Now-a-days the isolator that is used mostly in machine foundation is steel springs. The importance and application of isolator are not discussing here. The isolating materials other than this are:
- Natural and synthetic rubber
- lead and others
We are discussing here about rubber isolator. The efficiency isolation done by rubber depends on two properties of rubber; they are:
- rubber hardness(in durometer)
- its deflection properties
in case of deflection estimation, only that is observed in static cases, should not be used alone; this is due to the variability of modulus that encounters dynamic to static ratio. These value for different ranges of hardness are as below:
- Rubber of low durometer (around 30) this modulus is almost unity
- For increasing durometer(around 60) the modulus become around 1.8.
In 1951 Crede has evaluated minimum natural frequency that can be attained for rubber under loading of both
From the figure provided above we can conclude that by increasing thickness of rubber, natural frequency of it can be reduced. The damping ratio of it is observed to be increased considerably with increment of durometer hardness. The other influencing factors are:
-frequency of shear strain
-magnitude of shear strain
this variation of dynamic shear strain for different frequencies and damping ratio relation are shown in figure below.
Thus rubber can be used conveniently in some vibration isolation applications due to its high damping properties than many isolating materials. So, various commercial products are available as isolation pads or mounting. we will discuss some of this products in this blog.