In the modern American manufacturing plant, Variable Frequency Drives (VFDs) are everywhere. They are essential for controlling motor speed and reducing energy costs. But they come with a hidden price tag that often goes unnoticed until it’s too late.
VFDs can turn your electric motor into a self-destructing machine through a phenomenon called Electrical Erosion (or EDM currents).
If you have ever opened a failed motor bearing and seen a “washboard” pattern on the raceway (ridges that look like Ruffles chips), you are a victim of this phenomenon. Here is why it happens and, more importantly, 3 tips on how to stop it.
The Science: What is “Fluting”?
VFDs create high-frequency stray currents. These currents look for the path of least resistance to get to the ground. Unfortunately, that path often goes right through the motor shaft, through the rolling elements of the bearing, and into the frame.
Every time the current jumps from the ball to the raceway, it creates a microscopic arc flash. Over millions of revolutions, this pitting creates the distinct “Fluting” pattern. This leads to excessive noise, vibration, and catastrophic failure.
Tip #1: Listen for the “Scream”
Electrical fluting creates a very specific noise profile.
- The Tip: Unlike a lubrication failure which grinds or crunches, a fluted bearing often emits a high-pitched whine or scream at high speeds.
- The Action: If you hear this on a VFD-driven motor, don’t just replace the bearing with a standard steel one. It will fail again in weeks. You need to change the setup.
Tip #2: The Path of Resistance (Insulated Bearings)
The most robust solution is to block the current entirely.
- The Tip: Upgrade the non-drive end (NDE) bearing to an Electrically Insulated Bearing.
- The Tech: Manufacturers like SKF (INSOCOAT) and FAG (Current-Insulated) apply a plasma-sprayed ceramic coating to the outer or inner ring. This coating acts as a shield, preventing current from passing through.
- The Upgrade: For critical motors, consider Hybrid Ceramic Bearings. Since ceramic balls do not conduct electricity, they are immune to electrical erosion.
Tip #3: Ground the Shaft
If you can’t change the bearing immediately, you must divert the current.
- The Tip: Install a Shaft Grounding Ring (like AEGIS®) or a carbon brush system.
- The Action: These devices ride on the shaft and provide a safe, low-resistance path for the current to go to the ground, bypassing the bearings entirely.
Don’t Let Efficiency Kill Reliability
Saving $500 a month on electricity isn’t worth it if you burn through a $3,000 motor rewind and 8 hours of downtime every quarter.
At Ivor Bearings Inc., we specialize in motor reliability. We stock the specialized inventory that standard distributors don’t carry:
- Insulated Bearings: INSOCOAT (SKF), CoatMaster (FAG).
- Hybrid Bearings: Ceramic ball options for high-speed/VFD applications.
- Precision Motor Bearings: C3 clearance and electric motor quality (EMQ) grease.
Is your VFD killing your motors?
Let’s spec the right solution. contact us HERE, write at quotes@ivorbearings.com or call us at +1 305 769 9459.
