JPS61200311A - Bolt clamping structure for steam turbine casing - Google Patents

Abstract

PURPOSE:To keep off a shortage of clamping force due to a difference in thermal expansion of a bolt clamped work as well as to aim at prevention of a steam leakage, etc., by interposing a cylindrical sleeve washer, consisting of a material large in a coefficient of thermal expansion, on the circumference of a bolt. CONSTITUTION:A hole 6 is installed in an upper flange or a cover 2 consisting of a material small in a coefficient of thermal expansion, and a bolt 3 is pierced through this hole 6. And, this upper flange 2 is installed in a way of clamping a cap nut 5 tight to the bolt 3 via a sleeve washer 4 consisting of a material large in the thermal expansion coefficient. According to this method, a shortage of clamping force due to a thermal expansion difference between the bolt 3 and a clamped work of the upper flange 2 or the like is preventable from occurring owing to the sleeve washer 4 composed of the said material large in the thermal expansion coefficient. Therefore, a sealing effect is well improved and, what is more, prevention of a steam leakage or the like is made thus attainable.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is applicable to the tightening of flanges or lids of steam turbine casings or valve chambers, etc., using flanges or lids made of materials with a small coefficient of thermal expansion. It is used in technical fields to enable the combination of bolts made of materials with a high coefficient of thermal expansion.

[Conventional technology]

An overview of the conventional bolt tightening structure will be described below.

In the flange bolts of the casing of a steam turbine and the tightening bolts of the lid of the valve chamber, the coefficient of thermal expansion of the material of the flange or lid may be smaller than that of the material of the bolt in certain combinations of materials.

In this case, if a moderate tightening stress is applied to the bolt at room temperature,
At high temperatures, the tightening force is insufficient due to the difference in thermal expansion between Franz or the lid and the bolt.

This may cause steam leakage.

12% suitable for high temperature as flange or lid material
When using chromium steel, there is no problem if the same 12% chromium steel is used as the bolt material, but the above problem occurs when using refract alloy (Sokel base superalloy), which has excellent heat resistance and strength, as the bolt material. arise.

[Problem that the invention seeks to solve]

The object of the present invention is to prevent steam leakage due to insufficient bolt tightening force due to the difference in thermal expansion between the flange or lid and the bolt at high temperatures.

[Means for solving problems]

The present invention employs the following means to solve the above-mentioned problems. That is, a cylindrical sleeve washer made of a material with a large coefficient of thermal expansion, such as austenitic stainless steel, is interposed around the outer periphery of the bolt to fasten an object to be fastened, such as a flange or a lid.

[Effect]

According to the means described above, by using a sleeve washer made of a material with a large coefficient of thermal expansion for the bolt tightening side groove construction, by offsetting the small thermal expansion of the 7 runs or the lid, it is possible to prevent Steam leakage can be eliminated.

[Heaven's example]

Next, a sister example of the present invention will be described in detail with reference to the accompanying drawings.

The attached drawings show the bolt tightening structure of the present invention.

Lower flange f2) or force] Insert bolt 3 into chamber 1.

A through hole 6 for a bolt is provided in the upper flange or lid (hereinafter simply referred to as the upper flange) 2 which is made of an inverted slope having a small coefficient of thermal expansion.

Part of the flange 2 is fastened by tightening a cap nut 5 onto the bolt 3 via a sleeve washer 4 made of metal having a large coefficient of thermal expansion.

In the accompanying drawings, the thickness of the upper flange 2 is 11, and the thickness of the sleeve washer 4 is 12.

The effective strength l of bolt 8 is l = 1. +β2.

-1 Part 7 The thermal expansion coefficient of the inclination of the flange 2 is α1. The coefficient of thermal expansion of the material of the sleeve washer 4 is α2. Let α be the thermal expansion coefficient of the material of the bolt 3.

The amount of temperature rise when the temperature rises after properly tightening at room temperature.

ΔLl for upper flange 2.

Regarding sleeve washer 4 ΔL2゜ The bolt 3 is assumed to be Δt.

What is the difference in elongation between the bolt 3, upper flange 2, and sleeve washer 4 in this state?

ΔL−Δl−(Δ11+Δ12) -αlΔt・(αIllΔL1+α212Δ12)・・
...(1).

If the whole is kept warm, the temperature rise in steady state will all be equal. Namely.

Δ also = Δ also 1 = Δt2 ・ ・ ・ ・ ・
・・・ ・・・ ・・・ ・・・ ・ ・ ・
・・・ ・・・ ・・・ Since (2), ΔL・(αn・(αIn++α2n2))Δt...
・(3) becomes.

If all materials have the same coefficient of thermal expansion.

Since α=α1・α2・・・・・・・・・・(4), Δ also = α (1−(1,112 > l Δ also − O・・・ ・ ・・・ ・ ・
...(5), and there is no difference in elongation.

The coefficient of thermal expansion α1 of the material of the upper flange 2 is smaller than the coefficient of thermal expansion α of the material of the bolt 8, and.

If the coefficient of thermal expansion a2 of the material of the sleeve washer 4 is not larger than the coefficient of thermal expansion α of the material of the bolt 3, the right side of equation (3) will be a positive value.

That is, the total amount of elongation of the upper flange 2 and sleeve washer 4 is smaller than the amount of elongation of the bolt 3, and due to the difference in elongation, the tightening force of the bolt is insufficient, causing steam leakage.

In the present invention, the material of the sleeve washer 4 has a coefficient of thermal expansion α
2 is larger than the thermal expansion coefficient α of the bolt 8.

Rewriting the piece of cloth in equation (3) using the relationship 1=tJ, +g2.

ΔL・((α・αI)#, +(α・α2) 12.)
Δt...(6) Since α2>α and α>α1, 12・1. (7) If the thickness of the sleeve washer 4 is selected so that α2-α, then the right side of equation (6) becomes O.

That is, the bolt 3 will not suffer from insufficient tightening force due to the difference in thermal expansion.

〔Effect of the invention〕

As mentioned above (after refinement, it becomes a bolt tightening structure.

By using a sleeve washer, which is a material with a large coefficient of thermal expansion, it is possible to prevent insufficient tightening force due to the difference in thermal expansion between the bolt and the pre-tightened item (upper flange, lid, etc.). It is possible to prevent bending and leakage, and it is possible to combine ladle-sized bolts with a large coefficient of thermal expansion.

Brief Explanation of Drawing 4 The drawing is a sectional view showing a bolt tightening method according to the present invention.

l...lower 7 runs/or square chamber, 2...''The second part is Nranran. 3. Bolt, 4. Sleeve washer,
5... Fukuro Natsuto.

Claims (1)

[Claims] In a bolt tightening structure for a bolt to be tightened such as a flange or lid of a steam turbine casing or valve chamber, a cylindrical sleeve washer made of a material with a large coefficient of thermal expansion is interposed around the outer periphery of the bolt, and the bolt is tightened. A bolt tightening structure for a steam turbine room that prevents insufficient tightening force due to differences in thermal expansion of bolted objects.