Brush Holders. Two methods of securing the brush holders are employed. In [Fig. 3], the brush holders may be seen to be secured in position by being bolted through the end of the motor shell. [Fig. 8] shows the brushes mounted on a yoke which is secured to the motor shell. The yoke is of wood and provides the necessary insulation. Where the holders are fastened directly to the shell a block and washers of vulcabeston or other insulating material intervene to furnish the insulation between the shell and the holder. In practice the greatest difficulty experienced with brush holders is preventing them from becoming grounded by dirt and carbon dust which collects on the insulation.
Opening Cases for Inspection. Accessibility for inspection and repairs is essential in all railway motors. A lid is always provided directly over the commutator to facilitate inspection of the commutator and brushes. To open up the motor casing for more extensive inspection or repairs, three general schemes are employed. One is to have the lower half of the casing swing downward on a hinge as in [Fig. 9], which illustrates the Westinghouse No. 38 B motor. The armature may be placed either in the lower half, as shown in [Fig. 9], or in the upper half. When a motor of this type is to be opened the car is run over a pit, and the repair men work entirely from below.
Often the hinge pins are removed and the lower shell containing the armature is dropped down by means of a jack placed underneath.
Two handholes are usually provided in the bottom shell for observing the clearance between the armature and the pole pieces and also for removing dirt that may collect in the bottom of the shell. Another scheme is to have motors open from the top, either by hinging the upper part of the motor casing, as in [Fig. 3], or by having the top part of the casing lift off. Where this form of motor is used, the car body is hoisted clear of the truck, and the trucks are run out from under the car body before work is done on the motors. In this case, all the work can be done from above without the use of pits.
Fig. 9. Railway Motor. Lower Half of Casing Swung Down.
A third design is the box-frame motor casing, from which the armature can be removed endwise only. Such an arrangement is shown in [Fig. 10], which is a view of a No. 66 motor of the General Electric Company. In this motor a sufficiently large opening is provided in the ends of the motor casing to permit of the armature being removed endwise. A plate or head, which accurately fits into this opening, carries the armature bearing. In removing armatures from motors of this kind, the usual method is to take the motor out of the trucks and stand it on end with the pinion up. The bolts being removed from the end plate, the armature can then be hoisted out of the case by means of a special hook attached to the pinion. Another plan that has been used in removing armatures from such motors, is to place the motor in an apparatus where the armature shaft can be held between centers, as in a large lathe. The motor casing is then moved along in a direction parallel to the armature shaft, until the armature is exposed.
This latter box-frame type of motor is very compact; a stronger casing can be made for a given weight and space than if it were divided horizontally. Moreover, the magnetic circuit cannot be disturbed by imperfect contact between two parts of the casing. Where this type of motor is used, the bearings project inward under the commutator and armature, thus getting long bearings with a short motor, which is important where the room is limited, as, for example, in the case of a large motor mounted on a standard-gauge truck.
Fig. 10. Box-Frame Motor.