JB/T 6688-199312-point flange bolts and 12-point flange nuts - Technical specifications (English PDF)

3.1 Main indicators

3.1.3.1 Tolerance of screw thread

a. Tolerance of outer screw thread is 6g;

b. Tolerance of inner screw thread is 6H.

3.1.3.2

The biggest permissible value of surface roughness parameter for screw thread side Ra is 3.2µm.

3.1.4

When the material yield limit is not less than 932MPa, the wrenching force that the bolt can withstand shall not be less than the provisions in Table 5.

Table 5

Thread specification mm

M6 M8 M10 M12 M14 M16 M18 M20 M22 M24

Wrenching force

N-m

Thread specification mm

M27 M0 M33 M36 M39 M42 M45 M48 M52

Wrenching force

N-m

543.0 880.8 1153 1564 1926 2407 2926 3845 3845 3.1.5 When the material yield limit is not less than 932MPa, the wrenching force that the bolt can withstand shall not be less than the provisions in Table 6.

Table 6

Thread specification mm

M6 M8 M10 M12 M16 M20 M24

Wrenching force

N-m

Thread specification mm

M27 M30×3 M33×3 M36×3 M39×3 M42×3 M45×3

Wrenching force

N-m

777.5 1273 1593 2045 2544 3200 4076 3.1.6 Geometric tolerances of bolts and nuts shall be in accordance with the provisions in Table 7-1 ~ Table 7-3.

3.1.6.1 Coaxiality

4.7

Wrenching torque test of bolts. When torque reaches to the values in Table 5,

12-spline of bolts shall not produce the permanent deformation that influences the usage and sliding between wrenches. Accuracy of torque measuring device shall not be less than ±5%.

4.8

Wrenching torque test of nuts. When torque reaches to the values in Table 5, 12 point of nuts shall not produce the permanent deformation that influences the usage and sliding between wrenches. Accuracy of torque measuring device shall not be less than ±5%.

5.1

Bolts and nuts shall be submitted for inspection in batch. Each batch shall be made of materials with same type, same size and same furnace number. It shall conduct heat treatment according to the same specification.

5.2

Appearance of bolts and nuts shall be subject to 100% inspection.

5.3

As required, bolts and nuts can be subject to magnetic particle inspection or fluorescence detection.

5.4

Bolts shall be marked at the head-top by braille or concave characters. Nuts shall be marked at the supporting surface by concave characters. Marking symbol:

30CrMnSi and 40CrNiMoA use symbol “D”; 40Cr2MoV use symbol “Z”; GH2132 use symbol “G”.

5.5

Other acceptance rules and packaging shall be in accordance with GB 90

“Acceptance inspection, marking and packaging of fasteners”.

____________________

Additional Information:

The Standard was proposed by Nanjing Institute of Gas Turbine.

This Standard shall be under the jurisdiction of Nanjing Institute of Gas Turbine.

This standard is drafted by the following organizations: Nanjing Turbine & Electric

Machinery (Group) Co., Ltd., Nanjing Institute of Gas Turbine, Harbin Steam Turbine

Plant, and China Shipbuilding Industry Corporation 703 Research Institute.

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