frictional characteristics on brakes

8/11/2019 Frictional Characteristics on Brakes

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GUIDED BY PRESENTED BY

MR. ARUN JOSE ARAVIND SUDHE ASST. PROFESSOR PRN: 11008200DEPT. OF MECHANICAL ENGG.MLMCE


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A coefficient of friction is a value that shows the relationship between thforce of friction between two objects and the normal reaction between tobjects.

The coefficient of friction is shown by F=R. In that equation, F is tfrictional force, is the coefficient of friction, and R is the normal

GRIT: They are minute rough granules, as of sand or stone. Grit can ranfrom size 50m-700m.

Modern vehicles use disc brakes as an efficient method to have properbraking and are positioned near to the wheels which are seldom covered

Improper covering of the brake disc causes them to be embedded withexternal grit particles and rust.Humidity and the presence of grit particles in the air can influence thebraking effectiveness.

Friction coefficients for brake materials can be in a range of 0.07 to 0.7,most vehicles operate within a narrower range of 0.3 to 0.6.


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When the brake is applied, the contact between cast iron disc brake padproduces wear particles.

The wear particles move homogeneously through the contact zone until abrasive particle adheres to the disc.

Dirt and other particles from environment also may contribute to theabrasion process at the brake interface.

A few external grit particles tends to embed into the friction material

Some particles together with other contaminants may form a lubricating


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Wear on discs by brake pad is a primary cause.

Humidity.

Temperature difference between the disc brake and surroundings.

Presence of corrosive gases likeo carbon monoxideo sulphur dioxideo chlorineo nitric oxide.


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In this work three different size ranges of grit (silica sand), i.e. between 180 m , 180-355 m and 355-500 m , were used.

A series of short duration drag and stop mode tests are done.

Speeds of 4 m/s, 8 m/s, 10 m/s and 12 m/s is taken

Pressure of 0.6 MPa, 0.8 MPa and 1.0 MPa were used.

DRAG MODE test is done for about 120 seconds, with applied load of0.6MPa & 0.8MPa.

STOP MODE test was carried out at pad contact pressure of 1.0 MPa un

the disc stop completely.Evaluation of the grit particle embedment was conducted using SEM anoptical microscopy


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Coefficient of friction (CoF) VS grit size graph.

CoF

grit size

Fig. 2. different particle sizes tested at various speed


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Coefficient of friction values were higher with smaller particle of 50-18

They were assumed to fill up the pad cavities and increased the effectivcontact.

However, coefficient of friction values for grit particle of 180-355355-500 m were lower because the bigger particles create small inter

At low speed, the larger particle size groups tend to lower the coefficienfriction values.

The presence of grit particles is assumed to reduce the effective contactarea schematically illustrated in Fig. 2.

At medium sliding speeds of 8 and 10 m/s, presence of grit particle hassimilar effect but with small increase of coefficient of friction comparedgrit case.

Bigger particles were assumed to roll and mix faster with other wear debto quickly expand the effective contact area and help to accelerate themixing process.


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Fig. 3. Changes of effective contact areas (a) without grit particle and (b) with grit particle.

(a) (b)


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At higher sliding speeds, generation of wear debris was increased and thmixing process was accelerated.

(a)

Fig. 4. SEM images of (a) grit particles act as primary contact (b) wear debris as secondary plateaus at brpad interface.


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Test Rig.

Fig 6. Shows test rig for corrosion effect


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The brake disc is rotated at 50,60,70,80,90 & 100rpm.Pad pressure of 0.5MPa, 1MPa & 1.5MPa is applied each.

Corresponding coefficient of performance is noted.

Graph plotted.


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When grain size is high and rotation speed is high, coefficient of frictiis high

At higher sliding speeds of disc, generates wear debris which increasethe grit embedment and coefficient of friction.

Nature of brake pad increase or decrease rate of corrosion and therebycoefficient of friction.


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frictional characteristics on brakes

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