What a Monster!!!
Industrial balancing repair of the fan assembly.
It was truly an honour to be elected in the revival of this failed, old and tired 60″ diameter double width Richardson fan assembly. This unit would be around 35 to 40 years old. We need to respect these old fan units for all the hard work they have done throughout the years. We must also respect the original manufacturers of this fan; they made them to last.
What alerted the customer was a terrible vibration from the fan assembly. On assessment, we found cracks on the back plate all the way around the hub bolt holes. This is where the original cast steel hub was fixed. This caused a severe vibration destroying its support bearings as well as the centre impeller hub mounting. The client was very fortunate the shaft wasn’t damaged. More importantly, the hub did not separate from the impeller back plate. This could have been a catastrophic failure!!
What our team needed to do was fabricate new larger diameter bolt-on hub discs for both impellers.
This creates more support on the impeller back plate and therefore stiffens the impeller when running at speed. We included a taper-lock hub and bush for ease of fitment and alignment on site and introduced adequate stiffeners to the back plate to add further strength. Sounds very simple but there were hours of designing, manufacturing and machining to get there.
Even though the majority of the work was in the manufacturing of the hub discs to ensure the impellers run concentrically. It’s the balancing procedure that would make the difference whether the assembly will run smoothly or not. Balancing a double width fan assembly is not as straightforward as it may seem. To achieve the best possible result, we cannot rely on balancing each impeller individually and assume it’s good enough to return to the client. Theory tells us that this method is sufficient, but, in practice, it does not work. The reason behind this is that the residual dynamic unbalance from each impeller, even though small, will fight against each other and generate a vibration. This is only because these impellers sit back to back on a common shaft.
To avoid the possibility of this occurring, our strict procedure is to dynamically balance each impeller to G2.5mm/sec. Then we assemble the impellers on their common shaft to their normal running position and rebalance the assembly as a unit. Again, dynamically and again to G2.5mm/sec. This procedure guarantees the unit will not vibrate once reassembled on site.
The International Standards states that fan impellers are to be balanced to G6.3mm/sec. We, on the other hand, offer our clients a tighter tolerance of G2.5mm/sec and therefore a better result. This is why the feedback we receive from our clients on such projects is always positive. The fan has now been reassembled on site and happily running doing its job of giving out fresh air in one of Melbourne’s major high-rise buildings.
Quality guaranteed, Certificate of Balance upon request.
Dynamic Balancing of high speed rotating components increases bearing life, achieves smoother running conditions, increases service life and enhances the quality of the finished product.
To ensure quality workmanship, Indrotech periodically service and calibrate all balancing machines to continue to provide optimal productivity, accuracy and reliability.