Gearbox Cooling – 30-inch radial blade cooling impeller for a 1000kW gearbox
At Indrotech we love a challenge, and recently we were given one that was right up our alley. This involved an industrial gearbox that had failed bearing due to overheating.
This 1000kW gearbox was working hard in a dusty mining application. The first thing we had to look at was what type of fan that was being used to cool it down. At first glance we could see what the problem was. The type of impeller that was currently being used was an axial impeller.
This impeller was the wrong selection for this application. Typically, axial flow impellers are used in free air applications that involve ductwork and rely on the gap between the inside diameter of the duct to the impeller OD. This gap must be as small as possible to efficiently move the desired amount of air through the system. When an axial impeller is sitting in a motor or gearbox cowl of which has excessive space around it, what tends to happen is there is no flow through effect and cannot efficiently discharge that air. So, what happens in this case is, it gathers dust of which recirculates in the cowl and builds up on the impeller, bearing cover plate and the cowl opening causing the gearbox to overheat and thus causing bearing failure.
The solution was to replace this fan impeller with the appropriate type. This entailed designing an equivalent radial bladed centrifugal impeller of which generated the equivalent amount of air that the axial produced. But more importantly the air generated was sufficient to dissipate the heat generated by the gearbox and exhaust it at an acceptable rate that would also move the dust particles out.
As mentioned earlier, axial impellers rely on the gap between the blade OD to the open duct ID to move the air. A centrifugal impeller relies on the air being sucked through the centre of the impeller (the inlet) and disperses over its coned back plate and blades out through the cowl back opening. The cowl in this gearbox situation has an opening in the centre to draw air in.