carrier (rotor) and the hollow shaft carrying the sun wheel and provided with a passage for the rolled stock, are not without problems. 
     Thus, it is known to rotatably support the hollow shaft in the stand (stator), and to provide a drive gear wheel for transmitting the torque, either at one of its ends outside the two support positions, or between the two support positions. In this case, the roll carrier is either fully supported on the other end of the hollow shaft projecting from the stand (stator), i.e. by means of two bearings (as proposed in German Patent Specification DE-AS No. 16 02 153), or is supported at least by means of one bearing on this end of the hollow shaft and a second bearing in the stand (stator) (as proposed in German Patent Specification DE-OS No. 27 48 770). The hollow shaft must carry the sun wheel between a bearing for the roll carrier (rotor) on the hollow shaft and the stand (at least one bearing is necessary), the outer diameter of the hollow shaft being determined by the size of the sun wheel, whereas the inner diameter of the hollow shaft must be governed by the diameter of the rolled stock. The fact that the heavy and highly stressed roll carrier (rotor) is supported either fully or at least by one bearing on the hollow shaft means that this latter is considerably stressed, whereas the torque can only be transmitted to the roll carrier (rotor) by way of large sized drive gear wheels, which are directly connected to the roller carrier (rotor). 
     In a further proposed arrangement, the roll carrier (rotor) is supported by means of two bearings in the stand (stator), and the roll heads are disposed on the roll carrier (rotor) between the bearing positions, whereas the hollow shaft is rotatably disposed in the roll carrier (rotor) (the prospectus of Mannesmann Demag AG). However, the fact that the roll heads are disposed between the bearings makes the accessibility to the rolls and thus roll replacement difficult. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the invention is to improve the support for the roll carrier (rotor) carrying the roll heads, and for the hollow shaft carrying the sun wheel, in order to attain stable support with reliable torque transmission, and preservation of good accessibility to the roll heads comprising the rolls. 
     According to the invention, there is provided a skew-rolling mill for reducing solid or hollow cross-sections, comprising a roll carrier, a first hollow shaft rotatably mounted in the roll carrier and allowing passage of the rolled stock, a stand in which the rolls are supported rotatably independently of each other, three driven conical working rolls which are carried by the roll carrier, which are inclined to the rolled stock axis at 120° apart from each other and which are adjustable with respect to the rolled stock axis, and shafts which carry the working rolls, whose axes cross the rolled stock axis at short distances apart, and which are each drivably connected to a respective intermediate shaft by way of a respective bevel gear pair, each intermediate shaft carrying a spur gear which acts as an intermediate gear wheel and is engaged by way of a respective planet pinion with a sun wheel which is mounted on the first hollow shaft and can be rotated in such a manner as to control the relationship between the roll rotational speed and the roll carrier rotational speed so that the rolled stock passes through the rolling mill without rotating, each conical roll with its rolls shaft, the bevel gear mounted on the roll shaft, the intermediate shaft with the second bevel gear mounted thereon and the intermediate gear wheel being supported in a housing and combined into a respective roll head, the roll heads being inserted into the roll carrier so that they can be swivelled about the axes of the intermediate shafts parallel to the rolled stock axis in order to adjust the angle at which the roll axis cuts the rolled stock axis, the roll carrier extending in the form of a second hollow shaft which is supported in two positions in the stand and through which the first hollow shaft passes, the first hollow shaft being supported in the second hollow shaft at both ends of the second hollow shaft, one of the ends of the first hollow shaft which project from the second hollow shaft being connected in a non-rotatable manner to a drive gear wheel, and the other being connected in a non-rotatable manner to the sun wheel. 
     The dimensions (diameter and length) of the second hollow shaft can be such as to reliably ensure the strived-for stable support, even though free access from the front end of the rolling mill to the roll carrier and the roll heads carried thereby is maintained. 
     Desirably, the bearings which support the first hollow shaft in the second hollow shaft are disposed within bearings by which the second hollow shaft is supported in the stand. 
     Although the construction according to the invention makes it possible to provide a large sized drive gear wheel for the roll carrier (rotor) and to couple this directly to the roll carrier, the fact that the roll carrier extends in the form of a second hollow shaft readily makes it possible, to dispose the drive gear wheel for the roll carrier (rotor) between the two bearings of the second hollow shaft, and to connect it in a non-rotatable manner to the second hollow shaft, as the diameter of the second hollow shaft can be freely chosen to take into consideration the stress due to the torque. By disposing the drive gear wheel between the bearings, the overall axial extension of the roll carrier can be limited to the minimum necessary for accommodating the roll heads, and the reduction gearing for the drive gear wheel can be solidly supported in the stand (stator). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, wherein: 
     FIG. 1 is a cross-sectional view taken on the line I--I of FIG. 2, and 
     FIG. 2 is a cross-sectional view on the line II--II of FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     The reference numeral 1 indicates the stand--also known as the stator--of a skew-rolling mill, in which the hollow shaft 5 of the roll carrier 4--also known as the rotor--is rotatably supported in bearings 2 and 3. In this outer second hollow shaft 5, there is rotatably supported in bearings 6 and 7 an inner first hollow shaft 8, which ensures passage of the rolled stock 9 to the inclined conical rolls 10, the inner first hollow shaft 8 being protected against heat radiation from the rolled stock 9 by a double-walled cooled tube 11 which surrounds the rolled stock 9, and is fixed at one of its ends in the stand 1 and supported in the rotating roll carrier 4 at its other end by means of a bearing 12. 
     The roll carrier 4 is provided with three bores 13 formed from the front end and running parallel to the rolled stock axis. A roll head housing 14 is inserted by way of its cylindrical appendage 15 into each of the bores 13 so that it can be swivelled and fixed in position. A shaft 16 carrying a roll 10 and rotated by a bevel gear 17 is supported in each of the roll head housings 14. The roll shafts 16 together with the rolls 10 are axially adjustable. Bevel pinions 18, each of which is rotatably connected to an intermediate gear wheel 20 by means of a respective intermediate shaft 19, engage with the bevel gears 17. On inserting the roll heads 14 with their appendages 15 into the bores 13 in the roll carrier 4 the intermediate gear wheels 20 come into engagement with planet pinions 21 which are rotatably supported in the roll carrier 4 on pivots 22. The planet pinions 21 are also engaged with a sun wheel 23 which is mounted in a rotatably rigid manner on the inner first hollow shaft 8. A bevel gear 25 is rotated by a drive motor, not shown, by way of a shaft 24, and in its turn rotates a bevel gear 26, a shaft 27 and a gear wheel 28. The gear wheel 28 engages with a gear wheel 29, mounted in a rotatably rigid manner on the outer second hollow shaft 5 which is joined to the roll carrier 4, so that this latter is likewise rotated. By this means, the planet pinions 21 roll on the sun wheel 23, so that the rolls 10 are rotated by way of the intermediate gear wheels 20, the intermediate shafts 19, the bevel pinions 18 and the bevel gears 17 with their shafts 16, and thus carry out the rolling operation on the rolled stock 9. The axes of the rolls 10 cross the rolled stock axis at short distances apart. This inclined positioning of the rolls 10 generates the feed motion and determines the reduction of the rolled stock by means of the rolls 10. The rolled stock diameter, the roll diameter and roll rotational speed must be in a determined relationship to each other if the rolled stock is to pass through the rolling mill without rotating. In order to prevent rotation of the rolled stock when rolling under other relationships, the inner first hollow shaft 8 is correspondingly rotated with the sun wheel 23 mounted thereon. For this purpose, a drive gear wheel 30 is mounted in a rotatably rigid manner on the first hollow shaft 8, and is engaged with a pinion 31. A speed-controlled auxiliary motor, not shown, rotates the shaft 32 together with the bevel gear 33 mounted thereon, the bevel gear 34 engaged therewith, the pinion shaft 35 and the pinion 31 and drive gear wheel 30, to thus rotate the first hollow shaft 8 and its sun wheel 23 at the required rotational speed.