04-02-2013, 10:02 AM
Characterization of Friction Material Formulations for Brake Pads
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Abstract
New friction material formulations are compared
with a commercial brake friction material used in Light Rail
Transit (LRT) operating in Malaysia. Characterization
techniques such as SEM, TGA, XRD, friction and wear tests are
used to characterize the formulations as well as the commercial
material. Out of the 30 formulations made, two formulations viz.,
S1 and S2 closer to commercial material are presented in this
work. Formulation S2 exhibits better thermal stability and better
wear resistance. With the help of SEM analysis, physical
properties and XRD spectrum analysis, it is shown that
formulation S2 has same crystallinity as the commercial specimen
and can be considered for replacing the commercial material in
LRT brake pad applications. The cost of the brake pad would
reduce by half if they are made locally in Malaysia.
INTRODUCTION
The tribological application of phenolic resin-based friction
materials is usually limited owing to the relatively poor stability
and wear resistance. Therefore, it is imperative to incorporate
various reinforcing and filling constituents such as reinforcing
fibers, abrasives, binders, fillers, and friction modifiers (solid
lubricants) into phenolic resin-based friction composites for the
purpose of increasing the stability and wear resistance. [1].
Different kinds of fibers, e.g., metallic, glass, ceramic and
carbon fibers, have been used to replace asbestos. Among the
fibers mentioned above, the most frequently used metallic fiber
material is low carbon steel. Due to their good thermal stability
and high hardness, ceramic materials are also used. The
presence of ceramic fibers composed of alumina and silica
improves the wear resistance, insulating properties and high
temperature performance. It seems obvious that the addition of
different fibers could impose different effects on the
tribological behavior of semi metallic friction materials [2].
COMMERCIAL BRAKE PAD
Brake Pad
Fig. 1 shows a brake pad used in the PUTRA-LRT trains
running in Kuala Lumpur. Two such brake pads are used in
every hydraulic brake unit. There are 16 brake pads in every
train. 35 trains operated by PUTRA-LRT in and around KL are
fitted with this type of brake pads. These brake pads are
non-asbestos, non-lead and semi-metallic.
New Formulations of Brake Friction Materials
New formulations of brake friction materials are made using
the following ingredients: Resin, Iron oxide, Steel fiber,
Ceramic fiber, Organic fiber, Magnesium Oxide, Aluminium
Oxide, Barium, Sulphur, Graphite, Rubber, Novacite, Nipol
and friction dust. Values of Hardness, Specific Gravity, SEM.
RESULTS AND DISCUSSIONS
EDX Analysis
Table-1 shows the elemental composition of commercial, S1
and S2. It can be seen that S1 & S2 have difference
composition of elements compared to the commercial specimen.
The amount of carbon in S1 and the amount of Al in S2 are
comparable to the amounts present in the commercial specimen.
Both S1 and S2 have higher amounts of C, O, Al, S, Ca and Ba
compared to the commercial specimen. Correspondingly their
properties are different from commercial specimen and we
shall find which one exhibits closer behaviour compared to the
commercial specimen using SEM, TGA and XRD spectrums.
Friction and Wear
Talib et.al [5] have studied the friction and wear properties of
these formulations and reported the following results: Table-2
shows the co-efficient of friction and average thickness loss
values for the commercial as well as the formulations. It can be
seen from Table-2 that the friction coefficient of formulation
S1 is higher and the wear is lower compared to that of the
commercial specimen. Lower wear rate would increase the life
of the brake pad and higher friction coefficient would offer a
better performance compared to the commercial specimen. But
the wear of formulation S2 is negligible and the coefficient of
friction is slightly lower than the commercial specimen. The
thickness loss is only 0.01%, which indicates the integrity of
the formulation S2 is high.
CONCLUSIONS
Lower coefficient of friction and negligible thickness loss
make formulation S2 a better alternative to the commercial
brake pad. Formulation S2 can be improved further and
considered for manufacturing brake pads locally
Equal amount of carbon is present in specimen S1 and in
commercial specimen whereas specimen S2 has higher amount
of Carbon which indicates that it has the right amount of resin
to impart more integrity. Formulation S2 is able to offer better
wear resistance.