Fastening system unified type matching design method

Abstract

The invention discloses a unified type matching design method for a fastening system. The method comprises the steps that the design allowance of the thread length is determined; determining a size sequence corresponding to the total length of the bolt and the length of the polished rod section of the bolt according to the design allowance of the thread length; the value range of the bolt length under the tensile working condition is calculated; calculating the value range of the length of the bolt under the shear-resistant working condition; according to the value range of the bolt length under the tensile working condition and the value range of the bolt length under the shear working condition, the bolt size is selected from the size sequence according to the selection principle; and according to the index requirements of the application scene of the fastening system, the bolt model meeting the bolt size is determined, and bolt matching type selection is completed.

Description

Technical Field

[0001] The invention relates to a fastening system type matching design method, belonging to the technical field of fasteners. Background Art

[0002] Bolts are cylindrical threaded fasteners that are matched with nuts. They are a commonly used mechanical part, consisting of a head and a screw (a cylinder with external threads). The screw includes a bare section and a threaded section. The bare section is divided into tension-resistant bolts and shear-resistant bolts according to the dimensional tolerance accuracy. The threaded connection method used with bolts and nuts is one of the most commonly used fastening connection forms. Its main functions are fastening and force transmission. This connection form is easy to disassemble and can be reused. The thread is its most basic structural feature.

[0003] When threaded pairs are connected and matched, the length of the bolt end exposed from the nut in the assembled state is required to be as small as possible, but should not be less than 2 times the pitch; the length of the bolt thread retracted from the end face of the connected part is 2 to 3 times the pitch. In actual engineering applications, the clamping thickness of the connected parts varies, and the clamping thickness value varies randomly. If the above engineering design requirements are to be met under different application scenarios, then the reasonable value of the bolt thread section length becomes a key design factor.

[0004] After consulting relevant design manuals, standards, and literature, the design criteria and calculation methods for the length of the bolt thread section are summarized as follows:

[0005] (1) GB / T 3106 Nominal length and thread length of fasteners bolts, screws and studs

[0006] In the GB / T 3106 standard, the design value of bolt thread length is specified as follows:

[0007] l≤125mm, b=2d+6mm;

[0008] 125mm <l≤200mm,b=2d+12mm;

[0009] l>200mm, b=2d+25mm.

[0010] The problems with the above calculation method are as follows:

[0011] 1) According to the practice of fastener industry standard compilation, the length of the bolt thread segment is consistent under the same diameter d specification. However, according to the above calculation formula, as the bolt length increases, the bolt thread length is a variable value under the same diameter d specification, which does not meet the industry design specifications.

[0012] 2) The length of the bolt thread section calculated as above cannot meet the engineering design requirements of "the bolt thread section is indented 2 to 3 times the pitch of the end face of the connected part and the length of the bolt end exposed from the nut is as small as possible, but not less than 2 times the pitch". For example, if the nominal diameter of the bolt is MJ8, the thread length b = 2d + 6mm = 22mm, the nut is the height of the double hexagonal self-locking nut of 10.4mm, and the clamping thickness is 30mm, then the bolt length is ≥ (clamping thickness + nut height + 2 times the pitch) The minimum value, the bolt length is 44mm, and the rod length is 20mm, then the length of the thread section indented from the end face of the connected part is 10mm, 10mm is far more than 3 times the pitch, and the design is not optimized.

[0013] 3) In the actual production process, the length of the bolt thread section fluctuates slightly within a certain range, which is directly related to the thread finish, that is, (bolt thread section + thread finish) is a fixed value. If the thread finish becomes smaller, the length of the bolt thread section will increase accordingly. Therefore, the length of the bolt thread section should be a reference value rather than a fixed value. The bolt length and the bare rod length are fixed values. Therefore, the above calculation formula takes the length of the bolt thread section as a fixed value, which is unscientific, unreasonable and unrealistic.

[0014] (2) Patents on bolt product design do not mention thread length design methods

[0015] The design patents retrieved for bolt products, such as "CN113515821A Design method for heat-adapted countersunk bolts", mainly introduce the design method of countersunk bolts based on the condition of thermal expansion coefficient matching. The main design factor considered is the thermal expansion coefficient of the material, and the bolt length, a structural design factor, is not mentioned; "CN113673048A Bolts and their design methods" mainly considers the effect of torque on bolt elongation, and does not mention the bolt length design factor; "CN110348151A Wind turbine tower flange connection" mainly considers the design factor of bolt elongation, and does not mention the bolt length design factor. "Connecting bolt design method and device" is to model the tower, tower flange and connecting bolts respectively in ANSYS software, apply corresponding loads to the connecting bolts, calculate the piecewise linear interpolation function of the tower section bending moment and bolt stress, and calculate the maximum fatigue damage of the section. This is a mechanical calculation at the fastening connection system level and has nothing to do with the structural design factor of bolt length; "CN108133074A A bolt design method" is to perform finite element simulation in CAE software to calculate the bolt friction coefficient, bolt tightening coefficient, etc., but does not mention the bolt thread length design method.

[0016] (3) The fastener design manual does not provide a professional thread length design method

[0017] Professional books such as "Practical Handbook of Standard Fasteners", "Introduction to Fasteners", and "Practical Handbook of Fasteners" introduce thread types, tolerance accuracy, head shape structure, stress calculation, marking methods, etc., but there is no professional method for calculating thread length.

[0018] No standards, manuals or patents were found for reference on the unified design method of fastening systems under scenario mode. Summary of the invention

[0019] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art, to provide a method for designing a unified matching system for a fastening system, to select and match fasteners according to characteristic elements of scene attributes, to achieve a unified design of a fastening system under scene modes, and to provide a technical basis for the matching design of fastening systems under various scene modes.

[0020] The technical solution of the present invention is:

[0021] The present invention discloses a fastening system type matching design method, which comprises the following steps:

[0022] Determine the design allowance for thread length;

[0023] According to the design margin of the thread length, determine the size sequence corresponding to the total length of the bolt and the length of the bolt polished rod;

[0024] Calculate the range of bolt length under tensile conditions;

[0025] Calculate the range of bolt length under shear conditions;

[0026] According to the value range of the bolt length under the tensile condition and the value range of the bolt length under the shear condition, the bolt size is selected from the size sequence according to the selection principle;

[0027] According to the index requirements of the fastening system application scenario, determine the bolt model that meets the bolt size and complete the bolt matching selection.

[0028] Furthermore, in the above method, the design margin of the thread length is determined by:

[0029] c≥L0-H0

[0030] c=a1+b0

[0031] a1=A-2p

[0032] b0=B-2p

[0033] Among them, c is the design margin of thread length, L0 is the dimensional runout interval of bolt length L, H0 is the minimum variation interval of clamping thickness; A is the length of the bolt end protruding from the nut, B is the length of the bolt thread retracted from the end face of the connected part; p is the pitch.

[0034] Furthermore, in the above method, the size sequence corresponding to the total length of the bolt and the length of the bolt's bare rod section is determined according to the design margin of the thread length, specifically: take the combination of the total length of the bolt L and the length of the bolt's bare rod section ls under the condition that the formula L-ls=S+4p+c is satisfied to form a size sequence, wherein L is the total length of the bolt, ls is the length of the bolt's bare rod section, S is the nut thickness, p is the pitch, and c is the adjustment parameter.

[0035] Furthermore, in the above method, the value range of the bolt length under the tensile condition is specifically:

[0036] L≥H+2p+S

[0037] Among them, L is the total length of the bolt, p is the pitch, H is the clamping thickness, and S is the nut thickness.

[0038] Furthermore, in the above method, the value range of the bolt length under the shear resistance condition is specifically:

[0039] L≤H+S0+c+2p

[0040] Among them, L is the total length of the bolt, H is the clamping thickness, p is the pitch, S0 is the thickest nut thickness currently selected, and c is the design allowance for the thread length.

[0041] Furthermore, in the above method, the bolt and nut models that meet the bolt size are determined according to the index requirements of the fastening system application scenario, specifically:

[0042] When the bearing capacity in the index requirement is greater than or equal to 1100MPa, the bolt and nut model should be a combination of PH13-8Mo bolts and GH4169 nuts, a combination of 17-4PH bolts and PH13-8Mo nuts, or a combination of TC4 bolts and TC16 nuts;

[0043] When the bearing capacity in the index requirement is less than 1100MPa, the bolt and nut model should be a combination of 7055 bolts and 7075 nuts or a combination of 316L bolts and 304 nuts;

[0044] When the salt spray resistance time in the index requirement is greater than or equal to 480h, the surface of the bolts and nuts shall be T35 nano coating or zinc-nickel alloy coating;

[0045] When the temperature in the index requirement is above 300℃, the bolt and nut model should be a combination of GH4169 bolts and GH2132 nuts;

[0046] When the temperature in the index requirement is 100℃~300℃, the bolt and nut model should be a combination of TC4 bolts and TC16 nuts, a combination of PH13-8Mo bolts and GH4169 nuts, or a combination of 17-4PH bolts and PH13-8Mo nuts;

[0047] When the temperature in the index requirement is -100℃~100℃, the bolt and nut model should be a combination of 7055 bolts and 7075 nuts;

[0048] When the temperature in the index requirement is below -100℃, the bolt and nut model should be a combination of TC4ELI bolts and TC4ELI nuts or a combination of 316L bolts and 304 nuts;

[0049] When the disassembly and assembly in the index requirements requires repeated disassembly and assembly, the bolts and nuts should be copper-plated and molybdenum disulfide-coated;

[0050] When the disassembly and assembly in the index requirements is that there is no need for repeated disassembly and assembly, the bolt and nut models should be chemically passivated bolts and nuts.

[0051] Furthermore, in the above method, the selection principle is specifically: the bolt under the tensile condition selects the minimum value within the range of bolt length under the tensile condition, and the bolt under the shear condition selects the maximum value within the range of bolt length under the shear condition.

[0052] Furthermore, in the above method, the index requirements include strength index, stiffness index, installation index and environmental index.

[0053] Furthermore, in the above method, the strength index includes high and low temperature tensile strength, yield strength, cross-sectional shrinkage rate, elongation, impact toughness, stress brittleness, stress corrosion, fatigue, stress fracture, stress durability and hydrogen embrittlement; the stiffness index is the connection stiffness index after the fastener is installed; the installation index includes installation restrictions, number of disassembly and assembly, and maintenance and replacement; the environmental indicators include mechanical environment, thermal environment, natural environment and medium environment.

[0054] The beneficial effects of the present invention and the prior art are:

[0055] (1) The present invention uses a digital analytical design method to design the bolt thread length, proposes a digital analytical design formula from the forward design dimension, fills the design gap of digital analysis in the field of bolt design, changes the inaccurate method of thread design based on experience, and can meet the engineering design requirements in any connection scenario that the bolt thread section is indented 2 to 3 times the pitch of the end face of the connected part and the length of the bolt end exposed from the nut is as small as possible but not less than 2 times the pitch.

[0056] (2) Under the condition of specifying the bolt length sequence, the bolt polished rod length sequence is calculated with one click to ensure that the difference between the bolt length and the polished rod length under the same diameter specification is a constant value; at the same time, according to the development level of the bolt finishing technology, a reference value of the threaded section length is given.

[0057] (3) This method can be used to select the bolt length. Under the premise of meeting the engineering design requirements of "the bolt thread section is indented 2 to 3 times the pitch of the end face of the connected part and the length of the bolt end protruding from the nut is as small as possible but not less than 2 times the pitch", the tensile bolt length value can be quickly calculated with the goal of lightweight, and the shear bolt length value can be quickly calculated with the goal of maximum shear performance.

[0058] (4) This method provides a theoretical basis and technical support for the formulation of bolt product standards at all levels and the selection of bolt length in various application fields.

[0059] (5) The present invention adopts a mathematical analysis design method to design the thread length from a positive design dimension to meet all clamping thickness requirements.

[0060] (6) The present invention adopts a mathematical analysis design method to calculate the required bolt length with one click, avoiding multiple tedious calculations that reduce design efficiency and design accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a cross-sectional view of the threaded fastening connection system of the present invention; 1. bolt, 2. connected part-1, 3. connected part-2, 4. nut. DETAILED DESCRIPTION

[0062] The present invention is further described in detail below with reference to the accompanying drawings and specific implementation modes.

[0063] The present invention discloses a fastening system type matching design method, which comprises the following steps:

[0064] Determine the design allowance for thread length;

[0065] According to the design margin of the thread length, determine the size sequence corresponding to the total length of the bolt and the length of the bolt polished rod;

[0066] Calculate the range of bolt length under tensile conditions;

[0067] Calculate the range of bolt length under shear conditions;

[0068] According to the value range of the bolt length under the tensile condition and the value range of the bolt length under the shear condition, the bolt size is selected from the size sequence according to the selection principle;

[0069] According to the index requirements of the fastening system application scenario, determine the bolt model that meets the bolt size and complete the bolt matching selection.

[0070] Preferably, the design margin of the thread length is determined by:

[0071] c≥L0-H0

[0072] c=a1+b0

[0073] a1=A-2p

[0074] b0=B-2p

[0075] Among them, c is the design margin of thread length, L0 is the dimensional runout interval of bolt length L, H0 is the minimum variation interval of clamping thickness; A is the length of the bolt end protruding from the nut, B is the length of the bolt thread retracted from the end face of the connected part; p is the pitch.

[0076] Preferably, the size sequence corresponding to the total length of the bolt and the length of the bolt's bare rod section is determined according to the design margin of the thread length, specifically: take the combination of the total length of the bolt L and the length of the bolt's bare rod section ls under the condition that the formula L-ls=S+4p+c is satisfied to form a size sequence, wherein L is the total length of the bolt, ls is the length of the bolt's bare rod section, S is the nut thickness, p is the pitch, and c is the adjustment parameter.

[0077] Preferably, the value range of the bolt length under the tensile condition is calculated as follows:

[0078] L≥H+2p+S

[0079] Among them, L is the total length of the bolt, p is the pitch, H is the clamping thickness, and S is the nut thickness.

[0080] Preferably, the value range of the bolt length under the shear condition is calculated as follows:

[0081] L≤H+S0+c+2p

[0082] Among them, L is the total length of the bolt, H is the clamping thickness, p is the pitch, S0 is the thickest nut thickness currently selected, and c is the design allowance for the thread length.

[0083] Preferably, the bolt and nut models that meet the bolt size are determined according to the index requirements of the fastening system application scenario, specifically:

[0084] When the bearing capacity in the index requirement is greater than or equal to 1100MPa, the bolt and nut model should be a combination of PH13-8Mo bolts and GH4169 nuts, a combination of 17-4PH bolts and PH13-8Mo nuts, or a combination of TC4 bolts and TC16 nuts;

[0085] When the bearing capacity in the index requirement is less than 1100MPa, the bolt and nut model should be a combination of 7055 bolts and 7075 nuts or a combination of 316L bolts and 304 nuts;

[0086] When the salt spray resistance time in the index requirement is greater than or equal to 480h, the surface of the bolts and nuts shall be T35 nano coating or zinc-nickel alloy coating;

[0087] When the temperature in the index requirement is above 300℃, the bolt and nut model should be a combination of GH4169 bolts and GH2132 nuts;

[0088] When the temperature in the index requirement is 100℃~300℃, the bolt and nut model should be a combination of TC4 bolts and TC16 nuts, a combination of PH13-8Mo bolts and GH4169 nuts, or a combination of 17-4PH bolts and PH13-8Mo nuts;

[0089] When the temperature in the index requirement is -100℃~100℃, the bolt and nut model should be a combination of 7055 bolts and 7075 nuts;

[0090] When the temperature in the index requirement is below -100℃, the bolt and nut model should be a combination of TC4ELI bolts and TC4ELI nuts or a combination of 316L bolts and 304 nuts;

[0091] When the disassembly and assembly in the index requirements requires repeated disassembly and assembly, the bolts and nuts should be copper-plated and molybdenum disulfide-coated;

[0092] When the disassembly and assembly in the index requirements is that there is no need for repeated disassembly and assembly, the bolt and nut models should be chemically passivated bolts and nuts.

[0093] Preferably, the selection principle is as follows: the bolt under the tensile condition selects the minimum value within the range of bolt length under the tensile condition, and the bolt under the shear condition selects the maximum value within the range of bolt length under the shear condition.

[0094] Preferably, the index requirements include strength index, stiffness index, installation index and environmental index.

[0095] Preferably, the strength index includes high and low temperature tensile strength, yield strength, cross-sectional shrinkage, elongation, impact toughness, stress brittleness, stress corrosion, fatigue, stress fracture, stress durability and hydrogen embrittlement; the stiffness index is the connection stiffness index after the fastener is installed; the installation index includes installation restrictions, number of disassembly and assembly, and maintenance and replacement; the environmental indicators include mechanical environment, thermal environment, natural environment and medium environment.

[0096] Example

[0097] The unified design method for fastening system matching includes two aspects: the design and selection method of bolt thread length based on clamping thickness, and the unified design method for fastening system based on scenario matching. The design and selection method of bolt thread length based on clamping thickness, the bolt thread length designed by this method can meet the engineering design requirements that the bolt thread section is indented 2 to 3 times the pitch of the end face of the connected part and the length of the bolt end exposed to the nut is as small as possible, but not less than 2 times the pitch under any connection scenario; the bolt length selected by this method can meet the engineering design requirements of "the bolt thread section is indented 2 to 3 times the pitch of the end face of the connected part and the length of the bolt end exposed to the nut is as small as possible, but not less than 2 times the pitch", with the goal of lightweight, and the goal of the strongest shear performance, and the unified design method for fastening system based on scenario matching, fastener selection and matching are carried out according to the characteristic elements of scenario attributes, so as to realize the unified design of fastening system under scenario mode.

[0098] This method provides a theoretical basis and technical support for the compilation of standards for bolt products at all levels and the selection of bolt length in various application fields. This method also provides a technical basis for the matching design of fastening systems in various scenario modes.

[0099] like Figure 1 As shown, the fastening system includes: a bolt 1 , a first connected member 2 , a second connected member 3 and a nut 4 .

[0100] The present invention is a method for designing a fastening system with unified type matching, including a method for designing and selecting a bolt thread length based on a clamping thickness, and a method for designing a fastening system with unified type matching based on a scenario matching.

[0101] 1. Design and selection method of bolt thread length based on clamping thickness

[0102] It consists of two parts: the analytical formula for bolt thread length design and the calculation formula for bolt length selection. The analytical formula for bolt thread length design can quickly calculate and determine the length sequence of the bolt rod section under the condition of a given bolt length size sequence, and give a scientific and reasonable reference value for the thread length according to the development and change level of the bolt finishing process, thereby guiding the design and standard compilation of bolt products. The bolt products designed based on this formula can meet the engineering design requirements of "the bolt thread section is indented 2 to 3 times the length of the end face of the connected part and the length of the bolt end exposed from the nut is as small as possible, but not less than 2 times the pitch" under all clamping thickness conditions, and serve as a theoretical basis to promote the standardization of bolt products. The calculation formula for bolt length selection can calculate the clamping thickness and nut height in the fastening system with one click, and intelligently push the length of tensile or shear-resistant bolts, so as to achieve the design goals of lightweight tensile bolts and high shear performance of shear-resistant bolts.

[0103] (1) Analytical formula for bolt thread length design

[0104] The relevant symbols are explained as follows:

[0105] Table 1 Symbols

[0106] symbol unit illustrate A mm Length of the bolt end protruding from the nut B mm Bolt thread indentation length from the end face of the connected part H mm Clamping thickness ls mm Bolt rod length L mm Total length of bolt S mm Nut thickness p mm Pitch q mm Bolt end length L0 mm Bolt length L dimensional runout interval H0 mm Minimum change interval of clamping thickness S0 mm The thickest nut thickness currently selected b mm Thread segment length

[0107] According to the engineering design principle that "the bolt thread section is indented 2 to 3 times the length of the end face of the connected part and the length of the bolt end exposed from the nut is as small as possible, but not less than 2 times the pitch", the values ​​of A and B should be greater than 2 times the pitch, specifically:

[0108] A≥2p, let A=2p+a1, then a1≥0;

[0109] B≥2p, let B=2p+b0, then b0≥0;

[0110] according to Figure 1 As shown, H=ls+B=ls+2p+b0 ①

[0111] according to Figure 1 As shown, L=H+S+A=ls+2p+b0+S+2p+a1=ls+S+4p+a1+b0②

[0112] Assume q = 2p + a0, according to the current process level 1.5p ≤ q ≤ 2p, then -0.5p ≤ a0 ≤ 0 ③

[0113] according to Figure 1 As shown, L = ls + b + q = ls + b + 2p + a0④

[0114] ②-④, we get b=S+2p+a1+b0-a0

[0115] Assume a1+b0=c, then b=S+2p+c-a0⑤

[0116] From ③⑤, we can know that S+2p+c≤b≤S+2.5p+c⑥ [according to which we get the range of b value]

[0117] From ②⑤, we know that L=ls+S+4p+c, so L-ls=S+4p+c ⑦

[0118] From ①⑦, we can see that H=LS-2p-a1, so L=H+S+2p+a1⑧

[0119] According to formula ⑦, due to the design specifications of the fastener industry, L-ls is a fixed value (this value does not change under the same diameter specification); the size sequence of L itself has also been determined due to industry practices, generally a size sequence with a jump interval of 2mm. In order to ensure that ls in the product standard is also an integer sequence or an integer multiple of 0.5, S+4p+c is required to be an integer or an integer multiple of 0.5.

[0120] According to the above derivation, to determine the ls size sequence based on the L value, you only need to determine the c value, which is also a core design element, that is, the design margin of the thread length. In order to achieve the lightweight design goal, you only need to determine the minimum c value that meets the design requirements.

[0121] According to formula ⑧, when the clamping thickness H changes slightly (for example, H increases by 0.1mm), the selected bolt length L jumps from the previous dimension value to the next dimension value (assuming that the jump interval of L is 2mm), that is, L on the left side of the equation increases by 2mm. While S and 2p remain unchanged, H increases by 0.1mm, so a1 must increase by 1.9mm on the original basis, then a1≥1.9, so c≥1.9.

[0122] According to the above analysis process, c≥L0-H0 ⑨

[0123] Under different diameter specifications, according to formula ⑦⑨, find the minimum c value that can make L an integer under each specification. In order to cover all application scenarios, S at this time needs to be the thickness of the thickest nut.

[0124] After the c value is determined, the ls size sequence can be calculated with one click according to formula ⑦; the b value range can be calculated with one click according to formula ⑥, and a reasonable reference b value can be selected. This completes the entire design process.

[0125] (2) Calculation formula for bolt length

[0126] 1) Tensile bolt L ≥ H + 2p + S (take the minimum value of L) ⑩

[0127] Tensile bolts must take lightweight design requirements into consideration and ensure that the length of the bolt exposed from the nut is at least 2 times the pitch but as small as possible. Formula ⑩ meets this design requirement. At this time, it is only necessary to verify whether B is greater than 2 times the pitch.

[0128] Verify as follows:

[0129] Since the thread length design process is determined according to the thickness of the thickest nut, it can meet the engineering design requirements of "the bolt thread section is indented 2 to 3 times the pitch of the end face of the connected part and the length of the bolt end protruding from the nut is as small as possible, but not less than 2 times the pitch" under any clamping thickness conditions. Therefore, if the thickest nut is selected, it will obviously meet the requirements that both A and B are greater than 2 times the pitch.

[0130] If a thinner nut is selected, then L≥H+2p+S (take the minimum value of L). L may be smaller than the L value when the thickest nut thickness is selected, but L-ls is a constant, then ls becomes smaller, H remains the same, and then B becomes larger, which will definitely meet the requirement of being greater than 2 times the pitch.

[0131] 2) Shear bolt L≤H+S0+c+2p (take the maximum value of L)

[0132] According to formula ⑦ At this time, the bolt selected is the longest bare rod section ls that ensures that the bolt thread is retracted into the connected part by at least 2 times the pitch, which can achieve the strongest shear resistance. Since (b+q) is a fixed value, choosing the longest ls means choosing the longest bolt, and the longest bolt can definitely meet the requirement of exposing the nut by at least 2 times the pitch.

[0133] It has been verified that the bolts selected at this time can achieve the strongest shear resistance under the premise of meeting the basic design requirements of the project: "the bolt thread section is indented 2 to 3 times the pitch of the end face of the connected part and the length of the bolt end protruding from the nut is as small as possible, but not less than 2 times the pitch."

[0134] 2. Unified design method of fastening system based on scenario matching

[0135] For typical application scenarios of fastening connections, a comprehensive analysis is conducted on the working characteristics, load characteristics, environmental conditions, application requirements, structural forms, etc., and the attribute characteristics of the scenarios are extracted. The attribute characteristic elements of the scenarios mainly include load type and magnitude, salt spray conditions, high and low temperature environment, medium environment, functional requirements, installation requirements, etc. These attribute characteristic elements can be mapped to specific index requirements such as strength, stiffness, environment, and installation. These four types of indicators can cover the index requirements of all fastening system application scenarios, as shown in Table 2.

[0136] Table 2 Technical indicators of fastening system

[0137]

[0138]

[0139] According to the indicator requirements, the scenario requirements are layered and categorized, as shown in Table 3.

[0140] Table 3. Scenario demand statistics under indicator constraints

[0141]

[0142]

[0143] Fastener materials are selected based on load-bearing, temperature, etc., surface coatings are selected based on salt spray, disassembly, etc., and fastener head types are selected based on installation space, etc., thereby completing the unified design of the fastening system based on scenario matching.

[0144] (I) Taking the design of a double hexagon head bolt as an example, calculate the bolt thread length under the MJ6 specification and compile the dimension sequence of the product standard dimension table.

[0145] The formulas that need to be referred to during design are:

[0146] L-ls=S+4p+c ⑦

[0147] c≥L0-H0 ⑨

[0148] S is the thickness of the thickest nut currently. According to the new generation of fastener standards, the thickest nut thickness is the thickness of the double hexagonal self-locking nut. The thickness of the MJ6 double hexagonal self-locking nut is 8.1mm, and the pitch is 1.

[0149] L-ls=12.1+c

[0150] c≥L0-H0=2-0.1=1.9

[0151] according to And ensure that L-ls is the minimum value of c for an integer, so take c = 1.9

[0152] At this time, L-ls=14

[0153] According to the size sequence of L, the size sequence of ls is calculated with one click, as shown in the following table:

[0154] Table 4 Structural dimensions

[0155]

[0156]

[0157] According to formula ⑥S+2p+c≤b≤S+2.5p+c, 12≤b≤12.5, the reference value of b is the integer 12.

[0158] The design of the bare rod size sequence of the MJ6 double hexagon head bolt is completed as above, and the reference value of the threaded section length b under the MJ6 specification is designed. Other size sequences within the range of MJ4 to MJ24 can be designed according to this process.

[0159] (ii) Still taking a double hexagon head bolt as an example, select the bolt length required in a certain application scenario under the MJ6 specification.

[0160] (1) Tensile bolts

[0161] Application scenario: Use MJ6 double hexagonal self-locking nuts with a thickness of 8.1mm;

[0162] The clamping thickness is 8mm;

[0163] The bolt side uses an inner chamfer flat washer with a thickness of 1.5mm.

[0164] According to formula ⑩, the tensile bolt L≥H+2p+S (take the minimum value of L)=8+2+8.1=18.1. According to Table 4, L is 20 and ls corresponds to 6.

[0165] (2) Shear bolts

[0166] Application scenario: Use MJ6 double hexagonal self-locking nuts with a thickness of 8.1mm;

[0167] The clamping thickness is 10mm;

[0168] The bolt side uses an inner chamfer flat washer with a thickness of 1.5mm.

[0169] According to formula ①1, the shear bolt L≤H+S0+c+2p (take the maximum value of L)=10+8.1+1.9+2=22. According to Table 4, L is 22 and ls corresponds to 8.

[0170] (III) Taking the typical application scenario of section docking as an example, the fastening system is designed to match the overall type.

[0171] The butt bolts of several types of launch vehicle sections face high load conditions and need to be repeatedly disassembled and assembled, as well as facing conventional salt spray environments and operating temperatures in the medium temperature range. Based on this, a low-cost fastening system is designed.

[0172] For high load conditions, fasteners in Table 3 can be selected. Considering the low cost requirement, 17-4PH bolts + PH13-8Mo nuts are selected. This selection meets the requirements of the medium temperature zone. Considering the conventional salt spray environment and repeated disassembly and assembly requirements, the surface treatment of 17-4PH bolts is passivation + molybdenum disulfide coating, and the surface treatment of PH13-8Mo nuts is copper plating + molybdenum disulfide coating.

[0173] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

[0174] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A method for designing a uniform matching fastening system, characterized in that: The following steps are involved: Determine the design allowance for thread length; According to the design margin of the thread length, determine the size sequence corresponding to the total length of the bolt and the length of the bolt polished rod; Calculate the range of bolt length under tensile conditions; Calculate the range of bolt length under shear conditions; According to the value range of the bolt length under the tensile condition and the value range of the bolt length under the shear condition, the bolt size is selected from the size sequence according to the selection principle; According to the index requirements of the fastening system application scenario, determine the bolt model that meets the bolt size and complete the bolt matching selection.

2. The method for designing a fastening system matching system according to claim 1, characterized in that: The specific method for determining the design margin of the thread length is as follows: c≥L0-H0 c=a1+b0 a1=A-2p b0=B-2p Among them, c is the design margin of thread length, L0 is the dimensional runout interval of bolt length L, H0 is the minimum variation interval of clamping thickness; A is the length of the bolt end protruding from the nut, B is the length of the bolt thread retracted from the end face of the connected part; p is the pitch.

3. The method for designing a fastening system matching system according to claim 1, characterized in that: The size sequence corresponding to the total length of the bolt and the length of the bolt polished rod section is determined according to the design margin of the thread length, specifically: the combination of the total length of the bolt L and the length of the bolt polished rod section ls that satisfies the formula L-ls=S+4p+c is taken to form a size sequence, wherein L is the total length of the bolt, ls is the length of the bolt polished rod section, S is the nut thickness, p is the pitch, and c is the adjustment parameter.

4. The method for designing a fastening system matching system according to claim 1, characterized in that: The value range of the bolt length under the tensile condition is specifically: L≥H+2p+S Among them, L is the total length of the bolt, p is the pitch, H is the clamping thickness, and S is the nut thickness.

5. The method for designing a fastening system matching system according to claim 1, characterized in that: The value range of the bolt length under the shear resistance condition is specifically: L≤H+S0+c+2p Among them, L is the total length of the bolt, H is the clamping thickness, p is the pitch, S0 is the thickest nut thickness currently selected, and c is the design allowance for the thread length.

6. The method for designing a fastening system matching system according to claim 1, characterized in that: According to the index requirements of the fastening system application scenario, the bolt and nut models that meet the bolt size are determined, specifically: When the bearing capacity in the index requirement is greater than or equal to 1100MPa, the bolt and nut model should be a combination of PH13-8Mo bolts and GH4169 nuts, a combination of 17-4PH bolts and PH13-8Mo nuts, or a combination of TC4 bolts and TC16 nuts; When the bearing capacity in the index requirement is less than 1100MPa, the bolt and nut model should be a combination of 7055 bolts and 7075 nuts or a combination of 316L bolts and 304 nuts; When the salt spray resistance time in the index requirement is greater than or equal to 480h, the surface of the bolts and nuts shall be T35 nano coating or zinc-nickel alloy coating; When the temperature in the index requirement is above 300℃, the bolt and nut model should be a combination of GH4169 bolts and GH2132 nuts; When the temperature in the index requirement is 100℃~300℃, the bolt and nut model should be a combination of TC4 bolts and TC16 nuts, a combination of PH13-8Mo bolts and GH4169 nuts, or a combination of 17-4PH bolts and PH13-8Mo nuts; When the temperature in the index requirement is -100℃~100℃, the bolt and nut model should be a combination of 7055 bolts and 7075 nuts; When the temperature in the index requirement is below -100℃, the bolt and nut model should be a combination of TC4ELI bolts and TC4ELI nuts or a combination of 316L bolts and 304 nuts; When the disassembly and assembly in the index requirements requires repeated disassembly and assembly, the bolts and nuts should be copper-plated and molybdenum disulfide-coated; When the disassembly and assembly in the index requirements is that there is no need for repeated disassembly and assembly, the bolt and nut models should be chemically passivated bolts and nuts.

7. The method for designing a fastening system matching system according to claim 1, characterized in that: The selection principle is specifically as follows: the bolt under the tensile condition selects the minimum value within the range of bolt length under the tensile condition, and the bolt under the shear condition selects the maximum value within the range of bolt length under the shear condition.

8. The method for designing a fastening system matching system according to claim 1, characterized in that: The index requirements include strength index, stiffness index, installation index and environmental index.

9. The method for designing a fastening system matching system according to claim 8, characterized in that: The strength indicators include high and low temperature tensile strength, yield strength, cross-sectional shrinkage, elongation, impact toughness, stress brittleness, stress corrosion, fatigue, stress fracture, stress durability and hydrogen embrittlement; the stiffness index is the connection stiffness index after the fastener is installed; the installation index includes installation restrictions, number of disassembly and assembly, and maintenance and replacement; the environmental indicators include mechanical environment, thermal environment, natural environment and medium environment.

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