U.S. patent application number 13/056218 was filed with the patent office on 2011-08-18 for brake pad for braking systems, in particular for disc brakes.
This patent application is currently assigned to FRENI BREMBO S.P.A.. Invention is credited to Andrea Gavazzi, Marco Orlandi, Simone Turani, Massimiliano Valle, Paolo Vavassori, Konstantin Vikulov.
Application Number | 20110198170 13/056218 |
Document ID | / |
Family ID | 40429883 |
Filed Date | 2011-08-18 |
United States Patent
Application |
20110198170 |
Kind Code |
A1 |
Turani; Simone ; et
al. |
August 18, 2011 |
Brake Pad for Braking Systems, In Particular for Disc Brakes
Abstract
Brake pad for braking systems, in particular for disc brakes,
consisting of friction portion (10), tribologically active, and
mechanical support portion (20) which is intended to cooperate with
the actuating means of a braking system. At least friction portion
(10) is made from a ceramic matrix material obtained with a method
comprising the following operational steps: --preparing a mixture
of at least one siliconic type ceramic precursor, of particles of
hard materials suitable as abrasives, of particles of substances
suitable as lubricants and particles of metal
materials;--hot-pressing the mixture to obtain a preformed
body;--submitting the preformed body to a process of pyrolysis in
order to obtain ceramisation of the preceramic binder, thus
obtaining the ceramic matrix material. The mixture comprises a
catalyst suitable for favouring reticulation of said ceramic
precursor during the hot-pressing step and the pyrolysis process is
carried out a temperatures below 8000.degree. C. The mechanical
support portion (20) may be made in ceramic matrix material as one
piece with the friction portion or it may consist of a support
plate provided with lightening apertures.
Inventors: |
Turani; Simone; (Bergamo,
IT) ; Vikulov; Konstantin; (Bergamo, IT) ;
Gavazzi; Andrea; (Bergamo, IT) ; Valle;
Massimiliano; (Bergamo, IT) ; Vavassori; Paolo;
(Bergamo, IT) ; Orlandi; Marco; ( Milano,
IT) |
Assignee: |
FRENI BREMBO S.P.A.
Curno, Bergamo
IT
|
Family ID: |
40429883 |
Appl. No.: |
13/056218 |
Filed: |
December 23, 2008 |
PCT Filed: |
December 23, 2008 |
PCT NO: |
PCT/IB08/55519 |
371 Date: |
January 27, 2011 |
Current U.S.
Class: |
188/250B |
Current CPC
Class: |
F16D 2069/001 20130101;
F16D 2069/0483 20130101; F16D 2200/0039 20130101; F16D 2200/0069
20130101; C04B 35/571 20130101; F16D 2200/0043 20130101; F16D
69/027 20130101; F16D 2200/0086 20130101; F16D 69/025 20130101;
F16D 2069/0441 20130101; C04B 2111/00362 20130101; C04B 35/571
20130101; C04B 38/0022 20130101; C04B 38/0022 20130101; F16D 65/092
20130101; C04B 38/0054 20130101 |
Class at
Publication: |
188/250.B |
International
Class: |
F16D 65/092 20060101
F16D065/092; F16D 69/02 20060101 F16D069/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2008 |
IT |
PCT/IT2008/000543 |
Claims
1-37. (canceled)
38. Brake pad for braking systems, in particular for disc brakes,
comprising a friction portion tribologically active and a
mechanical support portion intended to cooperate with actuating
means of a braking system, at least said friction portion being
made from a ceramic matrix material obtained through a process
comprising the following operational steps: preparing a mixture of
at least one siliconic type ceramic precursor, of particles of hard
materials suitable as abrasives, of particles of substances
suitable as lubricants and particles of metal materials;
hot-pressing the mixture to obtain a preformed body; submitting
said preformed body to a process of pyrolysis in order to achieve
ceramisation of the preceramic binder, thus obtaining said ceramic
matrix material; said mixture comprising a catalyst suitable for
favouring reticulation of said ceramic precursor during said
hot-pressing step and said pyrolysis step being carried out at
temperatures below 800.degree. C.
39. Brake pad according to claim 38, wherein said pyrolysis process
is carried out reaching at maximum temperatures between 400 and
600.degree. C.
40. Brake pad according to claim 38, wherein said pressing step is
carried out at temperatures between 120.degree. C. and 150.degree.
C.
41. Brake pad according to claim 38, wherein said pressing step is
carried out at pressures between 250 and 500 Kg/cm.sup.2.
42. Brake pad according to claim 38, wherein said mechanical
support portion is made from said ceramic matrix material.
43. Brake pad according to claim 42, wherein said mechanical
support portion is made as one piece with said friction
portion.
44. Brake pad according to claim 42, comprising a reinforcing
element with lightening apertures, incorporated in said mechanical
support portion or arranged on the external surface of this
portion.
45. Brake pad according to claim 44, wherein said reinforcing
element is associated with said mechanical support portion for
co-pressing during said hot-pressing step.
46. Brake pad according to claim 38, wherein said mechanical
support portion consists of a support plate, provided with one or
more lightening apertures and associated with said friction
portion.
47. Brake pad according to claim 46, wherein said one or more
lightening apertures are made in the portion of said support plate
intended to be coupled with said friction portion.
48. Brake pad according to claim 46, wherein said support plate
comprises a perimetric frame that internally delimits an empty
space.
49. Brake pad according to claim 48, wherein said support plate
comprises a plate-like element suitable for closing the empty space
of said perimetric frame and in correspondence to which said
lightening apertures are made.
50. Brake pad according to claim 46, wherein said support plate is
provided with stiffening elements in correspondence to the points
on which the actuating means of said braking system are intended to
act.
51. Brake pad according to claim 46, wherein said support plate is
in metal.
52. Brake pad according to claim 46, wherein said support plate is
in non-metallic material.
53. Brake pad according to claim 38, wherein said mechanical
support portion consists of a support plate in non-metallic
material, associated with said friction portion.
54. Brake pad according to claim 38, wherein said mechanical
support portion consists of a support plate, said friction portion
associated with said support plate by co-pressing during said
hot-pressing step.
55. Brake pad according to claim 38, wherein said mechanical
support portion consists of a support plate, said support plate
associated with said friction portion in ceramic matrix material
subsequently to said pyrolysis step.
56. Brake pad according to claim 38, wherein said mixture comprises
between 5% and 10% in weight of ceramic precursor and catalyst,
between 20% and 30% of abrasives, less than 60% of metal materials
and less than 50% of lubricants.
57. Brake pad according to claim 38, wherein said at least one
ceramic precursor is selected from the polysiloxanes.
58. Brake pad according to claim 38, wherein said catalyst is
selected from organic coordination compounds with metals selected
from the group consisting of zinc, copper, aluminium, iron,
zirconium, vanadium, chromium, manganese, cobalt, nickel and
titanium and mixtures thereof.
59. Brake pad according to claim 38, wherein said abrasive
particles are powders selected from the group consisting of
silicium carbide, boron carbide, silicium, zircon, zirconium oxide,
periclase, corundum or spinel and mixtures thereof.
60. Brake pad according to claim 59, wherein said abrasive
particles are present as powders of two different particle sizes,
the ratio of the average diameters of the two powders being between
9 and 11.
61. Brake pad according to claim 60, wherein the weight ratio
between the abrasive powder of greater particle size and the powder
of lesser particle size is between 0.8 and 1.8.
62. Brake pad according to claim 38, wherein said metal particles
comprise particles selected from the group consisting of iron, iron
alloy, copper, brass, silicium and mixtures thereof.
63. Brake pad according to claim 38, wherein said lubricant
particles comprise graphite in powder, coke powders, powders of tin
sulphide and/or tin powders.
64. Brake pad according to claim 63, wherein graphite is present in
a percentage between 9% and 13% in weight of said mixture.
65. Brake pad according to claim 63, wherein coke powder is present
in a percentage lower than 35% in weight of said mixture.
66. Brake pad according to claim 63, wherein tin sulphide powder is
present in a percentage lower than 10% in weight of said
mixture.
67. Brake pad according to claim 63, wherein tin powder is present
in a percentage less than 5%.
Description
FIELD OF APPLICATION
[0001] This invention concerns a brake pad for braking systems, in
particular for disc brakes.
STATE OF THE ART
[0002] As is well known, a brake pad for braking systems, in
particular for disc brakes, generally consists of a metal support
plate associated with a layer of friction material which defines
the tribologically active part of the brake pad.
[0003] Traditionally the friction material is connected to the
plate with glue or by means of mechanical fixings, such as bolts or
rivets.
[0004] The metal plate essentially carries out a function of
mechanical support for the friction material and is suitable for
bearing the compression and bending stresses typically encountered
during use of the brake.
[0005] The plate cooperates with the actuating means (hydraulic
pistons) of the braking system to permit movement of the brake pad.
In correspondence to the plate seats for brake pad guiding pins and
for the friction material wear indicators are also made.
[0006] As is well known, weight reduction of the brake pads is much
sought after, especially for braking systems to be installed on
high performance vehicles (e.g. top range cars or motorbikes) which
can be used in racing and therefore subjected to considerable
stresses.
[0007] From this viewpoint attempts have been made by working on
the structure of the support plates, though these have been limited
to brake pads with the friction portion made of organic
material.
[0008] In fact brake pads for braking systems with friction portion
in organic material are well known. They are built with support
plates that have been lightened by making cuts or openings in them,
or by inserting portions of metal mesh. By way of example we refer
to French patent FR 2441100.
[0009] For some particular applications there are also brake pads
without a support plate. However these pads are very costly,
intended for the braking systems of competition cars and made
completely in carbon which in itself can guarantee suitable
resistance to mechanical stresses in operation.
[0010] As is well known, in creating the friction portions of pads
for high performance braking systems (i.e. top of the range cars)
the use of ceramic matrix materials has become increasingly
widespread. This is essentially due to the fact that ceramic matrix
friction materials--compared with friction materials obtained for
example by sinterisation of metal powders--not only give good
performances in terms of friction coefficient and resistance to
wear but also, because of their thermal refractoriness, reduce heat
transmission from the disc to the hydraulic braking system.
[0011] However, at time of writing it has not been possible to
considerably reduce the weight of pads made by using the
abovementioned ceramic matrix friction materials.
[0012] As is known, the ceramic matrix materials used to date do
not have particularly high properties of mechanical resistance. In
general, they are in fact very fragile and they fail suddenly by
collapsing.
[0013] This has impeded not only the creation of pads entirely
constituted of ceramic matrix material, without a support plate or
element, but also the use of lightened metal support plates.
[0014] The use of lightened support plates would not in fact
guarantee the pad adequate mechanical resistance. To this it must
be added that the traditional way of fixing the plate to the layer
of friction material--by gluing and/or by mechanical means of
fixing--require the plate to have an adequate area of contact with
the friction material.
[0015] The limits of mechanical resistance mentioned above are also
found in ceramic matrix materials made according to the production
technique based on polymer pyrolysis.
[0016] As is known, the technique of polymer pyrolysis is becoming
increasingly widespread in the creation of ceramic matrix
materials. Compared with other techniques the pyrolysis technique
offers various advantages from both the strictly operational
viewpoint and the characteristics of the final product.
[0017] More in detail, this technique involves a process of heating
a mixture of siliconic ceramic precursors (normally organic
siliconic polymers, such as polysilanes, polycarbosilanes,
polysilazanes and polysiloxanes) and appropriate fillers in a
controlled or inert atmosphere (e.g. argon flow) at temperatures
greater than 800.degree. C. to achieve the passage from organic to
inorganic polymeric structure, with the formation of silicium
oxycarbides (SiOC) and/or silicium carbides or nitrides (SiC or
Si.sub.3N.sub.4). The above precursors normally have high ceramic
yields: more than 50% of initial polymer weight is maintained in
the final material.
[0018] In particular, compared with the fusion technique the
pyrolysis technique allows better control of the form and purity of
the final product and the possibility of working at lower
temperatures (800-1500.degree. C.).
[0019] An example of the production process for friction material
with ceramic matrix by means of polymeric pyrolysis is described in
U.S. Pat. No. 6,062,351. The friction material is made by setting
out from a mixture of one or more organic ceramic precursors
(carbosil-siliconic resin), reinforcing fibres (e.g. fibres of
carbon, alumina, silicium nitride or carbide) and fillers (e.g.
powders of silicium carbide, graphite, alumina, mullite, silica,
titanium oxide, silicium or boron nitride). The mixture is then
cold-compacted in a mould. There follows a heating step within the
mould itself for polymerisation of the ceramic precursor and the
obtaining of a green body. The green body then undergoes pyrolysis
in an inert atmosphere at temperatures between 800.degree. C. and
1.100.degree. C.
[0020] As is known, in the production of pads for disc brakes with
the polymer pyrolysis technique, the friction portion in ceramic
matrix material is made as an element in itself. At the end of the
pyrolysis step the material then undergoes finishing processes and
grinding before being joined, by gluing or mechanical means (e.g.
bolts or rivets), to a support plate.
[0021] The friction portion cannot be made already directly joined
to the metal support plate because the temperatures reached during
the process of pyrolysis (above 800.degree. C.) would cause
unacceptable deformations of the plate.
[0022] This limit of the current pyrolysis technique, as of the
fusion technique, means that it is necessary to connect the
friction material to the plate only at the end of the pyrolysis
step. So in the production cycle a specific assembling step of the
plate and the friction portion must be envisaged, a step that may
be preceded by a step of grinding and finishing of the friction
portion.
[0023] The ways of connecting the support plate (by gluing or
mechanical means of fixing), together with the far from excellent
mechanical resistance properties of the ceramic matrix materials
employed, therefore contribute to considerably limiting--if not
wholly excluding--the possibility of reducing the weight of the
pads through intervention on the structure of the plates
themselves.
[0024] Another limit of polymer pyrolysis applied to the production
of ceramic matrix friction materials, and in particular to the
production of friction portions for pads, is the need to operate
with low heating velocity, this to the detriment of time schedules:
the pyrolysis step alone may require ten of hours.
[0025] With this regard it is described in details a particular
embodiment of the process described in the above mentioned U.S.
Pat. No. 6,062,351. The pyrolysis operational cycle envisages a
first step of heating from ambient temperature to approximately
150.degree. C. at a velocity of around 2.degree. C./min, followed
by a second heating step to 400.degree. C. at a velocity of
0.4.degree. C./min. The third and fourth heating steps are,
respectively, to 760.degree. C. at a velocity of 0.18.degree.
C./min and to 870.degree. C. at a velocity of 0.46.degree. C./min.
The product is then maintained at 870.degree. C. for about 4 hours
and then cooled to ambient temperature at a velocity of
approximately 1.2.degree. C. per minute. The heating step requires
an overall time of approximately 48 hours and the cooling step
about 12 hours.
[0026] Low heating velocities are necessary during the pyrolysis
step to limit damaging thermal stresses which, favouring the
natural phenomenon of material shrinkage and the formation of
microporosity due to the release of volatile organic substances
during pyrolysis, would lead to the formation of micro cracks, with
the risk of the finished product collapsing.
[0027] Presentation of the Invention
[0028] The purpose of this invention is therefore to eliminate the
drawbacks of the abovementioned state of the art by providing a
brake pad for braking systems, in particular for disc brakes,
which, though it is made with at least the friction portion in
ceramic matrix material, has a considerably reduced weight but
without compromising mechanical resistance.
[0029] A further purpose of this invention is to provide a brake
pad for braking systems that is completely in ceramic matrix
friction material and therefore without support plates, this
without compromising mechanical resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The technical features of the invention in accordance with
the abovementioned purposes can be clearly grasped from the claims
listed below, and its advantages will be rendered more evident by
the following detailed description, given with reference to the
attached drawings which represent one or more embodiments, purely
by way of example and not limitative, in which:
[0031] FIG. 1 shows a perspective view of a brake pad for braking
systems with ceramic matrix friction material, made according to a
first embodiment of the invention;
[0032] FIG. 1a shows a plan view of a brake pad for braking systems
with ceramic matrix friction material, made according to a variant
of the first general embodiment illustrated in FIG. 1;
[0033] FIG. 1b shows a section view of the brake pad illustrated in
FIG. 1a along the line II-II therein;
[0034] FIG. 1c shows a perspective view of the brake pad
illustrated in FIG. 1a;
[0035] FIG. 2 shows a perspective view of a brake pad for braking
systems with ceramic matrix friction material, made according to a
second embodiment of the invention;
[0036] FIG. 3 shows an exploded view of a support element used for
creating a brake pad according to a particular embodiment of the
invention;
[0037] FIG. 4 shows a plan view of the brake pad illustrated in
FIG. 2, from the side opposite the tribologically active one;
[0038] FIG. 5 shows a section view of the brake pad illustrated in
FIG. 4 along the line V-V therein;
[0039] FIG. 6 shows a plan view of a brake pad made according to a
first alternative embodiment of the invention, from the side
opposite the tribologically active one;
[0040] FIG. 7 shows a section view of the brake pad illustrated in
FIG. 6 along line VII-VII therein;
[0041] FIG. 8 shows a plan view of the brake pad made according to
a second alternative embodiment of the invention, from the side
opposite the tribologically active one;
[0042] FIG. 9 shows a section view of the brake pad illustrated in
FIG. 8 along the line IX-IX therein;
[0043] FIG. 10 shows a plan view of the brake pad made according to
a third alternative embodiment of the invention, from the side
opposite the tribologically active one;
[0044] FIG. 11 shows a section view of the brake pad illustrated in
FIG. 8 along the line XI-XI therein;
[0045] FIGS. 12, 13 and 14 show a diagram of, respectively, a
first, second and third form of application of the method according
to the invention;
[0046] FIG. 15 represents the trend of the friction coefficient in
function of the number of brake applications for three ceramic
matrix friction materials (of which two according to the invention)
which differ in particular for the maximum temperature at which
pyrolysis was carried out; and
[0047] FIG. 16 represents the trend of the friction coefficient in
function of the number of brake applications for a ceramic matrix
friction material made according to a particular form of
application of the method according to the invention.
DETAILED DESCRIPTION
[0048] This invention concerns a brake pad for braking systems, in
particular for disc brakes, which is made--at least for the
friction portion--with a special ceramic matrix material having
such properties of mechanical resistance as to permit intervention
on the mechanical support portion with view to reducing the overall
weight of the brake pad yet without compromising mechanical
resistance.
[0049] Anticipating what will be set out in detail below, the
properties of mechanical resistance of the abovementioned ceramic
matrix material allow different embodiments for the brake pad in
accordance with the invention, starting with a brake pad made
entirely in the abovementioned material and therefore without metal
support elements, right down to a brake pad with the friction
portion in the abovementioned ceramic matrix material and the
mechanical support portion made with a lightened support plate,
with some intermediate embodiments in between.
[0050] In the attached Figures the brake pad in accordance with the
invention is indicated as a whole by the number 1, while the
friction portion and the mechanical support portion are indicated
respectively by number 10 and number 20.
[0051] By "friction portion" 10 is meant the part of brake pad 1
which will be tribologically active throughout its working life,
and therefore the part that will be progressively worn through
use.
[0052] By "mechanical support portion" 20 is meant the part of
brake pad 1 which will cooperate with the actuating means of the
braking system (not illustrated in the attached Figures) to permit
movement of brake pad 1 and to transfer braking power to said
braking system (for example the calliper body of a disc brake).
Support portion 20 is therefore the part that will mainly bear the
mechanical stresses typically involved with the functioning of a
braking system.
[0053] As illustrated in particular in FIGS. 1 and 2, in
correspondence with support portion 20, seats 40 for the brake pad
guide pins may be made, as well as seats 50 (where envisaged) for
the wear indicators of friction portion 10.
[0054] As will be resumed in greater detail below, the ceramic
matrix friction material by which at least friction portion 10 of
brake pad 1 is made in accordance with the invention, not only has
excellent mechanical resistance properties in terms of resistance
to compression and of elastic module but may also be made in
different variants, suitable for tribological cooperation with both
brake discs in composite ceramic material (CCM) and with brake
discs in grey cast iron, assuring excellent performances in terms
of resistance to wear, of friction and of running-in (understood as
the time taken to achieve optimal functioning conditions).
[0055] In particular, with regard to performances in terms of
friction, it is pointed out that in comparison with traditional
materials there is an increase in the mean value of the friction
coefficient, correlated with its stability in time. It is further
pointed out that the friction coefficient value at start of braking
lies within the required operational intervals.
[0056] In accordance with the invention, the ceramic matrix
material with which at least friction portion 10 of brake pad 20 is
made is obtained through a method consisting of the following
operational steps:
[0057] a) preparing a mixture of at least one siliconic type
ceramic precursor, of particles of hard materials suitable as
abrasives, of particles of substances suitable as lubricants and
particles of metal materials;
[0058] b) hot-pressing the mixture to obtain a preformed body
(green body);
[0059] c) submitting the preformed body (green body) to a process
of pyrolysis in order to obtain ceramisation of the preceramic
binder, thus obtaining a ceramic matrix material.
[0060] In accordance with a feature characterising the invention,
the mixture comprises a catalyst suitable for favouring
reticulation of the ceramic precursor during the hot-pressing
step.
[0061] A suitable catalyst in the initial mixture for the reactions
of reticulation of the ceramic precursor (reactions of hydrolysis
and condensation in the polymeric chain) permits achievement of a
very high reticulation of the ceramic precursor already on
completion of the pressing step, and therefore the creation of an
extensive ramified polymeric structure within the preformed body
(green body).
[0062] High reticulation of the precursor carries a series of
advantages.
[0063] The preformed body (or green body) obtained at the end of
the hot-pressing step has such properties of mechanical resistance
as to make it easy to manipulate, with simplification of the
subsequent working process steps.
[0064] The extensive ramified polymeric structure created during
the pressing step has the effect of "keeping" the ceramic precursor
molecules during the pyrolysis step, reducing their volatility and
therefore increasing the ceramic yield.
[0065] This extensive ramified structure involves--at least
partially--the particles of the additives present in the initial
mixture (abrasives, lubricants, metals) which are thus incorporated
into the structure itself, with advantages both in terms of
performances (absolute value and stability of the friction
coefficient) and of wear resistance, as will be resumed below.
[0066] The extensive ramified polymeric structure is maintained in
the ceramic matrix material, although modified following the
chemical-physical transformations induced by the pyrolysis process,
and ensures that the final ceramic matrix material too will have
good properties of mechanical resistance, with special reference to
wear resistance, to the elastic module and to compressibility.
[0067] In accordance with another aspect characterising the
invention, the pyrolysis process is carried out at temperatures
below 800.degree. C.
[0068] The good mechanical properties that the extensive ramified
polymeric structure gives the preformed body (green body) mean that
the degree of progress of the pyrolysis process (temperature and
times) can be tailored as required. This in turn means that the
degree of ceramisation in the final ceramic matrix material can be
planned in function of the latter's performance
characteristics.
[0069] As will be resumed below, it was surprisingly found that
pyrolysis at temperatures below 800.degree. C. (and especially
between 400.degree. C. and 600.degree. C.) results in considerable
improvement in friction material performances.
[0070] The graphs in FIG. 15 show the results of braking tests
(friction coefficient in function of number of braking operations)
carried out on three different disc brake pads. Curves (a) and (b)
refer to two brake pads made in accordance with the invention, with
maximum pyrolysis temperatures of respectively 500.degree. C. and
700.degree. C. Curve (c) refers to a traditional brake pad with
maximum pyrolysis temperature of 900.degree. C.
[0071] A comparison of the graphs shows the increase of the
friction coefficient in the brake pads produced according to the
invention, an increase that is more pronounced in the brake pads
made with a pyrolysis temperature between 400.degree. C. and
600.degree. C.
[0072] As for wear resistance, the tests showed that on average the
brake pads produced according to the invention have greater
resistance to wear: an average wear value of approximately 0.005
mm/braking operation as against an average value of approximately
0.015 mm/braking operation in traditional type brake pads (made
with pyrolysis temperatures above 800.degree. C.).
[0073] As will be resumed below, carrying out pyrolysis (in
accordance with the invention) at temperatures below 800.degree.
C., and in particular between 400.degree. C. and 600.degree. C.,
makes it possible to co-press the basic mixture of the material
with a support element (e.g. a lightened metal plate). The support
plate (which may be metal but also non-metallic, such as composites
based on oxides with low heat conductivity) can in fact bear the
thermal stresses deriving from the pyrolysis process without
undergoing unacceptable heat deformations.
[0074] Operationally it is therefore possible to directly associate
the support plate with the preformed body and, therefore, with the
ceramic matrix material during the production steps of the friction
material. In this way it is no longer necessary in the production
process to envisage a special final assembling step for the
friction portion and the support element. At the end of the steps
of creating the friction material we therefore have a friction
material-plate unit which is easier to work for subsequent
finishing and any application of mechanical means of fixing.
[0075] Anticipating what will be resumed below, co-pressing of the
mixture directly on a support element with one or more lightening
apertures creates a unit in which the ceramic matrix material is
closely connected with the support element itself. During the
co-pressing step the mixture--still fluid--penetrates the
lightening apertures, creating a reciprocal grip relationship
between ceramic matrix material and support element, as may be seen
in particular from FIGS. 5, 7 and 9.
[0076] There follow detailed descriptions of some embodiments for
brake pad 1 in accordance with the invention. Subsequently the
production method for the ceramic matrix material will be
described.
[0077] In accordance with a first general embodiment of the
invention illustrated in FIG. 1, brake pad 1 is made entirely of
the abovementioned ceramic matrix friction material. Not only
friction portion 10 but also mechanical support portion 20 is in
this material.
[0078] Elimination of the traditional metal support plate
considerably reduces the overall weight of the brake pad. The
ceramic matrix material in accordance with the invention has a
specific weight of around 3 kg/dm.sup.3, whereas steel
(traditionally used for support plates) has a specific weight of
around 7.8 kg/dm.sup.3. Sizes being equal, a brake pad in
accordance with the invention may weigh as much as 1/3 less than a
brake pad with traditional steel plate and the friction portion in
a well known type of ceramic matrix material.
[0079] On this subject it is pointed out that already at the end of
the pressing step (and therefore prior to the pyrolysis step) the
preformed material has an excellent consistency which makes it
possible to achieve good details, such as for example the sharp
edges of the brake pad.
[0080] Preferably the mechanical support portion 20 is made as one
piece with the friction portion 10, using an apposite mould. FIG.
12 shows a diagram of the production steps of brake pad 1 as one
piece.
[0081] Alternatively the two portions, friction portion 10 and
mechanical support portion 20, can be made separately and joined
subsequently in a specific assembling step, for example by gluing
and/or application of mechanical fixing elements.
[0082] Advantageously, as envisaged in a special embodiment
illustrated in FIGS. 1a, 1b and 1c, the brake pad 1, made entirely
from the abovementioned ceramic matrix material, can be provided,
in correspondence to mechanical support portion 20, with at least
one open structure reinforcing element which allows penetration of
the friction material.
[0083] Insertion of an open structure reinforcing element in any
case reduces the weight of the brake pad in comparison with the use
of a traditional plate, while making a greater contribution to the
mechanical resistance of the brake pad itself.
[0084] The reinforcing element may cover the entire plane surface
of the mechanical support portion (as shown in FIG. 1c) or be
limited to a part thereof, for example the plane surface of the
friction portion.
[0085] The support element may be for example a plate-like body
provided with lightening apertures, for example a reticular
structure. Preferably the support element is metal (for example
steel) although non-metal materials may be used such as for example
composites based on oxides with low heat conductivity, able to
maintain their form and structure without undergoing significant
deformation when subject to the thermal stresses of the pressing
and pyrolysis process.
[0086] The support element may be incorporated into the mechanical
support portion or set on its external surface (as illustrated in
FIG. 1c), or again on the surface in correspondence to which the
actuating means of the braking system will come to bear.
[0087] Preferably the abovementioned reinforcing element is
associated with the mechanical support portion through co-pressing
at the hot-pressing step.
[0088] In accordance with a second general embodiment for the
invention, illustrated in particular in FIG. 2, only friction
portion 10 of brake pad 1 is made of the abovementioned ceramic
matrix friction material, while the mechanical support portion 20
consists of a support plate 21 provided with one or more lightening
apertures 25 or 26 and associated with the friction portion 10.
[0089] Preferably the lightening apertures 25 are obtained in the
portion of the support plate 21 which will be coupled with friction
portion 10.
[0090] Preferably the support plate 21 is metal, for example steel.
In this case, with regard to the first general embodiment for the
invention described above, there is a less pronounced reduction in
weight, yet still considerable in comparison with state of the art
technique inasmuch as it is linked only to a reduction in the
quantity of material forming the plate.
[0091] Advantageously, due to the fact that the ceramic matrix
material can be made with a pyrolysis process also at temperatures
between 400.degree. C. and 600.degree. C., it is possible to use
support plates (21) in non-metallic material, such as for example
composites based on low heat conducting oxides which have a
specific weight that is less than steel and maintain form and
structure without undergoing considerable deformation when
subjected to the thermal stresses of the pressing and pyrolysis
process.
[0092] In this case weight reduction can be more pronounced since
it is due not only to a reduction in the quantity of plate material
but also the use of materials with a specific weight that is less
than the traditionally used steel.
[0093] In accordance with a preferred embodiment, illustrated in
particular in FIGS. 3 to 9, the support plate 20 comprises a
perimetric frame 22, which delimits an internal empty space 26, and
a plate-like element 23 which is suitable for closing the
abovementioned empty space 26 by coupling with frame 22 and in
correspondence to which there are lightening apertures 25.
[0094] In greater detail, as may be seen in particular in FIG. 3,
perimetric frame 22 comprises--along the preferential development
direction of the brake pad--a first and a second profiled portion
31 and 32, opposite each other. Frame 22 is completed by two
connection portions 33 which join the profiled portions 31 and 32
at the extremities.
[0095] Advantageously, in correspondence to the first portion 31,
seats 40 can be made for the brake pad guide pins, as well as a
seat 50 for the wear indicator of friction portion 10.
[0096] Preferably the two connecting portions 33 are thinner than
profiled portions 31 and 32 in such a way as to define, with regard
to profiled portions 31 and 32, a lowered zone to function as seat
for the abovementioned plate-like element 23.
[0097] Preferably the lightening apertures 25, made in plate-like
element 23 to reduce the weight of support plate 21, are
distributed homogeneously over the whole surface of said plate-like
element.
[0098] In greater detail, plate-like element 23 may consist of
sheet metal with punched lightening apertures 25, or alternatively
of a metal mesh.
[0099] The frame 22 and the plate-like element 23 can be joined by
welding, gluing, by mechanical means of fixing or simply by
interlocking.
[0100] Preferably, as may be seen from FIGS. 5, 7 and 9, the
plate-like element 23 is associated with frame 22 in such a way as
to define with the latter a continuous surface in correspondence to
the face of brake pad 1 which will operate directly with the
braking system, which is to say the face opposite the
tribologically active one.
[0101] To this end, as may be seen in FIG. 3, the plate-like
element 23 has two side support wings 34, staggered with regard to
the main plane position and intended to abut in the lowered zone
defined by connection portions 33 of frame 22.
[0102] Advantageously, support plate 20 can be provided with
stiffening elements 24 in correspondence to the points on which the
actuating means of the braking system will bear.
[0103] In greater detail, as may be seen in FIGS. 6 and 8, the
stiffening elements 24 may be annular elements connected to the
plate-like element 23, in correspondence to which there are no
lightening apertures.
[0104] Stiffening elements 24 may be separate, as envisaged in the
embodiment illustrated in FIGS. 6 and 7, or be interconnected to
form a continuous structure as envisaged in the embodiment
illustrated in FIGS. 8 and 9.
[0105] Preferably the support plate 21 is co-pressed with the
mixture during the hot-pressing step, as illustrated in the diagram
in FIG. 13. In this way the mixture--still fluid--penetrates the
lightening apertures and takes on the form of the support plate,
creating close contact.
[0106] As may be seen in particular in FIGS. 4, 6 and 8, the
friction portion 20 is made in such a way that it covers the zones
of the plate bearing the lightening apertures 25.
[0107] Depending on the form of the brake pad it is nonetheless
possible to envisage the friction portion in ceramic matrix
material extending to cover, at least partially, zones in which
(for structural reasons) no lightening apertures are envisaged, as
in the embodiments illustrated in FIGS. 4, 6 and 8 where the
profile of friction portion 20 is shown by a dotted line.
[0108] In accordance with a third alternative embodiment,
illustrated in particular in FIGS. 10 and 11, the support plate 20
consists only of the perimetric frame 22 described above. Empty
space 26 delimited by frame 22 is a single lightening aperture
which is filled by the ceramic matrix material (as may be seen in
particular in FIG. 11).
[0109] Preferably the lightening apertures 25 have a surface area
of at least 5 mm.sup.2, and even more preferably 10 mm.sup.2. Where
only one lightening aperture 26 is envisaged (reinforcement plate
consisting of the perimetric frame alone) the area of the aperture
is comparable to the extent of the friction portion in ceramic
matrix material.
[0110] In FIGS. 1c, 3, 4, 6 and 8 the lightening, apertures 25 have
a square or rhomboid form. However apertures 25 may have different
forms, for example rectangular, circular, elliptical or even
irregular.
[0111] In accordance with a particular embodiment, the friction
portion 10 in ceramic matrix material may be made as an element in
itself and connected in a specific assembling step to support plate
21 by gluing or fixing means as illustrated in the diagram in FIG.
14.
[0112] Advantageously, intermediate embodiments may be envisaged,
between the first and second general embodiments described above,
in which the mechanical support portion is made with a support
plate and a layer of ceramic matrix material, bonded to form a
single body.
[0113] There follows a detailed description of the method for
creating the ceramic matrix material for brake pad 1 in accordance
with the invention.
[0114] As mentioned above, in its most general form of application
the method of the invention comprises at least one first step of
mixing the basic components, a second step of hot-pressing the
mixture and a third step of pyrolysis of the preformed body (or
moulded body).
[0115] The step of mixing the basic components of the ceramic
matrix material should preferably be done in a horizontal blade
mixer. However other types of mixers may be envisaged, depending on
the characteristics and quantities of the components to be
mixed.
[0116] In accordance with a preferable applicative embodiment for
the invention method, the step of mixing the various components
takes place in two stages.
[0117] In the first stage the polymeric ceramic precursor is mixed
with the appropriate catalyst (for reticulation reactions) in the
absence of the other components. In this way a more homogeneous
mixture is obtained in terms of catalyst distribution and therefore
(on completion of the pressing step) a reticulation of the
precursor spread throughout the mass of the material.
[0118] Advantageously, this first mixing stage is carried out for
sufficient time to ensure suitable mixing, preferably between 1 and
3 minutes.
[0119] In the second mixing stage all the other components are
added to the precursor-catalyst mixture: abrasives, lubricants and
metal materials.
[0120] Advantageously, this second mixing stage is carried out for
sufficient time to ensure suitable mixing, preferably between 3 and
5 minutes.
[0121] The hot-pressing step is preferably carried out with a
vertical press operating in compression on a steel mould.
[0122] Preferably, in cases where it is intended to directly bond
the friction component to a metal support (e.g. disc brake pad
support plate) during the production steps of the ceramic matrix
material, the mould should be a plate (or matrix) with a through
aperture and a perimetric section corresponding to the form to be
given to the body in ceramic matrix material (e.g. the friction
portion of the brake pad). The plate-matrix may be provided with
one, two or more apertures.
[0123] The operation begins by blocking one end of the through
aperture (preferably the lower one, with reference to a horizontal
orientation of the plate-matrix in the press) using the head of the
punch with which the press is provided. The aperture (which defines
a loading chamber) is then filled with the mixture. The upper end
is then closed with a metal plate of shape and thickness
appropriately selected in function of the brake pad applications.
With the plate suitably locked in position pressing is begun by
actuating the punch. The temperature inside the mould is measured
with thermocouples inserted in the mould itself.
[0124] Presses and moulds other than the one described above may be
envisaged.
[0125] Jointly with or separately from what is described above,
during the hot-pressing step the pressures exerted on the material
in the mould should preferably be between 250 and 500
Kg/cm.sup.2.
[0126] It was surprisingly discovered that application of pressures
within the range specified above has beneficial effects on the
performances of the final ceramic matrix material in terms of wear
resistance, friction and running-in (understood as the time taken
to achieve optimal functioning conditions).
[0127] An improvement in performance linked to application of
pressures as specified above during pressing was noted
independently of the pyrolysis process operational conditions.
[0128] An ameliorating synergic effect was also noted on final
ceramic matrix material performance through combining the pyrolysis
process at temperatures below 800.degree. C. (and in particular
between 400.degree. C. and 600.degree. C.) and the application of
pressing pressures between 250 and 500 Kg/cm.sup.2.
[0129] Jointly with or separately from the application of pressures
between 250 and 500 Kg/cm.sup.2, the pressing step should
preferably be carried out at temperatures between 120.degree. C.
and 150.degree. C. to permit fluidification of the ceramic
precursor and the achievement of viscosity values such as to
facilitate close contact and bonding between the precursor and the
other components of the mixture.
[0130] Jointly with or separately from what is described above, the
pressing step should preferably be carried out with alternate
cycles of application and release of force.
[0131] In accordance with a special applicative form of the method
the pressing step envisages three consecutive cycles of application
and release of force, each lasting about 30 seconds (15 seconds of
application and 15 seconds of release). There follows a final step
of continuous application of force for approximately 90-210
seconds. The overall pressing step requires a period of time that
varies between 3 and 5 minutes. The pressing times and temperatures
allow the well fluidified ceramic precursor to spread homogeneously
to all portions of the mould and among the particles of the various
mix components.
[0132] In accordance with an especially preferred implementation,
the support plate is co-pressed with the mixture of precursor,
catalyst and filler and then undergoes pyrolysis together with the
preformed body.
[0133] Carrying out pyrolysis (in accordance with the invention) at
temperatures below 800.degree. C., and in particular between
400.degree. C. and 600.degree. C., makes the operation expedient
and feasible. In fact the metal support plate can bear the thermal
stresses deriving from the pyrolysis process without undergoing
unacceptable heat deformations.
[0134] Thanks to the invention method it is therefore possible to
directly bond the support plate to the green body, hence to the
ceramic matrix material, during the friction material production
steps. On completion of the friction material creation steps we
therefore have a friction material/plate assembly which facilitates
the subsequent work processes of finishing and of any application
of mechanical fixing means.
[0135] As already mentioned, a characterising aspect of the
invention is that the pyrolysis process in carried out at
temperatures below 800.degree. C.
[0136] It was noted that the best results in terms of improving
friction material performances are obtained by carrying out the
pyrolysis process in such a way as to reach maximum temperatures
between 400 and 600.degree. C.
[0137] Advantageously, the pyrolysis process is carried out
envisaging a time at maximum temperature between 3 and 5 hours, and
preferably 4 hours.
[0138] During the pyrolysis process the velocity of heating the
preformed body (green body) from surrounding to maximum temperature
should preferably be between 4 and 6.degree. C./min, preferably
5.degree. C./min.
[0139] The pyrolysis process should preferably be carried out in an
isothermal kiln.
[0140] Advantageously, with view to avoiding oxidative phenomena
that would alter the ceramisation processes, pyrolysis is carried
out in an inert atmosphere.
[0141] The inert atmosphere should preferably be created with a
flow of argon or nitrogen, in cases where the formation of silicium
oxycarbides is preferred (with general formula SiO.sub.xC.sub.y) in
the ceramic matrix material.
[0142] Different atmospheres may also be envisaged, for example in
ammonia flow, in cases where the formation of silicium oxynitrides
is desired (with general formula SiO.sub.xN.sub.y) in the ceramic
matrix material.
[0143] In accordance with a special applicative form of the
invention illustrated in the diagram in FIG. 1, the support plate
is bonded to the already made friction material. On completion of
the pyrolysis step there may be a step of thickness grinding of the
preformed body in ceramic matrix material and, alternatively or
additionally, a surface finishing step for the ceramic matrix
body.
[0144] The essential purpose of these steps is to prepare the
ceramic matrix material body in such a way that it can be
subsequently coupled--in accordance with envisaged tolerances--with
support elements (e.g. a metal support plate) in order to create a
disc brake pad.
[0145] The method may also envisage, on completion of the above
steps of grinding and/or surface refinishing steps, a step of
assembly of the friction component with a metal support plate by
means of suitable fixing elements such as bolts, rivets or
glue.
[0146] Advantageously the surface finishing step should be carried
out after the step of assembling the friction component and the
support plate.
[0147] In accordance with an especially preferred applicative form
of the invention (already mentioned above and illustrated in FIG.
2) the elements supporting the friction component are bonded to the
latter directly during the steps of creating the friction
material.
[0148] On completion of the pyrolysis step there may be a step of
thickness grinding of the preformed body in ceramic matrix material
and, alternatively or additionally, an operational step of surface
refinishing of the ceramic material body on the exposed and not
covered parts of the plate.
[0149] In accordance with a general applicative embodiment for the
invention, the mixture to be pressed is composed as follows
(percentages expressed in weight with regard to the mixture):
ceramic precursor and catalyst between 5 and 10%; abrasives between
20% and 30%; metal materials not greater than 60%; lubricants not
greater than 50%.
[0150] As mentioned above, the ceramic polymeric precursor is of a
siliconic type and may in particular be selected from the group
comprising polysilanes, polycarbosilanes, polysilazanes and
polysiloxanes with general formula [--R.sub.1 . . . 2,
Si(C,N,B,O).sub.0.5 . . . 1.5--].sub.n.
[0151] Preferably the precursor should be selected from the
polysiloxanes, independently of the substituting functional groups
and of the degree of ramification of the polymer, with general
formula [--RSiO.sub.1.5--].sub.n, where R indicates hydrogen or an
organic functional group (alkylic, acrylic etc).
[0152] Even more preferably, the precursor should be selected from
the sesquisiloxanes and in particular the
polymethyl-sesquisiloxanes.
[0153] Mixtures of two or more different organic precursors may be
envisaged.
[0154] Advantageously, the ceramic precursor's weight percentage in
the mixture is between 6% and 9%.
[0155] Preferably the catalyst should be selected from organic
coordination compounds with metals selected from the group
comprising zinc, copper, aluminium, iron, zirconium, vanadium,
chromium, manganese, cobalt, nickel and titanium.
[0156] Advantageously, the catalyst is selected from the
acetonates, the beta-diketonates and the carboxylates. An
especially preferred catalyst is zinc or zirconium
acetylacetonate.
[0157] Advantageously, the catalyst is present with a
stoichiometric percentage with regard to the ceramic precursor,
preferably a percentage between 0.15% and 0.3% of the mixture
weight.
[0158] Preferably the ceramic precursor and catalyst used should be
in powder form. But components in other forms, such as fluids, may
also be used.
[0159] Preferably the abrasives consist of powdered silicium
carbide. However other materials with hardness properties such as
to function as abrasives may also be used, such as for example
boron carbide, silicium, zircon, zirconium oxide (zirconia),
periclase, corundum and spinel.
[0160] For simplicity in the description of abrasives below
explicit reference will be made only to silicium carbide, but this
should not be considered limitative. In fact the information
concerning silicium carbide should be extended to other abrasives
such as the ones listed above.
[0161] Advantageously, silicium carbide is in the form of powder in
two different particle sizes.
[0162] The relationship between the average diameters of the two
powders is between 9 and 11, and preferably 10.
[0163] Average diameter of a powder is intended as the value
corresponding to d.sub.50 of the particle size distribution curve.
In the following description, reference will be made to the
definitions of powders employed by the FEPA (European Federation of
Abrasives Manufacturers).
[0164] The differentiated particle size of the silicium carbide
powder means that a compatibly sized abrasive can be supplied to
all the remaining components of the mixture. The finest powder
blends with the fine lubricants and ceramic precursor (binder
resin) while the large particle powder blends with the larger sized
metal particles. This favours compaction of the material.
[0165] It is further noted that the finer powder blends and tends
to homogenise with the remaining material while the larger particle
powder remains "detached" from the other components of the
mixture.
[0166] So it may be seen that the two different particle sizes
result in abrasives that operate at different energy levels, to the
advantage of final friction material performances. When the smaller
particle size abrasives wear out there is a progressive "crumbling"
of the larger particle size abrasives. This results in an averagely
constant presence of smaller particle size abrasives.
[0167] Preferably the silicium carbide powders in the two different
particle sizes should have average diameters between 1 .mu.m and
600 .mu.m.
[0168] In accordance with a general applicative form of the
invention, the weight ratio between the silicium carbide powders of
greater and lesser particle size is between 0.8 and 1.8.
[0169] As will be resumed below, should the ceramic matrix friction
material be required to cooperate tribologically with a disc brake
in composite ceramic material the weight ratio between larger and
smaller particle size silicium carbide powder should be between 0.8
and 1.2, preferably 1.
[0170] Should the ceramic matrix friction material be required to
cooperate tribologically with a disc brake in grey cast iron the
weight ratio between larger and smaller particle size silicium
carbide powder should be between 1.2 and 1.8, preferably 1.5.
[0171] In accordance with a preferable applicative form of the
invention, the metal particles consist of particles in iron and/or
iron alloy.
[0172] Advantageously, metal particles replacing or in addition to
particles in iron and/or iron alloy consist of particles in copper
and/or brass.
[0173] Preferably the particles in copper and brass, individually
or mixed, are present in a percentage of less than 20% of mixture
weight.
[0174] The term "particle" is intended to comprise parts of
materials in the form of both powders and fibres.
[0175] As regards particles in ferrous materials, steel wool is
especially preferred.
[0176] Preferably the metal particles (iron, iron alloys, copper
and/or brass) in powder form should have an average diameter of
less than 300 .mu.m, whereas metal particles in fibre form (iron,
iron alloys, copper and/or brass) should have an average diameter
of less than 100 .mu.m and a length of less than 1 mm.
[0177] In accordance with a preferable applicative form of the
invention the lubricants consist of graphite in powder.
[0178] Advantageously, in replacement of or in addition to powdered
graphite, the lubricants may consist of powdered coke, tin sulphide
and/or tin.
[0179] Preferably the percentage of graphite should be between 9%
and 13% of mixture weight while powdered coke, tin sulphide and tin
(where envisaged) should have weights of less than 35%, 10% and 5%
respectively with regard to the mixture.
[0180] Advantageously, as will be resumed in the attached examples,
the use of powdered coke, tin sulphide and/or tin in combination
with graphite powders reduces the graphite content, bringing it
towards the lower extreme of the interval specified above.
[0181] Advantageously, graphite and/or coke powders have an average
diameter between 200 .mu.m and 800 .mu.m while tin sulphide and/or
tin powders have an average diameter of less than 100 .mu.m.
[0182] As mentioned previously, the ceramic matrix friction
material produced with the invention method may be used to
manufacture brake pads that cooperate tribologically with disc
brakes in composite ceramic material (CCM) or in grey cast iron,
guaranteeing optimum performance in both cases in terms of value of
friction coefficient stability and wear resistance.
[0183] Should the invention's ceramic matrix material be required
to cooperate with discs in grey cast iron, the mixture undergoing
the pressing step should have the following general composition
(percentages expressed in weight with regard to the mixture):
ceramic precursor and catalyst between 5 and 10%; abrasives between
20% and 30%; metal materials between 25% and 60%; lubricants
between 10% and 50%.
[0184] In greater detail, in accordance with a specific
implementation, the weight ratio between the silicium carbide
powder with greater particle size and the powder of lesser particle
size should be between 1.2 and 1.8, and preferably 1.5.
[0185] The greater size particle powdered silicium carbide (SiC) is
present in a percentage between 12% and 18% of mixture weight while
the percentage of finer SiC powder is between 6% and 12% of mixture
weight.
[0186] The metal particles consist of powdered iron, from 5% to 20%
of mixture weight, steel wool from 5% to 30% of mixture weight and
(where envisaged) copper and/or brass powder and/or fibres in
percentages less than 20% of mixture weight.
[0187] Overall the particles (powder and fibres) of iron and/or
iron alloys weigh between 5% and 60% of mixture weight.
[0188] Graphite, preferably in powder form, constitutes between 9%
and 12% of mixture weight. Where coke is envisaged the percentage
is less than 35% of mixture weight, whereas tin sulphide and tin
(where envisaged), preferably in powder form, should be less than
10% and 5% of mixture weight respectively.
[0189] When graphite is the only lubricant the percentage should
preferably be 12% of mixture weight. By way of example the addition
of 3% weight of tin powder permits reducing the graphite to
10%.
[0190] There follow descriptions of five specific examples of
making ceramic matrix materials, in accordance with the invention,
intended to cooperate with discs in grey cast iron.
EXAMPLE 1
[0191] Mix 780 grams of polymethyl-sesquisiloxane resin
(CH.sub.3--SiO.sub.3/2).sub.n in Wacker-Belsil.RTM. PMS MK Powder
(softening interval 50-60.degree. C.) and 20 grams of powdered zinc
acetylacetonate in a horizontal blade mixer for approximately 2
minutes. Then add 1.500 grams of powdered SiC class FEPA F36
(average diameter 525 .mu.m) and 1.000 grams of powdered SiC class
FEPA F220 (average diameter 58 .mu.m). Continue by adding 1.800
grams of copper in powder, 2.700 grams of steel wool, 1.000 grams
of iron in powder and lastly 1.200 grams of graphite in powder. The
second step of mixing is protracted for approximately 4
minutes.
[0192] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 15% of powdered
SiC F36; 10% powdered SiC F220; 18% copper in powder; 27% steel
wool; 10% iron in powder; 12% graphite in powder; 7.8%
polymethyl-sesquisiloxane resin; 0.2% zinc acetylacetonate.
[0193] The copper and iron powders have an average diameter of
approximately 200 .mu.m and approximately 250 .mu.m respectively.
The steel wool has an average diameter of approximately 80 .mu.m
and an average length of approximately 0.8 mm. The graphite powder
has an average diameter of approximately 600 .mu.m.
[0194] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the sesquisiloxanic resin.
[0195] The mixture is co-pressed with a lightened steel plate of
the type illustrated in FIG. 3, consisting of a perimetric frame
and a plate-like element with square lightening apertures of which
around 50% have a surface area of about 5 mm.sup.2 and the rest
about 10 mm.sup.2. The frame is about 5 mm thick while the
plate-like element is around 1 mm thick.
[0196] In greater detail, a plate (or matrix) is used, with a
through-going aperture of substantially rectangular perimetric
section corresponding to the form to be taken by the body in
ceramic matrix material. The aperture has a surface area of around
77 cm.sup.2 and a depth of about 8 cm.
[0197] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the lightened steel plate described above.
The quantity of mixture is defined in function of the final
thickness of the brake pad, taking into account that following
pressing there is a volume reduction of about 2/3. After
positioning the plate appropriately, pressing is carried out by
activating the punch.
[0198] The temperature inside the mould (measured by means of
thermocouples) is maintained around 120.degree. C. The maximum
pressure applied during pressing is around 400 Kg/cm.sup.2. Three
consecutive cycles of application and release of force are
envisaged, each lasting about 30 seconds (15 seconds of application
and 15 seconds of release). There follows a final step of
continuous application of force (without release) for approximately
150 seconds. The overall pressing step requires a period of
approximately 4 minutes.
[0199] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
500.degree. C. at a velocity of approximately 5.degree. C./min and
kept at 500.degree. C. for approximately 4 hours.
[0200] The friction portion in ceramic matrix material lastly
undergoes a finishing work process aimed at reducing thickness in
function of the brake pad's final use.
[0201] The brake pad thus obtained has a thickness of 19.75 mm
(including the thickness of the steel plate which is about 5 mm)
and a total weight of around 540 grams, of which 350 grams is the
weight of the friction portion in ceramic matrix material and the
remaining 190 grams of the lightened plate and the part of the
friction material that has filled the lightening apertures.
[0202] A traditional brake pad of the same form and functionality
weighs around 635 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 15%.
EXAMPLE 2
[0203] Mix 780 grams of polymethyl-sesquisiloxane resin
(CH.sub.3--SiO.sub.3/2).sub.n in Wacker-Belsil.RTM. PMS MK Powder
(softening interval 50-60.degree. C.) and 20 grams of powdered zinc
acetylacetonate in a horizontal blade mixer for approximately 2
minutes. Then add 1.500 grams of powdered SiC class FEPA F100
(average diameter 129 .mu.m) and 1.000 grams of powdered SiC class
FEPA F500 (average diameter d.sub.50 12.8 .mu.m). Continue by
adding 1.800 grams of brass in powder, 2.700 grams of steel wool,
900 grams of iron in powder, 1.000 grams of graphite in powder and
lastly 300 grams of tin in powder. The second step of mixing is
protracted for approximately 4 minutes.
[0204] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 15% of powdered
SiC F100; 10% powdered SiC F500; 18% brass in powder; 27% steel
wool; 9% iron in powder; 10% graphite in powder; 3% tin in powder;
7.8% polymethyl-sesquisiloxane resin; 0.2% zinc
acetylacetonate.
[0205] The brass and iron powders have an average diameter of
approximately 250 .mu.m and approximately 200 .mu.m respectively.
The steel wool has an average diameter of approximately 80 .mu.m
and an average length of approximately 0.6 mm. The graphite and tin
powders have an average diameter of approximately 400 .mu.m and
approximately 80 .mu.m respectively.
[0206] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the sesquisiloxane resin.
[0207] The mixture is co-pressed with a lightened steel plate of
the type illustrated in FIG. 6, consisting of a perimetric frame
and a plate-like element with square lightening apertures
reinforced with 3 circular elements set in correspondence to the
abutting zones of the braking system actuating means. Around 50% of
the apertures have a surface area of about 5 mm.sup.2 and the rest
about 10 mm.sup.2. The frame is about 5 mm thick while the
plate-like element is around 1 mm thick.
[0208] In greater detail, a plate (or matrix) is used, with a
through-going aperture of substantially rectangular perimetric
section corresponding to the form to be taken by the body in
ceramic matrix material. The aperture has a surface area of around
77 cm.sup.2 and a depth of about 8 cm.
[0209] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the lightened steel plate described above.
The quantity of mixture is defined in function of the final
thickness of the brake pad, taking into account that following
pressing there is a volume reduction of about 2/3. After
positioning the plate appropriately, pressing is carried out by
activating the punch.
[0210] The temperature inside the mould is maintained around
130.degree. C. The maximum pressure applied during pressing is
around 450 Kg/cm.sup.2. Three consecutive cycles of application and
release of force are envisaged, each lasting about 30 seconds (15
seconds of application and 15 seconds of release). There follows a
final step of continuous application of force (without release) for
approximately 210 seconds. The overall pressing step requires a
period of approximately 5 minutes.
[0211] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
400.degree. C. at a velocity of approximately 6.degree. C./min and
kept at 400.degree. C. for approximately 4 hours and 30
minutes.
[0212] The friction portion in ceramic matrix material lastly
undergoes a finishing work process aimed at reducing thickness in
function of the brake pad's end use.
[0213] The brake pad thus obtained has a thickness of 19.75 mm
(including the thickness of the steel plate which is about 5 mm)
and a total weight of around 560 grams, of which 350 grams is the
weight of the friction portion in ceramic matrix material and the
remaining 210 grams of the lightened plate and the part of the
friction material that has filled the lightening apertures.
[0214] A traditional brake pad of the same form and functionality
weighs around 635 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 12%.
EXAMPLE 3
[0215] Mix 780 grams of cyclopentasiloxane resin Wacker-Belsil.RTM.
RG100 and 20 grams of powdered zinc acetylacetonate in a horizontal
blade mixer for approximately 2 minutes. Then add 1.300 grams of
powdered SiC class FEPA F46 (average diameter 370 .mu.m) and 800
grams of powdered SiC class FEPA F280 (average diameter d.sub.50
36.5 .mu.m). Continue by adding 2.500 grams of steel wool, 300
grams of iron in powder, 1.000 grams of graphite in powder, 3.000
grams of coke in powder and lastly 300 grams of tin in powder. The
second step of mixing is protracted for approximately 4
minutes.
[0216] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 13% powdered SiC
F46; 8% powdered SiC F280; 25% steel wool; 3% iron in powder; 10%
graphite in powder; 30% coke in powder; 3% tin in powder; 7.8%
siliconic resin; 0.2% zinc acetylacetonate.
[0217] The iron powder has an average diameter of approximately 150
.mu.m. The steel wool has an average diameter of approximately 60
.mu.m and an average length of approximately 0.5 mm. The graphite,
coke and tin powders have an average diameter of approximately 700
.mu.m, approximately 600 .mu.m and approximately 90 .mu.m
respectively.
[0218] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the siloxanic resin.
[0219] The mixture is co-pressed with a mesh reinforcement body
about 1 mm thick, similar to the plate-like body with lightening
apertures illustrated in FIG. 3. Around 50% of the apertures have a
surface area of about 5 mm.sup.2 and the rest about 10
mm.sup.2.
[0220] In greater detail, a plate (or matrix) is used, with a
double section through-going aperture: the first has a
substantially rectangular perimetric section corresponding to the
form to be taken by the friction portion while the second has a
substantially rectangular perimetric section corresponding to the
form to be taken by the support portion. The aperture has a depth
of about 8 cm and, in correspondence to the first section, a
surface area of around 77 cm.sup.2.
[0221] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the mesh reinforcement body described above.
The quantity of mixture is defined in function of the final
thickness of the brake pad, taking into account that following
pressing there is a volume reduction of about 2/3. After
positioning the plate appropriately, pressing is carried out by
activating the punch.
[0222] The temperature inside the mould is maintained around
150.degree. C. The maximum pressure applied during pressing is
around 350 Kg/cm.sup.2. Three consecutive cycles of application and
release of force are envisaged, each lasting about 30 seconds (15
seconds of application and 15 seconds of release). There follows a
final step of continuous application of force (without release) for
approximately 210 seconds. The overall pressing step requires a
period of approximately 5 minutes.
[0223] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
600.degree. C. at a velocity of approximately 4.degree. C./min and
kept at 600.degree. C. for approximately 3 hours and 30
minutes.
[0224] The friction portion in ceramic matrix material lastly
undergoes a finishing work process aimed at reducing thickness in
function of the brake pad's end use.
[0225] The brake pad thus obtained has a thickness of 19.75 mm
(including the thickness of the reinforcement which is about 1 mm)
and a total weight of around 490 grams, of which 350 grams is the
weight of the friction portion in ceramic matrix material and the
remaining 140 grams of the reinforcement element and the part of
the friction material that has filled the lightening apertures.
[0226] A traditional brake pad of the same form and functionality
weighs around 635 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 23%.
EXAMPLE 4
[0227] Mix 780 grams of cyclopentasiloxane resin Wacker-Belsil.RTM.
RG100 and 20 grams of powdered zinc acetylacetonate in a horizontal
blade mixer for approximately 2 minutes. Then add 1.300 grams of
powdered SiC class FEPA F46 (average diameter 370 .mu.m) and 800
grams of powdered SiC class FEPA F280 (average diameter d.sub.50
36.5 .mu.m). Continue by adding 2.500 grams of steel wool, 300
grams of iron in powder, 1.000 grams of graphite in powder, 3.000
grams of coke in powder and lastly 300 grams of tin in powder. The
second step of mixing is protracted for approximately 4
minutes.
[0228] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 13% powdered SiC
F46; 8% powdered SiC F280; 25% steel wool; 3% iron in powder; 10%
graphite in powder; 30% coke in powder; 3% tin in powder; 7.8%
siliconic resin; 0.2% zinc acetylacetonate.
[0229] The iron powder has an average diameter of approximately 150
.mu.m. The steel wool has an average diameter of approximately 60
.mu.m and an average length of approximately 0.5 mm. The graphite,
coke and tin powders have an average diameter of approximately 700
.mu.m, approximately 600 .mu.m and approximately 90 .mu.m
respectively.
[0230] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the siloxanic resin.
[0231] The mixture is pressed without inserting any reinforcing
element or support plate.
[0232] In greater detail, a plate (or matrix) is used, with a
double section through-going aperture: the first has a
substantially rectangular perimetric section corresponding to the
form to be taken by the friction portion while the second has a
substantially rectangular perimetric section corresponding to the
form to be taken by the support portion. The aperture has a depth
of about 8 cm and, in correspondence to the first section a surface
area of around 77 cm.sup.2.
[0233] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the special closure element on the pressing
device. The quantity of mixture is defined in function of the final
thickness of the brake pad, taking into account that following
pressing there is a volume reduction of about 2/3.
[0234] The temperature inside the mould is maintained around
150.degree. C. The maximum pressure applied during pressing is
around 350 Kg/cm.sup.2. Three consecutive cycles of application and
release of force are envisaged, each lasting about 30 seconds (15
seconds of application and 15 seconds of release). There follows a
final step of continuous application of force (without release) for
approximately 210 seconds. The overall pressing step requires a
period of approximately 5 minutes.
[0235] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
600.degree. C. at a velocity of approximately 4.degree. C./min and
kept at 600.degree. C. for approximately 3 hours and 30
minutes.
[0236] The brake pad made entirely in ceramic matrix material
lastly undergoes a finishing work process aimed at reducing
thickness in function of the brake pad's end use.
[0237] The brake pad thus obtained has a thickness of 19.75 mm
(including the thickness of the reinforcement which is about 1 mm)
and a total weight of around 470 grams, of which 350 grams is the
weight of the friction portion in ceramic matrix material and the
remaining 120 grams of the support portion.
[0238] A traditional brake pad of the same form and functionality
weighs around 635 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 26%.
EXAMPLE 5
[0239] Mix 780 grams of polymethyl-sesquisiloxane resin
(CH.sub.3--SiO.sub.3/2).sub.n in Wacker-Belsil.RTM. PMS MK Powder
(softening interval 50-60.degree. C.) and 20 grams of powdered zinc
acetylacetonate in a horizontal blade mixer for approximately 2
minutes. Then add 1.500 grams of powdered SiC class FEPA F36
(average diameter 525 .mu.m) and 1.000 grams of powdered SiC class
FEPA F220 (average diameter 58 .mu.m). Continue by adding 1.800
grams of copper in powder, 2.700 grams of steel wool, 1.000 grams
of iron in powder and lastly 1.200 grams of graphite in powder. The
second step of mixing is protracted for approximately 4
minutes.
[0240] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 15% of powdered
SiC F36; 10% powdered SiC F220; 18% copper in powder; 27% steel
wool; 10% iron in powder; 12% graphite in powder; 7.8%
polymethyl-sesquisiloxane resin; 0.2% zinc acetylacetonate.
[0241] The copper and iron powders have an average diameter of
approximately 200 .mu.m and approximately 250 .mu.m respectively.
The steel wool has an average diameter of approximately 80 .mu.m
and an average length of approximately 0.8 mm. The graphite powder
has an average diameter of approximately 600 .mu.m.
[0242] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the sesquisiloxanic resin.
[0243] The mixture is co-pressed with a lightened steel plate
consisting of a perimetric frame of the type illustrated in FIG. 3.
The frame is around 5 mm thick and delimits a single central
lightening aperture.
[0244] In greater detail, a plate (or matrix) is used, with a
through-going aperture of substantially rectangular perimetric
section corresponding to the form to be taken by the body in
ceramic matrix material. The aperture has a surface area of around
77 cm.sup.2 and a depth of about 8 cm.
[0245] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the lightened steel plate described above and
with a further closure element with which the pressing system is
provided. The quantity of mixture is defined in function of the
final thickness of the brake pad, taking into account that
following pressing there is a volume reduction of about 2/3. After
positioning the plate appropriately, pressing is carried out by
activating the punch.
[0246] The temperature inside the mould (measured by means of
thermocouples) is maintained around 120.degree. C. The maximum
pressure applied during pressing is around 400 Kg/cm.sup.2. Three
consecutive cycles of application and release of force are
envisaged, each lasting about 30 seconds (15 seconds of application
and 15 seconds of release). There follows a final step of
continuous application of force (without release) for approximately
150 seconds. The overall pressing step requires a period of
approximately 4 minutes.
[0247] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
500.degree. C. at a velocity of approximately 5.degree. C./min and
kept at 500.degree. C. for approximately 4 hours.
[0248] The friction portion in ceramic matrix material lastly
undergoes a finishing work process aimed at reducing thickness in
function of the brake pad's end use.
[0249] The brake pad thus obtained has a thickness of 19.75 mm
(including the thickness of the frame which is about 5 mm) and a
total weight of around 520 grams, of which 350 grams is the weight
of the friction portion in ceramic matrix material and the
remaining 170 grams of the frame and the part of friction material
filling the single central lightening aperture.
[0250] A traditional brake pad of the same form and functionality
weighs around 635 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 18%.
[0251] Should the ceramic matrix material according to the
invention be required to function with discs in CCM, the mixture
for the pressing step has the following general composition
(percentages expressed in weight with regard to the mixture):
ceramic precursor and catalyst between 5 and 10%; abrasives between
20% and 30%; metal materials between 30% and 60%; lubricants
between 10% and 40%.
[0252] In greater detail, in accordance with a specific
implementation, the weight ratio between the silicium carbide
powder with greater particle size and the powder of lesser particle
size should be between 0.8 and 1.2, and preferably 1.
[0253] The greater size particle powdered silicium carbide (SiC) is
present in a percentage between 10% and 15% of mixture weight.
[0254] The metal particles consist of steel wool from 20% to 30% of
mixture weight (which may be wholly or partly replaced by powdered
iron) and (where envisaged) copper and/or brass powder and/or
fibres in percentages less than 20% of mixture weight.
[0255] Unlike the ceramic matrix material for cooperation with
discs in grey cast iron, the material for discs in CCM also
comprises silicium among the particles, preferably in powder
form.
[0256] Advantageously, silicium powder is present with a weight
percentage between 9 and 11% of the mixture, preferably 10%.
[0257] The silicium powder preferably has an average diameter of
less than 50 .mu.m.
[0258] Graphite, preferably in powder form, constitutes between 11%
and 13% of mixture weight, preferably 12%. Where coke is envisaged
the percentage is less than 20% of mixture weight, whereas tin
sulphide and tin (where envisaged), preferably in powder form,
should be less than 10% and 5% of mixture weight respectively.
[0259] There follow descriptions of five specific examples of
making ceramic matrix materials, in accordance with the invention,
intended to cooperate with discs in composite ceramic material
(CCM).
EXAMPLE 6
[0260] Mix 780 grams of polymethyl-sesquisiloxane resin
(CH.sub.3--SiO.sub.3/2).sub.n in Wacker-Belsil.RTM. PMS MK Powder
(softening interval 50-60.degree. C.) and 20 grams of powdered zinc
acetylacetonate in a horizontal blade mixer for approximately 2
minutes. Then add 1.200 grams of powdered SiC class FEPA F46
(average diameter 370 .mu.m) and 1.300 grams of powdered SiC class
FEPA F280 (average diameter 36.5 .mu.m). Continue by adding 1.800
grams of copper in powder, 2.700 grams of steel wool, 1.000 grams
of silicium in powder and lastly 1.200 grams of graphite in powder.
The second step of mixing is protracted for approximately 4
minutes.
[0261] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 12% of powdered
SiC F46; 13% powdered SiC F280; 18% copper in powder; 27% steel
wool; 10% silicium in powder; 12% graphite in powder; 7.8%
sesquisiloxane resin; 0.2% zinc acetylacetonate.
[0262] The copper and silicium powders have an average diameter of
approximately 150 .mu.m and approximately 40 .mu.m respectively.
The steel wool has an average diameter of approximately 50 .mu.m
and an average length of approximately 0.4 mm. The graphite powder
has an average diameter of approximately 300 .mu.m.
[0263] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the sesquisiloxanic resin.
[0264] The mixture is co-pressed with a lightened steel plate of
the type illustrated in FIG. 3, consisting of a perimetric frame
and a plate-like element with square lightening apertures of which
around 50% have a surface area of about 5 mm.sup.2 and the rest
about 10 mm.sup.2. The frame is about 5.5 mm thick while the
plate-like element is around 1 mm thick.
[0265] In greater detail, a plate (or matrix) is used, with a
through-going aperture of substantially rectangular perimetric
section corresponding to the form to be taken by the body in
ceramic matrix material. The aperture has a surface area of around
145 cm.sup.2 and a depth of about 8 cm.
[0266] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the lightened steel plate described above.
The quantity of mixture is defined in function of the final
thickness of the brake pad, taking into account that following
pressing there is a volume reduction of about 2/3. After
positioning the plate appropriately, pressing is carried out by
activating the punch.
[0267] The temperature inside the mould is maintained around
120.degree. C. The maximum pressure applied during pressing is
around 300 Kg/cm.sup.2. Three consecutive cycles of application and
release of force are envisaged, each lasting about 30 seconds (15
seconds of application and 15 seconds of release). There follows a
final step of continuous application of force (without release) for
approximately 90 seconds. The overall pressing step requires a
period of approximately 3 minutes.
[0268] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
500.degree. C. at a velocity of approximately 5.degree. C./min and
kept at 500.degree. C. for approximately 4 hours.
[0269] The friction portion in ceramic matrix material lastly
undergoes a finishing work process aimed at reducing thickness in
function of the brake pad's end use.
[0270] The brake pad thus obtained has a thickness of 16.4 mm
(including the thickness of the steel plate which is about 5.5 mm)
and a total weight of around 860 grams, of which 480 grams is the
weight of the friction portion in ceramic matrix material and the
remaining 380 grams of the lightened plate and the part of the
friction material that has filled the lightening apertures.
[0271] A traditional brake pad of the same form and functionality
weighs around 1.180 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 27%.
EXAMPLE 7
[0272] Mix 780 grams of polymethyl-sesquisiloxane resin
(CH.sub.3--SiO.sub.3/2).sub.n in Wacker-Belsil.RTM. PMS MK Powder
(softening interval 50-60.degree. C.) and 20 grams of powdered zinc
acetylacetonate in a horizontal blade mixer for approximately 2
minutes. Then add 1.200 grams of powdered SiC class FEPA F54
(average diameter 310 .mu.m) and 1.300 grams of powdered SiC class
FEPA F320 (average diameter d.sub.50 29.2 .mu.m). Continue by
adding 1.000 grams of silicium in powder, 2.700 grams of steel
wool, 1.200 grams of graphite in powder and lastly 1.800 grams of
coke in powder. The second step of mixing is protracted for
approximately 4 minutes.
[0273] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 12% powdered SiC
F54; 13% powdered SiC F320; 27% steel wool; 10% silicium in powder;
12% graphite in powder; 18% coke in powder; 7.8% sesquisiloxane
resin; 0.2% zinc acetylacetonate.
[0274] The silicium powder has an average diameter of approximately
35 .mu.m. The steel wool has an average diameter of approximately
70 .mu.m and an average length of approximately 0.6 mm. The
graphite and coke powders have an average diameter of approximately
500 .mu.m.
[0275] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the sesquisiloxanic resin.
[0276] The mixture is co-pressed with a lightened steel plate of
the type illustrated in FIG. 6, consisting of a perimetric frame
and a plate-like element with square lightening apertures
reinforced with 3 circular elements set in correspondence to the
abutting zones of the braking system actuating means. Around 50% of
the apertures have a surface area of about 5 mm.sup.2 and the rest
about 10 mm.sup.2. The frame is about 5.5 mm thick while the
plate-like element is around 1 mm thick.
[0277] In greater detail, a plate (or matrix) is used, with a
through-going aperture of substantially rectangular perimetric
section corresponding to the form to be taken by the body in
ceramic matrix material. The aperture has a surface area of around
145 cm.sup.2 and a depth of about 8 cm.
[0278] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the lightened steel plate described above.
The quantity of mixture is defined in function of the final
thickness of the brake pad, taking into account that following
pressing there is a volume reduction of about 2/3. After
positioning the plate appropriately, pressing is carried out by
activating the punch.
[0279] The temperature inside the mould is maintained around
130.degree. C. The maximum pressure applied during pressing is
approximately 250 Kg/cm.sup.2. Three consecutive cycles of
application and release of force are envisaged, each lasting about
30 seconds (15 seconds of application and 15 seconds of release).
There follows a final step of continuous application of force
(without release) for approximately 150 seconds. The overall
pressing step requires a period of approximately 4 minutes.
[0280] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
550.degree. C. at a velocity of approximately 5.degree. C./min and
kept at 550.degree. C. for approximately 4 hours.
[0281] The friction portion in ceramic matrix material lastly
undergoes a finishing work process aimed at reducing thickness in
function of the brake pad's end use.
[0282] The brake pad thus obtained has a thickness of 16.4 mm
(including the thickness of the steel plate which is about 5.5 mm)
and a total weight of around 880 grams, of which 480 grams is the
weight of the friction portion in ceramic matrix material and the
remaining 400 grams of the lightened plate and the part of the
friction material that has filled the lightening apertures.
[0283] A traditional brake pad of the same form and functionality
weighs around 1.180 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 25%.
EXAMPLE 8
[0284] Mix 780 grams of cyclopentasiloxane resin Wacker-Belsil.RTM.
RG100 and 20 grams of powdered zinc acetylacetonate in a horizontal
blade mixer for approximately 2 minutes. Then add 1.200 grams of
powdered SiC class FEPA F40 (average diameter 438 .mu.m) and 1.300
grams of powdered SiC class FEPA F240 (average diameter d.sub.50
44.5 .mu.m). Continue by adding 1.500 grams of brass in powder,
2.100 grams of steel wool, 1.000 grams of silicium in powder, 1.200
grams of graphite in powder and lastly 900 grams of tin sulphide in
powder. The second step of mixing is protracted for approximately 4
minutes.
[0285] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 12% powdered SiC
F40; 13% powdered SiC F240; 21% steel wool; 15% brass in powder;
10% silicium in powder; 12% graphite in powder; 9% tin sulphide in
powder; 7.8% siliconic resin; 0.2% zinc acetylacetonate.
[0286] The brass and silicium powders have an average diameter of
approximately 200 .mu.m and approximately 45 .mu.m respectively.
The steel wool has an average diameter of approximately 80 .mu.m
and an average length of approximately 0.8 mm. The graphite and tin
sulphide powders have an average diameter of approximately 750
.mu.m and approximately 90 .mu.m respectively.
[0287] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the sesquisiloxanic resin.
[0288] The mixture is co-pressed with a mesh reinforcement body
about 1 mm thick, similar to the plate-like body with lightening
apertures illustrated in FIG. 3. Around 50% of the apertures have a
surface area of about 5 mm.sup.2 and the rest about 10
mm.sup.2.
[0289] In greater detail, a plate (or matrix) is used, with a
double section through-going aperture: the first has a
substantially rectangular perimetric section corresponding to the
form to be taken by the friction portion while the second has a
substantially rectangular perimetric section corresponding to the
form to be taken by the support portion. The aperture has a depth
of about 8 cm and, in correspondence to the first section, a
surface area of around 145 cm.sup.2.
[0290] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the mesh reinforcement body described above.
The quantity of mixture is defined in function of the final
thickness of the brake pad, taking into account that following
pressing there is a volume reduction of about 2/3. After
positioning the plate appropriately, pressing is carried out by
activating the punch.
[0291] The temperature inside the mould is maintained around
130.degree. C. The maximum pressure applied during pressing is
around 450 Kg/cm.sup.2. Three consecutive cycles of application and
release of force are envisaged, each lasting about 30 seconds (15
seconds of application and 15 seconds of release). There follows a
final step of continuous application of force (without release) for
approximately 210 seconds. The overall pressing step requires a
period of approximately 5 minutes.
[0292] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
450.degree. C. at a velocity of approximately 5.degree. C./min and
kept at 450.degree. C. for approximately 4 hours and 30
minutes.
[0293] The brake pad thus obtained has a thickness of 16.40 mm
(including the thickness of the reinforcement which is about 1 mm)
and a total weight of around 760 grams, of which 480 grams is the
weight of the friction portion in ceramic matrix material and the
remaining 280 grams of the reinforcement element and the part of
the friction material that has filled the lightening apertures.
[0294] A traditional brake pad of the same form and functionality
weighs around 1.180 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 35.6%.
EXAMPLE 9
[0295] Mix 780 grams of cyclopentasiloxane resin Wacker-Belsil.RTM.
RG100 and 20 grams of powdered zinc acetylacetonate in a horizontal
blade mixer for approximately 2 minutes. Then add 1.200 grams of
powdered SiC class FEPA F40 (average diameter 438 .mu.m) and 1.300
grams of powdered SiC class FEPA F240 (average diameter d.sub.50
44.5 .mu.m). Continue by adding 1.500 grams of brass in powder,
2.100 grams of steel wool, 1.000 grams of silicium in powder, 1.200
grams of graphite in powder and lastly 900 grams of tin sulphide in
powder. The second step of mixing is protracted for approximately 4
minutes.
[0296] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 12% powdered SiC
F40; 13% powdered SiC F240; 21% steel wool; 15% brass in powder;
10% silicium in powder; 12% graphite in powder; 9% tin sulphide in
powder; 7.8% siliconic resin; 0.2% zinc acetylacetonate.
[0297] The brass and silicium powders have an average diameter of
approximately 200 .mu.m and approximately 45 .mu.m respectively.
The steel wool has an average diameter of approximately 80 .mu.m
and an average length of approximately 0.8 mm. The graphite and tin
sulphide powders have an average diameter of approximately 750
.mu.m and approximately 90 .mu.m respectively.
[0298] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the sesquisiloxanic resin.
[0299] In greater detail, a plate (or matrix) is used, with a
double section through-going aperture: the first has a
substantially rectangular perimetric section corresponding to the
form to be taken by the friction portion while the second has a
substantially rectangular perimetric section corresponding to the
form to be taken by the support portion. The aperture has a depth
of about 8 cm and, in correspondence to the first section, a
surface area of around 145 cm.sup.2.
[0300] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The quantity of mixture is defined in function of the
final thickness of the brake pad, taking into account that
following pressing there is a volume reduction of about 2/3. The
aperture is then filled with the mixture and the upper end closed
with the special closure element with which the pressing device is
provided.
[0301] The temperature inside the mould is maintained around
130.degree. C. The maximum pressure applied during pressing is
around 450 Kg/cm.sup.2. Three consecutive cycles of application and
release of force are envisaged, each lasting about 30 seconds (15
seconds of application and 15 seconds of release). There follows a
final step of continuous application of force (without release) for
approximately 210 seconds. The overall pressing step requires a
period of approximately 5 minutes.
[0302] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
450.degree. C. at a velocity of approximately 5.degree. C./min and
kept at 450.degree. C. for approximately 4 hours and 30
minutes.
[0303] The brake pad made entirely in ceramic matrix material
lastly undergoes a finishing work process aimed at reducing
thickness in function of the brake pad's end use.
[0304] The brake pad thus obtained has a thickness of 16.4 mm
(including the thickness of the reinforcement which is about 1 mm)
and a total weight of around 720 grams, of which 480 grams is the
weight of the friction portion and the remaining 240 grams of the
support portion.
[0305] A traditional brake pad of the same form and functionality
weighs around 1.180 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 39%.
EXAMPLE 10
[0306] Mix 780 grams of polymethyl-sesquisiloxane resin
(CH.sub.3-SiO.sub.3/2).sub.n in Wacker-Belsil.RTM. PMS MK Powder
(softening interval 50-60.degree. C.) and 20 grams of powdered zinc
acetylacetonate in a horizontal blade mixer for approximately 2
minutes. Then add 1.200 grams of powdered SiC class FEPA F46
(average diameter 370 .mu.m) and 1.300 grams of powdered SiC class
FEPA F280 (average diameter 36.5 .mu.m). Continue by adding 1.800
grams of copper in powder, 2.700 grams of steel wool, 1.000 grams
of silicium in powder and lastly 1.200 grams of graphite in powder.
The second step of mixing is protracted for approximately 4
minutes.
[0307] The mixture's overall composition is as follows (percentages
expressed in weight with regard to the mixture): 12% of powdered
SiC F46; 13% powdered SiC F280; 18% copper in powder; 27% steel
wool; 10% silicium in powder; 12% graphite in powder; 7.8%
sesquisiloxane resin; 0.2% zinc acetylacetonate.
[0308] The copper and silicium powders have an average diameter of
approximately 150 .mu.m and approximately 40 .mu.m respectively.
The steel wool has an average diameter of approximately 50 .mu.m
and an average length of approximately 0.4 mm. The graphite powder
has an average diameter of approximately 300 .mu.m.
[0309] A portion of the mixture thus obtained then undergoes a
hot-pressing step in a vertical press in order to obtain a
preformed body (green body), as well as the high reticulation of
the sesquisiloxanic resin.
[0310] The mixture is co-pressed with a lightened steel plate
consisting of a perimetric frame of the type illustrated in FIG. 3.
The frame is around 5.5 mm thick and delimits a single central
lightening aperture.
[0311] In greater detail, a plate (or matrix) is used, with a
through-going aperture of substantially rectangular perimetric
section corresponding to the form to be taken by the body in
ceramic matrix material. The aperture has a surface area of around
145 cm.sup.2 and a depth of about 8 cm.
[0312] The operation begins by blocking the lower end of the
through aperture, using the head of the punch with which the press
is provided. The aperture is then filled with the mixture and the
upper end closed with the lightened steel plate described above and
another closure element with which the pressing system is provided.
The quantity of mixture is defined in function of the final
thickness of the brake pad, taking into account that following
pressing there is a volume reduction of about 2/3. After
positioning the plate appropriately, pressing is carried out by
activating the punch.
[0313] The temperature inside the mould is maintained around
120.degree. C. The maximum pressure applied during pressing is
around 300 Kg/cm.sup.2. Three consecutive cycles of application and
release of force are envisaged, each lasting about 30 seconds (15
seconds of application and 15 seconds of release). There follows a
final step of continuous application of force (without release) for
approximately 90 seconds. The overall pressing step requires a
period of approximately 3 minutes.
[0314] There follows a step of pyrolysis in an isothermal kiln with
nitrogen flow of approximately 0.2 m.sup.3/h. The preformed body is
heated from ambient temperature (25.degree. C.) to approximately
500.degree. C. at a velocity of approximately 5.degree. C./min and
kept at 500.degree. C. for approximately 4 hours.
[0315] The friction portion in ceramic matrix material lastly
undergoes a finishing work process aimed at reducing thickness in
function of the brake pad's end use.
[0316] The brake pad thus obtained has a thickness of 16.4 mm
(including the thickness of the frame which is about 5.5 mm) and a
total weight of around 820 grams, of which 480 grams is the weight
of the friction portion in ceramic matrix material and the
remaining 340 grams of the frame and the part of friction material
filling the single central lightening aperture.
[0317] A traditional brake pad of the same form and functionality
weighs around 1.180 grams. The brake pad in accordance with the
invention therefore offers a weight reduction of around 30.5%.
[0318] On completion of the pressing step all the ceramic matrix
materials obtained following examples 1 to 3 and 4 to 6 above
demonstrated such excellent consistency as to facilitate the
achievement of good details (e.g. sharp edges of the brake pad) and
manipulation without particular difficulties. On completion of the
pyrolysis step the materials evinced good properties of mechanical
resistance (mechanical resistance module between 12 and 18 MPa;
elastic module between 5 and 10 GPa). The average density of the
materials was between 2.9 and 3.2 g/cm.sup.3. The average degree of
ceramisation was evaluated at approximately 70%.
[0319] Braking tests were carried out on the brake brake pads made
according to the invention with view to evaluating performances in
terms of friction coefficient, of coefficient stability in function
of the number of brake applications and of wear resistance.
[0320] The tests consisted in subjecting the samples to series of
50 braking operations.
[0321] The tests were carried out using braking systems provided
with discs in both cast iron and composite ceramic material
(CCM).
[0322] The tests showed no important differences in behaviour
between the application with cast iron discs and the application
with discs in CCM.
[0323] The tests revealed overall an average friction coefficient
of approximately 0.45 from the fifth to the thirtieth application
of the brakes. The value is fairly variable, with a minimum of
approximately 0.42 and a maximum of approximately 0.48. After the
thirtieth application of the brakes the friction coefficient
decreased slightly, settling at an average value of approximately
0.42. For each application of the brakes there was average wear of
approximately 0.005 mm.
[0324] The graph in FIG. 16 (number of brake application in
abscissa and friction coefficient value in ordinate) regards tests
carried out on a system with cast iron disc and a brake pad whose
friction component is in the ceramic matrix material of Example 1
above.
[0325] This invention therefore considerably reduces the weight of
brake pads for braking systems, in particular for disc brake
systems, with at least the friction portion in ceramic matrix
material, without compromising mechanical resistance.
[0326] This invention therefore considerably reduces working time
for the production of a friction component in ceramic matrix
material: from an average overall time of approximately 60-80 hours
(without considering assembly with the metal support) to an average
time of approximately 8-12 hours.
[0327] The ceramic matrix friction material made with the method
proposed in the invention offers performances, in terms of friction
coefficient and wear resistance, that are at least equivalent if
not superior to those of traditional ceramic matrix friction
materials. The friction coefficient found in the invention
materials is in fact on average 0.42-0.45 as against the values of
traditional materials, which are approximately 0.35-0.4.
[0328] Analogous considerations are valid with regard to wear
resistance. In the invention materials, average wear values are
approximately 0.005 mm/brake application, as against the values of
traditional materials that are approximately 0.015-0.020.
[0329] Braking tests further evidenced that the brake pads in
accordance with the various forms of implementing this invention
have appropriate resistance to the mechanical stresses generated by
the braking system actuators and the transmission of braking
power.
[0330] The method according to the invention moreover permits
simplification of brake pad and metal support plate production by
cutting out the specific step of final assembly of friction
component in ceramic matrix material and metal support plate.
[0331] Thus conceived, the invention has achieved its initial
goals.
[0332] Obviously in its practical implementation it may take on
forms and configurations different from what is illustrated above,
but without for this reason being excluded from the present context
of protection.
[0333] Furthermore, all the details may be replaced by technically
equivalent elements, and the sizes, forms and materials employed
may be substituted in accordance with necessities.
* * * * *