Reinforced concrete damping for steel machine structures.

[JohnMcNamara]

Hi All

This Paper is Well worth reading

http://www.mech.utah.edu/~bamberg/re...e%20Design.pdf

Light weight steel tubing with better damping than cast Iron.
Low cost.

Cheers

John

[BobWarfield]

That would be the "bible" for fabricated weldment + epoxy granite machine tool frames. Many excellent thoughts are there. One of my favorites.

Cheers,

BW

[giz]

Bamberg uses concrete in the build - I would be interested in his thoughts on using epoxy-granite. I am a former student, so I may shoot him an email asking his opinion as I am interested in employing his method in a personal build.

[JohnMcNamara]

Hi Giz and Bob

From My reading of it, it is the thin polymer boundary layer between the concrete shell and the segmented concrete sections that makes the significantly improved damping compared to just filling the tube with cement. That boundary layer is where the energy is dissipated as heat.

What is important is the polymer layer must be thin and the concrete must be in intimate contact with the steel shell and the concrete. (No gap) shrinkage would be a problem.
He has used a proprietary film. I wonder if a flexible paint would achieve the same result?

To reduce shrinkage a concrete additive has been used. Apparently the additive is based on aluminum powder that when added to the mix generates small bubbles of Hydrogen expanding the concrete to fill the space.

Slocum in Precision machine design uses tuned dampers in steel tubes.
http://www.amazon.com/Precision-Machine-Design-Alexander-Slocum/dp/0872634922]Amazon.com: Precision Machine Design (9780872634923): Alexander, H. Slocum: Books

Looks like MIT is the place to be.

Cheers

John

[BobWarfield]

For E/G, think of the Epoxy as your thin polymer layer. Lots of surface area through there for damping.

It works well. Subjectively, my machine is about 20% deader than an undamped mill. Finish is improved when milling. It was definitely worth the effort, which was not all that great since the machine was torn down anyway.

Cheers,

BW

[ckelloug]

Bamberg's thesis as I understand it is to create a shear damper by which a large mass in the middle of the polymer layer is caused to move out of phase to the tool itself causing energy dissipation in the polymer layer.

This is somewhat like E/G but basically works by the use of three homogenous layers: the machine, the polymer layer; and the weight inside of the polymer layer.

With E/G, there are some similar effects but I think you end up with a situation where there is a reflection and energy absorbtion at every interface between the epoxy and a mineral fragment. I believe the out of phase movement potential for every particle combined with the wave bounces at every density change make it very hard to get a resonance at higher frequencies in the material.

Bamberg's paper is interesting although I've heard a few people question his results as not working really well in practice. Regardless, it's an interesting read and has been discussed many times in the mammoth E/G thread. Just search for Bamberg.