Document bav1B85b2E5p13oEeVR5b5zqy

FILE NAME: Allied Signal Bendix (ASB) DATE: 1973 DOC#: ASB036 DOCUMENT DESCRIPTION: Report - Society of Automotive Engineers - Brake and Clutch Emissions Generated During Vehicle Operation 730548 Brake and Clutch Emissions Generated During Vehicle Operation Michael G. Jacko Research Laboratories, Bendix Corp. Robert T. DuCharme Automotive Control Systems Group, Bendix Corp. Joseph H. Somers Office of Air and Water Programs, Environmental Protection Agency THE CHRYSOTILE FORM of asbestos is a major constituent in automotive friction materials: disc pads, brake linings, and clutch facings. Asbestos is used because of its thermal sta bility, relatively high-friction level, reinforcing properties, and low cost. During operational engagement in the vehicle, the friction material and a metal rotor form a sliding friction couple which converts the kinetic energy of rotating members into heat, absorbs the heat, and gradually dissipates it to the surroundings. Friction material emissions are generated by wear. Abrasive and adhesive wear are considered to be the most important mechanisms below approximately 450F; thermal wear pre dominates above 450F. The organic constituents pyrolyze of oxidize and are emitted to the air as carbonaceous solid parti cles or gaseous reaction products. The asbestos fibers are pul verized into small particles which are either trapped in the brake (or clutch) housing, fall to the road, or are emitted to the atmosphere. Most of the asbestos is heated to tempera tures high enough to cause chemical conversion and is there fore trapped or emitted as olivine or forsterite particles When the large number of existing cars and trucks is con sidered, each with eight or more pieces of friction material in ----------------------------------------------------------------------- A B S T R * C T In order to define the extent of gas and particulate emissions from automotive brakes (and clutches), a combination separa tion and storage collection system was devised. Unique emis sions collectors for both disc and drum brakes and for a clutch were conceived, designed, and built as the main embodiment of this instrumentation. The hardware was installed on a ve hicle which was then driven through various test cycles to de termine the extent and type of brake emissions generated at low- and high-operating temperatures. Typical driving condi tions such as the Detroit Traffic Test as well as more abusive driving conditions such as fade tests were included. Typical original equipment and aftermarket friction materi als for both disc and drum brakes were used in the tests. Copyright Society of Automotive Engineers, Inc. 1973 All rights reserved. ' Brake relines were made to simulate typical consu m ers -:e practices. The brake emissions generated were remove.i >m the various collectors and mass balances were perform:: The particulates were processed and analyzed by a combin, : jf optical and electron microscopy to ascertain the aslv- content and the asbestos particle size distribution m ' - 'ar debris. Comparisons of emissions from new and used : n materials, from disc and drum brakes, and from origina. . upmen t and aftermarket materials were made. Finallv . an : \mate was made of the total emission of asbestos by ail i r.e vehicles in the country. On the average more than ' >f the asbestos is corverted. The contribution to the atmovphere is 5060 lb or 3.2% of the total asbestos emission. 2 the brake system plus more in the clutch mechanism, it be comes apparent that an air pollution problem may exist. Con sidered in another light, there are perhaps 1 billion pieces of friction material in vehicles in the United States gradually being pyrolyzed and ground to dust. The brake systems in the vehicles utilizing these friction materials can thus be consid ered as chemical reactors, each emitting organic and inorganic compounds including asbestos and its decomposition products to the atmosphere. The compositions of the gaseous and solid emissions are not well-known nor are the particle sizes and shapes of the solid emissions well-known. OBJECTIVES Because of the possible damage which asbestos emissions can produce in the human respiratory system, it is desirable to identify and quantify these emissions. Thus the objectives of this paper are to: 1. Describe the methodology used to generate, collect, and analyze brake and clutch emissions. 2. Report the asbestos contents in emissions from a test ve hicle. 3. Estimate the total asbestos emissions for all vehicles in the country. TECHNICAL APPROACH The detailed technical approach may be summarized as follows: 1. Select a suitable vehicle and linings representative of the marketplace. 2. Conceive, design, and build brake and clutch emissions collectors. 3. Test and check out a typical collector on an inertial dyna mometer and install instrumentation on the test vehicle. 4. Select and run suitable driving test schedules representa tive of consumer-type driving. 5. Collect and analyze emissions to obtain the asbestos con tent and the particle size distribution. 6. Estimate the asbestos emission for all passenger vehicles and extend the data to trucks to obtain a result for all vehicles operating in the United States. A passenger car was selected for testing because of the fol lowing factors: . 1. Vehicle braking cannot be simulated realistically on small- scale friction test machines with the present state-of-the art. 2. Full-scale brake and clutch dynamometers provide fairly good simulation and can be used for checking out the emis sions collection system; however, separate tests for brakes and clutches would be required thus increasing program costs. On the vehicle, disc and drum brakes and clutches can be tested simultaneously. INSTRUMENTATION METHODOLOGY AND CRITERIA - The collection of par ticulate and gaseous emissions from any vehicle friction couple has never, to the authors' knowledge, been reported in the lit erature. To define the extent of these emissions, a collection system was devised which combined the functions of separa tion and storage. Unique emissions collectors for both disc and drum brakes and for a clutch were conceived, designed, and built as the main embodiment of this instrumentation. The collectors separated the wear debris into three different fractions: a sump sample which included the wear debris on the lining surfaces, in the rivet holes, and on the brake drum; a surface sample which included the wear debris on the brake and collector shroud surfaces, and an airborne sample col lected on membrane filters. The major requirements for the emissions sample collection system may be summed up as follows: 1. Collect all particulate and gaseous emissions. 2. Store collected emissions unchanged. 3. Prevent intrusion of contaminants. 4. Maintain ordinary braking and clutching conditions. 5. Be operable at high temperatures. 6. Permit easy separation and analysis of emissions. MATERIAL SELECTIONS For the results to be represen tative of average consumer-type vehicle usage, a vehicle inter mediate between compact and luxury was selected. The ve hicle was equipped with front disc brakes, rear drum brakes, and a dry clutch. All friction material used contained asbestos. Three vehicle tests were run. The first vehicle test was run with the original equipment friction materials. The second vehicle test simulated a partial reline-fronts only relined-while the rears were repeated to give a replicate test and an indication of emissions trends for friction materials with continued use. The third vehicle test simulated a complete brake reline and included turned discs and drums. The friction materials selected for the program were representative of those supplied by the industry-five different manufacturers (Abex, Bendix, Raybestos-Manhattan, Thiokol, and Worldbestos) produced the original equipment and aftermarket disc pads and drum linings which were se lected in part because of their high-volume usage. VEHICLE INSTRUMENTATION - A passenger car of me dium weight (4850 lb test weight) produced in high volume was selected. It was equipped with a three-speed manual transmission, ventilated cast-iron disc brakes on the front, and cast-iron drum brakes on the rear. This vehicle was selected in order that the emissions from clutches and from disc and drum brakes could be tested simultaneously on a vehicle size representing a large percentage of the present vehicle popula tion. The vehicle was equipped with standard brake test instru mentation. A front disc brake collector and a rear drum brake collector were installed on the right side of the vehicle The clutch was sealed by closing the few holes in its casing. The left wheel brakes were left in their normal configuration and were used to monitor the operation of the shrouded brakes. Wear debris was taken from the left brakes as well as from those on the right. The amounts of debris formed and their compositions were used to demonstrate that the brake shroud- 3 MAXI ASSEMBLY in l e t aim FILTER SYSTEM Fig. 1 - Schematic diagram for airflow of typical particulate and gas collection system Fig. 2 Vehicle instrumentation (front seat area) Fig. 3 - Vehicle instrumentation (rear seat area) Fig. 4 - Schematic of disc brake shroud TO (MISSION STOflAOt U N IT 4 ing did not significantly affect the operation of the brakes on the right side. EMISSIONS COLLECTION SYSTEMS O V ERA LL SYSTEM DESIGN The basic design concept of each brake emissions collection system is shown in Fig. 1. Air from inside the vehicle was pulled through a bed which removed water and carbon dioxide from the air. The air then passed through a filter to remove all particles larger than 0.2 fjum(8 x 10" 6 in). The filtered air was then routed to the sealed brake assembly through clean Teflon tubing. The airstream, along with wear particles and gases, then passed out of the brake through Teflon tubing which was heated to avoid condensation. This stream passed through two filters to re move the airborne particles and preserve them for analysis. The stream then passed through three cold traps in order to condense and trap the gases evolved during braking and pre serve them for analysis. The remaining airstream then passed through a flowmeter, the vacuum manifold, and finally through an air pump run by the vehicle engine where it was expelled to the atmosphere. Fig. 2 shows, mounted in the front seat of tne test vehicle, the front brake inlet air filter and gas collection system, the clutch gas collection system, and the 12 position thermo couple switch and pyrometer used to monitor gas and filter trap temperatures. Fig. 3 shows, as mounted in the rear seat of the test vehicle, the rear brake air filter and gas collection system, the clutch air filter, and the electrical system (bat- -iii- Fig. 5 . Disc brake emissions collector assembly-exploded view 5 teries, inverter, and Variac) which were used to supply power to the heating coils. PARTICULATE FILTERS - The 47 mm filter holders joined in series were used for the collection of airborne particulates. Nuclepore filters were used. These filters are made from a smooth film of polycarbonate plastic with pores that do not restrict the flow of gases significantly as particle collection proceeds. Tl^e filter holders were heated by tape heaters wound around the outside and controlled by a variable trans former within the test vehicle. GAS COLLECTION SYSTEM - Three gas collector traps held at approximately -70C (-95F ) were used. A simple cold-finger trap, placed first, was used to remove and store the condensable vapors. These vapors included most of the or ganic degradation components from the brake lining. The second type of trap, of which two were used, contained acti vated charcoal and was used to collect the volatile hydrocar bons such as methane and other light gases. DISC BRAKE COLLECTOR - Fig. 4 shows a cross-sectional view of the disc brake collector. The rubbing seal was located at the hat or hub section of the rotor. The seal was a spring- Fig. 6 - Disc brake emissions collector showing thermal control aids N Fig. 8 Schematic of drum brake shroud 6 loaded graphite-filled Teflon seal of commercial manufacture. A view of major components of the collector is shown in Fig. 5; the system, as mounted on the vehicle, is shown in Figs. 6 and 7. The main portion of the shroud was coated with black oxide; a water-cooling system was added and an open "mag" wheel was used to aid in cooling the enclosed brake. DRUM BRAKE COLLECTOR Fig. 8 shows a cross sectional view of the collector along with the detail of the rubbing seal. The seal was of the same type as for the disc brake collector. The axle hub used to align the drum was modified with a piece that was concentric to the axle bear ings within 0.001 in (0.0025 cm). A tapered lead was used to facilitate mounting of the drum. The close tolerances on the concentricities were necessary in order to obtain reason able seal life. Figs. 9 and 10 show outboard and inboard views of the system as mounted on the test vehicle. CLUTCH COLLECTOR - Th clutch system consisted mainly of a filtered air inlet and an outlet to the sample storage system with all other external holes sealed. INERTIA DYNAMOMETER TESTS The front disc brake emission collector was tested on an in ertia dynamometer to check out its operation and its most Fig. 9 - Assembled rear drum brake emission collector critical part, the rotating seal. Thermal response tests were made with the results indicating that for normal operation the shrouded disc brake would operate at a slightly higher tempera ture than the normal brake configuration. A method was de vised to determine the leak rate of the collector. The rotating seal was largely responsible for the residual leak; the leak rate was reduced significantly by use of a very small amount of hightemperature grease. The rotating seal underwent durability test ing and survived 7 h at 50 mph. A second series of dyna mometer tests gave reproducible emissions and temperatures. Finally, a test was made in which the collector and especially the rotating seal were shown to be relatively leak-tight to ex ternal liquid and particulate contaminants. VEHICLE TESTS RATIONALE - For a given vehicle brake system, friction material wear is primarily a function of the duty cycle. For light-duty cycles, where pad and lining temperatures remain under 350F, low wear results and is primarily due to the abrasive and adhesive wear mechanisms. Heavier duty cycles at higher temperatures give some combination of thermal, abrasive, and adhesive wear. Under severe heavy duty where the use borders on abusiveness, brake fade may occur. The inability of the brakes to hold the friction level results in part from the formation of gases (and wear debris) at the interface. Although there are many acceptable original equipment manufacturers' friction material tests to measure a specific condition or combination of conditions, there is no one test which adequately matches normal driving conditions which would be representative of all vehicles. Consequently, it be came necessary to devise a rational and meaningful vehicle test driving schedule. SELECTED VEHICLE-DRIVING SCHEDULES A total of seven test schedules were chosen and each was followed by a measurements procedure (take emissions samples, meavire wear, inspect systems, and replace worn parts). The first three tests-Burnish, After-Burnish (A.B.) Baseline, and Detroit Traffic-represent the low-temperature tests. The final four tests--10 Stop Fade, After-Fade (A.F.) Baseline Fig. 10 Inboard view of assembled rear drum brake emissions col lector 7 15 Stop Fade, and Final Baseline-represent the high-tem perature tests. Burnish - During the Burnish, the original equipment and aftermarket linings mate an conform to the initial condition of the rotor whether it is in its original configuration, as-used condition after vehicle test 1, or its turned condition prior to vehicle test 3. It was anticipated that the emissions during Burnish would be different from those for worn-in linings. A.B. Baseline - This consisted of three days of Detroit Traffic Test. It was run at this time so that the other Base lines run at later times could be compared with the A.B. Baseline for the amount and type of emissions. Detroit Traffic Test - The Detroit Traffic Test is typical of urban driving and is used primarily to evaluate friction, life, and noise of commercial brake products. The normal operating range forvp$senger car brakes in the test is 180280F. This condition constitutes what a brake engineer calls a low-temperature wear test. Testing is intentionally accelerated to reduce test costs; consequently the test tends to be more severe than average driving. The end of the Detroit Traffic Test was the end of the low-temperature wear testing. 10 Stop Fade and Recovery - The 10 Stop Fade and Recovery was the fourth test sequence and the start of the heavy-duty or high-temperature testing. During this test the front brakes experienced temperatures above 500 F while the rear brakes experienced temperatures above 350F. The combination of increased temperature and increased duty was expected to change the amount and type of wear debris generated as compared with the previous low-duty tests. The Fade and Recovery Test was then followed by the Reburnish sequence. A.F. Baseline - This fifth test sequence was identical to the second and seventh test sequences (and similar to the third), but only the conditions of the friction materials had changed. This test was expected to determine the permanent changes in the amount and type of wear debris generated for friction materials taken through high-temperature and heavy-duty stops. 15 Stop Fade and Recovery - The sixth test sequence was the 15 Stop Fade and Recovery in which the friction materials were taken to even higher temperatures than for the 10 Stop Fade. The five additional stops performed after the brakes were already hot produced temperatures above Table 1 - Comparison o f Disc Brake versus Drum Brake Operating Conditions Parameter Disc Drum Type of system Airflow Emissions Third-body abrasive wear Open High Relatively few trapped Relatively none Closed Low Much trapped in sur faces and in sump Some 575F. This is abusive braking and rarely occurs. The emis sions generated were expected to be different again as com pared with the low-duty tests and the 10 Stop Fade. The Fade and Recovery Test was then followed by the Rebumish sequence. Final Baseline - The results of this seventh and last test sequence can be compared with the results of the identical second and fifth test sequences. This test concluded the determination of the effects that high-temperature and heavy-duty tests have on brake emissions. SAMPLING AND ANALYTICAL PROCEDURES GENERATION OF EMISSIONS During the braking pro cess, particulate emissions are generated by the rubbing ac tion of the friction materials and the rotors. The original equip ment manufacturer (OEM) brake configurations (left wheels of test vehicle) release emissions which reside in either of two areas depending on the brake type (Table 1). The disc brake releases much of the emissions to the atmosphere while a small amount remains in the brake. The drum brake re leases a smaller amount to the atmosphere and retains size able portions on the drum-rubbing surface and on the brake parts. The brake emissions collectors perform two functions not encountered in normal brake operation: they collect all the debris generated and fractionate the debris. Table 2 summarizes the particulate emissions samples produced. The OEM brake configurations release gaseous emissions which again reside in either of two areas. Most of the gaseous emissions are released into the atmosphere; some o f the high molecular weight materials distill from the hot surfaces and condense on the cooler brake parts. The emission transfer lines used in conjunction with the collectors therefore were heated so that almost all gaseous emissions could be transferred to the gas collection traps. PARTICULATES REMOVAL FROM COLLECTORS A detailed step-by-step procedure was prepared for the removal of brake emissions from the collectors. The amounts of debris collected at the various locations were used later to calculate the mass balances. A detailed step-by-step pro- Table 2 - Samples Produced by Brake Emissions Collection Sample Disc Brake Drum Brake Sump Surfaces Airborne Trapped debris*-includes that in rivet holes, on pads, and in caliper piston Accumulated on shroudnormally road dropout Airborne samples collected on filters Trapped debrts* - incudes that in nvet holes n linings, and on J.um surface" Accumulated on *n tutfaces* Airborne samples . lected on filters 'Normally not completely released during brake operation . Thu may be a "controllable" material which could be disposed o( pr-perly.) "Provides third-body wear. 8 cedure was also prepared for the sampling, handling, and analysis of the asbestos emissions. ANALYTICAL PROBLEM DEFINITION - The thermal and mechanical forces which act at the friction couple inter face produce a complex chemically and physically altered microstructure which cannot be accurately described at present. Table 3 gives an estimate of the chemical composi tion of wear debris. Asbestos is a complex inorganic material with the ap proximate composition formula: Mg3 (Si05) (OH)4 or 3MgO 2Si02 2H20 The basic unit has a Fibril form (1,2)*. Asbestos is readily identified when alone or in simple mixtures at high con centrations by these analytical methods: x-ray diffraction, thermal methods, microscopy, and infrared analysis. How ever in complex mixtures or at very low concentrations the analysis for asbestos is very difficult. In brake wear debris, the problem is compounded because the reaction products of asbestos, forsterite and olivine have similar elemental ratios and similar x-ray diffraction patterns. The only sensitive method which can be used is microscopy. In extremely low concentrations, asbestos is identifiable in the electron microscope by its physical shape (tubular fibril) which is distinguishable from that of other fibers and particles. At the beginning of the program, one optical (3) and three transmission electron microscopy (4-6) methods had been developed by others. Two of the electron microscopy methods were not suitable because they changed the fiber size dis tribution of the asbestos. ANALYTICAL METHOD SELECTED From the available analytical methods and the problems associated with brake wear debris analysis, the following considerations were necessary. Criteria and Flow Chart - Three important criteria had to be met by the analytical method used: The very small portion of brake debris used had to be representative of the much larger sample collected; the analytical steps could not degrade the particle size distribution of the asbestos fibers obtained; the results obtained must be indicative of the actual asbestos content of the sample. These criteria were met by the analytical scheme outlined in Fig. 11. Representative Sampling and Low-Temperature Ashing (LTA) - The analysis of brake wear debris indicated the presence of 20-30% by weight of polymeric and carbonaceous material, which in turn produced a fluffy appearance when the material was examined in the scanning electron microscope. The organic portion was therefore removed by LTA. Two representative samplings were used: the first in sample selection for LTA and the second in sample selection for dis tribution on a filter membrane for subsequent analysis. Selected Microscopy Methods - In the very early tests, wear debris from a sample dynamometer was collected on the filter train of the 8.0 p and 0.2 p Nuclepore filters. Both filters were examined by a combination of optical and transmission electron microscopy. The following observations were made: 1. Asbestos fibers longer than 20 p were obtained. 2. Very fine fibrils were extremely difficult to detect at less than 5000 diameters magnification. Based on the above studies, it was deemed necessary to employ two magnifications. To detect fibers greater than 2 p, a magnification in the range 10,000-40,000 diameters SUMP uuw - ISAM AS FOR SURFACtS SAMRLt) SUNPACU SAM PII (W(>OH(0) 1 WIMM RCPRtSNTATIVf FRACTION AIMOM NttAMn.lt U jlP IL T tR l HPILT(R | COMSINI | l( M M IA IK M SURFAC1S lA M P li LOW TIMRtRATURI A6H (LTA) 'Numbers in parentheses designate References at end of paper. WtlOMT RIRRCSfNTATlVI FRACTION Table 3 - Estimated Chemical Composition Characteristics of Wear Debris Description Percent Low molecular weight degradation products Polymeric components Carbonaceous material Inorganics: Mineral Olivine Oxides (from lining) F ejO j (from rotor) Asbestos 2-10] 12-20 1-5 1 M 0-30 %2040 0-10 5-15 < lj 20-30 70-80 oaTm tuTC on OJtfNUCLtPOM FILTC* OPTICAL MICROSCOPY: (GLASS S U D S MOUNT) ICOUNT I400X PMASC CONTRAST) DIVIO KLCCTAOM M C A O K I F * (CARSON II W O i w c w COUNT (2 2 .0 0 0 X 1 ------------------------- ' RCSULTf Fig. 11 - Flow chart of particulates analyses 9 was required. Table 4 shows the magnifications selected for use with the two microscopy techniques. Calculations from Microscopy Results - For each fibril or fiber found it was necessary to determine its dimensions and calculate the volume of asbestos found. Because of the large number o f fibers this procedure became tedious. To simplify fiber sizing, a microscopy count sheet was developed. Each fiber found by the appropriate microscopy method was classified into the proper size category containing the pro jected diameter and length of the fiber in question. The volumes were summed, converted to weight, and normalized for the entire sample weighed onto the filter. A computer program was subsequently developed to minimize computational time and to eliminate errors in the pro cessing of these calculations. The possible sources o f error associated with sample pro cessing and analysis were minimized through the use of statistical methods. The largest effect found on the asbestos analysis was the occasional occurrence of a large fiber. The extent of error increased as the percent of asbestos in the sample decreased. The data showed that the maximum devia tion for results with asbestos contents above 0.10% averaged 12-15% and had a maximum at approximately 20%. The maximum deviation increased for asbestos contents below 0.10% where errors for the small amounts of asbestos emis sion become less significant from the standpoint of air pollu tion. VEHICLE TEST RESULTS systems. Only one major problem occurred during the vehicle testing: during the 10 Stop Fade of vehicle test 1, the hardened steel ring on which the rotating seal slides became loose. The ring was reanchored and no further problem was encountered during the 15 Stop Fade or in any further test schedule. This result showed the durability o f the collector and rotating seal design and construction. For the 8100 miles of testing, only seven front and eight rotating seals were required. This was better than anticipated at the start of the program. Brake-Operating Temperatures - Frequent temperature monitoring was necessary for the successful completion of the vehicle tests. The temperatures were monitored at all four wheels (Table 6). The top portion of the table shows the effectiveness of the thermal control aids in keeping the temperatures of the shrouded disc brake well below the 400F region where the exponential wear rate begins. Since approximately 90% of the test miles were driven in the Detroit traffic circuit, it was necessary to monitor these temperatures carefully. The driver was instructed to take specific actions when greater than desired temperatures occurred. For example, during the Detroit traffic circuits the maximum allowable temperature was 330F. When this tem perature was reached the vehicle was stopped and allowed to cool to 300F. These cool-down periods were seldom necessary. The data at the bottom of Table 6 show that on a hot July day the temperature difference between the brakes remains fairly constant as the temperatures increase with the ambient. MILEAGE ACCUMULATIONS - The various driving schedules described earlier are listed in Table 5 with the Table 5 - Summary of Vehicle Mileage Accumulations average mileages and times for each test. The overall varia tion for the total mileage accumulation of all three vehicle tests was very low at 2.4%. These mileage variations were Schedule Average Test Miles Miles Days primarily due to the varying times taken to reach the Detroit Burnish 1 174 traffic circuit. Normally only one round trip was required 2 127 134 3 5 to obtain the four circuits. Rain, seal failure, thermocouple 3 100 malfunction, and other minor difficulties which required a A.B. Baseline 1 328 premature return to base added to the minimum mileage 2 348 348 4 5 3 368 possible. Detroit Traffic 1 1439 PERFORMANCE OF EMISSION COLLECTION 2 1430 1408 135 SYSTEMS - 3 1355 Rotating Seal Life The success of the vehicle testing 10 Stop Fade 1 47 depended heavily on the proper operation of the rotating 2 53 seals since they were the most critical parts of the collection A.F. Baseline 31 35568 53 * 0 2 339 347 4 5 3 347 15 Stop Fade 1 47 Table 4 - Microscopy Magnifications Selected for Asbestos 2 79 59 < 5 Fiber Analyses 3 52 Final Baseline 1 352 Fibers Detected, m 2 326 343 * 5 Microscopy Technique Minimum dx 1 Maximum d x 1 Totals 3 352 1 2756 Transmission electron at 22,000X 0.03 x 0.10 0.50 x 35 2 2702 2697 38 0 3 2632 Optical (phase contrast) at 400X 0.50 x 1.50 10 x 100 8090 Test Burnish Vehicle lest 1 A.B. Baseline Vehicle test 2 Table 6 - Brake Temperatures During Burnish and Detroit Traffic Circuits Remarks ________ Front Disc Brake_______ ________Rear Drum Brake Ambient Temperature, Right Left Right Left F (Shrouded) (Normal) AT (Shrouded) (Normal) AT Initial attempt (no thermal control aids) After 20 stops After 40 stops After 60 stops Rerun (with thermal control aids) After 10 stops After 40 stops After 60 stops After 100 stops After 160 stops 10 10 10 Range 70 49 65 68 50 Range 400 340 360 340-400 150 120 160 120-160 250 220 200 200-250 255 200 245 200-255 150 110 150 110-150 105 90 95 90-105 280 310 265 280 300 265-300 150 ISO 150 165 170 150-170 130 160 115 US 130 115-160 205 245 215 220 190 190-245 150 165 165 170 130 130-170 55 80 SO 50 60 50-80 Morning circuit (8:00 a.m.) 12 Mile and Woodward Michigan and Thud Adams and Woodward Adams and Woodward 12 Mile and Woodward Afternoon circuit (2:00 p.m.) 12 Mile and Woodward Michigan and Third Adams and Woodward Adams and Woodward 12 Mile and Woodward 79 80 82 82 84 90 91 91 91 91 Range 270 300 300 280 330 310 320 310 310 300 270-330 150 160 160 150 190 210 180 180 170 160 150-210 120 140 140 130 140 100 140 130 140 140 100-140 150 170 180 180 190 160 210 210 200 170 150-210 150 0 160 10 160 20 160 20 160 30 160 0 180 30 180 30 170 30 150 20 150-180 0-30 U For the 10 and 15 Stop Fade schedules, it was expected that the shrouded brake would retain the high temperatures longer than would the nonshroudetfbrake. In the course of the test it was necessary to increase the time interval after the fifth-to-seventh stops to allow for additional cooling. Fig. 12 gives the temperature versus stop relationship from the 10 Stop Fade of vehicle test 1. Data taken from an inertia dynamometer and a typical vehicle test were used as baseline data to which the shrouded disc brake was programmed. All other fade tests showed similar relationships. Mass Balances - The emissions samples were removed from the collectors and weighed. The results for vehicle test 1, which are typical of the other two tests, are given in Table 7. After each test the brake lining weight losses were also obtained. The distribution of the brake emissions was then obtained for the sump, surfaces, and airborne samples. Table 8 summarizes the distributions for the three vehicle tests. PERCENT ASBESTOS CONTENTS Each of the samples was analyzed for asbestos content by optical and electron microscopy as described earlier. For vehicle test 1, the range of asbestos contents in brake emissions varies from a high of 1.65% down to a low of 0.05% (Table 9). Of the 47 analyses reported, only two were above 1.00%. The overall average was 0.38%. For vehicle test 2, the range of asbestos contents in brake emissions varies from a high of 1.42% down to a low of 0.03%. Of the 43 analyses reported, only one was above 0.96% and FRONT SHAKES Table 7 Weights of Brake Particulate Wear Debris Collected Vehicle Test 1, g Front Brakes Rear Brakes Schedule R ight L eft R ight L eft Collector (Shrouded) (Normal) (Shrouded) (Normal) Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline 15 Stop Fade Final Baseline Totals Sump Surfaces Airborne Sump Surfaces Airborne Sump Surfaces Airborne Sump Surfaces Airborne Sump Surfaces Airborne Sump Surfaces Airborne Sump Surfaces Airborne Sump Surfaces Airborne Entire test 0.142 0412 0.061 0.083 0 644 0.130 0.201 2.010 0.237 0.580 1.212 0.013 0.191 1.764 0.259 0.616 5.943 0.120 0.154 2.011 0.375 0.967 13.996 1.195 17.158 0.116* 0.029 - 0.128 0.055 - 0.458 0.109 - 0.244 0.076 - 0.153 0.030 - 0.150 0.027 - 0.138 0.083 - 1.387 0.409 - 1.796 0.144 1.170 0.046 0.185 0.590 0.049 0.436 4.052 0.285 -0.335 0.371 0.017 0.060 0.652 0.030 -0.046 0.100 0.004 0 097 0.440 0.003 0.541 7.375 0.434 8.350 0.220 0.394 - 0 208 0.205 - 1.654 0.878 - 1.120 0.275 - -0.516 1.543 - -0.330 0.169 - 0.017 0.448 - 2.373 3.912 - 6.285 'Estimated from cumulative sample (0.145 g) taken during this schedule only. TENTER TURE (El TEMPERATURE l* | REAR SHAKES 2 4 S 10 2 4 10 12 faoe STOf NUMBER RECOVERY Fig. 12 - Brake temperature data during 10 Stop Fade Test 12 only three were in the range 0.50-0.96%; ail others were less than 0.50%. The overall average was 0.25%. For vehicle test 3, the range of asbestos content in brake em issions varies from a high o f 0.51% dow n to a low o f 0.003%. Of the analyses reported, three were in the range 0.20-0.51%; all others were less than 0.20%. The overall average was 0.07%. For all three vehicle tests, the overall average of asbestos content in the brake emissions was 0.23%. Independent Asbestos Analyses - To provide a systematic independent check on the asbestos analyses, the Environmental Protection Agency (HPA) arranged for Battelle Columbus Laboratories to analyze 24 samples generated during the Program. The Johns-Manville Research and Engineering Center also provided three analyses (7). In 19 of the 24 analyses, the Program results were slightly higher than the corresponding Battelle results (Table 10). The Program Table 8 - Distribution of Emissions*, % Front Brakes Rear Brakes Vehicle Right Left Right Left Test Collector (Shrouded) (Norma)) (Shrouded) (Normal) 1 Sump 6-31 Surfaces 63-89 Airborne 2-15 2 Sump 2-20 Surfaces 71-93 Airborne 2-22 3 Sump 2-38 Surfaces 46-86 Airborne 7-19 61-83 17-39 - 63-83 17-37 - - - - 8-22 72-88 3- 6 12-22 60-86 1- 2 9-36 61-87 l-ll 36-65 35-65 - 39-63 37-61 - - - - *The ranges give the lowest and highest percentage found for the seven driving schedules as a whole. Table 9 - Summary of Asbestos Analytical Results-Vehicle Test 1, Weight Percent Schedule Front Brakes Rear Brakes Right Left** Right Left Collector (Shrouded) (Normal) (Shrouded) (Normal) Burnish Sump Surfaces Airborne A.B. Baseline Sump Surfaces Airborne Detroit Traffic Sump Surfaces Airborne 10 Stop Fade Sump Surfaces Airborne A.F. Baseline Sump Surfaces Airborne 15 Stop Fade Sump Surfaces Airborne Final Baseline Sump Surfaces Airborne Average 0.813 0.398 0.144 (0.452)* 1.650 0.472 0.290 (0.804) 0.247 0.137 0.052 (0.145) 0.463 0.162 0.154 (0.260) 0.656 0.507 0.134 (0.432) 0.602 1.548 0.175 (0.775) 0.435 0.290 0.167 (0.297) 0.452 Average - 0.865 0.349 (0.607) 0.179 0.415 0.493 (0.362) 0.129 0.373 0.092 (0.198) 0.280 0.071 0.132 (0.161) 0.419 0.242 0.079 (0.247) 0.071 0.257 0.222 (0.183) 0.58S 0.324 0.145 (0.351) 0.301 * * 0.991 0.265 - 0.275 0.416 - * 0.439 0.472 - ** Average value for wheel where collection took place. **Not analyzed-indicates that analysis was not required. Test Schedule Collector 1 Detroit Traffic Sump Surfaces Airborne 10 Stop Fade Sump Surfaces Airborne 2 Burnish Sump Surfaces Airborne Detroit Traffic Sump Surfaces Airborne 3 Detroit Traffic Sump Surfaces Airborne Averages Program average: 0.247 Battelle average: 0.171 Ratio: Battelle/Program * 0.69 Table 10 Comparison of Analytical Results for Asbestos Front Disc Brakes Program JM Battelle 0.247 0.137 0.052 0.463 - 0.254 0.402 0.186 0.304 - 0.234 0.018 - 0.025 0.204 _ 0.005 - 0.21 0.011 0.001 1.22 - 0.31 0.28 0.10 0.62 - 0.006 0.135 - 0.016 0.265 Rear Drum Brakes Program JM Battelle 0.129 0.373 0.092 0.280 - 0.132 0.484 1.416 - 0.249 0.113 0.115 0.046 - 0.037 0.289 _ 0.002 0.006 - - - - 0.025 0.006 0.001 0.22 - 0.007 0.10 0.38 - 0.057 0.061 0.015 0.010 - 0.044 0.077 Clutch Program Battelle - 0.291 - - _ 0.007 - _ _ _ - 13 average was 0.24% while the Battelle average was 0.17% or 69% of the Program average. -Ihe Program data were ex pected to be higher for the following reasons: All larger fibers (bundles of fibrils) found were assumed to be cylinders of projected diameter and length, and a fiber with an elliptical cross section was actually smaller in volume than reported; all fibers were assumed to be 100% asbestos. Table 11 - Weight of Asbestos Generated During Braking-Vehicle Test 1, Mg/mile Front Brakes Rear Brakes Schedule Right Collector (Shrouded) Burnish Sump 6.77 Surfaces 9.42 Airborne 0.51 A.B. Baseline Total Sump Surfaces Airborne 16.70 0.04 1.04 1.15 Total 2.23 Detroit Traffic Sump 0.35 Surfaces 1.91 Airborne 0.09 10 Stop Fade A.F. Baseline Total Sump Surfaces Airborne Total Sump Surfaces Airborne 2.35 57.13 41.77 1.70 100.60 3.52 25.12 0.97 15 Stop Fade Total Sump Surfaces Airborne 29.61 78.89 1957.40 4.47 Final Baseline Total Sump Surfaces Airborne 2040.76 1.90 24.85 1.78 Total 28.53 Left* (Normal) Right (Shrouded) 58.11 0.92 59.09 1.01 7.47 0.74 9.22 0.39 10.50 0.18 11.07 - 22.11 0.47 22.58 0.71 4.43 0.07 5.21 5.47 0.19 5.66 1.61 4.05 0.01 5.67 Left (Normal) * 13.52 1.61 - 14.13 67.85 24.35 92.20 * * Not analyzed. (Partially degraded asbestos or olivine fibers were weak and mechanically reduced to nonfibrous material by the other analytical techniques; hence only the remaining asbestos fibrils were counted.) ASBESTOS EMISSIONS TRENDS - To compare the emissions properly, it was found necessary to calculate the asbestos emission factors for each sample in micrograms/ mile (Table 11). The values of these factors were obtained by multiplying the weights of brake debris generated by the appropriate asbestos percents then dividing by the miles per test schedule. Thus, either a high-asbestos content or a large sample gave a high factor. The following observations were made: Table 12 - United States Braked Motor Vehicle Population Private passenger cars (R.L. Polk estimate July 1, 1972: 83, 137,324) D.O.T. estimate July 1, 1972 Trucks: (R.L. Polkestimate July 1, 1971: 18,462,287) D.O.T. estimate July 1, 1972 (includes 897,456 truck tractors) Light 1Under 6000 lb gvw* 12,109,000 16000-10,000 4,952,000 10,000-14,000 125.000 14.000- 16,000 125.000 Medium 16.000- 19,500 645.000 .19,500-26,000 1,290,000 Heavy f 26,000-33,000 395,000 (Over 33,000 1,165,000 Buses: D.O.T. estimate July 1, 1972 Miscellaneous motor vehicles: motor cycles, etc. D.O.T. estimate July 1, 1972 Total motor vehicles in use** D.O.T. estimate July 1, 1972 96,397,000 403,000 3,787,000 121,400,000 Gross vehicle weight; estimates from 1970-1971 sales data extended by this study. This total includes approximately 1.5 million public vehicles (450,000 cars, 920,000 trucks, and 185,000 buses) but does not in clude 190,000 Department of Defense vehicles in worldwide use. Table 13 - Compilation of Annual Motor Vehicle Brake Friction Material Usage* Vehicle Description Amount Used, No. and Unit Weight per Unit, lb Passenger car Front disc pads only 9,660,000 axle sets 1.0 Front drum linings only 24,300,000 axle sets 1.8 Rear drum linings only 32,400,000 axle sets 1.3 Light truck Drum linings 4,730,000 vehicle sets 5.0 Medium truck or bus Drum linings 670,000 vehicle sets 15.0 Heavy truck Drum linings 781,000 vehicle sets 41.0 Miscellaneous (trailers, etc.) Drum linings " -- 'Calculated from Friction Materials Standards Institute, D O T., and Stanford Research Institute Data. Total Weight, lb 9,660,000 43,700,000 42,100,000 23,700,000 10,100,000 32,100,000 10,000,000 171,360,000 14 1. Asbestos emissions were higher for new friction surfaces and decreased with use. ~ 2. The drum brake produced more asbestos emissions than the disc brake initially with the difference decreasing as the friction materials continued in use. 3. Heavy (abusive) duty did not necessarily give a higher percent of asbestos; the large amount of debris produced, however, gave a significant rise in asbestos emissions. 4. Asbestos emissions from the brakes were found to decrease from fade or heavy-duty stops (highest) to burnish to moderate braking (lowest). 5. For the disc pads only, there was an increase in asbestos emissions with increased asbestos content in the friction material. (There was no such trend for the drum brake materials.) 6. Both the front disc pads and the drum linings of vehicle test 3 have wear comparable to that found in the other two vehicle tests, yet the asbestos emissions were significantly lower. (Both pads and secondary linings contained brass chips which may have been in part responsible for the more complete conversion of the asbestos in the brake emissions.) 7. For both disc and drum brakes the surfaces sample was the largest of the three (~92%), the sump sample was next (~7%), and the airborne sample was the smallest (~1 %). ESTIMATE FOR ASBESTOS EMISSIONS The purpose of the following discussion is to develop an estimate of total brake and clutch emissions from the United States population of motor vehicles in use on the roads and highways. Inputs include all of the test results described earlier together with a supplementary data base on United States motor vehicle population and usage and on friction material usage and consumption obtained from other sources. Because of the uncertainties in all of the data available, emissions can only be considered as a broad range, rather than as a single value, with the expectation that the true average emissions for both individual vehicles and the motor vehicle population in general will be within the range of values calculated below. DATA BASE - To calculate the asbestos emissions for all vehicles it was necessary to assemble the following data base. Number o f Vehicles in Use - Table 12 lists the total United States motor vehicle population as estimated by both De partment of Transportation (DOT), National Highway Traffic Safety and Federal Highway Administration (8), and by the R. L. Polk Co. (9). The Polk census is said to be more precise because it eliminates multiple registrations of the same vehicle. Polk considers that DOT estimates may be as much as 13% too high. Both Polk and DOT omit military vehicles but include all other motor vehicles that are statelicensed including police cars, school buses, and the like. Independently, the General Services Administration reports that 190,000 Department of Defense vehicles are m use worldwide. In addition, there are 6.6 million braked trailers and 38.4 million motor vehicles with dry clutches. Motor Vehicle Usage - The approximate total number of miles traveled by all United States motor vehicles was 1.249 trillion miles for 1972 according to a recent DOT estimate (8). The average annual mileage for passenger cars is 9978 miles while for trucks it is 9807 miles. An attempt was made to estimate the proportion of United States driving that takes place in predominantly hilly or mountainous areas where long steep grades are common. Basic data on miles driven in each state were obtained from DOT. The percentage of driving that takes place in mountainous areas, where abusive brake use may be necessary, is estimated to be 11.5% of all driving. The estimate is subjective to a large degree and may be high, but no better data have been located. Asbestos in Friction Materials - The data in Table 13 indicate that the total amount of asbestos contained in all of the automotive brake friction materials sold each year is calculated to be about 103 million lb which corresponds to ~ 1 18 million lb used prior to grinding, t wo of the most knowledgeable sources (10, 11) report that 90-120 million lb per year are used. A report from IIT Research Institute suggests that 67 million lb are used annually in brake linings (12). A Bureau of Mines Report (13) based on 1968 data credits only 50 million lb o f asbestos to automotive use, a number the authors find to be much too small. Ignoring the two latter values, the three estimates of asbestos contained in brake friction materials range from 90-120 million lb. Using the calculated vehicle of 118 million lb and assuming a 15% grinding and drilling loss, the maximum amount of asbestos incorporated in brake friction materials is taken to be 103 million lb per year. A compilation of data on clutch friction materials was also made (14). Based on these data, the total amount of asbestos contained in all automotive clutch friction materials sold each year is calculated to be about 4.5 million lb. AMOUNT OF FRICTION MATERIAL ACTUALLY WORN - For several reasons the amount of brake lining (and asbestos) worn away during a year is significantly less than the total amount installed on vehicles. Brake linings are seldom completely worn away. (Due to the geometry of brake Table 14 - Compilation of Calculations for Amount of Brake Friction Material Worn Away Annually Calculation Total Brake Friction Material. million lb Installed weight each year Discarded on relining, -25% Discarded on vehicles retired ( 7 million cars X 2.38 lb x 40% = 6 . 7 + 0 75 million light trucks x 5 lb x 40% =* 1.5 0.10 million medium trucks x 15 lb X 40% = 0.6 * 0.15 million heavy trucks x 41 lb X 40% = 2.4 + miscellaneous * 0.5) Amount worn away annually 171 4 42 7 11 7 117 0 IS systems, perhaps 10% of the lining is still left on a brake when lining wear-through occurs.) Linings are usually re placed in sets rather than piecemeal. As a consequence of this and other actions about 25% o f all brake linings are discarded at relining time. Furthermore, millions of vehicles are , retired from service each year, many with brake linings that are far from worn out. Perhaps the average retired vehicle has about 1/3 of its usable lining remaining, or 1/3 X 90% + 10% = 40% of the installed weight of the lining. Combining these figures, the amount of brake friction material worn away each year is calculated in Table 14. Employing the same reasoning for clutches, the amount of clutch material worn away is calculated to be 6.56 million lb. Summarizing, the combined total of brake and clutch friction material worn away annually is 117.0 + 6.6 = 123.6 million lb. Assuming that the average asbestos content is Table 15 - Distribution-Weighting Factors for Test Vehicle Simulation Test Schedule Required Airborne (Atmosphere) Road Dropout Disc brake: New friction couple Burnish 0.04 0.85 After 2632 miles . Composite 0.07 0.91 After 8100 miles Composite 0.06 0.93 After 20,000 miles Composite 0.06 0.93 Drum brake: New friction couple Burnish 0.01 0.54 After 2632 miles Composite 0 02 0.72 After 20,000 miles Composite 0.02 0.79 Vehicle Retention O'. 11 0.03 0.01 0.01 0.35 0.26 0.19 Table 16 - Severity-Weighting Factors for Test Vehicle Simulation Test Schedule Required Weighting Factor New friction couple Surfaces preparation Moderate braking Severe braking Renewal of friction surfaces Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline 0.013 0.013 0.934* 0.020 0.020 Determined by difference. Schedule Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline Table 17 - Total Asbestos Emissions Calculated from the Test Vehicle, Average for the Three Vehicle Tests Friction Couple Asbestos Emissions, ug/mile Vehicle Test Severity Per Weighting 1 2 3 Average Axle Factors Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Gutch Disc brake Drum brake Clutch 16.70 59.09 - 2.23 9.22 - 2.35 11 07 - 100.60 22.58 - 29 61 5 21 36.35 24.43 - 4.71 2.38 - 12.75 5.50 - 79.13 146.14 - 6 69 3 28 - 7.21 11.67 - 1.96 1.98 - 0.48 0.63 - 8.82 5.03 - 3.51 0.32 - 20.09 31.39 1.11 2.97 4.52 1.11 5.19 5.73 1.11 62.80 58.15 1.11 13.27 2.94 1.11 40.18 62.78 - 5.94 9.04 - 10.38 11.46 - 125.60 116.30 - 26.54 5.88 - 0.013 0.013 0.934 0.020 0.020 Total Weighted Emissions, Mg/mile 0.52 0.82 0.01 0.07 0.12 0.01 9.70 10.70 1.03 2.51 2.33 0.02 0.53 0.12 0.02 28.51 Schedule Burnish A B. Baseline Detroit Traffic 10 Stop l ade A i. Baseline Friction Couple Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Dutch Disc brake Drum brake Clutch Disc brake Drum brake Clutch Table 18 - Distribution-Weighted Asbestos Emissions from the Test Vehicle Asbestos Emissions, jig/mile Distr ibu tion-Weigh ting - Vehicle Test Per Factors 1 2 3 Average Axle Dropout Airborne 16.70 59.09 - 2.23 9.22 - 2.35 11.07 - 100.60 22.58 - 29.61 5.21 - 36.35 24.43 - 4.71 2.38 - 12.75 5.50 - 79.13 146.14 - 6.69 3.28 - 7.21 11.67 - 1.96 1.98 - 0.48 0.63 - 8.82 5.03 - 3.51 0.32 - 20.09 31.39 1.11 2.97 4.52 1.11 5.19 5.73 1.11 62.80 58.15 1.11 13.27 2.94 1.11 40.18 0.85 62.78 0.54 - 0.10 5.94 0.85 9.04 0.54 - 0.10 10.38 093 11 46 0 79 - 0.10 125 60 0.93 116.30 0.79 - 0.10 26.54 0.93 5.88 0.79 - 0.10 0.04 0.01 ' 0.01 0.04 0.01 0.01 0.06 0.02 0.01 0.06 0.02 0.01 0.06 0.02 0.01 Severity Weighting Factors 0.013 0.013 0.934 0.020 0.020 Total Weighted Emissions, >ig/mile Dropout Airborne 0.44 0.02 0.44 0.01 0.00 0.00 0.06 0.00 0.07 0.00 0.00 0.00 9.02 0.58 8.45 0.21 0.10 0.01 2.33 0.15 1.84 0.04 0.00 0.00 0.49 0.03 0.10 0.00 0.00 0.00 23.34 1.05 17 60% by weight, the amount of asbestos worn away as friction material wear debris is ~74 million lb. WEIGHTING FACTORS Two series of weighting factors were developed to handle the test vehicle data. D istribution-W eighting Factors - The distribution-weighting factors were calculated from the material recoveries in the shrouded and unshrouded brakes as indicated earlier. Estimates were made for both disc and drum brakes from the test vehicle for the amounts of the different samples dis tributed from the brakes. These estimates were made for the Burnish schedule, for the end of a complete vehicle test, and for the end of all three vehicle tests. For the drum brake, estimates were made for up to 40,000 miles. The factors are given in Table 15. Severity-Weighting Factors - The severity-weigh ting factors were calculated from the percentages of different braking modes: for new versus burnished friction materials, for severe (or abusive) versus moderate braking, and for the renewal of friction surfaces (postfade). The factors are given in Table 16. ASBESTOS EMISSION FOR TEST VEHICLES - The pro gram results were used to develop the following estimates. Per Mile Asbestos Emission - The total asbestos emission for the test vehicle can be estimated from the test results given earlier and the severity-weighting factors. The calculation is summarized in Table 17. The asbestos emissions for the disc brakes, drum brakes, and clutch from each vehicle test were averaged and used with the Burnish, A.B. Baseline, Detroit Traffic, 10 Stop Fade, and A.F. Baseline schedules. The corresponding severity factors were used to calculate the weighted emissions. The sum of the weighted emissions is the total asbestos emission expected from an average vehicle. Distribution - The total asbestos emissions per vehicle, as calculated above, are not merely deposited onto the ground or entirely emitted into the atmosphere. In general, the asbestos emission can and will probably end up in any of three different places: 1. Retained in the brake and/or disposed of during service. 2. Deposited on the ground. 3. Emitted to the atmosphere. The calculation in Table 18 shows that the largest part of the asbestos emission produced is emitted from the brakes and clutch as dropout material. The fate of the total asbestos emission calculated earlier for the test vehicle is shown in Table 19. Table 21 Estimated Emissions Factors for Trucks Friction Material Light Truck Medium Truck (Bus) Front drum brake 2.0 3.0 Rear drum brake 3.0 10.0 Clutch 2.0 4.0 Heavy Truck 5 0 30 0 6.0 Table 19 - Fate of Total Asbestos Emissions from Test Vehicle Fate Percent Road-dropout 81.9 Airborne 3.7 Retained in brake 14.4 Table 20 - Estimated Severity-Weighting Factors for Trucks -- Simulation Test Schedule Weighting Factor Licht truck New materials Moderate braking Moderate braking Abusive braking Surface renewal Medium truck and bus New material Moderate braking Moderate braking Abusive braking Surface renewal Heavy truck New materials Moderate braking Moderate braking Abusive braking Surface renewal Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline 0.013 0.013 0.874 0.050 0.050 0.013 0.013 0.7 74 0.100 0 100 0 01 3 0 01 3 0 674 0 150 0 150 Table 22 - Estimated Asbestos Emission per mile for Trucks Vehicle Light truck Medium truck (or bus) Heavy truck Asbestos Emission. ug/mile 87.51 290.72 951.12 Table 23 - Total Asbestos Emission for Trucks Vehicle Asbestos Emissions. lb Light trucks Medium trucks (or buses) Heavy trucks Total 32,300 16,300 32,900 81.500 Table 24 - Fate of Total Asbestos Emission for Trucks Asbestos Emission. Fate c,'o Road-dropout 87.9 Airborne 2.9 Retained in brake 9 2 18 ASBESTOS EMISSION ESTIMATE FOR ALL VEHICLES The test vehicle results can be extended to all passenger vehicles in the following manner. Passenger Can - The estimated total asbestos emission per year can be calculated from the following information: 1. Total asbestos emission per vehicle is 28.51 /ig/mile. 2. Number of miles per vehicle is 9978. 3. Number of passenger vehicles is 96,400,000. From the above, the estimated asbestos emission in pounds per year: 28.51 MB x 106 i x 9.978 X 103 ------ X 7 7 7 ~ mile-vehicle Mg year 454 g X 96.4 X 106 vehicles 3 60,400 lb per year The distribution of the total asbestos emission calculated for the test vehicle can be determined by applying the percent distributions given earlier. The fate of the 60,400 lb cal culated above for the test vehicle,is shown in Table 19. Trucks and Buses Truck brakes usually tend to operate at higher temperatures than passenger cars. Thus a greater proportion o f high-temperature use in severity weighting can be obtained by using a larger fraction o f the 10 Stop Fade asbestos emission. For trucks and buses, the test results are arbitrarily weighted, as given in Table 20. In addition to the severity factors, it is necessary to estimate the total average asbestos emission for a light truck, a medium truck (or bus), and a heavy truck. The value for the test car was 28.51 Mg/mile. Assuming that trucks have results proportional to the ratios o f the friction material weights, the asbestos emission for trucks are larger than for the test car by the factors shown in Table 21. A slightly larger factor is selected for the clutch as it is used more often in trucks than in passenger cars. The estimates for the total asbestos emission per light truck, medium truck (or bus), and heavy truck were cal culated using the severity and emissions factors given in Tables 20 and 21. These results are shown in Table 22. The total asbestos emission per year for light trucks can be calculated from the following information: 1. Total asbestos emission per vehicle is 87.51 Mg/mile. 2. Number o f miles per vehicle is 9807. 3. Number o f light trucks is 17,100,000. Estimated asbestos emission in pounds per year: 87.51 - ^ - X 106 -*-X 9.807 X i 03 TMi? x J J l _ mile Mg year 454 g X 17.1 X 10^ vehicles 3 32,300 lb per year The estimated value for the total asbestos emission from trucks and buses is shown in Table 23. The distribution-weighting factors for trucks were cal culated based on the following considerations. The truck drum brake is designed to be more open than the car drum brake and in many instances no splash shMds are used. Based on the estimates, that only about 25% as much debris re mains in a truck drum brake as compared with a passenger car drum brake, distribution-weighting factors for trucks were estimated. The distribution of the total asbestos emis sion estimate is shown in Table 24. SUMMARY AND CONCLUSIONS The purpose of this program was to obtain asbestos emis sion data from brakes and clutches for a vehicle during actual operation. Unique emissions collectors for a disc brake, drum brake, and clutch were conceived, designed, built, and in stalled on a vehicle. The vehicle was driven through various test cycles to determine the extent and type of brake emis sions generated at both low and high temperatures. Typical original equipment and aftermarket friction materials for both disc and drum brakes were used in the tests. Brake relines were made to simulate consumer-type practices. The particulates were processed and analyzed by a combination of optical and electron microscopy. Table 25 - Summary of All Brake and Gutch Emissions, pounds per years Vehicle No. of Vehicles Asbestos Emissions Dropout Distribution Airborne Brake Retention Passenger cars Light trucks Medium trucks and buses Heavy trucks Miscellaneous* 96.400,000 17,100,000 2,600,000 60,400 32,300 16,300 1,200,000 32,900 6.615,000 16,300* Totals 158,200 Percent of total 49,470 28,420 14,330 28,920 14,330 135,470 85.6 2,230 940 470 950 470 5,060 3.2 8,700 2,940 1,500 3,030 1,500 17,670 11.2 *Estimated equal to medium trucks as weights of friction material used for both categories are almost equal (Table 12). Includes motorcycles, trailers, etc. 19 The range of asbestos content in the brake emissions for vehicle tests 1 and 2 went from a high of 1.65% to a low of 0.03% for the 90 analyses; only three were above 1.00%. The overall average for vehicle test 1 was 0.40% and for vehicle test 2 was 0.25%. For vehicle test 3, the range of asbestos content was from a high of 0.22% to a low of 0.003% with an overall average of 0.07%. These data are comparable to those obtained in an unpublished dynamometer study (15). In none of the samples tested in this program was a 15% asbestos content found, as reported by Lynch of the U.S. Public Health Service (16). To compare the generation of asbestos emission properly, it was found necessary to calculate the emission factors for each sample in pig/mile. These values were obtained by multiplying the weight of generated brake debris by the appropriate asbestos percent followed by dividing by the miles per test schedule. Thus, either a high-asbestos content or a large sample gave a high factor. The estimates of total emissions and their distribution for the test vehicle were obtained by employing distribution- and severity-weighting factors. These data were then extended to all passenger vehicles and trucks and buses in the United States. The summary of the total asbestos emission estimates and their distribution are given in Table 25. On the average, more than 99.7% of the asbestos is converted. The contribu tion to the atmosphere is 5060 lb, or 3.2% of the total asbestos emission. These estimates are considered to be maxi mum values. The total asbestos emission estimates, and especially the airborne emissions estimate, are considerably lower than the 540,000 lb estimated by IIT Research Institute (12). ACKNOWLEDGMENTS The authors wish to acknowledge the support of the Environmental Protection Agency in this work through Contract No. 68-04-0020. The authors also wish to thank the following for their various contributions; R. D. Stapleton (sample collection and processing); R. M. Rusnak and D. G. Jones (microscopy analyses); P. R. Stewart (fabrication of collectors); H. M. Danbert (vehicle preparation); J. Gulvezan, A. Tomala, and W. R. Kee (rotating seal designs); C. Cowan and H. C. Morton of Bendix Automotive Control Systems Group (information on vehicle testing and friction materials); J. Lindsay (com puter program and processing); C. L. Gray and W. H. Houtman of the Environmental Protection Agency (suggestions made on brake emissions collectors), and J. P. Leineweber and S. Spiel of Johns-Manville Research and Engineering Center (asbestos analyses). Special thanks go to W. M. Spurgeon, Manager of the Materials and Processes Department, for his encouragement and suggestions throughout the program. REFERENCES 1. A. A. Hodgson, " Fibrous Silicates." Lecture Series No. 4, Royal Institute of Chemistry, London, 1965. 2. K. Yada, " Study of Chrysotile Asbestos by a High Reso lution Microscope." Acta Chrystallegraphica, Vol. 23 (1967), p. 704. 3. S. G. Bayer, T. A. Brown, and R. D. Zumwalde, " Equip ment and Procedures for Mounting Millipore Filters and Count ing Asbestos Fibers by Phase Contrast Microscopy." H.E.W. Public Health Service, February 1969. 4. R. E. Heffelfinger, C. W. Melton, and W. M. Henry, "Development of a Rapid Survey Method of Sampling and Analysis for Asbestos in Ambient Air." Interim Report to Na tional Center for Air Pollution Control, July 1970. 5. W. J. Nicholson, A. N. Rohl, and E. F. Ferrand, " Air Pollution in New York City." Presented to Second Interna tional Air Pollution Conference, Washington, D. C., December 1970. 6. J. Murchio, private communication, 1971. 7. J. P. Leineweber, private communication, September 1972. 8. National Highway Traffic Safety and Federal Highway Administration estimates, private communication, Jan. 18, 1973. 9. R. L. Polk & Co., private communication, Jan. 12, 1973. 10. Private communication, January 1973. 11. Private communication, January 1973. 12. C. F. Harwood, "Asbestos Air Pollution Resulting From the Wear of Braking Linings." Illinois Institute oi Technology Research Institute, April 1972. 13. T. C. May and R. W. Lewis, " Mineral Facts and Prob lems: `Asbestos.' " U. S. Bureau of Mines Bulletin 650. 1Q~0 edition. 14. Private communication, January 1973. 15. S. Spiel,dohnS'-Manville-Research-and Engineering, private communication, 1971, 16. J. Lyncq, " Btflkfc Lining Decomposition Products J. Air Poll.Corttrol Assoc., Vol. 18. (J968), No. 12. p " .'i 1973 This paper is subject to revision. Statements and opinions advanced in papers or discussion are (he author s and are his responsibility, not the Society's, however, the paper has Society of Automotive Engineers, Inc. T W O M N N V I V A * I A I A I A A t W V O M H V 1 0 0 0 * been edited by S/tfE'for.upiQirm styling and format. Discussion wul be rwith the paper if tn s 1published m SAC Tnwaciwnt. Eoc permission in this paper in full or in part, contact the SAE Publications Division jr-j authors. 2 0 page booklet. Printed in l S \