JPS631703A - Steam turbine diaphragm - Google Patents

Abstract

PURPOSE:To prevent the damage of a screw hole for a bolt, which tightens respective divide diaphragms of upper and lower parts and to obtain sufficient tightening force by providing the screw hole on an insert screw which is screwed into one of the diaphragms. CONSTITUTION:A steam turbine diaphragm is divided into upper and lower part on the center line of a desk to enable the assembly and disassembly. In this case, an insert screw 13, on which a screw hole 7a for upper/lower tightening bolt 7 is provided on a lower half diaphragm 46. The upper half diaphragm 4a is tightened to the lower half diaphragm 46 by the upper/lower tightening bolt 7. Therefore, it is possible to reduce tightening stress due to the deformation of the upper/lower diaphragms 4a, 4b on the tightening of the upper/lower tightening bolt 7 so as to prevent the damage of the screw hole 7a. In a base material with a lower strength such as a cast iron, it is also possible to obtain the sufficient tightening force.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a steam turbine diaphragm having upper and lower tightening bolts, and particularly when an excessive tightening force is applied to the female thread of the lower half diaphragm. The present invention also relates to a diaphragm fastening structure suitable for preventing damage to the diaphragm base material.

(Prior art) Steam turbine diaphragms have a structure in which they are divided into upper and lower halves on the horizontal center line of the disc to enable assembly and disassembly, but in recent years steam turbines have become more efficient. As one measure, as described in Japanese Patent Application Laid-open No. 51-46603, a diaphragm divided into upper and lower halves is fastened with bolts, and the joint surfaces are brought into close contact to prevent steam leakage from the joint surfaces. Structures to prevent this have been adopted. However, in such structures, problems such as damage to the female thread of the diaphragm 11 have recently been observed here and there.

Below, problems in the prior art will be explained using figures.

FIG. 3 shows an example of a longitudinal section of a steam turbine.

FIG. 4 is a sectional view taken along arrow tV-IV in FIG.
The figure is a perspective view showing the joint surface of the lower half diaphragm. The diaphragm 4 is located inside the steam turbine and is located in the casing 3.
and the rotor 1, and has the role of converting the thermal energy of the steam into kinetic energy and rotating the rotor 1 via the packet 2.

Therefore, the diaphragm 11 is activated during operation of the steam turbine.Furthermore, the upper half diaphragm 4a floats up due to the steam reaction force F, and the upper and lower half joint surfaces 6 open, and steam leaks from there, resulting in turbine efficiency. The upper and lower half diaphragms 4a and 4b are fastened and fixed with bolts 7 to prevent the diaphragms from lowering. In this state, during operation of the steam turbine, the diaphragm undergoes deformation due to the thermal influence of the steam in addition to the rotational force due to the steam reaction force described above. This is due to the difference in mass between the inner ring 4d and the outer ring 4o of the diaphragm, and the difference in heat conduction between the inner and outer rings themselves. In the case of the diaphragm 11 that is divided into upper and lower halves, this deformation occurs at the upper and lower half joint surfaces 6, which have the weakest rigidity in the diaphragm.
Therefore, the bolt 7 is designed to withstand not only the normal tightening force but also the stress caused by the opening deformation. However, recently, as an operating method aimed at increasing the efficiency of turbine plants, many turbines are performing daily start/stop operation, weekly start/strip operation, etc. In this type of operation, the temperature of the diaphragm increases.

Because the temperature is repeatedly lowered, the opening phenomenon due to thermal deformation occurs repeatedly. For this reason, excessive tensile stress is repeatedly applied to the bolt 7 and the female thread 8 of the lower half diaphragm 4b, and eventually the female thread 8 of the diaphragm, which has a lower material strength than the bolt 7, is damaged as shown in FIG. damage 9a and 9b occurs.

In order to prevent this damage to the female thread, there is a method of making the bolt 7 from mild steel with high elongation to reduce the stress applied to the female thread.
One possible method is to reduce the shank diameter of the bolt to ensure bolt elongation, but there is a problem in that sufficient tightening cannot be achieved against the aforementioned steam reaction force and thermal deformation of the diaphragm. In addition, a method of increasing the bolt diameter to relatively reduce the tightening stress of the female thread is to install a 10° support screw hole for lifting at the upper and lower half joint surfaces of the diaphragm, as shown in Figure 4. Since the bar attachment screw holes 11, the crush bin screw holes 12, etc. are drilled in a concentrated manner, it is difficult to apply the screw holes to recent compact diaphragms.

As described above, with the conventional fastening structure, there was a concern that problems could occur due to repeated thermal deformation due to frequent startup and shutdown of the turbine plant.

[Problem that the invention seeks to solve]

In the above conventional technology, the diaphragm is subjected to repeated thermal deformation due to the effects of daily start-stop operation and weekly start-stop operation aimed at recent high-efficiency turbine plants, and as a result, the upper and lower half tightening bolts are There was concern that the female thread part would be damaged.

An object of the present invention is to provide a fastening structure for upper and lower half diaphragms that has sufficient original upper and lower half fastening functions and does not damage the female threads of the diaphragms.

[Means for solving problems]

For the above purpose, use female threads for upper and lower half-tightening bolts.

This is achieved by providing an insert screw screwed into the lower half diaphragm.

[Effect]

The insert screw is manufactured using a material with the same strength as the upper and lower half tightening bolts, or a high tensile strength material. As a result, the female screw holes for the upper and upper tightening bolts provided in the insert screw can withstand tightening equivalent to or more than the bolts. Furthermore, the female screw hole of the diaphragm for attaching the insert screw has a tightening stress that is inversely proportional to the diameter of the female screw hole for the bolt, so it can have sufficient strength.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a detailed view of the fastened state of the upper and lower half diaphragms according to the present invention, and FIG. 2 is a perspective view of the joint surface of the lower half diaphragm according to the present invention. Lower half diaphragm 4
An insert screw 13 having a threaded hole 7a for the upper/upper tightening bolt 7 is screwed into b, and the upper half diaphragm 4a is fastened and fixed to the lower half diaphragm 4b by the upper/upper tightening bolt 7. It shows that In the diaphragm configured in this way, the stress Fb due to the tightening of the upper and upper tightening bolts 7 applied to the screw hole 13a for attaching the insert screw 13 of the lower half diaphragm 4b is Fb "Fa XA/B where Fb: Stress Fa of the external thread of the insert screw: Stress A of the internal thread of the insert screw: Thread area of the internal thread of the insert screw B: Thread area of the external thread of the insert screw From this, by changing the ratio of A and B as necessary, Since the tightening stress Fb due to the deformation of the upper and lower half diaphragms applied to the insert screw mounting screw hole 13a of the lower half diaphragm 4b is sufficiently reduced, damage to the screw hole of the diaphragm can be prevented. Damage to the screw holes 7a for the upper and lower bolts can be prevented by using the same material as the bolt 7 or high-strength steel for the insert screw material.

Furthermore, with this structure, the screw hole 13a of the diaphragm when the insert screw 13 is removed can be used as a screw hole for lifting, so there is no need to provide a separate screw hole for lifting. This is very advantageous for standardized diaphragms. Further, since the locking effect of the insert screw can be obtained, special locking work is not required.

〔Effect of the invention〕

According to the present invention, products for which the material strength of the base material cannot be expected,
For example, it should be possible to apply sufficient fastening force to cast iron, etc.

[Brief explanation of drawings]

FIG. 1 is a detailed view of the upper and lower half diaphragm fastening states according to an embodiment of the present invention, FIG. 2 is a perspective view of the joint surface of the lower half diaphragm according to the present invention, and FIG. 3 is an example of a longitudinal section of a conventional steam turbine. , FIG. 4 is a sectional view taken along the line ■-■ in FIG. 3, FIG. 5 is a perspective view of a conventional lower half diaphragm joint surface, and FIG. 6 is an explanatory diagram of a damaged state of the lower half diaphragm female screw. 4a... Upper half diaphragm.

Claims (1)

[Claims] 1. A steam turbine characterized in that, in a steam turbine diaphragm having upper and lower tightening bolts, female threads for the upper and lower tightening bolts are provided in insert screws screwed into the diaphragm. diaphragm. 2. The steam turbine diaphragm according to claim 1, wherein the insert screw is freely attachable and detachable, and the mounting screw hole of the insert screw also serves as a lifting screw hole. 3. According to claim 1, the insert screw and the upper and lower tightening bolts are prevented from loosening by changing the pitch of the inner and outer threads of the insert screw. steam turbine diaphragm.