2. Introduction
• A brake is defined as a mechanical device, which is used to absorb
the energy possessed by a moving system or mechanism by means
of friction.
• The primary purpose of the brake is to slow down or completely stop
the motion of a moving system, such as a rotating drum, machine or
vehicle.
• It is also used to hold the parts of the system in position at rest
3. Introduction
• The energy absorbed by the brake can be either kinetic or potential or
both.
• In automobile application, the brake absorbs the kinetic energy of the
moving vehicle.
• In hoists and elevators, the brake absorbs the potential energy
released by the objects during the braking period.
• The energy absorbed by the brake is converted into heat energy and
dissipated to the surroundings.
4. BRAKES CLASSIFICATION
• Mechanical brakes, which are operated by mechanical means such as levers,
springs and pedals.
Depending upon the shape of the friction material, they are classified as block
brakes, internal or external shoes brakes, disk brakes and band brakes.
Brakes are also classified into two groups according to the direction of the
actuating force, namely, radial brakes and axial brakes. Internal and external shoe
brakes are radial brakes, while disk brakes are axial brakes.
6. BRAKES CLASSIFICATIONS
• (ii) Hydraulic and pneumatic brakes, which are operated by fluid pressure
such as Oil pressure or air pressure.
• (iii) Electrical brakes, which are operated by magnetic forces and which
include magnetic particle brakes, hysteresis brakes and eddy-current brakes.
7. BRAKES
• Brake capacity depends upon
• (i) The unit pressure between braking surfaces
• (ii) The contacting area of braking surface
• (iii) The radius of the brake drum
• (iv) The coefficient of friction
• (v) The ability of the brake to dissipate heat that is equivalent to the
energy being absorbed
8. BAND BRAKE
• It consists of a flexible steel strip lined with friction material, which is pressed
against the rotating brake drum.
• When one end of the steel band passes through the fulcrum of the actuating
lever, the brake is called the simple band brake.
• The working of the steel band is similar to that of a flat belt operating at zero
velocity.
• The ratio of band tensions is given by,
• where,
• F1 tension on the tight side of the band (N)
• F2 tension on the loose side of the band (N)
• f co-efficient of friction between the friction lining and the brake drum
𝐹1
𝐹2
= 𝑒𝑓𝜃
9. BAND BRAKE
Considering the forces acting on the
taking moments about the pivot,
F2 x a – F x l
or F = (F2 x a)/l
10. DIFFERENTIAL BAND BRAKE
The ends of the band are joined
at A and B to a lever AOC
pivoted on a fixed pin or
fulcrum O.
It may be noted that for the
band to tighten, the length OA
must be greater than the length
OB.
When the frictional force helps to apply the brake, it is said to be self-energizing brake.
In case of differential band brake, when the F is negative or zero, then brake is self-locking.
