1. Introduction to V-Belt Drives
Module 4
Introduction to V-Belt Drives

2. Module Objectives After the completion of this module, the student will be able to:
A-Knowledge 1. Describe the function of the three basic components of a belt drive. 2. Define pitch and explain its importance 3. Define the pitch circle, pitch diameter and pitch length of a belt drive and explain their importance. 4. Describe how to calculate the pulley ratio and explain its importance. 5. Describe how to calculate the shaft speed and torque of a belt drive system. 6. List five types of belt drives and give an application of each. 7. List three types of V-belts and give an application of each. 8. Describe the operation of a V-belt drive. 9. Describe how to install and align a V-belt drive. 10. Describe how to determine belt tension for an application. 11. Describe three methods of adjusting belt tension. 12. Describe three methods of measuring belt tension and give an application of each

3. Module Objectives After the completion of this module, the student will be able to:
B-Skills: 1. Calculate pulley ratio. 2. Install and align a V-belt drive with a finished bore 3. Determine the belt deflection force for a given application 4. Adjust belt tension using an adjustable mounting base 5. Use a belt tension tester to measure belt tension

4. Introduction
There are three common methods to couple two shafts that are parallel with each other:
Chain drive
Gear drive
Belt drive

5. V-belt drive
The belt drive is the most common of the three methods, and the V-belt drive is the most common type of belt drive.
The v-belt is popular because
it is inexpensive,
requires no lubrication,
accepts greater misalignment than chains or gears,
absorbs shock loads

6. Basic components of the Belt drive

7. Function of the basic components of a belt drive
The belt
It is a continuous loop of material, usually rubber and other materials, which is stretched between the two sheaves.
It transmits speed and torque by means of the friction between it and the sheave grooves.

8. Function of the basic components of a belt drive
The driver sheave (pulley) is a grooved disk which is attached to the shaft of the drive or prime mover. It turns with the drive shaft and causes the belt to move.

9. Function of the basic components of a belt drive
The driven sheave (pulley) is a grooved disk which is attached to the driven shaft. It turns when the belt moves and in turn causes the driven shaft to rotate

10. The Pitch
Pitch is defined as the distance between a point and a similar corresponding point
Examples of pitch : screw threads, chains, and gears.

11. Pitch Circle, Pitch Diameter and Pitch Length of Belt Drives
The pitch circle is the circle that goes through the place on each disk where the speed and force are transmitted
The pitch circle is located somewhere inside the outer diameter of the sheave.

12. The pitch diameter
The pitch circle is important because it allows the operator to determine the pitch diameter
The pitch diameter, PD, is the diameter of the pitch circle.
The pitch diameter is important because it allows the operator to calculate the speed and torque transmitted to the driven shaft

13. The pitch length
The term pitch length is the length of the belt which is described by the point inside the belt that passes through the pitch circles of the two sheaves
The pitch length is important because it is used to size the belt

14. Calculating the pulley ratio
The ratio of the pitch diameters of the two sheaves is called the pulley ratio
different

15. Example 1
calculate the pulley ratio of the following belt drive system

16. Solution to Example 1
calculate the pulley ratio of the following belt drive system.
PR = 150/50 = 3/1
This is often stated as a 3:1 pulley ratio

17. Effect of Relative Disk Size on the Speed of the Driven Shaft

18. Effect of Relative Pulley Size on the Speed of the Driven Shaft
The larger pulley decreased the speed delivered to the driven shaft.

19. Effect of Pulley Ratio on Torque of Driven Shaft
the torque in the driver pulley is 5 Nm (T= force x radius = 5x1 = 5). The torque in the driven pulley, is 15 N-m (T = force x radius = 5x3=15). The larger pulley increased the torque delivered to the driven shaft.
The force applied to the surfaces of the pulleys is the same.
From these discussions, it is safe to say that the larger pulley turns slower but has greater torque
Complete skill 1 page 22

20. Central shaft systems
They started to be replaced by electric motors which were placed at individual machines.
This made power transmission
more efficient,
flexible, and
lower in first cost. It also
permitted higher speeds, which could enable even higher efficiencies and higher machine productivity.

21. Types and Applications of Belt Drives
Flat belt
V-belt
Timing belt
Round belt
Ribbed belt

22. 1. Flat Belts The flat belt was the first type of belt drive used
The power from these shafts was transmitted to each machine by means of two pulleys and a flat belt
Usually used as conveyors

23. Disadvantages of Flat Belts
not very efficient
they are bulky
they are not well suited to higher motor speeds
they require more maintenance than other types of belt drives

24. 2. V-Belts
The v-belt is a wedge-shaped belt which is made from a combination of rubber and textile material.
The v-belt is designed to grip the walls of a grooved pulley by wedging itself against the sides of a pulley groove as the belt is tightened

25. V-BELT OPERATION
They are the most common type of adjacent or parallel shaft-to-shaft drives used because they are:
quiet,
low in cost,
easy to maintain

26. The advantages of the v-belt
Operates at higher speeds
Transmits power more efficiently
Transmits power in a smaller size
Requires very little maintenance
The v-belt drive is commonly used in applications such as fan drives, air compressors, and car engines :
Disadvantage of V-Belts:
They can slip during operation

27. 3. Timing Belts (positive drive belt)
The timing belt (or positive drive belt) solves the problem of the slipping V-belts by using a belt and pulleys which have notches or teeth
As the drive pulley turns, its teeth engage the teeth of the belt and pull it. With this design, the belt does not slip and a constant speed is maintained at the shaft

28. Advantages of the Timing Belts
Does not slip and a
constant speed is maintained at the shaft

29. Timing Belts’ uses The timing belt is used in: Car engines
Axes of robots
Electronic circuit board assembly machines

30. 4. Round Belt It uses a circular cross-section.
Its main advantage is low cost.
It is mainly found in very light duty applications, where either the load is light or slip and efficiency are not important such as
vacuums and
printers,

31. 5. Ribbed Belt
The ribbed belt has ribs that run longitudinally (along the length) on the belt. These ribs are designed to seat in mating grooves in the sheaves
This type of belt has a greater area of the belt in contact with the sheave, which means that there is less wear on the belt or sheaves.

32. Types and application of v-belts
There are three main types of v-belts:
Classic
Narrow
Cogged
These belts look similar, differing mainly in
dimensions and internal construction

33. Classic V-Belt
The classic v-belt is designed for power transmission and general machine construction. It can handle light to heavy loads based on its belt width. The classic v-belt can be used singly but are often used in sets of more than one belt

34. Narrow V-Belt
It is similar to the classic v-belt but can handle twice the load of a classic v-belt of the same width.
Narrow V-Belt

35. Advantages of Narrow V-Belt
can handle twice the load of a classic v-belt
needs 50% less pulley width than classic v-belts.
used for more demanding applications
can be used singly but are often used in sets.
Narrow V-Belt

36. Cogged V-Belts
They show improved flexibility for better performance on small diameter pulleys.
They also reduce slippage and allow the belt to bend around sheaves with less effort.
This increases motor speed and efficiency.

37. Operation of the v-belt drive
The v-belt drive transmits power by increasing the distance between the two sheaves so that tension is created on the belt.

38. Operation of the v-belt drive
wedging action of the v-belt creates friction between the sides of the sheave, not the groove bottom.
The v-belt should ride high in the groove, with its top near the top of the sheave,
Normally, the v-belt does not touch the bottom of the sheave.

39. Typical V-Belt Construction
The belt consists of polyester or some other textile-based cording, rubber filler compound, and a neoprene envelope
The neoprene envelope makes the outside of the belt smooth

40. Sheave with Finished Bore Integral Hub
The sheaves used for v-belt drives are usually made of either
stamped steel halves which are pressed together,
die cast zinc, or
die cast aluminum.

41. Sheave with Finished Bore Integral Hub
In any case, the sheaves are normally attached to the shafts with an integral hub which has the keyseat built into sheave. This is called a finished bore or fixed bore hub.
finished bore or fixed bore hub.

42. Checking the sheave for wear
Use the Sheave Gauge below

43. Metric Belt Designation
Metric v-belt sizes are designated by pitch length and cross-section. Larger cross sections are required for more heavy duty applications.
The cross section is indicated by using a designated three-letter code. SPZ is a light-duty belt whereas SPC is for heavy-duty applications

44. Installing and Aligning the V-Belt Drive
V-belt drives are easy to install but it is important to do it correctly in order
to have the maximum life
Step 1. Mount and level the motor and the driven component
Step 2. Inspect the sheaves for cleanliness and wear. Clean or replace if necessary
Step 3. Mount the sheaves onto the shafts
Step 4. Mount the belt

45. Installing and Aligning the V-Belt Drive
Step 5. Align the sheaves
the goal of the alignment is to avoid twisting the belt
Misaligned sheaves will cause the belt and bearings to wear quickly

46. place a straight edge against the faces of the sheaves to align the sheave grooves and check the parallelism of the shafts

47. place a straight edge against the faces of the sheaves to align the sheave grooves and check the parallelism of the shafts

49. Using a string to align sheaves

50. Measurement of Vertical Alignment of Sheaves

51. Apply initial tension to the belt
Tension is necessary for the belt to grip the sheave
If the tension is too little, the belt will slip, causing the belt and the sheaves to wear quickly.
If the tension is too high, the bearings and the belt will also wear quickly

53. Installing and Aligning the V-Belt Drive
Step 7. Run the motor briefly to seat the belts
Step 8. Stop the motor and retighten the belt to the correct tension
Step 9. Retighten the belt after 24 to 48 hours of operation
Complete skill No. 2 page 23

54. Installing and Aligning the V-Belt Drive
Step 6. Apply initial tension to the belt
Tensioning the belt is a 3-step process:
Determine the tension needed.
Apply tension to the belt
Measure the tension

55. BELT TENSIONING
First we need to determining the required Belt Tension for an application.
Belt tension is measured by how much force is needed to deflect the belt a certain distance
Tension Tester

56. BELT TENSIONING
belt deflection force: the force needed to deflect the belt a certain distance
belt deflection method: the method used to measure belt tension using a tension tester.
Belt deflection method

57. Belt Deflection Force Table
This table is available from belt suppliers and shows the specific force for each belt, according the belt’s size; sheave size, operating speed, and whether or not it is new or old

59. The force levels listed in the table refer to the minimum level of tension force.
The upper limit of the acceptable tension force is 50% greater(e.g. Min value x 1.5).
The ideal tension is the lower of the two values. It represents the least tension needed to transmit the force and allow no slipping. If the tension is greater, more energy is lost through friction.
Turn to skill No. 3 & 4 page 32

60. BELT TENSION MEASUREMENT
Tension is applied to the belt by moving the driver motor away from the driven shaft. This can be done with either a pry bar, punch, or adjustable motor base.

61. Methods of measuring Belt Tension.
There are three ways that belt tension can be measured:
Hand pressure
Tension Tester
Spring scale and straight edge

62. 1. Hand Pressure Tension Measurement
To do this, strike the belt with your hand. It will feel alive and springy when it is tensioned correctly. If the tension is too low, the belt will feel dead. Too much tension will make it feel taut

63. 2. Tension Tester Tension Measurement (force deflection method)
The tension tester is a handheld device which measures belt tension by measuring the force needed to deflect the belt a certain amount
the belt should be deflected 0.4 mm per 25 mm of the belt span.

64. 2. Tension Tester Tension Measurement
To actually perform the test, the tester should be placed in the middle of the belt span and forced down until the belt is deflected by the proper amount.
The force indicated by the tension tester is then read. This force should be compared to a recommended force deflection range for that particular belt
Note:
The belt span is the distance between the points on the sheaves where the belt touches each sheave

65. 3. Spring Scale and Straight Edge Tension Measurement
The amount of deflection is measured by placing a straight edge across the belt span and measuring with a rule
Turn to skill No. 5 page 35

66. Complete the Activity 1. V-Belt Drive Analysis
Page 41
Complete the self review page 47