Generator Revolving Field Brush Replacement; Cleaning - Hobart JET-EX 4 Operation And Maintenance Manual

OM-2049

(1) Cleaning

If inspection reveals that brushes are gummy or sticking in the brushholders, they should be re-
moved and cleaned. Clean both the brushes and brushholders. Use a good, SAFE, commercial
cleaner. DRY ALL PARTS THOROUGHLY. Be sure brushes can move freely in brushholders.
WARNING: DO NOT USE A FLAMMABLE SOLVENT. DO NOT USE STEAM
CLEANER, OR SOAPS AND DETERGENTS UNDER PRESSURE.
C. Generator Revolving Field Brush Replacement
See Figure 5
(1) Disconnect leads (A) from connectors on brushholder caps (B).
CAUTION: When removing the lead wires, do so one at a time and replace each brush accord-
ingly, to insure that the lead wires are put back onto the proper brushes.
(2) Lift brush (D) from brushholder (C) for inspection. If brushes are worn unevenly or are shorter than
7/16 inch (11 mm), replace them.
(3) Inspect slip rings whenever brushes are removed for servicing brushes or brushholders. Note sur-
face conditions of rings. Surface should appear smooth and clean. Scoring or roughness of slip rings
may be caused by grit or abrasive substance in brushes, or by oil on the rings. Moderately rough slip
rings can be smoothed by holding grade 00 flint paper against their surface while the rings are revolv-
ing slowly. If the rings are badly scored, the unit must be sent to an overhaul facility for repair. After
cleaning slip rings, blow dirt and grit out of the unit with compressed air. Do not use over 25 psi (172
kPa) air pressure to blow dirt out.
(4) Slip new brushes into brushholder guides, and place caps on top, and screw them into the guides
to a "bottomed" position. The spring attached to the brush will determine the pressure at which the
brush contacts the slip rings.
(5) To fit new brushes to the slip rings, lay a strip of No. 00 sandpaper, smooth side down, on slip ring
surface, and draw the sandpaper in the direction of rotation of the slip ring, lifting the brush on the re-
turn stroke. Continue until the brushes have same curvature as the slip rings. Blow all carbon dust out
of the machine using not over 25 psi (172 kPa) air pressure.
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May 20/89