JPH0153142B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a nozzle ring for an axial steam turbine.
The present invention relates to a mold for an evanescent segmented casting pattern that is used when assembling the evanescent segmented casting pattern and manufacturing the assembled pattern by a cell molding method.

Conventionally, this type of nozzle ring has been a perforated nozzle for small turbines, and a welded assembly type nozzle for other types of nozzles, with the former having the disadvantage of being inexpensive but inefficient, and the latter having good efficiency but being expensive.

Figure 1 is a plan view of a nozzle block of a conventional welded assembly type nozzle ring, Figure 2 is a rear view of Figure 1, Figure 3 is a side view of Figure 2, and Figure 4 is A of Figure 2. -A sectional view. The nozzle block 1 has circular arcs 2 and 3 cut on both sides of the nozzle block, and the circular arcs 2 and 3 of the adjacent nozzle blocks 1 (Figure 4 shows two nozzle blocks, one of which is indicated by a chain double-dashed line). 3 can be brought into contact with each other. The nozzle block 1 has a groove G formed therein to form a blade surface 5 of the nozzle blade 4 at its bottom. The back of the blade with respect to the nozzle blade surface 5 is a circular arc 2, and a nozzle flow path 6 is formed between the circular arc 2 of one nozzle block and the blade surface 5 of the nozzle block adjacent to that nozzle block. The relationship between the arcs 2, 3 will be explained further later in the assembly description. A protrusion 7 is provided on the side surface of the nozzle block 1, into which a groove 14 of an inner ring 13, which will be described later, is fitted.
Since the nozzle ring has a circular arc in the assembled state and the nozzle block 1 forms a subdivided circular arc portion of the nozzle ring, the side surfaces 8 and 9 are made flat to simplify machining. The end surfaces 11 and 12 are made into parallel planes so that the nozzle ring becomes a flat plate in the assembled state.

Since the nozzle block 1 described above is made of stainless steel and is formed by cutting, the number of processing steps is extremely large.

FIG. 5a is a perspective view of another embodiment of the nozzle block, which differs only in dimensional proportions from the above embodiment. As shown in FIG. 5b, the nozzle blocks 1 are butted and welded together as part of a ring.

6 is a plan view of a nozzle ring assembled using the nozzle blocks shown in FIGS. 1 to 4, and FIG. 7 is a sectional view taken along line BB in FIG. 6. Nozzle block 1
is arranged on a circle with center C with circular arcs 2 and 3 in contact with each other. I will tell you how. The protrusion 7 of the nozzle block 1 is fitted into the circumferential groove 14 of the inner ring 13. Then, each nozzle is assembled and temporarily welded so that the line 16 appearing on the mating surface of the arcs 2 and 3 is aligned with the tangent line of the cylinder 15 whose center is aligned with the center C of the nozzle ring shown in FIG. Fix the space between blocks 1, and
At the ends, there are arc-shaped fillers 17, 18, which have the same inner and outer dimensions as the nozzle block 1 without the nozzle flow path 6.
19 and 21 and fix in the same manner. Then, the outer ring 22 which is in contact with the side surface 9 of the nozzle block 1 etc. is brought into contact and temporarily welded. After temporary welding as described above, assembly accuracy is measured and confirmed, main welding is performed, and both end faces and inner and outer circumferences are turned and ground.

Manufacturing a nozzle ring by such machining and welding requires (1) The mating surfaces of adjacent nozzle blocks 1 must be circular arcs 2 and 3 for manufacturing reasons, and these surfaces also become the inner walls of the nozzle flow passages 6. The shape of the flow path is restricted. (2) The machining process requires a large amount of man-hours. (3) Line 1 of mating surface
6 has to be properly drawn out before welding, which requires a large amount of assembly man-hours. (4) Since there are many parts, it takes time to weld. (5) Technical measures are required to avoid overall accuracy deterioration due to welding distortion during welding. There are many problems such as.

In order to avoid the problems related to welding (4) and (5) above, it is possible to manufacture a nozzle ring by only assembling, but in order to do so, it must be constructed only by assembling. Grooves or dovetails are required, making the construction more complex than a welded nozzle ring, and the number of machining steps is significantly increased because each component must be precisely finished to fit tightly together.

In order to solve the above problems, some products are manufactured by ordinary casting. However, distortions and inaccuracies peculiar to casting occur, making it difficult to obtain an accurate nozzle shape. Since each casting pattern is created according to the change of the nozzle, the cost for casting patterns becomes extremely high in the case of small-scale production. Therefore, even if there is some mismatch, the same nozzle ring will be used.

The invention disclosed in Japanese Patent Application Laid-Open No. 57-68261 is a method for manufacturing a turbine impeller, in which a mold is made by arranging segmented investment casting patterns. Applying this conventional example makes it easy to manufacture a nozzle ring, and the nozzle shape can be changed. Compared to the case of machining, the pattern can be selected much more freely than in the case of machining.The pattern corresponding to the surface that becomes the flow path can be a combination of a circle and a straight line, or a combination of two circles (not shown) or other curved lines or curved lines. The same applies to other surfaces of the flow path, so that an efficient shape can be achieved.

Here, a mold is used to create the segmented investment casting pattern for the nozzle ring. In this case, if there is a series of nozzle expansion ratios corresponding to steam conditions, it is necessary to prepare a mold for each nozzle expansion ratio. However, when molds are prepared in this way, the number of types of molds becomes extremely large, and when a small number of nozzle rings are manufactured, the initial cost of the product becomes high.

Therefore, in the present invention, the problem arose of how to inexpensively produce a divided disappearing pattern for a nozzle ring.

The present invention solves the above problems and provides a mold that can accommodate each expansion ratio without preparing a new mold for each expansion ratio. The aim is to reduce the cost of the molds used to manufacture rings.

In the present invention, a nozzle block and a blind block containing one nozzle in the shape of a sector in which the nozzle ring is divided in the radial direction or a straight line tangent to a small circle centered on the nozzle ring center are formed in an investment casting pattern, and Ceramic cells are produced using a divided investment casting pattern of a nozzle block whose adjacent partition surfaces are flush with the back surface of the blade of the nozzle flow path, and an investment casting pattern in which the divided investment casting pattern of a blind block is combined into an integrated structure. A mold used for manufacturing an investment casting pattern of the nozzle block in a method of manufacturing a nozzle ring of an axial flow turbine integrally by precision casting by making a mold and casting the metal, the mold being adapted to the nozzle expansion ratio. An axial flow system characterized by comprising a variable top mold to form a flow path shape and an unchangeable base mold, and the variable top mold can be exchangeably attached to and removed from the unchangeable base mold. This is a mold used to manufacture turbine nozzle rings.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 8 is a plan view of the investment casting pattern of the divided nozzle ring, which is a divided type in which the nozzle ring is divided in the radial direction and the blocks are circular arcs with small central angles. In this embodiment, the inner diameter surface 26 and outer diameter surface 27 of the nozzle ring are made integrally. That is, in the conventional welding assembly type nozzle block 1, the inner diameter surface is the outer diameter of the inner ring 13, and the outer circumferential surface of the nozzle ring 1 is the inner diameter of the outer ring 22. They do not make molds that correspond to the inner and outer rings. That is, in the embodiment of the present invention, the nozzle ring is completed as an integral mold. 9 is a rear view of FIG. 8, FIG. 10 is a left side view of FIG. 9, and FIG. 11 is an enlarged sectional view taken along the line C--C of FIG. 8. The height of the investment casting pattern between the end faces 23 and 24 is the same as the thickness of the nozzle ring. A reference hole 25 for assembly is provided on one of the end faces in the axial direction of the nozzle ring pattern assembled from the investment casting pattern of the nozzle block. The nozzle blade pattern 104 has a pattern blade surface 105 shape, but the pattern blade back surface 102 is not a circular arc, unlike the conventional welding assembly type or machining example, but has a circular arc surface R ₁ so that the nozzle space 106 can be formed optimally. It is arranged from the plane L ₁ . The blade back surface 102 and the opposite surface 103 of the vanishing material block have the same shape as the blade back surface 102 in front and back relationship. The shape of the blade surface 105 of the nozzle blade pattern 104 is changed depending on the steam expansion ratio.

A pair of molds for making the above-mentioned investment casting pattern are made as shown in FIGS. 12A and 12B, which are perspective views. That is, as shown in FIG. 12A, in comparison with FIG. 11, the base mold 28 has a surface 1031 corresponding to the surface ¹⁰³ , and a mold circular arc surface corresponding to the circular arc surface _R1 .
R ₁ ¹ and ^{a plane L 1 1} _{corresponding} to the plane L ₁ . The top 106 ¹ forming the nozzle space 106 in the base mold 28 is connected to the arc surface 103 ¹ of the base mold 28.
The protrusion 31 of the top 106 ¹ is fitted into the circumferential groove 29 of the top 106 1 , and is fixed from the lower surface of the base mold 28 with bolts (not shown) to enable installation and removal. Since the mold surface 105 ¹ corresponding to the shape of the pattern blade surface 105 of the top 106 ¹ changes depending on the vapor expansion ratio, only the top 106 ¹ can be converted. 25 ¹ is a mold for forming a reference hole 25 for assembly, and is implanted in the base mold 28 . The upper mold 32 is placed over the base mold 28. The upper mold 32 is the pattern wing back 1
A mold surface 102 ¹ having a shape corresponding to 02 is provided. The base mold 28 and the upper mold 32 have mating surfaces 33 and 3
4, 35 and 36 are brought into contact. Then, both the upper mold 32 and the base mold 28 are housed in a mold frame (not shown), the mold is assembled, and the molten fugitive material is poured to produce the divided pattern of the fugitive material shown in FIGS. 8 to 11.

An example of the above-mentioned division pattern made of vanishing material with different nozzle expansion ratios is the 13th division pattern.
14 is shown in the same cross section as FIG. 11, except that the shape of the nozzle blade surface 105 of the pattern is different, and the other parts are the same.

Figure 16 shows the end face 2 of the segmented investment casting pattern (numeral 37) using the investment material made as described above.
3 (FIG. 10) is placed on the jig 38 and the reference hole 25 is inserted into the positioning pin 25J implanted in the jig 38.
3 are in contact with each other, and the planes 102 and 103 are arranged in a fan shape so that the generatrix direction of the surfaces 102 and 103 is in the direction of contact with a small circular plate concentric with the center of the nozzle ring.

FIG. 15 is a plan view of the completed nozzle ring after machining. In the assembled investment casting pattern shown in FIG. 15, there are no bolt holes 42, seating bolt holes 43, knock pin holes 44, and tap holes 45, and finishing allowances are provided on both the inner and outer peripheral end surfaces. As shown in FIG. 16, on both sides of the segmented investment casting pattern 37 arranged in the shape of an arc in the middle, there are investment casting patterns 39 corresponding to fillers having a semicircular shape on both sides as shown in FIG. , 41 are arranged. Adhesive is applied to the contact surfaces of the above-mentioned investment casting patterns 37 and each of the investment casting patterns 37 and 39, 41 during assembly.

When the adhesive hardens, a monolithic investment casting pattern similar to the nozzle ring described in FIG. 15 is created.

It should be noted that, although it is the same as combining multiple divided investment casting patterns including nozzles as described above, the investment casting pattern of the nozzle ring is created by partially bonding each other and then combining the partially assembled patterns. It's okay.

Using the nozzle ring casting model thus produced, slurry coating, sanding, and drying are repeatedly performed by the known ceramic shell method. After that, the cast model of the vanishing material is eluted, and the remaining mold is fired at 600°C, and then further fired at 1000°C to obtain a ceramic mold.

In casting, stainless steel is melted in a vacuum melting furnace and poured into a ceramic mold that has been heated to a high temperature. Break out the mold and cut out the sprue and riser. Then, the nozzle is washed with caustic soda to dissolve the sand clogging the inside of the nozzle channel 6 and the sand adhering to the peripheral wall.

After that, the cast material is completed by heat treatment for annealing and tempering.

After rough machining of both end faces and the inner and outer diameter surfaces, holes for attachment to the turbine casing are machined in the axial direction of the end faces, and then both end faces are finished by grinding.

As described above, the present invention includes a variable top mold and an unchangeable base mold to form a flow path shape that matches the nozzle expansion ratio, and the variable top mold is replaceably attached to the unchangeable base mold. Since the mold is used for manufacturing the nozzle ring of an axial flow turbine, which is characterized by being removable, the shape of the nozzle flow path is changed according to the steam expansion ratio of the nozzle, so the mold is inexpensive. Preparation is now possible, and the initial cost can be reduced when manufacturing a nozzle ring for an axial turbine by a cell molding method using an investment casting pattern.

[Brief explanation of drawings]

1 to 7 are diagrams showing a conventional nozzle ring manufacturing method and a nozzle ring, in which FIG. 1 is a plan view of the nozzle block, FIG. 2 is a rear view of FIG. 1, and FIG. is a side view of FIG. 2, FIG. 4 is a sectional view taken along line A-A in FIG. 2, FIG. 5a is a perspective view of the nozzle block, FIG. 5b is a perspective view showing the nozzle block assembly, and FIG. 7 is a plan view showing the assembly of the nozzle block, FIG. 7 is a sectional view taken along line BB in FIG. 6, and FIGS.
The figure is a plan view of the divided investment casting pattern of the nozzle part.
Fig. 9 is a rear view of Fig. 8, Fig. 10 is a side view of Fig. 9, Fig. 11 is an enlarged sectional view taken along the line C-C of Fig. 8, and Fig. 12A and Fig. 12B are segmented investment casting. A perspective view of a pattern mold, FIGS. 13 and 14 are cross-sectional views taken along the line C-C in FIG. 8 showing other embodiments of the nozzle partial investment casting pattern, and FIG. 15 is a nozzle ring completed according to the present invention. FIG. 16 is a perspective view showing the assembly of the nozzle segmented investment casting pattern. 1... Nozzle block, 2, 3... Arc, 4...
...Nozzle blade, 5...Blade surface, 6...Nozzle flow path, 7
... Projection, 8, 9 ... Side surface, 11, 12 ... End surface, 13 ... Inner ring, 14 ... Groove, 15 ... Cylinder,
16... line, 17, 18, 19, 21... filler metal,
22... Outer ring, 23, 24... End face, 25... Reference hole, 26... Inner diameter surface, 27... Outer diameter surface, 28...
... Base mold, 29 ... Groove, 31 ... Projection, 32
... Upper mold, 33, 34 ... Matching surface, 35, 36
...Matching surface, 37...Divided vanishing casting pattern, 3
8... Jig, 39, 41... Loss casting pattern,
42... Bolt hole, 43... Bolt hole with seat, 44
...Knock pin hole, 45 ...Tap hole, 25 ¹ ...
...Mold, 25J...Pin, 102...Pattern blade back surface, 103...Opposite surface, 104...Nozzle blade pattern, 105...Pattern blade surface, 106...Nozzle space, 102 ¹ ...Mold surface, 103 ¹ ...face, 10
5 ¹ ...mold surface, 106 ¹ ...top, C...center,
G... Groove, L ₁ ... Plane, L ₁ ¹ ... Plane, R ₁ ... Arc surface, R ₁ ¹ ... Mold arc surface.

Claims (1)

[Claims] 1. A nozzle block and a blind block containing one nozzle in the shape of a sector in which the nozzle ring is divided in the radial direction or a straight line tangent to a small circle centered on the center of the nozzle ring are formed in an investment casting pattern, and are placed next to each other. A ceramic cell mold is created using a divided investment casting pattern of a nozzle block in which the abutting partition surface is flush with the back surface of the wing of the nozzle flow path, and an investment casting pattern in which the divided investment casting pattern of a blind block is combined into an integrated form. A mold used for manufacturing an investment casting pattern of the nozzle block in a method of manufacturing a nozzle ring of an axial flow turbine in one piece by precision casting, the mold having a flow path adapted to the nozzle expansion ratio. An axial flow turbine comprising a variable top mold to form a shape and an unchangeable base mold, the variable top mold being able to be exchangeably attached to and removed from the unchangeable base mold. A mold used to manufacture nozzle rings.