Introduction
1. The brakes must be
strong enough to stop the vehicle within the minimum possible distance in an
emergency. But this should also be consistent with safety. The driver must have
a proper control over the vehicle during emergency braking and the vehicle must
not skid.
2. The brakes must
have good antifade characteristics and their effectiveness should not decrease
with constant prolonged application.
Disc Brakes
As shown in fig a
disc brake consists of a cast iron disc bolted to the wheel hub and a stationary
housing called caliper. The caliper is connected to some stationary part of the
vehicle, like the axle casing or the stub axle and is cast in two parts, each
part containing a piston. In between each piston and disc there is a friction
pad held in position by retaining pins, spring plates etc., passages are
drilled in the caliper for the fluid to enter or leave each housing. These
passages are also connected to another one for bleeding.
Coating Of Ceramics On Conventional Brake Disc
In use, the ceramic
face requires a special carbon metallic friction pad, which deposits a layer of
material on the brake disc. This coupling provides the required conditions of
exceptional wear resistance, high and stable coefficient of friction.
The coated matrix
composite discs were first used on high performance motor cycles, where the
reduced gyroscopic effect had the additional advantage of making the cycles
easier to turn.Another company named Lanxide used aluminium as the disc
material. To provide necessary abrasion resistance, aluminium discs have to be
reinforced with a ceramic material, hence metal composite. They used silicon
carbide also to increase the strength.
Manufacturing
Of Ceramic Brake Discs
The composites for
producing fiber reinforced ceramic brake discs are short carbon fibers, carbon
powder, and resin mix. The process involves first compressing the carbon
fibers, carbon powder and the resin mix together and then sintering at1000
degree Celsius. In the furnace a stable carbon frame work created. This
consists of carbon fibers in a carbon matrix. Once cooled this material can be
ground like wood and the break disk obtains its final shape.
Together with silicon
the ground break disk blank is then inserted into the furnace a second time.
The pores in the carbon framework absorb the silicon melt like a sponge; the
fibers themselves remain unaffected by this process.
The ceramic material
is created when the matrix carbon combines with liquid silicon. This fiber
reinforced ceramic material cools over night and the gleaming dark grey break
disk is ready.
Advantages
Of Ceramic Brake Discs
1. Initial field studies have shown that
ceramic brake discs can still reliably bring an automobile to standstill even
after 300,000 kilometers. Brake disc changes will in future be unnecessary.
2. They are not subject to wear, are
maintenance free and are heat and rust resistant.
CONCLUSION
Ceramic brake discs
due to its advantages over the conventional brake discs are going to be the
brake discs for cars in future. The special combination in the ceramic brake
discs had turned the conventional brake disc into a material most suited for
making brake discs. With the success of this in Porsche turbo car, many other
racing cars and commercial vehicles are going to implement the ceramic disc in
their cars.
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