This standard applies to the manufacture and acceptance of 12-point head flange bolts and 12-point flange nuts (hereinafter referred to as bolts and nuts) for gas turbine power plants. JB/T 6688-1993 Technical conditions for 12-point head flange bolts and 12-point flange nuts JB/T6688-1993 Standard download decompression password: www.bzxz.net

Scope of application
Machinery Industry Standard of the People's Republic of China
Technical conditions for 12-angle head flange bolts and
12-angle flange nuts
JB/T6688—1993
This standard applies to the manufacture and acceptance of 12-angle head flange bolts and 12-angle flange nuts (hereinafter referred to as bolts and nuts) for gas turbine power plants.
Cited standards
GB3077
Thread finish, shoulder distance, undercut, chamferBasic dimensions of ordinary threads (diameter 1 to 600 mm)Tolerances and fits of ordinary threads (diameter 1 to 355 mm)Metal tensile test method
Technical conditions for alloy structural steel
GB3098.1 to 3098.4Mechanical properties of fastenersGB3099
GB3016
GB5276
GBn177
3 Technical conditions
3.1 Main indicators
Terms of bolts, screws, nuts and accessoriesNominal length of bolts, screws and studs and thread length of ordinary boltsFastenersSize codes and markings of bolts, screws, studs and nutsHigh-temperature alloy hot-rolled and forged bars for ordinary load-bearing partsThe material selection of bolts and nuts should be in accordance with the provisions of Table 1, Table 2 and Table 3. 3.1.1
30CrMnSi
40CrNiMoA
40Cr2MoV
GB2132
Approved by the Ministry of Machinery Industry in 1993—0601
Standard No.
GB3077
GBn177
Maximum Working Temperature
Implemented in 1994—0101
Material Grade
40Cr2MoV
Material Material brand
40Cr2MoV
Material brand
40Cr2MoV
0.38~0.45
Tensile strength
JB/T6688-1993
0.17~0.37
0.15~0.25
0.50~0.80
Main mechanical properties\
Tube strength
Note: 1) The main mechanical properties in the table are the values ​​at room temperature. Elongation
The heat treatment and surface treatment of bolts and nuts shall be in accordance with the provisions of Table 4. 3.1.2
Material grades
30CrMnSi
40CrNiMoA
40Cr2MoV
GH2132
Note: surface treatment is limited to nuts.
Threads of bolts and nuts
Thread tolerance
The external thread tolerance is 6g;
The internal thread tolerance is 6H.
Heat treatment
HRC30~36
HRC31~37
HRC29~35
Surface treatment
Cadmium plating
0.30~0.40
(not less than)
Folding surface yield
Impact absorption energy
1.50~1.90
Coating thickness
P≥1.5mm
The maximum allowable value of the surface roughness parameter Ra on the side of the thread is 3.2μm. 3~5μm
3~5μm
8~12μm
When the material limit is not less than 932MPa, the tightening torque that the bolt can withstand shall not be less than the provisions of Table 5. 3.1.4
Thread specification
Tightening torque
Weave specification
Plate tightening torque
Thread specification
Punching torque
Thread specification
Punching torque
M30×3
JB/T6688--1993
M33×3
M36×3
The shape and position tolerances of bolts and nuts shall be in accordance with the specifications in Table 71 to Table 7-3. 3.1.6
3.1.6.1 Coaxiality
Table 7--1
M39×3
Tolerance t
M42×3
M45×3
Basis for selecting tolerance
d(D)mm
Note: 1)
Note: 1)
JB/T66881993
The reference surface should not be part of the polished rod and the thread. If necessary, the reference plane d should be moved to a sufficient distance from the head of the bolt (avoiding the thread end) (maximum 3P).
Verticality
Tolerance t
Basis for selecting tolerance
t(D)mm
Part. If necessary, the reference plane d should be moved to a sufficient distance from the head of the bolt (avoiding the thread end). The reference plane should not be the polished rod and the medium thread.
(maximum 3P),
Table 7-3
Tolerance t
t-0.0021+0.05www.bzxz.net
t=0.00251+0.05
3.1.7 The surface of the bolt and nut shall not have cracks or burrs, and the thread shall not have broken threads. Basis for selecting tolerance
t||d(D)mm
4 Inspection rules
JB/T6688-1993
4.1 The tensile test of the specimen shall be carried out in accordance with GB228. Its tensile strength%, yield strength a, and elongation 80.s shall meet the requirements of Article 3.1.1. 4.2 The tensile test of the bolt shall be carried out in accordance with GB3098.1, and the test value shall not be less than the requirements of performance grade 9.8. 4.3 The hardness inspection of the bolt shall be carried out in accordance with GB3098.1 after heat treatment, and the test value shall comply with the requirements of Table 4. 4.4 Other tests of the bolt may be carried out in accordance with GB3098.1 as needed, and the test value shall not be less than the requirements of performance grade 9.8. 4.5 Guarantee of the nut The load test is carried out in accordance with GB3098.2, and its performance level is in accordance with the provisions of grade 9.0. 4.6 The hardness inspection of the nut is carried out in accordance with GB3098.2 after heat treatment, and the test value shall comply with the provisions of Table 4. 4.7 Torque test of bolts. When the torque reaches the value in Table 5, the 12-corner part of the bolt should not produce permanent deformation that affects use or relative sliding with the wrench. The accuracy of the torque measuring device should not be less than 5%. 4.8 Torque test of nuts. When the torque reaches the value in Table 5, the 12-corner part of the nut should not produce permanent deformation that affects use or relative sliding with the wrench. The accuracy of the torque measuring device should not be less than 5%. 5 Acceptance inspection, marking and packaging
5.1 Bolts or nuts should be submitted for inspection in batches. , each batch should be made of the same type, size and furnace material, and heat treated according to the same specification.
5.2 The appearance of bolts and nuts should be 100% inspected. 5.3 Bolts and nuts can be subjected to magnetic particle inspection or fluorescent inspection as required. 5.4 Bolts should be marked with convex or concave characters on the top surface of the head, and nuts should be marked with concave characters on the bearing surface. Marking symbols: 30CrMnSi, 40CrNiMoA use symbol D"; 40Cr2MoV uses symbol Z\; GH2132 uses symbol "G" 5.5 Other acceptance rules and packaging are in accordance with the provisions of GB90 "Fastener Acceptance Inspection, Marking and Packaging" Additional Notes:
This standard was proposed by Nanjing Gas Turbine Research Institute. This standard is under the jurisdiction of Nanjing Gas Turbine Research Institute. This standard was drafted by Nanjing Steam Turbine and Electric Machine Factory, Nanjing Gas Turbine Research Institute, Harbin Steam Turbine Factory, and the 703rd Institute of China Shipbuilding Industry Corporation.
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