When managing a mine which produces 6 million tonnes of bauxite a year, a nightmare becomes reality when a critical part of production machinery breaks and there are no spares. In this particular case, 3 blower rotors went down one after another in quick succession. Each assembly had two 3 lobe blower rotors weighing 490kg each. The situation became critical so the site put the entire blower rotor assembly weighing 1500kg on an aeroplane and flew it 1800km to Perth, Western Australia where they quickly ended up at VEEM Ltd. The airfreight alone cost $50,000.
VEEM immediately inspected the damaged rotors. Both the rotors had broken drive shafts. The engineer tasked with defining the cause, analysed the design of the rotors. These particular blower rotors were manufactured in India. The engineer discovered that the rotors had no radii in the shafts change in section (stepdown) which is a fundamental design flaw. VEEM also analysed the shaft material using their spectrometer in the foundry laboratory.
A redesigned shaft including radii at the changes in section and fitting tolerances measured against the existing shaft diameters was quickly drafted up and manufactured. VEEM used a better quality material for the shaft and stress relieved it via heat treatment.
Finally, the shaft was meticulously fitted. To do this, liquid nitrogen is used to shrink the shaft for a perfect fit. It is then dynamically balanced to ISO specifications and NDT analysis was performed to crack test the new rotors and NATA certified. Having machining, welding, balancing, NDT and a foundry in house enables VEEM to very quickly turnaround urgent jobs. By working 2 shifts the rotor assembly, it was soon back on an aeroplane and flown back to the mine.
VEEM Ltd have since fixed 8 of these blower rotors which all have the same inherent flaw.
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