| 1. | A crossrolling mill comprising a plurality of workpiece engaging rolls defining between them a roll aperture through which a workpiece passes during rolling, and a workpiece engaging tool associated with said rolls, the mill being characterized by said tool being a composite internal tool associated with said roll aperture and including a tapering piercing portion and a substantially cylindrical elongating portion, means for moving said tool along the axis of the mill relative to the rolls to accommodate a piercing operation in which the piercing portion of the tool coacts with the rolls and an elongating operation in which the elongating portion of the tool coacts with the rolls, and, means for reversing the direction in which the workpiece passes in use through said roll aperture so that piercing can take place in a first pass in one direction and elongation can take place in a second pass in the opposite direction, the profile of the rolls being such as to accommodate both piercing and elongating operations. |
| 2. | A mill as claimed in claim 1 characterized in that said means for reversing the pass direction of the workpiece includes means for reversing the direction of rotation of the rolls. |
| 3. | A mill as claimed in claim 1 characterized in that said means for reversing the pass direction of the workpiece includes means for reversing the feed angle of the rolls. |
| 4. | A mill as claimed in claim 1 characterized in that said tapered piercing portion of said tool is separable from said cylindrical elongating portion. |
| 5. | A mill as claimed in claim 1 characterized that said tool portions are permanently interconnected. |
| 6. | A mill as claimed in claim 1 characterized in that at least one of said tool portions is of hollow configuration to permit cooling fluid to be fed to the interior of the tool for cooling purposes. |
| 7. | A mill as claimed in any one of claims 1 to 6 characterized in that each roll is shaped to include first, second and third workpiece engaging regions, each first region defining an inclined inlet into the roll aperture for a workpiece pass in one direction, each second region defining an inclined inlet into the roll aperture for a workpiece pass in the opposite direction, and each third region defining the narrowest part of the roll aperture. |
| 8. | A mill as claimed in claim 7 characterized in that said second inlet has a steeper inclination than said first inlet. |
| 9. | A mill as claimed in claim 7 characterized in that said third roll regions define a substantially parallel roll aperture. |
| 10. | A mill as claimed in claim 7 characterized in that said rolls are cone rolls and said first, second and third regions of each roll are coaxial frustoconical portions. |
| 11. | A mill as claimed in claim 7 characterized in that said rolls are barrel rolls, said first and second regions being defined by frustoconical portions integrally connected at their bases by the third region which is a cylindrical portion. |
| 12. | A mill as claimed in claim 10 characterized in that there are three conerolls generally equiangularly spaced around the periphery of the workpiece. |
| 13. | A mill as claimed in claim 1 characterized in that said rolls are opposed cone rolls, each cone roll being secured to the end of an output shaft of a respective drive motor, and the drive motor and the roll comprising a single unit adjustably mounted on the frame of the rolling mill. |
| 14. | A mill as claimed in claim 13 characterized in that each drive motor is an hydraulic drive motor. |
| 15. | A mill as claimed in claim 13 characterized in that each motorroll unit further includes a carrying bracket through which the unit is adjustably secured to a rectilinear adjustment means for moving the unit towards and away from the intended axis of movement the workpiece in use. |
| 16. | A mill as claimed in claim 15 characterized in that said motorroll unit is adjustable about an axis parallel to said direction of rectilinear adjustment and passing through the axis of the workpiece in use. |
| 17. | A mill as claimed in claim 15 or claim 16 characterized in that said bracket of each motorroll unit is shaped to achieve a predetermined angular orientation of the rotational axis of each roll relative to the workpiece. |
| 18. | A mill as claimed in claim 10 characterized in that said cone rolls are each secured to the end of an output shaft of a respective hydraulic drive motor, and each drive motor and its roll comprise a single unit adjustably mounted on the frame of the rolling mill, each unit including a carrying bracket through which the unit is adjustably secured to a rectilinear adjustment means for moving the unit towards and away from the intended axis of movement the workpiece in use, and each unit being adjustable about an axis parallel to said direction of rectilinear adjustment and passing through the axis of the workpiece in use. |
| 19. | A method of producing seamless metallic tubing comprising passing a solid cylindrical billet of metal through a mill as claimed in any one of claims 1 to 18, so that the billet is pierced by the coaction of the pointed end of the tapered piercing portion of said internal tool and the rolls, and, at the end of this first pass of the workpiece through the mill, moving said internal tool to substitute the elongating portion of the tool for said tapering piercing portion and reversing the direction of flow of the workpiece through the mill so that a second, elongating pass is performed in a direction opposite to the first pass. |
| 20. | A method as claimed in claim 19 characterized in that the direction of movement of the workpiece is reversed between said first and second passes by reversing the direction of rotation of the rolls. |
| 21. | A method as claimed in claim 19 characterized in that said workpiece direction reversal is achieved by reversing the feed angle of the rolls. |
| 22. | A rolling mill comprising at least first and second opposed cone rolls, and characterized in that each cone roll is secured to the end of an output shaft of a respective drive motor, and the drive motor and the roll comprise a single unit adjustably mounted on the frame of the rolling mill. |
| 23. | A mill as claimed in claim 22 characterized in that each drive motor is an hydraulic drive motor. |
| 24. | A mill as claimed in claim 22 characterized in that each motorroll unit further includes a carrying bracket through which the unit is adjustably secured to a rectilinear adjustment means for moving the unit towards and away from the intended axis of movement the workpiece in use. |
| 25. | A mill as claimed in claim 24 characterized in that said motorroll unit is adjustable about an axis parallel to said direction of rectilinear adjustment and passing through the axis of the workpiece in use. |
| 26. | A mill as claimed in claim 24 or claim 25 characterized in that said bracket of each motorroll unit is shaped to achieve a predetermined angular orientation of the rotational axis of each roll relative to the workpiece. |
Technical Field
This invention relates to a cross rolling mill primarily, but not exclusively, for use in the production of seamless metallic tubing, and to a method of manufacturing such tubing.
Background Art
Conventionally the majority of seamless tubing is produced by piercing a solid billet in a rotary piercing mill and then passing the hollow bloom so formed to an elongating mill for conversion into thin or thick walled tube. Such mills may comprise two or more opposed workpiece engaging rolls but where only two rolls are used it is usual to provide guide means (such as rotatable guide discs or static guide shoes) for engaging and guiding the workpiece as it passes between the opposed rolls.
Disclosure of Invention
It is an object of the present invention to provide an improved rolling mill which is capable of carrying out two of the operations that are commonly used in forming seamless metallic tubing. It is a further object to provide a rolling mill having a simple and convenient roll arrangement. A further object of the present invention is to provide a method of manufacturing seamless metallic tubing.
In accordance with a first aspect of the present invention there is provided a cross-rolling mill comprising a plurality of workpiece engaging rolls defining between them a roll aperture through which a
workpiece passes during rolling, a composite internal tool associated with said roll aperture and including a tapering piercing portion and a substantially cylindrical elongating portion, means for moving said tool along the axis of the mill relative to the rolls to accommodate a piercing operation in which the piercing portion of the tool coacts with the rolls and an elongating operation in which the elongating portion of the tool coacts with the rolls, and, means for reversing the direction in which the workpiece passes in use through said roll aperture so that piercing can take place in a first pass in one direction and elongation can take place in a second pass in the opposite direction, the profile of the rolls being such as to accommodate both piercing and elongating operations.
Preferably said means for reversing the pass direction of the workpiece includes means for reversing the direction of rotation of the rolls.
Alternatively said means for reversing the pass direction of the workpiece includes means for reversing the feed angle of the rolls.
The tapered piercing portion of said tool may be separable from or permanently connected to the cylindrical elongating portion. Furthermore one or both of said portions may be of hollow configuration to permit cooling fluid to be fed to the interior of the tool for cooling purposes.
Desirably each roll is shaped to include first, second and third workpiece engaging regions, each first region defining an inclined inlet into the roll aperture for a workpiece pass in one direction, each second region defining an inclined inlet into the roll aperture for a
workpiece pass in the opposite direction, and each third region defining the narrowest part of the roll aperture.
Preferably said second inlet has a steeper inclination than said first inlet.
Desirably said third roll regions define a substantially parallel roll aperture.
Conveniently said rolls are cone rolls and said first, second and third regions of each roll are coaxial frusto-conical portions.
Alternatively said rolls are barrel rolls, said first and second regions being defined by frusto-conical portions integrally connected at their bases by the third region which is a cylindrical portion.
Preferably where the rolling mill employs cone-rolls then there are three cone-rolls generally equiangularly spaced around the periphery of the workpiece.
In accordance with a second aspect of the present invention there is provided a method of producing seamless metallic tubing comprising passing a solid cylindrical billet of metal through the mill so that the billet is pierced by the coaction of the pointed end of the tapered piercing portion of said internal tool and the rolls, and, at the end of this first pass of the workpiece through the mill, moving said internal tool to substitute the elongating portion of the tool for said tapering piercing portion and reversing the direction of flow of the workpiece through the mill so that a second, elongating pass is performed in a direction opposite to the first pass.
Desirably the direction of movement of the workpiece is reversed between said first and second passes by reversing the direction of rotation of the rolls.
Alternatively said workpiece direction reversal is achieved by reversing the feed angle of the rolls.
In accordance with a third aspect of the present invention there is provided a rolling mill comprising at least first and second opposed cone rolls, each cone roll being secured to the end of an output shaft of a respective drive motor, and the drive motor and the roll comprising a single unit adjustably mounted on the frame of the rolling mill.
Preferably each drive motor is an hydraulic drive motor.
Desirably each motor-roll unit further includes a carrying bracket through which the unit is adjustably secured to a rectilinear adjustment means for moving the unit towards and away from the intended axis of movement the workpiece in use.
Desirably said motor-roll unit is adjustable about an axis parallel to said direction of rectilinear adjustment and passing through the axis of the workpiece in use.
Preferably said bracket of each motor-roll unit is shaped to achieve a predetermined angular orientation of the rotational axis of each roll relative to the workpiece.
Brief Description of Drawings
One example of the invention is illustrated in the accompanying drawings, wherein:-
Figure 1 is a diagrammatic view of part of one example of a cross-rolling mill carrying out a piercing operation,
Figure 2 is a view similar to Figure 1 but illustrating an elongating operation,
Figure 3 is a view similar to Figures 1 and 2 but taken in a direction at right angles and illustrating guiding means associated with the mill rolls,
Figure 4 is a diagrammatic front elevational view of a three roll cone-rolling mill, and
Figure 5 is a diagrammatic side elevational view, to an enlarged scale, of part of the mill illustrated in Figure 4.
Best Mode for Carrying Out the Invention
Referring first to Figures 1, 2 and 3 of the accompanying drawings there is shown a cross-rolling mill having a pair of barrel rolls comprising an upper roll 10 and a lower roll 11. The rolls 10, 11 are arranged to be driven so that they rotate in the same direction of rotation (as is indicated by arrows 12 and 13 in Figure 3), their axes of rotation lying in parallel planes, but being inclined to each other in a known manner in order to impart a feeding motion to a workpiece engaged in the passed defined between the rolls.
As is apparent from Figures 1 and 2 each of the rolls 10, 11 is shaped to provide a pair of frusto-conical portions indicated in the case of roll 10 by reference to numerals 14 and 15 and in the case of roll 11 by reference numerals 16 and 17. In each case the frusto-conical portions are integrally connected by a cylindrical portion 18, 19 which is thus disposed between
its respective frusto-conical portions. It will be recognised that the cylindrical portion 18, 19 of each roll has a diameter which is equal to the largest, base, diameter of the respective frusto-conical portions and that the frusto-conical portions and the cylindrical portion are coaxial.
The mill further includes a tool generally indicated in Figures 1 and 2 by reference numeral 20. In effect the tool 20 comprises first and second portions namely a piercing portion ' 21 which is formed by the free end of the tool and which is shaped to a tapering configuration of generally bullet-shaped form, together with a generally cylindrical portion 22 which in the example illustrated is integral with the tapering portion 21. It is to be understood that if desired the portions 21 and 22 may be separately formed and interconnected in any convenient manner. Furthermore, either or both portions of the tool 20 may be hollow so that cooling water or other cooling fluid can in use be fed to the interior of the or each portion of the tool to effect cooling of the tool during use. The tapering portion 21 is arranged in use to act as a piercing tool whilst the cylindrical portion 22 will be used as an elongating tool as will be more particularly described hereinafter.
In the example illustrated in Figures 1 and 2 the maximum diameter of the piercing tool portion 21 is equal to the diameter of the cylindrical elongating portion 22. In a modification the portion 21 is separable from the portion 22 so that the piercing portion 21 can be readily changed if required after each piercing pass of the workpiece, in which event the maximum diameter of the piercing portion can be larger than the diameter of the cylindrical portion 22. Also if the aforementioned internal cooling is not used the tapered piercing portion 21 can be mounted on the end of the supporting bar which
will act as the cylindrical elongating portion of the tool.
The arrangement illustrated in Figures 1, 2 and 3 is capable of carrying out two separate operations that are normally required in forming seamless metallic tubing. Thus firstly a solid billet indicated by reference numeral 23 at the left hand end of Figure 1 will be advanced through the mill from left to right (as viewed in Figure 1) so that the billet is driven into engagement with the pointed end of the piercing portion 21 of the tool 20. During this pass of the workpiece through the mill the tool 20 is in a position in which the piercing portion 21 coacts with the cylindrical portions 18 and 19 of the rolls 10 and 11 to effect piercing. The workpiece or billet pierced during the first pass exits from the right hand side of the mill as is seen in Figure 1 in the form of a tube having relatively thick walls 24. The positioning of the portion 21 of the tool 20 in relation to the rolls to effect piercing will be well understood by the expert in the art. For given feed rates and material parameters the expert will recognise that the portion 21 must be sufficiently advanced in relation to the gorge of the rolls as to avoid excessive cross-rolling of the workpiece, but not so far advanced that drive from the rolls to the workpiece is lost causing a condition in which workpiece movement either does not commence or stalls.
The tool 20 is mounted so that its longitudinal position, relative to the rolls, can be adjusted along the axis of the mill. Thus at the end of the first pass, and prior to the commencement of a second pass, the tool is advanced from right to left until it assumes a position (as seen in Figure 2) in which a part of the cylindrical elongating portion 22 lies between the
cylindrical portions 18 and 19 of the rolls 10 and 11. At this point the rolls are moved towards the mill axis by a predetermined amount so reducing the roll aperture and the second pass is commenced with the workpiece moving in the opposite direction, that is to say from right to left. The workpiece is of course driven through the mill by the rotation of the rolls and thus the reversal of its direction of movement can be achieved either by reversing the direction of rotation of the rolls, or by altering the angular position of the rolls relative to one another to reverse the feed angle of the mill. In the course of the second pass of the workpiece between the rolls the workpiece will be elongated and its wall thickness will be reduced as it issues from the left hand side of the mill. The reduced wall thickness is indicated by reference 25 in Figure 2.
It will be noted in Figures 1 and 2 that the taper angle of the frusto-conical region 14 of the roll 10 is equal to that of the frusto-conical region 15 of the roll 10. Similar comments apply to the regions 16 and 17 of the roll 11. It must be recognised however that this representation of the taper angles is simply for convenience in the drawings. In practice, it is preferred that the taper angle of the frusto-conical regions 15 and 17 is greater than that of the regions 14 and 16 so that the tapering inlet between the roll 10 and 11 into which the workpiece is entered during the first pass has a shallower incline than the oppositely directed tapering inlet into the which the workpiece enters during the second pass. The reason for this is that a shallow taper angle is desirable during piercing of the solid billet, but a greater taper angle is desirable during elongation so as to minimise the axial length of the rolls. Since the second pass is in the opposite direction to the first pass then the use of different inlet taper angles for the passes is accommodated very
simply by arranging different taper angles for the regions 15 and 17 to those used in the regions 14 and 16 of the rolls.
In the case where just two rolls (rolls 10 and 11 in Figures 1 to 3) are used then it is necessary to guide the workpiece as it issues from the mill. Suitable guide means comprises a pair of guide elements 26 and 27 (see Figure 3) which are adapted to engage opposite sides of the workpiece (28 in Figure 3) as it passes between the rolls of the mill. Such guide elements may be in the form of rotatable, grooved, discs or alternatively a pair of static guide shoes may be used. If rotatable discs were used these would normally be driven and the profile of their peripheral grooves would suit both piercing and elongation passes of the workpiece. Some means would be provided for altering the direction of rotation of the rotatable discs to accommodate the change in direction of movement of the workpiece between piercing and elongating. As a further alternative such rotatable discs could be positively driven in one direction and allowed to freewheel in the opposite direction.
If static guide shoes are used then although it is possible to use one pair of guide shoes with a profile which is a compromise suitable for both piercing and elongating passes, it is in fact preferable to use two pairs of guide shoes one being profiled to accommodate the piercing pass and the other pair being profiled to accommodate the elongation pass. The mill would include a mechanism for indexing the pairs of static guides so as to bring the appropriate pair of guide shoes into position, (in which they are locked) at the end of the first pass, and before the commencement of the second pass. The guide shoes or guide discs guide the workpiece as it passes through the mill and maintain it on the rolling centre line of the mill. In addition they can
perform a sizing function by virtue of their engagement with the external diameter of the workpiece. Thus by adjustment of the guide shoes or discs the workpiece can be allowed to expand by a limited amount during rolling, or can be constrained by the shoes to ensure a slight reduction in diameter.
It will be recognised that the cross rolling mill will have facility for adjustment of the usual rolling parameters, and such adjustments will include the facility for movement of the rolls 10 and 11 towards or away from one another to adjust the wall thickness of the workpiece; movement of the rolls to change the feed angles; and movement of the tool 20 in an axial direction as previously mentioned.
During the second pass, when the mill is operating as an elongator, the roll aperture will have been reduced by moving the rolls towards the mill axis and the elongating portion 22 of the tool 20 forms, in conjunction with the cylindrical portions 18 and 19 of the rolls, a substantially "parallel" or cylindrical aperture of sufficient length to permit the reduced wall of the pierced billet to be adequately smoothed to exhibit the required tolerance and smoothness as a hot finished tube. The tapering inlet which is effective during the elongation pass (and which is defined by the frusto-conical regions 15 and 17 of the rolls) provides a means for obtaining a substantial wall-thickness reduction whilst the setting of the aforementioned guide elements 26 and 27, which are of course disposed between the rolls 10 and 11, will determine the outside diameter of the elongated tube. It will be recognised however that instead of using guide elements 26 and 27 it may be preferred to use additional rolls so that three or more opposed rolls are provided in the mill in which case the guide elements 26 and 27 are dispensed with and wall
thickness reduction and outside diameter are determined by the relative positioning of the three or more opposed rolls.
The tool 20, after it has been advanced to the position shown in Figure 2 in which the cylindrical portion 22 is disposed in part between the cylindrical portions 18 and 19 of the rolls, can, a) be allowed to float forward with the advancing elongated workpiece without constraint so as to be passed through the mill with the workpiece and to be removed in a separate operation and recirculated for later use (this of course requires a tool of greater length than the workpiece) or, b) be restrained so that its forward movement is in a fixed relationship with the movement of the workpiece (e.g. moves more slowly than the workpiece) or c) be initially restrained as in (b) and finally released upon completion of elongation as in (a) or d) be withdrawn on completion of rolling (if it is initially restrained) in the opposite direction to the elongation direction of rolling and then either be replaced by a new tool or be re-used.
A cross-rolling mill constructed in accordance with the foregoing description can thus perform two functions, for example initial piercing and then elongating, or alternatively, secondary piercing and elongating, secondary piercing and elongating being, in effect, a double elongating operation since the first pass is performed on a previously pierced workpiece. Capital cost is thus saved and operating costs will be reduced. Nevertheless the mill will produce excellent tolerances on the wall thickness of the seamless tubing and will achieve a high quality of surface finish. When used to perform secondary piercing the mill could be a
downstream component of a line including a primary piercing machine and some form of heating furnace.
Figures 4 and 5 are diagrammatic and illustrate a cone-roll mill. It can be seen that the mill includes a rigid stationary frame including an upright rigid mounting plate 31 generally in the form of an equilateral triangle from which the apices have been removed. The plate 31 has a centrally disposed aperture 32 through which the workpiece 33 passes in use. Equiangularly disposed around the aperture 32 are three identical roll support structures each of which comprises an hydraulic ram 34 the cylinder of which is rigidly secured to the plate 31. The three rams 34 are positioned with their longitudinal axes lying in a common plane parallel to the plane of the plate 31 and intersecting one another on an axis passing centrally through the aperture 32 at right angles to the plane of the plate 31. Extending from each cylinder 34 towards the aperture 32 is the push rod 35 of the ram each push rod 35 being connected by way of a coupling sleeve 36 to a respective elongate cylindrical slide member 37. Each slide member 37 has its longitudinal axis coextensive with the axis of its respective ram 34 and each is slidably received in a corresponding through-bore of a respective guide member
38 rigidly secured to the plate 31. At its innermost, free end each slide member 37 has a motor-roll unit secured thereto for adjustment relative thereto about the longitudinal axis of the guide member. The motor- roll units are indicated in Figure 4 by the reference numeral
39 and will be described in more detail in relation to Figure 5. It will be recognised however that each unit 39 can be moved rectilinearly towards or away from the axis which extends at right angles to the plate 31 and passes through the centre of the aperture 32, by operation of the respective ram 34. Furthermore by virtue of the adjustable connection between each unit 39
and its respective guide member 37 then the angular position of each unit 39 about the longitudinal axis of its respective guide member 37 can also be adjusted.
As can be seen from Figure 5 each motor-roll unit 39 is a self-contained unit comprising an hydraulic motor 41, a cone-roll 42 and a carrying bracket 43. The carrying bracket 43 is in the form of an angled metal member of substantial thickness having a first portion 43a which is rigidly secured to the housing of the hydraulic motor 41 and lies at right angles to the longitudinal axis of the motor 41, and a second, integral portion 43b which is adjustably secured to the respective slide member 37, the bracket being bent between the portions 43a and 43b so that the portion 43b lies in a plane disposed at a predetermined angle to the plane containing the portion 43a.
The output shaft of the hydraulic motor 39 protrudes at one end from the motor housing and has the cone-roll 42 directly secured thereto by a clamping arrangement housed within the roll 42. The cone-roll 42 comprises three frusto-conical regions rigidly secured together either by clamping or by being integrally formed. The three regions of the roll 42 comprise a first region 44 at the end of the roll remote from the motor 41, a second region 45 at the opposite end of the roll 42, that is to say adjacent the motor 41, and an intermediate, third region 46 lying between the regions 44 and 45. The angles at which the regions 44, 45, and 46 taper are such that in use when the rotational axis of the roll is at a predetermined operational angle in relation to the centre-line of the mill (the axis of material flow through the mill), then region 46 will present a portion substantially parallel to the mill centre- line, the region 44 will present a portion at a shallow angle to the mill centre-line, and the region 45
will present a portion at an opposite and steeper angle to the mill centre-line. Furthermore, although there are changes in surface angle at the junction of the three regions there are no steps in the outer profile of the roll 42 since the greatest diameter of the region 44 is equal to, and abuts the smallest diameter of the region 46, and similarly the largest diameter of the region 46 is equal to and abuts the smallest diameter or the region 45. As is also apparent from Figure 5 the taper angle of the region 46 is only slightly less than that of the region 44 but is more significantly greater than that of the region 45.
At its free end each slide member 37 is formed with a hollow boss 37a terminating in a flat end surface which lies accurately at right angles to the axis of the slide member 37. The boss 37a is circular, as is the portion 43b of the bracket 43. The upper face of the portion 43b of the bracket 43 is clamped against the flat face of the boss 37a by means of a screw clamping arrangement 47 which, when released, permits rotation of the portion 43b of the bracket 43 relative to the slide member 37 about the longitudinal axis of the slide member 37. Thus the whole of the motor-roll unit 39 can be adjusted about the longitudinal axis of its respective slide member 37 and can be clamped in a chosen orientation relative thereto by the screw clamping arrangement 47. The periphery of the boss 37a and the portion 43b of the bracket 43 are provided with graduation marks 48 or other indicia to facilitate setting of the unit 39 in relation to its respective slide member 37 in a predetermined position.
The angle subtended between the regions 43a and 43b of the bracket 43 is equal to the taper angle of the region 45 of the cone-roll 42 (that is to say is equal to half of the included angle of the region 45 of the roll
42). The three motor-roll units 39 are identical, and it will be recognised therefore that if a unit 39 is adjusted relative to its slide member 37 such that the axis of the slide member 37 and the axis of the respective unit 39 lie in a common plane at right angles to the plate 31 and the ram 34 of that slide member 37 is adjusted to move the unit 39 towards a cylindrical workpiece extending through the centre of the aperture 32 at right angles to the plane of the plate 31 then the portion 45 of the roll 42 will make line contact with the workpiece 33, the line of contact also lying in said plane containing the axis of the slide member 37 and the unit 39. In that position of the roll 42 there is defined a shallow tapering inlet between the workpiece 23 and the region 44 of the roll and an oppositely inclined steeper tapering inlet between the roll region 46 and the workpiece 43. This is the position illustrated in Figure 5, but is in fact a position which does not arise in use.
Rather than positioning the units 39 with their axes in planes at right angles to the plate 31 they are in fact adjusted about the axis of their respective slide members 37 to produce a feed angle. This orientation of the units 39 can be seen in Figure 4. Each unit 39 is disposed at the same angle in relation to the workpiece and the arrangement is such that in addition to rotating the workpiece relative to the plate 31 there is also a feed vector so that the workpiece is progressed through the mill. This will be well understood by the expert in the art. Extending outwardly on opposite sides respectively of the plate 31 will be workpiece support structures for supporting the workpiece regions projecting beyond the roll region of the mill.
The operation of the mill illustrated in Figures 4 and 5, when used to produce seamless metallic tubing, is as described above in relation to Figures 1, 2 and 3.
Thus there will be a first pass during which piercing takes place and in which the regions 44 and 45 of each roll 42 serve the primary function. During the piercing operation the tapering region of a tool equivalent to the tool 20 of Figures 1, 2 and 3 will coact with the rolls 42. During a second, elongation pass the tool equivalent to the tool 20 will have been moved longitudinally so that an elongation region of the tool coacts with the rolls 42. The pass direction is reversed between piercing and elongation and as described above in relation to the barrel-roll mill the direction of movement of the workpiece can be reversed either by reversing the direction of rotation of the rolls 42, or by adjusting the rolls 42 about the axis of their respective slide members 37 to reverse the feed vector.
In both the description of the barrel-roll mill and the description of the cone-roll mill convenient roll profiles have been mentioned. It should be understood that although careful choice of roll profile is essential to obtaining satisfactory results particularly with regard to surface finish, the invention is not restricted to the roll profiles disclosed herein, and there may be a choice of suitable profiles for any given application. Thus rolls with curved, both concave and convex, profiles may be used as may rolls wherein the profile includes definite steps rather than gradual diameter changes. Generally, as the expert will realise, where surface finish is of importance, rounded edges are preferred in the roll profile rather than sharp edges, such that there is a smooth transition between regions of the roll profile.
The expert will select the roll profile in accordance with, inter alia, the workpiece material and the required pass speed and it may vary, dependent upon the application, from a plain cylindrical profile to a
complex multi-sectional curved profile. Generally however the profile will be such as to provide, with the other rolls, a roll aperture and tapering inlets at both ends of the roll aperture to accommodate entry of the workpiece irrespective of its direction of movement. Ideally the inlet for the reverse pass (elongation) will be the more steeply tapered of the two.
It is to be recognised that the cone-roll mill described in relation to Figures 4 and 5 is of a particulary simple and convenient form inter alia in that it makes use of a motor-roll unit comprising a cone-roll, a drive motor, and a mounting bracket. Since the roll is mounted directly on the output shaft of the motor a particularly simple and compact arrangement can be provided which is capable of being mounted on an adjustment mechanism whereby the position of the unit is adjusted in relation to the frame of the machine, rather than simply adjusting the position of the roll as is often the case in known mills. The use of a motor-roll unit avoids the necessity for elongate drive shafts coupling the prime mover to the roll, and the provision of universal and/or constant velocity joints in the drive train between the prime mover and the roll. Desirably the motor of the unit is an hydraulic motor so that no gear box is needed. In this way the cost of the motor-roll unit, and thus the overall cost of the mill is minimised.
It should also be appreciated that a two roll version of the mill illustrated in Figures 4 and 5 can be produced if desired and in such an arrangement the two rolls are diametrically opposed on opposite sides of the workpiece and between the rolls some form of guide shoe or guide disc will be needed to support the workpiece. Furthermore, the use of a motor-roll unit as described above is not restricted to mills for manufacturing
seamless tubing. Thus the mill described in general terms with reference to Figures 4 and 5, and variants thereof utilizing the same type of motor-roll unit may be used in other metal rolling operations.