Patent Publication Number: US-2015078688-A1

Title: Bearing arrangement for rolling mill roll shaft

Description:
BACKGROUND 
     1. Field 
     Embodiments of the present invention relate to bearing arrangements for rotatably supporting roll shafts in a rolling mill. The invention is particularly suited for, although not limited in use to, high speed rolling mills having so called “cantilevered” roll shafts with axially projecting ends adapted to carry the work rolls. 
     2. Description of Related Art 
     As herein employed, “oil film bearing” means a bearing in which the rotating element is supported on a film of oil. “Hydrodynamic bearing” means an oil film bearing which relies on the high speed of the rotating element to pressurize the oil in a wedge-shaped film at the bearing load zone. “Hydrostatic bearing” means an oil film bearing which employs a positive pressure supply of oil to maintain a clearance between the rotating and stationary elements. 
     In a conventional high speed rolling mill, as depicted in  FIG. 1 , the roll shafts  10  are rotatably supported between first and second axially spaced radial bearings  12   a ,  12   b . Radial bearings  12   a  are located inboard of axially projecting first ends  10   a  of the roll shafts, and radial bearing  12   b  are located inboard of axially projecting second ends  10   b  of the roll shafts. Work rolls  14  are carried on axially projecting first ends  10   a  of the roll shafts, and third and fourth thrust bearings  16   a ,  16   b  on the second shaft ends  10   b  serve to fix the roll shafts in the axial direction. The radial bearings may be oil film bearings, and may typically comprise hydrodynamic bearings, with the thrust bearings comprising angular ball bearings. 
     In addition to having a limited useful life, thrust ball bearings have been found to lack the stiffness required to provide axial precision for the rolling operation. While radial hydrodynamic bearings operate satisfactorily, they have been found to compromise radial precision because the thickness of the oil films supporting the rolls varies in response varying bearing loads. 
     SUMMARY 
     Broadly stated, embodiments of the present invention address the above described problems by providing an improved bearing arrangement in which both the radial and thrust bearings are oil film bearings. 
     In exemplary embodiments of the present invention, the thrust bearings may be hydrodynamic bearings, but preferably will comprise hydrostatic bearings. Similarly, although the radial bearings may be hydrodynamic bearings, hydrostatic bearings are preferable. 
     Optimum stiffness is achieved by employing hydrostatic bearings for both the radial and thrust applications. 
     These and other features and advantages of present invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view through a roll stand employing a conventional bearing arrangement; and; 
         FIG. 2  is a sectional view through a roll stand employing a bearing arrangement in accordance with an exemplary embodiment of the present arrangement. 
     
    
    
     DETAILED DESCRIPTION 
     The components described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components that would perform the same or a similar function as well as the materials described herein are intended to be embraced within the scope of embodiments of the present invention. 
     In accordance with exemplary embodiments of the present invention, as depicted in  FIG. 2 , the roll shafts  18  are rotatably supported by axially spaced first and second radial bearings  20   a ,  20   b  respectively located inboard of axially projecting first and second shaft ends  18   a ,  18   b . Work rolls  22  are carried on the first shaft ends  18   a  and annular pressure plates  24  are mounted on and fixed relative to the second shaft ends  18   b . Third and fourth thrust bearings  26   a ,  26   b  act on opposite sides of the pressure plates  24  to axially fix the roll shafts. 
     The first and second radial bearings  20   a ,  20   b  may be hydrodynamic bearings, but hydrostatic bearings are preferred. Similarly, although the third and fourth thrust bearings  26   a ,  26   b  may be hydrodynamic bearings, hydrostatic bearings are again preferred. Maximum stiffness is achieved by employing hydrostatic bearings for the first and second radial bearings  20   a ,  20   b  and the third and fourth thrust bearings  26   a ,  26   b.    
     It is to be understood that while preferred embodiments of the present invention have been described, such embodiments should be considered as illustrative and may be modified by those skilled in the art without departing from the scope of the present invention, as defined by the appended claims.