11 September 2018

Drum brakes vs Disc brakes | Difference

A brake is a mechanical device that slows down a motion by absorbing energy from a moving system. Braking is done due to the friction between two surfaces. The heat generated during braking is the major problem nowadays so different brakes are used where this heating problem is resolved. 

Brakes are mainly classified into three main categories mechanical brake, hydraulic brake, pneumatic and electric brake. 

Nearly the same idea as the disk and drum brake the difference is its working. They both fall under the mechanical brake. Here, you can check it out the difference between disc and drum brake. 

What is a disc brakes?

The disk brake has a metal plate in the shape of a disk and a calliper that is attached to the wheel and the disk is rotated with the car wheel. The calliper is used on the pads for exerting power. The friction lining of the calliper comes into touch with a tiny part of the disk. The reaming part of the disk enables the surroundings to dissipate the heat. Two pads are used on either side of the disk and both pads are connected to the friction lining. Calliper is connected to the non-rotating part and on both pads it exerts force. When the brake paddle is pushed, the pads are pushed against the rotating disk as well, the friction between the disk and the pads will retard the speed of a car and prevent the disk.

What is a drum brakes?

The drum brake is a small drum that rotates with the wheel and has inside a pair of shoes known as brake shoes. When the brake paddle is pressed, the brake shoes are forced against the side of the drum walls and the brake is applied by means of friction.

Drum Brakes vs Disc Brakes | Difference between the drum and disc brakes : 

  • In the case of disc brakes friction surfaces are directly exposed to the cooling air, whereas in the drum brakes, the friction occurs on the internal surfaces, from which heat can be dissipated only after it has passed by conduction through the drum. 
  • The friction pad in the case of disc brakes is flat as compared to curved friction linings in the case of drum brakes means that there is uniform wear of friction pads. Adding that the friction pad material is not subjected to any bending, thereby increasing the range of materials from which to choose the suitable one. Generally, we use asbestos fibre with metal oxide fillers bonded with organic compounds as the material for friction pads. 
  • Unlike the standard drum brake, the design of the disc brake is such that there is no loss of efficiency due to expansion. As the system becomes hot, expansion of the drum of the internally expanding shoe type of brake tends to move the friction surfaces apart, causing a loss of effective pedal travel. On the other hand, disc expansion merely changes the relative positions on the friction surfaces slightly without tensing to increase the clearance. 
  • Disc brake weighs less than their conventional drum-type counterpart, so a saving of approximately 20 to 30 % is possible. 
  • The disc brake has comparatively better anti-fade characteristics as compared with drum brakes. 
  • Drum brakes are simple in design as compared to disc brakes. There are very small numbers of parts to wear or do not function properly. 
  • When required, replacing the friction pads is very easy compared to the type of drum where the brake lining must be either riveted or attached to the brake shoes with adhesives.
  • Changes in brake factor for a unit change in friction coefficient is much less in the use of disc brakes than it is for two leading shoes or the simple, leading or trailing shoe brakes. 
  • Compared to conventional drum-type brakes, the total frictional area of pads in disk brakes is very less. The approximate ratio of 1:4 means that disc brakes have greater pressure intensity than drum brakes. 
  • Drum brakes are purely mechanically operated whereas disc brakes are mechanically operated but also be linked with ABS system and some other advanced technology. 
  • Drum brake has less torque transmitting capacity and disc brake has high torque transmitting capacity in a small volume. 
  • Disc brakes are as easy to control and have a fast response time as compared to drum brakes. 
  • The drum brake may be self-locking while the disc brake lever.
  • Drum brake maintenance is cheaper than disk brake maintenance.
The above point implies that frequent relining would be necessary, due to an increased rate of wear. So that there are compensating factors are the following below :
  1. Pads can be made considerably thicker, for a given initial cost, so that more wear can take place before replacement is necessary. 
  2. New wear-resistant friction materials that are more suitable for disk brakes than for drum brakes have been developed.

Summary : 

The only factor limiting the more extensive use of disc brakes is their initial cost. However, with further improvement in design and savings due to increased production. It is hoped that ultimately this type may replace the drum type brakes altogether at least for medium to heavy vehicles.