Mechanical Engineering Interview Questions and Answers

Q1. What Kind Of Pipes Are Used For Steam Lines?
Pressure and temperature are two of the most important factors to be considered before selecting the type of material to be used. Steam is a compressible gas due to which the capacity of the pipe line depends on the size of the pipes and pressure of the steam. Since steam at even low pressure can be dangerous, extra care is to be taken. Galvanized pipes are usually not used for steam. Pipes made of mild steel with welded fittings are instead largely used.

Q2. What is the difference between shear center flexural center of twist and elastic center?
The shear center is the centroid of a cross-section. The flexural center is the center of twist, which is the point on a beam that you can add a load without torsion. The elastic center is located at the center of gravity. If the object is homogeneous and symmetrical in both directions of the cross-section then they are all equivalent.

Q3. What is the difference between Production and Manufacturing?

Q4. What is the difference between scavenging and supercharging?
Scavenging is process of flushing out burnst gases from engine cylinder by introducing fresh air in the cylinder before exhaust stroke ends.
Supercharging is the process of supplying higher mass of air by compressing the atmospheric air.

Q5. Why entropy change for a reversible adiabtic process is zero?
Because there is no heat transfer in this process.

Q6. What are two essential conditions of perfect gas?
It satisfies equation of state and its specific heats are constant

Q7. What is an accident?
An accident is an unexpected and unforeseen event which may or may not injury to a person or a machine tool.

Q8.  What are the standard sizes of drawing board as per Indian Standards?
As per Indian Standards: 1250×900,900×650,650×500,500×350,350×250 sizes are available.

Q9.  What are the functions of a scale?
a. To measure distance accurately.
b.  For making a drawing to scale either in full size, reduced size or enlarged size.

Q10.  What is a sketching?
This is the freehand expression of the graphic language.

Q11.  What do you mean by First Aid?
First Aid is immediate and temporary care given to a person who affected accidental injury or a sudden illness before the arrival of the doctor.

Q12.What is the difference between stalling in rotary compressions?
Stalling is alocal phenomenon and it occurs when how breajs away from the blades.
Surging causes complete breakdown of flow and as such it affects the whole machine.

Q13.What is pitting ?How it is caused?
Non uniform corrosion over the entire metal surface ,but occuring only in small pits is called pitting .it is caused by lack of uniformity in metal.

Q14. What is caustic embrittlement?
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 rivetted joints and around the rivet holes.

Q15. What is Drafting machine (Mini Drafter)?
A drafting machine is a tool used in technical drawing, consisting of a pair of scales mounted to form a right angle on an articulated protractor head that allows an angular rotation.

Q16. What are the advantages of gear drive?
Here are the advantages of gear drive:-

• It provides large range of speed and torque for same input power.
• It is compact and need less space.
• It offers more accurate timing than a chain system does, less friction loss and less noisy.
• It provides precise velocity ratio.
• It is used to get various speeds at different load conditions.
• There are different geometry of gears which offers different advantages for varied applications.
• In general it is useful for power transmission between two shafts.

Q17. What is ductile-brittle transition temperature?
The ductile brittle transition temperature is the minimum temperature in which a given material has the ability to absorb a specific amount of energy without fracturing.
As temperatures decrease, a material’s ability to deform in a ductile matter decreases. This is usually measured using on a case-by-case basis using a Charpy impact test.

Q18. What is the difference between rocket motion and a projectile motion?
The key difference is between the launch phase.
In a projectile motion once force is applied against gravity (or not) you dont apply additional force be it constant or varying to resist the motion or accelerate it further with some external source.
In rocket motion during the initial launch stage a continuous force is applied to do work against gravity.

Q19. Define Carnot engine.
It was an imaginary engine conceptualized by Carnot and this follows the Carnot cycle and provides 100% efficiency.

Q20. Differentiate P11 and P12 Pipes.
P11 the chromium molybdenum composition which has 1% of chromium and molybdenum by 1/4% .
Whereas P12 is the chromium molybdenum composition which has 1% of chromium and 2% of molybdenum.

Q21. What are the methods of extinguishing the fire ?

• Separating or removing the burning material from the neighborhood of the fire.
• Preventing the air flow to the fire.
• Lowering the heat created by burning materials.

Q22. What are the precautions to be taken to avoid fire?

1. The buckets along with sand should be placed inside the workshop.
   2. Switches and other electrical parts must be made of fireproof material.
   3. Carbon dioxide gas should be placed at required points in special containers.
   4. Fire extinguishers of suitable type should be placed at accessible places.\

Q23. What safety precautions should be observed while working in the workshop?

• Keep shop floor clean, free from oil and other slippery materials.
• Wear a proper dress and avoid loose clothing and loose hair.
• Wear shoes and avoid chapels.
• Avoid playing, loose talk and funning inside the shop floor.
• Keep good housekeeping and put all unnecessary items and rejected items in the scrap box.
• Learn everything about the machine before starting and clear all the doubts.
• Keep a safe distance from rotating and sliding parts.
• Never store inflammable materials inside or around the shop.
• Never play with electricity, fire, parts with sharp edge etc.
• Keep fire buckets and extinguishers ready for use.

Q24. Why gas turbine poer plant needs efficient compressor ?
Because a large portion of turbine work is eaten away by compressor and its inefficiency will affect net power output and cost of generation.

Q25. What is the effect of inter cooling in gas turbines ?
It decreases thermal efficiency but increases net output