Belt Friction Lab Report (Mechanical)
Introduction
A belt drive is known as a looped flexible strip which is used to make
easier the processes of machines and increase the efficiency of them. This
mechanism includes pulleys on each shaft and one or more belts may be connected
on each pulley to transmit rotary motion and power from one to others. Commonly
belt drives are used for the purpose of transmitting power between a source and
a load at a considerable distance. Belt drives are cost effective power
transmitting method and free of lubricants. In real world, belt drives are
widely can be seen in lathe machines, grinders, automotive systems such as fan
belt, air conditioning compressor motor etc. Belts are classified in various
types such as flat belts, V belts, and
synchronous belts and round belts as for their different application purposes.
Due to some beneficial facts such as easy installation, low maintenance, shock
absorption, high efficiency, belt drives are widely used in industrial
engineering applications.
Objectives
·
To study the frictional behavior and characteristics applicable for
belt drives.
·
To understand the effect of angle of lap around the pulley on torque transmission.
·
To study the effect of the friction in various types of belts (Ex:-
Flat, V, round belts etc.)
To evaluate the coefficient of friction between
the belt and pulley by using the results obtained experimentally
r1= Drive pulley
radius=Load pulley radius, ω1=Rotational speed of the drive pulley, ω2=Rotational
speed of the load pulley.
v= Belt speed
v=r1ω1=r2ω2
Thus, speed ratio; ω2:ω1 = r1:r2
If the
diameter=d, rotational spees in rev/min=N, the speed ratio can be written as; N2:N1
= d1:d2
When the drive torque=Ꞇ1 which acts in the same direction as the drive speed and the load torque=Ꞇ2 which acts opposite
to the rotation of the load pulley. Therefore;
Ꞇ1=(T1-T2)
r1 Ꞇ2=(T1-T2) r2
δN= The normal force between the
belt element and the pulley
δF= The
frictional force acting at the contact surface between the belt and pulley
Resolve forces horizontally;
Tcos(δβ/2)+δF-(T+δT)cos(δβ/2)=0
δβ 0, cos(δβ/2) 1
T+δF-(T+δT)=0
Therefore, δF=δT Resolving forces vertically;
δN-Tsin(δβ/2)-(T+δT)sin(δβ/2)=0 As
δβ 0, sin(δβ/2) δβ/2 δN-T(δβ/2)-(T+δT)(δβ/2)=0
δT(δβ/2) term can
be ignored as the second order terms Then, δN=Tδβ
Considering
Coulomb friction; δF<=µδN δT<=µTδβ
For infinitesimal
angles, thus dT<=µTδβ
According to V belts;
Resolving forces;
R=2Nsin(ϕ) N=R/(2Nsin(ϕ)
Friction forces
acting normal to the reactions can be written as F
F
F= µ’R
Methodology
·
Initially the arm was fixed in to the 0º position and
set up the v belt and the spring balance on the apparatus.
·
Then the load hanger was fixed on to the free side of
the belt and loaded the hanger in to constant load of 20.5N
·
Next the cord was placed on the pulley peg in a
clockwise direction and its load hanger was added.
·
Then the weights were gently added to the cord hanger
until the pulley was just on the point of slipping.
·
At that point two hanger loads and the spring balance were noted.
·
To check the spring balance the cord load was removed
and tried rotate the pulley by hand until the point of slip reached and the
spring balance was carefully observed.
·
The experiment was done to the both good and the worn
grove of pulley and repeated until it reached
180º.
In (T1/T2)
=µθ
corresponds to y=mx graph. Friction Coefficient can be calculated by the
calculating the gradient of this graph.
T1 and
T2 can be obtained by the experiment. Radius of the pulley is known.
Then, the maximum torque can be calculated by above mentioned data.
Coefficient of
the friction and maximum torque can be separately calculated according to
experimental values of Good Groove Belt and Worn Groove Belt
(I did not include the RESULTS part. Please kind enough to doi it on your own)
Discussion
Ø Practical
applications of belt drives
In the field of mechanical engineering there were many
kinds of belt drivers used in various kinds of applications. These belts drives
are in various shapes and they are functioning in various speeds in various
applications. The unique design of the belt drive is depend on the type of
application.
*
Automobile Engines
In automobile engines there are mainly two types of belt drives. Timing Belt is a notched flat belt
which allows the crankshaft to turn the camshaft. Other type of belt drive is serpentine belt also known as drive
belt. These types of belts are used to provide power to air conditioning
compressor, cooling fans, air injection pumps and to charger the DC battery by
alternator.
*
High Speed Drawing Machines
Different kinds of belts are used in various kind of drawing machines.
Heavy duty V- belt drives are commonly used.
*
Oil and Natural Gas Mining
In natural gas and oil mining, service rig is a versatile
piece of equipment used in entire mining process. Service Rig is equipped with
motors, pumps compressors and other equipment’s. Most of those machine parts
are driven by using belt drivers.
*
Gear Boxes
Automobiles manufactures use Continuous Variable
Transmission (CVT) in their productions more often newer days. Driven pulley
and the drive pulley of the CVT gear box is driven by a belt drive. Normally
V-Belt is used.
Ø
Effect
of pulley radius on belt tension
Belt tension must be sufficient to
overcome the slipping under the peak load. At rest (initial conditions) tension
along the whole belt is a same value. When it is transmitting the power,
tension in the pulling side increase and tension in the other side of the belt
will decrease. Increase tension in the tight side of the belt is equal to the
decrease tension in slack side.
Ratio between diameters of the driven
pulley and the drive pulley is the speed
ratio.
( (
In pulley and belt system, driven pulley
and drive pulley can be differed or equal in
diameter/radius. When the driven pulley is larger than drive pulley speed
of the drive pulley is higher. This incident can take place vice versa. Here the ratio between two radiuses of
pulleys plays an important role. Radius ratio of the two pulleys can be only
lie in a certain period for a specific pulley material and a belt (friction
coefficient of belt and pulleys changes when material of the pulleys and belts
changes). If a pulley ratio does not lie between limits, belt starts to slip.
To prevent the belt by slipping, always the pulley ratio must be within the
pulley ratio limits (Lowe and upper Limit).
Ø Advantages
and disadvantages of using belt drives as opposed to gear drives
In most of Engineering Applications power transmission takes a major
place due to the efficiency of the mechanism. Commonly, it can be seen belt
drives, chain drives and gear drives are used to transmit power in machines.
Concentrating to those power transmission methods, it can be clearly seen that
belt drives and chain drives activate in same manner. Gear drives transmit
power in a different manner rather than belt and chain drives.
When considering the advantages and disadvantages of belt drives as opposed
to gear drives, there are some facts can be identified clearly.
As Advantages;
*
Basically belt drives can transmit power between long distances.
*
Actually belt drives are simple to use and they have a low maintenance cost
*
Noise and vibrations are minimized by belt drives.
*
Parallel shafts are not needed when applying a belt drive.
*
Belt drives are cost effective and efficiency is higher than others.
*
Belt drives are activated free of lubrications.
As
Disadvantages;
*
Belt drives are only compatible to a limited speed
*
The ratio between velocities can be changed due to belt slips
*
Belt drives may be scathed when applying heavy loads on shafts and bearings
*
Usually, belt drives can be operated between a short temperature gap.
Usually, belt drives can be operated between a short temperature gap.
*
Frequently belt drives may be slipped and stretched.
Thus, angular velocity of belt drive can be varied.
*
Belt drives must be replaced instead of repaired.
Ø Power
transmissions and efficiency of belt drives
*
Belt drives are applied for machinery because for
transmitting power between long distances. That is the main purpose of using
belt drives in various machines.
*
Belt drives provide nearly 95% efficiency and continue a quiet operation.
*
Considering the power transmission, belt drives may
contain different speed ratios and variable speeds. The power can be
transmitted between widely mounted shafts.
*
In real world, air conditioning systems in
automobiles, fan belts, power steering systems are fulfilled with belt drive mechanisms.
*
There are
various types of belt drives such as Flat Belts, V Belts, Synchronous Belts,
Link Belts etc. Efficiency of those are varied due to their unique
characteristics. This efficiency mostly depends on the friction which is
originated between belt and the contacting surface.
Conclusion
Ropes, belts,
and clutches are the commonly using elements in machine that use friction to
transfer energy to one place from another place. Use of belts made with elastic
or flexible materials in industry is highly important in the conveying and
transmission of energy for long distances. In power transmission devices belts
are widely used as a successor for gears, shafts, and bearings in most of the
fields. ’Belt friction’ is an important thing to mention in power transmission
in most of the machines for long distances. Other benefits belt power
transferring is it simplifies the design of machines, lifetime, reliability,
and reduces the cost of machine maintenance and regarding cost.
The rope-belt friction
equipment borders on belt friction that explains the forces by friction in a
surface and a belt, like a belt goes through a bollard. When the force is
applied from one end only a portion of the force is transferred to the other
end through the pulley. The magnitude of the friction force goes up with the
amount of turns about the pulley. Above apparatus contains a loaded belt and
wall mounted fixed pulley, rope, flat belt, V-belts (incorrectly fitted and
appropriately fitted), hangers for weights, standard size weights. In this
experiment setting up time period is short because of the apparatus, and
measurements are taken in a simple manner, In the. Apart from usage in machines
mountain climbers and sailing crews should have general knowledge of belt
friction when preforming their basic tasks. Evaluating the coefficient of
friction between pulley and the belt is the aim of this experiment.
In summary, this lab experiment was meant about the relation between the
two tensions with respect to friction. Some scientific facts such as how the
tensions vary according to the load applied and by that to calculate the
coefficient of friction for each type of belt were learnt by this experiment.
By conducting these type of experiments as mechanical engineering students it
is easier to understand the application of belt drives in the field such as in
automobile engines and in machines where rotational motion is applied to
transmit power from a source to a load operating at a quite a distance.
References
·
A Look at Belt, Chain and Gear Drive Technology [Online]
Available
at : https://www.powertransmission.com/blog/a-look-at-belt-chain-and-gear-drive- technology/
[Accessed on 29th March 2019]
·
Basics of belt drives [Online]
Available
at : https://www.plantengineering.com/articles/basics-of-belt-drives/ [Accessed on 29th March 2019]
·
Mechanical Principles [Online]
Available
at: http://www.freestudy.co.uk/mech%20prin%20h2/outcome3t1.pdf [Accessed on 31st March
2019]
·
Belt Drive
Solutions for Oil and Gas Drilling Production [Online]
Available at:
http://www.gatesunitta.com/sites/all/themes/gates/download/IR/Product_Brochures_&_Catalogues/ Oil_&_Gas_Drilling_and_Production/Miscs/Oil_Gas.pdf
[Accessed on 31st March 2019]
Jost’s material handling provides innovative solutions for internal material handling needs for its customers so that it improves the efficiencies of their processes.
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