A Design Method for Flange Bolt Preloading Force Structure and the Flange Bolt Preloading Force Structure

Abstract

The present invention relates to the technical field related to steam turbines, and discloses a design method for the pre-tightening force structure of flange bolts and a bolt pre-tightening force structure. Among them, a design method for the pre-tightening force structure of flange bolts includes the following steps: S1: Determine the bolt tightening force; S2: Determine the type of disc spring and determine the characteristic value of the disc spring; S3: Calculate the deformation amount of the disc spring after being acted on by the bolt tightening force in step S1 according to the characteristic value of the disc spring; S4: Determine the height of the limit block, and the height of the limit block is equal to the flattened deformation amount of the disc spring minus the deformation amount calculated in step S3. When carrying out the fastening operation, there is no need to control the pre-tightening force by traditional methods such as controlling by tightening torque, controlling by nut rotation angle, or controlling by bolt elongation amount, making the fastening process easier to operate and convenient and fast.

Description

Technical Field

[0001] The present invention relates to the technical field of steam turbines, and specifically relates to a design method for the pre-tightening force structure of flange bolts and a bolt pre-tightening force structure. Background Technique

[0002] Bolts are one of the commonly used fasteners in machinery, and the pre-tightening force of bolts is closely related to their service performance. The pre-tightening force of bolts is related to the tightness and reliability of the connected parts, and too large or too small pre-tightening force will affect the connection quality. For example, if the bolt pre-tightening force is too large, over-tightening will occur; if the bolt pre-tightening force is too small, the connection strength and quality cannot be guaranteed.

[0003] The new steam flange of industrial steam turbines usually works in a steam environment of high temperature and high pressure. Coupled with the influence of the variable working conditions of the unit, the airtightness of the new steam flange becomes even more important. The airtightness is mainly achieved by the reliable connection of bolts. At present, the common methods for controlling the pre-tightening force in industrial steam turbines mainly include controlling by tightening torque, controlling by nut rotation angle, controlling by bolt elongation, etc. Because the on-site situation of the equipment is complex, these methods all have the characteristic of inconvenient on-site operation. Therefore, a reliable and convenient method for controlling the pre-tightening force is particularly important. In view of the above problems, this application is proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a design method for the pre-tightening force structure of flange bolts and a bolt pre-tightening force structure, and to achieve the purpose of controlling the size of the bolt pre-tightening force through the deformation amount of the disc spring. Finally, combined with the specifications of the new steam flange of industrial steam turbines, the corresponding disc spring structure is integrated and designed to achieve the purpose of convenient selection.

[0005] The present invention is realized through the following technical solutions.

[0006] A design method for the pre-tightening force structure of flange bolts of the present invention includes the following steps:

[0007] S1: Determine the bolt tightening force;

[0008] S2: Determine the disc spring model and determine the characteristic values of the disc spring;

[0009] S3: Calculate the deformation amount of the disc spring after being acted on by the bolt tightening force in the S1 step according to the characteristic values of the disc spring;

[0010] S4: Determine the height of the limit block, and the height of the limit block is equal to the flattened deformation amount of the disc spring minus the deformation amount calculated in the S3 step.

[0011] Furthermore, the characteristic values in the S2 step include stiffness, spring elastic modulus, spring Poisson's ratio, spring thickness, disc spring outer diameter, and spring inner diameter.

[0012] Further, the calculation formula in step S3 is as follows:

[0013]

[0014]

[0015]

[0016] Wherein, F is the bolt tightening force, E is the spring modulus of elasticity, μ is the spring Poisson's ratio, t is the spring thickness, h0 is the spring flattening deformation, D is the outer diameter of the disc spring, d is the inner diameter of the disc spring, and K1, K4 are calculation coefficients.

[0017] A bolt pre-tightening force structure includes a disc spring and a limit block. The disc spring and the limit block are both designed based on the above design method. In the tightened state, the inner wall of the disc spring abuts against the surface of the limit block.

[0018] Further, the disc spring is a spring with a supporting surface or a spring without a supporting surface.

[0019] Further, the height of the limit block is 0.1 - 0.2 mm.

[0020] Further, the surface of the limit block is provided with an anti-slip structure.

[0021] A fastener includes a bolt assembly and the above bolt pre-tightening force structure.

[0022] An industrial steam turbine is provided with the above bolt pre-tightening force structure.

[0023] An industrial steam turbine is provided with the above fastener.

[0024] Advantages of the present invention:

[0025] During the tightening operation, the screw rod passes through the disc spring, the limit block and the flange, and the nut is turned until the inner wall of the disc spring abuts against the surface of the limit block. At this time, the appropriate pre-tightening force is achieved, so that there is no need for traditional methods such as controlling by tightening torque, controlling by nut rotation angle or controlling by bolt elongation amount to control the pre-tightening force, making the tightening process easier to operate, convenient and fast. Description of the drawings

[0026] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] Figure 1 It is a schematic diagram of the overall structure of a flange and a fastener;

[0029] Figure 2 It is a schematic diagram of the structure of a disc spring and a limit block;

[0030] Figure 3 It is a schematic diagram of the structure of a disc spring. Specific embodiments

[0031] The following will be combined with Figures 1-3 to describe the present invention in detail.

[0032] A method for designing the pre-tightening force structure of a flange bolt of the present invention includes the following steps:

[0033] S1: Determine the bolt tightening force; After the model of the steam turbine unit is determined in the design, the specifications and characteristic values of the new steam flange and bolts are known, and the theoretical value of the bolt tightening force F can be obtained;

[0034] S2: Determine the disc spring model and determine the characteristic values of the disc spring; The disc spring is designed according to the selected model in the national standard, and its characteristic values such as stiffness are known. The characteristic values include stiffness, spring elastic modulus, spring Poisson's ratio, spring thickness, disc spring outer diameter and spring inner diameter. The disc spring is preferably a conical disc shape.

[0035] S3: Calculate the deformation amount of the disc spring after being subjected to the bolt tightening force in the S1 step according to the characteristic values of the disc spring; The calculation formula is

[0036]

[0037]

[0038]

[0039] Among them, F is the bolt tightening force, E is the spring modulus of elasticity, μ is the spring Poisson's ratio, t is the spring thickness, h0 is the spring flattening deformation (i.e., the height of the conical spring - the spring thickness), D is the outer diameter of the conical spring, d is the inner diameter of the conical spring, K1 and K4 are calculation coefficients. For the commonly used conical spring without a support surface, K4 = 1. When the flange and bolt specifications are determined, the major diameter D and the inner diameter d of the conical spring can also be regarded as known quantities.

[0040] For the conical spring with a support surface, the calculation formula is as follows:

[0041]

[0042]

[0043]

[0044] In the calculation formulas of C1 and C2, t is the nominal value of the conical spring thickness, and t' is the actual thickness of the conical spring.

[0045] After calculation by the formula, the deformation amount f of a single conical spring under the action of the tightening force F is obtained.

[0046] S4: Determine the height of the limit block. The height of the limit block is equal to the flattening deformation of the conical spring minus the deformation amount calculated in step S3.

[0047] The height h of the limit block is generally selected as 0.1 mm - 0.2 mm, preferably about 0.1 mm. When the value of h0 - h is equal to the deformation amount of the conical spring under the pre-tightening force, it can be considered that the theoretical pre-tightening force has been reached.

[0048] The material characteristics of the selected conical spring are similar to or consistent with those of the flange, so that during the working process, the thermal deformation amounts of the flange and the conical spring are maintained at a similar level, avoiding problems such as increased clearance and deteriorated pre-tightening effect due to a large difference in thermal deformation amounts between the flange and the conical spring.

[0049] According to the specifications of different types of industrial steam turbines, combined with the forms of the corresponding flanges and connectors, the specifications of the corresponding conical springs are calculated serially and then made into general data for convenient selection in the future. For example, the following table.

[0050] Nominal diameter Nominal pressure Bolt specification Disc spring specification DN A PN A M A A DN B PN B M B B DN C PN C M C C

[0051] A bolt pre-tightening force structure includes a conical spring 1 and a limit block 2. The conical spring 1 and the limit block 2 are both designed based on the above design method. In the tightened state, the inner wall of the conical spring 1 abuts against the surface of the limit block 2.

[0052] When performing the fastening operation, pass the screw through the disc spring 1, the limit block 2 and the flange 30. There is a groove on the flange 30, and the disc spring 1 is located in the groove. The diameter of the groove is larger than the diameter of the disc spring 1 after reaching the maximum deformation. Turn the nut 20 until the inner wall of the disc spring 1 abuts against the surface of the limit block 2. At this time, the appropriate pre-tightening force is achieved, thus eliminating the need for traditional methods such as controlling the tightening torque, controlling the nut rotation angle, and controlling the bolt elongation to control the pre-tightening force, making the fastening process easier to operate, convenient and fast.

[0053] Preferably, the disc spring 1 is a spring with a bearing surface or a spring without a bearing surface.

[0054] Preferably, the height of the limit block 2 is 0.1 mm.

[0055] Preferably, the surface of the limit block 2 is provided with an anti-slip structure, and the anti-slip structure is an anti-slip pattern or an anti-slip protrusion. After the fastening is completed, the anti-slip structure increases the friction between the disc spring 1 and the limit block 2, avoiding relative sliding between the disc spring 1 and the limit block 2. At the same time, after the limit block 2 is used once, the anti-slip structure deforms, so it is convenient to see that the limit block 2 has been used, preventing secondary use and causing problems such as fastening failure.

[0056] A fastener includes a bolt assembly and the above bolt pre-tightening force structure. The bolt assembly includes a screw 21 and a nut 20.

[0057] An industrial steam turbine is provided with the above bolt pre-tightening force structure.

[0058] An industrial steam turbine is provided with the above fastener.

[0059] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it. It cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A design method for the pre-tightening force structure of flange bolts, characterized in that: It includes the following steps: S1: Determine the bolt tightening force; S2: Determine the type of disc spring and the characteristic values of the disc spring; S3: Calculate the deformation of the disc spring after being subjected to the bolt tightening force in step S1 according to the characteristic values of the disc spring; The calculation formula in step S3 is: Wherein, F is the bolt tightening force, E is the spring modulus of elasticity, μ is the spring Poisson's ratio, t is the spring thickness, h0 is the flat deformation of the spring, D is the outer diameter of the disc spring, d is the inner diameter of the disc spring, K1, K4 are calculation coefficients, and f is the deformation of a single disc spring after being subjected to the tightening force F; for a disc spring without a supporting surface, K4 = 1; for a disc spring with a supporting surface, the calculation formula of K4 is as follows: In the calculation formulas of C1 and C2, t is the nominal value of the disc spring thickness, and t , is the actual thickness of the disc spring; S4: Determine the height of the limit block, and the height of the limit block is equal to the flat deformation of the disc spring minus the deformation calculated in step S3.

2. A design method for the pre-tightening force structure of flange bolts according to claim 1, characterized in that: The characteristic values in step S2 include stiffness, spring modulus of elasticity, spring Poisson's ratio, spring thickness, outer diameter of the disc spring, and inner diameter of the spring.

3. A bolt pre-tightening force structure, characterized in that: It includes a disc spring (1) and a limit block (2), and both the disc spring (1) and the limit block (2) are designed based on the design method described in any one of claims 1 to 2. In the tightened state, the inner wall of the disc spring (1) abuts against the surface of the limit block (2).

4. A bolt pre-tightening force structure according to claim 3, characterized in that: The disc spring (1) is a spring with a supporting surface or a spring without a supporting surface.

5. A bolt pre-tightening force structure according to claim 3, characterized in that: The height of the limit block (2) is 0.1 - 0.2 mm.

6. A bolt pre-tightening force structure according to any one of claims 3 to 5, characterized in that: The surface of the limit block (2) is provided with an anti-slip structure.

7. A fastener, characterized in that: It includes a bolt assembly and the bolt pre-tightening force structure described in any one of claims 3 to 6.

8. An industrial steam turbine, characterized in that: The bolt pre-tightening force structure described in any one of claims 3 to 6 is provided in the industrial steam turbine.

9. An industrial steam turbine, characterized in that: The fastener described in claim 7 is provided in the industrial steam turbine.

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