Lab report 5(To Determine the Coefficient of Friction of Flat and V Belts PDF

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lab report describing determination of coefficient of friction of flat and V belt....

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THERMODYNAMICS LAB REPORT

SUBJECT: COFFICIENT OF FRICTION OF FLAT BELT COFFICIENT OF FRICTIO OF V BELT SUBMITTED TO: UMAIR ASHRAF KHOKHAR SUBMITTED BY: MUHAMMAD ABUBAKAR SHAHZAD REGD.NO: 2020-ME-121 SECTION: C DEPARTMENT OF MECHANICAL ENGINEERING

1. Experiment no.05: To Determine the Coefficient of Friction of Flat and V Belts. 2. Objectives:  

To determine the co-efficient of friction of flat belt. To determine the co-efficient of friction of v belt.

3. Apparatus:      

Belt and Pully Apparatus Spring Balance Flat Belt V Belt Hanger Weights

4. Procedure: Flat Belt       

Put the Flat Belt on the apparatus and make the angle of the pully equal to 30◦. Put a weight on the hanger and calculate the tension corresponding to that weight. Repeat the experiment for another weight. Repeat the experiment for third weight such that you three values of tension at three different values for weights for a same value of angle. Repeat the procedure for other angles up to 150 with the step size of 30◦. Weight is also acting as a tension T1 and corresponding tension is T2. Now calculate the coefficient of friction at each value of angle using this formula: µ = (1/θ) * ln(T1/T2)

V Belt     

Put the V Belt on the apparatus and make the angle of the pulley equal to 30◦. Put a weight on the hanger and calculate the tension corresponding to that weight. Repeat the experiment for another weight. Repeat the experiment for third weight such that you three values of tension at three different values for weights for a same value of angle. Repeat the procedure for other angles up to 150 with the step size of 30◦.

 

Weight is also acting as a tension T1 and corresponding tension is T2. Now calculate the coefficient of friction at each value of angle using this formula:  µ = (sinα/θ) * ln(T1/T2)

5. Observations: Flat Belt: Angle (α) No. of Obs Degree Radian

Tensions (pounds) T1 = 1.5

T1 = 2.5

T1 = 3.5

T2

T2

T2

Co-efficient of Friction (µ) Mean Values µ1

µ2

µ3

1.

30

0.524

1.4

2.1

3.2

0.13

0.33

0.17

0.212

2.

60

1.047

1.4

2

3.1

0.07

0.21

0.12

0.132

3.

90

1.571

1.3

2

3.1

0.09

0.14

0.08

0.103

4.

120

2.094

1.2

2.1

2.9

0.11

0.08

0.09

0.093 Mean µ = 0.14

V Belt: Angle (θ) No. of Obs Degree Radian

Tensions (pounds) T1 = 1.5

T1 = 2.5

T1 = 3.5

T2

T2

T2

Co-efficient of Friction (µ) Mean Values µ1

µ2

µ3

1.

30

0.524

1.3

2.3

3.3

0.07

0.04

0.03

0.04

2.

60

1.047

1.3

2.3

3.4

0.03

0.02

0.01

0.02

3.

90

1.571

1

1.9

2.9

0.06

0.04

0.03

0.04

4.

120

2.094

1.2

2.2

2.9

0.03

0.01

0.02

0.02

Mean µ = 0.03

6. Theory:  Belts: “A belt is a loop of flexible material used to link two or more rotating shafts mechanically, most often parallel. Belts may be used as a source of motion, to transmit power efficiently or to track relative movement. Belts are looped over pulleys and may have a twist between the pulleys, and the shafts need not be parallel.” In a two-pulley system, the belt can either drive the pulleys normally in one direction (the same if on parallel shafts), or the belt may be crossed, so that the direction of the driven shaft is reversed (the opposite direction to the driver if on parallel shafts). [1]

 Types of Belts: There are following types of Belts: i. ii.

Flat Belt V Belts

a. Flat Belts: “Flat belts are designed for light-duty power transmission and high-performance conveying. They are best-suited for applications with smaller pulleys and large central distances. Flat belts can connect inside and outside pulleys and can come in both endless and jointed construction. They have a high-power transmission efficiency, are cost effective, and are easy to use and install.” [2]

Figure: Flat Belt [3]

Advantages of Flat Belts: The small bending cross-section of the flat belt causes little bending loss. The frictional engagement on the pulley outer surface requires only a small cross-section and makes flat belts very flexible, resulting in negligible energy loss. A flat belt does not require grooves, minimizing the energy loss and wear from the belt wedging in and pulling out from the grooves. Additional benefits of flat belts include energy savings, a long service life of belts and pulleys, less down time and high productivity, and low noise generation from a smooth belt operation. Flat belts can be installed simply and securely. Belts are tensioned to the calculated initial tension by means of simple measuring marks to be applied to the belt. There is a constant tension on the belt so the belt will not need to be re-tensioned.

Disadvantages of Flat Belts: A disadvantage of flat belts is their reliance on belt tension to produce frictional grip over pulleys. This high belt tension required to transmit power often shortens bearing life. Another disadvantage is their failure to track properly since they tend to climb towards the higher side of the pulley, which is why V-belts have grown in popularity.

Applications of Flat Belt: They are used in i. Countless Farming ii. Mining iii. Logging applications such as  Bucksaws  Sawmills  Threshers  Silo blowers  Conveyors for filling corn cribs or haylofts  Balers  Water pumps (for wells, mines, or swampy farm fields)  Electrical generators.

b. V Belts “V belts (also style V-belts, vee belts, or, less commonly, wedge rope) solved the slippage and alignment problem. It is now the basic belt for power transmission. They provide the best combination of traction, speed of movement, load of the bearings, and long service life. They are generally endless, and their general cross-section shape is roughly trapezoidal (hence the name "V").”

Figure: V Belt

The "V" shape of the belt tracks in a mating groove in the pulley (or sheave), with the result that the belt cannot slip off. The belt also tends to wedge into the groove as the load increases —the greater the load, the greater the wedging action— improving torque transmission and making the V-belt an effective solution, needing less width and tension than flat belts. V-belts trump flat belts with their small center distances and high reduction ratios. The preferred center distance is larger than the largest pulley diameter, but less than three times the sum of both pulleys. For high-power requirements, two or more V-belts can be joined side-by-side in an arrangement called a multi-V, running on matching multi-groove sheaves. This is known as a Multiple-V-belt drive (or sometimes a "classical V-belt drive").

Advantages of V Belts: i. ii. iii. iv. v. vi.

High power transmission capacity because V-grooves provide excellent grip. The functioning of the belt and the pulley is smooth and quiet. The V-belt drive provides compactness due to the small distance between the centers of the pulleys. Slip between the belt and the pulley is negligible. The axis can be horizontal, vertical or inclined. They can dampen vibration.

Disadvantages of V Belts: i.

The V-belt drive cannot be used for long distances due to greater weight per unit of length.

They are not applicable to the synchronous machines because they are not free from creep. The centrifugal tension prevents the use of belts at speeds below 5 m/s and above 50 m/s. The construction of pulleys for v-belts is more complicated than the flat belt.

ii. iii. iv.

Possible Errors:     

Parallax Error. Zero error of spring balance. Frictional and heat losses. If belts are under tensioned, they can slip. Slippage generates heat and will result in cracking and belt failure. If belts are over tensioned, belt and bearing life can be reduced.

Solutions:          

Keeping belts tight Taking up slacks of belts Running in new belts Dressing belts Rotate the drive two or three revolutions by hand and check the belt tension. To obtain the greatest amount of power from belts, the pulley should be covered with leather. Rotate the pulley not very fast because it will unbalance the pulley and the apparatus will not work properly. The belt should be installed on the pulley with maximum care as to give moderate strain on the pulley. The leather in the belt should be pliable, of fine close fiber, solid in its appearance, and of smooth polished surface To increase the driving power of belts, the circumference of pulleys should be increased.

References: [1] Needham (1988), Volume 5, Part 9, 207–208 [2] "Flat Belt Pulleys, Belting, Splicing". Hit N Miss Enterprises. Archived from the original on 17 March 2010. Retrieved 2010-04-04. [3] https://www.indiamart.com/proddetail/flat-belts-16198743673.html [4] Robert Grimshaw, Drive for Power Transmission Cassier's Magazine Vol. II, No. 9 (July 1892); pages 219–224.

[5] https://www.gamut.com/c/power-transmission/round-belt-pulleys-idlers [6] https://me-mechanicalengineering.com/belt-drives/...