The fitting bolts designed by FROMOR have substitute traditional hinged bolts and are widely used in shipbuilding, steam turbine, hydropower and other industries. Currently, two types of bolts are available, hydraulic tension and mechanical tension. The hydraulic tension is mainly applicable in pure shear occasions, while mechanical tension for complicate stress occasions. The hydraulic ultra fitting coupling bolt is one kind of bolt assembling by hydraulic expansion and contraction. It can provide a steady rigid connection between large flanges and will greatly facilitate the installation and disassembly processes.

Compared with ordinary coupling bolt, the ultra fitting coupling bolt can form interference fit between coupling bolt and flange hole (the magnitude of interference can be controlled by hydraulic pressure and the hydraulic pressure can be accurately calculated and determined) by the expansion of taper pipe, so as to transfer torque by transferring the shear force. Differently, the ordinary bolt transfers the torque by the friction between nut end flat and flange plate flat. In this way, torque transferring is directly related to the power, so the reliability is better.

Through elongating the bolt by hydraulic stretcher to rotate the nut, exert a certain preload to the nut, it also bring a certain friction between nut end flat and flange plate flat, which will act a dual role of insurance for transferring torque and power. At the same time, the installation and disassembly processes of ultra fitting coupling bolt are completely controlled by hydraulic pressure. The operation is reliable and precise, and with higher repetitive usage rate. So it is much more competitive.

There are inner and outer threads at the two ends of ultra fitting coupling bolt. And a tapered screw rod is at the middle. There is an expansion bushing with tapered inner diameter on the screw rod, which making up of one set of coupling bolts together with another two nuts. The outer circle of the bushing is a cylinder, the size of which will be determined by the requirements on clearance fit with screw hole. It is required that when the bushing expands to the expected state under certain hydraulic tension, expected magnitude of interference with bolts is formed. .