Mechanical Engineering Interview Questions & Answer

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Mechanical Engineering Interview Questions

Mechanical Engineering Interview Questions & Answer

Mechanical Engineering Interview Questions & Answer-You will always upgrade to the upper level or a new position in whatever business you work in only by answering or interviewing the questions with confidence and enthusiasms may be part of the process. Always remember, while giving interview you needs to have a soft smile on your face along with confidence and enthusiasm for the applied job and the industry itself.

We are providing you a set of ‘Mechanical Engineering Interview Questions & Answer, which will help you in your next Mechanical Engineering interview.

Mechanical Engineering Interview Questions & Answer:

1-What do you mean by heat treatment and why is it done?

Ans: it is the process or operation in which the heating and cooling of a metal or alloy is done in order to obtain desirable characteristics without changing the compositions.

Heat treatment is generally performed in the following ways:

  • Normalizing
  • Annealing
  • Spheroidising
  • Hardening
  • Tempering
  • Surface or case hardening

Some of the motives or purpose of heat treatment are as follows:

  • In order to improve the machinability of the metal.
  • To change the grain size.
  • To provide better resistance to heat, corrosion, wear etc.
  • In order to improve the hardness of metals.
  • For the softening of the metal.

2- State the difference between scavenging and supercharging?

Ans: Supercharging is the process of supplying higher mass of air by compressing the atmospheric air, whereas Scavenging is process of flushing out burnt gases from engine cylinder by introducing fresh air in the cylinder before exhaust stroke ends.

3- What is the difference between displacement pumps and centrifugal pump?

Ans: Displacement pump is a device which delivers a constant volume of liquid for each cycle at varying discharge (Q) pressure or HEAD, and Centrifugal pump is a device in which high velocity of the liquid will then produce a velocity head and at the same time producing a high flow rate.

4- What did you understand by cotter joint?

Ans: Cotter joints are used to connect two rods, which are under compressive or tensile stress. The ends of the rods are in the manner of a socket and shaft that fit together and the cotter is driven into a slot that is common to both pieces drawing them tightly together. The tensile strength of the steel is proportionate to the strength needed to offset the stress on the material divided by the number of joints employed.

5- What are the differences between pneumatics and hydraulics?

Ans: Pneumatics:

  • Pneumatics use air
  • Pneumatic power is less as compared to hydraulics power.
  • P components are smaller.
  • In pneumatics, air is leaked into the atmosphere.
  • Pneumatics obtains power from an air compressor.
  • Air is compressible.

Hydraulics:

  • Hydraulics use Oil.
  • Hydraulic power is more than Pneumatic power.
  • H components are bigger than P components.
  • Leaks in hydraulics cause fluid to be sticking around the components.
  • Hydraulics requires a pump.
  • Air is not compressible in Hydraulics oils.

6- What is caustic embrittlement?

Ans: It is the actual physical change in metal that makes it extremely brittle and filled with minute cracks. It occurs particularly in the seams of riveted joints and around the rivet holes.

7- What did you mean by timed cylinder lubrication?

Ans: For effective lubrication, lub oil needs to be injected between two piston rings when piston is at bottom of stroke so that piston rides in oil during upward movement. This way lot of lub oil can be saved and used properly.

8- State the causes of failure of boiler tubes?

Ans: These kinds of tubes usually are made from carbon steel and are subject to high rates of heat transfer, bending stresses due to uneven heating, especially at expanded or welded joints into headers or drums, external erosion from burners and flue gas, possible corrosion on the boiler side, and occasional manufacturing defects.

-Failure may occur due to following reasons:

  • High thermal ratings may lead to rapid failure if the internal fluid flow is reduced for any reason. The resultant overheating leads to a failure by creep, characterized by the bulging of the tube with the eventual development of a longitudinal split.
  • Fatigue cracking due to bending stresses occurs. These are associated with change of section and/or weld undercut, where tubes are expanded or welded into headers.

-Some Failure may also arise due to overstressing of a reduced section of metal.

  • Sudden failure of the boiler tube due to corrosion arises from embrittlement of the carbon steel due to interaction between atomic hydrogen from the corrosion process and the iron carbide present in the steel.
  • Defects in tube manufacture, although far from being a regular occurrence, can be a cause of serious trouble. Lamination in boiler tubes or score marks arising from the cold drawing of tubes give rise to premature failure and may promote corrosion at these regions.

9- Enthalpy and entropy are functions of one single parameter. Which is that?

Ans:  Temperature.

Mechanical Engineering Interview Questions & Answer

10- State the names given to constant temperature, constant pressure, constant volume, constant internal energy, constant enthalpy, and constant entropy processes.

Ans:  Isothermal, isochroic, isobaric, free expression, throttling and adiabatic processes respectively.

11- Why entropy change for a reversible adiabatic process is zero?

Ans: Entropy change for a reversible adiabatic process is zero because there is no heat transfer in this process.

12- How much resistance is offered to heat flow by drop wise condensation?

Ans: Nil

13- What is the use of flash chamber in a vapor compression refrigeration cycle to improve the COP of refrigeration cycle?

Ans: When liquid refrigerant as obtained from condenser is throttled, there are some vapours. These vapours if carried through the evaporator will not contribute to refrigerating effect. Using a flash chamber at some intermediate pressure, the flash vapour at this pressure can be bled off and fed back to the compression process. The throttling process is then carried out in stages. Similarly compression process is also done in two separate compressor stages.

14- Name the countries to which Horse power of I.C. engines can be expressed as RAC rating, SAE rating, or DIN rating belongs?

Ans: U.K., USA and Germany respectively.

15- State two essential conditions of perfect gas?

Ans: It satisfies equation of state and its specific heats are constant.

16- State the relationship between COP of heating and cooling?

Ans: COP of heating is one (unity) more than COP of cooling.

17- What is isometric drawing?

Ans: It is a 3-D drawing used by draftsmen, architects etc

18- How pipe flanges are electrically insulated?

Ans: Pipe flanges are protected from corrosion by means of electrolysis, with dielectric flanges. The piping system is electrically insulated by what is called a sacrificial anode. A bag of readily corrodible metal is buried in the ground with a wire running from the pipe to the bag so that the sacrificial anode will corrode first. If any electrical current charges the pipe, it also serves as a ground.

19- Why are LNG pipes curved?

Ans: LNG pipes are curved because LNG is condensed gas (-164 deg cel) so it can expand the pipes that is what engineers designed the LNG pipes are curve type.

20- Explain Otto cycle.

Ans: Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle of a four stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.

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