The pins are metal rods serving to assemble together two parts, and having ends that are threaded. Said pins are normally fastened via one of their ends in one of the parts, pass through the second part, and receive a clamping nut at the other end.
In aviation, the pins normally pass through both parts and receive a clamping nut at each end. In turbine rotors, the clamping nuts are difficult to access, and it is sometimes necessary to assemble and securely fasten the pins on one of the parts before assembling the other part. Such pins enable modular assemblies to be prepared, which make maintenance operations easier.
In such circumstances, each pin presents a middle collar having a non-circular outline, which collar is received in a groove formed in the bearing surface of one of the two parts, and, while the nut is being tightened on said part, comes to bear against an axial wall defining the groove. Thus, all the pins are initially fastened on said first part, and it only remains to put the second part into position and tighten the second set of clamping nuts.
The periphery of each collar is shaped to present flats which come to bear against a wall of the first part while the first nuts are being tightened, thereby preventing the pins from turning. There is thus the risk of damaging the first part, which is an expensive structural part, whereas the pin is inexpensive and disposable. This risk occurs during the initial assembly of the turbine, and also during subsequent maintenance operations requiring the rotor to be removed.
Furthermore, the groove in which the collars are implanted is wide, thereby leading to very significant flexibility, that is damaging to the dynamic behavior of the assembly.