Materials/Structure Performance
Gray Cast Iron in Rotors/Disc Ima Panther
University of Wisconsin – Milwaukee, College of Engineering & Applied Sciences
Bibliography Callister, William D. “10 & 11.” Materials Science and
Engineering: An Introduction 8e. N.p.: n.p., n.d. 369+. Print.
Ihm, Mark. “Cast Iron Properties.” Cast Iron Properties. In, n.d. Web. 28 Apr. 2016.
Properties of Gray Cast-Iron
• Wear resistant – able to break down which is used for the needed friction
• High heat capacity – resists warping • Strong under compression – needed when
under strong compressive force of brake
pads
• Weak & Brittle under tension – rotor is not put in tension from brake pads
Structure of Rotor
• The rotor itself is hollow & has drilled holes to get rid of mass
• The holes also helps the removal of dust & water
• The holes also help in heat dissipation of rotors
Processing
Introduction
• In order to reach the needed pearlite phase, the gray cast iron must be cooled at
a very slow cooling rate.
• Using the continuous cooling transformation diagram for a eutectoid
iron-carbon alloy shows that cooling rate
for the gray cast iron must have a 35
°C/s or even slower cooling rate
• The slower the solidification/cooling rate aids the carbon to diffuse and accumulate
into graphite
High Carbon Gray Cast-Iron
• 2.5-4.0wt% C • 1.0-3.0wt% Si
• The addition of silicon helps produce graphite
• Silicon is the stabilizing element in producing graphite instead of cementite
which makes it hard & brittle
Microstructure of Cast Iron observed in
Metallography lab
• Graphite nodules (addition of Mg) – reduces the area of stress concentrations in
the metal matrix which leads to a better
ductility
A simple disc brake system functions as
follows:
1. Press the pedal
2. Hydraulic system compresses brake fluid
to a high pressure
3. The pressure pushes the piston in the
caliper
4. Piston forces brake pads to clamp down
on rotor
5. Friction between the rotor & brake pads
causes the rotor to stop
Material Demands on a Disc Brake/Rotor
• Surface must be hard enough to withstand friction
• Resist warping due to high temperatures – an immense amount of friction from the
brake pads will cause a lot of heat
• Needs to hold up to the compressive force/clamping of the brake pads
Objective To describe why gray cast iron is used for
rotors on a vehicle by showing its
structure, how the structure is formed
through processing, and how the
properties also effect its performance.
