With the growing demand from industries to enhance the energy efficiency in their operations, inverter-controlled motors such as those featuring variable frequency drives (VFDs) are being increasingly favoured due to their versatility and control over operational speeds.
The uptake of inverter-controlled motors is expected to continue in the upwards direction as governments around the world mandate the use of energy-efficient products, with a global research predicting 6.5% annual growth in the global VFD market from 2020 to 2027.1
With the introduction of VFDs into an existing AC motor set up without any provision for grounding the shaft currents, there is a common bearing failure mode that occurs which is called Electric Erosion.
“What’s actually happening in the market is that more and more people are using VFDs and adding them to old motors which are already installed in their plants. If care is not taken to simultaneously update the motor’s bearings, this increases risk of current leaking from the motor and damaging the bearings,” says NSK Business Development Manager Nitin Verma.
The damage, as Nitin explains, occurs when electrical current passes through the contact point of bearing races and rolling elements during bearing rotation. What follows is sparks being generated in the thin lubricant film, causing the surface to be fused locally into an irregular shape – a pattern referred to as ‘Fluting’.
Traditionally, one way to prevent Electric Erosion in the bearings has been to deploy an insulated housing in the motor, but this requires special parts and assembly processes that might not align well with every application. Using non-conductive ceramic balls in the bearings is another option, but Nitin says this option is also not always cost-effective.
“Silicon carbide is a very expensive material, so to produce ceramic balls for bearings beyond certain sizes can be very costly, rendering this option counter-productive.”
To overcome this problem, NSK offers the HDY2 ceramic coated bearings, which are made available to industries in Australia through NSK’s long-term supply partner, BSC.
NSK’s bearings feature an alumina-based ceramic coating material sprayed on the exterior surface of the outer ring. The coating provides complete insulation to the bearing, while also providing excellent heat dissipation.
The NSK HDY2 bearings are designed to provide insulative resistance of 1000MΩ at 1000V DC, which is more than ten times the insulation performance offered by other conventional ceramic coated bearings.
“NSK’s bearings have also been tested and verified to provide shock resistance that’s three times superior to that of other ceramic coated bearings. NSK’s bearings also have a lower temperature differential than other ceramic coated bearings,” says Nitin.
NSK offers ceramic-coated variants in both deep groove ball bearing and cylindrical roller bearing ranges, encompassing bearing bore diameters from 50 to 110 millimetres.
What Nitin says places NSK’s ceramic coated bearings a head and shoulder above its competitors in the marketplace is the unique bonding technology, which ensures perfect binding between the alumina coating and the bearing steel.
“Without the perfect bond, the coating will get chipped off under shock loading and where there’s even a little bit of chipping on the coating, the insulation is lost completely. That’s why NSK uses a unique plasma spray technique to bond the alumina coating to the bearing outer ring – ensuring there’s no current leakage,” says Nitin.
Apart from being supply partners for NSK, the BSC branches across Australia bring years of experience that enable them to assist industrial customers with bearing selection for their applications.
As BSC State Sales Manager Shaun Glacken points out, motor repair companies and motor rewinders are one category of customers that can benefit from the NSK HDY2 ceramic coated bearings.
“As bearing specialists, the BSC sales and engineering teams can support our customers with all of their bearing-related problems. Often times, our customers may not even be aware of a solution available on the market. So, we take it upon ourselves to educate them and help minimise their risk of bearing failures. The market for NSK HDY2 may be niche, but it’s highly critical that when our customers need the product, we have it available to them.”