We have discussed the gear terminology and also the
various types of gears in our previous post. Today we will discuss one very
important type of gear used in industries i.e. Bevel gear in this post, where
we will see the basics of bevel gears and also we will find out the various
types of bevel gears here.
Bevel gears are generally preferred in order to
transfer the power between two intersecting shafts acting at any angles,
however there is one type of bevel gear i.e. hypoid bevel gear which is used to
transmit the power between two non-intersecting shafts.
There are lots of industrial applications where we
will have to change the direction of rotation of shaft and we will prefer to
use the bevel gears in those applications. Two intersecting shafts or non
parallel shafts those are co-planar could be assembled with bevel gears to
transmit the power from driving shaft to driven shaft.
In lots of industrial applications of bevel gearing
mechanism, it has been observed that mechanism of bevel gearing are generally
used in order to transfer the power and motion in between two shafts those are intersecting
and perpendicular i.e. at 90 degree with each other as we have displayed in
below figure to express straight bevel gear where two shaft are connecting each
other at right angle, but as we have discussed recently operating angle might
be any angle.
Classifications of bevel gears
Depending on the geometry of bevel gears, such gears
are divided in various types as displayed here.
Straight bevel gears
Straight bevel gears are the most common type of bevel
gear, where teeth will be straight like teeth in case of spur gear but teeth
will be taper from larger diameter of tooth to the smaller diameter of tooth in case of
straight bevel gear.
Shaping and coniflex, these are two cutting methods,
those are used to cut the straight bevel gear teeth to prepare the straight
bevel gear. 100 % straight teeth in straight bevel gears are not acceptable in
many applications as they will not permit any misalignment during assembly with
gearbox. Therefore there will be slightly curvature in teeth of straight bevel
gear and that is termed as crowning.
Also discuss
Spiral bevel gear
As we are well aware about straight bevel gear,
where there is one issue similar to spur gear i.e. engagement of teeth of
mating gears will not be gradual and hence there will be noisy operation of
straight bevel gear application. Now solution of this problem will be to cut
and prepare the curved teeth for bevel gear so that the engagement of teeth of
mating gear will be gradual and higher tooth to tooth contact as compared to
straight bevel gearing. Spiral bevel gear will provide the silent operation as
compared to straight bevel gearing.
Spiral bevel gears are the best choice to use where applications
are associated with high rpm and high torque. Spiral bevel gears are normally
preferred to use to transmit the power and motion between driving and driven
shafts those are typically at ninety degree orientation with each other.
As we have seen helix angle in helical gear, so
there will also be one angle called as spiral angle in spiral bevel gear which is
expressed as angle between an element of the pitch cone and the tooth trace.
Sometimes spiral angle of bevel gear is also called as mean spiral angle.
Zero bevel gears
Zero bevel gears are also a type of spiral bevel
gear but the spiral angle of teeth in case of zero bevel gears will be zero. In
case of zero bevel gears, the tooth curvature radius will be quite large and
hence, as displayed in following figure, zero bevel gear teeth are very similar
with teeth of straight bevel gear.
Let us consider the below figure, taken from arrow
gear, showing the difference between the spiral angle of zero bevel gear and spiral
angle of spiral bevel gear.
Hypoid bevel gears
Hypoid bevel gears are identical to spiral bevel
gears but the center lines of both shaft will not intersect to each other but as
we have discussed in case of spiral bevel gears center lines of both shaft were
intersecting to each other. Application of hypoid bevel gears could be seen in differentials
of automobiles.
Image courtesy: Google
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Let us go to our next post “Worm and worm gear”
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