SECTION 3 - BRUSH THEORY AND CHARACTERISTICS
Question 3:2 What Part Does Resistivity Play In A Brush?
Obviously the resistance of the material differs from one type to another depending on its ingredients.
Also there are crystalline layers that form in some materials as they are compressed which results in some carbon grades having a higher resistance through the thickness of the material than through the length of the material. This can be up to 10 times the longitudinal resistance in some materials. It is therefore very important how this type of material is cut into brushes.
As current flows through a given resistance it generates a proportionate amount of heat therefore, to handle the line current flowing to the armature a low resistance would be best but to limit the "cross face" currents a high resistance is preferable.
The cross face resistance can also be increased by using split brushes.
Finding a balance between these two opposing requirements can be quite difficult. The heat generated in the brush is important in creating the right environment to properly form the patina or film on the collector. This is further discussed in other section.
Too much heat however can be damaging to the brush, particularly the lead connections and collector surface.
Question 3:3 What Is Contact Drop Or Voltage Drop?
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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