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Effects of hardness on the lifetime of graphite brushes used for aircraft starter generators
Holle, Michael Jay
Holle, Michael Jay
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t11021_Holle.pdf
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2011-05
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Electronic dissertations
Electronic dissertations
Electronic dissertations
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Abstract
This study concentrates on the relationship between the hardness of three
different carbon/graphite brushes and the wear rate of the brushes and heat generated
within a 400 Amp starter generator. The method being proposed was to alternate the
starter generator from the starting mode and the generating mode, and run each
carbon/graphite brush in the starter generator for a set time and document both wear
rates and heat created.
The study originated with a starter generator overheating during normal usage.
The original hypothesis was that either excess carbon dust caused arcing, or the energy
required to form the carbon dust was releasing too much heat, and thus the brush was
too hard. The three carbon/graphite brushes chosen for this researched spanned the
range of hardness for this type of material.
This thesis analyzed the surfaces of the carbon/graphite brushes to correlate
grooves and pitting with the frictional coefficient. An optical microscope, AFM, and SEM
were used in the analysis of the surfaces. It was found that as the hardness of the brush
went up, the wear rate decreased while the overall heat on the inside of the starter
generator increased.
From this research it is evident that the hardness of the brushes is the key factor
in the excess heat in the starter generator. The energy that is expelled as heat as the
carbon brush gradually wears is directly correlated with the increase of operating
temperature. A harder brush will prolong the life of the brushes, but also increases the
operating temperature to more than the unit is capable of handling.
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Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.
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Wichita State University
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© Copyright 2011 by Michael Jay Holle. All rights reserved