does i need to balance one flywheel? 1

[181273]

i got a flywheel, with dimensions:
diameter:1530 mm
weight: 1335 kg
and wide: 90 mm
the speed of rotation is 1000 rpm...
the question is does i need to balance the fly wheel?? could somebody explain me why?

 

[ScottyUK]

Yes, you do need to balance it. And if you are seriously asking this question you should evacuate the inhabitants within a 500m radius around whatever you are building. Just in case it disintegrates because you didn't balance it properly.



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Sometimes I wake up Grumpy.
Other times I just let her sleep!

 

[181273]

i thought it, but the mechanical guy tell me that it´s no needed cause it´s a machined piece...of carbon steel, and it´s exactly the same all the piece....

 

[181273]

on other side... i want to know your opinion about the fact that the shaft is 180 mm diameter in the side the fly wheel is mounted...could somebody tell me if this diameter is ok for a inertia (I) of 404 kpm^2

 

[181273]

how could i show this guy he´s wrong without test it on the generator....??

 

[electricpete]

I agree with Scotty that it needs to be balanced. A competent person on-site needs to supervise the job to ensure safety.


With that said, if the piece is uniform, and you perform a runout test after installation (radial/rim runout for concentricity and axial/rim runout for wobble), then there is some degree of expectation that the piece is balanced although not foolproof (it were a cast piece then there could be internal voids... doesn't seem very likely with a flywheeel probably steel, but you never know).

Also you can do a qualitative static balance on an arbor or when installed onto the machine shaft in bearings. Position the flywheeel at a few different positions and it should always tend to move to a position with a certain side down. How fast is drops depends on magnitude of the unbalance and the friction of the bearings. You could in theory calibrate your test by attaching a known unbalance and seeing how fast that goes to the bottom. If your machine rotates much slower without the known unbalance, than the residual unbalnace is much lower.

The type of balance uncovered in the above type test is known as static unbalance. There can also be couple unbalance, but not very likely if you have a high D/L such as a flywheel, and you have good face runout.

Above is just some thought process and checks that can be considered, but in the end it's better not to take shortcuts when the stakes are high. Comments such as mine from an anonymous internet guy far away are no substitute for a competent person on-site to specify the tests and perform the necessary tests.

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[181273]

i agree with you... and I know that theory, but in example, if i see a excentricity due to a bad mounting process between shaft and fly wheel, in example 0,6 mm, how could this affects the bearings? vibrations?
the question is: no balance, and a bad mounting process... (the fly wheel is not at 90º with the shaft)... I hope you´ll understand...
not is posible to turn it easy, cause is mounted on the generator on site... and it´s giving problems of heat on the bearings.... or that´s what i think....

 

[181273]

and about the diameter of the shaft?? I know i ask a lot of things, but i got a problem and the guys from the mechanical department says that everything is ok...

 

[electricpete]

0.6 mm (600 micron) offset at 1,000 RPM will take a perfectly balanced machine and make it somewhere between G40 and G100 (not where you want to be)

This based on the chart page 5 of 11 here:

http://www.irdbalancing.com/downloads/TechPaper1BalQualityReqmts.pdf

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[electricpete]

flywheel not at 90 degree with the shaft is also a big problem.

180 mm shaft (~7") carrying 60"x 3.5" flywheel. That doesn't seem out of whack to me, but I guess it depends on a lot of factors (bearing location, bearing spacing, worst-case torque transmitted, proximity to resonance).

Another very strange thing about large diameter flywheels is that the inside diameter is larger when rotating than when stationary due to centrifigual force. For some very large flywheels that we have around 6' diameter, there are special key arrangements to cope with that. I'm not sure if it is a concisderation for your flywheel.


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[ScottyUK]

Good link ePete. Thanks.


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Sometimes I wake up Grumpy.
Other times I just let her sleep!