JPH0211746B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for manufacturing a runner for a hydraulic machine,
In particular, the present invention relates to a method of manufacturing a runner for a hydraulic machine in which the openings of sections of rib plates fixed in the circumferential and radial directions of the crown and band surfaces of the splittable runner are covered with cover plates.

[Technical background of the invention]

Generally, large Francis turbine runners are constructed so that they can be divided into multiple runner pieces due to production reasons or transportation requirements, and the multiple runner pieces are manufactured in advance at a factory and then delivered to the site. It is often assembled by transporting it. In this case, flanges are formed at the joints of each runner piece, and during assembly, the flange joint surfaces of the runner pieces are butted against each other.
The flanges are joined together by bolts. When flange-connected in this way, the flange protrudes from the surface of the runner crown or runner band, so when the runner rotates, the protruding flange stirs water, increasing the frictional resistance of the water and reducing hydraulic efficiency. There was a problem.

Therefore, in order to reduce the resistance caused by the protruding flanges, the flange joint portion of the runner is covered with a cover plate so that there are no partial protrusions around the entire periphery of the runner. Figures 1 and 2 show runners of this type of hydraulic machine, in which runner 1 has a runner crown 2a.
It consists of a runner band 2b and a plurality of runner blades 2c held between them. A plurality of rib plates 3 are welded to the upper surface of the runner crown 2a so as to intersect in a grid pattern in the radial and circumferential directions. Each of the openings in the area surrounded by these rib plates 3 is covered by a cover plate 4,
The entire circumferential edges of these cover plates 4 are welded together along welding lines indicated by reference numeral 5 in FIG. By covering the flange joint portion of the split runner with the rib plate 3 and cover plate 4 in this way, the underwater frictional resistance of the runner during rotation can be reduced. Similarly, rib plates 3, 3 are welded together on the runner band 2b side, and a cover plate 4 is applied and the joint portion is welded together. Note that a plurality of balance holes 6 are bored in the cover plate 4 in order to reduce the pressure difference acting on the inner and outer surfaces.

[Problems with background technology]

When the runner 2 configured as described above rotates at high speed underwater, high-frequency water pressure pulsations act on the surface of the cover plate 4, so that the cover plate 4 has the following effects, as shown in FIGS. 3 and 4. High frequency bending moments M _A and M _B are generated. In particular, the repeated stresses σ _C and σ _D generated near the center of the welding sides at both ends of the inner surface of each cover plate 4 are larger than the stresses generated in other parts. This is because the uniform bending stress of the cover plate caused by water pressure is maximum near the center of the welded side of the rib plate, and stress concentration occurs at the inner corner of the cover plate 4. .

Stress concentration also occurs in the balance hole 6 drilled in the cover plate 4 described above, but the stress concentration coefficient K _t of the balance hole portion is approximately equal to the stress concentration coefficient K _t of the circular hole edge in the flat plate that is subjected to bending. Equally about 20. On the other hand, the stress concentration coefficient at the corner reaches a value of 3.0 or more because the deformation of the cover plate 4 is restrained by the rib plate 3 and the radius of curvature at the corner is extremely acute. Become.

For example, in FIG. 5, if the thickness of the cover plate 4 is T, the thickness of the rib plate 3 is t, and the radius of curvature of the corner is r, then the stress concentration coefficient of the corner is K _t
mainly depends on T and r, and can be approximated by the following equation.

K _t = 1 + 0.19 (r / T) ^0.69 ... (1) By the way, in the conventional cover plate, T is 10 mm
As described above, since r is about 0.3 mm or less, K _t has a large value of 3.0 or more.

As described above, as a result of high repeated stress occurring in the welded joint of the cover plate 4 due to stress concentration at the corners, fatigue cracks are likely to occur, and once cracks occur, they propagate rapidly. It has been known. To prevent such dangers,
It is conceivable to increase the thickness of the cover plate 4 to reduce the bending stress, but in this case there are problems in that the weight of the runner increases, the performance of the water turbine decreases, and the manufacturing cost also increases.

〔the purpose〕

Therefore, the present invention aims to reduce the stress concentration coefficient at the welded joint of the cover plate 4 and increase the strength without increasing the thickness of the cover plate 4. An object of the present invention is to provide a method for manufacturing a runner in which grooves at corners are joined by fillet welding in the form of a concave curve, and the radius of curvature thereof is 9% or more of the thickness of a cover plate.

[Summary of the invention]

In order to achieve the above object, a method for manufacturing a runner for a hydraulic machine according to the present invention includes disposing rib plates extending in the circumferential direction and the radial direction on the surfaces of the runner crown and the runner band, and surrounding the runner with these rib plates. In a method for manufacturing a runner for a hydraulic machine in which the openings of the divided sections are covered with cover plates and the joints of each member are welded; Attach the cover plate to the runner, weld the corners of the joint between the two, then finish the welded part so that it becomes a curved surface, and then assemble the other end of the rib plate to the runner crown or runner band. After that, the work opening of the cover plate is covered with a blind lid, and the work opening of the cover plate is then welded and connected.

[Embodiments of the invention]

An embodiment of the method for manufacturing a runner for a hydraulic machine according to the present invention will be described below with reference to FIGS. 6 to 16.

The structure itself of the runner of the hydraulic machine manufactured by the present invention is exactly the same as the conventional one shown in FIGS. 1 and 2, and the runner consists of a runner crown 2a, a runner band 2b, and It is composed of a plurality of runner blades 2c sandwiched between a runner crown 2a and a runner band 2b.
A plurality of rib plates 3 are arranged in the radial and circumferential directions so as to form a grid on the surface. Each of the opening sections corresponding to the grid surrounded by the rib plate 3 is closed by a cover plate 4, and the entire circumferential edge of the cover plate 4 is welded to the rib plate 3. . These rib plates 3 are welded to the cover plate 4 prior to being welded to the runner crown 2a and runner band 2b.

As shown in FIG. 6, the cover plate 4 has an opening 7 for welding work formed approximately in the center thereof.

FIG. 7 is a partially cut away plan view of three adjacent cover plates 4, and this figure shows a state in which the openings 7 are closed with blind lids 8 and welded together, as will be described later. It shows.

Incidentally, before closing the opening 7 with the blind lid 8, as shown in FIGS. 8 and 9, the curvature is A fillet weld with a radius R is performed, and the rib plate 3 is welded to the runner crown 2a or the runner band 2b. The welding work at this time is performed through the opening 7 of the cover plate 4. 8 shows a cross section taken along the line - in FIG. 7, and FIG. 9 shows a cross section taken along the line - in FIG. 7, respectively. As is clear from these figures, a fillet weld 9 with a radius R is applied to the corner groove between the inner surface of the cover plate 4 and the rib plate 3. This radius of curvature R is
According to the above formula (1), the stress concentration is 9% of the plate thickness t of the cover plate 4 by performing cosmetic welding by TIG, or by glider processing or machining after fillet welding, so that the stress concentration is 2 or less. It is desirable to create a smooth curved surface with a value above.

After the welding work at the corner between the inner surface of the cover plate 4 and the rib plate 3 and the curved surface finishing work at the corner are completed, the rib plate 3 is attached to the runner crown 2a or the runner band.
b, and then welded to Figs. 10 and 11.
As shown in the figure, a blind lid 8 is placed over the opening 7 of the cover plate 4, and butt welding is performed along a welding line 10.

FIG. 13 is a distribution diagram schematically showing the uniform bending stress amplitude and the local stress amplitude on the inner surface of the cover plate 4, and the local stress amplitude on the inner surface of the cover plate 4 is shown by the two-dot chain line. In the stress concentrated part, the amplitude becomes larger than the uniform bending stress amplitude according to the following equation.

Local stress amplitude = stress concentration factor × uniform bending stress amplitude ... (2) In the case shown in Figs. 2 to 4, the stress concentration factor K _t1 at the corner is 3.0 or more, so the Fatigue cracks occur as a result of exceeding the fatigue strength of the cover plate material indicated by the dashed line F in the figure. In the same figure, K _t2 is the stress concentration coefficient corresponding to the radius of curvature at the corner, but the radius of curvature at the corner in those shown in FIGS. 6 to 9 is 9% of the thickness of the cover plate 4. As above,
K _t2 is 2.0 or less from the above equation (1), and the larger the radius of curvature, the smaller K _t2 becomes. Therefore,
The local stress near the center of the weld edge where the uniform bending stress within the cover plate plane is maximum is the balance hole 6.
Regardless of the position of the cover plate 4, the fatigue strength can be kept lower than the edge of the balance hose 6 and lower than the fatigue strength of the material of the cover plate 4 shown by the dashed line F in FIG. do not have. On the other hand, K _t3 is a stress concentration coefficient corresponding to the protrusion 10a of the weld line 10, and its value is
Depending on the shape of a, there may be as many as 3 to 4. However, the welded portion having this protrusion 10a is
As shown in FIG. 13, since the cover plate 4 is disposed at a position where the uniform bending stress is extremely low, the local stress amplitude is smaller than the value at the corner, and fatigue cracks do not occur.

FIG. 12 shows three opening sections 11, 11, 11 adjacent in the circumferential direction as another embodiment, in which each opening section 11 has an inner circumferential rib plate 12 and an outer circumferential rib plate 13. and radial side rib plates 14, 14 on both sides. The cover plate that covers the opening of the opening section 11 is composed of an inner cover plate 15, an outer cover plate 16, and an intermediate cover plate 18 that is arranged directly above the radial rib plate 14 and connects the inner and outer cover plates 15 and 16. Ru.

In actual manufacturing, as shown in FIG. 14, the inner edge of the inner cover plate 15 and the upper edge of the inner rib plate 12 are butted at right angles, and the grooves at the inner corners of both are aligned. Perform fillet welding with radius of curvature R. Similarly, the outer edge of the outer cover plate 16 and the upper edge of the outer peripheral rib plate 13 are abutted at right angles, and fillet welding with a radius of curvature R is performed on the grooves at the inner corners of both. It is desirable that the radius of curvature R of each of the fillet welds be formed into a concave curved surface that is 9% or more of the thickness of the cover plates 15 and 16. These welds are TIG
It is desirable to finish the curved surface into a smooth curved surface by performing cosmetic welding or by grinding or machining after fillet welding. Furthermore, at this welding stage, the inner peripheral rib plate 12 and the outer peripheral rib plate 13 are not welded to the crown or band surface of the runner, making it easy to automate fillet welding and finish curved surfaces by machining after fillet welding. Can be done. Therefore, it is relatively easy to finish a convexly curved fillet weld into a concave curved surface having a predetermined curvature, and actual measurement and management of the radius of curvature is extremely easy.

On the other hand, directly above the radial rib plate 14, the center portion of the intermediate cover plate 18 is brought into contact in a T-shape, and fillet welding is performed on the inner corner portion as described above. Note that a portion of the radial rib plate 14 is cut out for attaching a scallop 19.

Therefore, for example, in order to weld the inner rib plate 12 to the surface of the runner crown 2a, the inner peripheral rib plate 12 to which the inner cover plate 15 is welded is placed on the runner crown 2a, and fillet welding is performed at the inner and outer corners. Next, the radial rib plate 14 formed by welding the intermediate cover plate 18 is butted against both ends of the inner peripheral rib plate 12, and fillet welded to the runner crown 2a. Further, the outer peripheral rib plate 13 to which the outer cover plate 16 is welded is brought into contact with the outer end of the radial rib plate 14 to weld and connect the adjacent members. At this time, the outer peripheral rib plate 13 and the runner crown 2a
When welding the inner corner with the welding opening 7
It is necessary for a worker to enter the opening section through the welding section to perform welding work.

Finally, attach the blind lid 8 to the welding opening 7 formed in the cover plate, and connect the outer periphery of the blind lid 8 to the welding line 2.
The work is completed by welding the inner cover plate 15, the outer cover plate 16, and the left and right intermediate cover plates 18 along the line 0. FIGS. 15 and 16 show cross sections of welded joints according to this embodiment. The welding work procedure is not limited to the above-mentioned one, but the assembly procedure may be designed to minimize the welding work from within the opening section.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the rib plate surrounding the opening section and the cover plate are welded together before being welded to the runner crown or the runner band, and Since the curvature of the concave curved surface of the fillet weld is 9% or more of the thickness of the cover plate, the welding work is extremely easy and can be automated. As a result, it becomes possible to provide an accurate curvature to the welded joint, and it is possible to reduce the stress concentration factor for the welded part, thereby increasing fatigue strength and improving reliability.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view showing a part of a runner of a hydraulic machine covered with a cover plate, Fig. 2 is a plan view of the runner, and Fig. 3 is a cross sectional view taken along the line - in Fig. 2. FIG. 4 is a cross-sectional view taken along the line - in FIG. 2, FIG. 5 is an enlarged cross-sectional view showing the welded portion between the rib plate and the cover plate, and FIGS. 6 and 7 are cross-sectional views of the present invention. A plan view showing a cover plate of a runner manufactured according to one embodiment and a welded portion thereof, FIGS. 8 and 10 are cross-sectional views taken along the line -- of FIG. 7, and FIGS. 9 and 11. is shown in Figure 7.
FIG. 13 is a distribution diagram schematically showing the uniform bending stress amplitude and local stress amplitude on the inner surface of the cover plate, and FIG. 12 is a cross-sectional view along the line, FIG. FIG. 14 is a plan view showing the cover plate, FIG. 14 is an exploded perspective view of the cover plate, and FIG. 15 is a plan view of FIG. 12.
FIG. 16 is a cross-sectional view taken along the line - of FIG. 12. 2a...Runner crown, 2b...Runner band, 4...Cover plate, 11...Opening division,
12... Inner circumference rib plate, 13... Outer circumference rib plate, 14... Radial side rib plate, 15... Inner cover plate, 16... Outer cover plate, 18... Intermediate cover plate.

Claims (1)

[Claims] 1 Rib plates extending in the circumferential and radial directions are arranged on the surfaces of the runner crown and runner band, the openings of the sections surrounded by these rib plates are covered with cover plates, and the joints of each member are welded. In a method of manufacturing a runner for a hydraulic machine which is formed by joining together: After applying a cover plate that forms a working opening to one end of the rib plates that make up each section, and welding the corners of the joints between the two; , the welded part is shaped and finished to form a concave curved surface, and then the other end of the rib plate is assembled to the runner crown or runner band, and then welded together, and then a blind cover is installed in the working opening of the cover plate. A method for manufacturing a runner for hydraulic machinery, characterized in that it is covered and welded together.