Vibration Mounts
Vibration Mounts
(OP)
Hello Group,
I am working on selection of vibration isolators for one of our electrical cabinets which would be subjected to Sine sweep vibration test from 3 to 100 Hz (1 octave/ min for 2.5 hours) with peak acceleration of 0.7g(see attached pic for test plot).For preliminary analysis, I have selected 4 neoprene floor mounts (Grainger part# 4C988)and determined the natural frequency to be about 4.95 Hz. When I calculated the transmissibility (Q), I found that the max. Q of 50.4 is observed at resonant frequency 4.95 Hz (See attached excel sheet). Therefore, an input acceleration of 0.15 g is amplified to 7.5 g ( 50.4 X 0.15 g) at resonant frequency- kindly correct if my understanding is correct?
This brings to my next question, if Neoprene (damping ratio-0.05) is not sufficient, what other rubber materials I could use for my application. I had found that Butyl Rubber's damping ratio is about 0.2 which would be really good for my application but I am having hard time to find a vendor. If anyone can suggest vendors that would be great.
thanks
karthik
I am working on selection of vibration isolators for one of our electrical cabinets which would be subjected to Sine sweep vibration test from 3 to 100 Hz (1 octave/ min for 2.5 hours) with peak acceleration of 0.7g(see attached pic for test plot).For preliminary analysis, I have selected 4 neoprene floor mounts (Grainger part# 4C988)and determined the natural frequency to be about 4.95 Hz. When I calculated the transmissibility (Q), I found that the max. Q of 50.4 is observed at resonant frequency 4.95 Hz (See attached excel sheet). Therefore, an input acceleration of 0.15 g is amplified to 7.5 g ( 50.4 X 0.15 g) at resonant frequency- kindly correct if my understanding is correct?
This brings to my next question, if Neoprene (damping ratio-0.05) is not sufficient, what other rubber materials I could use for my application. I had found that Butyl Rubber's damping ratio is about 0.2 which would be really good for my application but I am having hard time to find a vendor. If anyone can suggest vendors that would be great.
thanks
karthik






RE: Vibration Mounts
RE: Vibration Mounts
RE: Vibration Mounts
Mike Halloran
Pembroke Pines, FL, USA
RE: Vibration Mounts
Thanks for the response. I understand that modifying the fn to fall out of test range will evade the resonance. However, to increase fn beyond 100 Hz I have to increase the stiffness of the mounts more than 2000 times (since mass is constant), which is impractical. To decrease it beyond 2 Hz, I can probably decrease the stiffness by decreasing the number of mounts which may not be ideal for shock absorption.
Please correct if my thinking is incorrect.
thanks
karthik
RE: Vibration Mounts
To push the Fn down below the range of interest, the key is to increase the static deflection, which may be a limit for geometric reasons.
Mike Halloran
Pembroke Pines, FL, USA
RE: Vibration Mounts
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RE: Vibration Mounts
thank you for your input. I have a vendor who fabricates vibration mounts out of Butyl rubber that has higher damping ratio of 0.2 (http://www.avproductsinc.com) which is an option. Also, I will further analyze my cabinet and electronics to determine its strength against 0.7g acceleration input, and its natural frequency (-to see if I can modify the design to have its natural frequency fall beyond 100 Hz)
thanks for the support
-karthik
RE: Vibration Mounts