quantification of energy losses with unbalance or misalignement ?

[alexsurf]

hello Guys,

Do you have an idea of quantification (some figures before and after job) of energy losses with unbalance or misalignement ?

thank

 

[electricpete]

This subject has gotten a lot of discussion over at maintenanceforums.com

My personal opinion is that the overwhelming motivation for keeping unbalance and misalignment as low as reasonably achievable is equipment reliability. The energy losses are small potatoes in comparison.

I have noticed there is one misconception by some folks about the relationship between vibration and energy losses. They tend to equate motion with losses. It is usually not the case. An undamped system vibrates without dissipating any energy. Damping factors in structural support are generally very low. The only effect that I think gives any noticeable energy dissipation is when the misalignment or unbalance increases the loading on a bearing, thereby increasing vibration.

If I were only looking for energy losses in rotating machinery, I would hunt it down with an infrared camera (looking for bearings, belts etc hotter than normal) rather than with a vibration analyser.


=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

Correction in bold:

"The only effect that I think gives any noticeable energy dissipation is when the misalignment or unbalance increases the loading on a bearing, thereby increasing friction.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[GregLocock]

I agree with the heat approach. One area where misalignment does lose substantial power is in automotive diffs - the casing is not stiff enough to really react the loads with the result that the hypoids mesh poorly at extremes of load condition. We are talking about losses of the order of 10s of hp due to that.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[alexsurf]

thank you guys

to summarize from my new point of view,
misalignment and unbalance increase vibration and heat up and bearing friction

-power consumption for industrial application loaded on not could be up to 10% HP for each phenomena ?
-so 20% HP in the worth case ?

 

[Tmoose]

"Journalists should be honest, fair and courageous in gathering, reporting and interpreting information.
Journalists should:
— Test the accuracy of information from all sources and exercise care to avoid inadvertent error. ....."

http://www.spj.org/ethicscode.asp

It is commonly suspected marketing folks sign a "different" document at graduation.
------------------------------------------------------

10% is way too high for a typical industrial app.
The power loss due to gross unbalance of an electric motor or fan would be barely measurable.

I believe in Greg L's example of a diff losing 20 HP while transmitting BIG torque, the misalignment was internal, not mis-aligned components operating thru couplings.

Losing 20 HP to "friction" is about like playing the entire output of one of those 50,000 BTU/hr propane or kerosene jet heaters on your components while they run.

 

[GregLocock]

OK, that is an extreme example... but do you know how much you are losing in your gearsets?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[alexsurf]

Thank Tmoose to have make it more realistic
so it means that misalignment and unbalance decrease because of something else ?

regarding unbalance and misalignment only, energy losses are also relative to :
-temperature (due to friction in bearing(#% HP?) and coupling(#% HP ?) )
-loading (increase of a local load decrease electrical efficiency = #% HP ?)
-movement is energy (noise and vibration=#% HP ?)
-rotational speed (electrical efficiency with variation of speed=#% HP ?)

I agree with you energy losses regarding temperature could about 1%-2% of HP (of course depending of the load condition).


So what about energy dissiped from vibration, rotational speed and load variation ??

 

[Tmoose]

I was not challenging Greg L's power loss estimate due to gear box distortion. I was just thinking out loud about what 20 HP of bearing or coupling heating would be like.

My take on gearbox losses as a percentage of transmitted power ("gears are 98% efficient - woo-hoo") in conventionally oil lubed gearboxes changed when we were testing a fancy water cooled geared spindle. It was spec'ed to transmit about 35 Kw, but used about 15% of that just to squirt oil around while transmitting nearly zero real shaft work. I posted some temp/time test results of that planetary gearbox we embedded in a machining center spindle. All tests >>should<< be real low HP since no machining is actually being done. (3% of zero is zero)

Note The gearbox oil and spindle housing got pretty toasty real quick at the higher speed ranges. The monitored Coolant flow and temp increase indicated the drive motor was working MUCH harder at 8000
rpm than just a few thousand rpm slower. And the power window on the motor's vector drive agreed. Kind of made sense with all 14 gears sitting in the bath tub squirting oil out thru the gaps between their teeth.

The gearbox manufacturer kept reciting the 3% efficiency mantra, claiming that many BTUs could not possibly be generated, but the gearbox would simply have none of it. Only when they re-ran their tests at higher speeds, and kept track of how many gallons of French river water they were actually pumping thru their test rig, did they begin to
believe our data.

When the BRM H-16 started making a lot more power improved oil management was listed as an important reason why.
Everybody thinks their oil pan baffle/scraper is worth 50 HP at 8000 rpm. I bet some might be.

I believe if grossly misaligning a pump or fan caused it to consume several extra HP the passively cooled bearing and coupling temps would skyrocket. Thus I also believe claims of energy savings from any typical alignment or balance improvement are, well, hopeful.

 

[GregLocock]

A simple model for the torque loss in a hypoid diff is

F+d.rpm+k*abs(T-T0)+c*rpm^2+.02*T

F is the friction

d is the damping term

k is a stiffness/misalignment related term

T0 is the torque where the gears mesh properly

c is for churning of the oil

.02 is a catch all inefficiency of the gearset.

There isn't much data around about the efficiency of diffs but that model is good enough for my purposes.






Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Tmoose]

I see Greg's churning factor stands alone to be added to the rest of the torque loss, IS NOT TORQUE RELATED, is rpm^2 related.

That is just how that planetary geared spindle behaved, and is the first time I recall seeing anything other than a "% of transmitted power" estimate for gear losses.