INTERVIEW SHORT QUESTION ANSWERS-GEARS          Mech Properties-1            Q.A. Riveted Joints            Q.A. Machine Design-1              Q.A. Different Loads          Introduction Gears


  1. Discuss the advantages and disadvantages of an involutes profile.


Advantages of involutes profile

  • Manufacturing is accurate and easy.
  • Pressure angle is constant
  • Velocity ratio remains the same by the change of center distance.

 Disadvantages of involutes profile

Followings are the disadvantages.

(i) Interference

(ii)  Vibrations

(iii)  Noise

(iv)  Heat generation

(v) Life reduction

(vi) Requires lubrication to increase life

Q.What is contact ratio? What should be the design range of the contact ratio?


It is a ratio of length of arc of contact to circular pitch in a gear drive. It represents the number of pairs of teeth in contact. It is also a ratio of the length of the line-of-action to the base pitch. The higher contact ratio means more power transmission. It’s minimum value should be 1.2. A high contact ratio ( 2 to 3) is highly desirable.

Q.State the differences between a pulley and a gear.


Differences between a pulley and a gear

Sr. No. Pulley Gear
1. It is flat round drum or grooved drum. It is having number of teeth all round the circumference.
2. Can lift a load, apply force or transmit power from one shaft to another shaft by friction using a belt, rope or a chain. Transmits power from one shaft to another shaft by friction by direct contact through teeth.
3. Distance between two pulleys shafts transmitting power (motion) is large. Gear has smaller distance between their shaft axes.
4. Velocity ratio is limited to 1:10 No limitation on velocity ratio. It can be as high as

1 :100

5. Efficiency is less because of slip.   high efficiency
6. Cheap Costly
7. Manufacturing is easy  difficult.
8. Shafts are parallel. Shafts may be parallel, may be perpendicular or intersecting or non- intersecting.
9. Can transmit less power. Can transmit large power

10. Noisy in operation.                                       Silent in operation.
11. Maintenance is more.                              Requires less maintenance.

12.Life is less.                                                       Life is more.

13. Limited peripheral speed.                            Unlimited peripheral speed

Q State the differences among various types of gears.


There are many types of gears such as spur, helical, Bevel, Worm gears. There are many differences among these. Selection of a particular type of gear for an application is not that easy. Selection depends on number of factors like space requirement, shafts arrangement, gear ratio, power to be transmitted, accuracy and quality level etc.

Sr. No. Spur gear Helical gear Bevel gear Worm gear
1. Used on parallel shafts. parallel or intersecting shafts. intersecting shafts.  non-parallel and non intersecting shafts.
2. Noisy Less noise Less noise Less noise
3. Can transmit less power more power  more power  transmit more power
4. Teeth are straight inclined  inclined  inclined
5. Causes vibrations  less vibrations  very less vibrations  no vibrations
6. Gear ratio is 1:1 to 6:1.  3:2 to 10:1. Straight bevel gears have gear ratio 3:2 to 5:1

Spiral bevel gears have 3:2 to 4:1

 5:1 to 300:1.
7. Used in automobiles, textile industry, washing machines, screw drivers, wind up alarm clocks  automobiles, textile industry, aerospace, conveyors  automobiles, textile industry, Used in automobiles,

conveyor system.

Q. Write on the selection of materials of construction for various types of gears.

Selection of materials of construction for gears depends on many factors like wear resistance, durability, fatigue strength, shear strength, static compressive strength, toughness, damping qualities, workability at elevated temperatures and low cost. Thus selection will depend upon the strength properties, method of manufacture and metallurgical characteristics. Fatigue strength and hardness are the topmost properties considered in the selection of materials. A summery for the gear materials is listed below:

TABLE: Selection of gear materials

Sr. No. Material Salient properties Practical application
1. Cast iron (CI) Less wear, less noise, Shock absorbing, easy to cast but low tensile strength Suitable for complicated shaped gears (helical gears), oil pump gears, camshaft gears and many other applications requiring large gears, spur gears
2. Cast steel (CS) High strength Made by casting  gears of high strength which are otherwise difficult to manufacture, spur gears
3. Plain carbon steels High fatigue strength, high tensile strength and high toughness Commonly used in industry
4. Alloy steels Less wear and high strength Frequently used in industry and in automobiles, spyur gears
5. Heat treated steels Long durability, high strength and high toughness Used for gears under excessive wear and heavy loads
6. Case hardened steels Hard outer surface Used for gears subjected to varying loads and shocks
7. Non Ferrous materials like High corrosion resistance Used in instruments and appliances
8. Non -metallic less vibrations, Less noise and less shock Used in instruments, appliances and toys