Non conductive rubber

[bradmo]

Hi, I have application where I need a 70-75 shore NR,chloroprene or similar compound with an insulation resistance of at least 80 000 mega ohms/mm2.
We are moulding a pad which sits under a railway track.
Anyone out there have a suitable formulation?
Regards
Brad

 

[btrueblood]

Dunno, your units are strange. Can you do the calculation so that you can specify the resistivity of the material in ohm-cm or ohm-m?

See

http://en.wikipedia.org/wiki/Resistivity

Secondly, you will need to specify the upper limit voltage, so that a minimum arc breakdown voltage (or dielectric strength) could be specified. Two seperate animals.

When you say similar compound, can you be a bit more specific about what environment the rubber will need to withstand? Nitrile rubber may be your best bet if oil/tar resistance is necessary, but if you can avoid petroleum compounds, EPDM will be better in general weathering resistance and ozone. You might want to have a compressive strength number in mind also.

For any rubber, the lower the carbon black loading, the better the resistivity and arc breakdown voltage, in general. But the specific type of carbon black used is also important.

Once you have some hard numbers for the above two values, talk to a rubber supplier. Oregon Rubber is one, if you are on the west coast, or you can search for one closer/more convenient via Google, Thomas, or Global Spec. Also try talking to a custom rubber molding shop.

 

[GrahamBennett]

There are a couple of rubber moulding shops in Malaysia that I know of already making rail pads in NR and EPDM-based compounds.