10+ Mechanical Engineer Interview Question Answer Part-5

Questions and answers(Interview )

Q1. What do you understand by shaft, axle and spindle?

A1. Shaft is a rotating member, in general, has a circular cross-section and is used to transmit power. Axle is a non-rotating member used for supporting rotating wheels etc. and do not transmit any torque. Spindle is simply defined as a short shaft.

Q2. What are the common ferrous materials for a shaft?

A2. Common materials for shaft are, hot-rolled plain carbon steel, cold-drawn plain carbon/alloy composition and alloy steels.

Q3. How do the strength of a steel material for shafting is estimated in ASME design code for shaft?

A3. Material property for steel shaft for ASME code is as follows, For commercial steel shafting

                      = 55 MPa for shaft without keyway

                     = 40 MPa for shaft with keyway

For steel purchased under definite specifications

                    = 30% of the yield strength but not over 18% of the ultimate strength in tension for shafts without keyways. These values are to be reduced by 25% for the presence of keyways in the shaft.

Q1. What is an equivalent stress?

A1. When a shaft is subjected to variable load, both the stress amplitude and mean stress can be conveniently represented as equivalent stress. The equivalent stress is conceptually an equivalent static stress.

Q4. What are the limiting values of the angle of twist of a shaft?

A4. The limiting value of angle of twist of a shaft varies from 0.3 deg/m to 3 deg/m for machine tool shaft to line shaft respectively.

Q5. What are the assumptions made to derive the equation for critical frequency? Why critical frequency is important in shaft design?

A5. The assumptions made to derive the equation for critical frequency are, The shaft is weightless, the weights are concentrated and bearings/supports are not flexible. The critical speed value helps a designer to set the limit of shaft speed. To avoid resonance, the shaft speed should be much higher or lower than the critical speed.

 Q.6.What should be essential qualities of a rivet and its material?

Ans: From the riveting procedure it is clear that a good rivet material must be tough and ductile. Steel (low carbon), coppers, brass are good candidates for rivets. According to Indian standard IS: 2998-1982 the material must have tensile strength of 40 MPa and elongation not less that 20 %. Further, the rivet shank must not be bent on itself through 1800 without cracking in cold condition. The same test must be done for rivet elevated to 6500 C and quenched.

Q.7.What are the uses of snap headed, counter shank headed, conical headed and pan headed rivets?

Ans: Snap heads are used mainly for structural work and machine riveting. Counter shank heads are employed for ship building where flush surfaces are necessary. Conical heads are used where riveting is done by hand hammering. Pan heads are required where very high strength is needed since they have the maximum strength, but they are very difficult to shape.

Q8. Name some of the common flat belt materials.

A8. Leather, rubber, plastics and fabrics are some of the common flat belt materials.

Q9. What is the correction factors used to modify belt maximum stress?

A9. Correction factor for speed and angle of wrap are used to modify the belt maximum stress. This correction is required because stress value is given for a specified drive speed and angle of wrap of 1800. Therefore, when a drive has different speed than the specified and angle of wrap is also different from 1800 , then above mentioned corrections are required.

Q10. What is the recommended center distance and belt speed for a flat belt drive?

A10. The recommendations are; the center distance should be greater than twice the sum of pulley diameters and the belt speed range should be within 15- 25 m/s.

Q11.How a V-belt section is selected?

A11.From the given table, depending upon the required power transmission, a belt section is chosen. However, the smaller pulley diameter should be less than the pulley diameter as mentioned for the chosen belt section.

Q12. Why angle of wrap correction factor and belt length correction factor is required to modify power rating of a belt?

A12. The power rating of V-belts are based on angle of wrap, α =1800 . Hence, for any angle of wrap, other than 180ο , a correction factor is required. Similarly, if the belt length is different from optimum belt length for which the power rating is given, then belt length correction factor is used, because, amount of flexing in the belt in a given time is different from that in optimum belt.

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