Transcript Document

PROJECT ON…
RK DUVVU
ISPAT
People are the most important and expensive
resources in the industry. The difference
between gain and loss in an industry depends
upon the skill of its employees and the extent
to which such skill can be effectively applied.
People are able to change, grow and develop,
while other industrial resources are concrete.
Growth and development is best achieved
through training.
The employee must be trained, tested and be
declared competent before he/she can accept
the responsibility of his/her post
GEAR TRANSMISSION
•
Gearing is a very vital form of transmission of
mechanical power.
•
Universally adopted for almost all machine
mechanisms.
•
Type of Gear Transmissions:
1.
Spur Gear,
2. Helical Gear,
3. Herring bone Gear,
4. Bevel Gear,
5. Rack and pinion,
6. Worm and worm wheel.
SPUR GEAR
Spur Gears in any
transmission
system
are
employed
for
changing the speed and
the torque and are
fixed on shafts either
rigidly or with sliding
traverse.
HELICAL GEAR
Helical Gears can be used for
transmitting motion between
parallel shafts as between
perpendicular shafts. Helical
gears used for transmission at an
angle are called SPIRAL GEARS.
Advantages of Helical Gears:
•Noiseless motion even at higher speeds.
•Smooth transmission of small gears with fewer teeth, at large
transmission ratio ( up to 15:1)
These gears must be rigidly installed on the shaft. These gears
result in an axial force in one direction depending upon the direction
of rotation and are used for transmitting small power.
HERRING-BONE GEAR
HERRING-BONE Gears
are pairs of Helical
Gears. These gears are
used for large power
transmission.
Advantages of Herring-bone Gears in addition to Helical Gears:
•No Axial Force. It is balanced axially in both direction of rotation.
•Large power transmission can be done at impact loads having
frequent starts (inching).
These gears also must be rigidly installed on the shaft.
BEVEL GEAR
Bevel Gear transmission
is
employed
for
transmitting
motion
from one direction to
the other at any angle.
In
general
90°
transmission is used
mostly.
WORM & WORM WHEEL
Worm and worm wheel gives
a large single stage speed
reduction in perpendicular
direction.
Such
transmission gives lower
efficiency of transmission
due to increased frictional
losses. For a noiseless
motion, worm 1 is usually
made of medium carbon /
alloy steel and the worm
wheel 2 of bronze (or in
some cast iron).
RACK & PINION
The rotary motion of
pinion 1 (small gear) is
transformed into linear
motion of the rack 2.
For transmitting large
power worm & worm
rack transmission is
employed.
SPUR GEAR NUMENCLATURE
SPUR GEAR NUMENCLATURE
Nomenclature
Module
Diametral Pitch
Pitch
Number of teeth
Pitch Circle Diameter
Tooth height
Addendum
Dedendum
Root circle diameter
Outside diameter
Distance between the axis of
the two mating gears t 1 & t2
Pressure angle
Symbol
m
D.P.
P
t
D
h
h’
h”
D1
Do
A
α
Formulae
m=p/Π = D/t
t/D = Π/p = 1/m
P= Π.m = 3.14m
t = D/m
D = t.m
h = 2.2 m
h’ = m
h” = 1.2 m
D1 = Do – 4.4m
Do = m (t+2)
A = (t1 + t2) m/2
20˚(usually) or 14½°
Tooth Thickness Measurement
Hx
Tooth Thickness = Sx
Tooth Depth = Hx
sx
Module (m)
1
1.5
2
2.5
3
3.5
4
5
6
7
8
9
10
Hx= 0.7485 m
0.75
1.12
1.5
1.87
2.24
2.62
2.99
3.74
4.49
5.24
5.98
6.73
7.48
Sx = 1.387 m
1.39
2.08
2.77
3.47
4.16
4.85
5.56
6.94
8.32
9.71
11.1
12.48
13.87
DEFECTS OF THE GEARS
•
•
•
•
Wear of one, few or all the teeth.
One or few teeth broken or twisted.
Burrs on the bore or the key way.
Burrs on the internal splines of the gear
bore or the tooth surface.
• Crack or damage on the rim or the bore of
the gear wheel.
LIMITS OF WEAR FOR DISCARDING
OPEN GEAR TRANSMISSION and the surface
speed up to 2 meter / second – The tooth
thickness (Sx) reduces due to wear by (0.5m) mm,
where m is the module, or about 33% of the
original tooth thickness.
CLOSED GEAR TRANSMISSION (GEAR BOXES)
for surface speeds over 2 meter / sec. – the tooth
thickness (Sx) reduces due to wear by (0.3m) mm
or about 20% of the original tooth thickness.
MESHING OF GEARS
The spur and helical gears must be assembled in such
a way that the axes of the meshing gears are
parallel and the distance between their axes is
correctly established.
The correct meshing of the spur and helical gears is
decided by applying blue paste on the teeth of the
driving gear, giving it several rotations and seeing
to the blue marks on the teeth faces of the
meshing driven gear.
(a) Correct meshing covering 70 – 80% tooth surface contact.
(b) Axis not parallel.
(c) Axis not parallel and distance between them is too small.
(d) Axis not parallel and distance between them is excess.
(e) Axis are parallel and distance between them is excess.
(f) Axis are parallel and distance between them is too small.
LUBRICATION
• Proper Lubrication with timely addition / replacement plays
vital role in maintaining the gear boxes with efficiency and
increasing its working life.
• Oil level should be checked in all the gear boxes oil
indicators / dip sticks.
• Oil level should be in between the minimum and maximum
limits of the dip stick (or indicator).
• Testing of the lubricating oils used to be carried out
periodically. The following tests are to be done…
1. Dirt contamination
2. Moisture
3. Volatile materials (Benzene, kerosene, spirit etc,)
4. Viscosity
5. Acidity
6. Alkalinity due to soda (Na2 Co3) etc.,