Bevel Gears
Bevel
gears are very popular type of gears used in various industrial
purposes. This particular type of industrial gears are intended for the
purpose of operating on intersecting axes, generally at right angles,
effective for working round the corners. Though bevel gears are more
often than not used at right angles, but effective design can make them
to work at other angles also. As two bevel gears meshes, the respective
vertices of their cones lie on a single point, which by the way is also
an intersection point of the shaft axes.
Bevel gears may come with spiral teeth. These are by shape are conical.
The speciality of these gears lies in the fact that minor adjustments
are easily allowed during the assembly stage and there is also
provision for displacement from deflection due to operating loads
without in any way concentrating the load at the end of the tooth.
Types
of Bevel Gears
There are different types of bevel gears that are generally available
depending on the nature of tooth design. They are the following:
Material
of Bevel Gears
Bevel gears are typically made out of metal and now plastic. In metal,
materials used are brass, aluminum, bronze, cast iron, steel that
includes hardened and stainless steel. In Plastics, typical materials
to make bevel gears include Polycarbonates, nylon, Delrin, acetal.
Selecting
the Best Bevel Gear
Some of the important factors to be noted in the selection process of a
bevel gear are given here. It must be remembered that all the points
need not apply in tandem but depending on the application, they must be
looked out for:
- Power transmission requirements
- Design life
- Corrosive elements
- Noise and heat generation. All of these factors determine
the success of the gear in a particular application. Four bevel gears
in a square make a differential gear, which can transmit power to two
axles spinning at different speeds, such as in an automobile.
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Why
use Bevel Gear Box?
A Bevel gearbox has advantages over say, a worm gear because of
efficiency, which is considerably higher. Another vital advantage is
that bevel gears offer the flexibility of 90 degree solution at ratio
that is lower.
Other advantages include:
» Good performance under high speeds and loads.
» Works particularly well for right-angle drives.
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Basic
Limitation of a Bevel Gear
- Bevel Gears have been observed to suffer from a basic
limitation making it sometimes not a preferred choice for application.
This limitation is because of the fact that in Bevel Gears often there
is no room or leverage provided for supporting it at both the ends
while the shafts intersects. This creates the problem of one or both
the gears displaying a tendency to overhang their supporting shafts.
This problem is referred to as the overhung load (OHL). It causes
further problems like deflecting the shaft, misaligning of gears
leading to poor tooth contact and consequently accelerating wear.
- The complicated tooth form of Bevel Gears is a limiting
factor in precision.
Accuracy
of the Bevel Gears
According to the international standards there is generally four types
of error. They are the following:
- Single Pitch Error - This type of error
is reported as the deviation found in the actual measured pitch value
between any of the tooth placed adjacently and the circular
pitch(theoretical) at mean cone distance.
- Pitch Variation Error - Error of the
Pitch Variation type is referred to the absolute pitch variation taking
place between any two of the tooth placed side by side at the mean cone
distance.
- Accumulated Pitch Error - Accumulated
Pitch Error is referred to as the difference found between the pitch
sum (theoretical) of a teeth interval and the total summation of
measured pitches(actual) for the same teeth interval taken at the mean
cone distance.
- Runout Error of Teeth - Runout Error of
Teeth is defined as the tooth runout, maximum taking place in the
radial direction. It is often measured by placing a ball or pin placed
between any two teeth at central cone distance.
Manufacturing
Bevel Gears
There are different ways available now for the manufacturing of Bevel
gears. But unlike the spur gears, Bevel gears can be made to have cones
that are shaped differently, depending on the type of manufacturing
process.
Highlights of the Manufacturing Process
- As shown in the image, these gear mates with a virtual
generating gear.
- The cutting blades copies the teeth of a virtual
generating gear.
- The virtual generating gear is rotated around its axis
(called the cradle). Please see the image.
Application
of Bevel Gears
- The bevel gear find suitable application in a variety of
industries. Prominent among them are the locomotives, printing press,
power plants marine applications, cooling towers, steel plants etc.
- A very common example of the application of Bevel gears is
found in the mechanism that is used for the hand drill. It offers the
advantage of a whole range of drilling options for them.
