Can anyone help me with a method on how to balance this elevator machine on the field. The rotor and sheave were static balanced separately in factory. But when together they are out of balance. I think they need dynamically balanced when running at higher speeds but and really dont know where to start.

Thanks!
Paul

Doc1.doc (30 Kb, 92 downloads) Machine

I think the key is; you don't know where to start - know when to stop! Call in a qualified consultant to do the job else you'll be in a world of - oh well, you're there.

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I think the key is; you don't know where to start - know when to stop! Call in a qualified consultant to do the job

Right

quote:

else you'll be in a world of - oh well, you're there.

Funny

In the US working on people conveying equipment has very high liabilities. Take these cautions seriously.

Maybe a little harsh on myself when I said "dont kow where to start". Although would appreciate any advice on what method should be used to balance such a machine. I am relatively new to the "oh well, you're there" world of balancing but I do understand that its not a sraight forward balance. Not prepared to take the expensive/easy option of calling a consultant. Would rather first try to learn on my own with maybe some advice from those who are prepared to share there experience/knowledge.

regards
Paul

Paul,
Does the motor run smooth without the sheave on it? If so, then you should be able to single plane balance the sheave on the motor. Have you made sure the proper size key was used? The wrong size key can cause unbalance. Usually balanced sheaves on balanced motors don't need to be re-balanced.

Ronnie

Ronnie

The sheave and rotor were both single balanced seperately within 200g. I think this may not be accurate enough for the speed that we are now running the machine. Do you think it is possible to re-balance the machine on site without removing the sheave.
Is it possible a 2-plane balance is needed/possible.

regards
Paul

Paul,
If the motor has a metal fan on the outboard end, then two plane using the fan as one plane and the sheave as the other. If it does not have an outboard fan, and the is no access to the outboard end of the rotor, then you would have to disassemble the motor and balance the rotor with the sheave on it in a balance stand. If you do balance it this way, the chances are you will never be able to replace the sheave without re-balancing. I would still attempt a single plane balance on the sheave before going to two plane.

Ronnie

Ronnie, this is an permanent magnet synchronous motor with an integrated sheave atached on to the rotor. No outboard fan, sorry if I was not to clear. Refer to drawing at start of thread.

Thanks
Paul

Paul,
My mistake. We have repaired electric motors for elevators in one of the shops I worked in and I assumed yours would be similar. I should have payed attention to your drawing. Regardless of design, two plane balancing requires two separate planes to add or remove weight from. If only one end is available, I don't see how you can consider two plane balancing. Maybe Sam's suggestion might not be a bad idea? Sorry I couldn't be more helpful.

Ronnie

Paul,

I suggest determining if balancing is needed at higher or normal speed. I suggest judging this based on at least one radial and one axial measurement, if you only have access to one bearing, as in picture. Try single plane balance and if radial and axial measurement are acceptable, then you are done. If radial is OK and axial is not, then you would have to find two balance planes and perform 2-plane or static-couple balancing.

Walt

Paul, wanting to get back to your basic question, I would like to ask the reason you find balance quality is not ok now? Are there vibrations, mainly in the horisontal plane maybe? We have had similar setups and the wiggle resonance (shaft twisting around a vertical centre symmetry axis) has been smack on the speed. As a temporary fix, the speed was taken down just 10 percent and really nobody noticed apart from vibration almost went away. During next summer revision the stand was stiffened up nicely with a few added bracket using existing holes. Resonance was raised some 22 percent and speed range could be used as designed.
If you recognize some for your case, you could make a bump test impacting the large disk at 3 or 9 o´clock and measure 2-200 Hz 90 degrees from it in the horisontal plane. What do you see and what is the problematic speed? If I am on the wrong path, I would suggest a bit of recordings of the actual runouts of various parts using a dial gauge. Goal would be to find where the dog is buried. Why is there a drastic change from balancing machine to real machine? Do you have capacity to measure vector? Do not give up.

Sounds to me like you have not balanced before. If so, you can't just go out and balance something. It's just not that easy.

First you need some training. Then you need the necessary equipment... analyzer, software, sensors, cables, a speed reference (optical, infrared, or laser tach). Once you have the training and tools, and have practiced a little, then it's possible to do this yourself.

But there really is a reason that consultants are paid to do this work.... they have the training, the tools, the technique, years of experience balancing all kinds of equipment under all kinds of circumstances, and finally, the tenacity to stay with the job until it's done.

This sounds to me like about a 2 hour job.

It's not like changing the oil in your car. Really, it's not.

Thanks for the info but I would have prefered you told me something I do not already know!

I admit I am very new to the balancing world but what I have is a willingness to learn, which I think is half the battle! For sure there is a place for consultants I come across them on a weekly bases in the elevator industry, completely agree with you there and many experts there are!

However, I would rather learn myself or be taught, rather than pay for the consultant which I do not think is neccessary for this job after all as you said..."2 hour job"!

How about sharing some of your consultancy knowledge or are you looking to paid.

I believe that Rusty meant that it would be a 2 hour job IF the person doing it actually knew what he was doing.

What this entails is verifying that the problem really is unbalance, understanding exactly how the equipment being used delivers its results (is the phase angle leading or lagging?) and the procedures of turning vibration data into a balance solution.

Get any one of these wrong and you could be talking about several days.

If you are in China, then its not worth your time asking a consultant to travel out from the US.

Equally, since consultants earn their keep by doing this sort of thing for a living, exactly why do you think anyone should give you the benefit of their experience for nothing?

Paul68

I am assuming the vibration is excessive.

Do you have balancing equipment, or at least instrumentation that displays vibration level?, if so please post your readings.

Is it possible to create an unsafe situation by the following?

You will need instrumentation to determine the vibration amplitude, and at what frequency it is concentrated at. If most of that vibration energy is concentrated at the operating frequency (RPM) of the "rotor" then it is possible that it is out of balance. If you do not have instrumentation you are basically guessing. Without balancing hardware the most you can do is test the effect of placing a weight around the rim of the sheave in various places and see if it effects the vibration, totally be trial and error. If the unbalance is entirely static (for example a disc with a heavy spot)you may get lucky and solve your problem.

My suggestion is that if you do not have the equipment and experience you are better off subcontracting the job out to a consultant (this is especially so for jobs that risk life, limb and property damage) for a proper analysis of the problem or apeal to the OEM, the owner of the elevator will thank you later for it.

Alan

Did some work for elevator companies over the years. Older gear, with curious direct mounted cable drum, so there were 3 bearings and 2 shafts. X---X----X . I got the feeling the flange joint in the middle lacked a good centering feature, so the balancing was correcting runout from changed centering. It required some creative taking because the elevator in a short building could only run less than a minute.

Paul,

I understand your eagerness to learn and applaud that effort. However, if this device is intended to transport human beings, those that have recommended a trained experienced consultant are correct.

My recommendation is that you hire a consultant to do the job AND train you on how it is done. Get your camcorder out and take notes and ask questions during the process! You may very well learn enough to do yourself the next time. One thing to consider as someone has pointed out: liability insurance is adequate in the US. Understand the culture in which you currently find yourself and determine what the implications may be if people become injured while using the device if you do decide to perform needed work.

A thousand different people on this board may all offer suggestions/solutions to your problem. The question is how will you articulate their replies and move forward?

Gary

Just some interim info. I mailed Paul and he has got some support just free of charge :-). The case is well understood, is interesting but pretty elementary and has nothing to do with safety of humans. In due time, I am sure Paul will inform you.

quote:

I admit I am very new to the balancing world but what I have is a willingness to learn, which I think is half the battle! For sure there is a place for consultants I come across them on a weekly bases in the elevator industry, completely agree with you there and many experts there are!

However, I would rather learn myself or be taught, rather than pay for the consultant which I do not think is neccessary for this job after all as you said..."2 hour job"!

How about sharing some of your consultancy knowledge or are you looking to paid.

Well Paul,
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