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GB/Z 32564-2016 English PDF (GBZ32564-2016)

GB/Z 32564-2016 English PDF (GBZ32564-2016)

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GB/Z 32564-2016: Nut design guide

This Guide gives guidelines for nut design in accordance with GB/T 3098.2, so as to prevent failure form of thread tripping when the static tension is overload.
GB/Z 32564-2016
GB
NATIONAL STANDARDIZATION GUIDANCE TECHNICAL
DOCUMENT OF THE PEOPLE 'S REPUBLIC OF CHINA
ICS 21.060.10
J 13
Nut design guide
(ISO/TR 16224.2012, Technical aspects of nut design, MOD)
ISSUED ON. FEBRUARY 24, 2016
IMPLEMENTED ON. JUNE 1, 2016
Issued by. General Administration of Quality Supervision, Inspection
and Quarantine;
Standardization Administration Committee.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Codes ... 4
4 Design principle ... 6
5 Calculation method of bolt and nut connection pair based on Alexander?€?s theory ... 13
6 Comparison between the specified values of GB/T 3098.2 and the
calculated results ... 17
Bibliography ... 21
Foreword
This Guide was drafted in accordance with the rules given in GB/T 1.1-2009. This Guide uses redrafting method to modify and adopt ISO/TR 16224.2012 Nut design guide (English version).
The technical differences and reasons between this Guide and ISO/TR
16224.2012. in normative references, this Guide used Chinese Standards to replace the International Standards (Clause 2), so as to comply with China's basic standards for fasteners.
This Guide was proposed by China Machinery Industry Federation.
This Guide shall be under the jurisdiction of National Technical Committee on Fasteners of Standardization Administration of China (SAC/TC 85).
Main drafting organization of this Guide. China Machine Productivity
Promotion Center.
Drafting organizations of this Guide. China First Automobile Co., Ltd.
Technology Center, Haiyan Yuxing Nut Co., Ltd., Shanghai Jinma High
Strength Fastener Co., Ltd., Zhejiang State Inspection Technology Co., Ltd., Dongfeng Commercial Vehicle Co., Ltd. Dongfeng Commercial Vehicle
Technology Center, Shaoxing Mountain High Pressure Fastener Co., Ltd.
This Guide is interpreted by Secretariat of National Technical Committee on Fasteners of Standardization Administration of China.
Nut design guide
1 Scope
This Guide gives guidelines for nut design in accordance with GB/T 3098.2, so as to prevent failure form of thread tripping when the static tension is overload.
This Guide is also applicable to non-standard nut or internal thread with bolt (in accordance with GB/T 192). However, dimension factors, such as the
width of the edges or other dimensions associated with the stiffness of the nut, the thread tolerances, etc., shall affect the load carrying capacity of bolt and nut connection pair. Therefore, the calculation results shall be subjected to validation test.
NOTE The "bolts" and "nuts" mentioned in this Guide are used as general terms for internal and external threaded fasteners.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 192, General purpose metric screw threads-Basic profile (GB/T
192-2003, ISO 68-1. 1998, MOD)
GB/T 196, General Purpose Metric Screw Threads - Basic Dimensions
(GB/T 196-2003, ISO 724.1993, MOD)
GB/T 3098.1, Mechanical Properties of Fasteners - Bolts, Screws and
Studs (GB/T 3098.1-2010, ISO 898-1.2009, MOD)
GB/T 3098.2, Mechanical properties of fasteners - Nuts (GB/T
3098.2-2015, ISO 898-2.2012, MOD)
ISO 18265, Metallic materials - Conversion of hardness values
3 Codes
The codes given below apply to this document.
AS - actual cross-sectional area of bolt, mm2
AS, nominal - thread nominal stress cross - sectional area, mm2
ASb - external thread shear area, mm2
ASn - internal thread shear area, mm2
C1 - correction coefficient of nut expansion
C2 - correction coefficient of bolt trip strength affected by thread bending C3 - correction coefficient of nut's tripping strength affected by thread bending d - external thread nominal diameter, mm
d1 - external thread basic small diameter, mm
d2 - external thread basic medium diameter, mm
d3 - external thread small diameter, mm
dA - equivalent diameter of AS, mm
D - nominal diameter of internal thread, mm
D1 - basic small diameter of internal thread, mm
D2 - basic medium diameter of internal thread, mm
DC - nut counterbore diameter, mm
Dm - average diameter of the counterbore section on nut effective height or screw thread length meff, mm
F - tension load, N
FBb - bolt breaking load, N
Fm - ultimate tensile load, N
Fp - guaranteed load, N
FS - trip load of bolt and net connection pair, N
FSb - external thread trip load, N
FSn - internal thread trip load, N
Fu - limit clamping force, N
Fy - yield clamping force, N
Hc - face chamfer height, mm
H - thread original triangle height, mm
m - nut height, mm
mc - nut critical height of screw thread failure and fracture failure probability, mm
meff - nut effective height, mm
meff, c - nut effective critical height of screw thread failure and fracture failure probability, mm
P - pitch, mm
Rm - tensile strength, MPa
Rmn - nut tensile strength, MPa
RS - strength ratio
s - nut side width, mm
Sp - guaranteed stress, MPa
x - shear strength / tensile strength ratio
??th - friction coefficient between threads
- bolt material shear strength, MPa
- nut material shear strength, MPa
4 Design principle
4.1 Forms of break which may appear during bolt and nut connection
pair when withstanding tensile load
When the bolt and nut connection pair is subjected to an overloaded static tension, the following three styles of failure may appear.
- bolt break when the threaded screw length is sufficient, nut or internal thread material strength is sufficient;
- external thread tripping when the threaded screw length is too short, nut or internal thread material strength is high;
C3 are empirically determined. Therefore, the effects of shear strength and tensile strength ratio x shall be taken into account in equation (5).
For other materials (such as stainless steel and non-ferrous metals), the value of x should be considered separately, as shown in reference [7].
4.3.2.2 Bolt and nut pitch deviation
Based on the results of the finite element analysis [8], the thread tripping occurred initially at the first buckled thread near the nut support surface, because in bolt and nut connection pair, there is no pitch deviation, the cut surface is smallest, the load is maximum. Therefore, for bolt and nut
connection pair with pitch deviation, the trip load FSb and FSn shall vary, because such deviation shall cause the load to be shared by each of the screw thread. From the point of view of the thread bearing capacity, it is more preferable that the bolt pitch is slightly smaller than the bolt and nut connection pair of nut pitch.
4.3.2.3 Friction coefficients between threads and bearing surfaces
As described in 4.2.2.2 and 4.2.3.2, the bolt breaking load FBb and the trip load FS of the bolt and nut connection pair shall be reduced when the
tightening load is applied.
The reduction of FBb is caused by the complex stress calculated by equation (4), in which the friction coefficient between the threads (??th) is significant. On the other hand, the decrease in FS is mainly due to the expansion of the nut caused by the slip of the thread. The effect of ??th on it is not clear. It shows that the greater the ??th, the higher the probability of occurrence of bolt breakage.
In the design procedure of 5.2, only the friction coefficient for some ranges is allowed to have a relative reduction of 5% of the breaking load.
In the future, it is proposed to introduce a breaking load (i.e., limit clamping force Fu) instead of 0.95 FBb, and the fastening correction coefficient C1' instead of C1.
5 Calculation method of bolt and nut connection pair
based on Alexander?€?s theory
5.1 General
Figure 3 summarizes the Alexander theory. For the bolt and nut connection pair combined by specific material performances, its trip load FS = min (FSb, FSn) and the screwing shear area, i.e., nut effective height meff, the number of step 3. considering the difference between the breaking load and the
guaranteed load, 0.98 FSn, min shall be taken as the guaranteed load Fp. Ensure that stress Sp is equal to Fp / As, nominal.
Affected by correction coefficient C3, the nut thread trip load of mandrel and nut connection pair is expected higher than the bolt and nut connection pair. about 14% higher for grade 5, about 10% for grade 8, grade 9, about 3% for grade 10; see Figure 1 and equation (5).
6 Comparison between the specified values of GB/T
3098.2 and the calculated results
6.1 General rules for obtaining specified values
It is well known that Alexander theory is the theoretical basis of GB/T 3098.2. But this theory is based on the hardness of the nut material, taking into account the other technical conditions of the bolts and nuts to determine the minimum nut height (see 5.2). Therefore, the minimum height of the nominal diameter nut ...

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