Improvements in or relating to Dynamo and like Electrical Contact Brushes.
Year: 1897

page_text: Date of Application, 23rd Apr., 1897-Accepted, 23rd Apr., 1898
COMPLETE SPECIFICATION.
Improvements in or relating to Dynamo and like Electrical Contact
Brushes.
I, LOUIS BOUDREAUX, of 42, Boulevard Bonne Nouvelle, Paris, in the Republic
of France, Engineer, do hereby declare the nature of this invention and in what.
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement: —
The electrical contact brushes indispensable for instance for dynamos must fulfil
certain conditions; their conductivity must be as great as possible in order not
to offer resistance to the passage of the current whilst their friction on the commu-
tator must be as little as possible.
It is obvious that a bar or block of copper brass or bronze would satisfactorily
answer the first, but would be far from satisfying the second requirement.
In order to realise the second condition it has been found necessary to divide the
metal constituting the brushes, and construct them in the form of metal strips,
plates, wire leaves, netting and powder.
The great tenacity and extreme ductility of copper or its usual alloys rendered
indispensable the latter mode of making the brushes, whereby is avoided the ex-
cessive friction between the commutator and brushes when made of a bar or block
of copper or alloy of great tenacity and ductility.
I have discovered means quite different from the mechanical division of the metal
constituting the brushes which will satisfy the above requirements.
This consists in modifying the molecular state of the metals employed so as to
lessen their tenacity and ductility, which is the object of the present invention.
I add to copper or to its alloys a small proportion of bismuth, antimony and cad-
mium, the nature of the resulting alloy being quite different from those used hither-
to the fibrous structure of the copper becomes crystalline, a small percentage of
bismuth antimony and cadmium rendering the copper very brittle.
The behaviour of such an alloy on a commutator is quite different from that of
the alloys used hitherto. While the use of copper results in considerable heating
owing to the great friction, the new alloy behaves in an admirable manner without
great frictional gripping or heating. It may be compared to a metallic powder
agglomerated by fusion and having its molecules easily detachable by the com-
mutator.
The alloys constituting my new brush can be produced by simply melting the
metals together or by placing the pulverised metals of suitable fineness in a mould
and heating them under pressure to the temperature required to melt them and
produce the alloy.
A convenient proportion of parts of the metals is to add to the copper or ordinary
copper alloy several hundredth parts of bismuth, antimony or cadmium or of
two or more of these metals combined.
Generally the addition of a few hundredth parts of each metal to be added to
the ordinary copper alloy, will give good results, but the proportion will vary
according to the results to be attained.

page_text: bismuth, antimony or cadmium or of two or more of these metals combined substan-
tially as described.
5. Dynamo and like brushes formed of copper alloy containing a small per-
centage of bismuth, antimony or cadmium or combinations of these metals and
provided with cooling or lubricating perforations substantially as described.
Dated this 23rd day of April 1897
BOULT & WADE,
Agents for the Applicant.