DISCLAIMER

Due to the vastness in this topic, it has been decided that each member in this group would present on twotopics each. Due to this each member will come twiceduring the presentation. So all students are requestednot to interrupt the presentation in the middle to ask doubts. They can note down all questions and can ask in the end. This however does not apply to faculties.

BRAKING SYSTEM

Presented By,

Aditya Gupta13ME01021

Akshay R13ME01022

B Sukesh13ME01024

Deepak Lamba13ME01025

K. Ramareddy13ME01026

• A brake is a mechanical device which inhibits motion, slowing or stopping a moving object or preventing its motion by converting it’s kinetic energy into other forms of energy.

• Our focus would be on railway braking system.

Introduction

Let’s look into the History of Braking System

Poor brakeman Brakeman is a person travelling for the purpose on those vehicles operated the brakes. Brakes were applied by operation of a screw and linkage to brake

blocks applied to wheel treads. The porters travelled in crude shelters outside the vehicles.

Picture Courtesy: Wikipedia

A traditional clasp brake: the brake shoe (brown) bears on the surface (tyre) of the wheel (red), and

is operated by the levers (grey) on the left

Picture Courtesy: Wikipedia

Unreliableas the application of brakes by guards depended upon them hearing and responding quickly to a whistle for brakes.

As train speeds increased it became essential to provide some more powerful braking system capable of instant application and release by the train driver.

Continuous brakeit would be effective continuously along the length of the train.

Abbot Ripton Rail Accident

Why it occurred?• Long stopping distances of express trains without continuous brakes.• Systematic signal failure in the adverse conditions of that day due to a vulnerability to accumulation of snow and ice.

In the words of a contemporary railway official, this showed that under normal conditions it required a distance of 700 m to 1100 m to bring a train to rest when travelling at 60 km/h to 70 km/h, this being much below the ordinary travelling speed of the fastest express trains. Railway officials were not prepared for this result and the necessity for a great deal more brake power was at once admitted.[

The braking system of the 1873 year steam locomotive

Steam Brakes

Schematic diagram for steam brake

Disadvantage: Steam lost pressure as it cooled. The hoses carrying the steam would freeze up and clog with ice in cold climates.

Solutions:

The chain brake. Hydraulic brakes. The Westinghouse air brake system. The simple vacuum system.

The Newark trials showed the braking performance of the Westinghouse air-brakes to be distinctly superior but for other reasons it was the Vacuum System that was generally adopted on UK railways.

By 1878 there were over 105 patents in various countries for braking systems, most of which were obviously stillborn

Schematic diagram of straight air brake system

Air Compressor

• Acts as a link between main reservoir and general air pipe.• Acts as a link between air pipe and

atmosphere• Provides insulation of general air

pipe with reservoir and atmosphere.

THREE BASIC FUNCTIONS:

Driver’s Brake Valve

• GENERAL AIR PIPE-carries pressurized air

• FLEXIBLE HOSES-connects air pipes of different bogies

• ANGLE COCKS-insulation when a bogie is removed.

THREE MAIN PARTS

Brake Pipe

• When a brake is applied air pressure gets exerted on the piston rod .

• It applies a force on the rigging, in turn applies force on shoes .

• Shoes applies frictional force on wheel .

Brake Cylinder

• A fault in the general pipeline leads to complete releasing of the brake without the driver to be warned in some way and without the possibility of restoring the action of the brakes, aspect particularly dangerous in terms of safety of the traffic.

• High pressure differences between the brake cylinders in the transitional stages.

• Requires a large amount of compressed air when commanding braking action, which, in case of long trains, involves the use of large main reservoirs.

• A long duration of the braking propagation rate in the long of the train.

Disadvantages

How do air brakes overcome the problem?

Straight air braking system

Braking occurs when pressure in brake pipe is greater than pressure in braking cylinder

Indirect air braking system

Braking occurs when pressure in brake pipe is less than

pressure in braking cylinder

Difference

In order to achieve this we should have one air distributer and auxiliary reservoir in each bogie as extra components in air braking system

Is it true that brakes are applied when pressure in brake pipe is less than that in brake cylinder?

(Source:-Brakes - Air Brakes for freight trains and passenger trains, 5th edition, November 2006, ISBN: 2-7461-1172-1)

Dependence of brake cylinder pressure wrt brake pipe pressure

Auxiliary Reservoir Air Distributer

Schematic diagram of indirect air brake system

To operate correctly, when increasing the general train brake pipe pressure, the airdistributor should ensure the following pneumatic connections, in the specified order:• Interruption of the pneumatic link between auxiliary reservoir and brake cylinder• Linking the brake cylinder to the atmosphere• Establishing a pneumatic link between the brake pipe and the auxiliary reservoir.

What is the main function of air distributer?

To operate correctly, in the case of pressure drop in the general train pipe, the air brake distributor must: • First interrupt the pneumatic link between auxiliary reservoir and pipeline• Then it should cut the pneumatic link between air brake cylinder and atmosphere • Finally it should establish the pneumatic link between the auxiliary reservoir and the

brake cylinder.

During application of brakes

Releasing the brake application

Connecting the brake pipe between two coaches

Why is this pipe used?

• Due to air compressibility and due to the length of the train, there will always be a time lapse between the reaction of the leading vehicle and the reaction of the rear one.

• Corresponding to the propagation rate of air pressure signal, the air distributors will come into action successively and the braking of vehicles begins at different times along the train so that, while some cars are slowing down, others are trying to push, still unbraked, from the rear.

• Due to this a longitudinal force is developed in train reactions causing stress to the couplers and affecting passenger comfort and sometimes even the traffic safety.

A problem associated with air braking system

Phases that occur during braking

(Source:-Karvatski, B.L. (1950), General theory of automated brakes (in romanian), OPED-C.F.R., Bucharest, 1950)Phases of train braking

Continuous-Passenger trainDotted line-Freight train

Mechanical Model of Train

Force applied during discs brakes Force applied during shoe brake

Electro-pneumatic braking system

Vacuum Braking System

Disadvantages:

It becomes inoperative if the train became divided. Air brake are more effective than vaccum brake for a given size of brake cylinder. An air brake compressor is usually capable of generating a pressure of 620 kPa vs only 100 kPa for vacuum . Ineffective at higher altitude. the existence of vacuum in the train pipe can cause debris to be sucked in.

Advantages:

• Vacuum can be created by a steam ejector with no moving parts.• Air brake system requires a noisy and complicated compressor.

A development introduced in the 1950s was the Automatic Vacuum System.

Why to have them??

Add braking power without having the thermal capacity limitations of the friction wheel or disc brakes.

Enabling shorter stopping distances

Which Trains have them??

Trains having incapacity of basic wheel-rail adhesion.Trains having need to diminish the wear of the friction based braking

systems.

Complementary Braking System

Magnetic Rail Brake

The magnetic rail brake is designated only for emergency braking and is usuallyautomatically released when the running speed is less than 50 km/h.

Advantage:

the wheel/rail adhesion independence. The friction between the braking surface and rail can sometimes significantly improve adhesion between

wheel and rail due to vigorous cleaning of the tread rails during operation. The gravity center of the bogie is lowered.

Disadvantage:

The frictional operation of the system. Interference of magnetic field with others electric systems.

Rotary eddy current brake 1 – metallic disc; 2 – magnets; 3 – housing; 4 – wheel.

Eddy Current Brake System

Advantage:

Disadvantage:

Improves rail safety by enabling shorter stopping distances. Reduced dependency between stopping distance and wheel/rail adhesion. Mitigating the thermal capacity problems of brake pads and discs. Avoiding harder application of conventional friction brakes leading to excessive wear of the pads and brake discs.

Thermal aspects: limitations being caused by the possibilities to dissipate the heat generated by the eddy currents in a relatively small mass. In case of a 10 mm air gap, the rail temperature increase does not exceed 100C. It was found that in approximately 10...20 minutes the temperature evens within the rail mass.

• The materials ability to resist fading at higher temperatures• Effect of water on brake fading• Ability to recover quickly from increased temperature• Service life as traded over vs wear of motor• Ability of material to provide smooth contact

IMPORTANT CHARACTERISTICS OF BRAKES

• Non-metallic materials: made up of combination of various synthetic substance• They are gente on rotors, produce large amount of dust, short life time

• Semi- metallic materials: Synthetics mixed with some proportion of flaked metals• More fade resistant, long lasting, high wear on wheels, require more force

• Fully metallic materials: composed of sintered steel without any synthetic adhesives• Used in race cars, long lasting, require high force, high noise

• Ceramic materials:Composed of clay, porcelain bonded to copper flake and filaments• Bad dissipator of heat, low sound, good durability (in between metal and

non metal)

TYPES OF BRAKE PADS

• Disc brakes uses calipers to squeeze a pair of pads against a disc inorder to create friction that retards the rotation of shaft

DISC BRAKES

• Over heating of discs and require proper heat outlet

• Discs will wear more frequently

MAIN PROBLEMS OF DISC BRAKES

• Main function of tread brakes is the brake application on wheel roling surface (tread)

• Features of tread brakes are • Weight reduction• Noise reduction• Cleans wheel surface• Less maintainance

TREAD BRAKES

• Two types of brake blocks are used

• L type blocks K type blocks

• K type blocks

BRAKE BLOCKS

• Breaking capacity depends on various major factors• Running speed• Weight• Thermal phenomena• Type of brakes

BREAKING CAPACITY

• Maximum possible breaking force at wheel rail contact should be less than wheel rail adhesion forces

Fb, max < Fa

• The empirical relation for friction co efficient (for cast iron braking shoes and wheel tread) was determined by few experiments depending on factors such as instantaneous velocity V, applied force on breaking shoe Fs or surface contact pressure ps

• But co efficient of friction is almost constant for plastic brake shoes(0.25) or brake pads(0.35)

• Among those the popular formula are

• UIC formula

• Karavatzki formula

Lhb bogies

Icf bogies