SECTION 3 - BRUSH THEORY AND CHARACTERISTICS
Question 3:7 What Can Be Done About Low Current Density?
Where low current density is preventing the formation of an adequate film, action must be taken to achieve satisfactory brush and commutator performance.
In large machines where there are a number of brushes per arm, by removing all brushes from one or more brush tracks the current in the remaining brushes can be raised to a satisfactory current density.
Watch for circumferential stagger which requires removal of brushes in equal number of forward and backward brushes from each arm.
If for some reason this is considered undesirable then a change of brush grade is necessary. For machines where brush removal is not possible, for example machines with one brush per arm or position, then different brushes must be used. These are usually high resistance, treated or resin bonded grades which have overload limitations but have been very effective when applied properly.
When making alterations to a machine for light load applications it is worth checking whether the machine is likely to be subjected to higher loads intermittently or may be moved to another location with increased load.
If this is likely to occur then somewhat of a compromise may be required to allow for both situations and it is recommended that the brush flexible leads be made larger than normal to accommodate for higher short current since the lead and connection to the brush is often the most vulnerable.
Question 3:8 What Cause A Brush to Wear Out?
The information has been drawn from experience of Morganite Taiwan Limited Application Specialists combined with a wide range of published information from major carbon supplier and motor manufacture. However, the material can not be downloaded, copied or used without written permission.
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