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Патент USA US3049457

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Aug. 14, 1962
J. MlLLET
3,049,448
METHOD FOR IMPROVING THE FRICTIONAL PROPERTIES
OF CARBON BRUSHES BY LOW PRESSURE
POLYETHYLENE IMPREGNATION
Filed March 10, 1959
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3,049,448
tates Patent
iIQ I
Patented Aug. 14, 1962
1
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3,049,448
The resistance of polythylenes to chemical agents is
remarkable. It is thus possible to envisage the utilisation
of these impregnation agents for other carbons than those
METHOD FOR IMPROVING THE FRICTIONAL
PROPERTIES OF CARBON BRUSHES BY LOW
PRESSURE POLYETHYLENE IMPREGNATIGN
intended for use as brushes in rare?ed and dry atmos
pheres. In elfect carbons impregnated with polyethylenes
Jacques Millet, Paris, France, assignor to Societe le Car
in accordance with the invention constitute friction mem
bers which are completely adapted to use in corrosive
surroundings such as joints for the chemical art for ex
bone-Lorraine, Paris, France, a French company
Filed Mar. 10, 1959, Ser. No. 798,537
Claims priority, application France Mar. 14, 1958
6 Claims. (Cl. 117—228)
ample.
10
The present invention relates to methods for improving
the frictional properties of carbon members, and to ap
plications of these methods.
In the past there have been used methods for improving
the properties of brushes operating at high altitudes, which
generally comprise the addition to the carbonaceous sub
In order that the invention may be more clearly under
stood, reference Will now be made to the accompanying
drawings, which show one speci?c embodiment thereof
by way of example together with a cross-section of a brush
made in accordance with the method of the invention, and
in which:
FIGURE 1 shows a cross-section through an immersion
stance which constitutes the brush of lubricating or hygro
bath adapted for operation in the open atmosphere,
scopic substances. The purpose of these substances has
FIGURE 2 shows a section through the bath of FIG
been to improve the contact, to lubricate the surface of the
Y‘URE 1 but enclosed within a chamber which may be
20 evacuated or placed under positive pressure,
collector and thus to avoid rapid wear of the brush.
The assignees of the present application have already
FIGURE 3 shows a cross-section through part of a
protected several processes for lubricating carbon or
brush treated in accordance with the invention, and
graphite operating in atmospheric conditions which are
FIGURE 4 shows the manner in which hydrogen atoms
dry and rare?ed.
I have established that surfaces covered by hydrogen
are distributed at the friction surface of a brush portion.
25
have obtained this condition by orientation of very long
chain molecules retained by absorption on the friction
In FIGURE 1 there is shown an absorbent carbon
brush 1 for electrical machinery which is placed in a bath
2 containing molten polythenes 3 that have been manu
factured at low pressure. This bath is arranged to be
surfaces so as to cover the latter with hydrogen atoms.
heated in any convenient manner as indicated by the ar
atoms have a particularly small coe?icient of friction. I
The process according to the invention consists in im 30 rows in the legend.
pregnating absorbent carbons with polyethylenes manu
FIGURE 2 shows the same arrangement as FIGURE 1
factured at low pressure.
but in this case the bath 2 is enclosed within a chamber \4
Polyethylenes manufactured at high pressure do not
which is sealed against the atmosphere and has an outlet
melt freely but exhibit a kind of softening under the
5 whereby said chamber may ‘be connected at will to a
in?uence of heat. This drawback due to a proportion of
pressure pump schematically illustrated at 6 or a vacuum
about 60% of subdivided chains renders the impregnation
pump schematically illustrated at 7 under control of a
of the carbons difficult on the one hand because it is
valve 8 rotatable within a casing 9 ‘and having a right
necessary to put them in solution, and on ‘the other hand
angle bore 10 as shown. By suitable rotation of the valve
does not give to the impregnated carbons a satisfactory
body 8 in any desired fashion, e.g. by a spindle passing
coe?icient of friction.
through the casing 9 to the outside, the bore 10‘ may be
On the other hand polyethylenes manufactured at low
connected as desired either to the pump 6 or the pump 7
pressure have a proportion of less than 20% of sub
by way of the conduit 11 or 112 respectively, and also to
divided chains Which gives them physical properties which
are very different from those referred to in the preceding
paragraph. In effect they show a crystalline state favour
ing friction, a high melting point which is above 110° C.,
stability to heat and to chemical agents, all of which
makes the impregnating material very suitable.
The impregnation is moreover facilitated by the Weak
viscosity of low pressure polyethylenes which actually
the outlet 5 at the same time. In this way the chamber 4
can be evacuated or subjected to positive pressure as de
sired and the valve 8 may be operated so as to effect these
physical conditions alternately: if desired the aforemen
tioned spindle may be connected to a rotation-imparting
device of any desired kind so that this alteration may be
effected automatically. The speed of rotation could be
adjusted to such requirements. The pressure pump 6, the
melt above a temperature of above 110° C. or so. This is
vacuum pump 7 and the valve 8 may be of any kind
a property which is well known to those skilled in the
art to which this invention relates and is in contradistinc
well known in industry and therefore need not be described
tion to high pressure polyethylenes which only soften at
any desired form, for example may be an electric motor
having a controllable speed for driving the aforementioned
elevated temperatures and do not melt.
here. Similarly the rotation-imparting device may take
Impregnation is effected by simple immersion in a
spindle by means of a belt or gear drive also well known in
bath of polyethylene maintained above 110° C. The
industry.
impregnation may be slow if there is no application of
The impregnation is effected by means of the apparatus
vacuum or pressure. It may, however, be made rapid
of FIGURE 1 or 2 as referred to above and the degree
and also more homogeneous if alternations of vacuum 60 of impregnation will naturally depend upon the time of
and pressure are utilised.
The introduction of a proportion of l to 8% by Weight
of polyethylene manufactured at low pressure into the
pores of a brush made from graphite for example, con
immersion and of the amount of pressure or vacuum
treatment.
FIGURE 3 shows a portion of a brush made according
to the invention in which 13 represents carbon or graphite
siderably improves its frictional properties under normal 65 particles and 14 represents the polyethylene impregna
atmospheric conditions, but even more so at low pressures.
tion, exhibiting a friction surface 15.
Thus a brush made from non-impregnated graphite has a
FIGURE 4 shows the distribution of hydrogen atoms
coe?icient of friction of 0.50 and a wear equal to 2 mm.
of the polyethylene impregnant which is illustrated by
per hour. After impregnation these characteristics are
its normal graphic formula. The friction surface is at ‘15,
as follows: coefficient of friction is 0.20, wear 15 microns 70 and 16 represents the metal, generally copper, of the
per hour during the whole period of the test capable of
commutator or other machine part with which the brush
being carried out for more than 500 hours.
is to come into contact. It will be understood that the
arise/14s
3
brush portion shown in FIGURE 4 is sub-microscopically
bath of molten low pressure polyethylene, thereby pro
ducing hydrogen atoms on the surface of said brush, said
small and is on a very much larger scale than that of
FIGURE 3.
polyethylene constituting said polymeric impregnating
substance.
I claim:
1. In a method for improving ‘the friction properties of 01
4. A method as claimed in claim 3, in which said
absorbent carbon brushes for electrical machines by im
brush is subjected to positive pressure during said im
pregnation.
pregnating a brush with a polymeric substance, the im
provement which consists in using low pressure poly
5. A method as claimed in claim 3, in which said brush
ethylene as the impregnating polymeric substance.
is subjected to a vacuum during said impregnation.
2. In a method for improving the friction properties of
6. A method as claimed in claim 5, in which said brush
is additionally alternately subjected to positive pressure
during said impregnation.
absorbent carbon brushes for electrical machines by im
pregnating a brush With a polymeric substance, the im
provement which consists in melting into a ‘brush a low
pressure polyethylene, said polyethylene constituting said
plymeric impregnating substance.
3. In a method for improving the friction properties
of absorbent carbon brushes for electrical machines by
impregnating a brush with a polymeric substance, the
improvement which consists in immersing a brush in a
15
References Cited in the file of this patent
UNITED STATES PATENTS
2,384,848
Peters ______________ __ Sept. 18, 1945
FOREIGN PATENTS
721,211
Great Britain ________ __ Jan. 5, 1955
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