I have found two identical motor/gearbox combos that have the same hp motor, same vfd settings, and are on same size conveyors, and one is running 12 degrees higher than the other.  The cooler of the two gearboxes is pulling 3 amps and the hotter one is pulling 2.4 amps both are grease filled gearboxes and sound identical when tested with ultrasonics. The conveyor they power has also been looked at with IR and no reason for the rise in temperature was located.  Does anybody have any ideas on what may be causing this?

Is your ambient temp. the same? Are the conveyors moving the same amount of product? Are they getting the same amount of airflow? Do you have the baseline pictures? Are they using the same grease? There are alot of variables to take into consideration. Do you have both pictures? Where are you seeing the 12 degree difference, is it overal or at one particular point on the gearbox?

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Justin Ardekani
PdM - Reliability Analyst
ASNT NDT Level II IR Thermographer
IACW UST Level I Ultrasound Inspector
The Snell Group
www.thesnellgroup.com

That wouldn't be an exposed shiny shaft on the gearbox, would it?

The ambient temp. is the same, they move the same amount of product, they have the same amount of airflow, the whole gearbox is 12 degrees hotter, and they both have the same type of grease in them.

The shiny area is the bore of the gearbox and the bolt head in the end of the shaft.

When inspecting mechanical equipment we seldom find two identical devices running at the same temperature. Small variences are to be expected. But differences are a warning light to slow down and evaluate all the variables, which you seem to have done. The fact that the gearbox pulling less amps is the warmer one is a concern, but how much of a concern?

Several comments: IR is a great tool for finding thermal differences in a wide variety of mechanical equipment, but it many times cannot point to what is causing the problem. Vibration analysis and oil and grease testing and possibly airborne ultrasound are what may be called for in this case. If those technologies are not available then you should trend the two gear boxes against each other being sure to keep all variables in control. If the delta T increases between the two gear boxes you'll have significant proof that something in getting worse.

Rob 

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Rob Spring, P.E.
ASNT NDT LIII #65375
The Snell Group
rspring@thesnellgroup.com
800-636-9820

Are both boxes filled with grease to the same level?  Too much, or too little lubricant affects temperature.  What type of grease, semi-fluid?  Same time on grease?

Could there be some heat transfer differential from the motors?

Have you visually inspected the gears for improper wear or alignment?

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Bill Galbraith

Hello Thermal Land! 

I would just like to add and agree with the group. Sounds like your digging in the right direction. I guess that's what "thinking thermally" does to ya. I have a boatload of gearboxes that I inspect Bi-monthly and no two are ever the same temperature. Keep a good history going and whatch them now as one instead of compareing the two together.Get the vibration guy doing the same thing.

I hate to ask any questions since most have been asked!

Keep us posted!!!

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Cary Weaver
cary.weaver@owenscorning.com
DoUSeeGreen.com
Maintenance Specialist
Thermology L3

Hello

I recently completed a inspection with basically the same problem.  On this particular case the problem was located utilizing thermal imaging and what it turned out to be was support related.  When the conveyor was charged with material the load caused the conveyor to move out of alignment as the gear box was supported from the structural conveyor support.  With no material on conveyor the temp returned to normal.  The other gear box and motor were supported independently of the conveyor support.  When the support was reworked the problem went away.

Neither Vibration or oil analysis were able to pinpoint the problem.  I collect LOTS of data other than I R.