Maintaining full control over ventilation and humidity is essential to growing mushrooms successfully. Costa, a leading grower and packer of mushrooms, had engaged BSC engineers to conduct regular testing at their facility in South Australia, which led to the discovery of critical reliability issues with a number of fan bearings.
BSC Engineering Solutions Manager Mark Slaughter says vibration analysis at the site had detected early signs of electrical fluting occurring within the fan motor bearings. This, however, could not be verified until the bearings were thoroughly studied in the workshop.
“We detected a number of bearing defects in the tunnel fans during our monthly vibration testing. So we removed the bearings from the motors and further investigation confirmed the presence of fluting.”
Fluting, as Mark explains, is damage caused to a motor bearing from an electrical current induced onto the shaft of a VFD (Variable Frequency Drive) driven machine. Voltage accumulates in the motor and gets discharged as an electrical arc through the bearing, leaving washboard-like ridges on the raceway, damaging the bearing. These voltages are destructive and can cause bearing failure at an exponentially faster rate. To fix fluting, the electrical current must be redirected.
“The washboard pattern is a clear sign of electrical fluting. But you can only see that when you open the bearings up. Another early sign of damage from electrical fluting is an audible high-frequency noise, which originates from the bearing balls travelling over the pitted and frosted areas of the raceway.”
However, the best way to detect electrical fluting at early stages of development is by conducting regular vibration analysis, as Mark explains, and this was how the BSC engineers first detected the issue for their South Australian client.
While there are ways to discharge the unwanted currents away from the bearings, Mark says none of these would be effective unless the underlying cause is identified and resolved, or at least mitigated as much as possible.
“There are ways of updating electrical motors to reduce the possibility of electrical fluting. Some of the common methods include the use of shielded cables, grounding the motor shaft, using insulated bearings and installing Faraday shields. However, unless the root cause of the stray currents is identified and dealt with, there will be an ongoing maintenance expense to replace the bearings.”
Mark recommends regular vibration analysis as the best way of preventing maintenance issues related with electrical damage.
“It’s easy to neglect the severity of such problems. After all, replacing the bearings is a quick fix. But, if the problem is not attended to and you simply replace the bearing, the new bearings could also fail within days, or sometimes even hours, depending on the severity of the discharge.”
As a leading supplier of industrial products and services, BSC works closely with a number of large manufacturers across Australia. Mark says it is part of BSC’s mission to help reduce maintenance costs for its clients.
“The loss from recurring down-times is almost always higher for a plant manager than the cost of replacing the components. That is why, in working with our clients, we always go the extra mile to identify where the root cause is and make sure they don’t have to incur ongoing maintenance expenses,” Mark concludes.
“We are still investigating the root cause of the electrical discharge. In the meantime, we have suggested to put in place measures including an insulated bearing in the rear of the motor and an earthing ring in the front of the motor. The next step for us would be to see whether there’s an easy solution to fixing the stray currents at the source. If we can do that, then we will be able to ensure that the problem goes away for good so the bearings can last longer.”
