JPH0444802Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] This invention relates to a windage reduction structure in a rotor impulse stage during operation of a steam turbine.

[Prior art and its problems]

The turbine casing is divided into two along a horizontal plane that includes the center line of the turbine axle, and consists of an upper casing and a lower casing each having a flange that extends in the left and right radial directions along the dividing plane. In a steam turbine equipped with a turbine casing that is sandwiched between an upper casing and a lower casing and housed inside the enclosure, and whose flange portions are joined via connecting bolts to assemble the two as one body, the turbine axle and An impulse vane wheel portion of a turbine axle consisting of a turbine disc concentrically arranged on the axle, a plurality of impulse vanes implanted on the outer peripheral end surface of the disc, and an impulse vane on the inner periphery of the upper casing. The structure of the rotor impulse stage of a steam turbine consists of an impulse blade in the upper half of the wheel and a plurality of nozzles arranged in a semicircle at opposite positions parallel to the axle center line. The impulse blade of the impulse blade wheel is placed on the lower casing side on the inner peripheral surface side of the lower casing facing the tip of the impulse blade, in order to prevent the effect of so-called ventilation loss caused by the steam flow being stirred and becoming turbulent due to the rotation of the turbine axle. In order to reduce ventilation loss, a partition wall or the like was provided with a predetermined gap on both the left and right sides of the part, and a structure shaped as if the impulse blade part had been inserted into a groove was used to reduce ventilation loss.

Description will be given below based on the attached drawings. FIG. 3 is a longitudinal cross-sectional view of a main part of a steam turbine equipped with a conventional windage reduction structure, and FIG. 4 is a cross-sectional view taken along the line -Q in FIG. 3. In the figure, turbine axle 1
is surrounded and held by an upper casing 8 and a lower casing 9 (details not shown), and is located on the right side of the balance piston 6 for balancing the thrust applied to the axle during turbine operation. It is equipped with a core turbine disk 2, and on the right side thereof there are arranged multiple stages of blade rows (not shown), etc., in which the steam flow after passing through an impulse impeller section 4, which will be described later, does work. There is. A plurality of impulse blades 3 are installed at predetermined intervals on the outer peripheral end surface of the turbine disk 2.
A nozzle chamber 11 in which a nozzle 10 protrudes from the inner circumferential wall of the upper casing 8 along the inner circumferential surface of the upper casing 8 at a position facing the impulse blade 3 in the upper half thereof in parallel to the axial center.
A plurality of them are connected to each other and arranged in a semicircular shape. Note that steam is supplied to the nozzle chamber 11 from the direction indicated by arrow A through a steam control valve (not shown), and is injected from the nozzle 10 toward the impulse blades 3 .

On the other hand, on the inner circumferential wall of the lower casing 9 at a position opposite to the tip of the impulse blade 3 in the lower half of the impulse blade wheel section 4,
A square groove 13 having a depth equal to the length of the impulse blade 3 plus a predetermined interval and a width equal to the width of the impulse blade 3 plus a predetermined interval on both sides, and is provided on the inner circumferential wall surface of the lower casing. A surrounding ring 14 projecting in a rectangular shape is provided so that a blade portion in the lower half of the impulse impeller part 4 can be loosely fitted into the square groove 13. This surrounding ring 14 is provided in advance at a predetermined position as an extra wall portion when the lower casing 9 is cast, and is cut into a predetermined shape when the lower casing 9 is machined.

However, as described above, this surrounding ring 14 is made by machining the surplus portion previously provided on the inner peripheral surface of the lower casing 9 into a predetermined shape, so this portion of the lower casing 9 is Since it is made thicker, it becomes heavier and more difficult to cast, which tends to lead to a decline in quality. Furthermore, since the wall thickness of the turbine casing becomes unbalanced, the thermal stress generated when starting and stopping the steam turbine increases, causing a problem of thermal fatigue.

[Purpose of invention]

The present invention was developed in view of the above points, and the purpose of the present invention is to provide a structure for reducing windage loss of a rotor impulse wheel portion, which does not place any burden on the lower casing and is simple and easy to manufacture and install. shall be.

[Summary of the invention] According to this invention, the above purpose is to provide an annular body divided into two along its own diameter line with flanges extending outward from both outer circumferential ends of the dividing surface along the dividing line. A surrounding ring is made of a thick plate and has a rectangular groove on its inner circumferential surface that allows the impulse blades to fit loosely while maintaining a predetermined spacing along the circumferential surface. This is achieved by positioning via pins and inserting so as to be held by both flanges of the lower casing.

[Example of idea]

Embodiments of this invention will be explained below based on the drawings. FIG. 1 is a longitudinal cross-sectional view of a main part of a steam turbine equipped with a windage reduction structure according to this invention, and FIG. 2 is a cross-sectional view taken along the line P in FIG. 1. In FIGS. 1 and 2, parts that are the same as those in FIGS. 3 and 4 are given the same reference numerals, and explanations of the same structures and functions as those of the prior art will be omitted to avoid duplication. shall be.

The feature of this invention is that the windage reduction structure of the impulse stage is made separately from the lower casing and is attached to a predetermined position of the lower casing via a tightening bolt.

That is, the annular body is divided into two along the diameter line, and one of the annular bodies is provided with a surrounding ring 15 having flanges 16 extending outward from both peripheral ends of the dividing surface along the dividing line. It is cut from a steel plate (for example, carbon steel or low alloy steel) by a method such as gas cutting, and then machined to a size that allows it to be inserted into a predetermined position of a predetermined size in the lower casing 9. The dimensions of the surrounding ring 15 are such that the radius of the inner peripheral surface is slightly larger than the radius of the turbine disk 2, the overall arc height is lower than the arc height of the lower casing 9, and the length in the flange direction is smaller than the lower casing 9. It requires enough length to be able to ride on and hold part of both flanges 9a. The width is set to be the width of the impulse blade 3 plus a predetermined interval and side wall thickness, with some margin. A rectangular groove 13 is provided along the inner circumference of the enclosure ring 15, which has been finished in this manner, and is dimensioned so that the impulse blades 3 can be fitted loosely thereinto while maintaining a predetermined spacing. The through holes 17 into which the tightening bolts 19 are inserted are formed in the ring flange portions 16 in an elliptical shape slightly bulging toward the flange in consideration of thermal expansion in the horizontal direction. A blind hole 23 of a predetermined depth into which the pin 21 is inserted is provided. At this time, the outer circumferential surface of the enclosing ring 15 excluding the flange portion 16 does not necessarily have to be machined into a correct circular arc shape, but has a polygonal shape that does not come into contact with the inner circumferential wall of the lower casing 9 and is finished at the level of a gas cut surface. It is sufficient to do so.

On the other hand, the lower casing 9 has a vertical center line of the turbine disk 2 perpendicular to the axle center line of the turbine axle 1 (hereinafter referred to as the enclosing ring center line), and an axial direction passing through the arc apex of the inner circumferential surface of the lower casing 9. A blind hole 22 in which a spacing pin 21 is installed centered on the intersection with the center line is placed on the inner peripheral surface of the lower casing 9, and the surrounding ring 15 is tightened with bolts on both flanges 9a with the center line of the surrounding ring 15 as a reference. Threaded hole 18 for coupling to the lower casing 9 via 19
A support seat 20 is provided, respectively.

The surrounding ring 15 made as described above is positioned at a predetermined position in the lower casing 9 by first inserting one end of the spacing pin 21 into its blind hole 22, and then the tightening bolt 19 is passed through the through hole 17 of the flange portion 16. Together with the screw hole 1 of the support seat 20 of the lower casing 9
8 is inserted and screwed together to fix the enclosing ring 15 to the lower casing 9, thereby completing the windage damage reduction structure of the impulse stage. In this case, the relative relationship between the impulse blade 3 and the surrounding ring 15 is almost the same as that of the windage reduction structure of the prior art, and since they are made separately, the manufacturing cost can be reduced and they can be made more precisely.

[Effect of idea]

As explained above, according to the present invention, the windage reduction structure that covers the impulse blade portion of the steam turbine impulse impeller that does not face the nozzle is created as a surrounding ring separate from the lower casing, and is positioned at a predetermined position on the lower casing. In addition, the rectangular groove to which the impulse blade is fixed has a shape similar to that of the conventional structure, so the windage reduction effect is comparable to that of the conventional device. Compared to the case where the lower casing is formed by cutting and machining, the production costs such as machining are significantly reduced, and there is no need to provide an excess wall in the lower casing. The shape can be simplified and casting costs can be significantly reduced. Furthermore, since there are no protrusions inside the lower casing, it is expected that concerns such as thermal fatigue caused by uneven distribution of thermal stress will be eliminated, and an extremely economical windage reduction structure can be provided.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view of a main part of a steam turbine to which a surrounding ring of a steam turbine casing according to an embodiment of the present invention is attached, Fig. 2 is a cross-sectional view taken along the line P in Fig. 1, and Fig. 3 is a conventional FIG. 4 is a vertical cross-sectional view of a main part of a steam turbine equipped with a windage loss reduction structure for a steam turbine casing, and FIG. 4 is a cross-sectional view taken along the line - in FIG. 3 in the direction of the Q arrow. 1... Turbine axle, 2... Turbine disc, 3
... Impulse blade, 4... Impulse impeller part, 7... Turbine casing, 8... Upper casing, 9... Lower casing, 10... Nozzle, 13... Square groove,
14...Windage reduction structure, 15...Enclosure ring, 1
6... (Enclosure ring) flange, 17... Through hole, 18... Screw hole, 19... Tightening bolt, 20
... Support seat, 21 ... Spacing pin, 22, 23 ...
Blind hole.

Claims (1)

[Claims for Utility Model Registration] 1. In a steam turbine equipped with a turbine casing consisting of an upper casing and a lower casing, the windage loss reduction structure of the impulse stage is a surrounding ring made separately from the lower casing, and A windage loss reduction structure for a steam turbine impulse stage, characterized in that the windage loss reduction structure for a steam turbine impulse stage is positioned on an inner wall of a lower central portion of a lower casing via a spacing pin, and is inserted so as to be held by both flanges of the casing. 2. In the windage reduction structure described in claim 1 of the utility model registration, the enclosing ring is an annular body divided into two along its own diameter line, and the enclosing ring extends outward along the dividing line from both outer peripheral edges of the screen. It is made of a thick plate in a shape with a flange extending in the direction, and after finishing it so that it can be inserted, an impulse blade can be fitted loosely along the inner peripheral surface while maintaining a predetermined interval. A windage loss reduction structure for a steam turbine impulse stage, characterized by having a square groove of the same size.