MECHANICAL ENGINEERING INTERVIEW QUESTIONS :-
1.)What causes hardness in steel ? How heat treatment alters properties of steel ?
Ans: The shape and distribution of the carbides in the iron determines the hardness of the steel. Carbides can be dissolved in austenite is the basis of the heat treatment of steel. If steel is heated above the A critical temperature to dissolve all the carbides, and then cooled, suitable cooling through the cooling range will produce the desired size and distribution of carbides in the ferrite, imparting different properties.
2.)What is the difference between streamline body and bluff body ?
Ans: In streamline body the shape is such that separation in flow occurs past the nearmost part of the body so that wake formed is small and thus friction drag is much greater than pressure drag. In bluff body the flow gets separated much ahead of its rear resulting in large wake and thus pressure drag is much greater than the friction drag.
3.)Define hydraulically efficient channel cross section.
Ans: The shape of such section is that which produces minimum wetted perimeter for a given area of flow and carries maximum
flow.
4.)What is the difference between alpha iron, delta iron and gamma iron ?
Ans: The bcc form of iron exists between room temperature and 910°C, and between 1400°C and the melting point at 1539°C. The lower temperature form is known as "alpha"-iron and the higher temperature form as "delta"-iron. The face-centered cubic form existing between 910°C and 1400°C is referred to as "gamma-iron".
5.)Explain the difference between the points of inflexion and contraflexure.
Ans: At points of inflexion in a loaded beam the bending moment is zero and at points of contraflexure in loaded beam the bending moment changes sign from increasing to decreasing
6.)What do you understand by eutectic ?
Ans: It is mechanical mixture of two or more phases which solidify simultaneously from the liquid alloy.
7.)Under what condition a convergent divergent nozzle required ?
Ans: When pressure ratio is greater than critical pressure ratio.
8.)What is the difference between isotropic material and homogeneous material ?
Ans: In homogeneous material the composition is same throughout and in isotropic material the elastic constants are same in all directions.
9.)What do you understand by catenary cable ?
Ans: A cable attached to the supports and carrying its own weight.
10.)What is the difference between basic hole and basic shaft ?
Ans: A basic hole is one whose lower deviation is zero and in case of basic shaft the upper deviation is zero.
11.)Why should a chain drive be used over a belt or rope driven drive? State pro`s and con`s?
The advantages of using a chain drives are:
- In a chain drive no slip occurrence takes place.
- The chains take less space as compared to rope or belts as they are made of metal and offer much strength.
- The chain drives can be used at both short and long ranges and they offer a high level of transmission efficiency.
- Chain drives can transmit more load and power as compared to belts.
- A very high speed ratio can be maintained in one step of chain drives.
Some of the cons of using a chain drive are:
- The cost of producing chain drives is higher as compared to that of belts.
- The chain drives must be serviced and maintained at regular intervals and henceforth their cost of ownership is high comparatively.
12.)Briefly explain the advantages of Cycloidal and Involute gears?
The advantages of the Cycloidal gears are as follows:
- Having a wider flank as compared to Involute gears they are considered to have more strength and hence can withstand further load and stress.
- The contact in case of cycloidal gears is between the concave surface and the convex flank. This results in less wear and tear.
- No interference occurs in these types of gears.
The advantages of Involute gears are as follows:
- The primary advantage of involute gears is that it allows the changing of the centre distance of a pair without changing the velocity ratio.
- The pressure angle remains constant from start to end teeth, this results in less wear and smooth running of the gears.
- The involute gears are easier to manufacture as they can be generated in a single curve ( the face and flank )
13.)What is Sentinel Relief Valve?
Ans. It’s a special type valve system. The valve will open when exhaust casing pressure is excessive (high). The valve warns the operator only; it is not intended to relieve the casing pressure.
14.)What is the difference between Specification,Codes, Standards?
Ans. Specification is describing properties of any type of materials. Code is procedure of acceptance and rejection criteria.
Standard is accepted values and compare
other with it.
15.) What is difference between Welding and Brazing?
Ans. In Welding concentrated heat (high temperature) is applied at the joint of metal and fuse together. In Brazing involves significantly lower temperatures and does not entail the melting of base metals. Instead, a filler metal is melted and forced to flow into the joint through capillary action.
16.)On what basis can sliding contact bearings be classified? Explain?
Sliding contact bearings can be classified on the basis of the thickness of the lubricating agent layer between the bearing and the journal. They can be classified as follows:
- Thick film bearings: These type of bearings have their working surface separated by a layer of the lubricant. They are also known as hydrodynamic lubricated bearings.
- Thin film bearings: In this type of bearings the surfaces are partially in direct contact with each other even after the presence of a lubricant. The other name for such type of bearings is boundary lubricated bearings.
- Zero Film Bearings: These type of bearings as their name suggests have no lubricant present between the contact layers.
- Externally or hydrostatically pressurized lubricated bearings: These bearings are able to without any relative motion support steady loads
17.)How does nitrous oxide help an engine perform better?
We know about how sodium chlorate acts as a way to store oxygen. You release the oxygen in sodium chlorate by heating it. It turns out that nitrous oxide (N20) works exactly the same way. When you heat nitrous oxide to about 570 degrees F (~300 C), it splits into oxygen and nitrogen. So the injection of nitrous oxide into an engine means that more oxygen is available during combustion. Because you have more oxygen, you can also inject more fuel, allowing the same engine to produce more power. Nitrous oxide is one of the simplest ways to provide a significant horsepower boost to any gasoline engine.
Nitrous oxide has another effect that improves performance even more. When it vaporizes, nitrous oxide provides a significant cooling effect on the intake air. When you reduce the intake air temperature, you increase the air's density, and this provides even more oxygen inside the cylinder.
The only problem with nitrous oxide is that it is fairly bulky, and the engine needs a lot of it. Like any gas, it takes up a fair amount of space even when compressed into a liquid. A 5-liter engine running at 4,000 rotations per minute (rpm) consumes about 10,000 liters of air every minute (compared to about 0.2 liters of gasoline), so it would take a tremendous amount of nitrous oxide to run a car continuously. Therefore, a car normally carries only a few minutes of nitrous oxide, and the driver uses it very selectively by pushing a button.
18.)Why does a car's engine get hot when it is running?
A car's engine is not efficient.
The engine works by converting chemical energy in the form of fuel to the mechanical energy (work) that drives the wheels and makes the car move.
But only about 20 to 30 percent of the chemical energy is actually converted to mechanical energy. What happens to the remaining 70 to 80%?
It gets converted to heat.
In fact, thermodynamics tells us that we cannot convert the fuel completely into work. This is the result of the famous Second Law of Thermodynamics
19.) What is the difference between drum brakes and disc brakes?
In Drum brakes a hollow drum is attached to the wheel of the vehicle called the hub and inside that hollow hub two break linings or shoes are fixed , with a mechanism of pushing them towards the inner surface of the hub and when we apply break pedal to stop the vehicle, the break shoes apply the force against the inner surface of the drum and stops the vehicle. It is of two types one is mechanical and the other is hydraulic based and in the hydraulic system 'Break fluid ' is used.
In case of Disc brakes there is a metal disk made up of high quality metal is fixed to the wheel having both the side of the disk fully polished and there are break shoes holding on both the side of the disk in opposite direction and when the break is applied both the break shoes press against the disc and hold together the disk tightly resulting in the immediate stop of the vehicle.
Disc brakes perform better in wet weather, because centrifugal force tends to fling water off the brake disc and keep it dry, whereas drum brakes will collect some water on the inside surface where the brake shoes contact the drums.
The disk breaks are also visible outer side of the vehicle and the drum brakes are built inside the hub
20.)Why do disc brake pads have holes?
Today's modern disc brakes were holed either with drilling or slotting. The reason for providing these holes in the disc brakes are as follows :-
(1.) To lessen the heat generation due to friction. The holes help the escape of heat.
(2.) The second reason is gas build up.This is not a problem in new disc brakes but the material used in the older disc brakes caused gases to build up.
(3.) The third reason is water. The water enter the pads surface and cause slippery.
So having drilled holes on a brake rotor makes it easy for heat , gas and water to be quickly moved away from the rotor surface , keeping the brake performance strong.
Cars typically have four-stroke gasoline engines, which means there are four strokes, or movements, to the moving parts inside the engine per rotation. Inside each cylinder is a piston, which moves up and down within the cylinder to compress the gas for combustion, and pushes the exhaust gases out after combustion. The piston is operated by an arm that attaches to the crankshaft, a shaft that extends through the bottom of the engine. The piston goes up and down twice during each rotation, hence the four strokes -- up, down, up, down. 
