I am designing a rubber component, which is used for vibration isolation. Vibration levels are varying throughout the frequency (1 to 200Hz). I want to know, which will be the most crucial parameter of designing?
whether i should give priority in material selection, to compare damping characteristics or i should give priority to the shape & size of component, which has effect on dynamic stiffness.
Natural rubber (NR) shows low dynamic stiffness, good load bearing properties, and low heat build-up. It is considered the best choice for vibration isolation applications.Low dynamic stiffness gives better isolation.Dynamic to static stiffness ratio is an important design element which is a measure of the resiliency.Due to low thermal resistance of NR,special EPDM with a better thermal resistance is used in vibration isolation.
Do not forget also to understand where in your structure this component will be inserted, because it can have different requirements depending on the transmissivity of the coupled parts and their structural dynamics.
Also, have a look at the damping and sizes of your object.
Regards,
Alessandro
Hi
As Allessandro points out - the isolator is a component that must have certain properties to do its job, namely - it must be weaker than the dynamic stiffness of the structure connecting to it.
There are two ways to put numbers on vibration isolation, Transmissibility and Effectiveness (the dB difference in response atyour position(s) of interest on the isolated side with rigid and isolated connection, respectively). The former is easy to measure while the latter is the more correct.
Watch out for anti-resonance in the rubber component. It will then become very stiff regardless of what you do, i.e. you must design anti-resonance to lie at 2 kHz or higher. Anti resonance will occur between 1st and 2nd (2nd/3r, 3rd/4th, etc) internal spring mode.
For the component to do its job, it must isolate as many dB as you deem necessary and it must be able to take up & endure the mechanical loads as well as the chemicals that are used in the application. It will age if exposed to UV light and excessive temperature, so you might want to shield it if you have something hot nearby or when placed outdoors.
Do not confuse damping (conversion of energy into heat) with isolation. These are different beasts and a rubber isolator involve both.
Take a look here for some rambling of mine on vibration isolation. http://qringtech.com/2014/01/28/need-to-know-about-vibration-isolation/
and on damping
http://qringtech.com/2014/06/22/designed-damping-types-mechanisms-application-limitation/
Sincerely
Claes
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