CN107644123B - Radial joint-riding screw structure static strength evaluation method - Google Patents
Radial joint-riding screw structure static strength evaluation method Download PDFInfo
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- CN107644123B CN107644123B CN201710780582.3A CN201710780582A CN107644123B CN 107644123 B CN107644123 B CN 107644123B CN 201710780582 A CN201710780582 A CN 201710780582A CN 107644123 B CN107644123 B CN 107644123B
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Abstract
The invention relates to a static strength evaluation method of a radial slotted screw structure, which examines the Stress condition on a slotted surface by calculating a three-dimensional finite element of the radial slotted screw structure, and carries out linearization processing on a paradigm equivalent Stress (Von Mises Stress) on a root path of each thread of a slotted screw and two adjacent components on the slotted surface. And for a certain thread ridge, dividing the sum of the maximum bending stress and the film stress on the path by the yield limit of the corresponding material at the corresponding temperature, and defining the sum as the material utilization rate of the thread ridge. The utilization rate of the material of each thread tooth of the joint-riding screw and the adjacent two components is not more than 1.0 and is used as the criterion of the static strength safety of the radial joint-riding screw structure. The invention adopts standardized flow calculation, and has the advantages of accuracy, convenience and high efficiency.
Description
Technical Field
The invention relates to the field of rotary machine design and calculation, in particular to a static strength evaluation method for a radial joint-riding screw structure.
Background
Blades having a T-root or double T-root are assembled into a root slot through a radial window formed in the rim. Each stage of such blades requires a locking blade to be mounted at the window, which is typically secured by two slotted screws that ride between the blade root and the rim. Such a structure is common to drum rotors. It is worth noting that the static and dynamic loads of the fore-and-aft blade are not taken by the cross-section of the screw, but are transmitted to the rim by shearing the thread ridge along the entire length of the thread.
When the static strength of the structure of the riding screw is evaluated, a formula is generally adopted for calculation and checking, the calculation process depends on empirical coefficients, and the empirical coefficients are related to specific material collocation and specific structure size. When the material or the size is changed, the original empirical coefficients are no longer applicable. In addition, the thread contact is a nonlinear process, and the local stress condition is difficult to calculate by using a formula.
Disclosure of Invention
In order to solve the problem that a formula calculation check evaluation method is inaccurate due to various factors such as empirical coefficient estimation limitation and thread contact nonlinearity, the invention provides a static strength evaluation method of a radial slotted screw structure, and the method has the advantages of accuracy, convenience and high efficiency.
In order to achieve the purpose, the invention adopts the following technical scheme:
1) establishing a three-dimensional model assembled by a riding screw and two parts which are locked and adjacent to the riding screw, dividing a finite element grid, and inputting material data and boundary conditions of load, temperature and contact;
2) calculating the static strength of the model with the thread contact by using a finite element algorithm;
3) selecting a joint-riding surface in the model as an examination surface, and respectively analyzing each thread tooth of the joint-riding screw on the examination surface and each thread tooth of two adjacent locking parts of the joint-riding screw as follows:
3.1) carrying out linearization treatment on the paradigm equivalent Stress (Von Mises Stress) of a certain thread on a specified path to obtain a film Stress (P)m) And bending stress, the specified path is especially the connection line between two adjacent fillets at the root of the thread,
3.2) taking the maximum bending stress (P) on the specified pathb,max) Which is related to the film stress (P)m) The sum is divided by the yield limit of the corresponding material at the respective temperature
Defined as material utilization, i.e. material utilization
4) On the examination surface, the material utilization rate of each thread tooth of the seam-locked screw and the two adjacent locking parts is not more than 1.0, and the static strength of the radial seam-locked screw structure of the fore shaft blade is considered to be safe.
The method comprises the steps of examining the stress condition on a joint-riding surface through three-dimensional finite element calculation of a radial joint-riding screw structure, carrying out linear processing on normal-mode equivalent stress on a path along the root part of a thread, deriving the material utilization rate, and taking the material utilization rate of each thread which is not more than 1.0 as the criterion of the static strength safety of the radial joint-riding screw structure of the fore shaft blade.
Compared with the prior art, the invention has the beneficial effects that:
1. the method aims at the problems that in the existing formula calculation and check, the original experience coefficient is not applicable due to the change of materials or sizes of the structure of the riding screw, and the local stress condition is difficult to calculate by using the formula because the thread contact is a nonlinear process.
2. The method is suitable for evaluating the static strength of the radial joint-riding screw for locking and connecting two adjacent components in the rotary machine, and particularly under the condition that the joint-riding screw mainly bears the axial shearing along the screw. The method is not only suitable for evaluating the static strength of the fore shaft blade, the wheel rim and the riding screw in the steam turbine, but also can be used for evaluating the fore shaft blade of the axial flow compressor, so the method has wider engineering application prospect.
3. The invention directly carries out three-dimensional finite element calculation on the radial joint-riding screw structure, and the materials and the structural sizes of the joint-riding screw and two adjacent components can be randomly given.
4. On the examination surface, namely the seam riding surface, the materials of the locking notch blades and the wheel rim are discontinuous, and the internal thread teeth cannot form a ring; the external thread of the slotted screw is subjected to a shearing action, and from the viewpoint of material mechanics, the physical significance of the dangerous cross section evaluated by using the slotted surface as the static strength is more clear.
Drawings
FIG. 1 is a schematic view of a fore-and-aft blade, rim and slotted screw assembly.
FIG. 2 is a flow chart of a static strength evaluation method of a radial slotted screw structure.
FIG. 3 is a flow chart of a method for evaluating static strength of a fore shaft blade, a rim and a slotted screw for a steam turbine.
FIG. 4 is a schematic view of the root paths of several threads of a slotted screw.
FIG. 5 is a graph of the results of a path stress linearization at the root of a particular thread.
FIG. 6 is a graph showing the material utilization of each thread of the locking blade.
FIG. 7 is a graph showing the material utilization of each thread of the rim.
FIG. 8 is a graph showing the material utilization of each thread of the slotted screw.
Detailed Description
The following will take the radial slotted screw structure of the fore shaft blade as an example, and will be further described in detail with reference to the method for evaluating the static strength of the fore shaft blade, the wheel rim and the slotted screw in the steam turbine with reference to the accompanying drawings:
as shown in figure 1, a blade 1 with a T-shaped blade root or a double T-shaped blade root is arranged in a blade root groove through a radial window on a wheel rim 3, after the blade is arranged, a locking blade 4 is arranged in the radial window, a seam-riding screw hole is drilled between the locking blade 4 and the wheel rim 3, and a seam-riding screw 2 is screwed in to complete the assembly.
The static strength of the radial slotted screw structure of the fore shaft blade shown in fig. 1 is evaluated, and the flow is shown in fig. 3 (fig. 2 is a flow chart of a static strength evaluation method for connecting two adjacent components by using the radial slotted screw in a locking mode in a rotating machine). Firstly, establishing a three-dimensional model assembled by the fore shaft blade, the wheel rim and the slotted screw, wherein the model contains the geometrical structure information which is as rich and detailed as possible including the screw thread, the size of the screw thread takes the tolerance fit and other factors into consideration, dividing a finite element grid for the model, and inputting material data, load, temperature and contact boundary conditions. And then, carrying out static strength calculation on the model with the thread contact by using finite element software to obtain stress distribution. Thirdly, selecting the interface between the fore shaft blade and the wheel rim in the model, namely the joint riding surface, as an examination surface, and respectively carrying out linearization treatment (as shown in figure 5) on the model equivalent Stress (Von Mises Stress) of each thread tooth of the fore shaft blade, the wheel rim and the joint riding screw on the examination surface on a specified path (as shown in figure 4) to obtain the film StressForce (P)m) And bending stress (P)b). As shown in FIG. 4, the predetermined path is a connection line between two adjacent rounded corners of the root of the thread. In FIG. 5, the horizontal axis represents the width (or length) of a given path, and the maximum bending stress (P) of the path is takenb,max) Which is related to the film stress (P)m) The sum is divided by the yield limit of the corresponding material at the respective temperature
Defined as the material utilization, i.e.
The horizontal axis in fig. 6, 7, 8 indicates the position of the thread on a certain part (blade or rim or screw), i.e. the second thread from bottom to top. The ordinate is the material utilization rate, which is expressed here only by the definition of the material utilization rate. Finally, if the material utilization rate of each thread tooth of the fore shaft blade, the wheel rim and the seam-riding screw is not more than 1.0 (as shown in fig. 6, 7 and 8) on the examined surface, the static strength of the fore shaft blade radial seam-riding screw structure is considered to be safe.
The invention is also suitable for evaluating the static strength of the radial riding screw for locking and connecting two adjacent components in the rotary machine, in particular to the situation that the riding screw structure mainly bears the shearing along the axial direction of the screw. For example, a flow chart of a method for locking a vane of an axial flow compressor is shown in FIG. 2.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (4)
1. The method for evaluating the static strength of the radial slotted screw structure is suitable for the situation that the slotted screw structure mainly bears axial shearing along a screw, and is characterized by comprising the following steps of:
1) establishing a three-dimensional model assembled by a riding screw and two parts which are locked and adjacent to the riding screw, dividing a finite element grid, and inputting material data and boundary conditions of load, temperature and contact;
2) calculating the static strength of the model with the thread contact by using a finite element algorithm;
3) selecting a joint surface in the model as an examination surface, and respectively carrying out linearization treatment on the joint screw on the examination surface and the normal form equivalent stress of each thread tooth of two adjacent locking components on an appointed path to obtain a film stress PmAnd bending stress PbThe specified path refers to a connecting line between two adjacent round corners at the root of the thread, and the maximum bending stress P on the specified path is takenb,maxWith film stress PmThe sum is divided by the yield limit of the corresponding material at the respective temperature
Defined as the material utilization, i.e.
Respectively calculating the material utilization rate of each thread tooth of the riding screw on the examined surface and the two parts adjacent to the riding screw in locking;
4) on the examination surface, the material utilization rate of each thread tooth of the seam-locked screw and the two adjacent locking parts is not more than 1.0, and the static strength of the radial seam-locked screw structure of the fore shaft blade is considered to be safe.
2. The method for evaluating the static strength of the radial slotted screw structure according to claim 1, wherein the slotted screw locks two adjacent parts, namely a locking blade and a rim of an axial flow compressor.
3. The method for evaluating the static strength of the radial slotted screw structure according to claim 1, wherein the slotted screw locks two adjacent parts, namely a locking blade and a rim of a drum turbine rotor.
4. The method for evaluating the static strength of the radial slotted screw structure according to claim 1, wherein the total stress on the specified path is a U-shaped curve between 0 and 1 of the width of a connecting line between two adjacent fillets at the root of a thread.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105183926A (en) * | 2015-05-07 | 2015-12-23 | 苏州纽威阀门股份有限公司 | Valve body optimization design method |
| JP2016162031A (en) * | 2015-02-27 | 2016-09-05 | 三菱重工業株式会社 | Stress calculation device and stress calculation method |
| CN106570204A (en) * | 2016-09-23 | 2017-04-19 | 西安交通大学 | Method for analyzing static strength characteristics of turbomachinery blade based on CPU+GPU heterogeneous parallel computing |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2016162031A (en) * | 2015-02-27 | 2016-09-05 | 三菱重工業株式会社 | Stress calculation device and stress calculation method |
| CN105183926A (en) * | 2015-05-07 | 2015-12-23 | 苏州纽威阀门股份有限公司 | Valve body optimization design method |
| CN106570204A (en) * | 2016-09-23 | 2017-04-19 | 西安交通大学 | Method for analyzing static strength characteristics of turbomachinery blade based on CPU+GPU heterogeneous parallel computing |
Non-Patent Citations (3)
| Title |
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| 《复杂结构井磨损套管连接螺纹的三维力学行为》;祝效华等;《石油学报》;20150630;第748-753页 * |
| 《节段式多级离心泵防导叶转动的方法》;牛卫杰;《GM通用机械制造》;20150131;第90-91页 * |
| 祝效华等.《复杂结构井磨损套管连接螺纹的三维力学行为》.《石油学报》.2015, * |
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Address after: No. 357, Shiqiao Road, Xiacheng District, Hangzhou, Zhejiang 310000 Patentee after: Hangzhou Steam Turbine Holding Co.,Ltd. Address before: No. 357, Shiqiao Road, Xiacheng District, Hangzhou, Zhejiang 310000 Patentee before: HANGZHOU TURBINE POWER GROUP CO.,LTD. |