Bolts made of high-strength steel, or which require a large preload, can be called high-strength bolts. High-strength bolts are often used for the connection of bridges, rails, high-pressure and ultra-high pressure equipment. The breakage of such bolts is mostly brittle fracture. High-strength bolts used in ultra-high pressure equipment require a large pre-stress to ensure the seal of the container.
1. Subject content and scope of application
This technical requirement specifies the technical requirements for the manufacture, installation and inspection of high-strength bolted joints of steel structures for mobile machinery. Content not specified in this technical requirement shall be implemented in accordance with relevant national standards. This technical requirement applies to mobile mechanical steel structures that require the application of high strength bolted connections. This technical requirement applies to quality control and construction methods for in-plant and on-site installation.
2, joint surface treatment
(1) Friction type high-strength bolt connection requires the joint surface at the joint to be closely attached and has a sufficient coefficient of friction. When the design requirements for the joint surface are not specified, the treatment shall be carried out as follows: sandblasting or shot blasting of the high-strength bolt joint surface to remove impurities such as rust and oil on the surface to reach the Sa2.5 level standard. The roughness is 50~75μm, and the friction coefficient must not be lower than 0.40. When the drawings are specified, they shall be implemented in accordance with the drawings.
(2) After the treated high-strength bolt joint friction surface, protective measures should be taken to prevent contamination of dirt and oil. Do not mark any of the friction surfaces on the high-strength bolted joints. It is especially necessary to prevent contamination of the connecting surface during storage in the factory, or during transportation and storage at the installation site. The installation unit should pay special attention to the characteristics of the clean friction surface of the connecting plate of the high-strength bolt and the connecting surface of the mother. It is not permissible to use the grinder to grind the connecting plate connection surface and the mating connection surface.
3. Test of anti-slip coefficient of friction surface of high strength bolt
The anti-slip coefficient test shall be based on the steel structure manufacturing batch, with a manufacturing batch of 2000t for a single project, and one batch of less than 2000t, and two or more surface treatment processes for the friction surface of a single project. Then each surface treatment process needs to be inspected. Three sets of test pieces per batch. If the connection is to spread to an external company, each company should perform an anti-slip coefficient test.
(1) The test piece for the anti-slip coefficient test shall be processed by the factory or the diffusion enterprise. The test piece and the steel structural member represented by the test piece shall be made of the same material, the same batch, the same friction surface treatment process and the same surface. State, and apply high-strength bolted joints of the same performance level in the same batch, and store under the same environmental conditions. The anti-slip coefficient test is carried out according to the test method of GB50205 "Code for acceptance of construction quality of steel structure engineering".
(2) The minimum value of the anti-slip coefficient test must be equal to or greater than the design specified value. When the above specified values ​​are not met, the friction surface of the component should be reprocessed. The treated component friction surface was re-inspected.
4. Connection and installation of friction type high-strength bolts for steel structures
(1) Preparation before installation
(2) Select qualified bolts, nuts and washers. The connection torque factor guarantee period is six months from the date of delivery.
(3) Bolts, nuts, and washers are not acceptable for the following conditions and are prohibited.
a, the source (manufacturer) is unknown;
b, the mechanical properties are unknown;
c, the torque coefficient k is unknown;
d, cracks, scratches, burrs, bends, rust, thread wear, oil stains, water wetted or defective;
e, no performance test report is attached;
f, mixed with other batch bolts;
g. Bolts with insufficient length, that is, those whose bolt heads are not exposed after tightening. Generally, the length of the end face of the protruding nut is preferably 2 to 3 threads.
h. The connection torque coefficient exceeds the guarantee period.
Pay special attention to waterproofing during transportation and storage.
(4) Before the construction of large hexagonal high-strength bolts, the torque coefficient of the high-strength bolt connection pair shall be re-examined according to the factory batch, and 8 sets shall be re-inspected in each batch. The average value of 8 sets of torque coefficient shall be within the range of 0.110~0.150. The deviation should be less than or equal to 0.010. The method for retesting the torque coefficient is carried out in accordance with the provisions of GB50205 "Code for the Acceptance of Construction Quality of Steel Structure Engineering". High-strength bolts should be installed in a short period of time after the test. 
Editor in charge: Hu Na
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