Spur Gears:
Spur gears are the most common type used. Tooth contact is primarily rolling, with sliding occurring during engagement and disengagement. Some noise is normal, but it may become objectionable at high speeds.
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Rack and Pinion.
Rack and pinion gears are essentially a linear shaped variation of spur gears The
spur rack is a portion of a
spur gear with an infinite
radius.
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Internal Ring Gear:
Internal gear is a cylindrical
shaped gear with the meshing
teeth inside or outside a circular
ring. Often used with a spur gear. Internal ring gears
may be used within a planetary gear arrangement.
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Helical Gear:
Helical gear is a cylindrical
shaped gear with helicoid
teeth. Helical gears operate with less noise and vibration than spur gears. At any time, the load on helical gears is distributed over several teeth, resulting in reduced wear. Due to their angular cut, teeth meshing results in thrust loads along the gear shaft. This action requires thrust bearings to absorb the thrust load and maintain gear alignment. They are widely
used in industry. A
negative is the axial
thrust force the helix
form causes.
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Helical Rack Gear:
Helical rack gears are linear shaped
and meshes with
a rotating helical gear.
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Double Helical Gear:
Double helical gear may have both
left-hand and right-hand
helical teeth. The double
helical form is used to balance the
thrust forces and provide additional gear shear area.
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Face Gear:
Face gears
are a circular disc with a ring of
teeth cut on one side. The gear teeth are tapered toward the center of the tooth. These gears typically mate with a spur gear.
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Worm Gear:
Worm gears teeth resembles ACME screw thread
which mates with a
helical gear, except that it is made
to envelope the worm as seen
along the worm's axis. Operation of worm gears is
analogous to a screw. The relative motion between these
gears is sliding rather than rolling. The uniform
distribution of tooth pressures on these gears enables use
of metals with inherently low coefficients of friction such
as bronze wheel gears with hardened steel worm gears. These
gears rely on full fluid film lubrication and require heavy
oil compounded to enhance lubricity and film strength to
prevent metal contact.
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Double Enveloping Worm Gear:
The double enveloping worm gear has a radial changing pitch diameter. This increases the number and amount of tooth shear area.
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Hypoid Gear:
Hypoid gears are typically found within the differential (rear axle) of automobiles. The gear arrangement allows the translation of torque ninety degrees. Hypoid gears are similar
to spiral bevel gears except that the shaft center lines do
not intersect. Hypoid gears combine the rolling action and
high tooth pressure of spiral bevels with the sliding action
of worm gears. This combination and the all-steel
construction of the drive and driven gear result in a gear
set with special lubrication requirements, including
oiliness and anti-weld additives to withstand the high tooth
pressures and high rubbing speeds.
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Straight Bevel Gear:
Straight bevel gears have tapered conical teeth which intersect the same tooth geometry. Bevel gears are used to
transmit motion between shafts with intersecting center
lines. The intersecting angle is normally 90 deg but may be
as high as 180 deg. When the mating gears are equal in size
and the shafts are positioned at 90 degrees to each other,
they are referred to as miter gears. The teeth of bevel
gears can also be cut in a curved manner to produce spiral
bevel gears, which produce smoother and quieter operation
than straight cut bevels.
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Spiral Bevel Gear:
Spiral bevel gears have a helical
angle spiral teeth.
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Screw Gear (Crossed Helical
Gear):
Screw gears are helical gears of opposite
helix angle will mesh when their axes
are crossed.
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