Frequently Asked Interview Questions | Job Interview Questions | Mechanical Engineering Test Questions :: TheMech.in
1. A hollow shaft of same cross-section area as solid shaft transmits
A. Same torque
B. Less torque
C. More torque
D. Unpredictable
Answer:
B. Less torque
2. In a cantilever beam, maximum deflection occurs at where
A. Bending moment is zero
B. Bending moment is maximum
C. Shear force is zero
D. Slope is zero
Answer:
A. Bending moment is zero
3. In a rectangular beam, when width, depth and length are doubled, the bending stress will be
A. Shall remain unchanged
B. Shall be doubled
C. Shall become ¼ th
D. Shall be halved
Answer:
C. Shall become ¼ th
4. In an I –section beam, the bending moment is resisted mainly by
A. Flanges only
B. Web only
C. Both by flanges and web
D. None of the above
Answer:
B. Web only
5. In internal combustion (I.C.) engines, combustion of fuel takes place in
A. Outside the cylinder
B. Inside the cylinder
C. Not in the cylinder
D. None of the above
Answer:
B. Inside the cylinder
6. Power available at the shaft of an I.C engine is known is
A. Brake horse power
B. Indicated horse power
C. Net indicated horse power
D. Pumping power
Answer:
A. Brake horse power
7. In internal combustion engine piston the maximum temperature occurs at
A. Ring section
B. Gungeon pin
C. Bottom centre
D. Top centre
Answer:
A. Ring section
8. A two-stroke engine is generally preferred to a four-stroke engine because
A. It offers low fuel consumption
B. It gives lesser shocks and vibrations
C. It can be easily started
D. It has smaller size for the same output.
Answer:
D. It has smaller size for the same output.
9. During idling process, a petrol engine requires
A. Lean mixture
B. Rich mixture
C. Variable mixture
D. None of above
Answer:
A. Lean mixture
10. Cavitation in a pipe will begin when
A. Pressure at any location reaches pressure equal to the saturated vapour pressure of liquid
B. Pressure becomes more than critical pressure
C. Flow is increased
D. Pressure is increased
Answer:
A. Pressure at any location reaches pressure equal to the saturated vapour pressure of liquid
11. Capillary action of liquid is due to the
A. Viscosity of liquid
B. Cohesion of liquid particles
C. Surface tension
D. Adhesion of liquid particles on the surface
Answer:
B. Cohesion of liquid particles
12. In one ton refrigeration machine, the term “one ton” implies
A. One ton refrigerant is used
B. One ton water can be converted into ice
C. One ton ice when melts from and at 0oC in 24 hours, the refrigerating effects is equivalent to 3000 kcal/hour
D. None of the above
Answer:
C. One ton ice when melts from and at 0oC in 24 hours, the refrigerating effects is equivalent to 3000 kcal/hour
13. In a refrigeration cycle, the moisture content is to be removed before it enters into which system
A. Cold side of system
B. Evaporator
C. compressor
D. condenser
Answer:
B. Evaporator
14. What is the difference between Pipe and Tube?
Ex. Iron Pipe, Carbon Tube, Steel Tube etc.
· Tube is defined by Outer diameter and Wall thickness (OD and WT). While Pipe is defined by Inner diameter (ID).
Example:
2 inch pipe have 2.375 inch outer diameter, where 2 inch tube have same 2 inch outer diameter.
· Tube is easily shaped by bending, where Pipe needs some mechanical work to shape it.
· Tube is tight then Pipe.
· Tube is applicable to non cylindrical sections like Square and Rectangular.
15. Is gate valve used for Throttling?
Gate valves are not suitable for throttling because the control of flow is difficult for the valve’s design, and the flow of fluid slapping against a partially open gate can cause extensive damage to the valve.
16. Why is the Suction pipe of Vapour Compression Refrigeration system insulated?
1. It prevents the suction line from sweating and dripping water inside the house.
2. The insulation also prevents the suction line attracting heat from the outdoors on its way to the condenser coil.
17. How does Welding damage Eye sight?
An Electric welding arc produces Ultraviolet light and the UV light (Sun burn) will damage the retina. Welding shields or Goggles with the proper shade (Automatic shading) of lens is the best protection for welders.
Light filtering curtains and reduced reflective surfaces help protect both welders and observers in the area.
18. Explain why BCC, FCC and CPH lattice packing and features of grain structure affect the Ductility and Brittleness of parent metallic materials?
Ductility is the mechanical property of a material. (It is the material’s ability to deform under the tensile stress without fracture). So it is depends on the atoms how they arranged in a lattice and its grain size. The ability to absorb the energy of the impact and fracture resistance depends on the arrangement of the atoms in a lattice and features of grain structure.
19. Why do you have Truss Bridges?
Truss bridges carry load in tension and compression rather than bending (Self weight + The weight of vehicles crossing it + Wind loads). A truss has the ability to dissipate a load through the truss work. The beams are usually arranged in a repeated triangular pattern, since a triangle cannot be distorted by stress.
20. Why I-section beam is preferred for heavy loading?
Cross sectional shape I, giving many benefits. It is very good for giving stiffness (less deformation on loading) and to withstand higher bending moments (as a result of heavy loading) on comparison with other cross-sectional shapes of same area. Also, it is very easy to manufacture. It will have more moment of inertia.
21. What is difference between Center of Mass and Center of Gravity?
Both terms are same when gravity is uniform. When gravity is non-uniform following are the terms:
The center of mass is a point that acts as if all the mass was centered there (the mass on one side of the point is equal to the mass on the opposite side). If supported at the center of mass, an object will be balanced under the influence of gravity.
The center of gravity is the point at which where the sum (vector) of the gravitational forces act on an object which will be balanced on that point.
22. What is the difference between Center of Mass and Centroid?
If the material composing a body is uniform or homogeneous, the density or specific weight will be constant throughout the body, and then the centroid is the same as the center of gravity or center of mass.
Centroid: Centroid is the point, where the whole area of plane is going to be act. It is valid only for 2D problems like plane figures, square plate etc.
The center of mass is a point that acts as if all the mass was centered there (the mass on one side of the point is equal to the mass on the OPPOSITE side). If supported at the center of mass, an object will be balanced under the influence of gravity.
23. What are the differences between Weight and Mass?
Mass is a measure of how much matter an object has. Mass is specified in Gram or Kilograms.
Weight is a measure of how strongly gravity pulls on that matter. Force is measured in Newton’s.
F=m.g
Thus if you were to travel to the moon your weight would change because the pull of gravity is weaker there than on Earth but, your mass would stay the same because you are still made up of the same amount of matter.
24. What is the difference between Projectile motion and a Rocket motion?
A projectile has no motor/rocket on it, so all of its momentum is given to it as it is launched. An example of a projectile would be pen that you throw across a room.
A rocket or missile does have a motor/rocket on it so it can accelerate itself while moving and so resist other forces such as gravity.
In mechanics point of view projectile don’t have any particular shape it is a point mass. Whereas rocket has a particular shape and hence it has center of gravity situated at particular point on its body. Therefore rocket motion comes under kinetics and projectile comes under kinematics.
25. What type of cooling used in High Voltage Transformer?
The big transformers you find on power poles usually use oil as a dielectric insulator, in smaller HV transformers, like the ones in TV’s are usually filled with resin.
26. What is honing of Cylinder Liners?
The honing equipment used has been manufactured by “Chris Marine”. The head of the honing device consists of four synchronized stones. For the initial honing diamond stones are used to break up the hardened surface in the scuffed areas. For the main honing very coarse and hard stones are used to produce a very desirable rough surface all over the liner.
The advantage, especially for the 2-stroke engines, is possibility to save the liner after a seizure, scuffing or blow-by or even to eliminate the ovality of the liner. Another advantage is that it is possible to machine a rough liner wall to obtain a well oiled surface.
27. What is the difference between Speed and Velocity?
Speed is scalar quantity and Velocity is a vector – velocity has both speed and direction.
Speed is expressed as distance moved (d) per unit of time(t). Speed is measured in the same physical units of measurement as velocity, but does not contain an element of direction. Speed is thus the magnitude component of velocity.
28. Difference between Yield Stress and Yield Strength?
Stress is a measure of the load applied to a sample relative to a cross sectional area of the sample. Strength is a quantification of the samples ability to carry a load. The terms “yield strength” and “yield stress” of a material are usually used interchangeably (correct or not). It is the stress which will just cause the material to plastically deform. If a material yields at 30,000 psi, the yield stress is 30,000 psi. If the part in question has a cross sectional area of 2 square inches, the strength at yield would be 60,000 pounds, but usually we just say the yield strength is 30,000 psi.
29. What is the difference between Yield and Ultimate tensile strength?
The yield strength is reached when the material becomes Non – linear (that is non elastic) and takes a permanent set when load is released. Material stretches but does not break. Ultimate strength is when it breaks and is higher than yield strength.
30. What is the difference between Flexural strength and Tensile strength?
Flexural strength is resistance offered against bending. Tensile strength is resistance offered against tensile force.
31. What is the difference between Shear and Tensile strength?
Tensile Strength for a Bolt is determined by applying a Force along it long axis. Shear Strength for a Bolt is determined by applying a Force across its diameter, as it would be loaded in a lug joint. Tensile strength is strength in tension when pulling force is applied. And shear strength is strength against cutting force which is known as shear force.
32. What is the difference between Tensile strength and Tensile modulus?
Tensile strength is the ultimate capacity of the material to resist a tensile load regardless of deflection.
Tensile modulus also known as Young’s modulus is a measure of the stiffness of an isotropic elastic material. It is defined as the ratio of the uni-axial stress over the uni-axial strain. It is determined from the slope of a stress-strain curve traced during tensile tests conducted on a sample of the material.
34. Normalizing operation is carried out in
a) Water
b) Oil
c) Air
d) Furnace
Ans.: c) Air
35. The main purpose of heat treatment of steels is to change the
a) Chemical composition
b) Mechanical properties
c) Surface finish
d) Physical properties
Ans.: b) Mechanical properties
36. Which of the following is a non-destructive test
a) Impact test
b) Charpy test
c) Cupping test
d) Radiography test
Ans.: d) Radiography test
37. Polymerization is associated with
a) Stainless steel
b) Cast iron
c) Thermoplastic
d) Duralumin
Ans.: c) Thermoplastic
38. The material of pattern in the investment casting is
a) Resin
b) Sand
c) Wax
d) Wood
Ans.: c) Wax
39. Shell moulding process requires
a) Wooden pattern
b) Plastic pattern
c) Sand pattern
d) Metal pattern
Ans.: d) Metal pattern
40. Liquid nitrogen containers can be made from
a) Ferritic stainless steel
b) HSLA steel
c) Titanium
d) Austenitic stainless steel
Ans.: d) Austenitic stainless steel
41. Stretching of rolled rings is done to
a) To meet dimensional requirement
b) To relieve stresses
c) To introduce stresses
d) To improve finish
Ans.: b) To relieve stresses
42. During manufacturing of spring, the coiling pitch is assumed to be larger than specified pitch by
a) 5-8%
b) 10-12%
c) 2-5%
d) none
Ans.: a) 5-8%
43. Metric thread have included angle:
a) 60°
b) 55°
c) 30°
d) None
Ans.: a) 60°
11. Which part of the cutting tool is prone to crater wear
a) Flank
b) Face
c) Shank
d) Base
Ans.: b) Face
44. The crater wear of a cutting tool is due to
a) Chemical action of the coolant
b) Excessive heat generated during cutting operation
c) Rubbing of tool against the work piece
d) Abrasive action of the chip
Ans.: d) Abrasive action of the chip
45. Crater wear is predominant in
a) Carbon tool steels
b) Tungsten carbide tools
c) High speed steel tools
d) Ceramic tools
Ans.: b) Tungsten carbide tools
46. Identify the single point cutting tool
a) Milling cutter
b) Hacksaw blade
c) Grinding wheel
d) Cutting tool used in a slotting machine
Ans.: d) Cutting tool used in a slotting machine
47. The angle between the tool face and the plane parallel to the base of the cutting tool is called
a) Lip angle
b) Cutting angle
c) Rack angle
d) Shear angle
Ans.: c) Rack angle
48. In metal cutting operation, the cutting angle is defined as the angle
a) between the flank and the horizontal machined surface
b) between the shear plane and the direction of tool travel
c) between the face of tool and the line tangent to the machined surface at the cutting point
d) between the tool face and the ground end surface of flank
Ans.: c) between the face of tool and the line tangent to the machined surface at the cutting point
49. The angle between the face and the flank of the single point cutting tool is known as
a) Rack angle
b) Clearance angle
c) Lip angle
d) Point angle
Ans.: b) Clearance angle
50. Cutting tool may be provided with large positive rack angle to
a) Have a better heat dissipation
b) Avoid rubbing with the finished surface
c) Increase the strength of cutting edge
d) Reduce the magnitude of cutting forces
Ans.: d) Reduce the magnitude of cutting forces
51. Single point thread cutting tool should ideally have
a) Zero rack angle
b) Positive rack
c) Negative rack
d) Normal rack
Ans.: a) Zero rack angle
52. With an increase in nose radius of single point cutting tools
a) Tool life increases
b) Excessive heat is generated
c) Surface finish deteriorates
d) Cutting speeds have to be kept small
Ans.: a) Tool life increases
53. Tool signature
a) Is a pictorial view of the tool
b) Outlines the orthographic projection of the tool
c) Represents complete specification of the tool
d) Is a numerical method of tool identification
e) Indicate life of tool
Ans.: d) Is a numerical method of tool identification
54. The cutting speed of a tool refers to
a) Revolution made by the tool in a specified time
b) Revolutions turned by the job in a specified time
c) Distance travelled by the tool in one revolution of the job
d) Rate at which cutting edge of the tool passes over the surface of work piece
Ans.: d) Rate at which cutting edge of the tool passes over the surface of work piece
55. Which is not the primary function of coolant in a metal cutting operation
a) To cool the tool and work piece and conduct the heat generated
b) To improve the cutting action
c) To help in giving bright shining surface to the job
d) To reduce the friction at the cutting point
Ans.: a) To cool the tool and work piece and conduct the heat generated
56. Choose the coolant that would be most appropriate for light cuts on aluminum alloys
a) Kerosene
b) Mineral oil
c) Soluble oil or emulsions
d) Straight fatty oil
Ans.: a) Kerosene
57. Tool life may be measured by the
a) Total time the tool has been in contact with the job
b) Quantity of material removed between the total sharpening
c) Number of work pieces machined between tool sharpening
d) Time for the flank wear to reach a certain dimension
e) Any one of the above
Ans.: e) Any one of the above
58. The tool life is influenced maximum by
a) Cutting speed
b) Tool material and geometry
c) Cutting fluid
d) Surface conditions of the workpiece
e) Skill of the operator
Ans.: a) Cutting speed
59. Seamless rings are made by the process
a) Super-plastic forming
b) Mandrel forging
c) Ring rolling
d) Diffusion bonding
Ans.: c) Ring rolling
2. Internal defects in material is detected by
a) Fluorescent penetrate check
b) Red dye check
c) Ultrasonic
d) Eddy current check
Ans.: c) Ultrasonic
60. Smaller the grains in steel
a) Higher the tensile strength
b) Higher the fatigue strength
c) Lower the creep
d) All the above
Ans.: a) Higher the tensile strength
61. Alloying element which lowers the hardenability in steel
a) Cobalt
b) Tungsten
c) Chromium
d) Aluminum
Ans.: d) Aluminum
62. Base element in Warp alloy is
a) Iron
b) Nickel
c) Cobalt
d) Aluminum
Ans.: b) Nickel
63. Glass bead peening on components done to
a) Improve creep strength
b) Improve fatigue strength
c) Improve finish
d) Impart further coating
Ans.: b) Improve fatigue strength
64. Forging is superior to casting due to
a) Better grain direction
b) Better flowability
c) Less internal defects
d) Higher strength
Ans.: a) Better grain direction
65. DOE in process control variance is
a) Department Of Energy
b) Design Of Experiments
c) Defects on external areas
d) None of the above
Ans.: b) Design Of Experiments
66. Strain rate is the lowest in
a) Hydraulic press
b) Counter blow hammers
c) Screw presses
d) Drop hammers
Ans.: c) Screw presses
67. Titanium is preferred in high pressure compressor blades due to
a) Higher strength
b) Lower density
c) High temperature strength
d) Higher strength to weight ratio
Ans.: d) Higher strength to weight ratio
68. Austenite is a combination of
a) Ferrite + austenite
b) ferrite+ cementite
c) Ferrite + graphite
d) cementite + gamma iron
Ans.: b) ferrite+ cementite
69. The unique property of cast iron
a) Malleability
b) Damping capacity
c) Hardness
d) Ductility
Ans.: b) Damping capacity
70. Charpy test is conducted to measure
a) Hardness
b) Fatigue resistance
c) Brittleness
d) Malleability
Ans.: c) Brittleness
71. Machinability of a metal depends on
a) Tensile strength
b) Hardness
c) Toughness
d) Both (a) & (b)
Ans.: d) Both (a) & (b)
72. For pure metals the recrystallization temperature is
a) 0.2Tm
b) 0.5Tm
c) 0.7Tm
d) 0.9Tm
Ans.: b) 0.5Tm
73. Impurity in the metal and alloy
a) Decreases the resistivity
b) Increases the resistivity
c) No effect
d) None of them
Ans.: b) Increases the resistivity
74. The increase in hardness due to cold working is called
a) cold hardening
b) hot hardening
c) work hardening
d) age hardening
Ans.: c) work hardening
75. Steel balls are manufactured by
a) casting
b) machining
c) sintering
d) spinning
Ans.: d) spinning
76. The mould is housed in a
a) flask
b) cope
c) drag
d) cheek
Ans.: a) flask
77. Cores are used to
a) make desired shapes in the casting
b) strengthen moulding sand
c) support loose pieces
a) remove pattern easily
Ans.: a) make desired shapes in the casting
78. The purpose of jigs and fixtures are to
a. Increased production rate
b. Increased machining accuracy
c. Facilitate interchangeable manufacturing
d. Enable employ less skilled operators
e. All of the above
Answer:
All of the above
79. Which one of the following methods produces gear by generating process
a. Hobbing
b. Casting
c. Punching
d. Milling
e. Broaching
Answer:
Hobbing
80. Tool life of the cutting tool is most affected by
a. Cutting speed
b. Tool geometry
c. Cutting feed and depth
d. Microstructure of material being cut
e. Not using coolant and lubricant
Answer:
Cutting speed
81. Metal in machining operation is removed by
a. Tearing chips
b. Distortion of metal
c. Shearing the metal across a zone
d. Cutting the metal across a zone
e. Pushing the metal with tool
Answer:
Shearing the metal across a zone
82. A feeler gauge is used to check
a. Radius
b. Screw pitch
c. Surface roughness
d. Unsymmetrical shape
e. Thickness of clearance
Answer:
Thickness of clearance
83. The impact strength of an material is an index of its
a. Toughness
b. Tensile strength
c. Capability of being cold worked
d. Hardness
e. Fatigue strength
Answer:
Toughness
84. If a material expands freely due to heating, it will develop
a. Thermal stress
b. Tensile stress
c. Bending
d. Compressive stress
e. No stress
Answer:
No stress
85. Ductility of material can be defined as
a. Ability to undergo large permanent deformation in compression
b. Ability to recover its original form
c. Ability to undergo large permanent deformation in tension
d. All of the above
e. None of the above
Answer:
Ability to undergo large permanent deformation in compression
86. Cast iron is characterized by minimum of following % of carbon
a. 0.2%
b. 0.8%
c. 1.3%
d. 2%
e. None of the above
Answer:
2%
87. Inconel is an alloy of
a. Nickel, chromium and iron
b. Nickel and copper
c. Nickel and chromium
d. Nickel and zinc
e. Nickel and lead
Answer:
Nickel, chromium and iron
88. Which of the following variable controls the physical properties of a perfect gas?
a. Pressure
b. Temperature
c. Volume
d. Atomic mass
e. All of the above
Answer:
All of the above
89. If heat be exchanged in reversible manner, which of the following property of the working substance will change accordingly
a. Temperature
b. Enthalpy
c. Internal energy
d. Entropy
e. All of the above
Answer:
Entropy
90. Compression ratio of I.C. Engine is
a. The ratio of volume of air in cylinder before compression stroke and after compression
b. Volume displaced by piston per stroke and clearance volume in cylinder
c. Ration of pressure after compression and before compression
d. Swept volume / cylinder volume
e. Cylinder volume / swept volume
Answer:
Volume displaced by piston per stroke and clearance volume in cylinder
91. Coefficient of friction is
a. Angle between normal reaction and the resultant of normal reaction and the limiting friction
b. Ration of limiting friction and normal reaction
c. The friction force acting when the body is just about to move
d. The friction force acting when the body is in motion
e. Tangent of angle of response
Answer:
Ration of limiting friction and normal reaction
92. Dynamic friction as compared to static friction is
a. Same
b. More
c. Less
d. May be less or more depending upon nature of surfaces and velocity
e. Has no correlation
Answer:
Less
93. How Cavitation can be eliminated in a Pump?
Cavitation means bubbles are forming in the liquid.
· To avoid Cavitation, we have to increase the Pump size to One or Two Inch;
· To increase the pressure of the Suction Head, or
· Decrease the Pump Speed.
94. Which pump is more efficient Centrifugal pump or Reciprocating pump?
Centrifugal pump.
Because flow rate is higher compared to reciprocating pump. Flow is smooth and it requires less space to install. Lower initial cost and lower maintenance cost.
95. Why Centrifugal Pump is not called as a Positive Displacement Type of Pump?
The centrifugal has varying flow depending on pressure or head, whereas the Positive Displacement pump has more or less constant flow regardless of pressure.
Likewise viscosity is constant for positive displacement pump where centrifugal pump have up and down value because the higher viscosity liquids fill the clearances of the pump causing a higher volumetric efficiency. When there is a viscosity change in supply there is also greater loss in the system. This means change in pump flow affected by the pressure change.
One more example is, positive displacement pump has more or less constant efficiency, where centrifugal pump has varying efficiency rate.
96. Why the centrifugal pump is called high discharge pump?
Centrifugal pump is a kinetic device. The centrifugal pump uses the centrifugal force to push out the fluid. So the liquid entering the pump receives kinetic energy from the rotating impeller. The centrifugal action of the impeller accelerates the liquid to a high velocity, transferring mechanical (rotational) energy to the liquid. So it discharges the liquid in high rate. It is given in the following formulae:
Centrifugal force F= (M*V2)/R.
Where,
M-Mass
V-Velocity
R-Radius
97. Why cavitation will occur in Centrifugal Pumps and not in Displacement pumps?
The formation of cavities (or bubbles) is induced by flow separation, or non-uniform flow velocities, inside a pump casing. In centrifugal pumps the eye of the pump impeller is smaller than the flow area of pipe. This decrease in flow area of pump results in increase in flow rate. So pressure drop happened between pump suction and the vanes of the impeller. Here air bubbles or cavities are formed because of liquid vapour due to increase in temperature in impeller. This air bubbles are transmitted to pump which forms cavitation.
98.What is Heat rate of a Power plant?
Heat rate is a measure of the turbine efficiency. It is determined from the total energy input supplied to the Turbine divided by the electrical energy output.
99.The highest value of Thermal conductivity is expected for
a.) Solid ice b.) Melting ice c.) Water d.) Boiling water.
Give the Thermal conductivity value.
Solid Ice – 3.48 W/mK
Melting Ice thermal conductivity value is low because temperature is less.
Water’s Thermal conductivity value is 2.18 W/mK.
100-What is a Hydrostatic system?
Hydrostatics is the study of fluid bodies that are
- At rest
- Moving sufficiently slowly so there is no relative motion between adjacent parts of the body
For hydrostatic situations
- There are no shear stresses
- There are only pressure forces that act perpendicular to any surface.
It’s a closed loop hydraulic systems. It comprises of motor and pump. Here pump supplies energy to motor and motor gives return energy to pump supply.
101-If you heat a piece of steel with a hole in the center will the diameter of the steel get bigger or smaller?
It gets bigger.
(Example: Always the bearings are heated first for new installation in a shaft.)
102-What is the difference between Blower and Fan?
Fan is an air pushing device. Either Axial or Centrifugal type systems are used to move the air in low pressure. It is rotated by a motor separately.
When the fan is a housing of blades and motor, then it called as Blower. It directs the air in a single path with high pressure.
103-How to find a Ductile-Brittle Transition Temperature in metals?
The point at which the fracture energy passes below a pre-determined point for a standard Impact tests. DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming.
104-What is Hydrodynamic Cavitation?
Hydrodynamic cavitation describes the process of vaporization in a constrained channel at a specific velocity.
Bubble generation and Bubble implosion which occurs in a flowing liquid as a result of a decrease and subsequent increase in pressure.
105) Difference between Performance and Efficiency?
· The accomplishment of a given task measured against preset known standards of accuracy, completeness, cost, and speed is called as Performance.
· Efficiency is defined as the input given and the work obtained from that input like money, time, labour etc. It’s the main factor of productivity.
106) What is the difference between Impact Force & Sudden Force?
· An impact is a high force or shock applied over a short time period when two or more bodies collide.
· A force which applies on the body (material) suddenly is known as sudden force.
107) Difference between Antifriction Bearing and Journal Bearing
Generally, journal bearings have higher friction force, consume higher energy and release more heat, but they have larger contact surface, so normally used in low speed high load applications. In anti friction bearings friction is less. One object just rolls over each other.
108) What is a Cotter joint?
A cotter joint is used to connect rigidly two co-axial rods or bars which are subjected to axial tensile or compressive forces. Here shaft is locked in place by a smaller pin that passes through the side of the lug and partly or completely through the shaft itself. This locking pin is named as cotter.
109) What is difference between Hardness and Toughness?
· Toughness is the ability of a material to absorb energy.
· Hardness is the ability of a material to withstand wear.
110) What is the difference between Toughness, Hardness and Strength?
· Toughness is the ability of a material to absorb energy.
· Hardness is the ability of a material to withstand wear.
· Strength is generally withstanding stresses, fatigue etc.
111) What is the difference between Strength and Stamina?
· Strength is capability over a short length of time.
· Stamina is the ability to keep going continuously.
————
112. How do you come to know air is Fully Saturated?
In its Dew point. (100% relative humidity condition).
113. What is the hottest part of refrigerant in the refrigeration System?
Compressor. (Some types of refrigeration system will reach up to 311 deg Celsius.)
114. How to measure Temperature of a Bearing?
Normally the temperature range from 80 degree to 110 degree Celsius. So the following temperature measurement devices are used.
· Dial Type Bearing Temperature Detector
· Stator Winding Temperature Detector
· Resistance Bearing Temperature Detector (Bearing RTD)
· Specialized in Pin type RTD
115. What is the purpose of Geyser Pressure Valve?
To release the pressure created inside due to evaporation of water.
116. What is a Sentinel Relief Valve?
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.
117. How is the excess Discharge Pressure prevented?
Discharge pressure prevented by a pressurized spike cushion. Here the system employs a pressurized cushion of air and a two o-ring piston, which permanently separates this air cushion from the water system. When the valve closes and the water flow is suddenly stopped, the pressure spike pushes the piston up the arrester chamber against the pressurized cushion of air. The air cushion in the arrester reacts instantly, absorbing the pressure spike that causes water hammer.
118. What does F.O.F. stand for in Piping design?
Face of Flange.
The F.O.F (Raised face and Flat face) is used to know the accurate dimension of the flange in order to avoid the minute errors in measurement in case of vertical or horizontal pipe lines.
119. What is Auto Dosing?
Auto dosing is an automated system of feeding the equipment with liquid products. It is the ideal way to ensure the correct calibrated dose at the right time every time in auto.
120. Difference between Codes, Standards and Specifications?
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Code is procedure of acceptance and rejection criteria.
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Standard is accepted values and compare other with it.
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Specification is describing properties of any type of materials.
121. Difference between Strainer and Filter
Strainer for coarse size, Filter is more accurate than Strainer.
122. What are differences between Welding & Brazing?
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.
123. What does a pump develops? Flow or Pressure
A pump does not create pressure, it only creates flow. Pressure is a measurement of the resistance to flow.
124. Which is heavier 1kg of Iron or 1kg of Cotton? and why?
Both of them have same weight. The only difference is the volume of Iron is small compared to Cotton.
125. What will be the position of Piston Ring?
In 180 degree angle the Top ring, Second ring and Oil ring are fixed. Position the ring approximately 1 inch gap below the neck.
126. Where Multi-stage pump used
Pressure washing of Aircraft, Trains, Boats and Road vehicles as well as Spray washing of industrial parts and Electronic components.
127. What is the function of Scoop in BFP (Boiler Feed Water Pump) in Thermal Power Station?
The Function of Scoop tube is regulating the varying amount of oil level in the coupling during operation of infinite variable speed.
128. In the Thermal Power Plant why Deaerator (D/A) placed on height?
To build a Very high pressure and the temperature for a boiler feed water pump and it discharge high pressure water to the boiler.
And to provide the required Net Positive Suction Head (NPSH) for the BFW pump and to serve as a storage tank to ensure a continuous supply of feed water during rapid changes in BFP.
129. How to determine the capacity of Refrigeration system? How we use Condenser coils, Compressor, Capillarity?
To determine the Refrigeration system by test of C.O.P and use the Condenser coils, Compressor, Capillarity, based on the properties
130. In orifice why the Pressure and Temperature are decreases?
Orifice is a small hole like a nozzle. When a high pressure fluid passes through the orifice, Pressure gets reduced suddenly and the velocity of the fluid gets increased. Also the heat transfer rate increases. We know that Heat transfer rate is directly proportional to the difference in temperature, Area and the Heat transfer coefficient. Heat transfer Coefficient remains constant for a fluid at a particular temperature.
Q= KA (T1-T2)
If the heat transfer rate increases, it seems the difference in temperature gets increased. There is no way in reduction of inlet temperature of the orifice. As a result, the outlet temperature of the orifice gets reduced. Hence the pressure and temperature gets reduced when it passes through orifice.
131. What is the difference between Bolt and Screw?
The main difference was based on the load acting on it, and the size. For smaller loads, screws are enough but in case of greater-loads, bolts are to be used. In bolt we give centrifugal force or tangential force and screw we give axial force for driving.
132-What is important to remember about radial bearings?
A turbine rotor is supported by two radial bearings, one on each end of the steam cylinder. These bearings must be accurately aligned to maintain the close clearance between the shaft and the shaft seals, and between the rotor and the casing. If excessive bearing wear lowers the he rotor, great harm can be done to the turbine.
133.How many governors are needed for safe turbine operation? Why?
Two independent governors are needed for safe turbine operation. One is an over speed or emergency trip that shuts off the steam at 10 percent above running speed (maximum speed). The second, or main governor, usually controls speed at a constant rate; however, many applications have variable speed control.
134How is a fly ball governor used with a hydraulic control?
As the turbine speeds up, the weights are moved outward by centrifugal force, causing linkage to open a pilot valve that admits and releases oil on either side of a piston or on one side of a spring-loaded piston. The movement of the piston controls the steam valves.
135.What is meant by critical speed?
It is the speed at which the machine vibrates most violently. It is due to many causes, such as imbalance or harmonic vibrations set up by the entire machine. To minimize damage, the turbine should be hurried through the known critical speed as rapidly as possible. (Caution, be sure the vibration is caused by critical speed and not by some other trouble).How is oil pressure maintained when starting or stopping a medium-sized turbine?
An auxiliary pump is provided to maintain oil pressure. Some auxiliary pumps are turned by a hand crank; others are motor-driven. This pump is used when the integral pump is running too slowly to provide pressure, as when starting or securing a medium-sized turbine.
136.Besides lubrication, what are two functions of lubricating oil in some turbines?
In larger units, lube oil cools the bearings by carrying off heat to the oil coolers. Lube oil in some turbines also acts as a hydraulic fluid to operate the governor speed-control system
138.Do you stop cooling-water flow through a steam condenser as soon as the turbine is slopped?
You should keep the cooling water circulating for about 15 mill or more so that the condenser has a chance to cool down gradually and evenly. Be sure to have cooling water flowing through the condenser before starting up in order to prevent live steam from entering the condenser unless it is cooled. Overheating can cause severe leaks and other headaches.
139.What is a radial-flow turbine?
In a radial-flow turbine, steam flows outward from the shaft to the casing. The unit is usually a reaction unit, having both fixed and moving blades.
140.What are four types of turbine seals?
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Carbon rings fitted in segments around the shaft and held together by garter or retainer springs.
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Labyrinth mated with shaft serration’s or shaft seal strips.
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Water seals where a shaft runner acts as a pump to create a ring of water around the shaft. Use only treated water to avoid shaft pitting.
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Stuffing box using woven or soft packing rings that are compressed with a gland to prevent leakage along the shaft.
141. What are two types of clearance in a turbine?
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- Radial – clearance at the tips of the rotor and casing.
- Axial – the fore-and-aft clearance, at the sides of the rotor and the casing.
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142.What is the function of a thrust bearing?
Thrust bearings keep the rotor in its correct axial position.
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143.What are some conditions that may prevent a turbine from developing full power?
- The machine is overloaded.
- The initial steam pressure and temperature are not up to design conditions.
- The exhaust pressure is too high.
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The governor is set too low.
- The steam strainer is clogged.
- Turbine nozzles are clogged with deposits.
- Internal wear on nozzles and blades.
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144.What is a stage in a steam turbine?
In an impulse turbine, the stage is a set of moving blades behind the nozzle. In a reaction turbine, each row of blades is called a “stage.” A single Curtis stage may consist of two or more rows of moving blades.
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145.What is a diaphragm?
Partitions between pressure stages in a turbine’s casing are called diaphragms. They hold the vane-shaped nozzles and seals between the stages. Usually labyrinth-type seals are used. One-half of the diaphragm is fitted into the top of the casing, the other half into the bottom.
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146.What are the two basic types of steam turbines?
- Impulse type.
- Reaction type.
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147.What are topping and superposed turbines?
Topping and superposed turbines arc high-pressure, non-condensing units that can be added to an older, moderate-pressure plant. Topping turbines receive high-pressure steam from new high-pressure boilers. The exhaust steam of the new turbine has the same pressure as the old boilers and is used to supply the old turbines.
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148.What is a combination thrust and radial bearing?
This unit has the ends of the Babbitt bearing extended radically over the end of the shell. Collars on the rotor face these thrust pads, and the journal is supported in the bearing between the thrust collars.
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