. Electric railway journal . e for any trouble whichan impregnating coil may de-velop later in service. The accompanying reproductionsof a pair of these records refer to the impregnation oftwenty-two Westinghouse No. 81 coils which were taggedas part of group 407. The records show the changes intemperature from the time the coils were placed in the tank,5 p. m. Feb. 3, 1913, to the time they were taken out, 5 p. next day. FIELD-COIL PRACTICE Field coils which are returned to the shops for impreg-nation are first tested as hereinafter described. If foundin good condition they are covered
. Electric railway journal . e for any trouble whichan impregnating coil may de-velop later in service. The accompanying reproductionsof a pair of these records refer to the impregnation oftwenty-two Westinghouse No. 81 coils which were taggedas part of group 407. The records show the changes intemperature from the time the coils were placed in the tank,5 p. m. Feb. 3, 1913, to the time they were taken out, 5 p. next day. FIELD-COIL PRACTICE Field coils which are returned to the shops for impreg-nation are first tested as hereinafter described. If foundin good condition they are covered with what is termed asacrifice tape of iy2-m. width cotton which is put on as following manner: Put on the leads, apply one layer offriction tape, one layer of Empire cloth 15 mils thick, placecanvas cap on the motor side of the field and complete withone layer of i^-in. Imperial waterproof tape and dip inSherwin-Williams air-drying varnish. ARMATURE AND COMMUTATOR PRACTICE After an armature coil has been wound on one of the. B. R. T. Electrical Shops—Temperature Records of Compound and Vacuum Tanks coil forms, the ends are taped and sleeving is placed onthe leads. The coil is then baked in an oven for two hours,after which it is dipped in Sherwin-Williams baking var-nish. The coils are then hung up to drip, as illustrated,after which they are baked for four hours. Upon completionof the second baking the coil is taken to the winding room,where both sides are covered with three thicknesses ofEmpire cloth, each layer 8 mils thick. This cloth is appliedwith shellac and covered with fish paper, which is tied onuntil the shellac is dried sufficiently to retain it. The coilsare now ready for the hot presses. The details of one ofthese presses are shown in an accompanying drawing. In
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