OIL FILM BEARING AND BUSHING

Abstract: An oil film bearing for rotatably supporting the journal surface of a rolling mill roll neck (12) on a hydrodynamically maintained oil film. The bearing includes a bushing (18) adapted to interrupt the load carrying continuity of the oil film and to subdivide the load zone into compound pressure zones.

Description: This invention relates to an improvement in oil film bearings of the type employed to rotatably support the journal surfaces of roll necks in a rolling mill. In the typical rolling mill oil film bearing, as depicted somewhat diagrammatically in Figures 1 and 2, the roll 10 has a neck section 12. The neck section 12 may be conical, as shown in Figure 1, or it may be cylindrical. A sleeve 14 is received on and fixed relative to the neck section 12. The exterior of the sleeve defines the journal surface 16 of the roll neck. A bushing 18 has an internal bearing surface 20 surrounding and rotatably supporting the journal surface 16. The bushing is contained by and fixed within a chock 22. The chock is closed at the outboard end by an end plate 24 and cover 26. A seal assembly 28 is provided between the roll and the inboard end of the chock 22. During normal operation of the mill, when the roll is rotating at adequate speeds for full hydrodynamic operation, a continuous flow of oil is fed through one of the sets of passageways 29 in the chock, feed openings 30 in the bushing and rebores 32 in the bearing surface 20. From here, the oil enters between the bearing surface 20 and the rotating journal surface 16 to form a hydrodynamically-maintained somewhat wedge-shaped oil film 34 at the bearing load zone "Z". The load zone is located on the side opposite to that of the load "L" being applied to the roll, and the pressure profile at the load zone is schematically depicted in Figure 1 at "P". Although not shown, it will be understood that in most cases conventional hydrostatic means are employed to create the necessary oil film between the journal and bearing surfaces when the roll is either not rotating or rotating at a speed slower than that required to create and maintain the hydrodynamic oil film 34. Oil is continuously drained from between the journal and bearing surfaces 16,20 at both the inboard and outboard ends of the load zone. The oil draining from the inboard end enters an inboard sump 36 enclosed by the seal assembly 28 and the adjacent surfaces of the chock, bushing and roll. Oil draining from the outboard end enters an outboard sump 38 enclosed by the end plate 24 and chock 22. The sumps 36,38 are interconnected by one or more passageways 40 drilled through the chock, and the outboard sump 38 is connected to a conventional lubrication system (not shown) which filters, cools and recirculates the oil back to the bearing for reintroduction between the bearing and journal surfaces 16,20. It is to be understood that as herein employed, the term "oil" is to be interpreted broadly to include all classes of lubricants employed in bearings of the type under consideration, including for example mineral oil, synthetic oils and mixtures of oils and oil additives. In GB-A-2010415 which discloses the combination of features according to the pre-characterising parts of claims 1 and 10, there is described a bearing for the wheel of a motor vehicle wherein the wheel hub includes a bushing supported on a hydrodynamically maintained oil film, the bushing comprising a cylindrical liner having an internal bearing surface on which the oil film is carried at a load zone, the oil being supplied to the internal bearing surface through inlet means associated with the bushing. In the present specification there is described an oil film bearing of the type shown in Figs. 1 and 2 but having increased stiffness. As herein employed, the term "stiffness" means the ability of the bearing to resist movement of the journal surface 16 relative to the bearing surface 20 in response to the application of the load L to the roll. Moreover, the bearing is able to operate at reduced temperatures by increasing the volume of oil flowing through the bearing. At the same time, a reduction in the volume of oil draining into the inboard sump 36 is achieved, thereby lessening the possibility of oil being lost through the seal assembly 28 as it undergoes normal wear. The ability of the bushing and chock to self-align themselves with respect to the journal surface of the sleeve as the roll undergoes deflection during loading is also improved. The foregoing advantages are achieved by employing a novel bushing and bearing assembly adapted to interrupt the load carrying continuity of the hydrodynamically maintained oil film in a manner which causes the load zone to be axially subdivided into compound pressure zones. The maximum pressure developed at each compound pressure zone is greater than that of the conventional unitary pressure zone Z shown in Figure 1, with the result that the overall stiffness of the bearing is increased. In a preferred embodiment of the invention to be described hereinafter in greater detail, the bushing has two wall sections defining cylindrical axially aligned internal bearing surfaces on which portions of the hydrodynamically maintained oil film are carried at the load zone. Oil is supplied continuously to the load zone via inlet means including feed openings in each of the internal bearing surfaces, and is removed continuously from opposite ends of the load zone as well as via outlet means axially interposed between the internal bearing surfaces. The feed openings and the outlet means are isolated one from the other by intervening portions of the cylindrical internal bearing surfaces. The outlet means preferably includes an axial space between the internal bearing surfaces. Preferably the two wall sections of the bushing are integrally joined by an intermediate web of reduced thickness to provide a unitary wall component, and the axial space between the internal bearing surfaces is constituted by a groove on the interior of the wall component. Alternatively, the two wall sections may be separate one from the other, with the axial space between the internal bearing surfaces constituting part of an axial separation therebetween. In order to maintain a higher maximum presure at each of the compound pressure zones, the volume of oil flowing through the bearing is increased. This increased oil flow removes more heat from the bearing and thus produces a beneficial lowering of operating temperatures. Preferably, the oil being removed from the load zone by the outlet means is drained back through the bearing chock to the outboard bearing sump. This lessens the amount of oil draining into the inboard bearing sump, and thus decreases the possibility of oil being lost through the neck seal as it undergoes normal wear. The outlet means is preferably located at the bearing centre, thereby subdividing the load zone into two identical compound pressure zones. The identical compound pressure zones create counteracting moments axially spaced equal distances from the bearing centre, thereby enhancing the self-alignment capabilities of the bearing. Alternatively, the outlet means may be located off-centre to provide unequal pressure zones designed to exert a resultant moment in opposition to external bending forces being applied to the roll. In the accompanying drawings, by way of example only:- Figure 1 is a somewhat schematic longitudinal sectional view taken through a conventional rolling mill oil film bearing; Figure 2 is a cross sectional view on an enlarged scale taken along line 2-2 of Figure 1, with the clearance between the journal and bearing surfaces exaggerated for purposes of illustration; Figure 3 is another somewhat schematic longitudinal sectional view taken through a rolling mill oil film bearing assembly and bushing embodying the present invention; Figures 4A and 4B are cross sectional views on an enlarged scale taken along lines 4A-4A and 4B-4B of Figure 3, again with certain dimensions exaggerated for purposes of illustration; Figure 5 is a longitudinal sectional view taken through the bushing shown in Figures 3 and 4; Figure 6 is a schematic illustration comparing the pressure profiles of the compound pressure zones of a bushing embodying the present invention with the pressure profile of the unitary pressure zone of a conventional bushing; and Figure 7 is a partial longitudinal sectional view of another bearing embodying the present invention. In Figures 3-7, features common to those of the prior art bearing assembly of Figures 1 and 2 have been identified by the same reference numerals. The bushing 50 includes two wall sections 50a, 50b defining cylindrical axially aligned internal bearing surfaces 20a, 20b on which portions of the hydrodynamically maintained oil film are carried at the bearing load zone. As shown in Figure 4B, oil is admitted between the journal 16 and the bearing surface 20b via inlet means comprising one of the two sets of passageways 29 in the chock, feed openings 30 extending through the bushing wall section 50b, and rebores 32 in the bearing surface 20b. Although not shown, it will be understood that identical sets of passageways 29, feed openings 30 and rebores 32 are associated with the bearing surface 20a. As with the prior art design, oil is removed from the ends of the load zone directly into the inboard and outboard sumps 36, 38. Additionally, however, oil also is removed from the load zone via an outlet means located between the internal bearing surfaces 20a, 20b. In the bushing embodiment illustrated in Figures 3-5, the two wall sections 50a, 50b are integrally joined by an intermediate web 50c, and the outlet means includes a groove 52 in the web defining an axial space "s" between the internal bearing surfaces 20a, 20b. Each of the feed openings 30 and rebores 32 is isolated from the groove 52 by intervening portions 20a', 20b' of the internal bearing surfaces, thus preventing the incoming oil from escaping directly to the groove 52 without first being directed to the load zone. As can be best seen in Figure 4A, the web 50c has drain openings 54 communicating with a cross bore 56 in the chock 22. The cross bore 56 is connected via passageways 58 to the outboard sump 38. The groove 52 axially subdivides the load zone into compound zones z₁,z₂, each respectively having pressure profiles schematically depicted at "p₁" and "p₂" in Figures 3 and 6. As shown in Figure 6, the maximum pressure "a" developed in each pressure zone z₁, z₂ is greater than the maximum pressure "b" developed in the conventional undivided load zone Z. This produces a beneficial increase in bearing stiffness. Again as shown in Figure 6, the twin pressure profiles p₁, p₂ produce equal opposing moments M₁, M₂ which act on opposite sides of the bearing centre to improve the self-aligning capabilities of the bearing. In order to maintain these higher pressures, the volume of oil flowing through the bearing must be increased by as much as 20% as compared to the oil flow through a comparable conventional bearing. This increased oil flow removes more heat from the bearing and thus produces significantly lower operating temperatures. Oil is continuously drained from both pressure zones z₁, z₂ into the groove 52. From here, the oil progresses through the drain openings 54, cross bore 56 and passageways 58 back to the outboard sump 38, which also receives oil from the outboard end of pressure zone z₂. In addition, oil draining from the inboard end of pressure zone z₁ into the inboard sump 36 also is directed back to the outboard sump 38 via passageways conduits 40. With this arrangement, although total oil flow through the bearing is increased, the amount of oil being drained into the inboard sump 36 is actually decreased by approximately 40%. Thus, potential oil loss occasioned by wear of the seal assembly 28 is significantly minimised. As can be best seen in Figures 4A and 4B, the groove 52 preferably extends a full 360° around the bushing axis, with alternatively usable sets of drain openings 54 located on opposite sides of a horizontal reference plane "x-x", and with alternatively usable sets of inlet openings 30 and rebores 32 located on opposite sides of a vertical reference plane "Y-Y". This allows the bushing to be rotated 180° after one side has become worn. In light of the foregoing, it will now be appreciated by those skilled in the art that various changes and modifications may be made to the foregoing without departing from the basic concepts of the invention. For example, the disruption in the load carrying continuity of the hydrodynamically maintained oil film might be achieved by locating the groove in the journal surface 16 rather than in the bearing surface 20 as herein illustrated. More than one groove might be employed to axially subdivide the bearing into more than two pressure zones. Also, the grooves need not be located at the bearing centre. In some cases, it might be advantageous to locate the groove slightly off-centre to unbalance the resulting moments M₁, M₂ and thereby create a resultant moment tending to oppose external bending forces being applied to the roll. As shown in Figure 7, the spacing "s" between bearing surfaces 20a, 20b might be achieved by physically separating the two wall sections 50a, 50b and by draining oil from the load zone via radial passage 60 and connecting passage 62 leading to the outboard sump 38.

Claims: A bushing for supporting a rotating journal (16) on a hydrodynamically maintained lubricant film (34), the bushing comprising a cylindrical wall (50a, 50b) having an internal bearing surface (20) on which the lubricant film (34) is carried at a load zone (Z), and inlet means (30, 32) through which lubricant is supplied to the internal bearing surface (20), and characterised by outlet means (52, 54) axially interposed between axially aligned portions (20a, 20b) of the internal bearing surface (20) for removing lubricant from the load zone (Z), the inlet means comprising separate inlets (30, 32) respectively passing through each of the axially aligned portions, and the outlet means (52, 54) being isolated from the inlet means (30, 32) by intervening portions of the internal bearing surface. The bushing of claim 1 wherein the outlet means (52, 54) includes means (52) defining an axial space ("s") between the said axially aligned portions (20a, 20b) of the internal bearing surface. The bushing of claim 2 wherein the axial space constitutes part of an axial separation between adjacent ends of wall sections (50a, 50b) respectively defining the said axially aligned portions (20a, 20b) of the internal bearing surface (20). A bushing according to claim 2 or claim 3 wherein the inlet means comprises feed openings (32) arranged on opposite sides of a vertical reference plane bisecting the bushing, and wherein the said axial space ("s") extends 360° around the bushing axis. A bushing according to claim 1 wherein the cylindrical internal bearing surface (20) comprises the interior surface of a unitary sleeve (50) having respective sections (50a, 50b) defining the said axially aligned portions (20a, 20b) of the bearing surface. A bushing according to claim 5 wherein the outlet means (52, 54) comprises a groove (52) in the said interior surface (20). The bushing of claim 6 wherein the outlet means (52, 54) further comprises drain openings (54) communicating with the groove (52) and extending outwardly therefrom through the wall of the sleeve (50) to the exterior thereof. The bushing of claim 7 wherein the inlet means includes feed openings (32) arranged on opposite sides of a vertical reference plane bisecting the bushing, wherein the groove (52) extends 360° around the bushing axis, and wherein the drain openings (54) are located on opposite sides of a horizontal reference plane bisecting the bushing. A bushing according to claim 1 comprising a unitary cylindrical sleeve (50) having the internal bearing surface (20), a circular groove (52) axially subdividing the internal bearing surface (20) into the said portions (20a, 20b), each portion having an inlet means (30, 32) associated therewith, and the outlet means (54) being in communication with the groove (52). A bearing assembly for use in a rolling mill wherein a journal surface (16) of a roll (10) is rotatably supported by a bearing surface (20), wherein oil is continuously applied between the said surfaces (16, 20) through inlet means (30, 32) and drained from between the said surfaces (16, 20) through outlet means (52, 54), and wherein the surfaces (16, 20) are radially separated at a load bearing zone (Z) by a hydrodynamically-maintained film (34) of the oil, characterised in that the inlet means comprises separate inlets (30, 32) passing through the bearing surface (20), and the outlet means (52, 54) is located between the respective inlets (30, 32) intermediate the ends of the load bearing zone (z) and is isolated from the respective inlets (30, 32) by respective intervening portions of one of the said surfaces (16, 20). A bearing assembly according to claim 10 wherein the outlet means (52, 54) comprises at least one circular groove (52) in the said one of the said surfaces (16, 20). A bearing assembly according to claim 11 wherein the load bearing zone (Z) is subdivided into two identical zones (z₁, z₂) by the, or one of the, circular groove(s) (52) located at the axial centre of the load bearing zone (Z). A bearing assembly according to claim 11 or claim 12 wherein the, or one of the, circular groove(s) (52) is provided in the bearing surface (20), and wherein oil is continuously drained from the load bearing zone (Z) via the groove (52). A bearing assembly according to any one of the claims 10-13 wherein the bearing surface (20) comprises the internal surface of a bushing (18) for supporting the rotating journal (16) on the hydrodynamically-maintained lubricant film (34). A bearing assembly according to claim 14 wherein the bushing (18) is contained by and fixed within a bearing chock (22). A bearing assembly according to claim 10 wherein the load bearing zone (Z) is subdivided by the said outlet means (52, 54) into two pressure zones (z₁, z₂). A bearing assembly according to claim 16 wherein the two pressure zones (z₁, z₂) are of equal axial length. A bearing assembly according to claim 16 wherein the two pressure zones (z₁, z₂) are of unequal axial length. A bearing assembly according to any one of the claims 10-18 further comprising means for defining inboard and outboard sumps (36, 38) for receiving oil from the inboard and outboard ends, respectively, of the load bearing zone (Z), and means for connecting the outlet means (52, 54) to the outboard sump (38). A bearing assembly according to claim 14 further comprising: a bearing chock (22); the bushing (18) being fixed within the bearing chock (22) and the combination of the chock (22) and bushing (18) being adapted to be received on the roll neck (12) with the bearing surface (20) of the bushing (18) surrounding the journal surface (16) of the neck (12); the outlet means including a circular groove (52) in the bearing surface (20), the groove being arranged to axially separate the bearing surface (20) into inboard and outboard pressure zones (z₁, z₂); the bearing surface (20) having oil feed openings on opposite sides of the groove (52); a seal assembly (28) at the inboard end of the chock (22), the seal assembly (28) being adapted to cooperate in sealing engagement with the chock (22) and the roll neck (12) to define a first sump (36) into which oil is continuously drained from the inboard pressure zone (z₁); a cover assembly (24) cooperating with the outboard end of the chock (22) to define a second sump (38) into which oil is continuously drained from the outboard pressure zone (z₂); and conduit means (58) communicating with the groove (52) arid the second sump (38) for continuously draining oil from the first and second pressure zones (z₁, z₂) via the groove (52) into the second sump (38). The use in a rolling mill of a bearing assembly according to any one of the claims 10-20.

Inventors: INNIS, CHARLES L., SALTER, LOWELL S., SIMMONS, THOMAS E.
Applicants: MORGAN CONSTRUCTION COMPANY (A MASSACHUSETTS CORPORATION)
Application year: 1988
Main classification: B21B31
IPC codes: F16C17, B21B45, B21B31, F16C33, B21B38