# Mechanical Interview Questions 12

Mechanical Interview Questions 12 contains questions...

111. What are the basic causes of the problem of rotor failure?

112. What are the differences between impulse and reaction turbines?

113. What is the difference between Critical speed & Whirling speed?

114. What is the significance of Torque(in N-m) given in the engine specification ?

115. What is the abbreviation of Welding rod 7018?

116. What are the uses of Graphite electrode in various field.

117. Difference between TIG & MIG welding

118. What is Specific speed of turbine?

119. Material of Aircraft turbine blade?

120. Do you know epicyclic gear box? What are the practical application of epicyclic gear box?

111. What are the basic causes of the problem of rotor failure?

 Normal wear.

 Fatigue failure due to high stress.

 Design deficiency.

 Aggressive operating environment

112. What are the differences between impulse and reaction turbines?

 The impulse turbine is characterized by the fact that it requires nozzles and that the pressure drop of steam takes place in the nozzles.

 The reaction turbine, unlike the impulse turbines has no nozzles, as such. It consists of a row of blades mounted on a drum.

The drum blades are separated by rows of fixed blades mounted in the turbine casing. These fixed blades serve as nozzles as well as the means of correcting the direction of steam onto the moving blades.

 In the case of reaction turbines, the pressure drop of steam takes place over the blades. This pressure drop produces a reaction and hence cause the motion of the rotor.

113. What is the difference between Critical speed & Whirling speed?

In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear.

As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases system vibration.

The resulting resonance occurs regardless of orientation.

Whirling Speed is due to the unbalanced forces acting on a rotating shaft.

114. What is the significance of Torque(in N-m) given in the engine specification ?

It give the moment about any point or simple rotation.

115. What is the abbreviation of Welding rod 7018?

7018=

70=tensile strength 70000psi

1= welding position

8=current flux

116. What are the uses of Graphite electrode in various field.

Graphite electrode is used in EDM.. and in Battery cells..

It is also used in electric arc furnaces to melt the steel .

117. Difference between TIG & MIG welding

Tungsten inert gas welding-non consumable electrode

MIG-Metal inert gas welding-uses consumable electrode

118. What is Specific speed of turbine?

The specific speed is defined as the the speed of the geometric turbine which can produce unit power at unit head

119. Material of Aircraft turbine blade?

Ni, Cr, Al, Traces of C

120. Do you know epicyclic gear box? What are the practical application of epicyclic gear box?

Epicyclic gear box consists of sun gear planetary gears and an annular called ring gear.

Different speed ratios are obtained by locking any one gear.

If you lock any two gear , direct gear will be obtained.

Mostly used in overdrives.

Wrist watch is a practical application of epicyclic gear box