Shaft unbalance caused by oversize key 1

[nisqually]

Hello,

I am in need of assistance. I am very new at this. I am told a larger than normal key on a shaft must be balanced with some mass added on the other side of the shaft. That's fine. But we are supposed to use a vibration test to verify the shaft is balanced properly. I assume the location of the extra mass would be opposite the key (180 degrees). Someone suggested the 4 run method can be used to verify balance. Can we attach some mass and just look at vibration in/sec in the frequency domain and assume the equipment is balanced if the overall vibration is below, say .11 in/sec- 0 to peak? I don't understand the units of permissible residual unbalance as in Appendix C of ANSI/AMCA 204. I do have a Commtest vb1000-T analyzer available to use.

This test is Monday. What do you suggest? I can't become an expert in a day so I'm looking for practical suggestions if possible.

Nisqually

 

[nisqually]

Thanks everyone for all the info. We finished the job last week. The end result was lower vibration readings.

Bearing#3 .09H .04V .08A
Bearing#4 .12H .03V .08A
These are in/sec 0-to-peak.

No chance of bringing in someone. Months of training hoops to get thru just to be able to walk into that place. They are having a reorg or mission re-alignment (misalignment for short). I believe they decided to let everything run to failure and bag predictive maintenance.

The management (although paid in triple figures) isn't too smart just adept politicians. There are more managers than electricians and millwrights. Very top heavy and very dumb.

 

[GregLocock]

Fair enough, sounds like a reasonable figure, what were your original readings? Cheers

Greg Locock

 

[nisqually]

Final -
Bearing#3 .09H .04V .08A
Bearing#4 .12H .03V .08A

Original -
Bearing#3 .18H .13V
Bearing#4 .31H .04V

These are all in/sec 0-to-peak.

No axial recored in original.

 

[jmack]

Nisqually,
Managers read eng-tips as well. Just for future reference, you might want to use words such as sub-optimal, instead of top heavy and dumb. Being right does not gaurantee success,... skilled negotiation will. 15% technical,... 110% interpersonal.

J MacK

 

[FredGarvin]

Hats off to Nisqually for that diagram.

 

[DanT]

nisqually, did you do some trim balancing, or chop the key to make it resemble a solid shaft/solid hub?

 

[Ralph2]

I second DanT request as well.
After all this I would like to know how you accomplished your balance as well. What masses did you add / remove and where.
Ralph

 

[nisqually]

Fred- thanks much for the compliment on the diagram.

JMack- thanks for the tip on interpersonal relations. i need all the help i can get in that area. have you ever worked for a company that has more v.p's than electricians? have you ever worked at a company where education is not valued?

DanT, Ralph2 - Don't try this at home. I don't think you can call what we did balancing but we did lower the vibe readings. We took a hose clamp and clamped a weight on the end of the shaft (all the way to the right in my diagram). We put it at 0, 120 and 240. 0 being the top of the shaft at the keyway. The lowest vibe readings were at 120 (I think it was 120. I don't have my paperwork with me, it's at home). We weighed the hose clamp (20 grams). We weighed the mass (8 grams). We made 28 gram mass and drilled and tapped a hole and bolted the mass on with a lock washer at the 120 position and took final readings. I have had time to read up since then. Our instrument can measure phase so next time I would like to do it right possibly using double plane balancing with phase. If there is a next time.

 

[GregLocock]

That's how we used to balance driveshafts on protos.

I always used 0,90,180, 270, a little bit of redundancy is no bad thing. Find the optimum between the two lowest out of those four. When you've found the best position fit another hose clamp in the same location. If that makes it better fit another one. If it is worse move the two apart in 10 degree stages until they are opposite (ie at (best angle+90) and (best angle -90)) Somewhere in there should be the correct solution!

The trick is getting a measurable reduction. Once you've got that you know you ar eon the right track and trial and error will let you home in on a solution.

Cheers

Greg Locock