Document 659bDmnY2ro7pB0rXVVqDY7p9

FILE NAME Ford FD DATE 0000 DOC FD023 DOCUMENT DESCRIPTION Internal Report - Asbestos Emissions From Brake Dynameter Tests | ASBESTOS EMISSIONS FROM BRAKE | I DYNAMOMETER TESTS by , - . T E. Anderson R. L. Gealer R. C. McCune J. W. Sprys J Scientific Research Staff Ford Motor Company " Dearborn Michigan 48121 SCIENTIFIC RESEARCH STAFF a CO \ ASBESTOS EMISSIONS EMISSIONS FROM BRAKE DYNAMOMETER TESTS by A. E. Anderson R. L. Gealer R. C. McCune J. W. Sprys Scientific Research Staff Ford Motor Company Dearborn Michigan 48121 d ' ABSTRACT Dynamometer tests ofa production disc brake provided new information on asbestos fiber emissions during breakin normal use and high temperature use conditions Both ambient air and brake cooling air were sampled isokinetically using 0.45 ...mfilters Examinatioonf test and background filters required a clarification process to maximize fiber detectability the use of transmission electron microscopy at 40,000 X for detection and electron diffraction for positive identification of asbestos fibers Most of the lining asbestos was - found to be converted to a fibrous material by the high flash temperatures of the braking surface Less than 0.02 of the lining wear was released as asbestos fibers The concentration of asbestos fibers in the urban atmosphere due to brake usage was conservatively estimated at less than 0.07 x 10 grams per cubic meter Based on this bound the use of brakes was judged to be not significant as a source of atmospheric asbestos i INTRODUCTION Asbestos has been a major constituent of automotive friction materials more than 50 years It . heat resitance and heat resistance to a brake lining used to impart strength and to enhance friction and flexibility wear proper- ties Most present brake linings use resin or rubber binders and chrysotile asbestos together with organi and inorganic friction modifiers and fillers _ The asbestos content varies with formulation from a low of 25 to about 65 by weight Minimum asbestos levels are found in some high performance * European disc brake linings which are highly filled with metals and inorganic constituents Brake linings in the U. S. average about 50 asbestos content tons S. Of a total U. . 25 Mkg annual asbestos consumption , 730 of 800,000 Mkg about 28,000 tons chrysotile asbestos are purchased annually for friction materials of all types 1 Of , consumes about 12,000 this it has been calculated that brake lining wear 11 Mkg tons asbestos per year Roughly an equal amount remains on brake shoes at the time of replacement or is manufacturing wastage Recent tests have shown that densely populated urban atmospheres often contain significantly higher asbestos concentrations than surrounding areas ; 2 Background asbestos levels in the atmosphere result from the 1 natural weathering of asbestos rock and soil as well as from mining ; farming and excavating commercial and industrial commercial and industrial The generally higher urban sources lining Brake lining and concentrations suggest facing clutch facing wear was suggested by Thomson 3 as a possible source for higher asbestos levels in the urban atmosphere Lynch 4 in a study undertaken by the Public Health Service reported the findings of several brake dynamometer and friction machine tests in which wear debris was trapped on a filter and subsequently examined by means a transmission electron microscope TEM He concluded 1 * free lining that fibers from brake wear seem to be an inconsequential health factor in urban air pollution Lynch detected no free fiber from an automobile clutch and a bus drum brake J but some free fibers were found in one test of an experimental disc brake ft With mounting concern over air quality in general and asbestos pollution in particular this study was initiated in 1970 to provide additional data on the asbestos emissions from disc brakes OBSERVATIONS OF LINING WEAR The near absence of free asbestos fiber from lining wear has been by using reported Luxon 5 ray diffraction and by Lynch 4 using the TEM transmission electron microscope Several authors have suggested that interfacial temperatures during braking could be high enough to decompose the chrysotile asbestos into fibrous thermal degradation products Ana- lytical relationships exist which permit calculation of interfacial tempera- ts ts 6 However several of the significant parameters are difficult to determine accurately for heterogeneous materials such as brake linings The bundles asbestos crudes larger fiber were calculated to reach their rapid . decomposition decomposition temperature during normal braking braking at speeds above 56 MPH as above 25 m an upper bound value and 18 MPH 8 s as a lower bound value An experimental approach was undertaken to provide closer bounds into Added insight the thermal decomposition of asbestos fibers in brake lining wear was attempted by process A small laboratory friction shock resistant Vycoy glass rubbing direct visualization of the frictional test machine was constructed using a thermal surface replacing the conventional cast iron in which the friction interface was directly viewed binocular microscope microscope 7 Scaled rubbing velocities were the thermophysical property differences between the glass with a low power 7-50 used to compensate for and cast iron Moderate scaled velocitics roughly equivalent to 12 MPH 5 / provided a view of initial burnishing intermittently incandescent operation resinous material asbestos crudes surrounding these During the asbestos crude was observed ; i products around the to pyrolize producing microbeads + " crude These organic products of of condensation resin degradation and tne apparently powdered asbestos decomposition products were seen to smear into platelets often of such size as to be discernible to the unaided eye At higher rubbing velocities over 30 MPH or 13 / ) the platelets formed a surface char layer under the action of more severe thermal and mechanical action ; The larger asbestos crudes then could be seen to glow } with apparent depth and for greater time durations often several seconds | The actual brake lining contact arca was only a few percent of the total 4 available surface with contact spots moving in a random manner with time Froin these friction visualization studies it appeared that local flash temperatures and severe mechanical action could be major factors in the breakdown of asbestos ribers for most brake usage Examination of the lining surfaces revealed the presence of fibrous magnesium silicate both crystalline Forsterite and amorphous phases Magnesium silicate is a thermal degradation product of chrysotile asbestos { Forsterite transformations have been reported to occur at 600 over period of hours Differential thermal analysis DTA studies in our laboratory indicated this transformation occurs within seconds at 820 ; : Special brake lining formulations were then prepared and tested on the glass visualization apparatus and a Friction Assessment and Screening Test FAST machine friction interface which Chemical reactions were found to would require a flash temperature take rise place at of 740 the to initiate when an equivalent of 35 MPH 16 m rubbing speed was used on the FAST machine At this same speed melting of inorganic lining additives and _, metal particles confirmed brake flash temperatures up to 980 . Based on these findings it would not appear surprising for few asbestos fibers to be emitted from brakes in normal usage However some during several mechanical removal of fiber appeared possible during the first first several brake applications with new linings ' + Also high brake temperatures possibly weaken organic the binders and cause increased fiber emissions could TEST PROCEDURES Complete sample collection and examination procedures along with sample data calculations are included as Appendixes I II and III Briefly the tests were performed as follows a new Pinto disc brake assembly was installed on a single station brake dynamometer in a room which was cleaned of extraneous asbestos sources Air from within the room was blown through a diffuser screen to provide a velocity distribution over the brake which ; i 1 : approximated that of vehicle usage The air stream in front of and behind the brake was sampled isokinetically using matched 0.45 ...m filters holders and air pumps Note the system schematic in Figure 1 and the actual test setup in Figure 2. | The brake exhaust air was discharged out of the building The first pair of filters were used during the first 82 burnish stops to represent Breakin conditions After further burnishing a second pair of filters collected samples during 560 t A third set of filters then were utilized in normal a high use brake applications temperature use test of 41 brake stops All brake applications were made from a 40 MPH 18 m equivalent speed Breakin and normal use tests employed brake torques corresponding to quarter gg 4.9 sdeceleration This torque level was doubled for the high temperature tests During the normal use procedure the test filter was located for 20 brake applications at each of 28 insure a representative grid locations in the exhaust duct throat 6 of the air flow over the brake This test to grid and filter may be seen in Figure 3 s \ A central collection site in the test grid was used for the breakin test and the final high temperature test Samples of the three pairs of filters breakin normal use and high temperature use were subjected to a clarification process involving low a temperature ashing to oxidize all organic material and mechanical action to it ... separate the particles This assures maximum detectability of asbestos fiber 2 RESULTS AND DISCUSSION Transmission electron microscopy at 40,000 magnification was used in the search for fibers At this magnification the ultimate fibrils appear to be above one millimeter 0.040 inch in diameter Quantity length and apparent calculation diameter measurements provided data for of asbestos fiber mass per unit of filter area Coupled with dimension mass and flow determinations from the dynamometer tests this data was used to calculate the emitted asbestos fiber concentration in the collected wear dust in the cooling air stream and from the brake lining worn The size distribution of collected fibers was not determined by this method since the clarification process involved sufficient mechanical action to reduce fiber bundles to the ultimate fibril size Additional Samples of the normal use test filters were examined on the TEM without recourse to the clarification process in an effort to determine the asbestos fiber size distribution Roughly 10 of the asbestos fiber was visible on the background sample based on the results from corres- ' ponding samples after clarification The largest observed fiber bundle was 0.20 km in diameter and over 1.1 um long > A similar direct TEM search of the normal use test filter revealed about % of the asbestos fibers observed after clarification percentage This reduced of visible fiber was attributed greater concentration of obscuring matter in the test filter However observed 0.13 largest asbestos fiber in the test filter 0.13 ...m in diameter to the the and over 1.2 mlong was about the same size as was found on the background background sample sample -6 , The similar Lo a fiber size low fiber . content \ of both backgrouanndd test filters distribution estimate However it appeared that the precluded quantity of the larger asbestos fibers on the test filter was no greater than that of the background filter This supports the observation from the lining wear visualization tests normal that brake wear degrades most of the asbestos fibers A brake lining grade of asbestos appears on the TEM as in Figure 4 The fiber bundles are composed of strong but weakly adhering fibrils of about 0.03 ...mroughly 1 microinch diamete Mechanical action causes the larger fibers to open into smaller fibers or even fibrils as illustrated in Figure 5 Contrast these raw material fibers with one of the larger fibers Figure 6 and one of the more typical fibrils Figure 7 from the normal use test filter 4 The similar low fiber content of both background and test filters required accurate clarification to permit an asbestos fiber count thus providing more fiber mass determination but obscuring the actual fiber size distribu- tion Therefore the calculations of fiber concentration Table 1 were expressed as asbestos mass per unit mass of lining wear dust and asbestos mass per unit mass of lining worn Asbestos fiber concentration in the ambient air background ) and ir the brake exhaust test was calculated in units of nanograms 10-9 grams per meter of air However the actual asbestos emissions from brake usage would be diluted substantially through mixing The asbestos concentration in urban air due to usage was estimated based upon existing automotive exhaust lead dilution data These calculations appear in Appendix III All the test results in Table 1 have been reported as ten times the " calculated test values to allow for possible losses in collection processing and counting These values therefore should provide upper bounds for asbestos emissions brake usage For example the local Detroit Michigan atmospheric ; asbestos concentration ranges from 0.5 to 13. nanograms per cubic meter The \ _ observed background asbestos value was 1.0 mfor the normal use test but . the is reported in Table 1 as 19 mThe low asbestos emissions . " test disc brake under normal use conditions is underscored by from 5 the addition of but 13 1 m1.3 mobserved in the undiluted exhaust air stream ' t a 1 TABLE 1 a ASPESTOS EMISSTONS FROM NORMAL USE BRAKING Dynamometer Data for a Production Disc Brake - Background Asbestos in Ambient Air Asbestos Fiber from Brake in Exhaust Air - Total Asbestos Fiber in Exhaust Air Estimated Brake Asbestos Fiber in Urban Air . Asbestos Fiber from Brake in Airborn Wear 19 x 10 m 13 x 10 m 32 x 109 m 0.07 x 10 m Dust ; 0.05 Asbestos Fiber Released from Lining Wear 0.02 * Reported values are times the observed test values to provide upper bounds } i first The lining wear rate during the 82 breakin stops was found to be about five times above the normal use rate Asbestos fiber release during breakin was also higher an average sevenfold the breakin wear is less than % of the total lining increase wear the However since increase of emitted asbestos fiber resulting from this temporary sevenfold be about % when averaged over the life of the linings increase would temperature High brake usage also increased lining wear rates in this case by a factor of eleven Asbestos fiber emissions increased by less then a factor of three Frequent vehicle operation under such high temperature -8- \ Conditions would lower lining life to levels far below present averages However even : if all brake wear provided the ; same fiber emission rate as _ found in the high temperature use test the percentage fiber release to the di atmosphere would still be under 0.06 of the lining wear . aa| remaining 1 The remaining brake wear was a mixture of fibrous organic and \ inorganic matter Forty percent of the estimated 62 to 77 collectable wear debris were accounted for by the test filter on the normal use test The remaining 15 to 30 presumably were retained on the lining edges the caliper spindle rotor wheel and tire Accurate measurement of this material was not due to the retention of dust from the ambient air possible added | More precise values of brake lining asbestos emissions or the particle determination of their i I size distributions appear possible for these low fiber concentrations only by testing brakes in an asbestos free atmosphere This approach was used in an EPA sponsored study 9 where filtered air was flowed through sealed brakes at a flow rate greatly reduced from normal CONCLUSIONS ' 1. . Automotive brake usage provides t a very small emission of asbestos fiber , less than 0.02 of the lining worn oe } rer 2 Automotive brake provides a very small asbestos fiber input to urban atmospheres estimated to be below 0.07 m , " a 3 Intense local heating and severe local mechanical action causes the decom- | et position of most asbestos fiber in brake linings during typical usage -10- SAMPLE FILTER PREPARATION Microporous membrane filters with 0.45 mpores were selected to assure high retention of asbestos fibrils and most of the wear dust powders A matched pair of Gelman sampling pumps and 35 mm diameter holders were used | Thin metal cones of 12 included angle were fabricated and sealed to the filter entrance These cones increased the tip entrance velocity to that of the exhaust air duct so isokinetic sampling could be achieved The cone tips were carefully matched in size Flowmeters and differential pressure indicators were installed in the system to monitor the filter airflow during each test 1 and to set the tip entrance velocity before each test Tests were performed on the unused filters to determine their weight change with variatioonf humidity. Filter weights were measured on a microbalance to the nearest 10 micrograms Filters were placed in the center of the designated exhaust duct grid and at a fixed position upstream of the brake but below the diffuser screen This latter ( background filter was the located where upstream air velocity equalled the average over the test grid In this way the sampling was isokinetic with essentially equal volume flows through both ) filters TEST PROCEDURE All brake stops were conducted from the same speed equivalent 40 MPH or 18 m to maintain fixed air flow conditions Burnish and normal use brake applications were at 0.25 g 2.45 sdeceleration and with a two minute time interval provided a peak rotor temperature - of 180 350 The number of brake applications were selected to provide about one gram of lining wear per test Breakin wear was monitored for the first 2 stops No sampling was performed for about 200 more brake applications while the linings and rotor developed essentially steady conditions -11- \ The normal use test was then performed on this burnished brake assembly Twenty brake applications were made under the same conditions with the test filter located sequentially at each of the twenty grid J ' locations The filter cone entrance velocity was adjusted match the grid velocity at each relocation . Four grids were used to monitor exhaust velocity _ Slight adjustments were sometimes required to compensate for drift which appeared to be external wind initiated A third test was performed to provide an estimate of the fiber emissions from a hot brake assembly As in the breakin test the test filter was positioned in central location for this procedure Thirty stops were made 0.5 g 4.9 sand minimal time interval until the rotor attained 410 770 This temperatuwraes then maintained by adjusting the application time interval Ten additional stops were made as the brake was allowed to cool All filter weight determinations were performed at equilibrium conditions and then corrected for humidity After use the filters were individually stored in covered glass containers Lining weights were taken after removal of wear debris but before they had cooled completely to minimize weight changes from water absorption stored in a dry jar Between tests the linings were The relevant test data are included in the following table A slight pad drag caused the outboard lining to wear above expectations on the normal use test Since this added work was not included in the lining wear rate calculations the specific wear is above the usual range for this lining on No adverse effect the test results would be expected to have resulted from this drag Similar pad drag effects may occur on cars when smooth road i conditions prevent pad knockback" Test Brake Speed RPM Brake Decel g ) Wheel Load kg Brake Applications Total Energy kW Max Apply Temp C Total Lining Wear g Lining Wear Rate kW Breakin 535 40 MPH 0.25 2.45 s 257 567 lb 82 0.938 1.25 hp 115 240 1.10 in 1.17 0.051 hp Normal Une Hi Temperature Use 535 40 MPH 535 40 MPH 0.25 2.45 s 0.50 4.9 s 257 567 lb 257 567 lb 560 41 6.405 8.54 hr 0.469 0.625 hp 115 240 410 770 1.60 1.07 0.25 0.25 in in 0.011 hr 2.28 2.28 in 0.100 0.100 ) hp _ -13- t SAMPL^ EXAMINATION APPENDIX II | PREPARATION AND EXAMINATION OF ASBESTOS CARRYING SAMPLES FROM TEST FILTERS - t 1 i All slides dishes scalpels and other utensils used in the following : acetone acetone preparations were cleaned in preartions followed by rinse in 200 proof ethanol 2. An area of measured dimension was selected at random from the test filter cut and placed particle side down on a clean glass slide Several drops of acetone were placed on the filter segment to partially dissolve and secure it to the plate The samples were ashed for a period of two hours by using a low temperature asher at a chamber pressure of 0.5 torr 70 Pa oxygen and power of 200 watts Several drops of a % solution of cellulose in amyl acetate were - placed on the residue and a clean watch glass was used to grind the mixture for a period of five minutes A second clean glass lide was then placed over the mixture of cellulose and residue and a smear obtained by pressing the two slides together and then sliding them apart The films thus formed were permitted to dry and then removed by scoring the edge of the slide with a scalpel and floating the film free from the slide in @ distilled water bath It was found that the film was most easily removed from the slide introduced in Step 6 Sample preparation techniques outlined below are reported by Selikoff et al in Reference 2 similar to those i 114- 8 Approximately electron microscone grids 3 mm finder grids were placed at random on the floating film and the film was lifted by putting a clean slide on top of the film and drawing the slide down through , ' the water so as to trap the grids between the slide and the film which F scould now cling to the slide ) J t approximately 9 A carbon layer of 0.06 ...mwas deposited on the film to prevent charging during examination in the transmission electron microscope TEMTEM Direct examination specimens were prepared by depositing a carbon layer on the dust side of the test filter and dissolving the filter in acetone Electron microscope grids were used both to support the sample and to provide grid location reference marks TEM EXAMINATION AND COUNTING PROCEDURES . Aproximately Approximately ten electron microscope grids were prepared for each of the five filter samples analyzed Four grids were arbitrarily selected from each sample and two grid squares on each grid were scanned for asbestos aw The individual grid squares are approximately 90 ...mon each side and were examined at a TEM magnification of about 40,000 For each grid area scanned photographs were taken where possible of the ( . chosen fibril for the purpose of determining first last and one randomly an average fibril diameter accurately j . Measurements were then made visually that is each fibril fiber or asbestos bundle was compared to known calibration marks on the electron microscope screen to estimate the lengths The length could be estimated to within 20 as determined by the photographic measurements The marks on the screen ore 0.5 cm apart corresponding to 0.125 um when a magnification of 40,000 is used This and was approach furthermore taken because it was impractical to photograph all the fibrils length measurements were not as critical as diameter measure- ments determining fiber volume Where both measurement methods were used the values providing the greatest indicated brake asbestos levels were chosen providing greatest The results are shown in the following table Sample ) 3 C D E F = ASBESTOS CONCENTRATION ON FILTERS Sample Identification : normal stop brakes Concentration ng cmof filter 15.32 Background for A ' normal burnished brakes " 1.06 7.98 Backgrounfodr C , 4.04 high temperature temperature burnished brakes 5.37 Background for E - not used insufficient sample Blank - unused filter 0.33 From photographic measurements of 120 chrysotile fibrils the asbestos fibril average diemeler was determined to be 0.0337 um with distributions similar to that observed by other workers 10 From 45 fibrils of triple jet- milled chrysotile the average diameter was determined to be 0.0316 ...mwith 1 standard deviation of 0.0063 ...m ASBESTOS IDENTIFICATION Asbestos can be identified in the transmission electron microscope . in one Such a of two ways 4 The first and absolute method is diffraction pattern is presented as Figure 8 by electron Measurement diffraction of diameters and correlation of these measurements with a known standard gives the interclanar spacings of the material Comparison of these spacings with the ASTM file identifies the material as chrysotile asbestos The second method of identification is by appearance Figure 9a represents an image of asbestos obtained in the TEM Fine lamellae are observed within the fibril which are parallel to the long axis This appearance is characteristic of chrysotile asbestos fibrils Because of the nature of the _ electron beam radiation and heat damage can occur in the material markedly