Re: [TCML] TAR

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Ed,

I'm not sure where to get the compound used say in NST's, but there are 
vast resources of manufacturers that manufacturer electronic grade 
potting compounds. Thermal conductivity, hardness, and flammability, are 
a few parameters to consider. They also make compounds for HV use (I 
think a silicone base).  Here is a site that does pretty well at 
explaining the various compounds available. Problem #1 is cost.
http://www.pottingsolutions.com/

At work, we had issues with corrosion in an electronic box used on city 
buses in a particular model where the box was subjected to "massive 
moisture". I redesigned the board with vertical fuse towers (1.75" ht) 
and used an electronic grade potting compound with a low hardness (like 
a soft rubber). It is simply a 2 part epoxy poored in the box to 1/4" 
below the top of the fuse towers. In this case, I used a low hardness 
epoxy to prevent surface mount components from ripping off the board 
during cure and shrinkage. In a transformer potting application, that 
would be going overboard.

Anyway, it is a good idea to call and talk with the experts if you are 
really seeking a potting compound. They could give the best advice about 
this.

Take care,
Bart

Ed Phillips wrote:
>    Does anyone know where to get the type of black "tar" used to pot 
> transformers?  Does anyone know the actual temperature at which it's 
> poured into the transformers?  Did a web search but got nowhere and 
> suspect that roofing tar or pitch probably isn't suitable.  I want to 
> pot a couple of GMHEI transformers in a cylinder to simulate the 
> secondary of a "spark coil" and don't want to mess with oil or the 
> like.  Paraffin wax doesn't work, at least for me, because of too many 
> bubbles - I've tried pretty hard to get rid of them [with the 
> exception of vacuum] without much luck.
>
> Ed
>
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