Stray Current in Rotor Pinion?
Stray Current in Rotor Pinion?
(OP)
I have a problem where rotor pinions that are initially press fit to the rotor shaft (and keyed) are becoming loose over time. I suspect stray current is the cause but I have no practical experience in evaluating this. The attached picture shows the pinion.
Here are the details and some of my questions:
The AC induction motor is on the inside of a motorized pulley (motor and gear reducer inside pulley shell). The motor is a 50Hz motor, made in Europe, and running in the U.S. on 460V/3PH/60Hz power. The motor is 4 pole, class H, 29.7 FLA. The stator housing is aluminum.
Does the errosion shown on the pinion shaft face and end in the picture look typical of that caused by stray current corrosion?
I don't seem to have this problem on motors with ferrous stator housings. Could the aluminum stator housing be a part of the problem?
Is the solution installing a current diverter ring on the rotor?
Is there a test I can run on the motor to determine the likeliness of stray current corrosion occuring?
Thanks for the help!
Here are the details and some of my questions:
The AC induction motor is on the inside of a motorized pulley (motor and gear reducer inside pulley shell). The motor is a 50Hz motor, made in Europe, and running in the U.S. on 460V/3PH/60Hz power. The motor is 4 pole, class H, 29.7 FLA. The stator housing is aluminum.
Does the errosion shown on the pinion shaft face and end in the picture look typical of that caused by stray current corrosion?
I don't seem to have this problem on motors with ferrous stator housings. Could the aluminum stator housing be a part of the problem?
Is the solution installing a current diverter ring on the rotor?
Is there a test I can run on the motor to determine the likeliness of stray current corrosion occuring?
Thanks for the help!





RE: Stray Current in Rotor Pinion?
RE: Stray Current in Rotor Pinion?
While a difficult path (through the gear train) one exists to ground. I assume this circuit is highly improbably though.
We see a brown thick fluid coating the motor when we also find this type of problem. The motor is cooled by a synthetic lubricant passing over the stator and drawing the heat away. The brown fluid is different from the dark oil we see when the lubricant retains some moisture. Fluid is also diffent from the gray paste that we have seen in other gear boxes that have failed mechanically. I'm not sure if this information adds to the discussion.
I'll try and get some information on the materials of construction of the shaft and pinion.
Thanks again for the help.
RE: Stray Current in Rotor Pinion?
I suspect some interaction between the coolant and the aluminum. Possibly an alcohol content. Do you use methyl alcohol to trap moisture?
Bill
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"Why not the best?"
Jimmy Carter
RE: Stray Current in Rotor Pinion?
Bearings will typically show a washboard type pattern. I'm not sure about bearings but I'd suspect you would find abnormal pitting on the contact surfaces.