Basic terms of mechanical engg. 3

Supercharging:
Actually, power output of engine depends on what amount of air enter into the engine through intake manifold. Amount of entry aiy if increased, then must be engine speed will increased. Amount of air will be increased by increasing inlet air density. The process of increasing inlet air density is supercharging. The device which is used for supercharging is called supercharger.Superchargeris driven by a belt from engine crakshaft. It is installed in intake system.

Turbocharging:Turbocharging is similar to the supercharging. But in that case tubocharger is installed in exhaust system whereas supercharger is installed in intake system. Turbocharger is driven by force of exhaust gas. Generally, turbocharger is used for 2-stroke engine by utilizing exhaust energy of the engine, it recovers energy otherwise which would go waste.

Governeor:Its function id to regulate mean speed of engine when there are variation in the load. If load incrases on the engine, then engine's speed must decrease. In that case supply of working fluid have to increase. In the otherway, if load decrease on the engine, then engine' speed must increase. In that case supply of working fluid have to decrease.Governor automatcally, controls the supply of working fluid to the engine with varying load condition.

Flywheel:It is the one of the main parts of the I.C. engine. Its main function id to store energy in the time of working stroke or expansion stroke. And, it releasesenergy to the crankshaft in the time of suction stroke, compression stroke & exhaust stroke. Because, engine has only one power producing stroke.

Rating of fuel:
S.I. Engine:
Octane number. Octane number indicates ability of fuel to resist knock.

C.I. Engine:
Cetane Number. Cetane number indicates ability of ignition of diesel fuel. That means, how much fast ignites diesel fuel.

Stoichiometric ratio:It is the chemically correct air-fuel ratio by volume. By which theoratically sufficient oxygen will be gotten to burn all combustible elements in fuel completely.

Heat Transfer:It is a science which deals with energy transfer between material bodies as a result of temperature difference.There are three way to heat transfer such as-ConductionConvectionRadiation

Thermal Conductivity:
It is the quantity of heat flows between two parts of solid material by conduction. In this case following consideration will be important fact-

Time------ 1 sec

Area of that solid material-------- 1 m²

Thickness of that solid material------ 1m

Temperature difference between two parts of that material------ 1k

Heat Exchanger:It is one type of device which can transfer heat from one fluid to another fluid. Example- Radiator, intercooler, preheater, condenser, boiler etc.

Refrigeration:
It is the process of removing heat from a substance. Actually, extraction of heat from a body whose temperature is already below the temperature of its surroundings.

1 tonne of refrigeration:It is amount of refrigeration effect or cooling effect which is produced by uniform melting of 1 tonne ice in 24 hours from or at 0 degree centigrade or freezing 1 tonne water in 24 hours from or at 0 degree centigrade.

Humidification:It is the addition of moisture to the air without change dry bulb temperatur.

Dehumidification:
It is the removal of moisture from the air without change dry bulb temperature.

Gear Train:Meshing of two or more gear. It can transmit power from one shaft to another shaft.

Heat Treatment:Operation involving heating and cooling of a metal in solid state for obtaining desirable condition without being changed chemical composition.Its object-increase hardness of metal.increase quality of metal ( heat, corrosion,wear resistance quality )improve machinability.

Ferrous Metal:1. Cast Iron - (2-6.67)%C, Si, Mn, P, S

2. Steel - (0-2)%C

3. Wrought Iron - 99.5% Fe

Non-Ferrous Metal:
1. Brass - (Cu+Zn)

2. Bronze -

(Sn+Cu) ------ Tin Bronze

(Si+Cu) ------- Silicon Bronze

(Al+Cu) ------- Aluminium Bronze

Allowance:
It is the difference between basic dimension of mating parts. That means, minimum clearance between mating parts that can be allowed.

Tolerance:
It is the difference between upper limit of dimension. It is also the permissible variation above and below the basic size. That means maximum permissible variation in dimensions.

Clearance:It is the difference in size between mating parts. That means, in that case the outside dimension of the shaft is less than internal dimension of the hole.

Stiffness:
It is the ability to resist deformation.

Toughness:It is the property to resist fracture.

Fatigue:When a material is subjected to repeated stress below yield point stress, such type of failure is fatigue failure.

Nuclear Fission:It is a nuclear reaction by which one big nucleous divided into two or more nucleous.

Nuclear Fussion:It is also a nuclear reaction by which one big nucleous will produced by adding two small nucleous.

Welding:It is the process of joining two similar or dissimilar metal by fusion.

Arc Welding -

* need D.C current

* produced (6000-7000) Degree Centegrade Temperature

Gas Welding -

* Oxy - acetylene flame join metals

* Oxygen & acetylene gas works

* produced 3200 Degree Centegrade Temperature

Machine Tool:It is the power driven tool. It cut & form all kinds of metal parts.

Example - 1. Lathe2. Drill Press3. Shaper4. Planer5. Grinding6. Miling7. Broaching8. Boring

Cutting Tool:

Tool Materials for Cutting Tool:
1. High Carbon Steel

2. High Speed Steel (W+Cr+V)

3. Carbide (W Carbide+Ti Carbide+Co Carbide)

Indexing:

It is the method of dividing periphery of job into equal number of division. Actually, it is the process of dividing circular or other shape of workpiece into equal space, division or angle.

Jig:
It is one type of device which hold & locate workpiece and also guide & control cutting tool. It uses in drilling, reaming and tapping.

Fixture:
It is one type of device which hold and locate workpiece. It uses in miling, grinding, planning & turning.