China piping solution supplier: www.epowermetals.com

Tightening torque standard of bolts

This article will list the tightening torque standards of various screws. When the user does not specify the tightening torque requirements, the standards we refer to.
It should be emphasized that: tightening torque and destructive torque are two concepts, and tightening force (torque) refers to the recommended value of screws screwed into the workpiece; Breaking torque (i.e. breaking torque) refers to the minimum value of breaking the screw (see the breaking torque standard of fasteners gb3098.13 for details). Obviously, the tightening torque is less than the breaking torque.

This is the tightening torque of ordinary bolts:

Bolt strength grade

Yield strength

N/mm2

Nominal diameter of bolt  mm
6 8 10 12 14 16 18 20
Tightening torque   N.m
4.8

5.6

6.8

8.8

10.9

12.9

240

300

480

640

900

1080

4-5

5-7

7-9

9-12

13-16

16-21

10-12

12-15

17-23

22-30

30-36

38-51

20-25

25-32

33-45

45-59

65-78

75-100

36-45

45-55

58-78

78-104

110-130

131-175

55-70

70-90

93-124

124-165

180-201

209-278

90-110

110-140

145-193

193-257

280-330

326-434

120-150

150-190

199-264

264-354

380-450

448-597

170-210

210-270

282-376

376-502

540-650

635-847

Continued from the above table:

Bolt strength grade

Yield strength

N/mm2

Nominal diameter of bolt     mm
22 24 27 30 33 36 39
Tightening torque    N.m
4.8

5.6

6.8

8.8

10.9

12.9

240

300

480

640

900

1080

230-290

290-350

384-512

512-683

740-880

864-1152

300-377

370-450

488-650

651-868

940-1120

1098-1464

450-530

550-700

714-952

952-1269

1400-1650

1606-2142

540-680

680-850

969-1293

1293-1723

1700-2000

2181-2908

670-880

825-1100

1319-1759

1759-2345

2473-3298

2968-3958

900-1100

1120-1400

1694-2259

2259-3012

2800-3350

3812-5082

928-1237

1160-1546

1559-2079

2923-3898

4111-5481

4933-6577

Tightening torque of metric bolts Q / STB 12.521.5-2000

Scope: this standard is applicable to the tightening torque of bolts with mechanical properties of grade 10.9 and specifications from M6-M39. This standard is not applicable to bolts with nylon washers, sealing washers and other non-metallic washers.

Material 45, 35CrMo or equivalent
Nominal diameter of thread(mm) Range Nm(kgfm) Target Nm(kgfm)
M6

M8

M10

M12

M14

M16

M18

M20

M22

M24

M27

M30

M33

M36

M39

8.8-14.7(0.9-1.5)

14.7-34(1.5-3.5)

34-74(3.5-7.5)

54-123(5.5-12.5)

84-196(8.5-20)

147-309(15.0-31.5)

201-427(20.5-43.5)

319-608(32.5-62.0)

471-829(48.0-84.5)

588-1030(60-105)

883-1470(90-150)

1130-1910(115-195)

1470-2450(150-250)

1860-3040(190-310)

2260-3630(230-370)

12(1.2)

25(2.5)

54(5.5).

89(9.0)

137(14)

230(23.5)

315(32)

460(47)

650(66.5)

810(82.5)

1180(120)

1520(155)

1960(200)

2450(250)

2940(300)

Note: if there are clear torque requirements in the design drawings, they shall be implemented according to the requirements of the drawings.
Appendix:

Selection of bolt preload and check of bolt strength

Bolts, as connectors, are widely used. Most of them are used in locomotives, aerospace and wind turbines with high strength and high stress, while most of the main components of passenger cars are used in low stress cycle, but there are still great hidden dangers. From a safety point of view, the components connected by bolts are very expensive. Therefore, when the bolts fail, the damage is not only their own, but the whole product.
Bolt connection is an important application in automobile assembly. According to relevant data, there are usually about 1500 ~ 2000 threaded fasteners on the engine, with more than 100 varieties and specifications ranging from M6 ~ M30, of which about 100 are closely related to the safety of the vehicle. As the most important bolt specification and preload selection in the assembly process, there are theoretical deficiencies and misunderstandings.
Whether threaded fasteners are used as connections or seals, or sub parts that need to be assembled, they all have a certain yield limit. In the assembly process, if the preload is too large and the deformation of the part exceeds the yield strength of the part, the part will damage the ring. Therefore, for the assembly to work stably and effectively for a long time, the designer must carry out standardized design for the bolt preload.

1. Selection of bolt preload

As an important connecting piece, the bolt must be tightened when the assembly is installed. Before the connection bears the working load, it is under the action of force in advance. This pre added force is the pre tightening force; The purpose of pre tightening is to enhance the reliability and tightness of the connection and prevent the gap or relative slip between the connectors due to the force on the assembly mounting parts during operation. Therefore, in the design of the assembly, the size of the pre tightening force must be standardized.

1.1 reasonable selection of preload

In professional bolt fastening assembly, standard wrenches are generally equipped, and wrenches of different lengths are used for bolts with different diameter specifications. The wrench length is about 15 times of the bolt diameter. On this basis, the use of professional mechanical tools can reflect the accurate tightening torque and achieve the quantitative preload, which is particularly important for some key and important parts. Once a large-size long wrench is used to tighten a small-size bolt, it will often lead to over tightening, damage the part itself and failure of the whole connecting member.
When tightening the nut, two or more parts are compressed and the parts themselves are compressed. Like the compression deformation of the spring, the parts themselves will produce a great force on the contact surface between the nut and the bolt and the assembly. This force will cause the bolt to undergo tensile deformation. After calculation, the stress is 1.3 times of the simple axial tension, When the tensile stress produced by the bolt exceeds the strength limit of the material, the bolt is broken. It is very unscientific to fasten bolts only according to the experience of operators for mass-produced products. When tightening small bolts with a long wrench, pay more attention to the preload to avoid excessive preloading.
When using a standard wrench, the applied force can refer to table 1.
Table 1 reference value of length and applied force of common specification bolt wrench

Bolt diameter d(mml M5 M6 M8 M12 M16 M20 M2A M30 M36
Standard wrench length Llmml 75 90 120 180 2A0 300 360 450 540
Apply force F0[N) 40 48 65 100 130 170 200 250 300

1.2 torque value of bolts with common specifications
Table 2 lists the tightening torque values corresponding to different performance grades of some common specification bolts.
For designers, how much pre tightening force is required at the connection to meet the working requirements of the parts and not less than the safety stress of the bolt, so it is necessary to calculate the minimum stress required at the location and use this value to select the appropriate bolt fasteners. The upper limit of the pre tightening force applied on the bolt fastener depends on the yield strength of the bolt fastener, and the lower limit depends on the minimum pre tightening force required to meet the work needs.
Table 2 tightening torque values of bolts with common specifications

Diameter specification (mm) Stress sectional area

As(mm²)

Performance level(GB/T3098.1-2010)
4.8 5.8 6.8 8.8 9.8 10.9 12.9
RPf/MPa(mm²] RP0.2/MPa(mm²)
340 430 480 D≤16:640
D>16; 660
720 940 1100
Coarse thread
M8 36.6 13.9 17.2 19.6 26.2 29.5 38.5 45
M10 58 27.6 341 38.9 51.9 58.4 76.3 89.3
M12 84.3 48.1 59.4 67.9 90.6 101.9 133.1 155.7
M14 115 76.6 94.6 108.1 144.2 162.2 211.8 247.9
M16 157 119.5 147.7 168.8 225 253.2 330.5 386.8
Fine thread
M8*1 39.2 14.9 18.4 21 28 31.6 41.2 48.2
M10*1 64.5 30.7 37.9 43.3 57.7 65 84.8 99.3
M10*1.25 61.2 29.1 35.9 41.1 54.8 61.6 80.5 94.2
M12*1.25 92.1 52.6 61.9 74.2 99 111.4 145.4. 170.2
M12*1.5 88.1 50.3 62.1 71 94.7 106.5 139.1 162.8
M14*1.5 125 83.3 102.9 117.6 156.8 176.4 230.3 269.5
M16*1.5 167 127.1 157.1 179.5 239.4 269.3 351.6 411.4

2. Reasonable selection of bolt specifications

The assembly of rolling stock, mechanical equipment and automobile is an important link to realize the production of assembly parts, especially large assembly parts. The connection between parts is usually realized by bolts, especially the bolts in key parts. Its connection quality determines the reliability of assembly parts. Because the value of the preload applied by the bolt affects the connection quality of the thread, it is very important to select the appropriate bolt specification on the premise of ensuring the appropriate preload assembly. For threaded fasteners, their performance parameters change within a certain range, so there is basically a reference value. Therefore, the designer must consider whether the bolt specification at the fastening connection meets the working strength requirements in terms of performance.

3. Strength calculation

3.1 bolted connections in the manual

The current bolt strength analysis in the automotive industry is basically based on the theoretical calculation (Mechanical Design Manual). Due to the high strength margin required by the safety factor, the strength of the selected bolt will be much higher than the required strength. When calculating, first determine the stress of the bolt according to the connection type, assembly, load state and other conditions, Then calculate the diameter of the dangerous section of the bolt or check its strength according to the corresponding strength conditions.
When the bolt is connected and assembled, the tensile strength condition of the dangerous section of the bolt is:
Where F2 is the total tension of the bolt, F0 is the pretightening force of the bolt, where is the relative stiffness of the bolt, and the value is 0.2-0.3.

3.2 strength calculation of bolt connection in vdi2230 standard

Vdi2230 “strength check of system calculation of high strength bolt connection” standard has been widely used in Germany and other countries. It is applicable to the strength check of high strength bolts. This standard is used to check the working stress under the maximum load.
Vdi2230 standard pays more attention to the size of each section of the bolt itself in terms of checking the bolt strength, and takes into account the bolt torsional stress caused by preload and the thread friction coefficient. Compared with the roughly enlarged relative stiffness coefficient in the mechanical design manual, this standard effectively reduces the waste of strength.

4. Conclusion

Threaded fasteners are widely used in rolling stock, aerospace, wind turbine and automobile, but the attention to high-strength bolts is far from enough. Accidents caused by bolt fracture have occurred frequently in recent years. It can be seen that although the bolts are small, their position is key. Major companies, especially international brands, are also very strict in the selection and design of high-strength bolts, However, accidents also occur due to insufficient bolt strength, which should arouse our attention to the design process. Compared with the calculation method in the mechanical design manual, the German vdi-2230 standard for systematic calculation and strength verification of high strength bolted connections pays more attention to the effective utilization of strength. Details such as temperature, section change and friction coefficient are considered in the calculation, which provides closer support for the strength verification of bolts.

PREV
NEXT

RELATED POSTS

Leave a Reply

*

*

Inquery now

SUBSCRIBE TO OUR NEWSLETTER

FOLLOW US

YouTube
العربية简体中文繁體中文NederlandsEnglishFrançaisDeutschItaliano日本語한국어LatinPortuguêsРусскийEspañolไทยTürkçe
  • Email me
    Mail to us