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

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

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

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

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

Basic components of the Belt drive

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.

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.

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

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

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.

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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,

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.

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

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

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

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

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.

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.

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.

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

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.

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.

Checking the sheave for wear Use the Sheave Gauge below

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

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

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

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

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

Using a string to align sheaves

Measurement of Vertical Alignment of Sheaves

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

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

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

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

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

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

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

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.

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

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

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.

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

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

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