Bolting Knowledge

When connecting bolts or screws, it is necessary to pay attention to some of their basic characteristics, and then conduct standardized operations according to different uses and properties of bolts. This article mainly analyzes some basic knowledge and essentials of bolt connection.

If the installation is on a thin steel plate, we will use self tapping screws and rivet fasteners, so the specification and reservation must be consistent. Since the installation is carried out on the large plane of the steel plate, the spacing of self tapping screws and rivet fasteners should be beautiful and neat, and should meet the design requirements. Attention should be paid to the distance between the edge of the steel plate and the screw installation. If the distance is too far from the edge, the firmness is not enough, It is too close to the edge and easy to crack the plate.

During the bridge installation and construction, steel structure bolt products will be used in large quantities. Due to the importance of the bridge, each batch of bolts used shall be sampled and tested, and the structural parts used for on-site matching bolts shall be tested for the anti slip coefficient. All results shall be enforced according to the national standards. It shall be ensured that the bolt materials and production batch numbers used are all products of the same batch. Not only the smoothness of the bolt, but also the edge of the connecting steel plate shall be inspected for burrs and roughness. After the bolt installation is completed, the torque shall be rechecked within 1 hour and 48 hours respectively. For the inspection essentials, refer to GB50205.

The torque recheck of steel structure bolts is very important. For this testing method and standard, the industry association issued a professional testing process, which is divided into torque method testing and angle method testing. It calculates the correct torque value according to a formula, and then uses a professional torque wrench for testing reference. If it is too tight, loosen it a little, and if it is too loose, tighten it a little, In principle, it is necessary to ensure that the torque preload of each bolt is the same. We draw a line on the tail end of the bolt and the vertical corresponding position of the nut to make a mark, then back up the nut by 60 degrees, and then screw the nut to the original position with a torque wrench. This is a simple process of torque re inspection. If the acceptable deviation in this process is less than 10%, it can be regarded as qualified. Since the plane of the steel plate is not absolutely flat, the connection between the head and the steel plate is uneven after the bolts are tightened. Therefore, a tolerance range is allowed for the torque value of each bolt. The corner detection method is similar.

Different from ordinary bolts, the installation process of steel structure bolts can be divided into a process of clockwise tightening, initial rotation and secondary tightening. The initial tightening and secondary tightening of bolts are not invalid operations, but in the process of repeated tightening, the bolt head and steel plate can better fit, and this process can also make the bolt stress more uniform. For exposed threads, like ordinary bolts, two turns of thread is the best. As for the hole location where the bolt passes through the steel plate, we cannot adopt the method of gas welding and burning, because the hole burned in this way is uneven in size and has too many burrs around, which will affect the bearing torque of the effective sectional area of the bolt during installation.