23-05: FRP-Carbon Twin Shaft for Axial Fan Blades and Validation on Cofimco’s 38FT Test Rig

Cofimco extensive research and laboratory tests pointed out in the development of an innovative shaft to connect the blade airfoils to the hub on large axial fans used on cooling towers and air-cooled condensers: the pultruded FRP-Carbon twin shaft. This type of connection gives to the blade very high strength by optimizing the material distribution in a peculiar shape and maintaining all the advantages of pultruded FRP-Carbon material as the reduction of the vibration level transmitted to the fan supporting structure and the high chemical resistance in the most aggressive environments like cooling towers. In addition, it allows the fan to operate without any speed to skip ranges when driven by VFD. The development of twin shaft was definitely possible thanks to extensive tests on the unique Cofimco 38ft test rig that allowed to validate the final solution in the most severe duty points, creating a strong reference and a solid structural basis for the introduction of the solution in the market. Scope of the present study is to show how the twin shaft design is capable to improve the blade load capacity on large fan sizes and the results achieved on the 38ft test rig.