COVENTRY UNIVERSITY

___

FACULTY OF ENGINEERING, ENVIRONMENT AND COMPUTING

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SCHOOL OF MECHANICAL, AEROSPACE AND AUTOMOTIVE ENGINEERING

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REPORT ON BRAKE DISC

by

M. KANAPICKAS

1

COVENTRY

2015

ContentsINTRODUCTION..............................................................................................................................................3

COMPONENT’S SERVICE CONDITIONS..........................................................................................................4

MATERIAL PROPERTY REQUIREMENTS.........................................................................................................6

IDENTIFYING THE MATERIAL.........................................................................................................................7

MANUFACTURING ROUTE SELECTION........................................................................................................10

REVIEW OF THE MANUFACTURING ROUTE................................................................................................12

ALTERNATIVE MATERIALS...........................................................................................................................13

DIFFERENCES BETWEEN CAST IRON AND SILICON CARBIDE BRAKE DISCS IN TERMS OF STRUCTURE AND MANUFACTURING.......................................................................................................................................14

APPENDICES.................................................................................................................................................16

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INTRODUCTIONA brake disc is a component of disc brake system, which is used to slow the vehicle down by turning it’s and brake disc’s kinetic energy into heat, through friction. The disc brake system itself consists of brake pedal assembly, mechanism which assists the driver by decreasing the braking effort (most of the time hydraulic or electric systems are used), brake calliper, hub and brake pads, which come in contact with the brake disc. When driver presses the brake pedal, pressure is then applied to brake callipers, by hydraulic fluid or electronically. That pressure on the brake calliper squeezes the brake pads, which then come in contact with spinning disc brake and slow the vehicle down. Friction between brake disc and brake pads generates heat, and amount of heat produced depends on few factors:

Mass of the vehicle; Speed of the vehicle; Frictional force between brake pads and brake disc;

It is brake disc that absorbs most of the heat, generated during braking. Ideally, it should get rid of that heat quickly. That is achieved thanks to the vents on the side profile of the brake disc, which allow heat to escape and in turn cool the disc down. Brake disc also has many small holes, drilled through the contact surface. These drilled holes have another important purpose. Brake pads have bonding agents and as they break down, they create layer of gas, which prevents brake pad from touching the rotor, because of the pressure in-between. These holes allow that gas, as well as other potential debris and water vapour to travel out. (Fenske 2015) Drilled holes also make the brake disc look aesthetic, thus making the entire assembly more visually attractive.

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Figure 1. How the brake disc works (How Stuff Works 2000)

COMPONENT’S SERVICE CONDITIONS

Like every component, brake disc has the specific environment of service. It will be exposed to average atmospheric pressure of 1013.25 millibars (101325 Pa) (Bell 2015) and come in contact with air, which is consists of:

78.08% nitrogen (N2), 20.95% oxygen (O2), 0.93% argon (Ar), 0.04% of other gases. (Shakhashiri 2015)

Brake discs are typically placed in locations, where they can easily come in contact with water. For example when driving on the wet tarmac or washing a car, water will be splashed on brake disc. This helps to cool it down, but can be an issue if the brake disc is made out of a material, which has corrosive properties. That is because when water, corrosive material (material, which has iron in it) and oxygen come in contact, rust can form on the surface of the brake disc, thus really compromising the braking performance. Other than that, when, braking pads do not squeeze the brake disc, it survives easily in this type of environment.

However, real challenge to the brake disc comes during braking. It is this type of environment that separates good discs from bad ones. First of all, during braking, the disc will have to withstand the high-speed impacts, caused by the pads smashing into it. This is not that big of an issue, because pressure equals to force divided by area, so the area, on which the force is applied, is inversely proportional to the pressure. Brake pads have relatively large and flat surface area on which the force

spreads, so discs will not experience bullet-like impacts and should stay intact. Still, this has to be considered when designing a brake disc. Another type of load that a brake disc experiences during braking is compressive stress. This is caused by the brake pads when they squeeze the disc. Compressive stress can make the brake disc bend and this is not something that is desirable. High temperatures is another point that must be

considered when designing this component. During heavy braking brake disc heats up to very high temperatures, because of the friction between the disc and the brake pads. It is brake disc that absorbs most of the heat. Under racing conditions disc bulk temperatures should normally be maintained in the range from 400 °C to 600 °C for

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Figure 2. Rusted brake disc (Ferguslea Engineering Ltd n.d.)

Figure 3. Ferrari 599XX glowing brake disk (YouTube 2011)

best performance. Disc face peak temperatures may be higher. (AP Racing 2015). There are metals that melt at this temperature range, for example:

Aluminium (660 °C) Aluminium alloys (463-671 °C) Lead (327.5 °C) Magnesium (650 °C) (The Engineering ToolBox n.d.)

Nowadays, most vehicles have anti-lock braking system (ABS) installed. ABS uses wheel speed sensors to determine if one or more wheels are trying to lock up during braking. If a wheel tries to lock up, a series of hydraulic valves limit or reduce the braking on that wheel. This prevents skidding and allows to maintain steering control. (Transport Canada 2015) ABS causes brake pads to pulsate by reducing and increasing the pressure on the calliper and automatically to the brake disc, so it experiences cyclic stress. This also happens on vehicles, which do not have anti-lock braking system. On these vehicles during emergency braking drivers are advised to brake by pulsating their foot on the brake pedal, thus inducing a cyclic stress on the brake rotor as well. Repeated cyclic stresses can cause progressive crack initiation and growth with eventual failure by fracture. Since the temperature of

brake disc fluctuates by a high margin, it will expand during heavy braking and contract once it cools down. What is more, brake discs absorb lots of heat very quickly. The energy dissipated in a stop is the sum of energy from three sources, kinetic, rotational and potential. However, during braking, brake discs

do not absorb 100% of this sum of energies, because some of it is lost

due to engine braking, aerodynamic drag as well as rolling resistance. Still, disc brakes do most of the work, to slow the entire vehicle down. Due to this, depending on how hard the brake pads squeeze the disc, brake disc can heat up to a high temperature very quickly and material experiences thermal shock. Lastly, brake discs are fixed to the axle at the geometrical centre of the disc and they spin at high speeds. They will have centrifugal forces acting along the surface of the disc in every direction. Because of this, yield stress occurs and the brake disc is pulled apart in every direction. This can cause brake disc to deform if it is made from a ductile material, or shatter to pieces if it is made out of material, which has brittle properties.

Overall, under non-braking conditions, brake disc survives in its environment without any difficulties. On the other hand, service conditions are really demanding and challenging for the component, because it has to withstand different combinations of mentioned loads and stresses.

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Figure 4. Cracked brake disc (Clio Sport 2012)

MATERIAL PROPERTY REQUIREMENTSBrakes are one of the most important components in a vehicle. They are vital to ensure the safety of passengers, so under no means they can fail. Since brake disc experiences many different combinations of loads and stresses it has to be made to withstand them. This can be achieved by choosing the right material to manufacture brake discs. To help choose this, material property requirements have to be identified first.

First of all, brake disc material must have high coefficient of friction (µ). Friction between the brake pads and brake disc is what stops the car, so the higher the frictional coefficient, the higher the frictional force, the more heat is produced, absorbed and emitted by the brake disc and the car stops faster. Hardness is another required property of the material. Rotors that are too soft may wear quickly, while rotors that are too hard may increase pad wear or be noisy. Poor-quality castings that lack the proper hardness and strength are more likely to warp or crack at high temperature. (Know Your Parts n.d.). Cracking is not something that is wanted from a brake disc. Having high fracture toughness will help small cracks to resist fracture. Among mechanical engineers there is a rule of thumb already mentioned: avoid materials with fracture toughness (K1C) less than 15 MPa.m1/2. (Ashby, Shercliff, Cebon 2014). Brake discs also have to be made of harder material than brake pads. That is because the latter component is cheaper and easier to change, once it wears. Compressive strength is a desirable property as well. Brake discs, which do not have enough compressive strength can warp under heavy braking and will have to be replaced.

Model’s brake disc is used on a performance car. Sometimes they are driven on racetracks, so disc will heat up to high temperatures during hard braking. Therefore it is essential to make the brake disc out of the material which has high melting temperature. As it was mentioned in the previous passage, the brake discs can reach peak temperatures that are higher than 600 °C. If a brake disc’s material has low melting temperature, it can melt during hard braking. That will deform the disc

and it will have to be replaced. Cast iron (particularly, gray cast iron), is the material of choice for almost all automotive brake discs (Maleque, Dyuti, Rahman 2010). Gray cast iron melts at about 1127 - 1204°C (The Engineering ToolBox n.d.), so similar

melting temperatures are required when selecting materials. Another thermal property that is required from

a material is to be thermally stable. Brake discs are designed to work in a space with

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Figure 5. Brake disc spin test (The Bloodhound Project 2014

certain dimensions. When materials get hot, they expand, so having a thermally stable material prevents brake disc from high expansion during braking. This expansion can cause the disc to become larger than the dimensions that it was designed to work in and, for example, the disc brake will start to grind into the brake calliper.

Brake disc’s material has to have moderate yield strength. While spinning at high speeds, brake disc will be pulled apart in every direction along the surface of the disc, because of the centrifugal load. Yielded component will not be suitable for braking and it can be dangerous. For example, if the brake disc yields during heavy braking, it can cause the brakes to lock up and increase stopping distance. Another property that is required from brake disc’s material is low density. Lightweight brake disc will:

Reduce drivetrain’s rotational inertia. Reduce the weight of the vehicle. Most importantly reduce the centrifugal load on the brake disc.

Centrifugal force (Fc) is equal to F c=mv2

r m – mass, v – velocity, r – circular radius.

(The Engineering ToolBox n.d.) So mass is proportional to the centrifugal force. However, when choosing a lighter material it is important to insure that it has all other mechanical properties suitable for brake disc applications. Also, since the brake discs absorb largest proportion of car’s kinetic energy, they must have good thermal conductivity, to help absorb and dissipate the heat quickly. If the material is not able to emit the heat fast, brake disc can heat up and some problems may occur. For example, overheated brake disc can lose its yield strength, because of increase of grain size, also braking efficiency might be reduced. Lastly, brake disc’s material has to have high immunity to corrosion. Corrosion is the loss of metallic properties of a metal as the metal reacts with the atmosphere or water. e.g. strength, lustre or shine and electrical conductivity. Rust is brownish red in color and is formed from the corrosion of iron. Other metals like copper and aluminium also corrode or weaken. For corrosion to occur both water and oxygen need to be present (Chemical Formula n.d.).

To sum up, brake disc’s material must have high coefficient of friction, be hard, resistant to fracture (K1C less than 15 MPa.m1/2), have high compressive strength as well as have high melting temperature. Also it has to be thermally stable, lightweight, have moderate yield strength and good thermal conductivity properties and high immunity to corrosion.

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IDENTIFYING THE MATERIAL Now that the material property requirements are identified, they will be used to identify the brake disc’s material. Identification will be performed using the CES EduPack 2015 software. Level 2 material universe, which contains 100 materials, will be used. To narrow down the list, certain constraints will be added. Those constraints are: fracture toughness = 15 MPa.m0.5, minimum melting point = 1000°C, good thermal conductor. This narrows down material list from 100 to 12. Materials, which meet these limits are: bronze; cast iron, ductile (nodular); cast iron, gray; copper; gold; high carbon steel; low alloy steel; low carbon steel; medium carbon steel; nickel; nickel-based superalloys, tungsten alloys. This list of materials needs to be narrowed down even more. This can be achieved by plotting materials on a graph, based on certain criteria. Two different graphs will be used to aid the correct material selection. On the first graph, X axis represents the price (GBP) of material for 1 kilogram. Since the brake disc is a mass-produced component, material from which it is made has to cost as little as other material properties allow. Y axis represents fracture toughness divided by density. Since high fracture toughness and low density are desired material properties, the higher the value of this division, the more suitable the material is for brake disc application.

Price (GBP/ kg)0.1 1 10 100 1000 10000

Fra

ctur

e to

ughn

ess

/ De

nsity

1e-5

1e-4

0.001

0.01

Gold

Nickel-based superalloys

Tungsten alloysNickelBronze

Cast iron, ductile (nodular)

Low carbon steel

Copper

Low alloy steelHigh carbon steel

Cast iron, gray

Medium carbon steel

Graph represents fracture toughness / density ratio and price (GBP/kg) of the materials.

Another graph will be generated. This time X axis represents the compressive strength of the material, while Y axis represents thermal conductivity divided by thermal expansion. Again, since high thermal conductivity and low thermal expansion are desired material properties, the higher the value of this division, the more suitable the material is for brake disc application.

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Compressive strength (MPa)0.01 0.1 1 10 100 1000 10000

Ther

mal

con

duct

ivity

/ T

herm

al e

xpan

sion

coe

ffici

ent

1e-4

0.001

0.01

0.1

1

10

100

Cast iron, gray

Medium carbon steel

Tungsten alloysGoldCopper

NickelLow carbon steel

Bronze

Nickel-based superalloys

Cast iron, ductile (nodular)

High carbon steel

Low alloy steel

Graph represents thermal conductivity / thermal expansion coefficient ratio and compressive strength of the materials.

These are the graphs that the software generated from the criteria. Gold, tungsten alloys, nickel-based superalloys, nickel, bronze and copper have similar fracture toughness to density ratio and some of them have slightly higher thermal conductivity to thermal expansion coefficient to ones that are coloured in blue on the graph. However, their price (GBP) per kilogram is very high. For example, it would cost more than 10 times to produce the same brake disc from copper, instead of high carbon steel. Brake disc is a component, which is produced in moderate quantities so materials, coloured in red on the graph are not suitable for the production and are discarded from further investigation.

MaterialDensity(k

g/m3Price(GBP/

kg)

Compressive

strength(MPa)

Hardness – Vickers(HV

)

Fracture toughness(MPA.m0.5)

Thermal conductivity(W/m.°C)

Thermal expansion(μstrain/°C)

Cast iron, ductile

7.05e3 – 7.25e3

0.339 – 0.377

250 – 790 MPa

115 - 320 22 - 54 29 – 44 10 – 12.5

Cast iron, gray

7.05e3 – 7.25e3

0.282 – 0.314

500 – 1.1e3 90 - 310 10 – 24 40 - 72 11 – 12.5

High carbon steel

7.8e3 – 7.9e3

0.326 – 0.364

335 – 1.16e3

160 - 650 27 - 92 47 - 53 11 – 13.5

Low alloy steel

7.8e3 – 7.9e3

0.351 – 0.389

400 – 1.5e3 140 – 639 14 – 200 34 – 55 10.5 – 13.5

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Low carbon steel

7.8e3 – 7.9e3

0.326 – 0.364

250 – 395 108 – 173 41 – 82 49 – 54 11.5 - 13

Medium carbon steel

7.8e3 – 7.9e3

0.326 – 0.364

410 – 1.76e3

120 – 565 12 – 92 44 – 55 10 - 14

Most suitable material

Cast iron, ductile Cast iron,

gray

Medium carbon steel

High carbon steel

Low alloy steel

Cast iron, gray

Cast iron, ductileCast iron,

gray

Material comparison table. Data was taken from CES EduPack 2015 software.

The table above compares the properties of the remaining six materials. Cast iron (gray) has the best overall package compared to the others. It is cheapest, lightest and has highest thermal conductivity, elsewhere it does not fall back from other materials. According to the table, model’s brake disc is made from gray cast iron.

MANUFACTURING ROUTE SELECTION Now that material from which the brake disc is made is known, it has to go through manufacturing process. Material has to be shaped into a brake disc and surface treated to be usable for brake disc application. CES EduPack 2015 software will be used to identify the potential suitable manufacturing routes and then select the most suitable one. Level 2 process universe will be used for this. First of all, choosing gray cast iron as the material for casting narrows down the shaping process list from 68 to 17. This list has to be reduced even more. This is achieved by applying some limits for the processes, which are: mass range – from 5 kg to 20 kg and range of section thickness – from 10 mm to 200 mm. List is reduced from 17 processes to 5. By plotting the graph, the most suitable processes can be identified. X axis on the graph represents relative cost index (per unit), while Y axis represents labor intensity.

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Relative cost index (per unit)Material Cost=6.28GBP/kg, Component Mass=1kg, Batch Size=1e3, Overhead Rate=69GBP/hr, Capital Write-off Time=5yrs, Load Factor=0.5

10 100 1000

Labo

r int

ensi

ty

very high

high

medium

low

Sand casting Investment casting

Evaporative pattern sand casting

Ceramic shell evaporative mold casting

Graph represents labour intensity and relative cost index of gray cast iron shaping processes.

This is the graph that software generated. It would not make sense to use investment casting, because it has bigger relative cost per unit index and is more labour intensive process, compared to different types of sand casting. Three processes are going to be investigated further.

1. Sand casting. This process consists of pouring molten metal into a sand mold, allowing the metal to solidify, and then breaking up the mold to remove the casting. The sand mold is expendable, so it would have to be remade for each individual casting. Sand casting allows very complex shapes, but the surface finish is rough and the surface detail is poor. Brake disc would need extra manufacturing processes, such as machining and polishing. Sand casting is the cheapest process of the three, but the most labour intensive one.

2. Ceramic shell evaporative mold casting. It is similar to sand casting except that the mold is made of refractory ceramic materials that can withstand higher temperatures. Because no cores are required, complex shapes can be produced. Undercuts and reentrant angles are feasible. Its advantages are good accuracy and surface finish. Brake disc would not require as much extra manufacturing as it would with sand casting. This process is relatively cheap as well and least labour intensive of the group.

3. Evaporative pattern sand casting. This process uses a mold of sand packed around polystyrene foam pattern that vaporizes when the molten metal is poured into the mold. Since the foam pattern itself becomes the cavity in the mold, the mold does not have to be opened into cope and drag sections. Complex shapes can be produced from this process. Like ceramic shell evaporative mold casting this process does not require much extra

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manufacturing. It is the most expensive process of the three, but not as labour intensive as sand casting. (Groover 2013)

Evaporative pattern sand casting is the best option. Even though it is the most expensive per unit, brake disc will have good surface finish and accuracy. This will require less machining and polishing. Because foam patterns are one-piece, they will also be easier to create and more accurate rather than sand patterns. Another benefit of evaporative pattern sand casting is that casting can be easier removed, as the mold does not have to be separated.

REVIEW OF THE MANUFACTURING ROUTE

In order to convert gray cast iron into a brake disc, material has to go through different processes. First of all, it has to be heated up and melted. Gray cast iron melts at the temperature range from 1130 °C to 1380 °C. (Granta 2015) Ideally, it should reach even higher temperatures to prevent premature solidification. Metal would have to be melted in a furnace made from the material, which has bigger melting temperature than gray cast iron. Otherwise the furnace would also melt. While the metal is being melt, foam pattern of the brake disc with cup and sprue (for molten metal pouring) has to be made. Since the component is mass-produced, automated molding operation should be set up to mold the patterns prior to making the molds for casting. Once the pattern is created, it is coated with a refractory compound to provide a smoother surface on the pattern and to improve its high temperature resistance. After that foam pattern is placed in a flask horizontally (surface of the brake disc foam is linear to the flask’s bottom). Foam pattern is then compacted with molding sand around it. The cup and sprue are exposed at the top. Once the cast iron melts, it is poured into the portion of the pattern that forms the pouring cup and sprue. As metal enters the mold, the polystyrene foam is vaporized ahead of the advancing liquid, thus allowing the resulting mold cavity to be filled (Groover 2013). The metal is allowed to cool down and solidify to form a solid brake disc. After that, it is removed from the sand, which can be reused for the next cast.

Once the casting is done, machining and surface treatment is next. Cup and sprue have to be accurately cut and sanded. After that, disc brake should be carefully inspected for any potential defects or errors that potentially could have appeared

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Figure 6. Lost foam casting process (Steel Founders’ Society of America 2004)

during casting. If they appear, brake disc has to be melted and casted again. If the component passes the check its surfaces must be machined next. Once this is achieved, brake disc must be drilled and slotted by the CNC machine. Holes have to be drilled on the surface, where the pads come in contact with the brake disc, and where the mounting points on the hub are. After that brake disc has to be polished. Finally, brake disc needs anti-corrosion surface treatment. UV-coating is the option to go for. During the UV coating process, the solvent function is essentially performed by water. Since the coat hardening is performed by UV irradiation and high temperatures are therefore not required, energy consumption is reduced. Additionally, the risk of affecting the geometric features on the disc, which may occur with other coatings applied under extremely high temperatures (more than 300 °C), is also reduced. (Brembo n.d.).

ALTERNATIVE MATERIALSEven though gray cast iron is the material of choice for the brake disc, there are alternative materials from which it can be made. One such material is carbon ceramic. The Brembo Group has been manufacturing carbon ceramic discs for automotive applications since 2002, when it first supplied these components for the Ferrari Enzo. This high performance material, made from a special mixture of powders, resins and fibres in a complex manufacturing process, has been used since the 1970s. Carbon ceramic offers substantial benefits in terms of performance - in both wet and dry conditions - weight, comfort, corrosion resistance, durability and high-tech appeal (Brembo n.d.). However, reason why it is not used on every production car is its price. When performing the material selection it was stated, that gray cast iron costs 0.282 – 0.314 GBP/kg. Carbon ceramic, also known as silicon carbide, costs 9.11 – 13 GBP/kg. This material is more than 30 times more expensive than gray cast iron, which only makes it suitable for high-performance production car and motorsport applications.

Another material, which is used for making brake discs is stainless steel. Its main advantage over cast iron is that it is much more corrosion resistive than gray cast

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iron. When identifying the material, one graph had fracture toughness and density ratio on Y axis as its parameter. When compared, stainless steel has much better ratio than gray cast iron. That ratio is almost 10 times bigger. However, stainless steel does not have the desired thermal properties of gray cast iron. They would have to be larger in diameter to be able to perform as good as gray cast iron. Stainless steel brake discs are the material of choice for bicycles and motorcycles. That is because their brake discs are more exposed, so they are exposed to more water. Also they are much thinner and smaller than car’s brake discs so they would get affected by corrosion much quicker.

Comparison between stainless steel and carbon ceramic brake discs will be performed to find out which one is the better option. It will based on the same criteria, when the gray cast iron was selected as the brake disc model’s material. It is worth mentioning that both materials have pretty much equal corrosion resistance.

MaterialDensity(k

g/m3Price(GBP/

kg)

Compressive

strength(MPa)

Hardness – Vickers(HV

)

Fracture toughness(MPA.m0.5)

Thermal conductivity(W/m.°C)

Thermal expansion(μstrain/°C)

Carbon ceramic

3.1e3 – 3.21e3

9.11 - 131e3 –

5.25e32.3e3 – 2.6e3

3 – 5.6 80 - 130 4 – 4.8

Stainless steel

7.6e3 – 8.1e3

3.69 – 4.07 170 – 1e3 130 - 570 62 - 150 12 - 24 13 - 20

Most suitable material

Carbon ceramic

Stainless steel

Carbon ceramic

Carbon ceramic

Stainless steel

Carbon ceramic

Carbon ceramic

Material comparison table. Data was taken from CES EduPack 2015 software.

From the graph it can be seen that carbon ceramic is more suitable than stainless steel for brake disc application. Brake disc used for the model is for a high performance, judging by its relatively large diameter and big brake calliper, so carbon ceramic brake discs would meet the high performance demands.

DIFFERENCES BETWEEN CAST IRON AND SILICON CARBIDE BRAKE DISCS IN TERMS OF STRUCTURE AND MANUFACTURING.

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Using carbon ceramic brake discs would have a definite advantage over gray cast iron ones in some areas. For example, carbon ceramic brake discs are much lighter, stronger, more durable, have better thermal properties. Their main disadvantage over regular cast iron brake discs is the price. For example, silicon carbide, which is one of the main ingredients of carbon ceramic brake discs, costs approximately 33 times more. (CES 2015). Since the carbon ceramic has much higher thermal conductivity, brake discs can be made in smaller diameter and they will dissipate heat as quickly. Due to the different frictional and thermal properties of iron and ceramic discs it is important to use a brake pad compound that has been specifically developed for ceramic brake discs. Some high performance brake pads, designed for extreme track use can be used with both iron and ceramic discs (Surface Transforms n.d.). Joining carbon ceramic brake disc would be no different than cast iron one. Bell is attached to the disc and then this assembly is connected to the vehicle.

Manufacturing carbon ceramic brake disc is much harder than cast iron. To manufacture the disc, silicon has to be mixed with carbon fibre. Carbon fibre is prepared by mixing two ingridients: heat molded resin and chalked pieces of raw carbon fibre. Carbon fibre is poured into the aluminium mold in the shape of the brake disc. After that mold is closed down and small press pushes down the cover to lightly compact the content. After that the mold enters large press, which applies up to 20 tonnes of pressure, while heating to about 200 °C. This compacts the carbon fibre and transforms the powder into plastic. After that mold is cooled down, by submerging it into cold water. Next, the brake disc is removed from the mold. Then computer machines smooth out the rough areas and drill ventilation holes. After that it is put into the oven, where it is kept for 2 days heated to about 420 °C. This transforms the plastic into carbon. Then the disc is put into high heat resistant container and is filled with silicon powder. After that it is put into the oven for 24 hours. Silicon powder melts in the oven and low level suction which draws the liquid silicon onto the disc ring. After this, silicon carbide is formed. Next, computer guided machine pours the mounting holes. Coat of protective paint, which shields the carbon from oxygen. This improves the durability of the brake disc. After this, cleaning and polishing is done by

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Figure 8. Carbon ceramic brake disc production phases (Brembo/SGL Group n.d.)

the robot. Finally, the brake disc is inspected by laser for any potential defects. (How It’s Made n.d.).

It is clear, that this is manufacturing route requires a lot more time and energy, compared to cast iron brake disc manufacturing. For this reason, silicon carbide brake discs are not suited for affordable, mass production vehicles, even though the material has supreme advantages over cast iron in many areas.

APPENDICESList of references:

1. Fenske, J. (2015) Drilled, Slotted & Vented Brake Rotors – What’s Best? [online] available from <https://www.youtube.com/watch?v=78wbht355R8> [15 November 2015]

2. Bell, M. (2015) What is the average air pressure at the surface of the Earth? [online] available from <http://iridl.ldeo.columbia.edu/dochelp/QA/Basic/atmos_press.html> [15 November 2015]

3. Shakashiri, B. (2015) GASES OF THE AIR [online] available from <http://scifun.chem.wisc.edu/chemweek/pdf/airgas.pdf> [16 November 2015]

4. AP Racing. (2015) Disc Temperatures [online] available from <https://www.apracing.com/Info.aspx?InfoID=36&ProductID=976> [16 November 2015]

5. The Engineering ToolBox (n.d.) Melting temperature of some common metals and alloys [online] available from <http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html> [16 November 2015]

6. Government of Canada (2015) What you should know about ... Anti-lock Braking System: ABS ... What is it? [online] available from <https://www.tc.gc.ca/eng/motorvehiclesafety/tp-tp13082-abs1_e-214.htm> [16 November 2015]

7. Know Your Parts (n.d.) The Importance of Quality Brake Rotors [online] available from <http://www.knowyourparts.com/technical-articles/importance-quality-brake-rotors/> [17 November 2015]

8. Ashby, M., Shercliff, H., Cebon, D. (2014) Materials: engineering, science, processing and design; North American Edition [online] 3rd edn. Oxford: Butterworth-Heinemann. available from <https://books.google.co.uk/books?id=sqaH1CNY2isC&lpg=PA249&dq=ashby%20%2215%20Mpa%22%20thumb%20toughness&pg=PA249#v=onepage&q=ashby%20%2215%20Mpa%22%20thumb%20toughness&f=false> [17 November 2015]

9. Maleque, M.A., Dyuti, S., Rahman, M.M. (2010) Material Selection Method in Design of Automotive Brake Disc [online] available from <http://www.iaeng.org/publication/WCE2010/WCE2010_pp2322-2326.pdf> [17 November 2015]

10. The Engineering ToolBox (n.d.) Centripetal and Centrifugal acceleration - force due to circular motion [online] available from <http://www.engineeringtoolbox.com/centripetal-acceleration-d_1285.html> [17 November 2015]

11. Chemical formula (n.d.) Corrosion [online] available from <http://www.chemicalformula.org/chemistry-help/corrosion> [17 November 2015]

12. Granta (2015) CES EduPack 2015 [online] available from <http://www.grantadesign.com/education/edupack/index.htm> [23 November 2015]

13. Groover, M. P., (2013) Principles of Modern Manufacturing. Singapore: John Wiley & Sons Pte. Ltd. [18 November 2015]

14. Brembo (n.d.) BREMBO'S NEW UV-COATED DISCS: MORE RESISTANCE AND LESS ENVIRONMENTAL IMPACT [online] available from <http://www.brembo.com/en/ComunicatiStampa/2012/Brembo_UV_Coated_Discs_EN.pdf > [19 November 2015]

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15. Brembo (n.d.) Carbon-ceramic discs [online] available from <http://www.brembo.com/en/car/original-equipment/products/carbon-ceramic-discs> [20 November 2015]

16. Surface Transforms (n.d.) Top 10 FAQs on Ceramic brakes, ceramic pads and carbon ceramic material [online] available from <http://www.surface-transforms.com/news.php?wnID=6442> [20 November 2015]

17. How It’s Made (n.d.) Ceramic Brake Discs [online] available from <https://www.youtube.com/watch?v=CAsafGWlSzI> [20 November 2015]

List of figures:

1. HowStuffWorks (2000) Parts of a disc brake [online] available from < http://auto.howstuffworks.com/auto-parts/brakes/brake-types/disc-brake1.htm> [23 November 2015]

2. Ferguslea Engineering Ltd (n.d.) Rusty-brake-disc-ferguslea-ayr [online] available from <http://www.ferguslea-ayr.co.uk/index.php/services/brake-disc-skimming/rusty-brake-disc-ferguslea-ayr/> [23 November 2015]

3. alexsmolik (2011) Ferrari 599XX glowing brake disk [online] available from <https://www.youtube.com/watch?v=y2Q4OpGCfME> [23 November 2015]

4. Snails (2012) Cracked brake disc [online] available from <http://www.cliosport.net/threads/cracked-brake-disc.637240/> [23 November 2015]

5. The Bloodhound Project (2014) Brake disc spin test [online] available from <http://www.bloodhoundssc.com/news/brake-disc-spin-test> [23 November 2015]

6. Steel Founders’ Society of America (2004) Lost foam casting process [online] available from <https://www.sfsa.org/tutorials/eng_block/GMBlock_13.htm> [23 November 2015]

7. Brembo (n.d.) Moisture resistance test [online] available from <http://www.brembo.com/en/ComunicatiStampa/2012/Brembo_UV_Coated_Discs_EN.pdf> [23 November 2015]

8. Brembo/SGL Group (n.d.) Carbon ceramic brake disc production phases [online] available from <http://www.carbonceramicbrakes.com/en/technology/Pages/production-steps.aspx> [23 November 2015]

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