Contact Surface Chart

Contact Suface Chart

C1-SMOOTH UNIFORM SURFACE

This indicates good performance. However, if the polish is mirror-like (glazed), high frequency chatter due to low current may be the cause. Check the side-faces of the brush for signs of vibration.

C2-OPEN TEXTURED SURFACE

This, again, indicates that brush performance is satisfactory. Actual appearance will depend on the type of grade.

C3-FINELY LINED SURFACE

Another satisfactory condition. Fine lines indicate the presence of dust in the atmosphere. This may be overcome by the use of filters or ducting the machine’s air supply from another area.

 

C4-FINELY STREAKY SURFACE

This is a further development of (3) above. The causes are normally atmospheric contamination or lack of load current.

C5-HEAVY GROOVED SURFACE

As (4) above, but problem is more severe or has been allowed to continue for longer.

C6-GHOST MARKED SURFACE

This may be associated with difficult commutation and can arise from incorrect neutral position, interpole problems or other causes of poor commutation.

 

C7-BURNT EDGES

Normally occurs on the trailing edge of the brush. Caused by poor commutation and heavy sparking.

C8-PITTED SURFACE

Indicates heavy under-brush sparking as a result of current overload or intermittent contact.

C9-LAMINATED SURFACE

This is an unusual condition caused by an armature winding fault and delivering Voltage surges during operation.

 

C10-DOUBLE-BEDDED SURFACE

This occurs as a result of brush tilting on a reversing machine, i.e. the brush beds itself in both directions of rotation. In itself this does not give any cause for concern.

C11-COPPER PARTICLES

Copper pick-up from commutator surface can result from copper drag problems or heavy peak loads. Can cause further commutator wear. Check brush grade.

C12-CHIPPED EDGES

Normally occurs on the leading (entering) edge of the brush. breakage can result from poor commutator profile, high micas, loose risers and severe brush instability.