Sleeveless cantilever drive for high torque applications

Abstract: Apparatus for mounting a mill roll on a mill drive shaft in which mounting concentricity is produced by the internal expansion of the drive shaft to engage the bore of the mill roll. A secondary clamping device provides additional lateral binding force on the mill roll necessary for the production of the required frictional forces for the transmission of driving torque from the shaft to the mill roll.

Description: In many industries, long products are obtained by passing the work product, i.e. a strand of copper, steel or other materials, between a pair of opposing rollers in a mill stand which are spaced apart by a specified gap, and contoured to some predetermined shape, and driven at a speed to pass the work product on to the next pair of rollers at an exit velocity which will be determined by the entrance velocity of the material undergoing reduction and the degree of reduction undergone by material passing between the rollers. The rollers for each of the shaping and reducing stands must meet some very demanding specifications in order to produce a final shape within the tolerances set by the customer. For instance, the surface contours of each pair of mill rolls must have an accurately matched profile to produce a predetermined cross section of the work product being squeezed and deformed by the pair of rolls. The rolls must not separate unduly due to the separating force produced by the work product passing between the opposing work rolls or an unacceptable change in cross section of the finished product causes rejection of the product by the customer. The resulting bending moment on each of the cantilevered (capstan) shafts is substantial during a rolling and forming operation, thus each cantilevered shaft must be robust enough to resist undue deflection when loaded. The opposing rolls must also rotate concentrically on the shaft on which they are mounted so as to be true during rotation. Eccentricity of either or both of the work rolls during operating is to be avoided due to the cyclic aberrations produced in the work product cross section during passage between a pair of rolls which rotate eccentrically. Roll eccentricity usually results during a roll replacement operation at a mill stand due to error accumulation of inaccurate components. Because of the exacting demands made by purchasers of the ultimate product produced by such a forming and rolling operation, and because of the complex nature of the many reforming operations required to take a billet to a wire for instance, mill operators have faced the above problems on a daily basis because the rolls which perform the reforming and shaping operations although very tough and extremely hard, still experience wear during operation and must be frequently replaced. A modern wire and rod mill may have as many as 20 30 mill stands operating in tandem to bring a billet down to its ultimate shape and if the rolls on a mill stand require frequent replacement, much productive mill time is lost if the roll replacement cannot be performed expeditiously. It is to overcome some of the deficiencies in the prior art roller mounting devices that this application is directed. This invention will also enable a manufacturer to reduce the total number of components required to secure a roller in a mill stand for true and accurate rotation therein. Because of the reduction of mounting components required when using the invention of this application, roll replacement is simplified and inventory may be reduced. Because the eccentricity of the work rolls is substantially reduced by the apparatus of this invention, drive fluctuation is reduced accordingly so that torque requirements for material reduction tend to be constant so as to prevent premature wear of mill stand components and other problems caused by fluctuating torque requirements due to roll eccentricity. This invention will prevent roll slippage on the cantilevered drive shaft, and because of the effective clamping action produced by this invention, overall safety of the millistand will be improved over prior art apparatus. Because of the fluctuating torque requirements of a mill having one or both rolls of a matched pair rotating eccentrically, fluctuating tensions are ever present in the material passing between successive mill stands. This invention will largely reduce these tension fluctuations. BACKGROUND OF THE INVENTION With the advent of the tungsten carbide roll, the frequency of replacement of the rolls in a mill stand has been substantially reduced, but the mill operators constant desire for higher and higher mill speeds to generate more product for a given time causes even the most wear resistant rolls to require re-dressing in a fairly short time. In the past, a pair of work rolls were each mechanically mounted on a robust stub shaft by means of an intermediary tapered sleeve. The sleeve is pushed into the space between the shaft and the work roll to externally expand and "lock" the work roll on the stub shaft by the tapered sleeve. Satisfactory, results have caused this type of mounting to be universally accepted in the mill reducing operations. Some operational problems can be expected to develop as the roll replacement operation occurs. One of the more significant problems resulting, is the eccentric rotation of one or both of the newly mounted rolls on the capstan drive after the mounting operation is completed. Although the mill operator has gone to great pains to assure that each capstan drive shaft is scrupulously clean, and that the polished intermediary tapered sleeves are also free of debis or other foreign material, often when the newly mounted mill rolls are rotated, they are not true, and the operator must de-mount, or twist or tap the roll to bring the eccentricity down to be within acceptable limits. There is little doubt that skilled workmen using a variety of centering techniques with the prior art devices could ultimately reduce the roll eccentricity to an acceptable run out. The only ingredients required to produce an acceptable degree of concentricity were time and a skilled mill operator. DE 680768C describes a drive and mounting arrangement for mounting and driving a tool or a workpiece on a shaft. In this prior art arrangement, the tool or workpiece sits on a hollow end portion of the shaft which is formed with a tapered cavity and a correspondingly tapered plug is forced into the cavity of the shaft to expand the shaft portion and secure the tool or workpiece on the shaft. The expanding force is applied to the shaft by a series of rollers mounted on a cage extending around the plug. Document DE-A-1811614 discloses a further drive and mounting arrangement for a cantilevered rolling mill drive shaft according to the preamble of claim 1. The present invention aims to improve the roll replacement time and reduce the work input required from the mill operator during the mounting of mill rolls. SUMMARY OF INVENTION The invention accordingly provides a cantilevered drive arrangement having the characteristic features of Claim 1. It is a further object of this invention to provide a method of mounting a work roll on a capstan drive which is rugged, swift and efficient and which mounting substantially eliminates the problem of roll eccentricity frequently present in the prior art methods of mounting. Accordingly, the invention further provides a method in accordance with Claim 4. The proposed method of mounting the work rolls is much swifter and simpler than prior art techniques BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a prior art device used to mount work rolls on a capstan drive of a mill; and Figure 2 is a partial sectional view of one embodiment of a cantilevered drive arrangement for a mill roll in accordance with this invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, a prior art device used for clamping a work roll to a mill capstan is illustrated. Figure 1 shows a single cantilever device 10 which would usually have a complimentary cantilever device operatively mounted in an adjacent opposing relationship for passing a work product there between. Device 10 comprises a robust shaft 12 (steel) which is mounted in suitable bearings for axial rotation. Shaft 12 has raised shoulder 14 arising therefrom which may be integral with the shaft, or in some cases removable therefrom (as a collar, etc.) Shaft 12 is tapered at 16 which taper is terminated at shoulder 18, and a threaded hub 20 protrudes therefrom. A counter bore 22 in shaft 12 is threaded as shown Shaft 12 also is provided with an elongated cross port 24 which passes completely through the shaft 12. A taper cylinder 30 (sleeve) is provided to fit over taper surface 16 of the shaft 12. Sleeve 30 is provided with slots 32, 34, 36 to permit the intermediary portions 38, 40, 42 and 44 to easily expand when pressed over the tapered surface 16. Sleeve 30 is provided with a raised shoulder 46 and an interior cylindrical bore 48 which is joined to taper 50. Annular surface 54 extends between bore 48 and shoulder 46. Sleeve 30 is provided with a pair of elongated ports 52 in opposed diametric relationship. A pressure cap member 60 is shown for pressing sleeve 30 over tapered surface 16. Cap member has a cylindrical surface 62 which is of slightly less diameter than bore 48 of sleeve 30. Cap 60 has a shoulder 64 (to mate with surface 54) and an internally threaded counter bore 66 (to be received on threads 20). A torque nut 68 is integral with cap 60. A bolt 70 is shown having head 72 and threads 74 (to mate with threaded counter bore 22) Cross key 76 is shown for passage through ports 52 and cross port 24. The assembly with a work roll 80 (shown in phantom) mounted on cantilever drive 10 is as follows: Sleeve 30 is inserted into the interior bore of work roll 80 and both pieces 30 and 80 are fitted over tapered surface 16. Cap 60 is now threaded onto threads 20 so that surface 54 is engaged by shoulder 64 but not pushing the tapered sleeve over the surface 16 so as to expand portions 38, 40, 42 and 44. At this time, cross key 76 is passed through ports 52 and 24 to wedge the work roll 80 tightly against the shoulder 14. Cap 60 is now advanced on threaded portion 20 of shaft 12 to expand the interposing finger portions 38, 40, 42 and 44 between the work roll and tapered surface 16. As the sleeve advances more radial force is exerted on the internal bore of work roll 80. A skilled operator will tighten cap 60 to a predetermined torque so as to apply sufficient wedging force to the shaft 12, sleeve 30 and roll 80 to cause these three parts to, in fact, become an integral assembly. Bolt 70 is now advanced in threads 22 to cause head 72 to engage the exterior surface of torque nut 68. Aperture 69 in torque nut 68 is a clearance hole for bolt 70. Bolt 70 serves as a locking device for cap 60. This type of assembly has functioned acceptably well in the steel industry for many years. Two complimentary capstans such as 12 are mounted in close proximity so that rolls such as 80 may simultaneously press a work product (usually steel) there between to reshape the work product to a new shape as it passes between the rolls 80. Because of the tremendous forces required to reshape the work product, the capstans are sturdy robust components mounted for rotation in heavy bearings The environment in which the mounting assembly as shown in Figure 1 must operate is typical of a steel rolling mill. Coolant is applied to the work rolls and to the work product to prevent the temperature of the rolls and the mounting assembly from departing to an unacceptable operating range. Scale is ever present and is an enemy of finely machined surfaces. Cross key 76 is wedged into post apertures 52 and 24 to wedge work roll 80 against shoulder 14 to prevent any accidental dislodgement from shoulder 14. A shimming collar (not shown) may be needed as a filler, to wedge work roll 80 in place. Because of the presence of mill scale and other foreign debris, the sleeve shaft tapered face often gives rise to roll eccentricity when the mounting operation takes place when using the prior art device of Figure 1. If the mounted roll does not rotate in a true fashion, the operator must release the torque on nut 68, and the force applied to cross key 76, so that work roll 80 may be re-seated on sleeve 30, by twisting the work roll or any other suitable re-seating manoeuvre. The tightening process is repeated until the eccentricity is reduced to an acceptable tolerance. This operation is repeated for the complimentary capstan and it will be understood that at times, considerable time may elapse during the work roll replacement process, and if the two work rolls rotate eccentrically, a work product having unacceptable variations in cross section, will unforturiately result. It is to eliminate the production of a defective work product and to reduce the time taken to change rolls such as 80 that this invention is directed. Figure 2 illustrates an embodiment of the present invention. Here, a roll clamping and driving arrangement 400 is shown having a cantilevered drive shaft 412 which is driven from one end (not shown). Drive shaft 412 is provided with an abutment 414 against which a mill roll 480 is located on the shaft 412. A cavity 416 formed in the other (illustrated) end of shaft 412 is threaded as shown with a buttress type thread 420 which has a very shallow slope on the slanting portion of the thread. The shaft 412 is provided with a threaded axial bore 470, opening onto end wall 426 of cavity 416, to receive a bolt 450. A plug 424 for reception in the cavity 416 is externally threaded to co-operate with the threads 420 of the cavity 416. Drive shaft 412 is threaded at 422 to permit a locking bell 476 to be advanced along the threads to clamp roll 480 against shoulder 414. Bolts 488 in bell 476 may provide the ultimate force on roll 480 to permit the transmission of drive torque from shaft 412 to roll 480. The system 400 functions as follows: Roll 480 is slid on drive shaft 412 until it engages shoulder 414. At this time, plug 424 is screwed into cavity 416 of shaft 412. It is imperative that plug 424 does not engage end wall 426 of the cavity 416 (for reasons which become obvious later) but is stopped just short of the end wall 426. Next bolt 450 is passed through the central bore 418 of plug 424 which is a clearance fit and the end 458 of bolt 450 is advanced into threaded bore 470 just sufficiently to have head 454 and thrust shoulder 452 engage the end of plug 424. End bell 476 is then screwed onto shaft 412 at threads 422 to engage roll 480 and lock it against shoulder 414. At this time, bolt 450 is tightened by inserting a hexagonal driving tool through access passage 474 into hexagonal receptacle 456 in head 454 to force plug 424 toward the end 426 of cavity 416 and expand the shaft 412 in the region beneath roll 480. By forcing the plug to move axially, the ramps on the buttress threads 420 on plug 424 are pushed against the corresponding ramps on the threads provided in cavity 416 to expand the shaft. Because of the shallow slope (in this instance 2.49°) and a relatively long length, i.e. 12 mm for the sloping surface, a large expanding force can be developed by tightening bolt 450 against plug 424. When shaft 412 has been expanded sufficiently, bolts 488 may be tightened against roll 480 to provide the final locking force for roll 480. Plug 472 may now be inserted into end bell 476 to prevent the entrance of debris from the operation of the mill stand of which shaft 412 is a part. The above construction of the applicant's invention dispenses with an intermediary sleeve such as sleeve 30 shown in Figure 1. The wedging action is therefore avoided and the resulting eccentricity problems are avoided. The changing of the work rolls is much less complicated and much less time consuming than prior art constructions.

Claims: A cantilevered drive arrangement (400) for a mill roll (480) of a rolling mill, in which: a drive shaft (412) is mounted for rotation about its axis from one end thereof; characterised in that : a cavity (416) in the other end of the drive shaft (412) defines a hollow closed cylinder having walls of a predetermined thickness at the said other end of the drive shaft; an exterior raised abutment (414) is provided on the drive shaft (412) adjacent one end of the said cylinder; access means (474) in said other end of the drive shaft (412) communicates with the said closed cylinder; shaft expanding plug means (424) is housed in said cylinder, the plug means (424) and cylinder being threadedly engaged and each having matching buttress type threads (420) with a very shallow pitch to the sloping surface; and means for imparting axial movement to the plug means (424) is provided to ramp said buttress threads (420) of the plug means (424) against the corresponding threads of said cylinder to expand the cylinder. A cantilevered drive arrangement as claimed in Claim 1 wherein the plug (424) has a clearance hole (418) passing through the central axis thereof, and bolt means (450) passes through the clearance hole (418) and threadably engages the shaft (412) at the end of the cylinder remote from the access means (474), the bolt means (450) being capable of imparting axial movement to the plug means (424) with respect to said cylinder, to expand the cylinder. A cantilevered drive arrangement as claimed in Claim 2 wherein a mill roll (480) is mounted on the shaft (412) over the cylinder, and a locking device (476) is threaded onto the end of the shaft (412) on threads carried on the external end of the shaft (412) adjacent the access means, the said locking means (476) engaging the mill roll (480) and forcing the mill roll (480) against the abutment (414). A method of mounting a mill roll (480) on a cantilevered drive arrangement in which a drive shaft (412) is mounted for rotation about its axis from one end thereof, which method comprises: providing a drive shaft (412) with a cavity (416) to define at the other end of the drive shaft a hollow closed cylinder having walls of a predetermined thickness; mounting the mill roll (480) over the drive shaft (412) against an abutment (414) on the drive shaft adjacent the cylinder defined at the said other end of the drive shaft; housing shaft expanding plug means (424) in the cavity (416); providing the cavity (416) and the plug means (424) with matching buttress type threads (420) having a sloping surface with a very shallow pitch; threadedly engaging the plug means (424) and the cylinder; and imparting axial movement to the plug means (424) to ramp the buttress threads (420) of the plug means (424) against the corresponding threads of the cylinder and thereby to expand the cylinder.

Inventors: FABRIS MARIO, FABRIS, MARIO
Applicants: FABRIS MARIO, FABRIS, MARIO
Application year: 1997
Main classification: B21B27
IPC codes: F16D1, B21B27, B21B13, B23B31