Vibe isolation for machine mounted on wood frame floor

[joepepitone]

I have a 3-phase converter installed on the 2nd floor of an older wood frame building. The phase converter is essentially a large electric motor which weighs about 400 pounds. The installer set it on a rubber pad with bolts running down into a piece of plywood attached to the wood frame floor. You can hear the vibration throughout the whole building.

How do I isolate the vibration? I am leaning to housed spring vibe isolation mounts. Should I also try to add some mass with a concrete pad or something?

 

[sms]

Yes, I think that spring mount will be your best bet. You may also need to add mass, but that will depend on your spring stiffness. You will have to tune the natural frequency of the system to isolate it and that means either adjusting mass, or adjusting spring stiffness. You want the natural freqency of the motor on springs to be about 10% of the motor running speed.

For more info check out this link...

http://www.fabreeka.com/tech/isolation_theory.pdf

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[rob768]

note that if you place it on soft springs, you may get large deflections. Don't know if the cabling and especially the cable connections are keen on that. I have seen a fire started through a fatigue failure in too rigid cable connections.

 

[IRstuff]

The Navy uses wire-rope isolators for much of their heavy equipment.

Note that the usual approach is to only get as low a natural frequency that will just reduce the vibration to a tolerable level, to minimize the translational motions.

TTFN

FAQ731-376

 

[Twoballcane]

To add to IR, check out Barry Controls for the wire rope isolators.

Tobalcane
"If you avoid failure, you also avoid success."

 

[sms]

To add to Rob, I have experienced situations where electrical connections essentially short cirucuited the isolation allowing the energy a path to the rest of the structure, and as a result the vibration was still unacceptable.

The design of the electrical connections will need to be reviewed.

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[Strong]

The rubber pad may actually be OK, but the base bolts may be acting as a vibration short circuit. The Fabreka link should provide some guidelines on how to isolate the bolts, or run the machine without base bolts as a test. Secondly, you may have insufficient support under the wood floor. If that's the case, then either move the machine or stiffen under the floor. You cannot use vibration isolator catalog charts to select vibration isolators when the foundation (floor)is flexible, since the simple charts and graphs are based on calculations for an infinitely rigid foundation. In general, you would need softer vibration isolators when the foundation is flexible.

Walt

 

[joepepitone]

What a great website.

Thanks to everyone who responded.

 

[sms]

Walt,

I didn't know you hung out here, good to see you...


Steve Schultheis

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[spciesla]

Steve - I didn't know you were sms on this site. No wonder your posts are so insightful. Keep posting on eng-tips and mantenanceforums.

Steve Ciesla

 

[Tmoose]

Basically the isolator deflection must be MUCH greater than the floor deflection. There is a discussion of isolating machinery on non-ground floor installations here. Vintage but helpful.

http://www.mason-industries.com/masonind/downloads/spec/complete/ashlec.pdf

And like other's said, look out for mechanical short circuiting that limits the free motion of the unit on the isolators.