Tightening and tightening friction bolts

Tightening the bolts of each connection is done in two stages. First, a number of bolts are tightened to full tightness to ensure that the contact surfaces are completely bonded together, then all the bolts are fully tightened in the hole. In the second stage, the bolts are pre-tensioned by additional rotation of the nut. In each of the stages of tightening the bolts, the bolts should be tightened from the part of the connection where the connection is more rigid and the plates deform less. In patches, the more rigid part of the connection is the middle of the connection plate. After tightening the middle bolts, maintaining symmetry and order, the side bolts are tightened up to the free edge of the connection plate. Then the middle bolts can be tightened to ensure that tightening the side bolts has not removed them from a fully tightened state.

In all stages of tightening the bolts, care should be taken to prevent the bolt and nut from rotating together. Full tightness in a bolt is defined as a condition in which a skilled worker cannot tighten the bolt with a conventional wrench without applying force to the wrench handle with his own weight. To pre-tighten such a bolt, the nut must be turned over by the amount specified in the table below. This additional rotation can be provided with the help of a long-handled wrench or with a conventional wrench using two workers or with an air wrench. The achievement of pre-tensioning must be confirmed by a calibrated wrench (torque meter).

If air wrenches are used to tighten the bolts, the air pressure must be adjusted so that in one step, the nuts are brought to the full tightness stage without turning the bolt and in the next step, the bolts are pre-tensioned by increasing the air pressure or by hand in the manner described above. Adjusting the air compressor involves the use of a calibrated wrench (torque meter) or successive trial and error and must be done with complete accuracy. It is not permitted to loosen and reuse bolts that have reached their preload limit. In high-strength bolt connections, the surfaces in contact with the bolt head or nut must not have a slope of more than one twentieth of the plane perpendicular to the bolt axis. If this condition is not met, the non-parallelism of the surfaces must be compensated for by using a sloped washer. The parts connected to each other with high-strength bolts must be fully mated and no filler sheet or any other deformable material must be placed between them, but the use of filler sheet with the same strength as the connecting parts and uniform thickness is permitted. When the parts are installed, all connecting surfaces, including the surfaces adjacent to the bolt heads and nuts, must be free of flaking parts and other waste materials. In particular, the contact surfaces of friction joints must be completely clean and free of rust, paint, varnish, oils, and other materials.