Belt and Rope Drives

Chapter: 8

Belt and Rope Drives

Learning Objectives

While reading and after studying this chapter, you will be able to:

• Enumerate the various types of belts used for the transmission of power.

• Discuss the merits and demerits of belt, rope and chain drives for transmission of power.

• Explain the terms slip and creep in belts.

• Deduce an expression for the length of a belt in an open belt drive and a cross belt drive.

• Derive an expression for the tension ratio in a flat belt drive and V-belt drive. 

• Explain the effect of centrifugal tension on power transmission by flat belt. 

• Design the flat belt drive, V-belt drive and rope drive using the basic equations. of belts.

SYLLABUS

Types of belt drives - Velocity ratio - Length of belt - Belt tensions - Tension ratio - Power transmitted - V-belt drive - Rope drive

INTRODUCTION

• Power can be transmitted from one shaft to another shaft either by flexible or non-flexible type of machine elements.

• In flexible elements, the centre distance can be changed conveniently and in non-flexible type of machine elements, the centre distance cannot be changed.

• The flexible type of machine elements are: belts, ropes, and chains. The non-flexible type of machine elements are: cams, gears, clutches, couplings, and power screws.

• Flexible machine elements are used for power transmission over long distances and non- flexible machine elements are used for over short distances.

• In belts and ropes, power is transmitted due to friction between them and the pulleys. In case of chain drives, sprocket wheels are used.

• When the distance between the shafts is large, then belts, ropes or chains are used. For smaller distances, gears are used.

• The amount of power transmitted depends upon several factors such as velocity of the belt, tensions in the belt, mass of the belt, arc of contact between the belt and smaller pulley, etc.

In this chapter, we shall study the fundamental concepts of flat belt drives, V-belt drives and rope drives.

1. Classification of Drives

As discussed above, drives can be broadly classified into flexible drives and non-flexible drives, as shown in Fig.8.1.

We have already studied about cam drives in Chapter 3, gear drives in Chapters 4 and 5, and clutches in Chapter 7. Thus this chapter focuses only on study of belt and rope drives.