An internal expanding brake consists of two shoes S1 and S2.
The outer surface of the shoes are lined with some friction material
(usually with Ferodo) to increase the coefficient of friction and to
prevent wearing away of the metal. Each shoe is pivoted at one end about
a fixed fulcrum O1and O2
and made to contact a cam at the other end. When the cam rotates, the
shoes are pushed outwards against the rim of the drum. The friction
between the shoes and the drum produces the braking torque and hence
reduces the speed of the drum. The shoes are normally held in off position by a spring .
The drum encloses the entire mechanism to keep out dust and moisture.
This type of brake is commonly used in motor cars and light trucks.
We shall now consider the forces acting on such a brake, when the drum rotates in the anticlockwise direction.
It may be noted that for the anticlockwise direction, the left hand
shoe is known as leading or primary shoe while the right hand sho…
An iris is a mechanism that is used as a compact solution to
close and open holes. It is made up of usually a series of metal plates
that can fold in on each other or expand out. Iris mechanisms are
commonly found in optical shutters (diaphragms). Irises are sometimes used in science fiction as doors.