BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini
SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX
Composite Friction Materials for Brakes and Clutches
R. Biczó1*, G. Kalácska2, Z. Szakál3, G. Fledrich4
Abstract: As a part of a broad tribological research this paper deals with composite friction materials used in brake
and clutch applications. Lists their main types searching for similarities and differences in manufacturing, takes into
consideration components used for production showing development trends in the past considering material and
construction. Finally it shows a glimpse into present and near future investigation and experiments to answer questions
and solve problems of the field of frictional material science.
Keywords: polymer, composite, frictional material, clutch, brake
1. INTRODUCTION
good wear resistance during operation. They should
possess the ability to resist heat induced deterioration,
impact and centrifugal force during friction. Tribological
performances and mechanical properties of the friction
materials depend on the mentioned components. For
instance fibers play a critical role in determining the
mechanical strength, thermal resistance, and friction and
wear properties of the materials. [11]
Typical components of polymer composite
friction materials for clutches and brakes can be
classified in the following groups: reinforcements,
binders, friction modifiers and fillers. The friction
materials are deformable, their task is to maintain a
sufficiently high and stable friction coefficient and a
Type
Subtype
Linings
Preferred application
mixing
Table 1. Manufacturing steps of brake linings
Brake lining
Disk pad
Blocks
Segments
heavy-duty use
fibrous
fiber,
reinforcement,
modifiers, dry
friction modifiers,
resin
liquid resin, 50 °C
Heating to 90 °C, 60-90 cm
preforming extrusion at 14-28 preform at 3-4
MPa
MPa
drying
2 h, 80 °C
organics: intensive
mixer, semimetallics:
less intensive blender
for organic blocks: as for
segments, for semimetallic
blocks: as for
semimetallic disk pads
pressed into preforms
at room temperature,
28-42 MPa
at 10-17 MPa
preheating
Manufacturing
steps
forming
to 90 °C, 15-30 min
rolling, partial
drying, fiber
aligning in the
tape
sizing
cutting to length,
forming, 150 °C
heat
treatment
grinding
curing: 4-8 h,
180-250 °C
a
hot-pressing, 3- hot pressed 5-15 min
10 min at 140- at 160-180 °C, 28-55
160 °C, cooling MPa
reheated, hotpressed
preforms cut,
bent at 170190°C
curing: 4-8 h
220-280 °C
a
2. OPERATING CHARACTERISTICS
10-30 min, 130-150 °C,
14-21 MPa,
slitting to width, grinding
of internal and external
radii
curing: 4-8 h, 220300 °C
a
curing: 5 h, 180 °C or 6
h, 280 °C
a + drilling, chamfering
gradually dissipates it into the atmosphere. A brake is a
sliding friction couple consisting of a rotor – disk or
drum – connected to the wheel or machine and a stator
on which is mounted the friction material. [7]
A clutch transfers the kinetic energy of a rotating
crankshaft – coupled to a power source – to the
transmission and wheels. Slippage results in the
Requirements of composite friction materials
derives from the operating characteristics of applications
they are used in. It demands brake and clutch friction
materials to be separately dealt from this scenario.
A brake converts the kinetic energy of the moving
vehicle or machine part into heat, absorbs the heat, and
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BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini
SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX
generation of heat, which is absorbed and eventually
dissipated to the atmosphere by the clutch. [7]
Both applications have dry and wet operation types. If
the friction couples are dry, heat is removed by
conduction to the surrounding air and other assembly
Type
Subtype
Preferred application
winding
preforming
mixing
coating
molding
Manufacturing
drying
steps
sizing
weaving
hot-pressing
curing
members. When the application operates in fluid, for
instance oil, this liquid absorbs the heat and maintains
low operating temperatures while trapping the wear
debris. [7]
Table 2. Manufacturing steps of clutch facings
Clutch facing
Fiber reinforced hybrid matrix composite
Sintered cermet
Paper based facing
facing
segments
trucks, heavy offmanual
automatic
road equipment
paper-made
soaked roll of
friction material
taken up onto a
winder
weaving
forming a reel of
wire
curable
ribbons with
preforming
preforms
designated widths
dry:
ingredients based
dry: fillers,
wet: fillers,
fillers,
on desired
modifiers
modifiers
modifiers
properties
strand run
through
premix picks applying adhesive
up viscous
to the core plates
mass, ~160
°C
molding
molding of
of mix
mix around
without
strand or
strands or
wire preforms
wire
cooling and
drying
desired shape
to a
to a specified to a specified
specified
pattern
pattern
pattern
4 min, 150thermal pressure
a
a
180 °C
bonding
a
a
24 h, 210°C
compacting
a
reducing or
neutral
atmosphere at
temperatures
high enough so
that the metallic
ingredients
adhere to each
other
sintering
coining or
recompacting
grinding
a
a
a
a
22
a
BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini
SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX
Fig. 2. Typical clutch facing types (from left to right):
first row: clutch facings [3]; industrial
technical friction materials, clutch segments [3]
second row: Schaeffler woven clutch facings;
Schaeffler woven facing with steel carrier plate
third row: cermet segmented facing with steel
carrier plate by Miba; Schaeffler paper based
friction materials
Fig. 1. Typical brake lining types (from left to right):,
first row: brake linings; molded brake linings;
second row: woven brake linings; roll linings;
third row: disc brake pads; brake shoes;
forth row: friction blocks; brake block [3]
4 COMPONENTS AND MATERIALS
3 MANUFACTURING STEPS
Components used during the creation process of
these materials – as mentioned before – can be fiber
reinforcements, binders, friction modifiers and fillers.
Typical fibers are aramid, glass, carbon, steel, cellulosic
fiber, thermoplastic fiber and asbestos in the past. The
latter became popular relatively fast due to it’s high
strengths and modulus, thermal stability, good wear
properties and the fact that this material could be used
also as a filler. Regarding strength and modulus aramid,
glass, carbon and steel can be taken into account as a
substitution. Aramid also has high thermal stability,
good wear properties and stable coefficient of friction.
Glass fiber is relatively cheap. In terms of thermal
stability aramid, carbon and steel fibers became popular.
[3]
In spite of different operating characteristics the
components and the manufacturing steps for clutch
facings and brake linings show some similarities as
shown in Table 1 and Table 2. By brake friction material
types – for main types see Figure 1 – the typical
manufacturing steps are mixing of ingredients,
preforming, forming by hot pressing, sizing to the
demanded dimensions, curing at high temperatures, then
final grinding. [7]
Clutch facing types – for main types see Figure 2 – have
more diversities in manufacturing steps – as seen in
Table 2 –which is a result of the fact, that three basic
types of clutch facing materials are available on the
market nowadays. They are fiber reinforced woven
clutch facings – some subtypes bonded onto a steel
carrier plate –, paper based friction materials usually for
oil-immersed clutches, and cermet segments for heavy
duty and high velocity applications. [7]
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BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini
SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX
Table 3. Issues with fibers
Fiber
Problems
Glass
expensive, extra care against pulp on mixing, alone not
adequate, needs other ingredients
week heat resistance causes fade, loses fiber form in high
shear mixing, molding, springs back, unsteady coefficient
of friction, low wear characteristic
Carbon
expensive, loses fiber form in mixing
Steel
heavy, corrodes, abrades disc, rotors, noise
Cellulosic fiber
low strength and modulus, low char temperature
Thermoplastic fiber
melts causing fade
Asbestos
health hazard
Aramid
Despite the wide range of advantages, suppliers had to
take a lot of disadvantages into account when decided to
use these fiber materials. Some of their problems are
shown in Table 3.
These trends developed throughout the last century and
decade showing enormous developments in both main
fields of friction materials. Table 4 shows how brake
friction materials changed since the 1870’s. [4] Although
fiber reinforced materials were present since the
beginning of the twentieth century, only after the
discovery of flexible resins could they spread widely on
the market. Another change in trends began in the 60’s
with the growing number of reports about the hazardous
effects of asbestos. Sweeping out the material from all
newly developed applications took more than thirty
years.
Table 4. Brake friction materials
Year
Material
Application
prior to 1870's
cast iron on steel
railroad car brake blocks and tires
~1897
wagon wheels and automobiles
~1930
hair or cotton belting (max 150°C)
woven asbestos reinforced with brass or other
wires
Molded linings with shorter chrysotile fibers,
brass particles and low ash bituminous coal
dry mix molded material
1930's
flexible resin binders
brake drum linings
1950's
resin bonded metallic brake linings
industrial and aircraft applications
1960's
Glass fibers, mineral fibers, metal fibers, carbon
and synthetic fibers (instead of asbestos)
automotive and trucks
1980's
NAO: non asbestos (fiberglass) reinforcement
brake drums on original equipment cars
1990's
carbon fibers
automotive brakes
~1908
~1926
Taking a look at the development which went through in
the field of clutches regarding constructions along with
friction materials in use, – see Table 5 – one can find
some similar dates assuming a common influence
compared to brake materials – for instance efforts to
replace asbestos – that affected the goals of the whole
friction material industry. The table also shows that the
construction and material development trends regarding
clutches became parallel only with single clutch discs
going through milestones in fields like lubrication
improving possibilities and utilization of newly
discovered friction material components, then taking
healthcare
and
environmental
protection
into
consideration. Most of the basic designs were developed
automobiles and trucks
automobiles and trucks
London underground
early, but only the availability of new materials and
machining methods allowed them to be realized.
5 DEVELOPMENT TRENDS
Working with polymer composites opens a wide
range of opportunities to develop new or better materials
experimenting with amounts of ingredients, untested,
new components or expanding or narrowing down
manufacturing steps. For instance Table 6 shows how
one of the suppliers, FCC examined the sensitivity of
some product characteristics to the different steps of
production in order to better understand how to
manipulate the characteristics of the final product from
the beginning steps of the whole process. [5]
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BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini
SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX
Year
1886
1889 1920's
1918 1920's
Table 5. Clutch friction materials vs constructions
('04)
-1920's 1900 - 1918
1900's 1920's -
Type of clutch
friction clutch
transmission
belt clutch
Year
1886
Friction material
leather belts
cone/bevel
friction
clutch
NAG
cone
x
Daimler
Al-cone
Daimler/Mercedes spring
band clutch
Weston
multidisc
oiled/dry
single
clutch disk
x
1889
camel hair
x
after
1889
leather belt soaked
into castor oil
x
after
1889
spring loaded pins/
leaf spring + leather
x
1918
metal
x
x
1918 -
x
oiled aluminium
oiled bronze and
1900's steel
1900's - riveted friction lining
x
x
1920's -
graphite lubricated
x
1920's -
ferodo asbestos
asbestos free (NAO)
linings
x
1990's -
x
Today’s development and experimental trends vary
among studying uncertain tribological phenomena,
effects of different fillers, the role of copper, solving
production induced problems or searching for
possibilities to use bio materials taking environmental
protection into consideration. Basavarajappa et al
examined dry sliding characteristics of glass-epoxy
composite with various volume percentage of filler
materials finding their contribution significant in early
stage of wear. [2] Gurunath et al experimented
successfully with a newly developed resin in order to
avoid shrinkage, a major problem that occurs at the end
of the production of friction materials using phenolic
resin as binder. [6] Kumar et al focused on metallic
fillers, especially copper, which was found best
performer regarding friction and wear of brake frictional
materials. [8] Investigating further it came out, that
copper powder is very effective to reduce the sensitivity
of the friction coefficient to dynamic variations in
pressure and speed. [9] These studies led to the
conclusion, that inclusion of copper improves all major
properties of frictional materials also at production scale.
[10] Bakry et al investigated the effect of agriculture
fibre wastes – corn, sugar bars and palms fibres – on
friction coefficient and wear. The aim of the work was to
replace composite components with environmentally
friendly friction material for brake linings and clutch
facings. It turned out, that they are capable of increasing
friction coefficient and decreasing wear. [1]
Table 6. F.C.C. sensitivity analysis – production steps affecting product features
Step
Composition
Bending of raw materials
Density
friction characteristic
Strength
peeling resistance
Resin impregnation, hardening
Bonding onto core plates
Affected item
thermal resistance, friction
characteristic
peeling and abrasion resistance
Density
thermal, peeling and abrasion
resistance
Bonding/
Strength
peeling and abrasion resistance
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BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini
SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX
6. CONCLUSIONS
Composite friction materials’ history developed
alongside with the evolution of brake, clutch and
industrial application construction. Milestones that
pushed it forward were the discovery and utilization of
flexible resins, the growing popularity then the banning
of asbestos considering healthcare. Nowadays trends
turn in the direction of environmental protection
experimenting with environmental friendly components
such as plant fibers and fillers or bio-degradable friction
materials.
There are still open questions about friction behavior
under different conditions, wear characteristic
sensitivity, thermal loads and responses, manufacturing
steps etc. The field of composite frictional materials is so
wide-spread and still an undeveloped land, that it grants
a wide range of research opportunities for present and
future investigations, experiments and studies.
[7]
[8]
[9]
[10]
[11]
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Authors addresses
1
Roland, Biczó, PhD student, Institute for Mechanical
Engineering Technology, Szent István University, Páter
Károly u.1, Gödöllő, Hungary, [email protected]
2
Gábor, Kalácska, DSc, professor, Institute for
Mechanical Engineering Technology, Szent István
University, Páter Károly u.1, Gödöllő, Hungary
[email protected]
3
Zoltán,Szakál,PhD, lecturer Institute for Mechanical
Engineering Technology, Szent István University, Páter
Károly u.1, Gödöllő, Hungary,
[email protected]
4
Gellért, Fledrich, PhD, associate professor, Institute for
Mechanical Engineering Technology, Szent István
University, Páter Károly u.1, Gödöllő, Hungary,
[email protected]
*
26
Contact person
Roland, Biczó, PhD student, [email protected]