This is a publication written especially for electrical maintenance men with the purpose to offer helpful suggestions in a short form.
Difficulties occurring on electrical machines result from and/or mechanical causes. Each interference affects the brushes and even more the commutator or slipring.
Notions like Herz' contact surface, arc, raising arc, patina (electrical decomposition brush and collector), friction, wear and chattering are largely known features.
The commutation is in very close relation with the physical and chemical conditions of the surfaces of brush and commutator.
It changes periodically because of the mechanical effect of the sliding movement, the current flow and the various atmospheric influences, changing sliding conditions provokes variable behavior in the commutation.