GEH-5304A
33
Commutator Check Chart
For Com par ing Com m utator S ur face Mark ings
SATISFACTORY COMMUTATOR SURFACES
LIGHT TAN FILM over entire commu-
tator surface is one of many normal
conditions often seen on a well-
functioning machine-
MOTTLED SURFACE with random fil m
pattern is probably the most frequently
observed condition of commutators in
industry.
SLOT BAR-MARKING, a slightly dark-
er film appears on bars in a definite
pattern related to number of conductors
per slot.
HEAVY FILM can appear over entire
area of efficient and normal commu-
tator and, if uniform, is quite accept-
able.
STREAKING on the com mutator surface signal s the
beginning of serious metal transfer to the carbon
brush. Check the chart below for possible causes.
THREADING of commutator with fine lines results
when excessive metal transfer occurs. It usually
leads to resurfacing of commutator and rapid brush
wear.
GROOVING is a mechanical condition caused by
abrasive material in the brush or atmosphere. If
grooves form, start corrective action.
COPPER DRAG, an abnormal bui ld-up of com m utator
material, forms most often at trailing edge of bar.
Con-dition is rare, but can cause flashover if not
checked.
PITCH BAR-MARKING produces l ow or burned spots
on the commutator surface. The number of these
m arkings equals half or all the num ber of poles on the
motor.
HEAVY SLOT BAR-MARKING can involve etching
of trailing edge of commutator bar. Pattern is re-
lated to number of conductors per slot.
CAUSES OF POOR COMMUTATOR CONDITION
Frequent vi sual inspecti on of commutator surfaces can warn you when any of t he above conditions ar e developing s o that you can take early corrective ac tion. The chart below may indi-
ca te some possible c auses of these conditions , suggesting the proper productive mainte nance.
Type of Brush
Light Unbal anced B rush In Use Conta mination
Electrical Electrical Electrical Armature Shunt Pressure Abrasive Porous Abrasive
Adjustment Overload Load Connection Field (Light) Vibration Brush Brush Gas Dust
Streaking X X X X X X
Threading X X X X
Grooving XX
Copper Dra g XXX X
Pitch Bar-Marking X X X X X
Slot Bar-Making X X X
HOW TO GET THE MOST VALUE FROM THIS CHART
The purpose of the C ommutator Check Chart is to he lp you spot unde s irable commuta tor conditi ons as they develop so you can take corrective act ion bef ore the condition bec omes serious.
This chart will also serve as an aid in recognizing satisfactory surfaces.
The box cha rt abov e indicat es the importa nce of selec ting the correct brush and having the right operating conditions for optimum brus h li fe and c ommutator wea r.
For additional informat ion or he lp with ca rbon brush applica tion or commutation proble ms . Contact your nearest G E Sales Office or Di s tri butor.