Note: Descriptions are shown in the official language in which they were submitted.
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Ml~lUKE COMPOSITION FOR FRICTION MATERIAL
D~CRIPTION
BACKGROUND OF THE INVENTION
1. F;eld of the ;nvent;on
The present invention relates to the composition of
a mixture for friction material and more specifically to
a mixture for brake material suitable to be applied in
the field of brake materials for light and heavy
vehicles. An object of the present invention is to
provide a mixture of this kind that contains no
substances that are toxic or harmful to the health.
2. Description of The Pr;or ~rt
It is known that brake material, more commonly known
as friction material, is made up of a composition of
materials comprising a base structure of brake material
and also chemical additives typical for the field of use
of the brake material itself.
The fields of use may be divided into three sectors:
a. Low load field of use: this is the field generally
comprising light vehicles such as mopeds, cars, etc. in
which the characteristics required of the mixture are
those of having a high friction coefficient, as short
stopping distances or times are required. The heat
developed over a short time dissipates in an equally
short time.
b. Medium load field of use: this field includes uses
of medium severity such as brakes for industrial
machinery, brakes for cranes, etc., in which a higher
temperature resistance and a lower friction coefficient
is required compared to the low load field mentioned
above; in fact in this case the braking loads involved
are higher and the stopping times are longer.
c. High or serious load field of use: this field
includes the use of serious loads such as trains,
military armoured vehicles, speed brakes for cranes, etc.
in which a high temperature resistance is required due to
the large amount of heat developed, along with a low
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friction coefficient because short braking times and
distances are not required.
In any case in all these fields of use, the mixture
used according to the prior art contains as basic
materials, although in variable proportions, asbestos,
lead and zinc, which are notorious environmental
pollutants and constitute a health risk.
It is also known that the chemical and physical
characteristics of these braking materials containing
asbestos do not give a satisfactory response to the
phenomenon known as "FADE", which consists in a fall in
the friction coefficient level due to the increase in
temperature and the failure to recover the original level
of said coefficient in time for the next braking
operation.
WO-A-92/11337 describes a composition for friction
materials comprising at least a lubricant, a titanium
compound and either zirconium metal or a zirconium
compound. Optionally a resin can be included. The resin
is identified as IOTA lllSX and/or lllH. Other optional
components are baryta and talcum, oxide of black iron,
copper sulphite', calcium carbonate, zinc, aluminium.
SUMMARY OF THE INVENTION
In view of the problems illustrated above, the
present invention has the object of providing a mixture
composition for friction material that does not have
among its component materials asbestos, lead and zinc, so
that it does not cause environmental pollution and above
all does not damage the health.
Another object, no less important than the above, is
to provide a mixture composition of friction material
that substantially solves the problems of "FADE", and the
materials of which do not crystallise during working,
even in critical conditions such as high speeds or heavy
; 35 loads.
~J\
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An object of the present invention is a mixture
composition for friction material comprising, in
percentage by weight with reference to said mixture:
from 24~ to 32~ of a base alloy including (in~ percentage by weight with reference to said alloy):
from 25~ to 35~ of zirconium oxide ZrO2;
from 30~ to 40~ of titanium oxide TiO2;
~."~,0~ S~
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from 25~ to 35~ of a solid lubricant for
friction material formed of a mixture of graphite and
molybdenum disulphide;
from 21~ to 24~ of a mixture of phenolic resins in
powder form, which polymerise at between 155~ and 160~,
including approximately 30~ in weight, with respect to
the weight of said mixture, of a friction powder;
from 11~ to 15~ of copper sulphide;
from 7.5~ to 9.5~ of baryta or barite;
from 21~ to 28~ of silver or amorphous graphite; and
from 3.5~ to 4.5~ of nitrylic type rubber in power
form, heat resistant and with a granulometry of between
200~m and 300~m.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described in
greater detail with the addition of examples that clarify
and illustrate further advantages offered by the present
invention.
According to the present invention the mixture
composition for friction material is made up of a base
alloy and additive materials.
The base alloy comprises, with reference to the
weight of the alloy itself, in percentage by weight:
zirconium, present as a dioxide, between 25~ and
35~. This material is a temperature stabiliser and at
high speed allows the friction coefficient to increase;
titanium, present as a dioxide, between 30~ and 40~.
This material greatly reduces wear on the braking surface
and is an excellent temperature stabiliser at low and
high speed;
a solid lubricant present in the alloy in a
percentage by weight of between 25~ and 35~, made up of
a mixture if graphite and molybdenum sulphide. This
mixture is of fundamental importance to give effective
lubrication at high speeds and to stabilise the friction
coefficient.
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A commercially available solid lubricant material of
this type is known by the trade name of "Lubolidn.
The base alloy described above replaces in the
present invention the braking alloys known from the state
S of the art, based on asbestos, lead and zinc.
The base alloy according to the invention is used in
an amount of between 24~o and 32~ by weight with respect
to the total weight of the mixture, together with a
mixture of phenolic resins and other additives.
The phenolic resins in this mixture are resins in
powder form that polymerise at between 15S~C and 160~C
and serve, along with a usual friction powder, to bind
the components in the base alloy together to form the
braking material.
The amount of phenolic resins and friction powder
used in the mixture according to the present invention is
between 21~ and 24~ by weight with respect to the total
weight of the mixture.
The friction powder forms approximately 30~ of the
mixture of resins and powder. As phenolic resins, a
resin may be used that forms an excellent binding agent
for the metallic ingredients in the powders.
An indication of a resin of this type is a phenolic
resin J 1506 H produced by Massara, Bollate (MI), Italy,
which has a viscosity at 25~C of 200/220x10-6 m2/sec, a
pellet flow of 30/50 m/m at 135~C~ a nitrogen content of
3.4/4.0~, a specific weight of approximately 1.26~ a
gelling time at 150~C of 1 minute, a moulding temperature
of 150-160~C at a pressure of 120/200 kg/cm2.
It is also possible to use a phenolic resin in
powder to bind the components in fibre form. A resin of
this type is the resin J 1109 I~ produced by Massara,
Bollate (MI), Italy.
This resin has a viscosity at 25~C of 54/72x10-6
m2/sec, a h~ m; n content of 7.3 ~ 7.9~r a pellet flow at
150~C of approximately 60 m/m, a gelling time at 150~C of
approximately 2 and 3/4 minutes, a specific weight of
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approximately 1.42, a vulcanisation temperature of 150-
160~C at a pressure of 120-200 kg/cm2.
A preferred ratio for use of these two resins J 1506
H and J 1109 H is approximately 1:2.
As a friction powder it is possible to use a powder
manufactured by Massara, Bollate (MI), Italy under the
trade name J 4106 D, which has a suitable granulometry, a
maximum solubility in acetone of 20~ and a specific
weight of approximately 1.12.
The friction powder is used as a reagent integrating
the base alloy to ensure optimum distribution of the
~ braking properties .and to guarantee .that the friction
coefficient for braking is restored in sufficient time.
The mixture also contains, as stabilising additives,
the following:
copper, in the for~ of a sulphide, in a percentage
by weight of between.11~ and 15~ and, for preference,
between 12~ and 13% with respect to the weight of the
mixture. This is used to control the temperature, as it
ensures a uniform and progressive decrease of the
temperature developed during operation, and, in
particular, at high speeds;
baryta (or barite), in a percentage by weight of
between 7.5~ and 9.5~ with respect to the total weight of
the mixture. This is used in the mixture as a "charge"
to reduce wear of the friction material and noise during
braking;
silver (or amorphous) graphite, in a percentage by
weight of between 21~ and 28~ and, for preference,
between 24~ and 25~ with respect to the total weight of
the mixture. This is used in combination with the baryta
to develop and support the characteristics of the latter;
nitrylic type rubber in power form, heat resistant
and preferably with a granulometry of between 200~m and
300~m, in a percentage by weight of between 3.5~ and 4.5~
and, for preference, 4.0~ with respect to the weight of
the mixture. This is used to give the friction material
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the necessary softness and elasticity, greatly reducing
noise. The proportions of rubber indicated above with
respect to the other components is sufficient to ensure
that the "FADE" effect is not produced.
The composition as described in precedence is
particularly suited for applical~ion in the field of c
medium loads.
For application in the field of low loads, which
require a high friction coefficient, the following are
added to the composition as illustrated above:
aluminium in powder form, in a percentage by weight
with respect to the total weight of the mixture of
between 4.0~ and 6.0~. Addition of this material has a
purely electromagnetic function, breaking the magnetic
waves created during braking. Furthermore, this material
does not attack the braking surface;
brass in flakes, in a percentage by weight of
between 5~ and 7~ and, for preference, 6.0~ with respect
to the total weight of the mixture. The addition of this
material ensures a perfect mechanical seal between the
component materials and, furthermore, distributes the
working temperature in a uniform manner over the whole
braking surface.
Should application of the mixture composition as
described above be in the field of heavy or severe loads,
the following materials should be added to said
composition:
iron wool, for preference with fibres of between 2mm
and 3mm in length, in a percentage by weight of between
17.0~ and 20.0~ with respect to the total weight of the
mixture and, for preference, in a percentage by weight of
between 17.5~ and 19.0~. This is used to give the
mixture the necessary mechanical strength and seal of all
the component materials in the mixture;
corundum (or emery powder), in a percentage by
weight of between 0.09~ and 0.15~ and, for preference,
between 0.10~ and 0.12~ with respect to the total weight
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of the mixture. This is used to increase the friction
coefficient. It should be noted that an excessive amount
causes increased noise during operation, as well as
scratches on the braking surface.
S To obtain the braking material, the base alloy
comprising zirconium, titanium and the "Lubolid/' type
solid lubricant is mixed together with the synthetic
graphite, the special phenolic resins and the other
components of the composition in the required
proportions. The mixture is then vulcanised in special
oleodynamic hot presses ensuring continuous monitoring of
correct and constant vulcanisation, polymerisation and
temperature control.
Before being mixed, all the components are carefully
checked and made to undergo tests to ensure that the
resulting proportions will be correct and to guarantee
the total absence of humidity.
During mixing it is of essential importance that the
presence of any humidity be checked as, for example, a
humidity level of over 60~ might seriously alter the
chemical characteristics of the working components. To
avoid this phenomenon, a component with a high
dehydration factor is added to the mixture, in a
proportion suited to react with the other components. In
effect during operation at a temperature of 180~ in the
presence of water the hydrogen molecules can cause small
explosions, which are the cause of damage to the braked
surface.
This damage is invisible to the naked eye, but
causes cracks and splits in the brake surface during
continued use.
In the composition described above, according to the
present invention, the materials are combined in such a
way as to ensure that they do not crystallise, even under
heavy working conditions, thus improving efficiency and
maintaining their characteristics intact over a period of
time.
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Furthermore, given the presence of diamagnetic
materials, the negative ef~ects of magnetisation of the
braking surface, which are seen in the mixture
compositions of friction materials according to the prior
S art and which result in blockage of one surface on the
other during operation, are avoided.
Another advantage of the present invention is the
elasticity of the braking materials obtained in this way,
which is such that it allows perfect the braking element
to adapt perfectly to the braking surface. This makes it
possible to distribute the braking action homogeneously
over the whole surface area, opti.mising effectiveness and
also obtaining a homogeneous distribution of the heat
generated, thus avoiding any excessive local
concentration of heat that might result in cracking and
splitting of the mixture of materials.
Another advantage lies in the fact that, unlike the
braking materials according to the prior art, which are
subject to corrosion because of the high percentages of
metallic materials they contain, thus resulting in
serious damage to the braking surfaces, as well as high
noise levels during operation and sparking, according to
the present invention these problems are solved, as the
materials used to form the mixture are not subject to
corrosion.
A further advantage lies in the fact that according
to the invention the mixture obtained has a specific
weight reduced by 25~ when compared with cast iron
brakes, and by 65~ when compared with synthetic ones.
This gives greater manoeuvrability during installation
and replacement operations.
A further advantage lies in the fact that the
mixture according to the invention is subject to less
wear during operation that the mixtures according to the
prior art.
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Examples will now be given of tests carried out on
the mixture for friction materials according to the
invention.
~ The mixtures used in the tests given below are
mixtures for use in medium load applications, in the
sense defined in the above description.
~xample 1
Procedure for tests carried out on "Ranzicunan test
bench
A sample of the friction material under ~m; n~tion
was made to operate against a rotating metal drum,
pressing it against said drum at a pressure varying
during the course of the test, so as to maintain the
braking moment and the final test: temperature constant.
The speed of rotation of the drum was adjustable in order
to enable tests to be carried out at different
temperatures.
Drum characteristics:
Material: cast iron, with the following typical
20 chemical composition:
Ca = 3.25
Si = 2.lO
Mn = 1.3
Cr = 0.20-0.40
Mo = 0.20-0.40
P = 0.10
S = 0.25
Brinnell Hardness: HB 197-225
Structure: perlytic, uniformly distributed layers of
graphite, no cementite.
Size: 0149.50 mm
State of surface: Ra = 0.4-0.#
Test characteristics:
Working surface: 6 cm (adapted to suit the surface
of the drum)
Initial thickness: 7.60 mm
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The test was made up of three periods of operation,
alternating with cooling periods. For each period the
machine operates for a time enough to create a friction
level of 166,000 kgm, so as to give a total operation
S over the three periods of 498,000 kgm. As the braking
moment of the machine is known, and is 100 kgm., it is
possible to calculate the duration of each test period.
Results of the test:
PERIOD DURATION SPEED min.f av.f max.f
TEMP.
minutes (km/h) (~C)
I 92 8 0.32 0.38 0.41 190
II 60 12.5 0.35 0.39 0.40 240
III 42 18 0.36 0.38 0.39 290
Duration transient equivalent to 5,000 turns of the
machine, due to test-contratest adaptation. The results
were obtained after this transient. The average friction
coefficient (av.f) refers to the duration of the test and
not to an average of the values (max.f) and (min.f),
which are instantaneous ~alues.
Thickness of the test element at the end of test:
7.30 mm
Wear on test element: 0.030 mm
Specific wear: U = 12 x S = 12 x 0.030 = 0.36
cm3/106kgm (valid relat~ion on the basis of the size of
the test element and the test characteristics)
State of test element surface: very smooth, absence
of cracks or scratches
Final diameter of drum: 149.50 mm
Wear on drum: practically unappreciable
State of the surface of drum: very smooth, absence
of cracks or scratches
Friction coefficie~t with constant progress over
long periods
Noise level: very low
~xa~le 2
Method used for tests ~ith Ranzi L.R.C. machine
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Machine characteristics:
n = 7200 rpm (92 km/h) Operating speed
j = 0.250 kg.cm/sec Flywheel moment of inertia
K = 0.1 mm/turn Scale constant
S R = 1:8=0.125 Leverage ratio
Mn = 1.65 kg.cm Machine internal moment of
inertia
Mt = 1130/l Braking moment, dependent on the
stopping space "l" given in the
test
Test element characteristics:
r = 1.35 cm Average radius of braking track
A = 7 cm Working surface
S = 7.00 mm Initial thickness of test element
Four series of five braking operations each were
carried out; interval between each operation
approximately 20 sec., with a pressure adjustable by
application of an applied weight (P) in kg and the
specific weight (p) in kg/cm is as follows:
P = 0.875 x p
By calculating the pressure, using the surface area
i --
(A) of the test element, the force (F) acting thereon is
obtained:
F = p x A
For each single braking operation the test machine picks
up the temperature by means of a thermo-couple inserted
in the contratest element, as well as the stopping
distances.
The friction moment of the hraking material is the
following:
Mr = Mt - Mn = 1130 - Mn
= lm
(lm being the average s~opping distance for a series of
braking operations).
The average friction coefficient is the following:
fm = Mr/F x r
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Test results:
p p F lm av.f Max.T
(kg) (kg/cm2) (ka) (mm) (~C)
7 8 56 45 0.35 150
8 9.1g 64 39.0 0.37 200 ~ .
9 10.28 72 34 0.39 230
10 11.43 80 31 0.39 250
State of the test element surface: very smooth, without
cracks or splits.
State of the controtest element surface: very smooth,
. without cracks or splits.
Thickness of the test element after testing: 7.00 mm
Wear on test element: not appreciable
Specific wear: U = A/EK x d/N x 10 x d/N = o.oo
in which:
A = working surface
EK = cynetic energy of flywheel
d = reduction in thickness in hundredths of mm
20 N = number of braking operations carried out
Wear in contratest element: not appreciable
Sparking: absent
Smoke: absent.
Conclus1ons
From example 1 (constant moment) it is possible to
see the variation in friction coefficient with
temperature.
The variation in average friction coefficient with
pressure can be seen from example 2. As can be clearly
seen, the average friction coefficient initially tends to
increase as the specific pressure increases, but then
stabilises at a value of around 0.39. From a comparative
analysis of the values in the two tests it is possible to
deduce that the friction coefficient increases within a
fairly restricted range o~ values with speed, remaining
extremely constant at low 5peeds.
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From the results of the tests it is possible to
deduce that the braking materials object of the present
invention are fully capable of providing all the
-advantages indicated.
The present invention is not restricted to the
embodiment described herein, but comprises all
alternative versions thereof, obtained using equivalent
technical methods, included in the scope of the following
claims.
