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European Journal of Applied Sciences – Vol. 10, No. 6

Publication Date: December 25, 2022

DOI:10.14738/aivp.106.13535. Mawuli, S. E., Anthony, S., & Akintunde, D. O. (2022). A Conceptual Review of Automobile Disc Brake Friction Materials. European

Journal of Applied Sciences, 10(6). 492-505.

Services for Science and Education – United Kingdom

A Conceptual Review of Automobile Disc Brake Friction Materials

Seckley Emmanuel Mawuli

Department of Mechanical Engineering

University of Mines and Technology, Tarkwa, Ghana

Simons Anthony

Department of Mechanical Engineering

University of Mines and Technology, Tarkwa, Ghana

Dahunsi Olurotimi Akintunde

Department of Mechanical Engineering

Federal University of Technology, Akure, Nigeria

ABSTRACT

Providing an alternative filler material for brake pads is crucial because the use of

asbestos as filler material in brake pads has some health risks. It is known that

asbestos can cause Asbestosis and Mesothelioma. This has, therefore, ignited

widespread research into development and finding of eco-friendly brake friction

organic materials. In this paper, some works done by various researchers in a bid

to finding suitable environmentally friendly and best performed compositions for

brake friction materials have been presented. The use of natural fibres such as

maize husks, coconut shell, palm kernel shell, cocoa beans shell, bagasse,

periwinkle shell, sawdust and banana peels as reinforcement to replace asbestos in

the production of brake friction materials with high mechanical properties, stable

friction, high wear resistance, lightweight, low environmental impact and low cost

have been presented. This extensive survey, however, shows that there is no

research on the suitability of other materials such as other types of periwinkle

shells, coconut shell ash and kaolin to replace asbestos as major ingredients in a

brake friction material. There is, therefore, the need to continue to research into

and develop low-cost non asbestos organic brake pad materials for better brake

performance.

Keywords: Brake pads, asbestos, filler, organic materials.

INTRODUCTION

According to [1], a brake plays a vital role in any automotive so as to slow down the vehicle or

to stop the vehicle completely. During the application of brake, friction between brake pads and

rotating disc causes the vehicle to stop or slow down by converting kinetic energy of the vehicle

into heat energy. Therefore, a brake pad material should maintain a sufficiently high friction

coefficient with the brake disc, not decompose or break down in such a way that the friction

coefficient with the brake disc is compromised at high temperatures. [2] reported that brake

pads are important components of braking system for all categories of vehicles equipped with

brake discs; and according to them, brake pads are steel backing plates with friction materials

bounded unto the surface facing the brake disc and are placed in the wheel assembly to

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Mawuli, S. E., Anthony, S., & Akintunde, D. O. (2022). A Conceptual Review of Automobile Disc Brake Friction Materials. European Journal of Applied

Sciences, 10(6). 492-505.

URL: http://dx.doi.org/10.14738/aivp.106.13535

continuously clamp and hold wheels to slow them down or completely stop their motion. From

the perspective of [3], brake friction materials play an important role in a braking system. The

ideal brake friction material should have constant coefficient of friction under various

operating conditions such as applied loads, temperature, speeds, mode of braking and in dry or

wet conditions so as to maintain the braking characteristics of a vehicle. They should also be

resistant to heat, water and oil, have low wear rate, high stability, exhibits low noise and should

not damage the brake disc. The major components of brake system are callipers, brake linings,

master cylinder and hydraulic boost units, rotors, brake pedals, cables, pipes, hoses, sensors

and electronic systems controlling the operation of the brakes. Brake lining materials generally

are asbestos, metals, non-asbestos organics (NAO) and ceramics based.

The traditional way of producing brake pad using asbestos fibres is a source of concern to

manufacturers and end users because of the carcinogenic nature of asbestos. [4] reported that

asbestos during application releases hazardous gases, which cause damage to health.

Therefore, many investigators are now using natural fibres to replace carcinogenic asbestos

fibres in brake pad production. According to [5], there has been great need to minimize the use

of asbestos fibres in brake pad production. And in order to achieve this, researchers are

investigating and applying agricultural waste as raw materials for brake pad production as

being reported by [6]. In order to achieve the properties required of brakes, most brake

materials are not composed of single elements or compounds, but rather are composites of

many materials. More than 2000 different materials and their variants are now used in

commercial brake components [7]. According to [8], Herbert Frood is credited with inventing

the first brake lining material in 1897. It was a cotton-based material impregnated with

bitumen solution and was used for wagon wheels as well as in early automobiles. His invention

led to the founding of the Ferodo Company, a firm that still supplies brake materials today. The

first brake lining materials were woven, but in the 1920’s these were replaced with moulded

materials that contained crysotile asbestos fibres, a plentiful mineral. In 1930s, Ferodo changed

to thermosetting resins and produced moulded instead of knitted linings. Resin-bonded

metallic linings were introduced in the 1950’s, and by the 1960’s the so-called ‘semi- mets’ were

developed. [5] again stated that in 1970, glass fibres were introduced but their brittleness led

to their limited application while aramid fibre which was introduced in 1984 as brake pad

material was found to have the same comparative advantage as asbestos, however, it is very

soft. Also in 1974, sepiolite was also proposed to replace asbestos because of the similar

property it exhibits with asbestos but its limitation is that it causes inflammation of the lungs

and pulmonary interstitial fibrosis which is also caused by crocidolite asbestos. Potassium

titanate which was also in use was also associated with a cancer called mesothelioma. In 1992,

ceramic fibre was introduced as an alternative to asbestos but its brittle nature also

necessitated its limited application. Furthermore, a paper type fibre was introduced in 1998 to

replace asbestos though it is associated with the problem of degrading very quickly at

temperature above 150 oC. The fabric type was introduced in 1999 but its high porosity gave

rise to a high flow rate and permeability of fluid which were among its limitations. This brought

about the introduction of sintered materials in 2001. However, these materials degrade at a

much higher temperature and also have a high production cost. [5] further revealed that no

single material could achieve all the desired attributes for an automobile brake pad. Different

constituents of materials were therefore introduced to overcome the challenges encountered

in finding suitable materials for an automobile brake pad.

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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 6, December-2022

Services for Science and Education – United Kingdom

In 1984, the fillers, with the carbonate, Molybdenum trioxide and Titanate, helped to increase

the temperature of the brake pad material to 135 oC, suppressing low frequency brake noise

and also providing heat stability for the material. Moulded linings were made by combining

fibres with resin and polymerizing resin under elevated pressure and temperature [4]. [9]

reported additive effects of different non-asbestos materials on friction lining; the result of

which sensitized increased utilization of asbestos free organic, semi-metallic and metallic

friction lining materials. Consequently, many studies have been done and are still on going for

development of not only asbestos-free brakes but also less temperature generating pads for

better human health and technical efficiency.

A BRIEF LOOK AT TYPES OF BRAKE PADS

According to [10], there are numerous types of brake pads, depending on the intended use of

the vehicle. Literature has listed the main types of brake pads that are commonly used in today's

vehicles as; metallic pads, semi metallic pads, non-asbestos organic or ceramic pads, carbon- carbon pads, eco-friendly materials pads and asbestos pads.

Metallic Pads

These are metallic matrix reinforced with steel, copper or other metals [10]. They have high

strength and high thermal conductivity but great wear damage, increased squeal noise and

vulnerable to corrosion.

Semi Metallic Brake Pads

According to [10] again, these types of brake pads are made from about 30 % to 65 % metal.

They are combination of metals and organic materials, commonly made from steel wool, wire,

copper or other metals. These types of brake pads are considered to be very durable, but also

may wear brake rotors faster. Again, semi-metallic brake pads may not function well in very

low temperatures.

Non-asbestos Organic or Ceramic Brake Pads

This type of brake pads, commonly referred to as NAO, is made from organic materials such as

fibre, glass, rubber and even kevlar. These types of pads are usually softer and do not create

much noise, but they tend to wear faster and create a lot of dust. They have high strength, high

thermal and wear resistance, lightweight and low level of noise but quite brittle and increased

wear in high temperatures [10].

Carbon-carbon Pads

They are similar to ceramics but with superior properties as stated by [10]. They have high

friction properties, high thermal resistance, high wear resistance and lightweight but not

efficient at low temperatures and expensive to produce (high material and manufacturing

costs).

Eco-friendly Materials Pads

This is the use of natural fibres such as sisal, flax, hemp, kenaf, jute, coconut shell, banana peels

or palm kernel fibres as reinforcement. They have high mechanical properties, stable friction

coefficient, high wear resistance, lightweight, low environmental impact and low cost but they

tend to agglomerate at mixing and wear from environmental conditions [11].