Abstract:
A hot gas valving system for a ground-based power generation system includes a gas flow conduit having a wall and defining a path for fluid flow and a butterfly valve located in the wall and transversely across the path for fluid flow. The butterfly valve includes a first raceway defined by an inner ring and an outer ring, a second raceway defined by an inner ring and an outer ring, a combination of ball bearings and roller bearings retained in each raceway, an axle rotatably mounted in the inner rings of each raceway and cooperably rotatable therewith, and a baffle mounted longitudinally along the axle and extending from the axle into the path of fluid flow. Upon rotation of the axle, the baffle restricts or permits fluid flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application No. 60/959,326 filed Jul. 12, 2007, which is hereby incorporated herein by reference, in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to bearings and in particular to bearings for butterfly valves in ground-based power generation systems. 
     BACKGROUND 
     A ball-roller bearing comprises an inner ring and an outer ring that define raceways for a combination of roller elements comprising balls and rollers. The travel of the rollers in a ball-roller bearing may be guided by a channel in the outer ring or in the inner ring. 
     SUMMARY 
     The present invention resides in one aspect in an improvement in a ground-based power generator that comprises a hot gas valving system that includes a butterfly valve in a gas flow conduit. The improvement comprising that the butterfly valve is mounted in the conduit by a ball-roller bearing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, partly cross-sectional view of a butterfly valve mounted in two ball-roller bearings that are disposed in back-to-back relation to each other with roller guide channels on the outer rings, close to the load zones; 
         FIG. 2  is a schematic, partly cross-sectional view of a butterfly valve mounted in two ball-roller bearings that are disposed in face-to-face relation to each other with roller guide channels on the outer rings, away from the load zones; 
         FIG. 3  is a schematic, partly cross-sectional view of a butterfly valve mounted in two ball-roller bearings that are disposed face-to-face relation to each other with roller guide channels on the inner rings, close to the load zones; 
         FIG. 4  is a schematic, partly cross-sectional view of a butterfly valve mounted in two ball-roller bearings that are disposed in back-to-back relation to each other with roller guide channels on the inner rings, away from the load zones; and 
         FIG. 5  and  FIG. 6  are schematic cross-sectional views of illustrative embodiments of bearings as described herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Many ground-based power generation systems, including turbine generator systems, produce hot gases that need to be vented in a controlled manner, and for this purpose, the generation systems include gas flow conduits (such as flues) that are equipped with butterfly valves. A butterfly valve has a valve baffle mounted on axles that extend from opposites sides of the valve baffle and that are mounted on the gas flow conduit. A butterfly valve may be subject to extreme conditions of temperature, pressure, and/or exposure to corrosive chemical species in the gas. 
     An improved butterfly valve for a hot gas venting system in a ground-based power generation system comprises ball-roller bearings. The ball-roller bearings may enable the axles to pivot with the valve baffle, or they may permit the valve baffle to pivot relative to the axles. Optionally, the ball-roller bearing may be used for a butterfly hot air bleed valve. 
     There are several possible configurations for a ball-roller bearing as described herein, relating to variations on the location of a guide channel for the roller (whether the inner ring or the outer ring comprises a guide channel, if not both) and whether the rollers are closer to the load zone than the balls, or farther away. In addition, when two ball-roller bearings are used on coaxial axles, the ball-roller bearings may be in face-to-face or back-to-back arrangement. 
       FIG. 1  shows a butterfly valve  42  that comprise a baffle  44  mounted on an axle  46 . The axle  46  is mounted in two ball-roller bearings  10 ,  30 , that are mounted in the wall of a hot air bleed conduit  48  of a ground-based power generation system. The expected directions of the axial and radial loads on the bearings are shown by the arrows in the drawing. Ball-roller bearings  10  and  30  are arranged back-to-back with roller guide channels on the outer rings, close to the load zones. Thus, ball-roller bearing  10  comprises an inner ring  12  and an outer ring  14 . The inner ring  12  and the outer ring  14  cooperate to define a raceway for a set of balls  16  with contact angles a. The outer ring  14  defines a guide channel  18  for a set of rollers  20 . The rollers  20  are disposed in guide channel  18  with their axes of rotation A R  parallel to the axis of rotation of axle  46 . Similarly, ball-roller bearing  30  comprises an inner ring  32  and an outer ring  34 . The inner ring  32  and the outer ring  34  cooperate to define a raceway for a set of balls  36  with contact angles a. The outer ring  34  defines a guide channel  38  for a set of rollers  40 . 
       FIG. 2  shows the butterfly valve  42  mounted in two ball-roller bearings  210 ,  230 , that are arranged face-to-face with roller guide channels on the outer rings, away from the load zones. Thus, ball-roller bearing  210  comprises an inner ring  212  and an outer ring  214 . The inner ring  212  and the outer ring  214  cooperate to define a raceway for a set of balls  216  with contact angles a. The outer ring  214  defines a guide channel  218  for a set of rollers  220 . Similarly, ball-roller bearing  230  comprises an inner ring  232  and an outer ring  234 . The inner ring  232  and the outer ring  234  cooperate to define a raceway for a set of balls  236  with contact angles a. The outer ring  234  defines a guide channel  238  for a set of rollers  240 . 
       FIG. 3  shows the butterfly valve  42  mounted in two ball-roller bearings  310 ,  312  arranged face-to-face with roller guide channels on the inner rings, close to the load zones. Thus, ball-roller bearing  310  comprises an inner ring  312  and an outer ring  314 . The inner ring  312  and the outer ring  314  cooperate to define a raceway for a set of balls  316  with contact angles a. The inner ring  312  defines a guide channel  318  for a set of rollers  320 . Similarly, ball-roller bearing  330  comprises an inner ring  332  and an outer ring  334 . The inner ring  332  and the outer ring  334  cooperate to define a raceway for a set of balls  336  with contact angles a. The inner ring  332  defines a guide channel  338  for a set of rollers  340 . 
       FIG. 4  shows the butterfly valve  42  mounted in two ball-roller bearings  410 ,  430  arranged back-to-back with roller guide channels on the inner rings, away from the load zones. Thus, ball-roller bearing  410  comprises an inner ring  412  and an outer ring  414 . The inner ring  412  and the outer ring  414  cooperate to define a raceway for a set of balls  416  with contact angles a. The inner ring  412  defines a guide channel  418  for a set of rollers  420 . Similarly, ball-roller bearing  430  comprises an inner ring  432  and an outer ring  434 . The inner ring  432  and the outer ring  434  cooperate to define a raceway for a set of balls  436  with contact angles a. The inner ring  432  defines a guide channel  438  for a set of rollers  440 . 
     In a particular embodiment, a ball-roller bearing for use as described herein may comprise rings and rollers made from a stainless steel alloy such as BG-42, per Aerospace Material Specification AMS 5749. The rings and rollers may bear a thin, dense chrome plate. The balls may be made from silicon nitride ceramic, for example, Si 3 N 4 . In various specific embodiments, such bearings may have one or more of the characteristics set forth in the following Table 1A (in which dimensions are stated in inches, unless otherwise indicated). 
     
       
         
               
               
               
             
               
               
             
           
               
                 TABLE 1A 
               
               
                   
               
             
             
               
                 Contact Angle 
                 40° 
                 [DEG] 
               
               
                 Preload, Axial 
                 N/A 
                 [LB] 
               
               
                 Preload, Radial 
                 N/A 
                 [LB] 
               
               
                 Dynamic Load Rating Radial/Axial 
                 N/A 
                 [LB] 
               
               
                 (ABMA STD 9) 
               
             
          
           
               
                 Assembly Identification Marking 
                 MIL-STD-130 
               
               
                 Lubrication 
                 Shipped Dry 
               
               
                 Preservation/Packaging 
                 MIL-STD-197 (ITB-4001-PB1) 
               
               
                 Bearing Weight 
                 Approx. .35 LB 
               
               
                 RINGS 
               
               
                 Material/Specification 
                 BG42/AMS-5749 
               
               
                 Heat Treat Condition/Hardness 
                 HRC 60 MIN. 
               
               
                 Shoulder Height, Outer/Inner 
                 25% Roller/50% Ball (Min) 
               
               
                 Raceway Curvature, Inner/Outer 
                 51.4%/52.4% 
               
               
                 ROLLER NUMBER (Nominal Size) 
                 23 (ø5 mm × 6.5 mm L) 
               
               
                 Material/Specification 
                 BG42/AMS-5749 
               
               
                 Heat Treat Condition/Hardness 
                 HRC 60 MIN. 
               
               
                 Diameter Variation Per Set 
                 .000100 
               
               
                 BALL NUMBER (Diameter) 
                 24 (ø 3/16″) 
               
               
                 Material/Specification 
                 Si 3 N 4 /ASTM-F2094, Class II 
               
               
                 Heat Treat Condition/Hardness 
                 N/A 
               
               
                 Balls Precision Grade 
                 Grade 24C or Better 
               
               
                 (ABMA STD #10) 
               
               
                 SEALS, SHIELDS 
                 N/A 
               
               
                 Materials/Specification 
                 N/A 
               
               
                 Style 
                 N/A 
               
               
                   
               
             
          
         
       
     
     A bearing as in Table 1A may have a diametral clearance (after plating) of about 10 micrometers (um) to about 40 um (about 0.0004-0.0016 in.) for the rollers and about (about 0.0021-about 0.0037 in.) for the balls. 
     A particular example of a bearing as described by Table 1A is depicted in  FIG. 5 . Bearing  510  comprises an inner ring  512  and an outer ring  514 . The inner ring  512  and the outer ring  514  cooperate to define a raceway for a set of balls  516  with contact angles a. The outer ring  514  defines a guide channel  518  for a set of rollers  520  that have axes of rotation AR. The bearing  510  has an axial width W of about 1.6 cm (about 0.625 in.). The outer ring  514  has an outside diameter D o  of about 2 inches, while the inner ring  514  has an inside diameter Di of about 2.5 cm (about 1 in.). The centers of the balls  516  are disposed in an annual configuration in which their centers disposed along a circle having a diameter D BC  of about 3.73 cm (about 1.47 in.), whereas the rollers  520  are disposed in an annular configuration in which their axes of rotation disposed along a cylinder having a diameter D AR  of about 3.7 cm (about 1.46 in.). 
     Bearing  510  is expected to have the following bearing loads carrying capacities (static) as shown in Table 1B, where it is assumed that radial capacities are additive and two bearings will share a total radial load and the axial load may be borne by either bearing: 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1B 
               
               
                   
                   
               
               
                   
                 Radial 
                 Axial 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Ball row 
                 6.8 kiloNewtons (kN) 
                 28.7 kN (6458 lbs) 
               
               
                   
                   
                 (1539 pounds (lbs)) 
               
               
                   
                 Roller row 
                 2.5 kN (5544 lbs) 
                 n/a 
               
               
                   
                 Per bearing 
                 3.5 kN (7083 lbs) 
                 28.7 kN (6458 lbs) 
               
               
                   
                   
               
             
          
         
       
     
     In other specific embodiments, such bearings may have one or more of the characteristics set forth in the following Table 2A (in which dimensions are stated in inches, unless otherwise indicated). 
     
       
         
               
               
               
             
               
               
             
           
               
                 TABLE 2A 
               
               
                   
               
             
             
               
                 Contact Angle 
                 45° 
                 [DEG] 
               
               
                 Preload, Axial 
                 N/A 
                 [LB] 
               
               
                 Preload, Radial 
                 N/A 
                 [LB] 
               
               
                 Dynamic Load Rating Radial/Axial 
                 N/A 
                 [LB] 
               
               
                 (ABMA STD 9) 
               
             
          
           
               
                 Assembly Identification Marking 
                 MIL-STD-130 
               
               
                 Lubrication 
                 Shipped Dry 
               
               
                 Preservation/Packaging 
                 MIL-DTL-197 (ITB-4001-PB1) 
               
               
                 Bearing Weight 
                 Approx. .062 LB 
               
               
                 RINGS 
               
               
                 Material/Specification 
                 BG42/AMS-5749 
               
               
                 Heat Treat Condition/Hardness 
                 HRC 60 Min. 
               
               
                 Shoulder Height, Outer/Inner 
                 25% Roller/50% Ball (Min.) 
               
               
                 Raceway Curvature, Inner/Outer 
                 51.4%/52.4% 
               
               
                 Roller Number (Nominal Size) 
                 19 (ø5 mm × 5 MM L) 
               
               
                 Material/Specification 
                 BG42/AMS-5749 
               
               
                 Heat Treat Condition/Hardness 
                 HRC 60 Min. 
               
               
                 Diameter Variation Per Set 
                 .000100 
               
               
                 BALL NUMBER (Diameter) 
                 28 (ø⅛″) 
               
               
                 Material/Specification 
                 Si 3 N 4 /ASTM-F2094, Class II 
               
               
                 Heat Treat Condition/Hardness 
                 N/A 
               
               
                 Balls Precision Grade 
                 Grade 24C or Better 
               
               
                 (ABMA STD #10) 
               
               
                 SEALS, SHIELDS 
                 N/A 
               
               
                 Material/Specification 
                 N/A 
               
               
                 Style 
                 N/A 
               
               
                   
               
             
          
         
       
     
     A bearing as in Table 1A may have a diametral clearance (after plating) of up to about 40 um (about 0.0016 in.) for the rollers and about 53 to about 78.7 um (about 0.0021-about 0.0031 in.) for the balls. 
     In a particular embodiment of a bearing characterized in Table 2A, bearing  610  has an axial width W of about 1.2 cm (about 0.47 in.), an outside diameter Do of about 4.13 cm (about 1.625 in.), and an inside diameter Di of about 1.9 cm (about 0.75 in.). The centers of the balls  616  are disposed in an annual configuration having a diameter D BC  of about 1.14 inch, whereas the rollers  620  are disposed in an annular configuration in which their axes of rotation have a radius D AR  of about 3 cm (about 1.2 in.). 
     Bearing  610  is expected to have the following bearing loads carrying capacities (static) as shown in Table 2B, where it is assumed that radial capacities are additive and two bearings will share a total radial load and the axial load may be borne by either bearing: 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2B 
               
               
                   
                   
               
               
                   
                 Radial 
                 Axial 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Ball row 
                 3.24 kN (729 lbs) 
                 16.2 kN (3646 lbs) 
               
               
                   
                 Roller row 
                 15.7 kN (3526 lbs) 
                 n/a 
               
               
                   
                 Per bearing 
                 18.9 kN (4255 lbs) 
                 16.2 kN (3646 lbs) 
               
               
                   
                   
               
             
          
         
       
     
     In other embodiments, the balls, rollers and rings may be made from other materials. 
     A ground-based power generation system in which a ball-roller bearing-mounted butterfly valve may be used is disclosed in U.S. Pat. No. 5,953,898 to Dryden, dated Sep. 21, 1999, which is hereby incorporated herein by reference.  FIGS. 2 and 3  of the Dryden patent show the use of a butterfly valve for controlling hot flue gas flow prior to discharge. The butterfly valve may be equipped with a ball-roller bearing as described herein, as shown in any one of  FIGS. 1-4  of this application. 
     The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. In addition, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. 
     Although the invention has been described with reference to particular embodiments thereof, it will be understood by one of ordinary skill in the art, upon a reading and understanding of the foregoing disclosure, that numerous variations and alterations to the disclosed embodiments will fall within the spirit and scope of this invention and of the appended claims.