WELDED TYPE FRANCIS RUNNER
United States Patent 3797965
A welded type Francis runner adapted to be sectionalized into a plurality of units for transportation wherein the crown ring and the band ring of said runner are sectionalized along a plane in the direction of the axis of said runner, but the blades of said runner are not sectionalized.
US Patent References:
Method of production of turbine blandes
Murray - March 1929 - 1706703
Method of making turbine blades
Back - October 1931 - 1829179
Hydraulic machine
Baumann - July 1935 - 2006340
Wide propeller blade manufacture
Gruetjen - January 1949 - 2457889
Runner for hydraulic machines having a center portion and an outer segmented portionsecured together to provide an assembled runner
Schmidt - March 1957 - 2784936
Method of production of turbine blandes
Murray - March 1929 - 1706703
Method of making turbine blades
Back - October 1931 - 1829179
Hydraulic machine
Baumann - July 1935 - 2006340
Wide propeller blade manufacture
Gruetjen - January 1949 - 2457889
Runner for hydraulic machines having a center portion and an outer segmented portionsecured together to provide an assembled runner
Schmidt - March 1957 - 2784936
Inventors:
Tonooka, Hidenori (Hitachi, JA)
Okuni, Tetsuo (Hitachi, JA)
Ito, Hideo (Hitachi, JA)
Kawano, Michitada (Hitachi, JA)
Jimbo, Tadashi (Hitachi, JA)
Fukasu, Shunichi (Tokyo, JA)
Okuni, Tetsuo (Hitachi, JA)
Ito, Hideo (Hitachi, JA)
Kawano, Michitada (Hitachi, JA)
Jimbo, Tadashi (Hitachi, JA)
Fukasu, Shunichi (Tokyo, JA)
Application Number:
05/146068
Publication Date:
03/19/1974
Filing Date:
05/24/1971
View Patent Images:
Export Citation:
Assignee:
Hitachi, Ltd. (Tokyo, JA)
Primary Class:
Other Classes:
416/233, 416/213R
International Classes:
F03B3/12; F03B3/00; F01D5/14
Field of Search:
416/186,190,233,213,232 29/156.8R
US Patent References:
Primary Examiner:
Powell Jr., Everette A.
Attorney, Agent or Firm:
Craig, And Antonelli
Parent Case Data:
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of the copending U.S. Pat. application Ser. No. 854,220 filed on Aug. 29, 1969, now abandoned.
Claims:
What is claimed is
1. A welded type Francis runner comprising: a crown ring adapted to be carried by a main shaft extending along the axis of said runner, said crown ring including an outer peripheral ring having a cylindrical seal extending in parallel with the axis of said runner to prevent water from flowing in large quantity into the interior of said crown ring and a runner boss disposed within said outer peripheral ring and provided with means for fastening said runner boss to said main shaft; a plurality of blades in a predetermined contour equiangularly disposed around the axis of said runner and fixed at their one ends to the undersurface of said crown ring; and a band ring to which are fixed the other ends of said plurality of blades; wherein each of said plurality of blades consists of five separate parts connected together, each of said plurality of blades having a hollow portion formed on the side of said blade facing the entering flow and adjacent said crown ring, said hollow portion being formed by first and second of said five separate parts constructed as a pair of steel plates which are press-formed into a predetermined contour forming a leading edge section of said blade, said steel plates having a sufficient strength to withstand the water pressure and being joined together with deposit metal, a third of said five separate parts being a steel plate connected to both of said first and second parts to form a trailing edge of said blade immediately adjacent said hollow portion, fourth and fifth of said five separate parts being connected together to form a solid blade portion exhibiting a solid blade cross-section and extending from said band ring to said hollow portion, said fourth and fifth parts being connected to said first, second and third parts, the thickness of each of said blades being gradually reduced from parts, the thickness of each of said blades being gradually reduced from the side of said crown ring toward the side of said band ring.
2. A welded type Francis runner as specified in claim 1 wherein
3. A welded type Francis runner as specified in claim 1, wherein
4. A welded type Francis runner as specified in claim 1, wherein said outer peripheral ring, said runner boss and said band ring are sectionalized into at least two sections along at least one common plane which contains the axis of said runner, wherein portions of both ends of respective edge blades located adjacent edges of said sections extend beyond said edges at one side of said plane, said edge blades being fixedly connected to the rings of their respective sections along those end portions of the edge blades other than said extended portions, the edges of said rings extending along said common plane in the assembled condition, and wherein said sections are joined together along said common plane by fastening means with said extended portions of the blades being joined to corresponding aligned portions of said rings of respective adjacent sections with deposit metal.
5. A welded type Francis runner as specified in claim 1, wherein said fourth part is a cast steel member which forms the flow entering section of the blade on the side of the blade adjacent said band ring, wherein said third part is a steel plate which forms the flow discharge section of the blade on the side of the blade adjacent said crown ring, wherein said fifth part is a further steel plate which forms the flow discharge section of the blade on the side of the blade adjacent said band ring, wherein each of said steel plates are press-formed into predetermined contours respectively, and wherein a stainless steel plate is overlaid on the rear surface of said fifth part relative to the direction of water flow, the width of said discharge section formed with said third and fifth parts being so increased from the side of said crown ring toward the side of said band ring that said blade has a substantial constant thickness from the side of said crown ring toward the side of said band ring along the line between said discharge section and said entering section formed with said first and second parts and said fourth part.
1. A welded type Francis runner comprising: a crown ring adapted to be carried by a main shaft extending along the axis of said runner, said crown ring including an outer peripheral ring having a cylindrical seal extending in parallel with the axis of said runner to prevent water from flowing in large quantity into the interior of said crown ring and a runner boss disposed within said outer peripheral ring and provided with means for fastening said runner boss to said main shaft; a plurality of blades in a predetermined contour equiangularly disposed around the axis of said runner and fixed at their one ends to the undersurface of said crown ring; and a band ring to which are fixed the other ends of said plurality of blades; wherein each of said plurality of blades consists of five separate parts connected together, each of said plurality of blades having a hollow portion formed on the side of said blade facing the entering flow and adjacent said crown ring, said hollow portion being formed by first and second of said five separate parts constructed as a pair of steel plates which are press-formed into a predetermined contour forming a leading edge section of said blade, said steel plates having a sufficient strength to withstand the water pressure and being joined together with deposit metal, a third of said five separate parts being a steel plate connected to both of said first and second parts to form a trailing edge of said blade immediately adjacent said hollow portion, fourth and fifth of said five separate parts being connected together to form a solid blade portion exhibiting a solid blade cross-section and extending from said band ring to said hollow portion, said fourth and fifth parts being connected to said first, second and third parts, the thickness of each of said blades being gradually reduced from parts, the thickness of each of said blades being gradually reduced from the side of said crown ring toward the side of said band ring.
2. A welded type Francis runner as specified in claim 1 wherein
3. A welded type Francis runner as specified in claim 1, wherein
4. A welded type Francis runner as specified in claim 1, wherein said outer peripheral ring, said runner boss and said band ring are sectionalized into at least two sections along at least one common plane which contains the axis of said runner, wherein portions of both ends of respective edge blades located adjacent edges of said sections extend beyond said edges at one side of said plane, said edge blades being fixedly connected to the rings of their respective sections along those end portions of the edge blades other than said extended portions, the edges of said rings extending along said common plane in the assembled condition, and wherein said sections are joined together along said common plane by fastening means with said extended portions of the blades being joined to corresponding aligned portions of said rings of respective adjacent sections with deposit metal.
5. A welded type Francis runner as specified in claim 1, wherein said fourth part is a cast steel member which forms the flow entering section of the blade on the side of the blade adjacent said band ring, wherein said third part is a steel plate which forms the flow discharge section of the blade on the side of the blade adjacent said crown ring, wherein said fifth part is a further steel plate which forms the flow discharge section of the blade on the side of the blade adjacent said band ring, wherein each of said steel plates are press-formed into predetermined contours respectively, and wherein a stainless steel plate is overlaid on the rear surface of said fifth part relative to the direction of water flow, the width of said discharge section formed with said third and fifth parts being so increased from the side of said crown ring toward the side of said band ring that said blade has a substantial constant thickness from the side of said crown ring toward the side of said band ring along the line between said discharge section and said entering section formed with said first and second parts and said fourth part.
Description:
BACKGROUND OF THE INVENTION
Recently more larger and larger machinery and equipment are installed in hydraulic power plants, and the runners accordingly become large size so that there arises the problem for transportation of runners.
In general many runners each comprising a crown ring, a plurality of runner blades and a band ring, are made of cast-steel, but in case of very large runners there arises the difficulty of casting each component part into one piece and of transporting such large size runners to the power plants. To overcome this difficulty, the runners have been previously sectionalized into a plurality of units for transportation to the power plants where the units are assembled into a runner by welding or other manners.
In the conventional Francis type runners their blades are also sectionalized at the same time that the runners are sectionalized and assembled by welding at the power plants or installation sites. However, the runner blades have a very complex profile and are easily susceptible to distortions when welded, so that they are difficult to be assembled exactly as designed. Therefore, the efficiency is inevitably dropped. Furthermore welding is followed by laborious hand-finishing the surface of the blade, especially the welded joints, which for example takes about 8,000 hours in case of a unit as large as 160,000 kilo watts. To overcome this problem, there has been proposed a method in which the blades are not sectionalized and the crown ring and the band ring are sectionalized by a plurality of planes containing the lines along which the runner blades are welded to the crown and band rings. However, this method has been found unsatisfactory because of the complex contour of the runner blades. In general the sectionalized units are assembled together by bolting flanges provided on the units respectively or welding, but when the runner is sectionalized by the planes containing the lines along which the blades are joined to the crown and band rings as described above, it is extremely difficult to form these flanges. Furthermore, it becomes difficult to align the axis of the bolt with the direction in which the centrifugal force produced when the runner is rotated exerts upon the units. Even when welding is employed instead of bolting for assembly of the units, it is apparent that welding may be much simplified when the weld lines are straight rather than curved.
As described above, many difficulties arise in fabrication of very large runners so that there has been employed a method for sectionalizing or subassemblying the crown and band rings of the runners and welding these subassemblies and the runner blades into a runner. Meanwhile, in order to reduce the weight of large size runners, there has been proposed to use the hollow runners. In this manner, the large capacity presses must be employed in order to form a crown ring from one steel plate so that the very large dies must be prepared, but they are very expensive. Therefore, it is desired to press-form steel plates by a small press. The same is true in case of the hollow large blades formed by putting two sheets of steel plate together.
SUMMARY OF THE INVENTION
Therefore one of the objects of the present invention is to provide a welded type Francis runner comprising subassemblies which may be transported in a simple manner and assembled together on an installation site by welding without adversely thermally affecting the blades.
Another object of the present invention is to provide a method for manufacture of a welded type Francis runner and especially of a crown ring and blades of a very large welded type Francis runner.
Another object of the present invention is to provide a welded type Francis runner light in weight compared to its dimmensions.
Briefly stated, the present invention provides a welded type Francis runner adapted to be sectionalized into a plurality of units in which its crown ring and band ring are sectionalized along a plane in the direction of the axis of the runner, but the runner blades are not sectionalized by this plane.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a side view illustrating a subassembly which comprises one half of a welded type Francis runner in accordance with the present invention;
FIG. 2 is a side view illustrating a subassembly which comprises one quarter of a welded type Francis runner in accordance with the present invention;
FIG. 3 is a top view thereof;
FIG. 4 is a sectional view taken along the line IV -- IV of FIG. 1;
FIG. 5 is a fragmentary perspective view illustrating a portion of a runner blade nearer to the crown ring; and
FIG. 6 is a fragmentary perspective view illustrating a portion of the runner blade nearer to the band ring;
FIG. 7 is a perspective view illustrating a subassembly which comprises one half of a welded type Francis runner in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a crown ring generally indicated by 5 comprises a runner boss 6 of cast steel having a plurality of internally threaded holes 23 which are used for mounting the crown ring 5 on a shaft (not shown), a ring 7 consisting of a plurality of steel plates, which are welded together and to the outer periphery of the boss 6 at 30 and an outer peripheral ring 8 which consists of a plurality of structural members welded together and to the outer periphery of the ring 7 at 31 and has a cylindrical seal 22 extending from the outer periphery of the ring 8 in parallel with the axis of the runner. The cylindrical seal 22 serves to prevent a large amount of water from entering into the interior of the runner. To facilitate the transportation of the welded type Francis runner, it is linearly sectionalized or subassembled into one half as shown in FIGS. 1 and 7 or into one quarter as shown in FIGS. 2 and 3, and these sectionalized or subassembled structual members are welded together or joined together at flanges 20 by bolts and nuts at a plant.
A plurality of runner blades 9, the detail of which are illustrated in FIGS. 4 - 6, are welded at 36 to the undersurface of the crown ring 5, which is assembled into a unitary construction as described above. Each of the runner blades 9 comprises steel plates 10, 12, 15 and 17 which are press-formed into a predetermined shape, a cast-steel member 11 and a stainless steel member 13 over layed upon one surface of the steel plate 17 by explosion welding. As shown in FIG. 5, the steel plates 10 and 15, which are press-formed to have a predetermined profile and a hollow A, are welded together at 32. It is noted that the width of the hollow A is gradually reduced toward a band ring 14 as indicated by the broken lines in FIG. 5 and that the cast-steel member 11, which are welded to the steel plates 10 and 15, is not provided with a hollow. The reasons why the runner blades are formed in such manner as described above are that the high pressure generally exerts on the blades 9 on the side of the crown ring 5 while the low pressure on the side of the band ring 14 so that the thickness of the blade at one end thereof to be joined to the crown ring 5 must be increased as practicably as possible to increase the strength at the joint, but the section of the blade on the side of the band ring 14 may have a sufficiently high strength even though its thickness is too thinner to form a hollow.
The pressed-steel plates 12 and 17 are welded to the discharge sides of the steel plates 10 and 15 and the cast steel member 11 at 34 and 35 respectively. One end of the steel plate 12 is welded to the runner boss 6 at 37 while the other end to the steel plate 17 at 38, thereby forming the discharge section of the blade 9. As previously described, the stainless steel plate 13 is welded upon the face of the steel plate 17 by explosion welding, and this face is the rear surface of the steel plate 17 relative to the direction of water flow. The stainless steel 13 welded on the rare face of the steel plate 17 serves to encounter the cavitation. In the type Francis runners, the cavitation generally occurs due to that the blades of this type have a complex profile and that the peripheral speed of the blades on the side of the band ring 14 is greater than that of the blades on the side of the crown ring 5. As a result, negative pressure exerts on the rear surface of the steel plate 17 to cause cavitation.
In the instant embodiment, the stainless steel plate 13 extends approximately one half of the length of the blade 9, but in actual practice the cativation occurs at a smaller portion on the side of the band ring 14. In the embodiment the stainless steel plate 13 is shown as being welded to the blade beyond such a small portion at which the cavitation most frequently occurs because the blade of present invention consists of a plurality of sectionalized structual members and the explosion welding is employed as described above. Therefore when the blade is formed from one steel plate, stainless steel may be, for example, overlaid at a portion at which the cavitation tends to occur very often.
In the instant embodiment, the steel plates 12 and 17, which form the discharge section of the blade 9, have their width increased as they approach toward the band ring 14 from the crown ring 5. As described previously, the thickness of the blade is gradually made thinner as it approaches toward the band ring 14 from the crown ring 5. As a consequence, when the steel plates 12 and 17 having the same thickness along the entrance edges are to be welded to the steel plates 10 and 15 and the cast-steel member 11, there is a difference in thickness between them along the weld lines, so that the distortion caused by the weldings is inevitably increased. As shown in FIGS. 3, 4 and 5, the blade 9 has an air foil cross-section so that when the weld line is so selected as to approach nearer to the center-line in the direction of length of the blade as it approaches toward the band ring 14, the thickness at the discharge edges of the steel plates 10 and 15 and the cast-steel member 11 becomes equal to that of the discharge section forming members 12 and 17. In other words, the width of the members 12 and 17 is gradually increased as they approach toward the band ring 14, whereby they may be welded to the steel plates 10 and 15 and to the cast-steel member 11 with their surfaces flushed and the distortion caused by weldings may be minimized.
The surface of the cast-steel member 11 is hand-finished, but the steel plates 10, 12, 15 and 17 and the stainless steel plate 13 are all press-formed so that the hand finishing may be eliminated. Therefore the time required for fabrication of the blades 9 may be much reduced. If a high-capacity machine press is employed to form one-piece blades the production time may be further reduced. If the hollow A is not preferable from the standpoint of mechanical strength the stiffners such as round bars may be fixed to the holes formed through the steel plates 10 and 15 to extend across the hollow A and welded to the plates 10 and 15. Thus the blades 9 may be reinforced in a simple manner. The provision of the hollow A is advantageous in that the weight of the blade may be reduced. The discharge-section is of course formed by the use of the plates 10 and 15. In the instant embodiment, however, the steel plates 12 and 17 are employed because the discharge edge is long and because of the welding techniques.
Although in the above-mentioned embodiment the hollow blades are composed of steel plates and casting plates, it goes without saying that the blades can be produced by only the steel plates.
The other ends of the blades 9 whose one ends are welded to the crown ring 5 as described above are welded to the band ring 14. That is, the cast-steel members 11 are welded at deposite metal 39 to the band ring 14 while the steel plates 17 and the stainless steel plates 13 welded on the faces thereof are welded to the band ring 14 at deposite metal 40.
The band ring 14 also consists of a plurality of sectionalized structural members as in the case of the crown ring 5 to facilitate the transportation of the runner. The structural members may be welded or bolted together through holes 24 at flanges 21.
The Francis runner in accordance with the present invention comprises the crown ring 5 and the band ring 14, each of which consists of a predetermined number of sectionalized or subassembled structual units for facilitating the transportation, and a plurality of blades 9 which are secured between the crown ring 5 and the band ring 14 by welding or other fixing manners. The contour of the one end of the blade 9 to be joined to the crown ring 5 is greatly different from that of the other end of the blade 9 to be joined to the band ring 14. In addition, the position of the one end of the blade 9 to be joined to the crown ring 5 is greatly different from that of the other end to be joined to the band ring 14. Therefore, if both of the crown ring 5 and the band ring 14 are sectionalized by one plane, this sectionalizing plane will not pass through both of the joints between the blades 9 and the crown and band rings 5 and 14. However, according to the instant embodiment, the runner is sectionalized into a plurality of structual members by a plurality of planes which are in parallel with the axis of the runner, but the blades 9 are not sectionalized or divided into a plurality of structual members even though they intersect the sectionalizing planes and bridges the adjacent two crown and band ring units 5 and 14.
Both of the ends of the blade 9 which intersects the sectionalizing plane are partly welded to the crown and band ring subassemblies and the portions of the ends of the blade to be joined to the adjoining crown and band ring units are free ends. That is, as shown in FIGS. 2, 3 and 7, some portions of the ends of the blade 9 extend beyond the boundaries of the subassemblies of the crown and band rings 5 and 14 and these extended portions are welded to the adjoining subassemblies at the installation site.
As described above, the subassemblies of the crown and band rings 5 and 14 are prepared by sectionalizing them by vertical planes for facilitating the transportation, but the blades 9 are not sectionalized at all, so that they are not distorted when welded. In addition, it is not necessary to finish the blade members at the installation site, and the welding along the straight weld lines in case of assemblying the crown and band rings may be automated so that the welding time and hance the installation time may be much reduced. Even when the subassemblies are joined together at the flanges 20 and 21, the joining lines are straight so that the bolts may be easily positioned with respect to the direction in which the subassemblies tend to separate from each other under the centrifugal force.
The blades 9 may be constructed by assembling the steel plates and the cast-steel structual members so as to form the hollow portion within the blade at a portion where the thickness of the blade is thick. In addition large runners may be constructed by employing small capacity presses, which means that large runners may be constructed economically.
The subassemblies are assembled by welding or by bolting at the flanges as described above, and in general the subassemblies of the band ring 14 whose wall thickness is thinner than that of the crown ring 5 are welded together while the crown ring subassemblies are joined together by bolting at the flanges. However when the runners are used in pump turbines, the band ring 14 is longer in the direction at a right angle to the axis of the runner so that the band ring is assembled by bolting. In some cases, both of the subassemblies of the crown and band rings are assembled by welding. However, it should be noted that the blades are welded to the crown and band rings.
It is understood that the blades having hollows, may also be used in the runners of the type in which their crown and band rings do not consist of the subassemblies.
Recently more larger and larger machinery and equipment are installed in hydraulic power plants, and the runners accordingly become large size so that there arises the problem for transportation of runners.
In general many runners each comprising a crown ring, a plurality of runner blades and a band ring, are made of cast-steel, but in case of very large runners there arises the difficulty of casting each component part into one piece and of transporting such large size runners to the power plants. To overcome this difficulty, the runners have been previously sectionalized into a plurality of units for transportation to the power plants where the units are assembled into a runner by welding or other manners.
In the conventional Francis type runners their blades are also sectionalized at the same time that the runners are sectionalized and assembled by welding at the power plants or installation sites. However, the runner blades have a very complex profile and are easily susceptible to distortions when welded, so that they are difficult to be assembled exactly as designed. Therefore, the efficiency is inevitably dropped. Furthermore welding is followed by laborious hand-finishing the surface of the blade, especially the welded joints, which for example takes about 8,000 hours in case of a unit as large as 160,000 kilo watts. To overcome this problem, there has been proposed a method in which the blades are not sectionalized and the crown ring and the band ring are sectionalized by a plurality of planes containing the lines along which the runner blades are welded to the crown and band rings. However, this method has been found unsatisfactory because of the complex contour of the runner blades. In general the sectionalized units are assembled together by bolting flanges provided on the units respectively or welding, but when the runner is sectionalized by the planes containing the lines along which the blades are joined to the crown and band rings as described above, it is extremely difficult to form these flanges. Furthermore, it becomes difficult to align the axis of the bolt with the direction in which the centrifugal force produced when the runner is rotated exerts upon the units. Even when welding is employed instead of bolting for assembly of the units, it is apparent that welding may be much simplified when the weld lines are straight rather than curved.
As described above, many difficulties arise in fabrication of very large runners so that there has been employed a method for sectionalizing or subassemblying the crown and band rings of the runners and welding these subassemblies and the runner blades into a runner. Meanwhile, in order to reduce the weight of large size runners, there has been proposed to use the hollow runners. In this manner, the large capacity presses must be employed in order to form a crown ring from one steel plate so that the very large dies must be prepared, but they are very expensive. Therefore, it is desired to press-form steel plates by a small press. The same is true in case of the hollow large blades formed by putting two sheets of steel plate together.
SUMMARY OF THE INVENTION
Therefore one of the objects of the present invention is to provide a welded type Francis runner comprising subassemblies which may be transported in a simple manner and assembled together on an installation site by welding without adversely thermally affecting the blades.
Another object of the present invention is to provide a method for manufacture of a welded type Francis runner and especially of a crown ring and blades of a very large welded type Francis runner.
Another object of the present invention is to provide a welded type Francis runner light in weight compared to its dimmensions.
Briefly stated, the present invention provides a welded type Francis runner adapted to be sectionalized into a plurality of units in which its crown ring and band ring are sectionalized along a plane in the direction of the axis of the runner, but the runner blades are not sectionalized by this plane.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a side view illustrating a subassembly which comprises one half of a welded type Francis runner in accordance with the present invention;
FIG. 2 is a side view illustrating a subassembly which comprises one quarter of a welded type Francis runner in accordance with the present invention;
FIG. 3 is a top view thereof;
FIG. 4 is a sectional view taken along the line IV -- IV of FIG. 1;
FIG. 5 is a fragmentary perspective view illustrating a portion of a runner blade nearer to the crown ring; and
FIG. 6 is a fragmentary perspective view illustrating a portion of the runner blade nearer to the band ring;
FIG. 7 is a perspective view illustrating a subassembly which comprises one half of a welded type Francis runner in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a crown ring generally indicated by 5 comprises a runner boss 6 of cast steel having a plurality of internally threaded holes 23 which are used for mounting the crown ring 5 on a shaft (not shown), a ring 7 consisting of a plurality of steel plates, which are welded together and to the outer periphery of the boss 6 at 30 and an outer peripheral ring 8 which consists of a plurality of structural members welded together and to the outer periphery of the ring 7 at 31 and has a cylindrical seal 22 extending from the outer periphery of the ring 8 in parallel with the axis of the runner. The cylindrical seal 22 serves to prevent a large amount of water from entering into the interior of the runner. To facilitate the transportation of the welded type Francis runner, it is linearly sectionalized or subassembled into one half as shown in FIGS. 1 and 7 or into one quarter as shown in FIGS. 2 and 3, and these sectionalized or subassembled structual members are welded together or joined together at flanges 20 by bolts and nuts at a plant.
A plurality of runner blades 9, the detail of which are illustrated in FIGS. 4 - 6, are welded at 36 to the undersurface of the crown ring 5, which is assembled into a unitary construction as described above. Each of the runner blades 9 comprises steel plates 10, 12, 15 and 17 which are press-formed into a predetermined shape, a cast-steel member 11 and a stainless steel member 13 over layed upon one surface of the steel plate 17 by explosion welding. As shown in FIG. 5, the steel plates 10 and 15, which are press-formed to have a predetermined profile and a hollow A, are welded together at 32. It is noted that the width of the hollow A is gradually reduced toward a band ring 14 as indicated by the broken lines in FIG. 5 and that the cast-steel member 11, which are welded to the steel plates 10 and 15, is not provided with a hollow. The reasons why the runner blades are formed in such manner as described above are that the high pressure generally exerts on the blades 9 on the side of the crown ring 5 while the low pressure on the side of the band ring 14 so that the thickness of the blade at one end thereof to be joined to the crown ring 5 must be increased as practicably as possible to increase the strength at the joint, but the section of the blade on the side of the band ring 14 may have a sufficiently high strength even though its thickness is too thinner to form a hollow.
The pressed-steel plates 12 and 17 are welded to the discharge sides of the steel plates 10 and 15 and the cast steel member 11 at 34 and 35 respectively. One end of the steel plate 12 is welded to the runner boss 6 at 37 while the other end to the steel plate 17 at 38, thereby forming the discharge section of the blade 9. As previously described, the stainless steel plate 13 is welded upon the face of the steel plate 17 by explosion welding, and this face is the rear surface of the steel plate 17 relative to the direction of water flow. The stainless steel 13 welded on the rare face of the steel plate 17 serves to encounter the cavitation. In the type Francis runners, the cavitation generally occurs due to that the blades of this type have a complex profile and that the peripheral speed of the blades on the side of the band ring 14 is greater than that of the blades on the side of the crown ring 5. As a result, negative pressure exerts on the rear surface of the steel plate 17 to cause cavitation.
In the instant embodiment, the stainless steel plate 13 extends approximately one half of the length of the blade 9, but in actual practice the cativation occurs at a smaller portion on the side of the band ring 14. In the embodiment the stainless steel plate 13 is shown as being welded to the blade beyond such a small portion at which the cavitation most frequently occurs because the blade of present invention consists of a plurality of sectionalized structual members and the explosion welding is employed as described above. Therefore when the blade is formed from one steel plate, stainless steel may be, for example, overlaid at a portion at which the cavitation tends to occur very often.
In the instant embodiment, the steel plates 12 and 17, which form the discharge section of the blade 9, have their width increased as they approach toward the band ring 14 from the crown ring 5. As described previously, the thickness of the blade is gradually made thinner as it approaches toward the band ring 14 from the crown ring 5. As a consequence, when the steel plates 12 and 17 having the same thickness along the entrance edges are to be welded to the steel plates 10 and 15 and the cast-steel member 11, there is a difference in thickness between them along the weld lines, so that the distortion caused by the weldings is inevitably increased. As shown in FIGS. 3, 4 and 5, the blade 9 has an air foil cross-section so that when the weld line is so selected as to approach nearer to the center-line in the direction of length of the blade as it approaches toward the band ring 14, the thickness at the discharge edges of the steel plates 10 and 15 and the cast-steel member 11 becomes equal to that of the discharge section forming members 12 and 17. In other words, the width of the members 12 and 17 is gradually increased as they approach toward the band ring 14, whereby they may be welded to the steel plates 10 and 15 and to the cast-steel member 11 with their surfaces flushed and the distortion caused by weldings may be minimized.
The surface of the cast-steel member 11 is hand-finished, but the steel plates 10, 12, 15 and 17 and the stainless steel plate 13 are all press-formed so that the hand finishing may be eliminated. Therefore the time required for fabrication of the blades 9 may be much reduced. If a high-capacity machine press is employed to form one-piece blades the production time may be further reduced. If the hollow A is not preferable from the standpoint of mechanical strength the stiffners such as round bars may be fixed to the holes formed through the steel plates 10 and 15 to extend across the hollow A and welded to the plates 10 and 15. Thus the blades 9 may be reinforced in a simple manner. The provision of the hollow A is advantageous in that the weight of the blade may be reduced. The discharge-section is of course formed by the use of the plates 10 and 15. In the instant embodiment, however, the steel plates 12 and 17 are employed because the discharge edge is long and because of the welding techniques.
Although in the above-mentioned embodiment the hollow blades are composed of steel plates and casting plates, it goes without saying that the blades can be produced by only the steel plates.
The other ends of the blades 9 whose one ends are welded to the crown ring 5 as described above are welded to the band ring 14. That is, the cast-steel members 11 are welded at deposite metal 39 to the band ring 14 while the steel plates 17 and the stainless steel plates 13 welded on the faces thereof are welded to the band ring 14 at deposite metal 40.
The band ring 14 also consists of a plurality of sectionalized structural members as in the case of the crown ring 5 to facilitate the transportation of the runner. The structural members may be welded or bolted together through holes 24 at flanges 21.
The Francis runner in accordance with the present invention comprises the crown ring 5 and the band ring 14, each of which consists of a predetermined number of sectionalized or subassembled structual units for facilitating the transportation, and a plurality of blades 9 which are secured between the crown ring 5 and the band ring 14 by welding or other fixing manners. The contour of the one end of the blade 9 to be joined to the crown ring 5 is greatly different from that of the other end of the blade 9 to be joined to the band ring 14. In addition, the position of the one end of the blade 9 to be joined to the crown ring 5 is greatly different from that of the other end to be joined to the band ring 14. Therefore, if both of the crown ring 5 and the band ring 14 are sectionalized by one plane, this sectionalizing plane will not pass through both of the joints between the blades 9 and the crown and band rings 5 and 14. However, according to the instant embodiment, the runner is sectionalized into a plurality of structual members by a plurality of planes which are in parallel with the axis of the runner, but the blades 9 are not sectionalized or divided into a plurality of structual members even though they intersect the sectionalizing planes and bridges the adjacent two crown and band ring units 5 and 14.
Both of the ends of the blade 9 which intersects the sectionalizing plane are partly welded to the crown and band ring subassemblies and the portions of the ends of the blade to be joined to the adjoining crown and band ring units are free ends. That is, as shown in FIGS. 2, 3 and 7, some portions of the ends of the blade 9 extend beyond the boundaries of the subassemblies of the crown and band rings 5 and 14 and these extended portions are welded to the adjoining subassemblies at the installation site.
As described above, the subassemblies of the crown and band rings 5 and 14 are prepared by sectionalizing them by vertical planes for facilitating the transportation, but the blades 9 are not sectionalized at all, so that they are not distorted when welded. In addition, it is not necessary to finish the blade members at the installation site, and the welding along the straight weld lines in case of assemblying the crown and band rings may be automated so that the welding time and hance the installation time may be much reduced. Even when the subassemblies are joined together at the flanges 20 and 21, the joining lines are straight so that the bolts may be easily positioned with respect to the direction in which the subassemblies tend to separate from each other under the centrifugal force.
The blades 9 may be constructed by assembling the steel plates and the cast-steel structual members so as to form the hollow portion within the blade at a portion where the thickness of the blade is thick. In addition large runners may be constructed by employing small capacity presses, which means that large runners may be constructed economically.
The subassemblies are assembled by welding or by bolting at the flanges as described above, and in general the subassemblies of the band ring 14 whose wall thickness is thinner than that of the crown ring 5 are welded together while the crown ring subassemblies are joined together by bolting at the flanges. However when the runners are used in pump turbines, the band ring 14 is longer in the direction at a right angle to the axis of the runner so that the band ring is assembled by bolting. In some cases, both of the subassemblies of the crown and band rings are assembled by welding. However, it should be noted that the blades are welded to the crown and band rings.
It is understood that the blades having hollows, may also be used in the runners of the type in which their crown and band rings do not consist of the subassemblies.