U.S. patent application number 10/379756 was filed with the patent office on 2003-09-11 for ceramic materials for friction linings.
Invention is credited to Bauer, Moritz, Huener, Ronald, Winkelmann, Peter.
Application Number | 20030167969 10/379756 |
Document ID | / |
Family ID | 27740696 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030167969 |
Kind Code |
A1 |
Huener, Ronald ; et
al. |
September 11, 2003 |
Ceramic materials for friction linings
Abstract
Ceramic friction linings comprising a material consisting
essentially of metal oxides which are present in the form of a
sintered ceramic or in the form of ceramic particles bound by
carbon and/or carbides, processes for producing them and their use
in combination with ceramic friction bodies, in particular for
high-performance brakes
Inventors: |
Huener, Ronald; (Baar,
DE) ; Bauer, Moritz; (Augsburg, DE) ;
Winkelmann, Peter; (Thierhaupten, DE) |
Correspondence
Address: |
ProPat, L.L.C.
2912 Crosby Road
Charlotte
NC
28211-2815
US
|
Family ID: |
27740696 |
Appl. No.: |
10/379756 |
Filed: |
March 5, 2003 |
Current U.S.
Class: |
106/36 ; 501/88;
501/99; 508/100 |
Current CPC
Class: |
C04B 2235/3826 20130101;
F16D 69/025 20130101; C04B 35/76 20130101; C04B 2235/48 20130101;
C04B 2235/3262 20130101; C04B 2235/407 20130101; C04B 2235/446
20130101; C04B 35/04 20130101; C04B 2235/3445 20130101; C04B 35/195
20130101; C04B 2235/3839 20130101; C04B 2235/3206 20130101; F16D
69/026 20130101; F16D 2200/0043 20130101; C04B 2235/3294 20130101;
C04B 35/80 20130101; C04B 2235/386 20130101; C04B 35/013 20130101;
C04B 2235/3281 20130101; C04B 2235/3293 20130101; C04B 2235/3817
20130101; C04B 2235/3843 20130101; C04B 2235/5248 20130101; C04B
2235/80 20130101 |
Class at
Publication: |
106/36 ; 508/100;
501/88; 501/99 |
International
Class: |
C09K 003/14; F16D
001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2002 |
DE |
102 10 175.2 |
Claims
1. A ceramic friction lining comprising a material consisting
essentially of metal oxides which are present in the form of a
sintered ceramic or in the form of ceramic particles bound by
carbon and/or carbides, wherein the material has a mass fraction of
at least 50% of metal oxides.
2. A ceramic friction lining as claimed in claim 1, wherein the
metal oxides are selected from among oxides of at least one of the
metals of the group consisting of Ti, Zr, Al, B, Si, Ca and Mg.
3. A ceramic friction lining as claimed in claim 1, wherein the
crystal structure of the metal oxides is a layer lattice.
4. A ceramic friction lining as claimed in claim 1, wherein the
metal oxides are selected from among magnesium aluminosilicates,
talc and magnesium oxide.
5. A ceramic friction lining as claimed in claim 1 which has a mass
fraction of at least 50% of magnesium oxide.
6. A ceramic friction lining as claimed in claim 5, wherein the
magnesium oxide is bound by carbon or carbides.
7. A ceramic friction lining as claimed in claim 1 which comprises
carbides of metals of the group consisting of Si, Ti, Fe, Ni and Cr
either individually or in admixture with one another.
8. A ceramic friction lining as claimed in claim 7 in which silicon
carbide is present.
9. A ceramic friction lining as claimed in claim 1 in which further
additives selected from among inorganic binders, substances which
modify the coefficient of friction, friction promoters and
lubricants are present, with the sum of the mass fractions of the
additives in the materials being below 50%.
10. A ceramic friction lining as claimed in claim 1, wherein the
materials comprise heat-resistant fibers or whiskers in a volume
fraction of up to 35%.
11. A ceramic friction lining as claimed in claim 10, wherein the
fibers are selected from among aramid fibers, acrylic fibers,
cellulose fibers, carbon fibers and metal fibers or steel, copper
or its alloys.
12. A ceramic friction lining as claimed in claim 1, wherein the
materials have a mass fraction of from 10 to 30% of carbon
fibers.
13. A ceramic friction lining as claimed in claim 9, wherein the
substances which modify the coefficient of friction are selected
from among copper, tin, antimony, manganese(II) sulfide, antimony
trioxide and tin(II) oxide.
14. A ceramic friction lining as claimed in claim 9, wherein the
friction promoters are selected from among aluminum oxide,
zirconium dioxide, zircon (ZrSiO.sub.4), silicon carbide and
silicon dioxide.
15. A ceramic friction lining as claimed in claim 9, wherein the
lubricants are selected from among molybdenum disulfide, graphite
and boron nitride.
16. A ceramic friction lining as claimed in claim 1 which contains
additions of carbon, copper or tin.
17. A friction system capable of withstanding high temperatures
comprising friction linings as claimed in claim 1 and friction
bodies made of ceramic materials.
18. A friction system as claimed in claim 17, wherein the friction
bodies comprise C/SiC or C/C--SiC materials.
19. A method of use of a friction system as claimed in claim 17 as
a brake system, comprising combining disks with a friction lining
of claim 1 with friction bodies made of ceramic materials.
20. The method of use of claim 19, wherein the friction bodies
comprise C/SiC or C/C--SiC materials.
21. A method of use of a friction system as claimed in claim 17 as
a clutch system, comprising combining disks with a friction lining
of claim 1 with friction bodies made of ceramic materials.
22. The method of use of claim 21, wherein the friction bodies
comprise C/SiC or C/C--SiC materials.
23. The method of use as claimed in claim 19 in rail vehicles,
aircraft or motor vehicles.
24. The method of use as claimed in claim 21 in motor vehicles.
25. A process for producing a friction lining as claimed in claim
1, wherein a shapable mixture of pulverulent metal oxides,
additives and thermally curing organic binders is produced in a
first step, the mixture is brought into the desired shape by
pressing in a second step and the shaped mixture is cured with the
aid of the thermally curing organic binders in a third step, and
the green body produced in this way is carbonized in a fourth step
at temperatures above 650.degree. C. and in the absence of
atmospheric oxygen.
26. The process as claimed in claim 25, wherein metals selected
from the group consisting of Si, Ti, Fe, Ni and Cr are added to the
shapable mixture and form carbides in the fourth step with the
carbon produced in the carbonization.
27. The process as claimed in claim 25, wherein the metals are used
in such an amount that the sum of the mass fractions of carbon and
carbides in the material forming the friction lining is in the
range from 5 to 50%.
28. A process for producing a friction lining as claimed in claim
1, wherein a shapable mixture of pulverulent metal oxides,
additives and, if desired, organic plasticizers is produced in a
first step, the mixture is brought into the desired shape by
pressing in a second step and the shaped mixture is sintered in a
third step at temperatures of from about 1000.degree. C. to about
1500.degree. C.
Description
FIELD OF THE INVENTION
[0001] The invention relates to ceramic materials for friction
linings.
BACKGROUND OF THE INVENTION
[0002] In the search for suitable brake linings for
high-performance brake systems using ceramic brake disks, the
conventional organically bonded brake lining compositions reach
their limits because of the high temperatures and high wear rates
which occur. This becomes particularly clear in the case of
friction pairings in which C/SiC or C/C--SiC is used as brake disk
material. These materials are a ceramic which consists essentially
of silicon carbide and secondary phases comprising silicon and
carbon and is reinforced with carbon fibers, for example as
described in DE-A 197 10 105. These materials are, as is known,
produced by infiltration of porous C/C intermediate bodies (carbon
reinforced with carbon fibers) with liquid silicon and reaction of
at least part of the carbon with this to form silicon carbide.
Temperatures of 1000.degree. C. and more occur at the friction
surface during braking in the case of such brake disks, which can
result in decomposition of organically bonded brake linings.
[0003] In DE-A 197 27 587, the problem of the high operating
temperatures during braking in a combination of brake disks
comprising a short-fiber-reinforced C/SiC ceramic and a brake
lining having an organically bonded matrix is solved by the brake
disk being designed so that its thermal conductivity perpendicular
to the disk surface is at least 20 W/m-K. Due to this high thermal
conductivity, it is possible to use conventional, organically
bonded brake linings in conjunction with the ceramic brake disk.
However, the operating lives which are achieved for the linings are
not satisfactory.
[0004] DE-A 197 27 586 discloses a combination of a C/SiC brake
disk and a corresponding C/SiC brake lining, with the C/C
intermediate body of the brake lining having a higher density
(lower porosity) than the surface regions of the C/C intermediate
body of the brake disk. This leads to a C/SiC having a relatively
low strength being formed after liquid silicization of the C/C
intermediate body of the brake lining because of its relatively low
silicon carbide content. However, the overall frictional and wear
behavior, in particular the comfort characteristics, is not yet
satisfactory: constant friction values are not obtained, the noise
during braking is too loud and the performance when wet is
unfavorable. DE-A 197 27 585 discloses the combination of a
short-fiber-reinforced C/SiC ceramic brake disk and a brake lining
comprising a sintered metal material or an inorganically bonded
material comprising a ceramic binder phase which is preferably
obtainable by complete or partial pyrolysis of at least one
preceramic polymer and metal particles. Although this brake lining
is able to withstand high temperatures, this system, too, is not
yet satisfactory in respect of the braking behavior. DE-A 107 11
830 describes a process for producing friction linings for
combination with brake disks comprising fiber-reinforced ceramic,
in which a pressed body produced from carbon and metal particles is
sintered.
[0005] It is therefore an object of the invention to provide
friction linings which can be used in combination with friction
bodies or friction disks made of ceramic materials, in particular
C/SiC ceramic, do not decompose even at high temperatures and offer
a constant frictional behavior and good comfort
characteristics.
SUMMARY OF THE INVENTION
[0006] The present invention accordingly provides friction linings
comprising a material consisting essentially of metal oxides which
are present in the form of a sintered ceramic or in the form of
ceramic particles bound by carbon and/or carbides, wherein the mass
fraction of metal oxides in the material is at least 50%.
[0007] The mass fraction of metal oxides in the materials of these
friction linings is preferably at least 60% and in particular at
least 70%. The metal oxides can also be mixed oxides and preferably
comprise at least one oxide of the elements of the group consisting
of Ti, Zr, Al, B, Si, Ca and Mg. Preference is given to metal
oxides which crystallize in layer lattices and have good
tribological properties as a result of this crystalline structure.
They will hereinafter also be referred to as "sheet ceramics".
Preference is given to using magnesium aluminosilicates, talc which
are also referred to as metal oxides, and particularly preferably
magnesium oxide (MgO) as sheet ceramics. In the case of these
preferred materials and the particularly preferred magnesium oxide,
mass fractions of at least 50% of these oxides with the same
preferred ranges are also used in the material of the friction
lining. According to the invention, the friction linings further
comprise additional additives such as inorganic binders, substances
which modify the coefficient of friction, friction promoters or
lubricants, with the sum of the mass fractions of these additives
in the friction lining preferably being below 50%.
[0008] The present invention further provides friction systems
capable of withstanding high temperatures, in particular brake
systems, comprising friction linings whose materials consist,
according to the invention, essentially of metal oxides and brake
disks comprising ceramic materials, in particular C/SiC or C/C--SiC
materials. The friction linings are preferably used in the form of
brake linings for ceramic brake disks, in particular those made of
carbon-fiber-reinforced nonoxide ceramic. Here, the ceramic is
typically stronger and harder than the lining material. The
friction linings of the invention are particularly preferably used
as brake linings for C/SiC brake disks or as friction partners for
clutch bodies or disks made of C/SiC. The material of the friction
linings is particularly advantageous for ceramic counterbodies
having a high SiC content and is particularly well suited to
friction bodies which have a mass fraction of SiC of at least 60%
in the composition of the friction surface.
[0009] The present invention further provides for the use of the
friction linings of the invention in clutch systems and brake
systems for rail vehicles, aircraft and motor vehicles, preferably
in combination with friction disks made of ceramic materials, in
particular friction disks made of C/SiC or C/C--SiC materials.
[0010] If the friction lining is made up essentially of sintered
ceramic, the cohesion of the material is due to oxide-ceramic
bonding during sintering. If instead essentially preformed ceramic
particles are used, bonding within the friction material is
effected, according to the invention, by means of carbon or
carbides which are formed, in particular, during a thermal or
carbonization treatment. Friction linings which are based on
magnesium oxide and are bound by means of carbon or carbides have,
in particular, surprisingly been found to be very effective and
thermally stable. Additions of carbon, copper or tin, preferably in
mass fractions of up to 10%, and inorganic bonding based on
carbonized organic precursors for pyrogenic carbon have a positive
effect on the coefficient of friction, the wear and the mechanical
strength of metal oxide based materials for friction linings. The
mass fractions of carbon and/or carbides in the materials of the
friction linings are at least 5%.
[0011] Magnesium oxide is known as additive in a small amount of up
to 20% in combination with reinforcing fibers which are not
asbestos, inorganic fillers and heat-curable resins for brake
lining compositions from U.S. Pat. No. 5,866,636. In the composite
material of these brake linings, MgO performs the task of removing
deposits on the brake disk and thereby suppressing low-frequency
noise during braking. Relatively high contents of MgO lead to
increased damping of the low-frequency brake noise, while
relatively low contents lead to reduced wear of the friction
partner and to higher resistance to fading. These opposed
requirements result in a desired volume fraction of from 3 to 20%
for the MgO. It is not stated that such lining compositions can be
used together with ceramic brake disks. For the reasons set forth
in the introduction, in particular because of the high operating
temperatures, organically bound lining materials can be readily
used only in particular cases, as described in DE-A 197 27 586.
[0012] However, in combination with friction disks, in particular
brake disks made of ceramic materials, the use of materials having
high mass fractions viz. at least 50%, preferably at least 60% and
particularly preferably at least 70%, of metal oxides, preferably
comprising hard sintered sheet ceramic, in particular MgO, has
surprisingly been found to be particularly advantageous for brake
linings. Thus, both the hardness of these materials and the
associated wear resistance and also the excellent sliding
properties of the sheet ceramics are particularly favorable and
make them suitable for combination with brake disks made of ceramic
materials.
[0013] A further advantage of the use of metal oxides and ceramics
in which they are present as main component of friction materials
in brake linings is their comparatively low thermal conductivity.
Since the heat generated in the contact layer of the friction
pairing on rubbing together has to be kept away from the brake shoe
or caliper but high temperatures around 1000.degree. C. and above
are generated in the case of ceramic brake disks during braking,
the thermal insulation action of the metal oxides is
advantageous.
[0014] The tribological properties of the friction pairing are
influenced essentially by the type of inorganic binder phase of the
friction material. In contrast to conventional organically bound
friction materials, the metal oxides and the further additives are
bound by oxide ceramic bonding or by means of phases of carbon
and/or carbides. The binder phase is thus formed by thermally
stable compounds which are not decomposed at the use temperatures.
The inorganic binder phase is typically formed in the thermal
treatment of the green body of the friction material.
[0015] The present invention further provides a suitable process
for producing the materials for the friction linings.
[0016] In the variant with inorganic binding by means of carbon
and/or carbides, a shapable mixture of pulverulent ceramic or metal
oxides, additives and organic binders is produced in a first step.
The mixture is then, for example, brought into the desired shape by
pressing and cured with the aid of the thermally curable organic
binder. The green body produced in this way is carbonized, i.e.
treated thermally to eliminate the volatile constituents of the
organic components. This is carried out by customary methods,
generally at temperatures above 650.degree. C. and in the absence
of atmospheric oxygen. The organic binders have the task of
strengthening the shaped body and being converted during the
carbonization into carbon or into carbides by further reaction, and
this carbon or these carbides then form(s) the inorganic binder
phase. Preference is therefore given to organic binders which give
a high carbon yield on carbonization, e.g. phenolic resins,
melamine resins, polyimides, pitches, epoxy resins or
polyurethanes. If not only carbon but also carbides are to be
present in the inorganic binder phase, then these are, according to
the invention, preferably formed during the thermal treatment of
the green body from the decomposition products of the organic
binder and additions of carbide-forming metal. The carbide-forming
metals preferably include at least one of the metals from the group
consisting of Si, Ti, Fe, Ni and Cr. Particular preference is given
to an inorganic binder phase of silicon carbide being formed during
the thermal treatment. The thermal treatment is typically carried
out at temperatures of at least 1200.degree. C. The amount of
organic binder and, if applicable, the added metal, used in the
mixture is selected so that the sum of the mass fractions of carbon
and carbides is in the range from 5 to 50% in the friction material
after carbonization or carbide formation. The mass fraction is
preferably at least 10% and particularly preferably at least 15%.
The use of this binder phase has the advantage that the carbon
formed additionally functions as substance which modifies the
coefficient of friction (lowers the coefficient of friction) and
the carbides can function as substances which modify the
coefficient of friction or as friction promoters (substances which
increase the coefficient of friction).
[0017] In the variant with oxide ceramic bonding, a ceramic body is
produced by the shaping and sintering processes customary in the
ceramics industry. The additives to the friction material are
usually added prior to sintering at about 1000.degree. C. up to
about 1500.degree. C., depending on the nature of the metal oxides.
Typical compositions have mass fractions of metal oxides of at
least 50% and preferably at least 70%.
[0018] Although a distinction is formally made between the oxide
ceramic bonding and the bonding by means of carbon or carbides, it
is also possible to realize mixed forms of these two types of
bonding in the same material. This is, for example, the case when
carbon- or carbide-forming substances together with metal oxides
which have a melting point lower than MgO or sinter at temperatures
significantly below the melting point of MgO are added as
additives. The mass fraction of carbon and/or carbides in the
material of the invention is advantageously at least 5%. If
desired, carbon and/or carbides, in particular graphite or silicon
carbide, may be added as additives to the starting mixtures.
[0019] In a further advantageous embodiment of the invention, the
friction linings of the invention contain fibers or whiskers as
additive. They can act as reinforcing component for the material or
as materials which modify the frictional behavior. Use is typically
made of carbon fibers, heat-resistant polymer fibers, whiskers of
metals or compounds such as oxides, borides, carbides or nitrides,
metal fibers or turnings in volume fractions of up to 35%. Carbon
fibers in mass fractions of from 10 to 30% have been found to be
particularly advantageous, since they combine a good reinforcing
action and good tribological properties. Among polymer fibers,
aramid fibers, acrylic fibers and cellulose fibers are particularly
useful. As metal fibers, use is typically made of fibers of steel,
copper or copper alloys.
[0020] In the friction linings of the invention, it is possible to
use further additives, namely substances which modify the
coefficient of friction, e.g. Cu, Sn, Sb, MnS, Sb.sub.2O.sub.3 and
SnO, or lubricants such as MoS.sub.2, graphite and boron nitride or
friction promoters such as Al.sub.2O.sub.3, ZrO.sub.2, ZrSiO.sub.4,
SiC and SiO.sub.2, in each case in small amounts. For the purposes
of the present invention, the expression small amounts means that
the mass fraction of the additive concerned is in each case not
more than 5% of the mass of the friction lining.
* * * * *