Development of asbestos free brake pads using corn …lejpt.academicdirect.org/A31/129_144.pdfseparate container and appropriate quantity of hardener added; with resin to hardener

Leonardo Electronic Journal of Practices and Technologies

ISSN 1583-1078

Issue 31, July-December 2017

p. 129-144

129

Engineering, Environment

Development of asbestos free brake pads using corn husks

Wisdom ASOTAH1*, Abraham ADELEKE2

1Department of Materials Science and Engineering,

2Obafemi Awolowo University, Ile – Ife, Osun State, Nigeria

E-mail(s): 1 [email protected]; 2 [email protected].

* Corresponding author: phone: 08164027907, 08105862661

Received: July 01, 2017 / Accepted: November 25, 2017 / Published: December 30, 2017

Abstract

The development of asbestos free brake pads using corn husks as alternative filler was

studied with a view to replacing asbestos, which has been known to be carcinogenic.

Corn husks was sourced and milled, before been sieved into sieve grades of 100 and

200 μm. The varying proportions of the as-screened corn husk fibres and silicon carbide

were mixed with fixed proportions of graphite, steel dust and resin to produce brake

pads by using compressional moulding. The hardness, compressive strength, density,

flame resistance, wear rate and porosity of the products were then determined. The result

obtained showed that the brake pad produced with the corn husk passing the finer 100

μm screen gave better compressive strength, higher hardness, lower porosity and lower

rate of wear, consequent on the finer distribution of the corn husks particles in the

matrix. The results obtained for the brake pads were then compared with that of

commercial brake pad (asbestos based and optimum formulation laboratory brake pad,

corn husk based). The results were found to be in close agreement suggesting that corn

husk can be used in the production of asbestos-free brake pads.

Keywords

Corn Husks; Density; Porosity; Hardness; Brake Pads; Wear rate; Flame resistance; Ash

content

Introduction

The purpose of friction brakes is to decelerate a vehicle by transforming the kinetic


Wisdom ASOTAH, Abraham ADELEKE

130

energy of the vehicle to heat, via friction, and dissipating that heat to the surroundings [1].

According to [2], brake pads are steel backing plates with friction material bound to the

surface facing the brake disc. They are components of disks brakes used predominantly in

automobiles. When we apply brakes, the brakepads or shoes, squeeze against the brake drums

or rotors, converting kinectic energy into thermal energy via friction.

Mechanical brake system are divided into the disk and drum brakes. Brake shoes are

located inside a drum for drum brake type so that on application of brakes, the brake shoe is

forced outward and pressed against the drum. Disc brakes operate in similar way except that

while drum brakes are enclosed disc brakes are exposed to environment.

By the arrangement, particulate materials that gradually wear from brake pads are

carried away by breeze into surrounding especially those from disc brakes. Most worn particles

from drum brakes are retained within enclosed drums and inhaled by mechanics when they

open up wheels for maintenance and repairs and gradually poison the human system [3].

According to Elakhame et al., asbestos has some few engineering properties that makes

it suitable for inclusion in brake linings [4]. Some of these include its good sound absorption,

resistance to heat, fire and affordability. Brake pads generally consist of asbestos fibres

embedded in polymeric matrix along with some other ingredients. Use of asbestos fibres is no

longer acceptable because of its carcinogenic nature leading to development of new asbestos-

free friction materials for brake pads.

Studies conducted in 1989 by National Institutes of Health published a report that

showed a high population of brake mechanics were afflicted with pleural and peritoneal

mesothelioma which were linked to chrysotile and asbestos exposure [3].

Consequently, researchers have turned to non-asbestos friction materials as an

alternative. There is hence, a concentration on industrial and agro - waste materials. Curent state

of knowledge have seen researchers replace asbestos with organic materials such as bagasse

[2], palm kernel shells (PKS) [4], and banana peels [10]. According to Elakhame et al., typical

formulations consists of more than 10 ingredients and and more than 300 materials of different

brands [4]. The works show a similar interest in finding a substitute for asbestos as a friction

material in brake linings, hence the purpose of this research is to show that corn husks can be

an alternative friction material in brake linings.

These waste usage will not only be economical but also result in foreign exchange and

environmental control [4]. Olabisi and Ademoh reported that the coefficient of fricion of maize


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131

husk was determined as 0.5 at density of 45-80Ib/ft3 [3]. In contrast, friction coefficient in the

range of 0.30-0.70 is normally desirable when using brake lining material [4]. Based on these

factors, corn husk was conceived as a possible friction material alternative to asbestos.

The main objective are to develop asbestos free brake pads by using of corn husks as a

friction material. Performance evaluation of the produced samples include density, hardness,

microstructural analysis, wear rate, ash content tests, porosity and compressive strength. The

significance of this work lies in the advantage that it provides to our local automotive industry

while minimizing the danger caused by asbestos to health and environment.

Material and Methods

The experimental brake pads were developed from carefully selected materials [1] and

following the procedure as described by [3], [5], [6] and the products were evaluated with the

test methods elaborated by Elakhame et al [4].

The materials used were: Phenolic resin (phenol formaldehyde), corn husks particles,

steel dust, graphite and silicon carbide shown in Figure 1.

Silicon Carbide

Corn Husks

Graphite

Steel Dust

Figure 1. Research materials

The role of each materials indicated in Table 1.

Table 1. Materials used and their functions

S/N Material Function

1 Phenolic Resin (Phenol Formaldehyde) Binder / Matrix

2 Silicon Carbide Heat Resistant Material

3 Steel Dust Abrasive

4 Graphite Lubricating Material

5 Corn Husk Filler Material



132

The base raw material, corn husk was collected from a farm centre, properly sun-dried

and cleaned to remove impurities. Thereafter, it was crushed with hammer and milled into

powder using ball milling machine (Model 87002 Limoges-France, A50, …, 43). After this, it

was sieved to pass 100 and 200 μm screen apertures.

Specimen brake pad production

The technique of powder metallurgy as described by [5], [6] was adopted.

The production of brake pad consists of a series of unit operations including mixing,

cold and hot pressing, cooling, post-curing and finishing [7].

For each formulation, quantities expressed in percentage, weights presented for fillers,

abrasives, friction modifier and reinforcement were measured into the mixing vessel and

thoroughly mixed for 15 minutes to ensure homogeneity.

The desired amounts of phenolic resin (phenol formaldehyde) was poured into a

separate container and appropriate quantity of hardener added; with resin to hardener

percentage of 64.3% to 35.7% to form the binder, that was thoroughly stirred for about 10

minutes to obtain a uniform mixture.

Thereafter, the binder mixture was poured into the powdered friction material mixture

and stirred further to obtain a paste-like homogenous mixture.

The formed paste was poured into mould cavities that already had powdered talc applied

for ease of component removal after casting, cold pressed and allowed to cure for 90 minutes

[3]. The general methodological phases are shown in Figure 2.

Figure 2. General methodological phases

Raw Materials

Sourcing

Materials

Processing

Fabrication of Mould/

Plate Metal

Mixing Compacting

Surface Finish Curing

Optimization of Product

Formulation


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133

The formulations used to produce the brake pads are shown in Table 2.

Table 2. Specimen formulations in (g*)

S/N Ingredients A B C D E

1 Corn Husks 40 45 50 55 60

2 Silicon Carbide (SiC) 26 21 16 11 6

3 Graphite 5 5 5 5 5

4 Resin 14 14 14 14 14

5 Steel Dust 15 15 15 15 15

g* - represents grams (a unit of mass)

The mixture of resin, graphite and steel dust that weighed 34 g was blended with varying

proportions of corn husks and silicon carbide that weighed 66 g, to make brake pads that

weighed 100 g [4].

Figure 3 shows the picture of the samples of organic brake pads produced using corn

husks as filler.

Figure 3. Produced samples

Specimen brake pad analysis. Brinell hardness Test

The resistance of the composites to indentation was carried out through the Brinell

hardness testing equipment to BS240, using a Tensometer (M500-25KN, Gunt Hamburg

Hardness Tester and WP300) pressing hardened steel ball with diameter D into a test specimen.

Based on ASTM specification, a 10 mm diameter steel ball was used and the load applied P

was kept stable at 3000 kg/f.

The diameter of the indentation d was measured along two perpendicular directions,

using an optical micrometer screw gauge.



134

The mean value was taken and incorporated into Eq. (1) to obtain the Brinell Hardness

Number (BHN) [4].

𝐵𝐻𝑁 = 2𝑃 ÷ 𝜋𝐷 (𝐷 − √(𝐷2 – 𝑑2) ) (1)

Where: P - the load applied; D - the diameter of hardened steel ball into a test specimen;d - the

diameter of indentation.

Compressive strength Test

The compressive strength test was carried out using the Tensometric Machine. The

samples of diameter 29.40 mm were subjected to compressive force, loaded continuously until

failure occurred. The load at which failure occurred was then recorded.

Ash content Test

About 1.20 g ± 0.1 g of the sample was weighed in a cooled crucible previously oven

dried by heating in a furnace at 5500C for 1 hour.

Then the samples were charred by heating on a hot plate thereafter. The charred samples

were thereafter taken into the furnace and heated at 5500C for 1 hour, then cooled in a desiccator

and weighed. This cycle of heating, cooling and weighing was repeated until a constant weight

is obtained. The % ash was obtained as, Eq. (2):

% 𝑎𝑠ℎ = (𝑊2 − 𝑊0) /(𝑊1 − 𝑊0) × 100 (2)

Where: W0 - weight of empty crucible; W1 - weight of crucible + sample; W2 - weight of crucible

and residue i.e. after cooling.

Density Test

The true density of the samples will be determined by weighing the samples mass on a

digital weighing machine, which would divide the volume. The volume was obtained via liquid

displacement method.

The formula is show in Eq. (3), below:

𝐷𝑒𝑛𝑠𝑖𝑡𝑦 (𝜌) = ( 𝑀 ÷ 𝑉) × 10 (3)


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135

Where: M - the mass of test piece (g); V - the measuring volume of test piece (cm3) by liquid

displacement method.

Wear Rate Test

The wear rate for the samples was measured using pin on disc machine by sliding it over

a cast iron surface at a load of 1 kg, sliding speed of 125 and 250 rev/min, and sliding distance

of 2000 and 4000 m. All tests were conducted at room temperature. The initial weight of the

samples was measured using a single pan electronic weighing machine with an accuracy of

0.01 g.

During the test, the pin will be pressed against the counterpart rotating against a cast

iron disc (hardness 65 HRC) of counter surface roughness of 0.3 μm by applying the load.

A friction detecting arm connected to a strain gauge held and load the pin samples

vertically into the rotating hardened cast iron disc. After running through a fixed sliding

distance, the samples were removed, cleaned with acetone, dried, and weighed to determine the

weight loss due to wear. The differences in weight measured before and after tests give the wear

of the samples. The formula used to convert the weight loss into wear rate is in Eq. (4) [8]:

𝑊𝑒𝑎𝑟 𝑟𝑎𝑡𝑒 = 𝑊𝑒𝑎𝑟 𝑟𝑎𝑡𝑒 = 𝑆/𝑊 (4)

Where: ΔW is the weight difference of the sample before and after the test (mg); S - total sliding

distance (m).

Porosity

A sample of diameter 29.40 mm with a different height thickness of as thick as possible

was used. The specimens was weighed to the nearest mg, and then soaked in oil and water

container at 90-1000C for 8 hours.

The samples were left for 24 hours and then taken out from the oil container. Finally,

the test samples were weighed to the nearest mg.

The formula to calculate porosity is given as Eq. (5) [4]:

𝑃𝑜𝑟𝑜𝑠𝑖𝑡𝑦 (𝜌) = (𝑀2– 𝑀1) ÷ 𝐷 × 100 ÷ 𝑉 (5)

Where: D - the density of test oil and water; M2 - the mass of test piece after absorbing oil and

water (g); M1 - the mass of test piece (g); V - the volume of test piece (cm3).



136

Results and discussions

Brinell hardness Test

Figure 4, shows that variation of hardness with composition with sieve grades of 100

μm and 200 μm.

Figure 4. Variation of hardness with composition

The 100 μm and 200 μm formulations are however too closely related in sizing. The

samples 100 μm sieve grade of different formulation A-E, have the highest hardness value of

254, 235, 228, 222 and 211 HB, respectively.

The higher hardness value for the 100 μm compared to the 200 μm is as a result of the

reduced particle size of the corn husk fibre. This results in the increase in the surface area,

leading to an increasing bonding ability to the resin.

The more homogenous distribution of the filler and resin, as the particle size gets finers

is due to proper bonding and closer packing distance This is in agreement with results from

other research [4].

Compressive strength Test

Figure 5, shows that the compressive strength of the samples follows similar trends to

that of the hardness value.

254235 228 222 211 212 218 208 211 201

0

50

100

150

200

250

300

100μm

100μm

100μm

100μm

100μm

200μm

200μm

200μm

200μm

200μm

A B C D E A B C D E

Har

dn

ess

(H

B)

Composition (g)


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137

Figure 5. Variation of compressive strength with composition

Ideally, the higher the density; which is the ratio of the amount of matter to volume, the

higher the compressive strength.

Density Test

Figure 6, shows the results of the density.

Figure 6. Variation of density with composition

Generally, density decreased as the corn husk particles increased in composition and

particle size. The trend in the density can be attributed to the increase in the volume of the

particle size, leading to a less close packing density.

This leads also leads to a decrease in homogeneity of the friction lining composites. The

111 109 108 110101

109 10599 98

89

0

20

40

60

80

100

120

100μm

100μm

100μm

100μm

100μm

200μm

200μm

200μm

200μm

200μm

A B C D E A B C D E

Co

mp

ress

ive

Str

en

gth

(K

pa)

Composition (g)

1,7411,621

1,504

1,786

1,3011,446 1,421

1,31 1,251 1,206

00,20,40,60,81

1,21,41,61,82

100μm

100μm

100μm

100μm

100μm

200μm

200μm

200μm

200μm

200μm

A B C D E A B C D E

De

nsi

ty (

g/cm

3)

Composition (g)



138

100 μm particle sizes has a higher density. This is due to the close packing of the corn husk

particles, creating more homogeneity in the entire composite phase.

Figure 7, shows the variation between the compressive strength and the density.

Figure 7. Variation of density with compressive strength

The results shows that the higher the density, the higher the compressive strength, due

to close packimg of the particles leading to reduced interatomic spaces between the particles.

Lower porosity of the specimen was observed for composition with lower sieve grade.

Compositions of 100 μm, generally show lower porosity compared to compositions 200 μm.

This result can be attributed to better dispersion of particles and good interfacial bonding

with the resin. Theoretically, a high porosity will lead to higher water and oil absorption, which

will lower the friction coefficient and lead to an increase in the wear rate of the brake pads [4].

Ash content Test

From Figure 8, it can be seen that the % value of the ash content increases as the particle

size increased.

85

90

95

100

105

110

115

1 2 3 4 5 6 7 8 9 10

Co

mp

ress

ive

Str

en

gth

(K

Pa)

Density (g/cm3)

Series1 Series2


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139

Figure 8. Variation of ash content with composition

The 100 μm brake pad specimens had a lower ash content compared to the values

obtained for the 200 μm. This increase in ash content as sieve grade increases can be attributed

to an increase in pores sizes as the sieve grade increases. With increasing pore sizes, less close

packing, the charring of the specimens will yield a higher ash content. This is due to less proper

bonding between the resin and the filler – Corn Husk Particles [4].

The lower the particle size at optimum composition, the better the dispersion and lower

the ash content value.

The results of the wear rate showed an increase in the wear rate as particle size and

composition increases. This can be easily attributed to a lower bonding ability of the resin to

the filler – Corn Husk Particles. The increase in wear is also as a result of less closing packing

density. The wear, which is the loss of material or the erosion of a material from its derivative

position as a result of mechanical action of the opposite surface.

Another characteristic factor that increases the wear rate is the porosity of the specimen.

The higher the porosity, the higher was the wear rate.

The wear rate is a very important factor in the determining the friction coefficient.

Ideally, the lower the wear rate, the higher the friction coefficient.

41

43 4344

46

4243 43

48 48

36

38

40

42

44

46

48

50

100μm

100μm

100μm

100μm

100μm

200μm

200μm

200μm

200μm

200μm

A B C D E A B C D E

Ash

Co

nte

nt

(%)

Composition (g)



140

Porosity

Figure 9, shows the variation of porosity, hardness with composition. Lower porosity

of the specimen was observed for composition with lower sieve grade. Compositions of 100

μm, generally show lower porosity compared to compositions 200 μm.

Although, the values obtained for the porosity show infintesimal difference, the effect

on the hardness of the composite is pronounced.

Comparing compositions of 100 μm and 200 μm for formulations A, a 0.06% change in

porosity, results in a 42 HB value of hardness. This result can be attributed to better dispersion

of particles and good interfacial bonding with the resin.

Theoretically, a high porosity will lead to higher water and oil absorption, which will

lower the friction coefficient and lead to an increase in the wear rate of the brake pads [4].

Figure 9. Variation of porosity with hardness

Wear rate Test

Figure 10, relates the values of the wear at different speeds (30 min, 1 kg, 12 5rev/min

and 250 rev/min (g/km)).

0,91 0,91 0,92 0,92 0,98 0,97 0,93 0,89 0,93 0,91

254235 228 222 211 212 218 208 211 201

0

50

100

150

200

250

300

100μm

100μm

100μm

100μm

100μm

200μm

200μm

200μm

200μm

200μm

A B C D E A B C D E

Har

dn

ess

, Po

rosi

ty (

HB

, %)

Composition (g)

Series1 Series2


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Figure 10. Variation of wear rate with composition

It shows the increase in wear rate as particle size. The graph shows a higher elevation,

which is a higher wear rate for formulations of the 200 μm formulations.

The results of the wear rate showed an increase in the wear rate as particle size and

composition increases. The increase in wear, which is a loss of material due to mechanical

action can be easily attributed to a lower bonding ability of the resin to the filler – Corn Husk

Fibre- as percentage composition of filler increases. The increase results in less closing packing

density, which leads to an increase in rate of wear.

Figure 11, relates the wear to the Brinell hardness and it shows that the lower the wear

rate, the higher the hardness value. This inverse realtionship between the wear rate and the

hardness can be attributed to the reduced porosity as wear rate reduces.

A lower porosity, as shown in Figure 9 is directly related to a reduction in particle size

which results in better interfacial bonding.

Improved interfacial bonding, due to better dispersion of the fibres in the matrix will

lead to an improved hardness value as shown in Figure 11. This can also be attributed to an

increased coeffieicnt of friction as particle size and porosity decreases.

11

11,5

12

12,5

13

13,5

14

14,5

100μm100μm100μm100μm100μm200μm200μm200μm200μm200μm

A B C D E A B C D E

We

ar R

ate

(g/

km)

Composition (g)

Series1 Series2



142

Figure 11. Variation of hardness, wear rate with composition

The results of this research work indicates that samples containing 100 μm of

formulation (A-E) gave better properties than those of 200 μm formulation.

Hence, the lower the sieve grades of corn husk particles, the beter the properties. The

100 μm sieve size results were compared with that of commercial brake pads (asbestos based)

as shown in Table 3.

Table 3. Comparison of the results obtained with standard

Property @ 100 (μm) Optimum formulation

laboratory brake pad (Corn

Husk based)

Commercial brake pad

(asbestos based)

Hardness, Brinell (at 3000 Kgf) 254 – 211 101

Porosity (%) 0.91 - 0.98 0.52

Ash Content (%) 41 – 46 54

Density 1.741 – 1.301 1.320

Compressive Strength ( KPa) 111 – 101 110

Wear Rate (g/km) 12.191- 13.782 3.800

The results are in close agreement. However, the higher hardness value is due to the

presence of SiC, which helps to increase the hardness of the brake pad composite.

Conclusions

The formulation of non-asbestos brake pads using corn husks as a filler, presents an

industry alternative to the carcinogenic asbestos used in commercial production. Physical and

wear tests were carried out and the results obtained were found to compare well with those of

150

170

190

210

230

250

270

290

1 2 3 4 5 6 7 8 9 10

Har

dn

ess

, We

ar r

ate

(H

B, g

/km

)

Composition (g)

Series1 Series2 Series3


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143

asbestos based friction lining material. From the results, the conclusion reached showed that

the samples 100 μm sieve grade of corn husk fibre gave the best properties of all.

Compressive strength, hardness, densities and porosity of the samples produced were

observed to decrease with increase in sieve aperture size while wear rate and percentage

charrred increasd as the sieve aperture size increased. The higher the percentage volume of the

corn husk particles from A –E, the higher the porosity, density, wear rate and percentge charred.

Hence, based on the above tests properties of the brake pads composite, corn husks as filler can

be used as an alternative to existing fillers, such as asbestos, in brake pad composites.

Non asbestos brake pads made from corn husks are therefore very suitable ecofriendly

replacement for asbestos and many agro-biomass friction materials in automotive brake pads.

From Table 3, the deviation of the some of the properties values such as the hardness

from the asbestos based brake pads can be attributed to the individual properties of the

component elements.

The presence of silicon carbide and steel dust, materials of high hardness will lead to an

increase in the overall hardness value compared with pads made from asbestos. Another factor

is the process technology and manufacturing parameters such as the powder mixing duration,

compaction pressure, compaction duration, post curing temperature and time [9]. This variation

in process parameters would lead to a variation in the properties obtained.

References

1. Blau P.J., Compositions, functions and testing of friction brake materials and their

additives, Being a report by Oak Ridge National Laboratory for U.S Dept. of Energy, 2001.

2. Aigbodion V.S., Akadike U., Hassan S.B., Asuke F., Agunsoye J.O., Development of

asbestos free brake pad using bagasse, Tribology in Industry, 2010, 32, p. 12-18.

3. Olabisi A.I, Ademoh N.A., Development and evaluation of maize husks (asbestos - free)

based brake pad, Industrial Engineering letters, 2015, 5 (2), p. 67-80.

4. Elakhame Z.U., Alhassan O.A., Samuel A.E., Development and production of brake pads

from Palm Kernel composites, International Journal of Scientific and Engineering Research,

2014, 5, p. 735-744.



144

5. Edokpia R.O., Aigbodion V.S., Obiorah O.B., Atuanya C. U., Evaluation of the properties

of eco-friendly brake pad using egg shell particles–gum, Arabic ScienceDirectR, Elsevier

B.V. DOI: 10.1016/j.rinp.2014.06.003, 2014.

6. Bashar D., Peter, Madakson B., Joseph M., Material selection and production of a cold-

worked composite brake pad, World Journal of Engineering and Pure and Applied Science

(WJEPAS), 2012, 2 (3):96.

7. Gurunath PV and Bijwe J., Friction and wear studies on brake-pad materials based on

newly developed resin, Journal of engineering tribology, 2007, 263 (7), p. 1212-1219.

8. Osterle W., Griepentrog M., Gross T., Urban I., Chemical and microstructural changes

induced by friction and wear of brakes, Wear, 2001, 251, p. 1469-1476.

9. Talib R.J., Mohmad S.S., Ramlan K., Selection of best formulation for semi-metallic brake

friction materials development, Powder Metallurgy, Dr. Katsuyoshi Kondoh (Ed.), ISBN:

978-953-51-0071-3, 2012.

10. Masrat B., Sheikh S.S., Owais B., Friction and wear beahviour of disc brake pad material

using banana peel powder, International Journal of Research Engineering and Technology,

2015, 4, p. 650-659.

Documents

Development of asbestos free brake pads using corn …lejpt.academicdirect.org/A31/129_144.pdfseparate container and appropriate quantity of hardener added; with resin to hardener