SECTION 3 - BRUSH THEORY AND CHARACTERISTICS
Question 3:16 Why Do Some Sliprings And Commutators Have Spiral Grooves?
Grooves have been used on sliprings for a long time but are sometimes also introduced on commutators of larger DC traction motors with some success.
The spiral grooves provide the following benefits:
The groove ''sweeps'' across the brush face and interrupts the arcing under the brush thereby reducing the Iikelihood of grooving.
The spiral groove provides cooling under the brush face and also assists in cleaning dust away from the brush face.
The grooves also break up the cushions of air that may form under a brush which cause unstable contact between the brush and the ring or commutator.
Note: The spring force will be less than for a solid brush of the same nominal dimensions as the area of the grooves under the brush must be deducted from the brush face area. The required force will be calculated on that lesser area.
The current density calculation is affected in a similar way.
Question 3:17 What Is The "S Cooling Factor"?
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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