Compositions, Functions, and Testing of Friction Brake Materials


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OAK RIDGE NATIONALLABORATORY
MANAGED BY UT-BATTELLE FOR THE DEPARTMENT OF ENERGY

ORNL/TM-2001/64

Compositions, Functions, and Testing of Friction Brake Materials and Their Additives

September 2001

UT-BATTELLE
ORNL-27 (4-00)

DObJMENT

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This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

ORNLITM-2001/64
Metals and Cer,arnics Division
Compositions, Functions, and Testing of Friction Brake Materials and Their Additives
Peter J. Blau
.
August 200 1
Prepared for U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy,
Office of Transportation Technologies
Prepared by OAK RIDGE NATIONAL LABORATORY
Oak Ridge, Tennessee 3783 l-6285 managed by
UT-B ATT.E,LLE, LLC for the
U.S. DEPARTMENT OF ENERGY Under contract DE-AC05OOOR22725

Preface

This report was prepared as an information resource for the development of advanced brake

.

materials for heavy vehicles. This research is sponsored by the U.S. Department of Energy,

Office of Transportation Technologies. It is part of an initiative aimed at reducing the running

resistance while improving the safety of on-highway heavy trucks. Selected information on

aircraft brake materials was included for comparison purposes. Data in this report have been

compiled from a variety of commercial and non-commercial sources. The validity of the data in

this compilation is the responsibility of the originators, and information contained herein should

be used mainly as a guide and for the sake of comparison. Normally, IS0 units are used in

ORNL reports, but in this case, the units have been ,reported in the measurement systems that

were used in the original references. They reflect the diversity in current preferences for units of

measure in the commercial brakes industry.

In addition to Dr. Sidney Diamond, DOE, Office of Transportation Materials, and Dr. Phil Sklad, Metals and Ceramics Division, ORNL, I would like to thank those who reviewed the drafts of this document and made useful suggestions for improvement. In particular, I’d like to thank Rena Hecht Basch, Dr., Sr. Technical Specialist, Ford Research Laboratory, Safety Research and Development Department, for her practical comments.

Peter J. Blau Metals and Ceramics Division Oak Ridge National Laboratory

Contents

1.0 Introduction ........................................................................................................

1

2.0 Purpose and Scope of this Report.. ..................................................................

2

3.0 Brake Materials and Additive Functionality ..................................................

2

3.1 Abrasives .....................................................................................................

3

3.2 Friction to Producers/Modifiers ...................................................................

3

3.3 Fillers, Reinforcements, and Miscellaneous.. ..............................................

5

3.4 Binder (Matrix) Materials.. ..........................................................................

6

3.5 Asbestos.. .................................................................................................. .;. 6

3.5.1 Wear of Asbestos Materials ..............................................................

6

3.5.2 Regulations and the Current Use of Asbestos in Brakes.. .................

7

3.5.3 Possible Replacements for Asbestos in Brakes.. ...............................

7

4.0 Brake Friction Designations and Typical Compositions ................................

8

4.1 Edge Codes ..................................................................................................

8

4.2 Friction Brake Compositions for Aircraft and Ground Vehicles .................

9

4.2.1 Aircraft Brake Formulations .............................................................

9

4.2.2 Automotive Brake Pad Formulations.. ..............................................

11

4.2.3 Passenger Car and Truck.Brake Disc and Drum Materials.. ............. 16

5.0 Brake Material Test Methods and Apparatus.. ..............................................

18

5.1 The FAST Machine .....................................................................................

19

5.2 The Chase Machine .....................................................................................

19

5.3 Other Sub-Scale Testing Machines ..............................................................

20

5.4 Inertial Dynamometers and FMVSS Tests ..................................................

20

6.0 References .....................................................................................................

20

Appendix - Thermophysical Properties of Selected Materials.. ............................... 23

. . . .
111

1.0 Introduction

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

vehicle to heat, via friction, and dissipating that heat to the surroundings. As a part of a

commercial truck or automobile, brake materials have additional requirements, like resistance to

corrosion, light weight, long life, low noise, stable friction, low wear rate, and acceptable cost

versus performance. There are two common types of friction brakes - drum/shoe brakes and

l

3

disk/pad brakes. The design of the brakes affects heat flow, reliability, noise characteristics, and

ease of maintenance.

History records the use of many kinds of materials for brakes (‘friction materials’). For example, wagon brakes used wood and leather. In fact, many current brake materials still contain organic-based materials, like polymers and plant fibers. Emerging. railroad technology in the 1800’s required brake materials to perform under high loads and speeds. Friction experiments were conducted with iron brake shoes in the 1870’s (see, for example, Fig. 1).

0.50 I I I I I I ,.

0.40 -

-c-CAST IRON BRAKE BLOCKS ---Q---WROUGHT IRON BRAKE BLOCKS -

0.30 -

0.20 -

0.10 -

0.00 I-

I

I

I

I

I

I

-I

0

10

20

30

40

50

60

70

SPEED (mph)

Figure 1. Test results from the work of Captain D. Galton (1878) using a special
railroad wheel brake simulator and steel test wheels. .

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 [Weintraub (1998)].

According to Nicholson(l995), Herbert Frood is credited with inventing the first brake lining

materials in 1897. It was a cotton-based material impregnated with bitumen solution and was

used for wagon wheels as well as 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 molded materials that contained

.

crysotile asbestos fibers, a plentiful mineral. Resin-bonded metallic linings were introduced in

the 1950’s, and by the 1960’s so-called ‘semi-mets’ were developed. These contain a higher

amount of metal additives. Table 1 from Nicholson (1995) lists some common brake materials.

Table 1. Historical Compositions of Automotive Friction Brake Materials

Material Description
Cast iron on steel Hair or cotton belting (limited by charring at about 300” F) Woven asbestos with brass and other wires for increased strength and performance Molded linings with shorter chrysotile fibers, brass particles, and low-ash bituminous coal Dry-mix molded material to replace cast iron brake blocks that produced metallic dust that shorted electric train rails Flexible resin binders developed along with more complex formulations Resin-bonded metallic brake linings Glass fibers, mineral fibers, metal fibers, carbon and synthetic fibers to provide semi-metallics with higher performance than asbestos [beginning of safety issues with asbestos) Non-asbestos (fiberglas) materials
Suggested use of carbon fibers

Application(s) railroad car brake blocks and tires wagon wheels and early automobiles automobiles and trucks
“ “ “
London underground
brake drum linings
industrial and aircraft applications automotive and trucks
brake drums on original equipment cars automotive brakes

Approximate Year
prior to 1870’s ca. 1897 ca. 1908 ca. 1926 ca. 1930
1930’s 1950’s 1960’s
1980’s 1991

2.0 Purpose and Scope of this Report
The purpose of this report is to present a survey of commercial brake materials and additives, and to indicate their typical properties and functions, especially as regards their use in heavy trucks. Most truck pad and shoe materials described here were designed to wear against cast iron. Brake material test methods are also briefly described. This report does not address issues associated with the fabrication and manufacturing of brake materials. Since there are literally thousands of brake material additives, and their combinations are nearly limitless, it is impractical to list them all here. Rather, an attempt has been made to capture the primary constituents and their functions. An Appendix contains thermo-physical properties of some current and potential brake materials.

3.0 Brake Materials and Additive Functionality
Brake pad and shoe additives serve a variety of functions. Even a difference of a percent or two of additive concentration can affect performance, so composition control is important. This report lists additive materials by function. Information is referenced using the first author’s name and year. If the information is from a handbook or commercial source, the reference will be listed by publisher or by company name. According to Nicholson (1995), it is conventional to list compositions of brake additives in volume percent, but not all authors do so.
‘One can group brake materials and additives based on their expected functions as follows:

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Compositions, Functions, and Testing of Friction Brake Materials