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RustyCas

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I know I have at least one overhung fan with roller-skidding at the drive-end bearing (direct coupled). Bearings are double-row cylindrical. Basically the fan is very well balanced with near perfect alignment, so there is little to no load on the bearing. It runs hotter than the other bearing and occasionally has very high acceleration levels with normal velocity (less than 0.05 ips). This started soon after we replaced the bearings. I ran the install so I'm confident the bearing is "right" and we've checked the clearance and the lube since then. When the noise jumps up, one or two shots of grease is all it takes.

Need to get some load on the bearing, so I think I need to lower the motor a little to introduce some misalignment. But the coupling is a gear coupling, so I'm unsure of how much, or angular vs offset or some combination. Fan runs 1200 rpm. With any other type coupling I wouldn't hesitant; just not sure with a gear coupling.

I'm sure some of you have run into this. What say you?

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Danny Harvey

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Rusty,

Without specifics, I would say that any significant degree of introduced alignment would damage bearings long before it would damage any type of coupling.

Check the catalog alignment tolerances for the coupling and you will likely see that it is far looser than the tolerances you use. You should be able to move to the edge of acceptable standards without exceeding the coupling tolerance.
John from PA

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http://www.machinedesign.com/basics-design/cylindrical-bearings

The technique of an out of round raceway is often used in aero derivative gt's.
Sinski

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Reply with quote  #4 
Double-row cylindrical bearings on a fan? I have not seen that before but would it be possible to go to a lower load rated bearing such as a cylindrical single row or even a double-row ball bearing? 
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