GEARS AND ITS CLASSIFICATION
Often we hear the term gear which is most vital mechanical element in engineering as well as daily life use. We say gears as connectors or links which allows to transmit motion when direct contact is established. The motion is transmitted only when there is rolling or sliding contact between two mating parts. No motion can be transmitted along common normal.
Depending on the position of axis of shaft three types gears are known
1) Gears with parallel shaft ( spur, helical, herringbone & rack pinion )
2) Gears with intersecting shaft ( straight bevel & spiral bevel )
3) Gears with skew shaft ( hypoid gear & worm gear )
GEARS WITH PARALLEL SHAFT
SPUR GEARS
These are characterized by teeth parallel to shaft axis. The whole width of each tooth is in direct contact with the mating gear tooth. This generates high impact and noise at the time of contact and at high speeds
HELICAL GEARS
This is another classification of parallel shaft gears where teeth are slightly curved, having some helix angle. The two mating gears should must have angle of teeth in opposite direction for engagement or mating.
The big advantage in such gears is that there is gradual engagement or disengagement as a result of which less stress and noise is witnessed in these gears at high speeds. On the other hand end thrust are unavoidable in the direction along the axis of gear, which adds to its disadvantage.
HERRINGBONE GEAR
A double helical gear, such gears have right helix and left helix angle separated by groove at the middle. The helix angle is 45 degrees and must not exceed this limit. When groove is absent in between two helix angle then it is known as herringbone gear. Such gears also facilitates the advantage of reduced noise and impact under high operational speed.
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