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江西科技学院本科生毕业设计（论文）
GEAR AND SHAFT INTRODUCTION
Abstract:
The important
position of the wheel gear and shaft can't falter
in
traditional machine and modern
machines. The wheel gear and shafts mainly
install the direction that delivers the
dint at the principal axis box. The passing to
process to make them can is divided
into many model numbers, use ding for many
situations respectively. So we must be
the multilayer to the understanding of the
wheel gear and shaft in many ways.
Key words:
Wheel
gear; Shaft
In the force
analysis of spur gears, the forces are assumed to
act in a single
plane. We shall study
gears in which the forces have three dimensions.
The reason
for this, in the case of
helical gears, is that the teeth are not parallel
to the axis of
rotation. And in the
case of bevel gears, the rotational axes are not
parallel to each
other. There are also
other reasons, as we shall learn.
Helical gears are used to transmit
motion between parallel shafts. The helix
angle is the same on each gear, but one
gear must have a right-hand helix and the
other a left-hand helix. The shape of
the tooth is an involute helicoid. If a piece of
paper cut in the shape of a
parallelogram is wrapped around a cylinder, the
angular
edge
of
the
paper
becomes
a
helix.
If
we
unwind
this
paper,
each
point
on
the
angular
edge generates an involutes curve. The surface
obtained when every point
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江西科技学院本科生毕业设计（论文）
on the edge generates an involutes is
called an involutes helicoids.
The
initial contact of spur-gear teeth is a line
extending all the way across the
face
of the tooth. The initial contact of helical gear
teeth is a point, which changes
into
a
line
as
the
teeth
come
into
more
engagement.
In
spur
gears
the
line
of
contact
is parallel to the axis of the rotation; in
helical gears, the line is diagonal
across the face of the tooth. It is
this gradual of the teeth and the smooth transfer
of
load
from
one
tooth
to
another,
which
give
helical
gears
the
ability
to
transmit
heavy loads at high
speeds. Helical gears subject the shaft bearings
to both radial
and thrust loads. When
the thrust loads become high or are objectionable
for other
reasons,
it
may
be
desirable
to
use
double
helical
gears.
A
double
helical
gear
(herringbone) is
equivalent to two helical gears of opposite hand,
mounted side by
side on the same shaft.
They develop opposite thrust reactions and thus
cancel out
the thrust load. When two or
more single helical gears are mounted on the same
shaft, the hand of the gears should be
selected so as to produce the minimum thrust
load.
Crossed-helical,
or
spiral,
gears
are
those
in
which
the
shaft
centerlines
are
neither
parallel
nor
intersecting.
The
teeth
of
crossed-helical
fears
have
point
contact with each other, which changes
to line contact as the gears wear in. For this
reason
they
will
carry
out
very
small
loads
and
are
mainly
for
instrumental
applications,
and
are
definitely
not
recommended
for
use
in
the
transmission
of
power.
There
is
on
difference
between
a
crossed
helical
gear
and
a
helical
gear
until they are mounted in mesh with
each other. They are manufactured in the same
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江西科技学院本科生毕业设计（论文）
way. A pair of meshed crossed helical
gears usually have the same hand; that is, a
right-hand
driver
goes
with
a
right-hand
driven.
In
the
design
of
crossed-helical
gears,
the
minimum
sliding
velocity
is
obtained
when
the
helix
angle
are
equal.
However, when the
helix angle is not equal, the gear with the larger
helix angle
should be used as the
driver if both gears have the same hand.
Worm
gears
are
similar
to
crossed
helical
gears.
The
pinion
or
worm
has
a
small number of teeth,
usually one to four, and since they completely
wrap around
the pitch cylinder they are
called threads. Its mating gear is called a worm
gear,
which is not a true helical gear.
A worm and worm gear are used to provide a high
angular-velocity
reduction
between
nonintersecting
shafts
which
are
usually
at
right
angle. The worm gear is not a helical gear because
its face is made concave to
fit
the
curvature
of
the
worm
in
order
to
provide
line
contact
instead
of
point
contact.
However,
a
disadvantage
of
worm
gearing
is
the
high
sliding
velocities
across the teeth,
the same as with crossed helical gears.
Worm
gearing
are
either
single
or
double
enveloping.
A
single-enveloping
gearing is one in which the gear wraps
around or partially encloses the worm.. A
gearing
in
which
each
element
partially
encloses
the
other
is,
of
course,
a
double-enveloping worm gearing. The
important difference between the two is that
area
contact
exists between
the teeth
of double-enveloping gears
while only
line
contact between those of single-
enveloping gears. The worm and worm gear of a
set have the same hand of helix as for
crossed helical gears, but the helix angles are
usually quite different. The helix
angle on the worm is generally quite large, and
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江西科技学院本科生毕业设计（论文）
that on the gear very small. Because of
this, it is usual to specify the lead angle on
the worm, which is the complement of
the worm helix angle, and the helix angle
on the gear; the two angles are equal
for a 90-deg. Shaft angle.
When
gears
are
to
be
used
to
transmit
motion
between
intersecting
shaft,
some of bevel gear is
required. Although bevel gears are usually made
for a shaft
angle of 90 deg. They may
be produced for almost any shaft angle. The teeth
may
be cast, milled, or generated. Only
the generated teeth may be classed as accurate.
In a typical bevel gear mounting, one
of the gear is often mounted outboard of the
bearing.
This
means
that
shaft
deflection
can
be
more
pronounced
and
have
a
greater effect on the contact of teeth.
Another difficulty, which occurs in predicting
the stress in bevel-gear teeth, is the
fact the teeth are tapered.
Straight
bevel
gears are
easy
to
design
and simple
to
manufacture
and give
very well results in service if they
are mounted accurately and positively. As in the
case of spur gears, however, they
become noisy at higher values of the pitch-line
velocity. In these cases it is often
good design practice to go to the spiral bevel
gear,
which is the bevel counterpart of
the helical gear. As in the case of helical gears,
spiral bevel gears give a much smoother
tooth action than straight bevel gears, and
hence are useful where high speed are
encountered.
It is frequently
desirable, as in the case of automotive
differential applications,
to
have
gearing
similar
to
bevel
gears
but
with
the
shaft
offset.
Such
gears
are
called
hypoid
gears
because
their
pitch
surfaces
are
hyperboloids
of
revolution.
The tooth action
between such gears is a combination of rolling and
sliding along a
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江西科技学院本科生毕业设计（论文）
straight line and has much in common
with that of worm gears.
A shaft is a
rotating or stationary
member, usually
of circular cross section,
having
mounted
upon
it
such
elements
as
gears,
pulleys,
flywheels,
cranks,
sprockets,
and
other
power-transmission
elements.
Shaft
may
be
subjected
to
bending, tension,
compression, or torsional loads, acting singly or
in combination
with one another. When
they are combined, one may expect to find both
static and
fatigue strength to be
important design considerations, since a single
shaft may be
subjected to static
stresses, completely reversed, and repeated
stresses, all acting at
the same time.
The word “shaft” covers numerous
variations, such as axles and spindles. an
axle neither is a shaft, wither
stationary or rotating, nor subjected to torsion
load. A
shirt rotating shaft is often
called a spindle.
When either the
lateral or the torsional deflection of a shaft
must be held to
close limits, the shaft
must be sized on the basis of deflection before
analyzing the
stresses.
The
reason
for
this
is
that,
if
the
shaft
is
made
stiff
enough
so
that
the
deflection is not too large, it is
probable that the resulting stresses will be safe.
But
by
no
means
should
the
designer
assume
that
they
are
safe;
it
is
almost
always
necessary
to
calculate
them
so
that
he
knows
they
are
within
acceptable
limits.
Whenever
possible,
the
power-transmission
elements,
such
as
gears
or
pullets,
should
be
located
close
to
the
supporting
bearings,
this
reduces
the
bending
moment, and hence
the deflection and bending stress.
Although the von Misses-Hacky-Goodman
method is difficult to use in design
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江西科技学院本科生毕业设计（论文）
of shaft, it
probably
comes
closest
to
predicting
actual
failure.
Thus it is
a good
way of checking a shaft that has
already been designed or of discovering why a
particular shaft has failed in service.
Furthermore, there are a considerable number
of shaft-design problems in which the
dimension are pretty well limited by other
considerations, such as rigidity, and
it is only necessary for the designer to discover
something about the fillet sizes, heat-
treatment, and surface finish and whether or
not shot peening is necessary in order
to achieve the required life and reliability.
Because
of
the
similarity
of
their
functions,
clutches
and
brakes
are
treated
together. In a
simplified dynamic representation of a friction
clutch, or brake, two
inertias I1 and
I2 traveling at the respective angular velocities
W1 and W2, one of
which may be zero in
the case of brake, are to be brought to the same
speed by
engaging
the
clutch
or
brake.
Slippage
occurs
because
the
two
elements
are
running at different speeds and energy
is dissipated during actuation, resulting in a
temperature
rise.
In
analyzing
the
performance
of
these
devices
we
shall
be
interested
in
the
actuating
force,
the
torque
transmitted,
the
energy
loss
and
the
temperature
rise.
The
torque
transmitted
is
related
to
the
actuating
force,
the
coefficient of friction,
and the geometry of the clutch or brake. This is
problem in
static, which will have to
be studied separately for earth geometric
configuration.
However,
temperature
rise
is
related
to
energy
loss
and
can
be
studied
without
regard
to
the
type
of
brake
or
clutch
because
the
geometry
of
interest
is
the
heat-dissipating
surfaces.
The
various
types
of
clutches
and
brakes
may
be
classified as flows:
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