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Flat and
V-Belts
INTRODUCTION:
Factors for Selection of Belt Drive:
The following factors must be considered while
selecting a belt drive:
1. Speed of driving and driven shaft.
2. Speed reduction ratio.
3. Power to be transmitted.
4. Centre distance of hafts.
5. Space available.
6. Layout of shaft.
Factors on which Coefficient of Friction
Depends:
The coefficient of friction between belt and
pulley depends upon the following factors-
1. Belt material.
2. Pulley material.
3. Belt slip.
4. Belt speed.
Classification of Flat Belt Drives:
Flat belts can be used for horizontal, vertical,
quarter—turn, right—angled, crossed and reversed drive. Flat belt drives are
classified as:
Slip in Flat Belt drive:
Slip is the relative motion between the belt and
the pulley rim. The slip is given by, s = total percentage slip on the
pulleys
Crowning of pulley rim:
Selection of Flat—Belts from Manufacturers
Catalogue:
The following information is required to select
the flat—belt from manufacturer’s catalogue:
1. Power to be transmitted
2. Input and output speeds.
3. Centre distance available.
The basic procedure for belt selection from the
catalogue of the Dunlop Rubber Co. (India) Ltd. is as follows:
1. Calculate the maximum power transmitted by the
belt from the rated power:
2.For this purpose a factor called ‘arc of contact’ factor Fd
is used to calculate the corrected power to be transmitted be the belt:
3. Calculate the corrected power rating for the
belt:
Where v = belt velocity, rn/s
4. Calculate the product of (width x number of
plies):
Width x number i of plies = corrected
power/corrected kW rating
5. Select the standard belt width and number of
plies
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Thus the belt
creeps backward. This phenomenon is called creeping of belt;
Creep = (F1 — F2)/(btE)
Where F1, F2 = tensions on the tight and slack
sides respectively b, t = width and thickness of belt respectively
E = Young’s modulus of elasticity of belt
material.
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V-BELTS
Characteristics of V—Belt Drive The
characteristics of V — belt drive are:
1. It requires a grooved pulley.
2. The belt comes into contact with the sides of
the pulley groove only.
3. The belts are endless.
4. It gives more positive drive than flat belts.
5. The slip of thebelt is less as compared to flat
belts.
7. V- belts are used as a matched set.
8. The pulley groove angle is 40°.
9. They are suitable for speed ratio upto 7 and
belt speed upto 25 rn/s.
10. The size of a V — belt is specified by the
cross—section followed by inside length.
1.2.2 Equivalent coefficient of friction
Fig. 1.1 shows a V - belt in a grooved pulley. The
normal force on the belt face is,
What is power rating of a belt?
It is the power transmitting capacity of a belt
based on 180° angle of arc of contact and a speed of 1440 rpm of the faster
pulley.
Are the angles of groove in a
V-belt pulley equal to angle of V-belt? If not, why?
·
No, because the V-belt contracts
while transmitting power, therefore the pulley groove angle is made a little
smaller than the angle of belt.
·
If this is not done then the belt
will start touching the bottom of the pulley groove in a very short period of
operation and no allowance will be available after some wear of the belt.
List at least four materials for flat
belt?
2. Fabric
3. Balata
4. Rubber
the advantages and
disadvantages of Flat belt, V-belt, rope and chain?
Advantages:
1. Can be used for short as well as long centre
distances.
2. A number of shafts can be driven in the same or
opposite directions from a single driving sprocket.
3. More compact drive as compared to belt and rope
drives.
4. High efficiency.
5. More positive drive, i.e. less slip.
6. No fire hazards and temperature effects.
7. Can be easily replaced.
1. Unsuitable for precise motion due to polygonal
effect and wear of joints.
2. Require precise alignment of shafts.
3. Require proper maintenance, lubrication and
slack adjustment.
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