Brakes

Chapter: 9

Brakes

Learning Objectives

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

• Differentiate between brake and clutch; brake and dynamometer.

• Explain the working principle of simple and double shoe brakes and also derive expressions for braking torque for different directions of rotation of drum. 

• Understand the arrangement of simple and differential band brakes.

• Explain the self-energizing and self-locking brakes.

• Derive expression for total braking torque about fulcrum in differential band brake for different directions of rotation of drum.

• Explain the arrangement done. in band and block brake system.

• Describe the principle of operations of an internal expanding shoe brake.

SYLLABUS

Types of brakes - Single block and double block brakes – Simple and differential band brakes Band and block brakes – Internal expanding shoe brakes.

INTRODUCTION

• A brake is a mechanical device by means of which motion of a body is retarded for slowing down or to bring it to rest, by applying artificial frictional resistance.

• In this process of regulating the motion, the brake absorbs either kinetic energy of the moving member or potential energy given up by objects being lowered by hoists, elevators, etc.

• The capacity of any brake depends upon the unit pressure between the braking surfaces, the coefficient of friction between them, velocity of brake drum, heat dissipation capacity of the brake, etc.

• A dynamometer is a brake incorporating a device to measure the frictional resistance applied. This is used for measuring the driving force or torque transmitted and hence the power developed by the machine. It may work on the principle of absorption or transmission.

• Clutch Vs Brake: The functional difference between a clutch and a brake is that a clutch connects two moving members of a machine, whereas a brake connects a moving member to a stationary member.

1. Types of Brakes

Depending upon the shape of the friction material, the mechanical brakes are classified as shown in Fig.9.1.

• Brakes may also be divided into two groups, depending upon the direction in which the force is applied, as:

(a) Radial brakes: In radial brakes, the force acts radially on the drum. The radial brakes may be sub-divided into external brakes and internal brakes.

Examples: Band brakes, block brakes, internal expanding brake.

(b) Axial brakes: In axial brakes, the force acts axially on the drum. 

Examples: Cone brakes and disc brakes.