Following the catastrophic collapse of the motor cooling fans on several underground mining pump sets, Marshall Day Acoustics was asked to investigate the reasons for their failure in service. The pumps involved were mounted in sets of three and four on mobile carts, used underground to supply emulsion oil to Longwall mining machinery at BHP Appin Colliery, Appin, NewSouth Wales.

These 360kW DC motors operate the underground coal mining machinery that can be up to 540m in length along the coal face and move forward cutting the underground coal seam. Failure of the motor cooling fans
represents a significant hazard issue with potential for the operators and the mine equipment itself, valued in excess of $100M per set.

Marshall Day Acoustics was requested to undertake torsional vibration measurements on the Toshiba motors and Kamat hydraulic piston pumps to determine the reasons and causes for the cooling fan failures. The survey by Marshall Day Acoustics indicated a number of significant issues including below acceptable standard quality fabrication of the cooling fan impellers, poor vibration monitoring techniques of vibration levels by external contractors who had monitored vibration levels on a regular basis.

In addition, the choice of couplings between the electric motors and pump sets created significant problems owing to torsional stresses building up within the spiders used to connect the two metal halves of the coupling. Tests on the polymeric spiders indicated significant internal stresses that caused heat and melting of the internal components; a clear sign of torsional vibration.

Marshall Day Acoustics conducted a week long survey on a representative cart with 3 pump sets to determine the vibration levels and causes of the cooling fan failures. It was found that a combination of factors including sub-standard welding and inappropriate coupling choices, contributed to the failure of the pump impellers. As a result of the survey by Marshall Day Acoustics, Toshiba undertook to change the cooling fan impellers to cast iron models and the pump supplier changed the couplings to a grade which did not suffer the
torsional problems of the previous model.

As a result of these changes, the risk to mine operators and damage to equipment was avoided. Production of the Appin Colliery was resumed.