Abstract:
An oil film bearing for supporting a roll neck in a rolling mill, suitable in particular for transmitting high bearing forces when the bearing partners are slightly and slowly moved with respect to each other, has a bearing surface into which are incorporated rods made of a friction-reducing material (e.g., low friction compounds), which extend in a substantially perpendicular direction to the bearing surface. The rods are deformed during heat processing to define a bearing surface. The bearing partner, such as a roll sleeve, rests on the free face of the deformed rods.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of prior application Ser. No. 14/350,001, filed Apr. 4, 2014, which was the National Stage of International Application No. PCT/IB2012/002511, filed Oct. 4, 2012, which claimed the benefit of Provisional Application No. 61/543,235, filed Oct. 4, 2011, the contents of which applications are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The invention is directed to a further advancement in the field of oil film bearings and more particularly to bearings used to rotatably support the necks of rolls in a rolling mill. 
     BACKGROUND OF THE INVENTION 
     An example of an oil film bearing is the “MORGOIL” bearing, which is available from Siemens AG, Linz, Austria. The MORGOIL bearing has a hydrodynamic design which distributes the bearing load over a relatively large area. A film of oil on which the bearing operates has immense load carrying capacity and, when functioning as intended, eliminates wear caused by metal-to-metal contact. When used on a rolling stand, the oil film is constantly maintained by the hydrodynamic action of the rotating sleeve which fits over the roll neck, and a nonrotating bushing mounted in the chock. 
     A rolling mill oil film bearing typically comprises a sleeve axially received on and rotatably fixed to a roll neck. The sleeve is surrounded by a bushing contained in a chock mounted in a rolling mill housing. In service, the sleeve is rotatably supported on a thin film of oil hydrodynamically maintained at the bearing load zone between the sleeve and the bushing. 
     The sleeves may be either internally cylindrical for use on cylindrical or “straight” roll necks, or they may be internally tapered for use on tapered roll necks. Moreover, the sleeves may be “self locking” or “non-locking”. Self locking sleeves are frictionally fixed to the roll necks by interference fits, whereas non-locking sleeves require keys or the like to effect a mechanical inter-engagement with the roll necks. 
     With reference to  FIG. 1 , one such sleeve is shown at  13  as a component part of a rolling mill oil film bearing  12 . The sleeve  13  is removably received on a tapered section  16  of the roll neck and is rotatably fixed to the roll neck by keys  14  or the like. The sleeve is surrounded by a bushing  18  and fixed in a bearing chock  20 . In service, as previously noted, the sleeve is rotatably supported on a thin film of oil (not shown) hydrodynamically maintained at the bearing load zone between the sleeve and the bushing. 
     With reference to  FIG. 2 , it will be seen that the sleeve  13  has an internally tapered section  21  with a length L, an end section  22  extending axially beyond the outboard end of the internally tapered section, and a cylindrical outer surface  23  surrounding the internally tapered section. The cylindrical outer surface has a diameter D (also commonly referred to as the “journal” diameter). The internally tapered section has a taper angle a, a minimum thickness t at its inboard end, and a maximum thickness t′ at its outboard end adjacent to the end section  22 . Keyways  15  co-act in mechanical interengagement with the keys  14 , with both the keys and the keyways being located outside of the internally tapered section  21  and exclusively within the end section  22 . 
     With reference to  FIG. 3 , it will be seen that a modern “MORGOIL” lubrication system delivers a controlled supply of oil to the bearings. When the roll is turning, the sleeve, fitted over the roll neck and secured by a key to prevent slippage, turns within the stationary bushing which is secured to the chock. Bearing load is distributed over the entire load zone and the continuity of the oil film is ensured by delivery of the oil through internal passages within the chock to the journal. Hydrostatics are used in oil film bearings when sustained operation under high load and low speed is required, when the mill is operating in a reversing mode, frequently changing the turning direction or when the mill is required to start under load after long stops. A high pressure pump feeds lubricant into the load zone of the bearings, assuring full film operation of the bearing under all rolling conditions. 
       FIG. 4  illustrates a cross-sectional view taken through a sleeve and bushing showing lubrication conduits, and ports for introducing and expelling lubricant. 
     To protect the bushing body against mechanical destruction from metal-to-metal contact with the sleeve, the bushing body is filled with so called white metal, which is a relatively soft metal providing emergency bearing characteristics.  FIG. 5 a    is a section through the bushing  18  and shows that the quite ductile white metal filling  17  is supported by shoulders  19 . With the continuing effort to reduce the size of the mills while increasing their output, the specific load capacity of bearings has increased as well. To meet this need MORGOIL introduced a High Strength Babbitt (HSB) white metal bearing material. This proprietary babbitt resulted in higher bearing capacity.  FIG. 5 b    illustrates a MORGOIL bushing with HSB. 
     Significant limitations of the standard white metal bushings as well as the HSB bushings includes the risk of segregation between the steel bushing and white metal, high cost, and limited bearing capacity during emergency operating conditions, such as low oil pressure or non-stable oil film conditions. 
     SUMMARY OF THE INVENTION 
     The present invention provides an oil film bearing having improved operating characteristics relative to the traditional MORGOIL bearings, including the HSB bushings. 
     An oil film bearing in accordance with the present invention, suitable in particular for transmitting high bearing forces when the bearing partners are slightly and slowly moved with respect to each other, has a bearing surface made of a friction-reducing material (e.g., low friction compounds). The bearing surface can be formed using a plurality of rods or a powder material. The rods are deformed during heat processing to define a bearing surface. Similarly, the powder can be compressed into a pre-form and heated (sintered) to define a bearing surface. The bearing partner, such as a roll sleeve, rests on the free face of the deformed rods or sintered powder material. The low friction material can include a polytetrafluoroethylene (PTFE) material or other known materials such as ultra high molecular weight (UHMW) polymers. In a preferred embodiment, a glass-reinforced PTFE material is utilized to define the bearing surface. 
     In one embodiment of the present invention, an oil film bearing for rotatably supporting a roll neck in a rolling mill includes a rotating sleeve section and a bushing. The bushing includes a bearing block having a low-friction bearing surface. The outer surface of the rotating sleeve section is rotatably supported on a film of oil on the low-friction bearing surface. 
     The present invention is also directed to a bushing for use in an oil film bearing of the type employed to rotatably support a roll neck in a rolling mill. The bushing has an inner surface engaging a rotating sleeve section. The outer surface of the sleeve section is adapted to be rotatably supported on a film of oil at a load zone of the bearing. The bushing comprises a bearing block and a low-friction bearing surface connected to the bearing block and supporting the outer surface of the rotating sleeve section. 
     A bearing assembly in accordance with the present invention offers higher load capacity for the same size bearing with reductions in both initial and operational cost. Furthermore the specific low friction bearing surface offers a significantly lower coefficient of friction as compared to the given white metal technologies. This yields significantly better protection of the sleeves under any kind of emergency situation. The low friction bearing surface is also completely resistant against any kind of chemical influences resulting from the oil or any kind of inclusions in the oil. Therefore the present invention offers a significantly longer lifetime as compared to standard white metal bushes. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions (for example, in non-rotational applications) do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a rolling mill oil film bearing of the prior art. 
         FIG. 2  is a cross-sectional view of a sleeve of a rolling mill oil film bearing of the prior art. 
         FIG. 3  is a diagram of a lubrication system for oil film bearings. 
         FIG. 4  is a cross-sectional view of a sleeve and bushing of an oil film bearing. 
         FIG. 5 a    is a cross-sectional view of a bushing of an oil film bearing. 
         FIG. 5 b    is a perspective view of a bushing of an oil film bearing. 
         FIG. 6  is a cross-sectional view of a bearing assembly suitable for use with a bushing of the present invention. 
         FIG. 7  is a cross-sectional view of a bearing suitable for use with a bushing of the present invention. 
         FIG. 8  is a cross-sectional view of a bearing suitable for use with a bushing of the present invention. 
         FIG. 9  is a cross-sectional view of a bushing according to one embodiment of the present invention, subsequent to heat deformation. 
         FIG. 10  is a cross-sectional view of a bushing according to another embodiment of the present invention. 
         FIG. 11  is a cross-sectional view of a bushing according to another embodiment of the present invention. 
         FIG. 12  is a cross-sectional view of the bushing of  FIG. 9 , prior to heat deformation. 
         FIG. 13  shows the bushing of  FIG. 9  prior to a heat setting process. 
         FIG. 14  shows the bushing of  FIG. 13  subsequent to a heat setting process. 
         FIG. 15  depicts a manufacturing process of an oil film bearing in accordance with the present invention. 
         FIG. 16  shows the bushing of  FIG. 14  including an integrated distance measurement sensor. 
         FIG. 17  is a partial view of an oil film bearing with an integrated axial sensor in accordance with the present invention. 
         FIG. 18  is an elevational view of a mold and bearing preform including a powdered PTFE or similar material. 
         FIG. 19  is a perspective view of the bearing preform of  FIG. 18  as removed from the mold. 
         FIG. 20  depicts the powdered PTFE material of  FIG. 18  installed within a rigid bearing housing. 
         FIG. 21  is a detailed view of the bearing assembly  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings,  FIG. 6  is a cross sectional view taken through a bearing assembly having a neck seal  1 , coolant seal  2 , chock  3 , roll neck  4 , sleeve  5 , babbitt  6 , key  7 , bushing  8 , thrust bearing assembly  9 , hydraulic bayonet lock  10  and locking segment  11 .  FIG. 6  depicts a MORGOIL KL-type bearing. The present invention primarily relates to the bushing  8  and babbitt  6 . 
       FIG. 7  is a cross-sectional view of a MORGOIL type-N bearing also suitable for use with a novel bushing  8  of the present invention.  FIG. 8  is a cross-sectional view of a MORGOIL type SN bearing, which is also suitable for use with a novel bushing  8  of the present invention. Applications of the present invention are not limited to particular classes of oil-film bearings. A wide variety of bearings could be practiced in accordance with the present invention. Aspects of the present invention can be suitably applied across a wide variety of bearing types, size, classification and designs. 
       FIG. 9  illustrates the babbitt surface  46  of bushing  8  of the present invention. Babbitt surface  46  defines a slide bearing. As described above, an oil film is established between babbitt surface  46  and a sleeve or other component. Bushing  8  has a bearing block  40  or support which can have any shape and form and in case of oil film bearings is a ring into which are incorporated rods  42  made of a friction-reducing material, in particular glass-reinforced polytetrafluoroethylene (PTFE), which extend in a substantially perpendicular direction to the bearing surface. The bearing partner, such as sleeve  5  in  FIG. 6 , rests on the free face of the rods. 
       FIGS. 10 and 11  are cross-sectional views taken through bushing  8  showing block  40  and boreholes  44 . In the illustrated embodiment, the boreholes  44  are generally cylindrical and may have a surface texture promoting adhesive between the block  40  and the rods  42 . In other embodiments, the boreholes  44  may be non-cylindrical. In yet other embodiments, the boreholes  44  may include undercuts or other structure to promote the interconnection between the rods  42  and the block  40  before and/or subsequent to heat deformation. For example, the boreholes  44  may include threads or similar structure. A variety of undercuts or other structure could be employed within the boreholes  44  to promote the connection between the rods  42  and the block  40 . The rods  42  need not be cylindrical but could take another form. The rods  42  need not match the borehole  44  configuration, for example a square rod  42  could be inserted into a round borehole  44  or vice-versa a round or oval rod in a square or oval hole. Rods  42  may assume a variety of different configurations. For example, two or more differently sized rods  42  may be inserted into two or more differently sized boreholes  44 . In some applications, it may be beneficial to include two or more differently sized rods  42  and boreholes  44  to improve coverage of the bearing surface. As shown, the upper edges of the boreholes  44  may be chamfered, beveled or otherwise configured. 
       FIG. 12  is a cross-sectional view of bushing  8  showing block  40  and rods  42  prior to heat deformation. Rods  42  are inserted into the boreholes  44  during a manufacturing process. Rods  42  may include rods of different diameters. For example, two or more differently sized rods  42  may be inserted in two or more differently sized boreholes  44 . The use of differently sized rods  42  may be beneficial so as to maximize the coverage of the rod material subsequent to heat deformation.  FIG. 9  shows rods  42  subsequent to heat deformation. Additional machining of the deformed ends of rods  42  may be required to yield a suitable bearing surface  46 . 
       FIG. 13  shows the bushing  8  with rods  42  inserted into boreholes  44 .  FIG. 14  shows the bushing of  FIG. 13  subsequent to a heat setting process during which the rod  42  ends are deformed to define a bearing surface. 
       FIG. 15  depicts a manufacturing process during which a pair of semi-cylindrical dies  50  are inserted into the bushing  8  and are expanded by a hydraulic cylinder  52 . Using force and temperature, the dies  50  engage and deform the rods  42  to define a generally cylindrical PTFE bearing surface. 
     The manufacturing process would include steps of defining boreholes in the bushing block  40 , inserting PTFE rods  42  into the boreholes, heat treatment of the PTFE rods  42  to temperature resulting in a degree of plasticity, inserting the die halves  50  and hydraulic cylinder  52  into the bushing block  40 , and expanding the die halves  50  to engage and deform the PTFE rods  42  into a generally cylindrical PTFE bearing surface. Additional machining steps of the deformed rod  42  ends may be necessary to configure the bearing surface. 
     In accordance with the present invention, the boreholes  44  may be perpendicular to the bearing surface or may be offset relative to the bearing surface. The boreholes  44  may be closed or open-ended, and may include holes of two or more different sizes. Moreover, the boreholes  44  may be cylindrical, structured or tapered along their lengths. The top edges of the boreholes  44  may be chamfered. 
     In accordance with the present invention, the rods  42  may be formed from a low friction material such as, but not limited to, a polytetrafluoroethylene (PTFE) material, or materials made from other types of low-friction polymers such as ultra high molecular weight (UHMW) polymers. The rods  42  may be reinforced with glass fibers or other strengthening fibers such as, but not limited to, KEVLAR, carbon fiber, ceramics, and nano-fibers. The rods  42  may be equally sized, or two or more differently sized rods  42  can be utilized within a given bushing. For example, the rods within a bushing may have different diameters, lengths, materials, etc. 
     The bearing block  40 , structure or ring of the oil film bearing of the present invention is preferably formed of a steel alloy, such as a quenched and tempered and/or hardened steel alloy. The area of the bearing surface inside the bearing block, ring or structure may be open to the ends or closed by raised edges. 
     The rods  42  may be arranged in the bearing block  40  in rows which run perpendicular to the bearing surface, or in any appropriate angle to the preferred direction of movement. The rods  42  may be placed in rows, with neighboring rows being offset from each other by a distance such as, but not limited to, a distance equal to half of the spacing between the rods in a row. 
     The low friction bearing surface of the oil film bearing of the present invention may be covered by additional and specific coatings to increase the surface protection and/or reduce the overall coefficient of friction. Novel coatings, such as advanced nanoparticle coatings, may be utilized to provide further protection or enhanced performance for the low friction bearing surface. Lubricants on the bearing surface may include specific additives which optimize their use on low friction surfaces. The lubricants may also include additives which protect the entire oil system or circuit of the entire oil-film application against contamination from specific types of bacteria which cause bio-corrosion. 
     Sensors may be provided within the bearing of the present invention to provide temperature, flow and/or pressure information. Sensors may also be provided to provide information relevant to conditions such as, but not limited to, lubrication conditions, the presence of water contamination, and pH conditions. 
     The sensors may also be provided to detect the presence of certain biologics, such as corrosion-causing biologics. Microbiologically-Influenced Corrosion (MIC), also known as microbial corrosion or biological corrosion, is the deterioration of metals as a result of the metabolic activity of microorganisms. There are several bacteria known to cause microbiologically influenced corrosion of carbon steels, stainless steels, aluminum alloys and copper alloys in waters and soils with a pH range of approximately 4-9 and a temperature range of approximately 10° C. to 50° C. These bacteria can be broadly classified as aerobic (requiring oxygen to become active) or anaerobic (oxygen is toxic to the bacteria). Sulphate reducing bacteria (SRB) is anaerobic and is responsible for most instances of accelerated corrosion damages to ships and offshore steel structures. Iron and manganese oxidizing bacteria are aerobic and are frequently associated with accelerated pitting attacks on stainless steels at welds. 
     As shown in  FIG. 16 , a radial distance measurement sensor  60  which dynamically surveys any changes in the oil-film thickness may be integrated into the bushing and/or low friction bearing surface. The measurement may be accomplished via induction (or other techniques), and may be integrated into a specific oil film bearing condition monitoring system as a standalone system and/or integrated into an existing overall mill control system. 
     As shown in  FIG. 17 , an additional axial sensor  62  may be integrated into the bushing to survey and control the axial movement and/or displacement of the sleeve. This may be accomplished via induction (though not limited to that approach), and may be integrated into a specific oil-film bearing condition monitoring system as a standalone system and/or integrated into an existing overall mill control system. 
       FIGS. 18-21  depict an alternative approach to manufacturing a bearing assembly. In this approach, a powder (granular) PTFE material is molded by means of powder forming processes similar to those used for ceramics or powdered metal. The PTFE or similar powder is compacted in suitable mold, the resulting molding is then removed from the mold, heated to a temperature above the crystalline melting point to effect fusion of the individual particles, and cooled in a controlled manner to give the final molded article. The compaction process is generally known as preforming and the heat treatment as sintering. 
       FIG. 18  depicts a powdered PTFE or similar material molded into a PTFE preform  80  using a rigid preform mold  82 . Powder compaction can be applied to yield the resulting preform  80  of powdered PTFE material. The PTFE preform  80  is generally a plate having a generally smooth upper surface  84  and a plurality of generally cylindrical protuberances (pins  86 ) at the lower surface. 
       FIG. 19  illustrates a portion of the preform  80  as removed from the preform mold  82 . The preform  80  can subsequently be processed to define the bearing surface. 
       FIG. 20  illustrates the preform  80  from  FIG. 18  inserted into a bearing block  88  (similar to bearing block  40 ) with the pins  86  being aligned and inserted into boreholes  90  of block  88 . A single preform  80  thus defines a plurality of pins  86  in comparison to the separate pin approach described earlier. In the separate pin approach, seams resulting from the separate pins may create turbulence in the oil film. Therefore, using a single preform  80 , instead of separate individual pins or rods  42 , may reduce turbulence or create turbulence-free laminar flow.  FIG. 21  shows the boreholes in detail. In one embodiment, the boreholes may be tapered (conical) to assist in retaining the PTFE pins within the boreholes  90 . In yet other embodiments, the boreholes  90  may include undercuts or other structure to promote the interconnection between the pins  86  and the block  88  before and/or subsequent to heat deformation. For example, the boreholes  90  may include threads or similar structure. A variety of undercuts or other structure could be employed within the boreholes to lock the connection between the pins  86  and the block  88 . The pins  86  need not be cylindrical but could take another form. The pins  86  need not match the borehole configuration, for example a square pin could be inserted into a round borehole or vice-versa a round or oval rod in a square or oval hole. 
     Once the preform  80  is inserted into the bearing block  88 , pressure and heat may be applied to further compact the PTFE powder prior to sintering. Sintering the PTFE preform  80  involves heating it to a temperature above the crystalline melting point of about 340 C (621 F) until the individual PTFE particles coalesce and lose their identity. Compaction of the preform  80  may be achieved in a manner similar to that described above (using a hydraulic ram and curved dies). In another approach, compaction may be achieved using hydrostatic forces (using a high pressure fluid to compact the preform  80 ). Sintering may be achieved using, for example, known electric oven processes. Depending on the application, sintering may take place away from the bearing block  80  using an external die or form and with the shaped PTFE bearing later inserted into the bearing block. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.