Page 16 - Ferodo car racing

Auto Parts / New Pad Technology
NEW PAD TECHNOLOGY

SILOXANE THE BACKGROUND:

In the braking world, “Ceramic” is a word that is heard a lot. PERFORMANCE REQUIREMENTS
However “Ceramic” can merely indicate that the product contains
something, anything, that is not “organic.” Organic means a Whilst issues of Noise, Vibration and Harshness (problems
substance whose molecular structure is largely based upon associated and known in the industry by the generalised
carbon. However for an engineer to understand a material as abbreviation “NVH”) have become of paramount importance
ceramic, he or she knows that this must mean that its performance for the braking of road vehicles, they are of little concern in
defining core must be non-organic. In the case of a friction racing. Broadly speaking the performance requirements on
material this is the resin – the glue which holds the pad together; the track are as follows:
the matrix that holds the other components in place, allowing
them to do their job. For over 100 years this job has been, High Friction. Very high decelerations are required, often from
and continues to be done in brake pads almost exclusively systems that are not servoassisted. The combination of
by a phenolic resin. A highly durable, versatile binder, yet aerodynamic downforce and large, sticky tires means that
resolutely an “organic” material. the limiting factor in braking is often the force applied via the
driver’s foot rather than road/tire adhesion. The requirement
The appeal of a non organic based brake pad is simple: Phenolic for maximum braking torque from the available muscle power
resins begin to decompose at temperatures above 300-400°C. means that materials with a high coefficient of friction µ are
In a racing pad, where these temperatures would be regarded preferred - in other words those materials that translate the
as a operating minimum that’s bad news. It means the pads highest possible percentage of the applied force into vehicle
wears more as the carbonaceous material decomposes, that deceleration No fade. Fade is the term used for a decrease in
the pedal becomes spongy as the pad looses its rigidity and friction performance at high temperatures. High vehicles
that the brake will fade, as gaseous decomposition products speeds, high decelerations, frequent brake applications and
try to escape at the disc/pad interface. The problem is, no one limited cooling (ducting air creates drag) means that discs and
had ever found a viable alternative to the phenolic based pads get very hot – upto 900°C. Yet Ì must be maintained
brake pad, aside from the sintered metal compounds. These even under these extreme conditions.
C
latter materials work well in motorcycle racing, but the far higher Low pad compressibility. This results in shorter pedal travel,
M weight of a car makes heat transfer to the caliper an almost one of the driver’s key requirements. Ideally the pad compres-
insurmountable problem in auto racing. Additionally, as es- sibility will be the same at all temperatures and will not change
Y
sentially an incompressible block of metal, sintered pads are throughout a race.
CM often judged to lack the “feel” that a racing driver requires, The “right” friction history. This is sometimes called “stop
being little more than an on/off switch for the brake. shape” or “time history” and refers to how the friction coeffi-
MY
cient varies through a brake application. As such it is the
CY
However, in DS1.11 and DSUNO Ferodo Racing can offer response of the braking system to increasing temperature
a true “ceramic” race brake pad. The resin binding system with decreasing speed. This is as close to an objective
CMY
replacing the traditional phenolic is described as a “Siloxane” description of the hard-to-define brake “feel” as is possible
K
In layman’s terms, this means that the 3D molecular network to make.
that holds the pad together is formed from chains of silicon Generally speaking, drivers of cars with greater downforce
rather than carbon atoms. These are impervious to temperature. prefer a flat response (this is because the last thing a driver
In fact, at about 700°C, they actually undergo a chemical needs is friction ramping up at the apex of the bend, just as
phase transition which actually pulls the pad together even downforce is reducing due to his lower speed: result; wheel
more strongly. Additionally, the cured (i.e “set” during the lock!) whereas those vehicles with less downforce often prefer
manufacturing process) resin, being a hard, abrasive ceramic, rising friction through the stop. DS1.11 is an example of a
has friction enhancing properties. So there’s a double benefit. material with a flatter stop shape, whilst DSUNO has a rising
No phenolic carbon to decompose so wear is low and an torque output (see graph) Initial bite. How quickly the brake
abrasive substructure that keeps the friction coefficient (µ) high! responds to the driver’s pedal. Almost exclusively, the quicker
the better.
DS1.11 is recommended for FIA GT, Touring Car, Formula Pad and Disc life. Not always important but vital in endurance
cars, Group N and Stock Car (NASCAR) in the USA. DSUNO racing where the number of pit-stops must be minimised and,
is used in rally applications and sprint races, though drivers not least, economically in that fewer disc and pad changes
who appreciate it’s very high friction have also been using means fewer disc and pad purchases.
it for touring car and group N applications too. Both are
characterized by long life, high µ and a firm pedal under all
conditions, but the torque profile of DS1.11 during a brake
application is flat, whilst that of DSUNO rises, making them
complementary compounds, depending on vehicle type and
driver preference.

Generalized chemical structure of siloxane.

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