Experimental study of the process of the static and dynamic balancing of the axial fan impeller by ball auto-balancers

The process of the static and dynamic balancing of the impeller of the axial fan by ball auto-balancers is experimentally investigated. The influence of auto-balancers on sections of the racing and the run-out of the fan and the efficiency of the auto-balancers in the cruising sections are studied. It is shown that the vibrations of the impeller occur with the frequency of its rotation. This means that the usual and aerodynamic unbalances are the main sources of vibrations and they are similar to each other; both unbalances give rise to vibrations with the rotor frequency. It is shown that the impeller has two resonant frequencies (although the impeller itself is a short rotor and has one resonant frequency). This is because the impeller is mounted into a massive corps and dynamically it behaves like a long rotor. The larger resonant frequency of the impeller is almost 2 times lower than its operating frequency. Therefore, it falls into the area of the beginning of balancing with a margin. It is shown that the presence of one auto-balancer does not worsen the racing process of the fan. It is shown that in the run-out when the rotor passes through the resonant velocities, the value of the vibration accelerations and the duration of the passage of the velocities: – in the presence of one auto-balancer are decreased insignificantly by 20–40 %; – in the presence of two auto-balancers are decreased significantly by 60–80 %. These are explained by the following: in auto-balancers at the run-out there is retention of the balls and balls are retained in the balancing positions almost until the rotor stops. It is shown that dynamic balancing occurs faster than static balancing. It is shown that on the cruising steady motion: – one auto-balancer, mounted from the side of the impeller (the shank), significantly reduces vibration accelerations in its plane and almost does not reduce vibration accelerations from the side of the shank (the impeller); – two auto-balancers significantly reduce the vibration accelerations of the impeller in all planes. It is shown that the attachment of additional masses to the fan protective casing reduces its vibrations, but does not reduce the loads on the bearings.