Microproject on gears

1. GEAR DRIVE
A gear drivehas three main functions: to increase torque from the
drivingequipment(motor)to the driven equipment, to reducethe speed
generated by the motor, and/or to change the direction of the rotating
shafts. The connection of this equipmentto the gear box can be
accomplished by the use of couplings, belts, chains, or through hollow
shaft connections.
Speed and torque are inversely and proportionately related when
power is held constant. Therefore, as speed decreases, torque increases
at the same ratio.
The heart of a gear driveis obviously the gears within it.
Gears operate in pairs, engaging oneanother to transmit power
What is gear ?
A gear is a machine component which is used to transmit mechanical
power from one shaft to another shaft by engaging its teeth
Gear are one of the most used method of mechanical power
transmission in the machine .
Power transmission by the gear have almost 100% efficiency

2.  Spur Gear
Spur gears transmit power through shafts that are parallel. The teeth of
the spur gears are parallel to the shaft axis. This causes the gears to
produceradialreaction loads on the shaft, but not axial loads. Spur
gears tend to be noisier than helical gears because they operate with a
single line of contact between teeth. While the teeth are rollingthrough
mesh, they roll off of contact with one tooth and accelerate to contact
with the next tooth. This is differentthan helical gears, which have
morethan onetooth in contact and transmittorque moresmoothly.
 Helical Gear
Helical gears have teeth that are oriented at an angle to the shaft, unlike
spur gears which are parallel. This causes morethan one tooth to be in
contact duringoperation and helical gears are capable of carryingmore
load than spur gears. Dueto the load sharing between teeth, this
arrangementalso allows helical gears to operate smoother and quieter
than spur gears. Helical gears produceathrust load duringoperation
which needsto be considered when they are used. Mostenclosed gear
drivesusehelical gears.

3.  Double Helical Gear
Double helical gears are a variation of helical gears in which two helical
faces are placed next to each other with a gap separating them. Each face
has identical, but opposite, helix angles. Employing a double helical set of
gears eliminates thrust loads and offers the possibility of even greater
tooth overlap and smoother operation. Like the helical gear, double
helical gears are commonly used in enclosed gear drives.
 Herringbone Gear
Herringbonegears are very similar to the doublehelical gear, but they
do not have a gap separating the two helical faces. Herringbonegears
are typically smaller than the comparable doublehelical, and are ideally
suited for high shock and vibration applications. Herringbonegearing is
not used very often dueto their manufacturingdifficultiesand high cost.

4.  Bevel Gear
Bevelgears are most commonly used to transmit power between shafts
that intersect at a 90 degreeangle. They are used in applicationswhere a
right angle gear driveis required. Bevelgears are generally more costly
and are not able to transmit as muchtorque, per size, as a parallel shaft
arrangement.
 Worm Gear
Worm gears transmit power through right angles on non-intersecting
shafts. Worm gears producethrustload and are good for high shock load
applicationsbut offer very low efficiency in comparison to the other
gears. Dueto this low efficiency, they are often used in lower horsepower
applications.

5.  Hypoid Gear
Hypoid gears look very much like a spiral bevel gear but they operate on
shafts which do notintersect, which is the case with a spiralbevel gear. In
the hypoid arrangementbecause the pinion is set on a differentplane
than the gear, the shafts are supported by the bearings on either end of
the shaft.
Specificationof gears
Axes relationship: Somegearing configurationsmay require the transfer
of motion between oddly angled axes. Hypoid gearsallow for mesh
between non-intersectingaxes and bevel gears can be fabricated to work at
nearly any axes angle.
Handedness: Gears with teeth not parallel to the gear axis are subject to
left or right handedness. This dictates the direction the teeth curvein and is
importantfor worm drives, hypoid gears, helical gears and some bevel
gears.
Internal gears: Some gears may have an inverted tooth structure, so that
gear teeth pointinwardstowardsthe gear center, rather than outward like
a normal(external) gear. Internal gears have the same rotation direction.
Rack and pinions, worm gear sets and hypoids cannotbe interpreted at
internalgears.
Lubrication: Most gearing arrangementsrequire lubrication to reduce
friction and extend the service of the gear. Specialty lubricants are madefor
high-pressure designsor gears with brass.

6. Type of
Gears
Applications of gears
Spur
 Clocks
 Pumps
 Wateringsystems
 Household appliances
 Clothes washing and dryingmachines
 Power plants
 Material handlingsystems
 Aerospaceand aircrafts
 Railwaysand trains
Helical  Same as spur gears but with greater loads and
higher speeds(see above)
 Automobiles(transmission systems)
Bevel
 Pumps
 Power plants
 Material handlingsystems
 Aerospaceand aircrafts
 Railwaysand trains
 Automobiles
worm
 Instruments
 Lifts and elevators
 Material handlingsystems
 Automobiles(steering systems)
Rack and
pinion
 Weighing scales
 Material handlingand transfer systems
 Railwaysand trains
 Automobiles(steering systems)

7. Key Terms
Driving Gear: The gear closest to the power source
(motoror engine) and attachedto the driving shaft that
provides the initialrotationalinput
Driven Gear: The gear or toothedcomponent attached
to the driven shaft which is impactedby the driving gear
and exhibits the final output
Idler Gear: A gear placed between the driving gear and
driven gear; typically employed to allow for the
transmissionofmotionwithout a change in the direction
of rotation
Gear Ratio: The ratio between the output value to the
input value; typically expressed as the number of teeth of
the driven gear (output) to number of teeth of the driving
gear (input)
Tooth Profile: The cross-sectional shape of the gear’s teeth
Axes Configuration: The orientationofthe axes—along
which the gear shafts lay and around which the gears
rotate—inrelation to eachother
Torque: Also referred to as moment or moment of force;
the measure of the rotational or twisting force which
causes an object to rotate
Axial Load: The thrust force parallel to the gear shaft
Efficiency: The percentage value of the ratio of output
power (i.e., input power minus power loss) to the input
power

8. Advantages of gear drive
 It is positive drive hence velocity remains constant
 Provision for changing velocity ration can be made with the
help of gear box
 Its efficiency is very high
 It can be used even for low speed
 It is compact in construction
Disadvantages of gear drive
 They are not suitable when shaft distance
 At high speed noise and vibration happens
 It requires lubrication
 It has no flexibility

9. Materials used for gears
 Cast iron providesdurability and easeof manufacture.
 Alloy steel providessuperior durability and corrosion resistance.
Mineralsmay be added to the alloy to further harden the gear.
 Cast steel provideseasier fabrication, strong workingloadsand
vibration resistance.
 Carbonsteels are inexpensiveand strong, but are susceptible to
corrosion.
 Aluminum is used when low gear inertia with some resiliency is
required.
 Brass is inexpensive, easy to mold and corrosion resistant.
 Copper is easily shaped, conductiveand corrosion resistant. The
gear's strength would increase if bronzed.
 Plastic is inexpensive, corrosion resistant, operationally quiet and
can overcomemissing teeth or misalignment. Plastic is less robust
than metal and is vulnerableto temperaturechanges and chemical
corrosion. Acetal, delrin, nylon, and polycarbonateplastics are
common.
 Other material typeslike wood may be suitable for individual
applications.