1. Flat belt.pdf

sd

1. Belt
Machines Design By RS Khurmi2005
Prepared by: Phua CL

2. Learning outcomes
•Successful students will be able to:-
•identify the types of belts
•determine the ratio of belt tensions and effect of centrifugal tension

9. Mobius Belt

10. https://www.yout
ube.com/watch?v
=RpVSn_ZZCOI
https://www.y
outube.com/
watch?v=m7r
am9-X-2s

17. Slip of The Belt
•Sometimes, the frictional grip between the belts and the pulleys
becomes insufficient.
•This may cause some forward motion of the driver without
carrying the belt with it that is called slip of the belt.
•Velocity ratio

18. Example 18.1 An engine running at 150 r.p.m. drives a line shaft by means of a belt. The
engine pulley is 750 mm diameter and the pulley on the line shaft is 450 mm. A 900 mm
diameter pulley on the line shaft drives a 150 mm diameter pulley keyed to a dynamo
shaft. Fine the speed of dynamo shaft, when
1. there is no slip
2. there is a slip of 2% at each drive.

20. 1.Anengineshaftrunningat120r.p.m.isrequiredtodriveamachineshaftbymeansofabelt.Thepulleyon
theengineshaftisof2mdiameterandthatofthemachineshaftis1mdiameter.Ifthebeltthicknessis5mm;
determinethespeedofthemachineshaft,when
(i).thereisnoslip;and
(ii).thereisaslipof3%.
[Ans. 239.4 r.p.m.; 232.3 r.p.m.]
Tutorial

22. Open belt
•Length of the belt
•Angle of contact

23. Example 1
[9.905m]
Find the length of open belt drive.

25. •Length of the belt
•Angle of contact
Crossed belt

26. Example 2
Diameter of pulley A is 200mm. Find the length of cross belt drive.
[4975mm]

27. Consider a flat belt partly wound round a pulley so that the angle of lap is Ɵ, shown below. And let T
1and T
2be the
tensions in the belt when it is about to slip in the direction shown. If the tension at the ends of an element subtending
and angle ????????????at the centreTand T+ dTand the reaction between the belt and the pulley is R, then resolving force
radially,
(2.1)
(2.1)
(2.2)

28. If the belt is used to transmit power between 2 pulleys. T
1and T
2are tight and slack side tensions respectively.
If vis the speed of the belt in m/s and T
1and T
2 are in newtons, then
(2.3)
(2.4)

31. 2.Apulleyisdrivenbyaflatbeltrunningataspeedof600m/min.Thecoefficientoffrictionbetweenthepulley
andthebeltis0.3andtheangleoflapis160°.Ifthemaximumtensioninthebeltis700N;findthepower
transmittedbyabelt.
[Ans. 3.974 kW]
Tutorial

32. Consider a belt of mass mper unit length, wound round a pulley of radius ras shown in figure below. Let the
speed of the belt be vand the centrifugal tension be T
c.
If Fis the centrifugal force acting on an element of the belt subtending an angle ????????????at the centre, then revolving
forces radially,
. . . (2.6)
Effect of centrifugal tension

33. Effect of centrifugal tension
This is the tension caused by the centrifugal force on the belt and is additional to the tension due to the
transmission of power.
If allowance is made for this additional tension in determine the ratio of the belt tensions, equation (2.1) becomes
(2.7)
radial
tangential

34. Effect of centrifugal tension
??????
1−??????
??????and ??????
2−??????
??????are the effective driving tensions, ??????
1and ??????
2are now total tension in the belt.
Allowing for centrifugal tension, equation (2.4) becomes
(2.8)
From equation (2.8) the power transmitted is a maximum when
The maximum power is then obtained by substituting this value of ??????
??????and the corresponding value of vin equation (2.8)
(2.9)

37. 5.Aleatherbelt,125mmwideand6mmthick,transmitspowerfromapulley750mmdiameter,whichrunsat500
r.p.m.Theangleoflapis150°andµ=0.3.Ifthemassof1m
3
ofleatheris1Mgandthestressinthebeltisnotto
exceed2.75MN/m
2
,findthemaximumpowerthatcanbetransmitted.
[Ans. 18.97 kW]
Tutorial

38. The End