11:25:00
This paper generally reveals to us
the mechanical drives like belt and chain that is use in power transmission.
Others are ropes and gears etc.
Introduction
Transmission of power from a source
such as an engine or motor, through a machine to an output is one of the most
common machine tasks. An efficient means of transmitting power is through
rotatory motion of a shaft that is supported by bearings. Power transmission
drives include chain, belt, rope,
gears etc. These drives are designed to translate the input, which generates
the power to the output or connection.
BELT DRIVE
A belt is
a loop of flexible material used to link two or more rotating shafts
mechanically. Belts may be used as a source of motion, to transmit power
efficiently, or to track relative movement. Belts are looped over pulleys. In a
two pulley system, the belt can either drive the pulleys in the same direction,
or the belt may be crossed, so that the direction of the shafts is opposite.
As a
source of motion, a conveyor belt is one application where the belt is adapted
to continually carry a load between two points. Belts are the cheapest utility
for power transmission between shafts that may not be axially aligned. Power
transmission is achieved by specially designed belts and pulleys
BELT TYPES
1.Flat
belt
2.V
belt
3.Circular
belt
4.Metal
belt
Advantages
of belt drives include:
1.
No lubrication is required, or desired.
2.
Maintenance is minimal and infrequent.
3.
Belts dampen sudden shocks or changes in loading.
4.
Quiet, smooth operation.
5.
Sheaves (pulleys) are usually less expensive than chain drive sprockets and
exhibit little wear over long periods of operation.
Drawbacks
of belt drives that are more important in some applications than others
are:
1.
Endless belts usually cannot be repaired when they break. They must be
replaced.
2.
Slippage can occur, particularly if belt tension is not properly set and
checked frequently. Also, wear of belts, sheaves, and bearings can reduce
tension, which makes retensioning necessary.
3.
Adverse service environments (extreme temperature ranges, high moisture, oily
or chemically filled atmospheres,etc.) can damage belts or cause severe
slipping.
4.
Length of endless belts cannot be adjusted
Design considerations — Belt type, belt materials, belt and sheave construction,
power requirements of the drive, speeds of driving and driven sheaves, sheave
diameters, and sheave center distance are key belt drive design considerations.
Basic to power transmission design with belt drives is to maintain friction
developed between the belt and the sheave or pulley contact surface.
Belt friction
Belt
drives depend on friction to operate but, if the friction is excessive, there
will be waste of energy and rapid wear of the belt. Factors which affect belt
friction include belt tension, contact angle and the materials from which the
belt and pulleys are made.
Belt tension
Belt
tensioning adjustment can be made using a tension meter or other type of spring
scale. Improper tensioning can reduce power transmission performance levels.
i.Too much tension can generate lateral forces in the drive
system resulting in a shortened life for belts, bearings, and other components.
ii. Synchronous
belts do not rely on tension for grip and require less tensioning force than
V-belts, however a loose belt can allow the drive to “Jump teeth” at startup.
iii. Tight
synchronous belts tend to make more noise.
iv. Too
little tension can:
a. Allow
slipping for a V-belt; causing excessive sheave and belt wear.
b. Cause
belt to sag; which can result in a snapped belt during startup or during peak
loads
Belt wear
i. Wear
due to rolling ii. Wear due to contact with the pulley.
ROPE DRIVE
The rope
drives are widely used where a large amount of power is to be transmitted from
one pulley to another over a considerable distance.
The rope
drive use the following two types of rope
Fibre
rope: which is made from fibrous materials such as hemp, maliana, and cotton
Wire rope:
this is made of many kind of metals such as copper, bronze, steel wire etc
Rope drive
as been applied in various mechanical systems e.g elevators, mine hoists,
cranes, conveyors et
CHAIN DRIVE
A chain
drive is similar to a belt drive but it enables a higher power to be
transmitted without slip. A chain drive system requires lubrication and some
maintenance.
A chain is
made up of a series of links with the links held together with steel pins. This
arrange makes a chain a strong, long lasting way of transmitting rotary motion
from one gear wheel to another.
They
transmit power in a positive manner through sprockets rotating in the same
plane. Chain drives have high efficiency and there is no slip. The only
maintenance required, after a careful alignment of elements is lubrication.
Power
transmission chains are primary of two kinds; roller and silent
Roller chains
are probably the most common and are used in a wide variety of low speed to
high speed drives
Silent
chains are mostly used in high speed drives.
Each link of a chain drive transmits load in tension to and from sprocket
teeth. Because of the positive driving
characteristics
of a chain drive, it requires only a few sprocket teeth for effective
engagement that allows higher reduction ratios than are usually permitted with
belts. Load capacity of chain drives can be increased with multiple-strand chains.
GEAR DRIVE
Gears are
means by which power is transmitted from source to application. A gear drive is
used when the distance between the driver and the follower is small. Geared
transmission drive the machine of modern industry.
A wide variety
of gear materials are available today for the designer. Depending on the
application the designer may choose from materials such as wood, plastics,
aluminum, bronze, cast iron, steel etc.
REFERENCES
J. J. Uicker; G. R. Pennock; J. E.
Shigley (2003). Theory of Machines and Mechanisms (3rd ed.). New York: Oxford
University Press. ISBN 9780195155983.
B. Paul (1979). Kinematics
and Dynamics of Planar Machinery. Prentice Hall.
Stiesdal, Henrik (August
1999), The wind turbine: Components and operation (PDF),
retrieved 2009-10-06
Musial, W.; Butterfield,
S.; McNiff, B. (May 2007), Improving Wind TurbineGearbox Reliability (PDF),
National Renewable Energy Laboratory, retrieved July 2, 2013
"Experts predict nine-, 10-speed transmissions to
dominate in North America". Autoweek. May 13, 2013.
