ALL ABOUT HYDRAULIC BREAKING AND BRAKE LINING TO THE SHOE;

Q.. Explain the details of hydraulic braking system

Answer

The brakes which operate under liquid pressure are called hydraulic tracks Hydraulic brake system works on “Pascals principle;which states that the confirmed liquid transmits  pressure without loss equally in all directions.

Front Wheel

Construction

It contains a master cylinder and wheel cylinder filled with liquid under low pressure when brakes Applied. The
fluid (or) liquid used is called brake fluid, which is a composition of glycerine and alcohol (or) castor oil, denatured alcohol and
some additives The master cylinder is connected to wheel cylinders at each of the four wheels by tubing. Each wheel brake
contains a hub (or) brake drum which is installed inside the wheel and rotates, whereas the two brake shoes arranged inside the
hub are in stationary position Brake shoes have heat and wear resisting lining on their surfaces

Operation

The brake pedal is connected to the master cylinder through linkages. When brake is pressed, the piston forces the fi
Into master cylinder, Therefore, the pressure of fluid increases in the complete system. This pressure is transmitted to cach
wheel cylinder, thereby causing the pistons to move outwards, which in turn forces out the brake against the brake drums (o)
hubs. Therefore, the brakes are applied
When the pedal is released, there is a pressure drop in the master cylinder due to which the pressure decreases in the
entire hydraulic system. Hence, the brake shoes get out of contact with hub (or) drum. Therefore, the pistons get settled in the
actual positions due to retracting spring force Thus brakes are released

 

Q.. What are the various materials used for brake lining?

Answer:

Materials used for Brake Lining

There are two main varieties They are,
(i). Solid-woven type
(ii). Moulded type

(i).Solid-woven Type

The asbestos-base, non-metallic linings generally have
an average coefficient of friction of 0.4 upto a temperature of
round 260°C and fade is not a matter of serious concern upto
300°C. The maximum temperature they can resist is around
350°C. It can be improved further by zinc wire inclusion. Zinc
conducts away some of the heat from the working surface
and thus slightly reduces the maximum temperature reached
by the particular brake mechanism. Zinc-wire lining also have
better anti-fade characteristics and wear resistance as
compared to non-metallic type.

(ii) Moulded Type

These are moulded directly from the “mix” containing
asbestos fibers along with resin powders and fillers. They
have an average coefficient of friction of 0.4 and temperature
resistance from 400 to 450°C. They possess good anti-fade
and anti-wear properties.
Example

Ferodo 2629 F (asbestos-based)                                                          Rane 9011 DC (asbestos-free).

 

Q.. Explain the methods of fastening brake lining
to the shoes.

Answer:

Methods of Fastening Brake Lining to the Shoes

It is mainly done by two methods,
1. By riveting
2. By using synthetic resin adhesives.

Using synthetic resin adhesives have greater
efficiency, better heat dissipation, free from scoring action,
increased life of lining, upto 20% less cost as compared to
riveting method.
The brake linìngs for cars and light vehicles are
attached with adhesives whereas for commercial vehicles,
riveting method is still preferred.

Procedure

1. Preparing the Surface

Both the binding surface of the brake shoe and liner
Surface area roughened by shot blasting and sanding
respectively. After this, they are degreased in a solvent vapour
bath, solvent being trichloroethylene in general.

2. Adhesive Application

After surface preparation, adhesive (containing
solvents) is applied on liner and shoe and the solvents are
send off. This evaporation of the solvent must occur before
The shoe and liner are brought together. This is usually accelerated by placing the coated parts in a suitably ventilated oven at about 80 degree celcious.

3. Curing

After the solvents are evaporated, the parts are kept
dry for few hours and then are clamped together and heated
under pressure to effect the curing of the adhesive. This is
carried out in an oven at a temperature of 145°C to 200°C. The
time interval required is inversely related to the temperature.

Example

At 150°C, time required is 30 minutes, whereas at 180°C,
it is only 4 minutes.

4.Cooling

After curing is complete, the assembly is removed from
the oven and is allowed to cool before releasing the pressure.
Extra adhesive, if any, is then removed and the bond strength
is then tested.

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