balancing machine for turbine shaft!!!

[turbinecrazy]

Hi there guys....

I am fairly new on the site......and must say what a wonderful site this is.....

Basically what i need from you geniuses out there is a basic balancing design for a model turbine shaft....

I have been doing some research but not really succeeded in it....

Is there anyway somebody can help me please....


Thanks

[neilw20]

turbinecrazey.

1. How heavy is the shaft?

2. How long is it.

3. How do you intend to support it while balancing. Dynamic at speed I assume.

4. How fast do want to spin it?

5. Easiest way to drive it is a flat belt, and be able to spin it in both directions.

6. Will you remove or add material to achieve balance?

I class myself 'expert' in the balancing area, ego not withstanding.
I will be able to tell you what won't work.

[turbinecrazy]

thanks so much for your reply....

the mass of the shaft is 0.839 kg....

the length of the shaft is 165mm....

yes dynamic at speed....

I would want it to spin at 120000 rpm....

yes a have designed it to be driven by a belt but i have designed with a vee-belt....

I would add components to the shaft....

[neilw20]

3. How do intend to support it while testing?

You need to be able to press the back of a belt against it to spin it.

While measuring the un balance it will be free spinning.
Any drive force will introduce unwanted extra unbalance.

Low tune. The bearing assembly has some freedom of movement radially in 1 plane. Usually horizontal.
or
high tune. The bearing assembly(s) react FORCE against a solid body.
Force usually measured by ceramic piezo crystal or accelerometer.

Do have any electronic experience?

[turbinecrazy]

i have designed the test jig...and as you explained i have accomplished everything besides the electronics....

I have done my research and i work at a highly precision company and they are more than will to help me but no time factor....

so basically i need to know more about where and how to mount the accelerometers....and programming...

[neilw20]

You may consider the VERY easy way to do it.

Low tune. Allow the bearing mounts to deflect slightly. Rubber mount to bench.

Now spin the shaft in one direction and let the support(s) deflect.
As it is free spinning bring a felt tip marker near the shaft at the bearing and let it just touch.
Do the same for the other end.
Now spin it in the opposite direct and do the same with the marking pen offset slightly right or left.
After stopping you should have two sets of marks. Average the angular position and this is the heavy spot.

Running in both directions cancels phase errors introduced by the support system. Once you figure the phase error (possibly 30 degrees) you can just keep using the same direction nad just compensate your guessed angular position. The accuracy of the position becomes apparent. See 90 degrees below.

As an experiment two opposed hose clips or tiewraps can be slid around to add/remove/rotate weight while experimenting.

When the indicated position moves 90 degrees you are getting very close, and this indicates an angular error positioning the correction.

To do this with electronics is not trivial and requires synchronous detectors and many special techniques to filter the signal from the noise.

With a low tune system - the resonant frequency of the mounts is below the balance frequency, and the deflection is dependent on speed, unbalance and the mass of the workpiece. Calibration is a bit hit and miss.

With a high tune system - the resonant frequency of the mounts is above the balance frequency, and the force measured is dependent proportional to 1/speed squared and the unbalance of the workpiece. Mass of workpiece has little effect on the signal. Calibration can be well defined.

The the marking pen (IMHO) is the way to begin. Marking pen only works for low tune system.
I do car tail shafts on the vehicle with a piece of chalk ! It is that easy.
and the worm drive hose clips just get left there as the correction.

I have balanced shafts like this up to 8000 RPM
The faster it goes, the longer the stick with the chalk held on the end. SAFETY FIRST!

I will watch this space...

[Praised1]

Hi Turbinecrazy,

I see you located in SA - so am I whereabout are you? I am buliding a smaller version of a KJ66 turbine and would like to know if you have built/are building something similar?

[fz1]

I see this guy made a balancer just for what you are wanting to do. I hope this might be of some help.

http://www.technologie-entwicklung.d...cing_tool.html

[turbinecrazy]

hi there thanks for the info....

Yep i am busy building a KJ66 for a university project....i am from cape town South Africa.....

[Praised1]

Hi TC,

Just wana know how far are you with the project? Have you made the NGV and Turbine yet?

[turbinecrazy]

nope was concentrating on my balancing of my shaft.......but that should easy to do....so thats the least of my worries.....

[obrif]

For a dynamic balancer specially designed for micro turbines try to contact
kmiklos@vnet.hu and he will help you for sure.
I have one of his balancers and managed to balance a wren 54 shaft to less than 5mg on turbine wheel and compressor.