How to dampen noise coming from a thin-walled rectangular aluminum extrusion

[toothless48]

Hi, I am working on a project with thin-walled aluminum extrusions (4" x 4" x 1/8" x 6' LG) that are bolted to a large machine that produces a lot of vibration. The concern (not yet proven, but suspected) is that the tubes will act as an acoustic chamber and produce a lot of nuisance noise. Redesigning the connection to the machine would make things a bit more complicated and is the least preferred option.

I am looking into cheap options to dampening the sound. The solution would preferably be reversible for serviceability, since there is a connectorized wire that runs through the tube, but it's not a deal-breaker.

Options I have thought of:
- Sand - the tube is not completely closed, so this would probably not work
- Expanding foam - this compromises a bit on the serviceability, but it would be acceptable. The bigger question - will expanding foam actually dampen the noise?
- Rubber sheet stuffed into the tube - would this work? Hopefully this would not become cost-prohibitive.
?

Thank you for reading!

 

[BrianE22]

Someone at my old company tried the expanding foam inside a vibrating aluminum shaker table. It help with noise for awhile. But eventually the foam broke apart and didn't do much.

 

[IRstuff]

The bigger question - will expanding foam actually dampen the noise?

Seems to me that an even bigger question is how you think the noise is propagating and where. There are different levels of density of foam, but that presumes the noise is propagating internally down the bore. Is that even a plausible scenario vs. just propagating as a 6' long tube vibrating in air?

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[toothless48]

@BrianE22 Thanks for the input. Good to know that it helped. We will be much lower in amplitude than a shaker table, so it might be a solution.

@IRstuff That is an interesting point, didn't think about that at all. This is something we are going to have to access.

 

[BrianE22]

After the fact, Sorbathane is a great damper (assuming the walls of the tube are vibrating).

 

[GregLocock]

Lead or steel shot is a good substitute for sand and doesn't fall out of holes as much.

Loose particles are much better dampeners than solids or foams, just less practical.

Until you know what frequencies are involved any advice is going to be generic.

Cheers

Greg Locock


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[Tmoose]

"a large machine that produces a lot of vibration."

Does the entire machine just wiggle like Lauren Bacall at 1:49 in "To have or have not" ?" ?
Do the middle areas of exterior walls resonate and emit the scream of the gear mesh frequencies of the gears inside ?

Can you hear the machine now?
What does it sound like?

 

[Strong]

There are many methods and materials available for isolated mounting connections, volume treatment, and surface wall damping. A lot of the design issues involve dominant vibration frequency that can excite structural and acoustic resonances causing amplification and sound radiation efficiency based on surface dimensions. The best surface damping is called "constrained layer damping". I have used this method with success on large aluminum airfoil blades on air cooled cooling tower. Here is one source for damping materials:

https://www.rathbun.com/e-a-r

Walt