For me, it was telecom transformers for SNCF.

Fox's Mercantile a écrit le 15/01/2019 Ã* 19:51Â*:
On 1/15/19 11:13 AM, Phil Allison wrote:
** The process is commonly known as " vacuum impregnation "
-Â* completed transformers are placed inÂ* tank of resin or
varnish and the air pressure reduced until all air pockets are filled.

Actually, the vacuum allows the bubbles to expand enough to
float to the surface and pop.

I did this with hand wound transformers at TRW using Poly
Urethane, and in my shop mostly with casting resins.

The vacuum chambers at TRW were nice, but I found that using
a modified pressure cooker works fine for the size jobs I have.