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GEARS CLASS NOTES INTERVIEW SHORT QUESTION ANSWERS

GEARS CLASS NOTES INTERVIEW

SHORT QUESTION ANSWERS 

Question answers makes a topic highly

clear and understood. This helps in the

design & manufacture of gears. Gears are

used in power transmission.

  1. Discuss the advantages and disadvantages of

        an involutes profile.

A.
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?

A.
It is a ratio of contact arc length to circular pitch. This is 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.

A.

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.  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 limit 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.

A.
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 space requirement, shafts arrangement, gear ratio, power  transmitted, accuracy and quality level.

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
 noise is less
Less noise
3.
Can transmit less power
more power
 more power
 transmit more power
4.
Teeth are straight
inclined
 teeth 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.
A.

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. Table gives the summery
of gear materials.

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 helical gears. oil pump gears, camshaft gears, 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

 

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