3. INTRODUCTION TO GEAR.
Gear is one of the important machine tool elements which is
an integral and inevitable part of power transmission
system.
They find applications in Automobiles, gear boxes, oil
engines, machine tools, industrial machinery, agricultural
machinery, geared motors etc.
To meet the difficult service conditions the gear should have
robust construction, reliable performance, high efficiency,
economy and long life.
The gear drive should be free from noise and should ensure
high load carrying capacity at constant load ratio.
4. FUNCTION OF GEAR
1. To transmit torque from the driving shaft to driven shaft.
2. To reduce the speed generated by prime mover.
3. To change the direction of rotation through idlers.
5. CLASSIFICATION OF GEAR
The gears are classified as fallows:
1.According to the position of axes of shafts.
A. When shaft axes parallel:
Spur gear
Helical gears
Herringbone gears
Rack and pinion
B. When shaft axes intersecting
Straight bevel gears
Spiral bevel gears
C. When shaft axes non-intersecting and non parallel
Hypoid gears
Worm gears
Screw gears
6. CLASSIFICATION OF GEAR
2. According to the peripheral velocity of the gears
Low-velocity gears
Medium velocity gears
High velocity gears
3. According to the type of gears
External gear
Internal gear
Rack and pinion
4. According to the position of teeth on the gear surface
Straight gear
Inclined gear
Curved gear
7. GEAR MATERIALS
1. Metallic Materials
A. Ferrous metals - For high load.
Cast iron
Cast steel
Medium and high carbon steels
Alloy steel
B. Non-ferrous metals- For light load.
Aluminium
Bronze
2. Non- metallic materials
Wood
Plastic or fibre
8. SELECTION OF GEAR MATERIALS
The proper selection of gear material depends on :-
Amount of power to be transmitted.
Size and weight of the gear.
Service period of the gear.
Degree of accuracy required.
Method of manufacture to be used.
9. ADVANTAGES OF GEAR
1. Transmit more power than other type of drive.
2. Transmission efficiency is high.
3. It requires less space.
4. Maintenance is easy.
5. They have zero slip.
6. They have good durability and precision.
10. DISADVANTAGES OF GEAR
1. Gear design and manufacturing is expensive.
2. Installation is difficult.
3. Tooth wear may occur during power transmission.
4. Inaccuracies in gear tooth cause noise and vibrations.