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.
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. |
|
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.
