Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE PRODUCTION OF FRICTION DISCS
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Background of the invention
The present invention concerns the production of
friction discs of carbon-carbon composite materials, which
are particularly intended for use as friction members
having structural strength in brakes or clutches comprising
one or more discs associated with other discs or with pads
or shoes
It is known that a member comprising carbon-carbon
composite material may be produced by preparing a fibrous
s~strate of carbon or carbon precursor material which is
carbonised, then ~ollowed by densification of the substrate.
This operation results in a member comprising carbon fibres
embedded in a carbonaceous "matrix".
Densification of the substrate may be effected for
example by chemical deposit of carbon in the vapour phase,
by means of one or more cycles comprising liquid impregnation
of carbonisable materials, carbonisation and graphitation,
or by a combination of those two methods.
It is also known that the properties of the member
which is finalIy produced largely depend on the
arrangement of the initial fibrous substrate~
Summary of the invention
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The essential aim of the present invention is to
produce particular fibrous substrates in the form of a
disc which:
- on the one hand, are easy and economical to produce
and
on the other hand, impart excellent levels of
performance in regard to frictional effect to the discs
produced after the conventional carbonisation and/or
densification operations.
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This aim is attained in accordance with the inventionwhich provides a process wherein a strip of material
composed of fibres is wound around a cylindrical mandrel,
and which is characterised in that it comprises at least
one of the following operations:
a) at the same time as the strip of material composed
of fibres is wound around the mandrel, it is
subjected to a radial needling operation, the
strip then comprising a plurality of layers of
fibres of different orientations and lengths, and
b) the winding produced is radially compressed so as to
produce circumferential undulations in all the layers
forming the winding.
The roll which is produced after one or other or both
operations is optionally:
- carbonised if the fibres used comprise a carbon
precursor material, and then
- cut up perpendicularly to its axis to form a large
number of disc members which form the substrate of a
plurality of discs, if the width of the strip is
sufficient for that purpose.
The roll or the disc members are then subjected to a
densification treatment:
- either by putting them in a furnace so that they receive
therein, at a temperature of 1000C, a chemical deposit
of earbon in the vapour phase, which forms the matrix
o~ the material,
- or by subjeeting them to at least one operation of
impregnation by means of liquid hydrocarbons such as
eoal tar, followed by a carbonisation and graphitation
operation~
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This second possible process which is intended if
necessary to remove local porosity in the substrate or to
reduce the total period of time required for producing the
matrix may be effected between a third and four-fifths of
production of the final density by chemical vapour phase
deposition.
The densified discs are then subjected to a heat
treatment at a temperature of from 1600 to 2500C, depending
on the use to which they are to be put.
The main advantages afforded by brake discs which are
produced in accordance with the process of the present
invention are as follows:
- no wastage of fibres during production of the disc,
- speed and ease of deposit of the matrix, due to the
form of the substrate.
ease of production of the substrate on an industrial
scale,
- very good mechanical strength in respect of braking
couple,
- good resistance to wear, due to the generally highly
inclined orientati.on of the fibres with respect to
the friction surfaces,
- excellent dimensional stability of the disc during
the heating efect caused by braking:
. on the one hand, in regard to the disc, because of
the zero coefficient of expansion in respect of
thickness (the condit:ion of parallelism of the faces
is retained),
. on the other hand, in regard to the fibres or groups
of fibres, there cannot be any local geometrical
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change in the surface which could promote the
occurrence of hot spots,
- very good resistance to radial delamination due to the
radial needling action and/or the undulations, those two
processes separately or in combination reducing the
adverse effects of the polar anisotropy of the winding,
- a very high level of compression and tensile strength
in the axial direc-tion of the disc, and
- the heat due to the friction effect can be very easily
removed, towards the interior of the disc.
It should be noted that the above-indicated process
includes a number of variations which are also part of the
present invention.
Brief description of the drawings
_
lS Other aims, fea-tures and advantages of the process and
the alternative forms -thereof will be apparent from the
following description which is given by way of non-limiting
example and with reference to the accompanying drawings in
which:
Figure 1 is a diagrammatic view of the winding-
needling operation,
Figure 2 is a diagrammatic view of a preferred type
of circumferential undulation,
Figures 3A and 3B are diagrammatic views of means
for producing the circumferential undulations shown in
Figur0 2, and
Figure 4 shows the operation of winding a particular
strip of fibres.
Detailed description of the drawin~s
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Referring to Figure 1, four layers of fibres are
wound simul-taneously around a cylindrical mand~l 1. The
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mat layers 2a and 2b are ~ormed by short fibres (for
example from 3 to 5 cm) which are disposed randomly in
the plane of the layer.
The layers 3 and 4 are formed by unidirectional
fibres 5 which are possibly disposed on a thin plastic
carrier which can be removed by heat, and which are
oriented, with respect to the a~is of the mandrel:
- towards the right, in respect of the layer 3, and
- towards the left, in respect of the layer 4.
The angles at which the fibres are oriented may be
for example between 30 and 60, according to circumstances.
Figure l shows the angles as being equal at 45.
The mandrel l rotates in the direction indicated by
arrow 9.
While the windlng 8 is progressively being formed,
a needling bar 6 provided with a large number of needles
7 continually alternatively perforates the winding 8. By
virture of the projections or spurs on the needles, the
result of the needling operation is to pull out short
fibres which are initially disposed on the mat layers
comprising short fibres 2a and 2b, and to arrange them
in radial directions with respect to the winding 8.
When the needlèd winding 8 is sufficiently large in
diameter, the mandrel l is removed.
The winding 8 enjoys very good cohesion and can be
handled without having to take special precautions. It
is advantageous for the winding 8 to be made from layers
of fibres of carbon precursor material such as cross-
linked polyacrylonitrile. This resul-ts in the winding
being less fragile, which permits both the needling
operation ancl the radial compression operation. In
that case, the substrate is subjected to an additional
carbonisation operation.
Figure 2 shows undulations in the layers at the
inside periphery pf of the radially compressed winding,
which are as marked as the undulations in the layers
at the outside periphery Pf. In order to produce that
type of undula-tion, it will be seen that it is essential
in the radial compression operation substantially and
simultaneously to reduce the diameters of the outside and
inside peripheries Pi and Pi of the winding.
Figure 2 also shows that there are real undulations
around any circumference of the winding, thereby forming
notches or xecesses which are disposed in a staggered
arrangement relative to each other, at the inside and
outside peripheries.
Referring now to Figures 3A and 3B, the needled
winding 8 is disposed within a rigid cylinder 10, coaxially
therewith (axis 11). Radial compression sector members 12a
and 12b are disposed between the cylinder 10 and the winding
8. The longitudinal direction of the sector members is
and remains parallel to the axis of the cylinder throughout
the compression operation. The sector members are identical
in length to the winding 8 and the cylinder 10.
A radial force and a radial movement are imparted to
the sector members 12a and 12b in such a way that the
sector members 12b are displaced radially at a higher
speed than the sector members 12a.
Disposed at the centre of the needled winding 8,
coaxially therewith and with the cylinder 10, is a
compressible cylindrical core member 13 which is of the
same axial length as the members 10 and 8.
The core member 13 may either comprise an elastomer
or an assembly of mechanical components, but in both cases
the diameter of the core member must be reduced during
the radial compression operation. At its periphery (and
over its entire axial length), the core member 13 has
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raised surface portions 13a, the longitudinal direction
of which is parallel to the axis of the core member 13.
There is a regular alternation as between sector members
12b and raised surface portio:ns 13a in the angular space
which is around the axis 11, thereby to produce properly
repetitive undulations such as those which can be seen in
Figures 2 and 3B, in the radial compression operation.
The resulting winding with undulations is then cut
up perpendicularly to its axis into ring or disc members
which form substrates for discsand which are subjected
to a densification treatmentO
The discs which are finally produced, being provided
with their notches or recesses, can be put to many uses.
Mention may be made of the following:
15 . when the disc is used as a rotor or rotary member,
it will be driven in rotation by key or pin members
which are fixed to the inside of an aircraft wheel
rim, for example, by way of all or some of the notches
formed by the undulations in the outside periphery
of the disc, and
when the disc is used as a stator, it will be
immobilised by means of key or pin members which are
fixed to a non-rotating shaft, by means of all or
some of the notches formed by undulations in the
~5 inside periphery of the disc.
A first alternative form in accordance with the
invention concerns producing discs, the wound substrate
of which is subjected only to the operations disclosed in
Figure l. Therefore, that substrate is not subjected to
the operation of form.ing the undulations by radial
compress.ion as descr.ibed with reference to Figures 2, 3A
and 3B, but except for that step, the method of producing
the di.scs is strictly the same.
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A second alternative form according to the invention
concerns the production of discs wherein the wound substrate
is not subjec-ted to the radial needling operation, but on
the other hand is subjected to the operation of forming
undulations by radial compression and all the operations
described hereinbefore.
In this second alternative form of the process,
referring to Figure 1, the substrate may comprise:
- either the succession of layers 2a, 3, 2b, 4 as
descrlbed hereinbefore (but without being radially
needled),
- or the succession of layers 3 and 4, the layers 2a
and 2b thus being omitted,
- or a strip as illustrated in Figure 4.
In the single case of the strip shown in Figure 4,
the substrate is made disc by disc and not by long
cylinder members which can subsequently be cut up into
discs, as in all the other embodiments.
The strip illustrated in Figure 4 comprises a warp
14, the width b of which is only two thirds of the total
width a of the disc. The weft 15 of the strip on the
other hand is of a width corresponding to the full width
a of the finished disc.
Thus, the friction surfaces of the disc will be
subjected to wear, in braking operations,in regard to a
disc thickness which has only weft threads which are
therefore perpendicular to the disc surfaces. In order to
enhance the final operational stahility of the surfaces
of the disc, the weft threads are not woven with warp
threads but are simply assembled by two sets of stitches
which are produced by machine parallel to the longitudinal
axis of the strip.
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A third alternative form in accordance with the
invention is concerned with the production of discs from
a substra-te which is wound and radially needled in a
manner strictly in accordance with the description
relating to Figure 1. The substrate is then placed in
the equipment described with reference to Figures 3A
and 3~, except that the equipment is slightly modified:
all the parts outside the winding (cylinder me~ber 10
and sector members 12a and 12b) are unchanged, but the
compressible core member 13 with the raised surface
portions 13a is replaced by an incompressible core member,
the diameter of which is identical to that of the mandrel
1 shown in Figure 1. The radial compression operation is
then performed, which has the effect of producing
undulations which are clearly marked in the peripheral
regions of the winding 8, and undulations which are
increasingly less marked at diameters which progressively
move towards the diameter of the mandrel 1.
This third embodiment of the process of the invention
therefore makes use of a property of radial compressibil-
ity of the wound needled substrate, which makes it possible
to reduce and form undulations in the initial outside
periphery of the winding, without reducing or forming
undulations in the inside periphery.
Suchi radial compressibility of the substrate will be
enhanced (see Figure 1) if on the one hand the thickness
of the short-fibre layers 2a and 2b is increased and if
on the other hand no circumferential tension is applied
to the layers of fibre during the winding and needling
operations.
The attraction of the alternative forms of the
invention may be that they permit a saving in production,
if use of the di.scs is limited in each of the cases in
questions, to particular situations of use.
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