The Diseases Of Electrical Machinery 1904
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4
THE DISEASES OF
this case also the only remedy is to turn down the
commutator.
Carborundum for Grinding Commutators.—It
may here be mentioned that recently for the purpose
of grinding down the commutator surface, carbor-
undum is used instead of glass-paper. This can now
be obtained in the form of carborundum-paper in
different degrees of fineness. With this material it is
possible to do something that one cannot do with
glass-paper, that is, to grind down those commutators
that have the insulation between the segments made
of too hard material. This is rendered possible by
the hardness of carborundum. The author now uses
carborundum exclusively in his practices. On no
account must emery be used.
Wrong Placing of the Brush.es.—A cause of
sparking is often the wrong position of the brushes,
since the segments are so burnt by the sparks that
afterwards, when the brushes are correctly adj usted,
sparkless working is still impossible. Since in different
modern types of machines various types of armature
winding are employed, it is of no use giving a general
rule for the position of the brushes, and it could lead
very easily to the wrong result. While one could
formerly say that at no-load the brushes might stand
exactly in the middle between two pole shoes, and
must be rocked forward with increasing loads, this is
nowadays not the case. Modern machines are more
and more so wound that with a two-pole drum arma-