Wire Vibration
Wire Vibration
(OP)
Dear All,
I believe I have a unique problem. To best describe it, I would request you to first have a good look at the attached sketch:
- This machine runs a steel wire at about 3000 RPM.
- The wire needs to continuously run WITHOUT any vibrations.
- The Two green pulleys are mechanically attached and move in Up/Down Directions.
- The wire between the two green pulleys runs smooth, then all of a sudden starts to vibrate for a few seconds then go back to run smoothly.
- We increased the wire tension; but that did not help!
- changing the drive speed did not help!
- We replaced the pulleys; but that also did not help!
- This vibration occurs even if the green pulleys are stationary; but worsens when these pulleys move!
I'm no mechanical engineer and was wondering if this vibration was due to:
- Wheels imbalance (supplier confirmed all are balanced).
- Improper wire tension.
- The configuration/arrange of the pulleys WILL cause Vibration. i.e. This machine was incorrectly designed!!
What is it!!!
I appreciate your help and advise.
Thanks,
Husam
I believe I have a unique problem. To best describe it, I would request you to first have a good look at the attached sketch:
- This machine runs a steel wire at about 3000 RPM.
- The wire needs to continuously run WITHOUT any vibrations.
- The Two green pulleys are mechanically attached and move in Up/Down Directions.
- The wire between the two green pulleys runs smooth, then all of a sudden starts to vibrate for a few seconds then go back to run smoothly.
- We increased the wire tension; but that did not help!
- changing the drive speed did not help!
- We replaced the pulleys; but that also did not help!
- This vibration occurs even if the green pulleys are stationary; but worsens when these pulleys move!
I'm no mechanical engineer and was wondering if this vibration was due to:
- Wheels imbalance (supplier confirmed all are balanced).
- Improper wire tension.
- The configuration/arrange of the pulleys WILL cause Vibration. i.e. This machine was incorrectly designed!!
What is it!!!
I appreciate your help and advise.
Thanks,
Husam





RE: Wire Vibration
Just a thought, is the wire clean and dry? I was wondering if its caused by fluctuation in friction between the green pulleys and the wire, for example if there was oil on the wire as it contacts the pulley and then slips until it runs on another part of the wire without oil and no sliping.
RE: Wire Vibration
I wouldn't expect it to _not_ vibrate, some.
... but I suspect the resonance that's allowing the wire to sing, is actually in the structure that connects the pulleys, especially the carriage connecting the two moving pulleys.
Have you guys ever designed or built a wire saw before?
Did you take one apart to see how it worked?
Why is yours different?
Mike Halloran
Pembroke Pines, FL, USA
RE: Wire Vibration
If my interpretation of your sketch is correct, I believe the wire is rubbing against the sides of the blue & red pulleys shown on the left, as is passes between them. Due to the fact that these two pulley axes of rotation are tilted out of the plane of view, the contact forces between the wire and pulley are not purely radial about the pulley axis. There is also an axial force on the wire that causes it to rub against the sides of the blue/red pulley groove where it enters/exits. This stick/slip sideways rubbing condition causes the wire to vibrate, just like a bow being dragged across the strings of a violin.
You can resolve the problem by changing the position/orientation of all three red/blue pulleys. First, the rotational re-location of these pulleys should only be about a vertical axis passing through the wire center. Second, all of the pulley operational axes of rotation should be parallel to your XZ (horizontal) plane. Third, the center lines of the wire where it enters/exits any given pulley groove should both lie in a common plane that is normal to the pulley's axis of rotation.
Hope that helps.
Terry
RE: Wire Vibration
- DesertFox, the Wire is DRY. Almost clean and Not Slippery.
- Mike, You absolutely right. It is a 2.5 Meter wide Wire Saw machine; but why would you expect it to resonate!
- The Carriage that is shown in the sketch was merely symbolic. i.e. The system is much more sophisticated than this; but I wanted to show that there is a link between the moving pulleys. It is actually made out of guides, non-slip belt, etc. that don't interfere with the path of the wire. Nevertheless, I want to stress that the vibration comes and goes, even if these pulleys are NOT moving! The frequency of the vibration reoccurrence seems to increase as the two pulleys move up and down.
- Terry, the Wire is about 1.5mm in dia. and the pulleys are indeed rotated; but not more than 5 Degrees out of plane. It is made just so those to avoid the wires intersection close the left green pulley.
- The right Blue and green pulleys are all in the same plane and we have used "Pulley Pro" laser alignment tool to verify that. Assuming that the tilts in the other pulleys would cause vibration; wouldn't this vibration be killed as it enters the right blue pulley?
- We have of thought of all these alignment issues Terry mentioned earlier, and have made sure all is aligned; but to no success.
- I was wondering: is it an issue with Forces? I read something about pulleys tension side, and slack side. Do you guys think it's got something to do with it? Also, these are custom pulleys (300mm Outer Dia, 10mm Inner Dia [2 X SKF 6000Z Bearings], and 10mm width). What would I specify for the maximum values when we send it for balancing (or re-balancing)?
Hope this explains my dilemma,
Husam
RE: Wire Vibration
To a mechanical engineer, everything's a spring.
You desperately need one on site.
... not a spring; a mechanical engineer.
One red flag; 2 cheap bearings, 10mm ID x 26mm OD x 8mm wide, supporting a pulley made of 10mm plate of some unspecified material. The bearings can't be properly suppored on the OD unless there's a hub or a shaft you haven't mentioned. There are too many ways for that to turn out badly, and too many details unrevealed to properly evaluate what's going on. That's why you need an ME, right there.
Mike Halloran
Pembroke Pines, FL, USA
RE: Wire Vibration
RE: Wire Vibration
It took me a couple of days to think about what you guys are saying. But still, I have a few questions before I call a mechanical engineer:
-How does the pulley material (steel vs. Alum.) have an effect on the vibration?
-What about the pulley ID? Is there a way to suggest a better one? I. E. Is 20mm better than 10mm? Is 30mm better than 20mm? Where do we stop?
-What do we request the maximum value to be when we send the pulleys to be balanced?
-How does the wire tension affect vibration? And what are the forces in play here? To me, the sum of all forces across all pulleys is zero; but then again how does the tension side and slack side of the pulleys affect vibration?
- On the bearings side, what a good bearing? I thought a bearing that can go up to 14000RPM is good for 3000!
All these thoughts run through my head and can't find an answer to!!
Need your thoughts on this!
Thanks
Husam
RE: Wire Vibration
I'm guessing about the details, but something doesn't add up, mounting two bearings that are each 8mm thick in what I'm guessing is just a 10mm thick plate.
I'm also guessing that you're driving the whole thing with a 2-pole AC motor, which is going to introduce strong variations in tension with each revolution, in phase with the AC power. If that is the case, I'd make the motor pulley heavier, and all the other pulleys lighter, than they are now.
A few photographs or drawings would help keep us out of speculative blind alleys...
Mike Halloran
Pembroke Pines, FL, USA
RE: Wire Vibration
Steel tends to dampen vibrations better than aluminum.
I assume you have a splice somewhere in the cable. How "smooth" is it? That section of the cable going over a pulley might be setting of the vibration.
RE: Wire Vibration
Attached is sample pictures of the wheels for your reference. Note that the wheels become thicker towards the center. the bearings are mounted inside machine grooves to the exact size of the bearings OD. The drive motor is high torque 3 phase frequency driven motor.
But what's your opinion on my other questions; Pulley ID's, Balance values to be requested, etc.
Brian,
With respect to the wire splice, I have checked it and found it to be smooth. I don't think that the splice causes the vibrations, as these vibrations are intermittent does not seem to follow a pattern!
Regards
Husam
RE: Wire Vibration
Well I think you can rule out bad balance of pulleys otherwise it be happening every revolution and your saying it only happens now and then, I still think it's down to friction and or slipping of wire or pulleys.
RE: Wire Vibration
The outer rim of the pulleys are lined with an anti abrasion PU Layer (about 8mm wide X 12mm deep) that is grooved to provide a seating for the wire. The wire is already set to maximum tension. Though I'm not sure if it is slipping of not, HOW can I find out if it is??
Regards
Husam
RE: Wire Vibration
The bearing bore in the pulley should be a press fit to the bearing OD.
The pulleys do have to be balanced because of the multi-piece construction. I would just ask for balancing at 3000 rpm or above, with a time limit as a tolerance.
WRT slipping, any smooth pulley that's transmitting power to or from a belt or wire must be slipping in order to transmit the power.
Even with a 3-phase motor, extra mass on the motor pulley should help.
... but the irregular nature of the vibration suggests that it's more of a natural frequency thing than a forced vibration thing.
Have you been able to measure the frequency spectrum?
Mike Halloran
Pembroke Pines, FL, USA
RE: Wire Vibration
Timelord
RE: Wire Vibration
How do you calculate the resonant frequencies of the wire, and how do we measure the frequency spectrum?
Regards
Husam
RE: Wire Vibration
Have you got a smartphone?
There just has to be an app that can record a sound sample and then show you its spectrum.
Mike Halloran
Pembroke Pines, FL, USA
RE: Wire Vibration
RE: Wire Vibration
RE: Wire Vibration
Regards
Husam
RE: Wire Vibration
I wish to thank you all for your comments, suggestions and advise. I've found the culprit! As simple as it may sound; but the problem was looking us at the eyes and we couldn't see it. It was a wheels misalignment problem.
Our technicians were using basic alignment techniques, and a laser pulley alignment tool (used for engine pulleys); but this does not work (or is not applicable) for this machine. We are not using belts; it's a wire. What needs to be aligned is not the pulley faces; but rather the wire grooves. When they realized this, and made correction in a crude way, the vibration dissipated almost completely.
Now, we are sourcing a laser alignment tool to allow us to have precision alignment of all the wheels.
Again, thank you all for your help and support.
Regards
Husam