3. PISTON:
A piston is a cylindrical engine component that
slides back and forth in the cylinder bore by forces
produced during the combustion process.
The piston acts as a movable end of the
combustion chamber.
Its purpose is to transfer force from expanding
gas in the cylinder to the crankshaft via a piston
rod.
4. PISTON MATERIALS:
The most commonly used Piston
materials are
• Cast Iron
• Aluminium Alloys
Cast iron pistons are used for moderately rated
engines with piston speed below 6m/s.
Aluminium alloy pistons are used for highly
rated engines with piston speed above 6m/s.
5. CAST IRON:
Cast iron is a group of iron-carbon alloys with a
carbon content greater than 2%.
Carbon (C) ranging from 1.8–4 wt%, and silicon (Si)
1–3 wt% are the main alloying elements of cast
iron.
Types of Cast Iron
Grey cast iron
White cast iron
Malleable cast iron
Ductile cast iron
6. Cast Iron Characteristics:
It is hard.
Brittle.
Non-malleable (i.e. it cannot be bent, stretched or
hammered into shape).
More fusible than steel.
Very good in compression.
7. ALUMINIUM ALLOYS:
Aluminium alloys (or aluminum alloys) are alloys in
which aluminium (Al) is the predominant metal.
The typical alloying elements are copper,
magnesium, manganese, silicon, tin and zinc.
Cast aluminium alloys yield cost-effective products
due to the low melting point.
8. Aluminum Alloy Characteristics:
High operating temperatures
Outstanding corrosion resistance
Lightweight
Very good strength and hardness
Good stiffness and strength-to-weight ratio
Excellent EMI and RFI shielding properties
Excellent thermal conductivity
High electrical conductivity
Good finishing characteristics
Full recyclability
9. Applications for Aluminum:
Aluminum castings improve automotive fuel
efficiency by contributing to weight saving
requirements
Aluminum is used in a broad range of networking
and infrastructure equipment in the telecom and
computing industries because RF filter boxes and
housings require heat dissipation
In handheld devices, aluminum castings provide
EMI/RFI shielding, rigidity, and durability with
minimal weight
Because of aluminum’s excellent electrical
performance and shielding properties, even in high-
temperature environments, die cast aluminum is
ideal for electronic connectors and housings
10. PROPERTIES
PROPERTIES ALUMINIUM CAST IRON
Atomic Number 13 26
Crystal Structure FCC FCC
Melting Point (°C) 660.2 1204
Boiling Point (°C) 2480 2862
Mean Specific Heat (0-
100°C) (J/goC)
0.900 0.444
Thermal Conductivity (0-
100°C) (cal/cms.°C)
0.57 0.163
Electrical Resistivity at
20°C (Ω.cm)
2.69 9.61
Density (g/cm3) 2.6898 7.874
Poissons Ratio 0.34 0.29
Young's modulus 70 211
Brinell hardness 160-550 200-1180
11. Advantages of Aluminium over cast iron:
High thermal conductivity (approx 3 times that of
cast iron
Less variation in temperature from the crown to the
piston rings.
Density of aluminium is about one third that of cast
iron. Therefore light weight construction and less
inertia forces.
12. CONCLUSION:
Piston material and design contribute to the overall
durability and performance of an engine.
Cast aluminium alloy is lightweight and has good
structural integrity and low manufacturing costs.
The light weight of aluminium reduces the overall mass
and force necessary to initiate and maintain acceleration
of the piston.
This allows the piston to utilize more of the force
produced by combustion to power the application.
Hence Aluminium Alloy is used for
Pistons.
