Mysterious black insulation stuff?

[Ford]

Hi,

I'm an undergrad who came into posession of some large power electronics things. Upon investigation I noticed two of these things are absolutely filled with this hard black rubbery stuff. I think it's insulation, brittle due to age, but I'm not sure. I'd like to remove it so I can get a better look at the parts inside these devices and I'd also like to know if what I'm looking at is actually some sort of old rubber insulation. I've elected not to mess with any of it further in case it's some sort of dangerous material containing asbestos and what not (I've been told these devices are quite old).

Any information on what it is would be helpful, as I can't find anything about it (or pictures) online by searching along the lines of "transformer black electrical insulation" or "power electronics rubber insulation" etc. If anyone has an advice on how to remove it I'd be glad to get that too. I don't care to save or reuse the devices, so destructive methods are acceptable.

Here are pictures of the mystery stuff: https://imgur.com/a/hzTQPSS


Thanks and I'm glad to join the forums.

[Shock]

It's called Potting Compound.

[helius]

The common encapsulants (potting compounds) are silicone, epoxy, and urethane. Removing them is a messy process but it is possible.
There was a video linked several years ago here about decapsulating a power transformer, I wonder if I can find the link...

[gcewing]

Here's a video from Mr. Carlson's Lab where he depots an old power transformer filled with tar:



Whether his method would work for you depends on what kind of potting compound your device has.

[helius]

Here's a video lesson from PACE showing more typical encapsulants.


There's an emphasis on equipment sold by PACE in that time period (not currently available from them), but the principles are the important part. It is also possible to soften certain resins by just boiling them in water. That is not ideal from a high-reliability electronic standpoint, but it does work, and most circuitry can survive being boiled if given sufficient time to dry out before power is applied.

[perieanuo]

hi,
there are lot of rosin compounds out there, each of them has specific use cases. each case need to be studied, we tested several solutions for laser manufacturing for example (it had to be moisture proof, sealed for avoiding power modification for the laser diode etc etc).
so for some apps you need specific rosin compound, for others it may be different (for example, if the board is heating a lot you may choose other rosin)
fluidity is also an important parameter in pcb compounds
regards, pierre

[Shock]

There's an emphasis on equipment sold by PACE in that time period (not currently available from them)

They actually still sell those type of tools, but they aren't really intended for diy or a single use.

https://paceworldwide.com/mc-65-microchine
https://paceworldwide.com/lf-15-thermopart-lapflo-handpiece
https://paceworldwide.com/smr-multi-function-pulse-heat-rework-station

[helius]

They actually still sell those type of tools, but they aren't really intended for diy or a single use.

When you find the link to buy Freon TF, let me know, 'k?
I am also interested in any devices like the SU-101 spray unit shown @13:15.

OP: The larger device is a neon sign transformer. When messing with these, you do need to observe the one-hand-in-pocket rule: 15kV at 30mA can really sting. It is potted either in tar or silica-loaded urethane; you may be able to tell by touching the material with a red-hot pin and smelling the smoke. I seem to remember that the potting is required for anti-arcing protection on that type of unit.