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.

Analysis

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.

*        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 29^th March 2019]

·         Basics of belt drives [Online]

Available at : https://www.plantengineering.com/articles/basics-of-belt-drives/ [Accessed on 29^th March 2019]

·         Mechanical Principles [Online]

Available at: http://www.freestudy.co.uk/mech%20prin%20h2/outcome3t1.pdf [Accessed on 31^st 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 31^st March 2019]