SECTION 2 -BRUSH DESIGN, MANUFACTURE AND APPLICATION
Question 2:8 Why Do Some Brushes Have An Insert Fitted In The Face?
Where there is a problem of insufficient lubrication preventing a brush for building up a film then one alternative is to fit a graphite insert in the face of the brush.
There would generally be found on slip ring motor brushes, where the high copper content is required for starting and peak loads. At normal operating current, which may be below full load, a suitable patina may not develop resulting in copper dusting and excessive slip ring wear. In these case a graphite insert can be fitted to assist patina formation.
It is normally possible to avoid using an inset by an appropriate choice of an alternative grade or alternation to the number of brushes in circuit. A brush white insert is, however, an option that is available for specific cases.
Another type of brush with insert that has begun to appear relatively recently, consists of a normal brush with a special inset of a mildly abrasive material.
These so called "Surface Rounding Brushes" are intended to give a gentle grinding action to the commutator which will clean the commutator surface and aid in diminishing or removing burn marks or minor flat spots. They ar not an instant cure for all problems but have been used with success in some situations which would have deteriorated and eventually required remachining of the commutator. Sometimes the insert is relatively short in the "r" dimension and wears away completely leaving a totally standard brush to continue on for the rest of the life of the brush.
The usual procedure is to fit these special brushes for a short time on one arm only to treat a developing problem then remove them and revert to standard brushes.
Question 2:9 Why Do Some Brushes Have Saw Cuts In The Face?
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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