The two planes of "Two plane" balancing 2

[geesamand]

I have two questions that has nothing to do with how to balance a rotor - it has to do with the terminology. It's about cleaning up my communications with vendors about balancing requests.

Terms not in quotes are as defined in ISO 1940-1. Terms in quotes are balancing terms I've hear used but did not find within 1940-1.

I know that when a "single plane" balance is performed, only the resultant unbalance is managed and resultant moment unbalance is not. When a "two plane" balance is performed, both the resultant unbalance and resultant moment unbalance are controlled.

I've read ISO 1940-1 cover-to-cover but this question is not readily answered:
Q1)
Does this mean that the "single plane" = resultant unbalance, and the second plane in "two plane" balance = resultant moment unbalance? In other words, resultant moment unbalance and resultant balance are each the virtual "planes" referred to in the term "two plane" balance? (in this case, the "two plane" would suggest two orthogonal planes) Or....
Does "single plane" mean that there is a single balance tolerance and/or correction plane, and "two plane" mean that two tolerance and/or correction planes are used? (in this case, the "two plane" suggests two parallel planes, both perpedicular to the rotating axis)

I'm leaning toward the second case since resultant moment unbalance doesn't have the same units of measure as resultant unbalance (g*mm^2 vs. g*mm).

Q2) When a two plane balance is required, is it possible to directly specify the maximum resultant moment unbalance, or must we declare two tolerance planes and apply an ISO balance grade to each tolerance plane?

Thanks for any insights. I've been reading ISO 1940-1 and feel it is a relatively complete treatment of the subject - if there is another "must-have" standard document, I would appreciate a pointer to that also.

David

 

[electricpete]

Does this mean that the "single plane" = resultant unbalance, and the second plane in "two plane" balance = resultant moment unbalance? In other words, resultant moment unbalance and resultant balance are each the virtual "planes" referred to in the term "two plane" balance?

No.

(in this case, the "two plane" would suggest two orthogonal planes)

No, not orthogonal. The two planes would be parallel, at different axial locations along the shaft.

Does "single plane" mean that there is a single balance tolerance and/or correction plane, and "two plane" mean that two tolerance and/or correction planes are used? (in this case, the "two plane" suggests two parallel planes, both perpedicular to the rotating axis)

That's a little tricky. I tend to think single plane uses single plane balance algorithm (one trial run). Two plane balance uses two plane balance algorithm (two trial runs). But a single plane balance can utilize two correction planes... for example half weight at each position on each end of the machine.


=====================================
(2B)+(2B)' ?

 

[geesamand]

Thanks, I see your point that correction planes need not match the location or number of tolerance planes.

Might it be less tricky if a re-state the question as:
Does "Single plane" mean that there is a single balance tolerance plane, and "two plane" mean that two tolerance planes are used? (in this case, the "two plane" suggests two parallel planes, both perpedicular to the rotating axis). (Noting that in the "single plane" case, at least one correction plane is used, and in the "two plane" case, at least two correction planes are used)

David

 

[electricpete]

Does "Single plane" mean that there is a single balance tolerance plane, and "two plane" mean that two tolerance planes are used?

No. I would say single plane and two plane describe the model of the rigid rotor in the balance algorithm.

=====================================
(2B)+(2B)' ?

 

[GregLocock]

Terrific question, I think, but kind of muddled.

here's some questions you might want to think about.

1 Do the accelerometers, or force gauges, measuring the imbalance vibration/forces have to be in the same plane as the correction weights?

2 Do the accelerometers or force gauges have to be measuring in the same direction?

3 Could you measure say acceleration in one place and direction, and force in another, and still get a solution?

4) in the right system could you measure vibration in two directions at one location and get a solution?

The answers are N N Y Y(but not generally practical). Make sure you know why.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[geesamand]

Greg, thanks for the quiz. I would have gotten the first three, and I've seen the fourth case performed, but I couldn't tell you offhand how the math works out.

I'm not a balancing vendor - I simply know when couple imbalance is risky to our products and when it must be controlled. The challenge I need to overcome in the short term is accurate drawing notes to be used by vendors to perform a two-plane balancing.

The part in question has traditionally been balanced in one plane, but the current generation is 1.5x longer along the rotating axis than past designs. In operation, the part is mounted on a taper fit to the shaft and rotates on the end of the shaft, overhanging both bearings. The part is balanced on a mandrel that fits the taper. The part shape does not offer two good correction planes, so the engineer is looking to perform a single plane balance (as we have always done) and then measure the residual couple imbalance. If the couple imbalance is excessive, we expect to scrap that piece. Right now I'm focused on how to make a clear, simple requirement for maximum couple imbalance.

Based on the standards, the traditional way of monitoring couple imbalance is by checking balance quality at two tolerance planes, whereby the magnitude of the balance quality and location of the declared tolerance planes controls the magnitude of the couple imbalance. That seems like a bunch of artificial construction just to perform a single-plane balance and watch over couple imbalance, but we can do that if we must.

Given that, is there a clear way to give a single-plane balancing requirement (say, G2.5 at 350rpm) and single correction plane, and also ask for a direct report of the couple imbalance? Would a limit in g*mm^2 be enough information to measure and report overall couple imbalance?

 

[geesamand]

Here is one resource that actually puts forth definitions that answer the questions I've put forth:

From:

http://www.balancetechnology.com/pdf/balancing_basics202.pdf

"Dynamic unbalance is also referred to as two plane unbalance, indicating that correction is
required in two planes to fully eliminate dynamic unbalance. A two plane balance
specification is normally expressed in terms of w·r per plane and must include the axial
location of the correction planes to be complete. Dynamic unbalance captures all the
unbalance which exists in a rotor."

With the exception of the fact that they simplified the tolerance planes to be equal to two correction planes, this seems to be a reasonable reference point.

David

 

[Tmoose]

Some turbine rotor specs require that the phase of the residual two plane unbalances left in a rotor must be less than 90 degrees. Or maybe it was the other way around.

 

[geesamand]

That makes sense, if you're trying to keep a relatively tight control on couple unbalance.