Spiral Bevel Gears
Spiral
Bevel Gears are the type of industrial gears that are quite similar to
helical gears in nature. Compared to straight Bevel gears they have a higher
potential for load transmission. This is made possible by cutting the teeth
in the shape of a curve. As the image shows Spiral bevel Gears have curved
and oblique teeth that comes in contact with each other in a gradual and
smooth manner from one end to the other.
Well-designed spiral bevels have been seen to have two or more teeth that
is in touch always. The property of overlapping tooth action is able to
transmit motion more quietly, efficiently and smoothly as compared to
straight bevel gears. Spiral Bevel Gears are applied where there is
necessity of greater torque strength and for transmitting power between
shafts where the orientation to each other is at 90-degree.
Manufacturing Spiral Bevel Gears
The Spiral bevel Gears are generally made from case hardened material and
further carburised for attaining the case depth. It is necessary to equip
Spiral Bevel in pairs, this ensures proper mounting distance. They are also
lapped in pairs to ensure a proper wearing in and for accommodating a truly
just contact pattern.
There are many methods for manufacturing of Spiral Bevel Gears. Two types
are given here:
- Face-milled Spiral Bevel Gears
For the production of face-milled spiral bevel gears, it is the
grinding done to the contacting surfaces that forms the final step in
manufacturing. Generally two different specialty machines are applied
for generating teeth for a face-milled spiral bevel gear.
- Face-hobbed Spiral Bevel gears
For the production of Face-hobbed Spiral Bevel gears, hard cutting is
the final manufacturing process. Here a same machine is applied for
rough cutting as well as to finish cut the gears.
Basic Parameters of Spiral Bevel Gears
Given below are listed some of the typical parameters concerning the size,
appearance in the manufacturing of standard Spiral Bevel Gears. Though it is
to be noted here these are very generalized parameters, and it is quite
likely that Spiral Bevel Gears with different specification is also
available.
- Pitch Diameter - 3-100 inches
- Gear Ratio - 1:1 to 9:1
- Carburizing capability to 48" of pitch diameter
- Die quenching capacity to 44" of pitch diameter
Recommended
use of Spiral Bevel Gears
A perfect working of the Spiral-bevel gear is obtained where peripheral
speeds are more than 1000 ft/min or 1000 revolutions/minute (r/min).
Compared to straight-bevel gears, transmission of motion is more smooth and
quiet. Not only for high speeds, spiral-bevel gears are also a good option
for some type of lower-speed applications.
Key Features of Spiral Bevel Gears
The key features of Spiral Bevel Gears are the following:
- A smooth Tooth engagement
- A quiet operation
- Good strength
- Provides a high level of efficiency from 97 to even 99%
- High permissible speeds
- Greater load sharing as a result of direct contact between more than
one tooth
Application of Spiral Bevel Gears
Spiral-bevel gears find vast use in rotorcraft applications. Where they
transfer motion and power through non-parallel shafts. In helicopters,
spiral-bevel gears are applied mainly in main-rotor and tail-rotor gearboxes
for driving the rotors. In case of tilt-rotor applications, they are used as
interconnecting drive systems which provides the vital mechanical connection
between two prop-rotors for situations where one engine starts
malfunctioning.
Basic Limitation of Spiral Bevel Gears
Though the spiral-bevel gears are hugely popular in rotorcraft
applications, but it cannot be ignored that they are also the primary source
of vibration in gearboxes, consequently a source of noise in the interiors
of cabin.
