CARBON BRUSH FACE ANALYSER

1. Dense, shining sliding faceProblem free operation (REFER H)

2. Slight porous sliding faceProblem free operation (REFER H)

3. Eroded brush faceCauses: Electrical overload, poor brush contact, low spring pressure or brush binding in holder

4. HairliningCauses: Underloaded, influence of dust, oil or grease (REFER D)

5. Tracking with hair-lining and groovesCauses: like 4, but more advanced (REFER D)

6. Broken edgesCauses: High commutator or mica, commutator excessively out of round, brush chatter or machine vibration (REFER G)

COMMUTATOR CONDITIONS

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Australian Locations

* 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.

* 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.

7. Burning of leading or trailing edgeCauses: Difficult commutation, heavy sparking due to brushes out of neutral position, defective interpoles

(REFER C)

8. Copper nestsCauses: Pick up of copper particles, often

following copper drag (REFER B)

9. Double facing on split brushCauses: Tilting of the brush in reversing machine due to excessive clearance in

brush holders

A. Grooving

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.

B. Copper Drag

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.

C. Bar Edge Burning

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.

D. Threading

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.

E. Even Slot Bar Marking

Film condition related to the electrical design of the armature windings. Minimised by the appropriate brush grade selection.

F. Starry Commutator

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.

G. Uneven Bar Burning or Marking

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.

Calculation to measure spring pressure

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.

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.

Constant ConnectionsPrecision Machining Brush Holders Monitoring Services Carbon Brushes Slip Rings

Spark free

Destructive sparking across allbrushes, streamers

Intermittentpinpoint sparking

Very lightsparking on some brushes

Light sparking across mostbrushes

Medium to strongsparking across allbrushes

1.00

1.25

1.50

2.00

2.50

3.00

www.cortela.com.au

www.cortela.com.auPh 1800 800 659