To study various types of gear- Helical, cross helical, worm, bevel gear.
APPARATUS USED :- Arrangement of gear system.
THEORY :-
1. Definition of gear
2. Classification of gear
3. Diagram of different type of gear
4. Working and construction of different type of gear
5. Advantage & disadvantage of gear
6. Application of gear
7. Example of gear
GEAR :- Gear are used to transmit motion from one shaft to another shaft or between a shaft or slide. This is accomplished by successively engaging teeth.
CLASSIFICATION OF GEAR :- Gears can be classified according to the relative position of their shaft axis are follows:
A: PARALLEL SHAFT
(i) Spur gear
(ii) Spur rack and pinion
(iii) Helical gears or Helical spur gear
(iv) Double- helical and Herringbone gear
B: INTER SECTING SHAFT
(i) Straight bevel gear
(ii) Spiral bevel gear
(iii) Zerol bevel gear
C: SKEW SHAFT
(i) Crossed- helical gear
(ii) Worm gears( Non-throated, Single throated, Double throated)
Spur gear:- They have straight teeth parallel to the axes and thus are not subjected to axial thrust due to teeth load.
Helical gears:- In helical gears, the teeth are curved, each being helical in shape. Two mating gears have the same helix angle, but have teeth of opposite hands. At the beginning of engagement, contact occurs only at the point of leading edge of the curved teeth. As the gears rotate, the contact extends along a diagonal line across the teeth. Thus the load application is gradual which result in now impact stresses and reduction in noise. Therefore, the helical gears can be used at higher velocities then the spur gears and have greater load – carrying capacity.
DOUBLE HELICAL AND HERRING BONE GEARS :- A- double- helical gear is equivalent to a pair of helical gears secured together, one having a right – hand helix and the other a left hand helix. The tooth of two raw is separated by a grooved used for too run out.
If the left and the right inclinations of a double – helical gear meet at a common apex and there is no groove in between, the gear is known as herring bone gear.
CROSSED – HELICAL GEAR :- The used of crossed helical gear or spiral gears is limited to light loads. By a suitable choice of helix angle for the mating gears, the two shaft can be set at any angle.
WORM GEAR :- Worm gear is a special case of spiral gear in which the larger wheel, usually, has a hollow or concave shape such that a portion of the pitch diameter is the other gear is enveloped on it. The smaller of two wheels is called the worm which also has larger spiral angle.
BEVEL GEAR :- Kinematically, the motion between two intersecting shafts is equivalent to the rolling of two cones, assuming no slipping. The gears, in general, are known as bevel gear. When teeth formed on the cones are straight, the gear are known as straight bevel and when inclined, they are known as spiral or helical bevel.
CONCLUSION :-
APPLICATION :-
1. Bevel gears are used for the drive to the differential of automobiles.
2. Spur rack and pinion are used in a lathe.
3. Helical gears are used for greater load at higher velocities.
4. Gears are used in different machinery.
VIVA QUESTIONS:-
1. Define gears with classification, advantage and disadvantage. Application.
2. Gear terminology.
3. Law of gearing.
4. Write down the formulae for length of path of contact, length of arc of contact, contact ratio.
5. Formation of teeth profile.
6. About interference and under cutting.
7. Write down the formulae for minimum number of teeth required for wheel to avoid interference.
8. Write down the formulae for minimum number of teeth required for pinion to avoid interference.
9. Write down the formulae for minimum number of teeth required for rack and pinion to avoid interference.