CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No.

61/968,119, filed March 20, 2014, the entire contents of which are incorporated by reference herein.

BACKGROUND

[0002] The present disclosure is related generally to bearings for supporting rollers in rolling mill applications, and in particular to a system and method for controlling the bearing setting of roller support bearings rotatably supporting a mill roll.

[0003] U.S. Patent No. 8,757,890, the entire contents of which are incorporated by reference herein, discloses an apparatus and method for setting rolling element bearings in rolling mills (e.g., back-up rolls in rolling mill applications). The bearings at each end of the mill roll are coupled through a center rod, or "tension rod" that extends through the mill roll to couple the two end bearing assemblies and allows dynamic control of the bearing setting during use (e.g., by integrating a hydraulic cylinder) so that the bearings can be set with low axial clearance and prevented from becoming overly tight when heated up from cold to operating temperature.

[0004] Two types of bearings find widespread use in such rolling mill machinery, those being the tapered roller bearing and the cylindrical roller bearing, each of which is capable of carrying heavy radial loads. Tapered roller bearings lend themselves to adjustment in that the axial positions of the supporting races relative to each other control the radial clearance or play, and may even eliminate the radial clearance altogether. This in turn provides control of the size of the load zone, that is, the angular measure corresponding to the number of rollers in the bearing which are actually under load at any instant. Notwithstanding this capability, tapered roller bearings, when used to transmit extremely heavy loads such as in rolling mills, are usually manufactured with their tapered rollers arranged in four rows, and with the tapers of adjacent rows oriented oppositely. This makes adjustments in the field difficult, and for all practical purposes these multi-row bearings are adjusted at the factory through the selection of spacers. There the bearings are usually set with axial clearance. However, the profile of the raceway on the cone or inner race is not perfectly circular nor is its axis perfectly coincident with the axis of rotation. These imperfections add to the overall runout of the roll body during rolling.

[0005] If the bearings supporting a roll in a rolling mill are improperly set, various problems can ensue. For bearings which have too much endplay, there is an increased chance of roller skidding (i.e. low load zone) and lower bearing life (as the load zone decreases, the load per roller ratio increases, and bearing life decreases). Conversely, for bearings set with too much preload, there is the risk of bearing burn-up, which is generally a catastrophic damage and cannot be easily repaired. Although suggested in U.S. Patent No. 8,757,890 to provide temperature control of a center rod with a heating element, a need still exists for a particular method and apparatus to achieve good control over the bearing settings from a cold state through steady-state operating conditions that offers reliable and robust performance and is convenient and cost effective to implement.

SUMMARY

[0006] In one aspect, the invention provides a roll assembly for a rolling mill. The roll assembly includes a roll having a roll body defining an exterior roll surface operable to contact a work piece or an adjacent work roll engaged with the work piece during a rolling process. The roll includes a first axial end, a second axial end, and a central bore defining a central axis. A first tapered roller bearing assembly rotatably supports the first axial end of the roll, and a second tapered roller bearing assembly rotatably supports the second axial end of the roll. A non- rotating, hollow center shaft is positioned within the central bore of the roll, and the center shaft is coupled to a first chock supporting the first tapered roller bearing assembly and to a second chock supporting the second tapered roller bearing assembly, such that applying and releasing tension in the center shaft manipulates a bearing setting of the first and second tapered roller bearing assemblies for an amount of axial clearance or axial preload. The center shaft defines an interior cavity receiving a flow of heated fluid to expand the center shaft and limit tightening of the bearing setting when the roll expands during use. [0007] In another aspect, the invention provides a method of operating a roll assembly for a rolling mill. A roll is provided having a roll body defining an exterior roll surface, the roll including a first axial end, a second axial end, and a central bore defining a central axis. A tapered roller bearing assembly is provided at each of the first and second axial ends of the roll for rotatably supporting the roll. A non-rotating, hollow center shaft is positioned within the central bore of the roll, the center shaft being coupled to a first chock supporting the first tapered roller bearing assembly and being coupled to a second chock supporting the second tapered roller bearing assembly, such that applying and releasing tension in the center shaft manipulates a bearing setting of the first and second tapered roller bearing assemblies for an amount of axial clearance or axial preload. An initial bearing setting is set by applying and/or releasing tension in the center shaft prior to start-up of the rolling mill. Pressure is applied to a work piece through an adjacent work roll or directly by the exterior roll surface as the roll rotates to perform a rolling process on the work piece. A fluid is heated and flowed within an interior cavity defined in the center shaft during warm-up of the roll from a cold start whereby the temperature of the roll increases from ambient temperature to a steady state temperature due to the rolling process. The center shaft is expanded via the heated fluid as the roll expands due to normal heating from the rolling process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig 1 A is a schematic view of a four-high rolling mill operating on a work piece.

[0009] Fig. IB is cross-sectional view of a prior art roll assembly of a rolling mill, the roll assembly having a roll mounted with a solid center shaft and rotatably supported at the ends by tapered quad bearing assemblies.

[0010] Fig. 1C is a detail view of an operator end of the roll assembly of Fig. IB, illustrating a dust cap placed over the end of the center shaft.

[0011] Fig. ID is a detail view of a drive end of the roll assembly of Fig. IB.

[0012] Fig. 2 is a cross-sectional view of a roll assembly having a roll mounted on a hollow center shaft having first and second open ends for passage of a temperature control fluid. [0013] Fig. 3 A is a detail view of a drive side portion of the roll assembly of Fig. 2, having a collection device coupled to the second open end of the center shaft to catch a temperature control fluid exiting the center shaft.

[0014] Fig. 3B is a cross-sectional view of the collection device, taken along line 3B-3B of Fig. 3A.

[0015] Fig. 4 is a cross-sectional view of an operator end of a roll assembly having a two- way flow device provided within a hollow center shaft. The roll assembly includes a manifold cover coupled to the end of the center shaft, and an extended cover compared to Fig. 1C.

[0016] Fig. 5 is a cross-sectional view of a drive end of the roll assembly of Fig. 4, illustrating the second end of the two-way flow device and a plug closing the end of the hollow center shaft.

[0017] Fig. 6 is a front view of a perforated annular spacer shown in cross-section in Figs. 4 and 5.

[0018] Fig. 7 is a chart illustrating, for one exemplary back-up roll assembly, the effect of roll expansion on bearing load zone, with a non-temperature controlled solid tension rod.

DETAILED DESCRIPTION

[0019] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0020] As shown in Fig. 1A, a four-high rolling mill 10 can be operated to roll a work piece 12 to a reduced thickness. A pair of inner work rolls 14 contact the work piece material directly and are supported by a pair of corresponding outer back-up rolls 16 to manage the high loads present as the work piece is compressed. Each of the schematically illustrated back-up rolls 16 of Fig. 1A is provided in practice as a roll assembly 16 as shown in detailed cross-section in Fig. IB. The roll assembly 16 includes a roll 18 having an exterior working surface 20 within a central portion or roll body, in this case for contacting one of the work rolls 14. Flanking the surface 20 of the roll body and provided adjacent either end 17A, 17B of the roll assembly 16, is a tapered quad roller bearing assembly 24, resulting in a directly mounted, tapered-quad-tandem- mount (TQTM) arrangement. The roller bearing assemblies 24 are mounted on tapered end sections or "roll necks" 26 of the roll 18 and are coupled to a center rod 28, or tension rod, through corresponding housings, or chocks 30. A tapered sleeve 31 is provided on each roll neck 26, radially within the rolling elements of the bearing assemblies 24. The chock 30 on the left side of Fig. IB is an adjustable chock provided on the first end or operator end 17A of the roll assembly 16, which is opposite a drive end 17B of the roll assembly 16, which is the end adjacent corresponding ends of the work rolls 14 that are coupled to and driven by a drive source (e.g., a pinion stand). The chock 30 at the drive end 17B is a non-adjustable chock 30. The adjustable chock 30 is coupled to the center rod 28 with a setting nut 32, which is used to set the cold tension or cold axial clearance in the center rod 28, which is in turn applied to the roller bearing assemblies 24. A lock nut 34 is positioned behind the setting nut 32 and used to lock the setting nut 32 in place, once the desired center rod tension or axial clearance has been established. An end cover 36 couples the center rod 28 to the corresponding chock 30 at each end. The center rod 28 is generally provided as a solid rod, and as discussed in U.S. Patent No. 8,757,890, the bearing setting will tighten as the roll 18 heats up from cold start-up operation. As such, the bearing setting for such a roll assembly 16 may need to be set outside the optimal range, toward a looser setting to allow for tightening into an acceptable range when the roll 18 is up to steady state operating temperature.

[0021] Fig. 1C is a detail view of the operator end 17A of the roll assembly 16 of Fig. IB. As shown, a cover or dust cap 38 is positioned over the first end 28 A of the center rod 28 and the nuts 32, 34 engaged therewith. Fig. ID is a detail view of the drive end 17B of the roll assembly 16 of Fig. IB. As mentioned above, the drive end 17B of the roll assembly 16 is the end adjacent a drive coupling (not shown) that drives an adjacent work roll in contact with the roll body of the roll 18. Neither end 17 A, 17B of the roll assembly 16 is configured for receiving or transferring torque. Rather, the roll 18 is driven by the frictional contact with the adjacent driven work roll 14. Thus, both of the first and second axial ends of the roll 18 are free from drive couplings.

[0022] Fig. 2 illustrates a roll assembly 116 (e.g., a back-up roll for a rolling mill such as a four-high rolling mill) including aspects of the present application. The roll assembly 116 can be substantially identical to the roll assembly 16 of Fig. IB in many respects, except as noted herein. As such, the basic elements of the roll assembly 116 are given reference numbers that coincide with those of the roll assembly 16, incremented by 100, and the basic features of the construction are not repeated.

[0023] As opposed to a solid center rod, the roll assembly 116 is provided with a hollow center shaft 128, or "tension tube", which defines an internal channel or cavity 140. As described in further detail below, fluid is circulated through the internal cavity 140 of the center shaft 128 to provide precise control of the bearing setting by purposely manipulating the thermal expansion of the center shaft 128 to offset the effects of thermal expansion of the roll 118 occurring naturally from the rolling process during warm-up.

[0024] The center shaft 128 of the roll assembly 116 of Fig. 2 includes a first open end 128 A defining a fluid inlet, and a second open end 128B defining a fluid outlet. The inlet end 128 A is shown at the adjustable, operator side 117A, but this may optionally be reversed. The center shaft 128 may be formed as a seamless tube in some constructions. A temperature control fluid circuit is provided in communication with the internal cavity 140 of the center shaft 128 via the fluid inlet at the first end 128A and the fluid outlet at the second end 128B. The temperature control fluid circuit includes fluid lines or conduits extending between the first end 128 A and the second end 128B, external to the center shaft 128. The temperature control fluid circuit includes a reservoir 144, a pump 146 operable to draw fluid from the reservoir 144, and a heater 148 operable to heat the fluid. Although shown downstream of the reservoir 144 and the pump 146, the heater 148 may optionally be located inside the reservoir 144. The temperature control fluid circuit is schematically represented in Fig. 2 to convey the particulars of one exemplary embodiment, and it should be realized that the exact configuration, including the arrangement and number of components is optionally variable in many respects. The fluid circulated by the temperature control circuit can be a liquid or a gas, or a combination of these. In some embodiments, the fluid is oil.

[0025] The amount of heating of the center shaft 128 with the temperature control fluid circuit may be variable by one or more means including but not limited to: varying the flow rate via the pump 146, varying or shutting off the flow rate with one or more valves or restrictions (not shown), or varying the amount of heat supplied to the fluid from the heater 148.

[0026] As shown in Figs. 3 A and 3B, a fluid collection device 160 can be positioned at the second end 117B of the roll assembly 116 to receive fluid from the fluid outlet defined at the second end 128B of the center shaft 128. The fluid collection device 160 is generally formed as an enclosure surrounding the second end 128B of the center shaft 128 and including an outlet 162 in fluid communication with the fluid reservoir 144. As shown, the fluid collection device 160 can further include a baffle 166 through which the second end 128B of the center shaft 128 extends. The baffle 166 can be constructed of a flexible material (e.g., rubber or other elastomer) in order to allow relative vertical movement or adjustment of the center shaft 128 with respect to the fluid collection device 160. For example, the baffle 166 may be formed as a sheet with a vertical slit 168 to allow passage of the center shaft 128. The baffle 166 flexes to gape open around the center shaft 128, but generally biases closed to limit the amount of fluid that might otherwise escape from the device 160. The baffle 166 may be configured to allow an adjustment range of the axis A of the center shaft 128 of +/- h (i.e., a total of 2h) in the vertical direction. Fig. 3B illustrates the second end 128B of the center shaft 128 in both the upper and lower limit positions in phantom line. In some constructions the total adjustment range 2h may be 3 to 6 inches. This vertical adjustment is utilized to accommodate varying stack heights of the rolls during the rolling process. Roll body turndown will reduce the total stack height.

[0027] Prior to operation, the rolling mill is set up for a rolling process. This includes, among other things, setting the tension or axial clearance in the center shaft 128 to achieve the desired initial bearing setting for the two bearing assemblies 124. This is done by rotating the setting nut 132 on the center shaft 128 to which it is threaded. As described above, the tension in the center shaft 128 controls the amount of initial axial preload in the bearing assemblies 124. This preload force can be defined by a specified applied torque on the setting nut 132. If the roll assembly 116 requires axial clearance at start-up, the setting nut 132 is then backed off a prescribed amount from the preloaded setting to provide the roll assembly 116 its desired cold endplay setting , or axial clearance. The lock nut 134 is tightened against the setting nut 132 to keep the setting nut 132 in position. With the center shaft 128 at the prescribed tension, or axial clearance, for the desired starting bearing setting, the roll 1 18 begins rotating as the rolling mill begins operation on a work piece. Due to various factors such as heat in the work piece and/or heat of running friction, the roll 118 expands, both axially and radially, during use of the rolling mill, as the roll 118 warms-up to ultimately achieve a steady state temperature substantially higher than ambient temperature. Due to the mechanical arrangement, expansion of the roll 118 will reduce the axial end play in the bearing assemblies 124. At least during this time span of warming-up, the temperature control fluid circuit is operable to limit the uneven thermal expansion between the roll 118 and the center shaft 128 by heating the center shaft 128, which tends to increase the amount of axial end play in the bearing assemblies 124.

[0028] As the rolling mill heats up through this transient phase from cold start-up to steady state mill operation, the pump 146 operates to drive a flow of fluid through the circuit, including through the cavity 140 inside the center shaft 128. Before reaching the fluid inlet defined at the first end 128 A of the center shaft, the fluid absorbs an amount of heat from the heater 148. Some of this heat is transferred into the center shaft 128 to drive thermal expansion of the center shaft 128, which would otherwise not heat up as much as the roll 118 during the transient phase from cold start-up to steady state operation. Thus, the flow of heated fluid through the center shaft 128 compensates for the thermal growth of the roll 118 so as to alleviate the tightening of the bearing setting that would otherwise occur due to expansion of the roll 118. Fluid exits the fluid outlet defined at the second end 128B of the center shaft 128 and returns to the reservoir 144. The collection device 160 of Figs. 3 A and 3B, or an alternative thereof, may be utilized to receive the flow of fluid from the cavity 140 and return the fluid to the reservoir 144 for further pumping and heating.

[0029] A method of controlling the temperature of the fluid entering the center shaft 128 may take one of several forms. In one method, a fixed "final" temperature is established for the center shaft 128, based on empirical data or estimates of the total thermal expansion of the roll 118 from cold start-up to steady-state condition. These thermal estimates are primarily based on anticipated mill speed. Generally, the faster the speed, the greater the roll expansion. This control method does not require any feedback loop. The final temperature for the center shaft 128 is pre-established and the fluid inlet temperature is fixed. Another method involves measuring stress (i.e., force acting through the center shaft 128) and using a feedback loop. If the measured stress is greater than a threshold value for a given separating force, the temperature of the fluid is raised in order to increase the length of the center shaft 128 and thus reduce the induced thrust acting on the bearing assemblies 124. The measured shaft stress is directly related to the induced thrust and actual operating load zone at the bearing assemblies 124.

[0030] Incorporating the above described structures and/or methods narrows the range of bearing setting from cold (ambient) setting to steady state operating temperature. This improvement can allow the mill operator to operate the bearing assemblies 124 within an optimized range for bearing setting (and load zone). Referring to Fig 7, the diamond-marked plot labeled "tension rod only" demonstrates how the load zone (angular measure of the rollers under load) changes as the roll 118 expands due to temperature increase due to normal use when a solid center rod 28 is provided. As can be seen, the normal temperature change during warm- up can cause the load zone to start in an acceptable but lower than desired angular range, and transition through the ideal range toward an upper limit for bearing preservation. For example, the load range can vary from 120 degrees (or even as low as 110 degrees or 90 degrees) all the way to 180 degrees, to exhibit a range or variance of 60 degrees or more. In some constructions, the load zone under steady- state operation may be preferred to be at 130 degrees or slightly over (e.g., 130 degrees to 150 degrees). Because the bearing setting can tighten by a substantial amount during warm-up (e.g., 0.250 inch total between both bearing assemblies 124, leading to the load zone increases mentioned above), this typically results in the need to start the roll assembly 116 at a much looser initial (cold) bearing setting. For example, to prevent the load zone from exceeding 180 degrees (at which a higher risk of burn-up exists), the setting of the bearing assemblies 124 at start-up may correspond to a load zone of less than 120 degrees if no thermal compensation is employed.

[0031] With the thermally-compensated center shaft 128, heated by the temperature control fluid circuit, a tighter setting for the bearing assemblies 124 is allowed at start-up, with less risk of reaching excessively high load zone after warm-up. For example, a bearing load zone range of 130 degrees to 150 degrees (i.e., not less than 130 degrees and not more than 150 degrees) for each of the bearing assemblies 124 may be maintained throughout operation, including cold start-up through the transient warm-up period, extending to the final steady state operating temperature with only a 20 degree load zone change, or less. During operation, the temperature control fluid circuit further allows fine tuning of the bearing setting (and corresponding load zone) by control of one or both of the amount of heating of the fluid and the flow rate. For example, the heater 148 can be adjusted to a lower level or turned off, or the fluid may even be cooled or chilled by an additional feature of the temperature control circuit.

[0032] In another construction as shown in Figs. 4 and 5, the center shaft 128 can be configured with a two-way flow device to allow fluid to enter and exit on the same end (e.g., operator end 217A) of a roll assembly 216. The roll assembly 216 of Figs. 4 and 5 can be in conformance with the above description of the roll assembly 116 with the exception of the features and operation as specifically noted. Reference numbers are incremented by 100. Figs. 4 and 5 illustrate the ends 217A, 217B of the roll assembly 216 with the understanding that the remainder of the roll assembly 216, including the bearing assemblies, can be provided in accordance with the above description and the additional drawings referenced there.

[0033] As shown in Fig. 4, the two-way flow device includes a thin-wall tube 260 provided within the interior cavity 240 of the center shaft 228. The tube 260 has an outer diameter smaller than the inner diameter of the interior cavity 240. One or more perforated spacers 264, or "centering disks", are provided to center the tube 260 within the cavity 240 of the center shaft 228. Each perforated spacer 264 includes an outer circumferential surface 266 in contact with the wall of the center shaft 228 defining the interior cavity 240, and further includes an inner circumferential surface 268 in contact with the outer wall of the tube 260. The material between the outer and inner circumferential surfaces 266, 268 is formed as an annulus and includes one or more openings or apertures 270 to allow fluid flow. However, the particular shape of the spacers 264 and the formation of the apertures 270 are only illustrative of one possible example.

[0034] At the first end 217A (e.g., operator side) of the roll assembly 216, the first end 228A of the center shaft 228 and a corresponding first end 260A of the tube 260 are engaged with a manifold cover 274 as shown in Fig. 4. The manifold cover 274 includes both a fluid inlet 276 in fluid communication with the interior of the tube 260 and a fluid outlet 278 in fluid communication with the annular space radially outside the tube 260. The apertures 270 in the centering disks 264 allow fluid flow as it returns from the second end 217B (e.g., drive side) of the roll assembly 216. In other constructions, the inlet and the outlet are reversed. Looking at Fig. 5, it can be seen that the tube 260 is shorter than the center shaft 228 such that the second end 260B of the tube 260 is spaced to the interior side from the end 228B of the center shaft 228. A plug 280 is provided to close the second end 228B of the center shaft 228. In other

constructions, the shaft 228 may be manufactured without an opening to obviate the need for plugging, or the opening at the second end 228B may be closed in an alternate manner from that shown. Comparing Fig. 4 to Fig. 1C, it can be seen that the roll assembly 216 of Fig. 4 includes an alternate cover or dust cap 238 that leaves the manifold cover 274 (and the fluid connections) exposed. In the event that the center shaft 228 is provided as a retrofit to replace an existing conventional roll assembly having a solid tension rod, the existing dust cap 38 can be swapped out and the alternate dust cap 238 installed.

[0035] In operation, the pump 246 drives the fluid from the reservoir 244 to flow into the center tube 260 via the fluid inlet provided in the manifold cover 276. The fluid flows from the first end 260A to and out of the second end 260B of the tube 260. From there, the flow direction is reversed at the plug 280 and the fluid flows back to the first end 217A of the roll assembly 216 through the annular passage between the outside of the tube 260 and the inside of the wall defining the interior cavity 240 of the center shaft 228. The fluid, having transferred a quantity of heat into the center shaft 228, exits the fluid outlet 278 in the manifold cover 274 and returns to the reservoir 244. As with the first embodiment, the fluid here is not limited to liquids, and may be partially or entirely in gaseous phase (e.g., steam).

[0036] Methods of operation as described with respect to the roll assembly 116 of Figs. 2-3, including but not limited to particular bearing settings and load zone ranges, temperature control methods, the general manner of compensating for roll growth by artificially expanding (by heating in excess of the natural heating from the rolling process) a hollow center shaft, etc. are also applicable to the alternate embodiment of Figs. 4-6. Reference is made to the above description. [0037] It should be understood that not all aspects of the invention are limited to a TQTM- equipped back-up roll. The use of a tensioned center shaft, the ribbed cup design of TQTM and further, the inventive concepts defined herein, may be applied in other applications.