| 摘要 |
Varnishes for impregnating the coil of an electro-magnet in two stages are as follows. The coil is first vacuum- and pressure-impregnated with a varnish of the phenoplast type produced by the condensation of formol (30 per cent solution) and of cresol, with an added oil drier to 65-90 per cent by weight of the cresol. A natural resin plasticizer is added and the mixture dissolved in trichlorethylene. The coil is then dried at 80 DEG C. and a second impregnation effected, after which it is baked for six to ten hours at 110 DEG C., which leaves the varnish still incompletely polymerized, in which condition the coil is suitable for transportation but can still be shaped. The coil is then installed in its housing, which is filled with a varnish similar to the above but capable of more rapid polymerization, the drying oil now being in the proportion 40-60 epr cent of the weight of the cresol. No plasticizer is added and the varnish is heated to 80-100 DEG C. for fluidity. The unit is next baked six hours at 115 DEG C., six at 125 DEG C. and eight at 170 DEG C., which polymerizes the second varnish and completes the polymerization of the first. |
