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In every type of engine piston plays most important role. It's used in all type of engine like motorbike engine, car engine, generator, aeroplane engine reciprocating engine and lots of more engines that have the use of piston. Commonly piston is made up of aluminium alloy Piston is to be found in the cylinder of an engine. Piston helps in working and producing results. Piston covers three opening by its sides. Piston conveys the force of explosion to the crankshaft with the help of connecting rod inside the cylinder and also creates the guides and bearing for the small end of connecting rod.
BBC Dome piston website.jpg
Piston of a car engine it is supported and powered by a car engine crankshaft. Piston be in motion upwards the gap among its top surface and the closed and of the cylinder is reduced. As the piston is in motion and moves downwards the gap above it is increased. When the piston is shifted upward the gas trapped in the space is compacted and when piston is shifted downward the gas in the space is expanded. Piston is connected to a crankshaft via a connecting rod and piston helps crankshaft in moving in a circular motion through the connecting rod when piston moves up and down. The crankshaft rotates clockwise as the piston is pressed downwards awaiting the piston reaches the lowest point of its travel. The pact is such that rotary motion of the crankshaft origin the piston to move upward and downward freely inside the cylinder of an engine. A side force is caused and which is applied by a piston on a cylinder wall. The charge is packed together into the peak end of the cylinder called the combustion chamber. This is realized by the upward side force. It should have some clearance to let the piston move freely in a cylinder. Piston fits closely inside the cylinder. Ideally it would completely gas tight yet completely free to move up and down inside the cylinder. Seeing as the maximum leakage takes place when the gas is hottest much of oil film lubricating and pressures are highest the piston will be burnt or carbonised. Following combustion the gasses include probably tiny amounts of sulphur dioxide, water vapour, carbon dioxide which possibly will include the lubricating oil and direct of corrosion of the engine parts. Piston rings are fitted in grooves to reduce the gas leakage.
As being an important component of an engine a piston should have a better service life then the other components of engine. As engine has high temperature so the component used to make a piston should have high thermal conductivity so a piston should be forged aluminium alloy so it can work easily under high temperature .A piston should have light weight so piston can easily move up and down.
1b. Essential Material Attributes
The component use for piston should have the attributes which can be help for piston to work easily.
Component use for piston should be capable of the following attributes.
It should be of low cost.
It should be available in market.
It should have high strength.
It should have thermal conductivity.
It should have high ductility.
1c.Comparing with engineering materials
There are four kinds of engineering materials.
Metals(Ferrous and non-Ferrous metals)
Component needed to manufacture a piston should have the power to bear conditions take place in an engine. Ferrous metals include cast iron and steel which can be considered for manufacturing for a piston. Difference between cast iron and steel is cast iron has worst corrosion resistance then steel. Steel can be found suitable for manufacturing a piston. But if we talk about non-ferrous metals aluminium alloy is better than steel because it has reduced weight, high thermal conductivity, high ductility, high strength and high corrosion resistance then steel and it is easy to manufacture.
Ceramics have three types
Ceramics cannot be considered for manufacturing of a piston because ceramics have low strength and low ductility.
Polymers are of three types.
Polymers are not be considered for a manufacturing of a piston because polymers have the properties which are not suitable for manufacturing of a piston such as low thermal conductivity and low stiffness.
Composite materials have all the qualities to manufacture the piston .it have reduced weight, high thermal conductivity, high strength and high ductility but composite materials are more expansive from aluminium alloy that's why it cannot be considered for manufacturing of a piston.
1d. Causes of failure of the component
A component fails when it fails to achieve the desired requirement of a mechanism and fails to work properly.
Failure of a piston may have many reasons like failing to work under the atmosphere of an engine. A piston should be manufactured by material which can stand on the requirements needed to manufacture a piston.
Low Thermal Conductivity
Bad corrosion resistance
If piston is made up of a component which has low thermal conductivity then it won't be helpful for a piston to work properly in an engine because the temperature of engine is very high.
1. To prevent the failure of a piston it should be manufactured by a component which has high thermal conductivity.
2. A piston should be manufactured while keeping all the conditions in the mind which occur in an engine.
3. Piston should be manufactured by a component which has several mechanical properties like (hardness, strength and good corrosion resistance).
Tensile test are carried out for several reasons. It is used to find out the toughness and the ductility of a material. Tensile properties commonly include the material requirements to ensure the quality. Ductility refers to the capability of a material to deform lastingly with no breaking, when stresses are applied. Toughness is the capability of a material to survive stresses before breaking and is calculated by measuring the area under stress-strain curve. The tensile test is performed by positioning a particularly shaped specimen in the top of testing machine. The specimen is pulled at a distance from end to end in a mechanical loading system. Mostly the tensile tests are performed at room temperature and the tensile load is applied slowly. The unit for the measurement of the tensile strength is Pascal or Newton per square meter (N.) and it is classify by the following equation.
Tensile strength (Pa) =
Figure 2.1Tensile test machine
Tensile test specimen has a gage length of 2.0 in and an area =0.5.during the test the specimen yield under a load of 32,000 ib. The corresponding gage length=2.0083.this is the present yield point .the maximum load of 60,000 is reached at a gage length 2.60 in
An aluminium alloy rod is taken and its dimension is noted i.e. cross sectional area, height the rod is placed into the machine and the test starts.
The force of on the machine is gradually increased until the breaking point of the rod is reached. And the valve of the force is noted.
Mechanical properties of aluminium alloy in an annealed state.
Yield strength, tensile strength and ductility for several of the common metals. These properties are sensitive to any prior deformation, the presence of impurities, and heat treatment to which the metal has been subjected.
Data analysis and results. This section reviews some of the further important consideration involved in the tensile .These include
Data recording and analysis
When a material is tested then the objective usually is to find out whether material is suitable or not for its proposed use. It must be form the same source and have under gone the same processing steps. The specimen must be as nearly identical as possible so difference in the test result as far as possible, only the variability in the testing process.
The body of an aircraft should be constructed by aluminium alloy because aluminium alloy have high density and high strength; the body of an aircraft is one of the most important parts of an aircraft so it should have the mechanical properties which are helpful for an aircraft. Air craft should have light weight so aluminium alloy has that property of light weight that's why Boeing 757 is constructed be aluminium alloy. Aluminium alloy have high corrosion resistance this property for aluminium ally is also helpful because it gives better service life to the body of an air craft. Aluminium alloy have durability and it's a long lasting material. While keeping these properties in mind body of an aircraft is manufactured by aluminium alloy.
The body of a car is manufactured by steel
Glasses: A glass is a ceramic material. Usage of glasses takes place daily in our life. Glasses are formed by melting raw materials and then shapes are made after cooling the raw materials. Melting process is not required for forming a glass; glasses are also formed by vapour deposition, by sol-gel processing of solutions and by neutron irradiation of crystalline materials. Most usually glasses are in use are non-metallic glasses but metallic are the one most commonly used in these past years.
Advantages of glass
Manufacturing glass by sol-gel process can be helpful in reducing air pollution.
Glasses can be easily recycled.
Disadvantages of glass
Glasses are breakable.
Glasses are high cost materials.
Aluminium: They are considered by a relatively low density, high electrical, thermal conductivity and a resistance to corrosion in various frequent environments including atmosphere. It is not soluble in water under normal circumstances. Aluminium is not easy to decompose because the metal is strongly electropositive. Aluminium is easily formed by good quality of high ductility. Aluminium ductility is retained even at very low temperature. Aluminium has high affinity for oxygen. The mechanical strength of aluminium may be enhanced by cold work.
Advantages of aluminium
Aluminium can be easily recycled.
Aluminium has high toughness.
Disadvantages of aluminium
Aluminium is very expensive.
If aluminium is mix with water daily intake of it can cause disease like memory lose and allergy
Plastics: It is defined as any non-metallic that can be moulding the shape. Most of plastics are composed of nitrogen, oxygen, hydrogen and carbon. Possibly the great number of different polymers materials come under the classification of plastics. At the present age the use of plastic materials continues increasing.
Most commonly plastics are classified as:
Thermoplastics: The plastics which soften on the application of heat with or without pressure but require cooling to set them to shape are known as thermoplastic materials.
Thermosetting: The plastics which have need of heat and pressure to mould then in to shape are known as thermosetting.