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.
2. Why Cavitation will occur in Centrifugal Pump and not in Displacement Pump?
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.
3. 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.
4. Explain Bicycle Rear Wheel Sprocket working?
Rear wheel sprocket works under the principle of ratchet and pawl.
5. What are the different types of fits? Explain?
On the basis of Indian standards fits can mainly be categorized into three groups:
� Clearance Fit: These types of fits are characterized by the occurrence of a clearance between the two mating parts. The difference between the minimum size of the hole and the maximum size of the shaft is called the minimum clearance, the difference between the maximum size of the hole and the minimum size of the shaft is known as maximum clearance.
� Interference Fit: In these types of fits the size of the mating parts are predefined so that interference between them always occurs. The tolerance zone of the hole is completely below the tolerance zone of the shaft.
� Transition Fit: As the name suggests these type of fit has its mating parts sized limited to allow either clearance or interference. The tolerance zone of the hole and the shaft overlaps in case of such fits.
6. For a shaft designated as 40 H8/f7, calculate the tolerances.
Given: Shaft designation = 40 H8/f7
The shaft designation 40 H8/f 7 means that the basic size is 40 mm and the tolerance grade for
the hole is 8 ( i. e. I T 8) and for the shaft is 7 ( i. e. I T 7).
Since 40 mm lies in the diameter steps of 30 to 50 mm, therefore the geometric mean diameter,
D = Square root of (30 x 50) = 38.73 mm
We know that standard tolerance unit,
i = 0.45 x Cube root of (D) + 0.001 D
i = 0.45 � 3.38 + 0.03873 = 1.559 73 or 1.56 microns
i = 1.56 � 0.001 = 0.001 56 mm ...(1 micron = 0.001 mm)
The standard tolerance for the hole of grade 8 (IT8)
= 25 i = 25 � 0.001 56 = 0.039 mm
The standard tolerance for the shaft of grade 7 (IT7)
= 16 i = 16 � 0.001 56 = 0.025 mm
7. What are the factors that can affect the Factor of safety selection?
The factor of safety is used in designing a machine component. Prior to selecting the correct factor of safety certain points must be taken into consideration such as:
� The properties of the material used for the machine and the changes in its intrinsic properties over the time period of service.
� The accuracy and authenticity of test results to the actual machine parts.
� The applied load reliability.
� The limit of stresses (localized).
� The loss of property and life in case of failures.
� The limit of initial stresses at the time period of manufacture.
� The extent to which the assumptions can be simplified.
The factor of safety also depends on numerous other considerations such as the material, the method of manufacturing , the various types of stress, the part shapes etc.
8. What is heat treatment and why is it done?
Heat treatment can be defined as a combination of processes or operations in which the heating and cooling of a metal or alloy is done in order to obtain desirable characteristics without changing the compositions. Some of the motives or purpose of heat treatment are as follows:
� In order to improve the hardness of metals.
� For the softening of the metal.
� In order to improve the machinability of the metal.
� To change the grain size.
� To provide better resistance to heat, corrosion, wear etc.
Heat treatment is generally performed in the following ways:
� Normalizing
� Annealing
� Spheroidising
� Hardening
� Tempering
� Surface or case hardening
9. What are the rules that must be kept in mind while designing castings?
Some of the points that must be kept in mind during the process of cast designing are as follows:
� To avoid the concentration of stresses sharp corners and frequent use of fillets should be avoided.
� Section thicknesses should be uniform as much as possible. For variations it must be done gradually.
� Abrupt changes in the thickness should be avoided at all costs.
� Simplicity is the key, the casting should be designed as simple as possible.
� It is difficult to create true large spaces and henceforth large flat surfaces must be avoided.
� Webs and ribs used for stiffening in castings should as minimal as possible.
� Curved shapes can be used in order to improve the stress handling of the cast.
10. What are the points in the stress strain curve for steel?
Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.
Part 1 | Top 10 Basic Mechanical Engineering Interview Questions and Answer
Part 2 | Top 10 Basic Mechanical Engineering Interview Questions and Answer
Part 3 | Top 10 Basic Mechanical Engineering Interview Questions and Answer
Part 4 | Top 10 Basic Mechanical Engineering Interview Questions and Answer
Part 5 | Top 10 Basic Mechanical Engineering Interview Questions and Answer
Part 6 | Top 10 Basic Mechanical Engineering Interview Questions and Answer
Part 7 | Top 10 Basic Mechanical Engineering Interview Questions and Answer
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