PLAN No. 1074. COIL IMPREGNATING AND PAINTING
After the coils have been wound, and before or after they have been taped, they must usually be impregnated or saturated with an insulating compound. The last process in finishing the coil ordinarily consists in painting it.
In impregnating, the coils are placed in a large steel cylinder, which is then hermetically sealed by bolting its removable top fast to it. With a power pump the air is exhausted from this cylinder. The impregnating compound—a sort of waterproof paint or varnish—is then forced in and is caused to permeate every interstice of each coil. The compound is then pumped out of the cylinder, and the impregnated coils are removed. To render them waterproof, some coils are painted with a brush instead of being impregnated, but before painting they are heated in a drying oven, which drives out all moisture. Where the coils are light in weight, little physical effort is required, but where they are heavy considerable exertion may be necessary, although cranes and hoists are usually provided.