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This chart provides a quick reference for both commutators and brushes to aid in achieving the best performance from your brushes.
To ensure good machine performance, early detection of existing or
developing problems is most important.
Costly unscheduled down time can be avoided when appropriate corrective
action is taken.
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The physical appearance of the commutator and patina gives an
indication of the overall brush performance.
Inspecting brushes already removed from the machine can also provide valuable information about the machine condition.
The following are examples of the more common faults
experienced in commutator and slip ring machines.
CARBON BRUSH FACE ANALYSER
3. Eroded brush face
1. Dense, shining sliding face
2. Slight porous sliding face
Problem free operation (REFER H)
Causes: Electrical overload, poor brush contact,
low spring pressure or brush binding in holder
4. Hairlining
5. Tracking with hair-lining and grooves
Causes: like 4, but more advanced (REFER D)
6. Broken edges
Causes: High commutator or mica, commutator excessively
out of round, brush chatter or machine vibration (REFER G)
7. Burning of leading or trailing edge
8. Copper nests
9. Double facing on split brush
Problem free operation (REFER H)
Causes: Underloaded, influence of dust, oil or grease (REFER D)
Causes: Difficult commutation, heavy sparking due to
brushes out of neutral position, defective interpoles
(REFER C)
Causes: Pick up of copper particles, often
following copper drag (REFER B)
Causes: Tilting of the brush in reversing
machine due to excessive clearance in
brush holders
Calculation to measure spring pressure
1.00
Spark free
1.25
Intermittent
pinpoint sparking
1.50
Very light
sparking on some
brushes
2.00
Light sparking
across most
brushes
2.50
Medium to strong
sparking across all
brushes
3.00
Spring Pressure =
Measured Force
Brush Thickness x Brush Width (Ensure units eg. g/cm2 and PSI are consistent)
As spring pressure is a value that descibes the downward force exerted on to the sliding
face, it is important that large angles either at the brush face or on top of the brush be taken
into consideration. The following shows the loss in spring factor due to brush angles. Poor
commutation through brush instability can be caused by the brush holder being too high off
the sliding surface. Set brush holder height to manufacturer specifications or as a guide we
recommend 1.5mm-3.0mm. Care should be taken when adjusting holders to ensure brushes
remain in the neutral position and correctly aligned.
Destructive
sparking across all
brushes,
streamers
COMMUTATOR CONDITIONS
A. Grooving
B. Copper Drag
C. Bar Edge Burning
D. Threading
Commutator wear due to electrical
or mechanical wear.
Mechanical:
Abrasive grade or contaminated
atmosphere.
Electrical:
Low spring pressure.
Remedy:
* Ensure correct and consistent spring pressure.
* Ensure constant and clean supply
of cooling air.
* Change brush grade.
Copper deposits from bars
to the slots of a commutator.
Causes can be from excessive
friction between brushes and
commutator, contamination,
defective interpoles, incorrect
spring pressure, commutator
bars softened by overheating. Remedy:
* Check spring pressure.
*Check interpole gap.
* Change grade to one of lower
friction.
* Correct machine faults.
Electrical wear due to several
conditions.
Remedy: * Check for high mica.
* Check brush neutral position.
* Ensure correct and consistent
spring pressure.
* Change grade for better commutating ability.
Condition is caused by low current
density or atmospheric contamination.
Remedy:
* Ensure correct and consistent spring pressure.
* Increase current density.
* Change brush grade.
* Ensure constant and clean supply of cooling air.
F. Starry Commutator
G. Uneven Bar Burning
or Marking
E. Even Slot Bar
Marking
Film condition related to the
electrical design of the armature
windings. Minimised by the
appropriate brush grade selection.
Random passes of current flow
caused by low spring pressure,
over filming or overloaded
conditions.
Remedy:
* Ensure a correct and consistant spring pressure.
* Change grade for better commutating ability.
H. Problem Free Commutator
Surface
A uniform film that remains stable during
seasonal change or variations in load. Film can
vary in appearance from light to dark.
Copper deposits from bars to bars.
Commutator out of round. Armature
winding fault. High commutator or
mica segments, stall burns.
Remedy: * Machine commutator.
* Lightly stone burn marks away.
* Test motor windings.
PRODUCTS AND SERVICES
Precision Machining
GET CONNECTED
www.cortela.com.au
Ph 1800 800 659
Brush Holders
Monitoring Services
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Carbon Brushes
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International Locations
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