Balancing variables to get a stable and accurate job and suppliers

[AlbertFM]

Hello all,

I have a couple of problems that I would like to share with you...

I am balancing a magnetic rotor that must turn to 90.000 rpm (1500 Hz). With my actual system I am facing some problems and I am thinking on getting a new one. I need to be awared about what can be determinant and also find suppliers that can make a great job.

Here thee is a list of all the questions that I have regarding balancing. Please any answer or supplier (used to balance high speed systems) recomendation will be pleased.

-Which is the best way to “fix”/support the rotor to the balancing system?
-How must the balancing systems supports be designed (geometry, stiffness, mass, material…)?
-How does the ambient temperature affect to the balancing system?
-Which is the best system to drive the rotor?
-Which is the best rpm to balance the rotor?
-Is it good process to balance the rotor supported by and with its bearings assembled?
-Is it possible that balancing with the bearings assembled damage them?
-How does/can the magnetism of the rotor affect to the balancing process/system?
-Would it be interesting to use a stabilization process to complete the balancing one (p.e., Balance, speed up the system and balance again)?
-Would it be good to use a magnetic Taco instead of a photo one?
-Which is the correct and complete procedure to balance a system like ours?
-How must the balancing machine be fixed to the floor (rigid fix or insulated fix)?
-Which is the better machine arquithecture for our system?
-Is it good or not that the engine that drives the rotor is assembled on the balancing machine?
-Which is the accuracy recommended for our system?

Many thanks!

 

[Ralph2]

As an operator of a Schecnk hard bearing balance machine for 15 years CAB690 Frame5.

Our machine is capable of balancing up to 5,000 rpm although the rule of thumb is to balance only at a sufficient speed to provide enough energy (unbalance forces)that will create a stable reading. Thus I very seldom have to physically spin the rotor much past 2,000 rpm. As the unbalance forces measured are proportional to the speed a rotor balanced at 500 rpm will still be balanced at 5000.... Providing the rotor does not change shape at the higher speed.

At your 90,000 rpm I would hazard a guess that it will go through several critical speeds thus changing shape and influence the balance. The solution to this is to balance at the operating speed.. which gets pretty involved at your speed I would think...

Ambient temperature has no significant effect just so long as “everything” is the same temperature… local differences of temperature make a big difference.. as in the heat from your hand can create a displacement that is measurable.

On occasion we balance a rotor in its own bearings (ball). There is some dampening when using this method and the correction locations as well as the magnitude will not be as precise. As far as damaging them… never have yet but then the speeds are relatively low and the duration of the run is relatively short.

Mounting the machine… solid and isolated …if… you expect to meet the manufactures claimed 95% reduction. If the machine is not solid / isolated you will likely approach 75% reductions. And, ours is not isolated and there have been times when a frequency of something else in the shop creates erratic readings on the balance machine.

Contact some balance manufacturers... plug for.. Schenck they will be glad to have a salesman call

 

[AlbertFM]

Ralph, first of all tanks for your reply.

I am in contact with a Schenck salesman but I want to get some technical information to understand better our problem.

- We're not the manufacturers of the rotor but we have been told that the critical speeds are over the nominal speed. However, when we drive it, it's true that we face some ponts with higher vibrations. We think that may be are ressonances of static parts of the mounting. What it is sure is that the rotor is buit in layers from different materials so there is the possiblity to face a change on its dimmensions (microscope variations). This is a reason why we would like to balance at high speeds.

- We add bearings to avoid temperature problems. Before we hold the rotor with a nylon "gadgets" but when we drove it to 5000 rpm it was heated locally and measurements were not stable.

- Bu adding bearings we thought to find an stable system but what's true is that it depends to a lot of factors such as the tension of the belt. Even if we balance under tolerance, We never know if the rotor is well balanced until we test it. Sometimes yes and sometimes not, depending on the mounting. This is the reason why I ask a lot of things regarding the mounting, fix, drive...

We would like to contact somebody who balances a system like ours; magnetic, high speed and big accuracy.

Thanks again for all your information.