Document Yr0wE4MK2GjxE17yKo5nG5rD8

FILE NAME: Z< DATE: : DOC#: Z< DOCUMENT DESCRIPTION hZWZ tE> SOCIETXi PAP_ PREPRINT: Subject to revision. Per. !!!!!!!!!!!!!!!!!!!!~~========~!Ii!!:!:1 mission to puWisll fIlis paper. in full or in 14. part. aftw ifs ".......afion .nd with credit to .... euthw _ 'ihe Society may .. ob- Nq...... faiMCI upon Th. Society is not re- sponsible far .......... flit opinions acIv.ncecf in pa- pers or cliseuaions .t its IlAeetfftCJL /}' C; C Cc SS e -- $/"lcf~"'I!J.~~+6I11\t.... "'6 11", "";5 WHAT'S NEW IN BRAKE LININGS NEWn.1 R. Mc CUEN Chevrolet Fi"lg"lne Dept. Chevrolet Motor DiV. General Motors Corp. " .... ~ .....--~..... ..: : .I' '.. . ~i"' .'.!'.' ~ ~ i'11 For presentation at the SAE ANNUAL MEETING Sheraton-CadilIac &Statler Hotels D~Lroit, Michigan January 12-16, 1959 Writte!" discussion of this paper will be accepted by SAE until Feb. 16, 1959. Three double-spaced copies are appreciated. SOCieTY of AUTOMOTIVE ENGINEERS,Inc., 485 Lexington Avenue,New York 17, N. Y. What's new in brake Iinings_1959_substitutes.max WHAT'S IffltI IN BRAKE LIDNGS INTROIlJCTION The dp.velop~ent of brake linings capable of meeting all the requirements of the progr~ssi're American passenger cars is one or the most pressing problems otautomotive e~in~ering. Great effort is expended annually by the automobile industry to develop the most eI'fective braking SY8 "erns PQssible. It is in the development or improved linings that perhaps the greatest effort is being .ade. Ml1lion:s ot dollars are spent on expp.rimental engineering, and millions of miles of brakes tests are made each year to pr~tuce efficient. dependablp. brRKe linins. Th-are are numerous brake designs currently being carried on in the industry, hoth he!"E' and abroad. These engineering deSigns cover disc type, band type, water-cooled and oil-immersed brake systems. However, regardless of the brake des1gn under discussion. a review of friction materials tod~ is essentially a studr ot two linings -- tne o-ganic type and the metal1ic type. It is the intention ot this paper, therefore, t:> :-e'~trict its sUCJect matter to thl:!Be two baaic lining matenala. Tc be .'lcceptable to the automobile manUacturers~ present day linings must have the r.,] :'CWi.1g characteristics; Wearing abUitz. Without sacrificing any other attributes~ a hrlkE" lining !!JUst have a low wear rate. 2. MLAimal friction variations. Brake linings must have a high ~~~!ficient of friction that is equal at all four wheels and c('):'}sistent -:In all cars to prevent pull, "~l'aubinea:s" or other ~r~atic braking ~onditions. 3. ~~i~tance to hiah temperat.ure and fading. Lining!" n11l!'4t he ca;)able of withstanding and dissipating heat to prevent brake fade, which is 8 temporary reduction of brake effectiveness rp.~llting from heat, and linin~s muet have adequate mechanical strength through all operating temperatures. 4. L~'ing surface must ne com,gatible with mating surfaee to prevent galling, excessive wear or heat checktng or the drume. S. Consistency or performance in all braking slstellU5. The majority or cars are still equipped with unassisted braking systems. 'nlere~()re~ brake linings must engage smoothly with low effort and opera~e effectively with bot.h standard and power brakes. ~. '~ietness or operation. Quietly operating brakes are an important ccmfort factor in passenger cars, therefore. lining and drum engagement sounds must stay below the audible level. 7- Lcw cost. In this era of cost-conscious engtneering, it is eSsential that the expenditures fer brake lining fabri~ation and warrantY' sErvtclng be (;Ulltrolled. What's new in brake Iinings_1959_substitutes.max - 2- 'rh' '~o!l"potmding of friction materials that successfully meet all these requiremer.ts is the specialty of some of the anonymous heroes of the automotive industry. The uninitiated might think that, with a st,ahle brake design and evaluation reduced to simple terms, the friction material compounder's job would be routine. This is far "rom th~ case. The many influences on brake performance, resulting from variations in vehicle wei&ht~7 climates, road conditions, vehicle equipment and driving habits, ~ake the engineering of brake lining friction materials a most challenging assif~ment, and a highly secretive operation. The formula of a brake lining i~ the well-.ruareed sec-ret of the supplier, 'While other brake components are used cOJl'l'l!only thr,u~h(ut the industl'j". BASIC DRUM AND SFOE BRAKE D~IGNS For purposes of clarity, all data presented herein applies to a drum and shoe orake 0 0 ' thf' duo-servo type. (Fig. 1) The two other drum and shoe brake de- s1.gat; g"nera _ly c~lIIployed are the two 1 eadim: shoe type and two trailing shoe type. (Fi'5.:'} 1'h~re .s also a one leading one trailing shoe type in general use -which is not gho~. JRGANIC 3RAKE LI~ Al_ Am~rican passenger cars use organic brake linings. There are two o~ganic :iniigs ~ich are Classified by their method of fabrication. Organic drY miX "is hasinlly a gray-white ~o!!!pound of asbestos, filler I!'.aterials and powdered ~esi~s w.hi~r. is :horoughly mixed, preformed to shape, and placed under heat and' pre5su;~ untL. i: for!'!a eo hard, sutQ-likp. hoard. Then it is cut and bent into in- di~.riiual arc:late segments and attached to the shoe. . Organi: wet mix is a compound of asbestos, organic fillers and liquid resins tha~ h&s a sray-brown eolor when blended. The compound lS prOCe5t1ed b:r any of severa~ ~ifferent methods WhiCh include high pressure extruding, screw extruding, ca:endering and Jther processes. Figure 2 shows a step in the high pressure extruding process. The extruded lining 1s being removed f"rom :1 die that hag f'ormed it in~c a long slab that will be compressed to a unifortl! density under heat and pressure. JIgani= dningo are generally rom'posed of s-ix basfe ingredients. Asbestos, Wit~ its high heat resistance and high coefficient of friction in contact with iron and stee~. :s the basic material. Friction modifiers, such as the oil of the cashew nut shell, give lining~ desired ::-1., tior: qualities. F~:lers are a wide variety ot mat~rlalB, ~uch ao rubber scrap7 which RTe added tc :i.'"!ings to) control noise, wear or other brake characteristics. 01.ri..g agent~ and/or 3ccel.erators Rrp. added to a linin~ compound to produ/~' ~ecuir"'d ~l- errrical reactions in the ingredients. M~teria]~ for special efects are added to compounds to improve overall ~r-'ii<":!'ll! ::>eT'cr!!!t',nee. They in~lude powdered lead, brass chips and aluJl'Iinum power3. 3~nders, whi~h a~e predominantlY phenolic resins. hold all the other insr~c~en~s tgetrer ar.d are se:ected t~ govern the plly~ical otrength of the material at r:J..,?r ':el':')era'ures. What's new in brake linings_1959_substitutes.max -J- organic o~ake l1nings have ~~v~ral di~tinct and important characteri~iea, regardless O~ ~Olo" they are ~ompounded: I'hE:' f:~bl"i~a.ting ~ost is lOll m g~np.'r;;al. ..~ ~ A tigh initial f:oiction is inherent with organic linings, alcng wit.'l a light pedal effort which hardens With usage. .3. 'ThE'Y' vary only s'Lightly in effectiveness with speed tJ.. Th~'Y show a mOderate chang~ in ef'f'ectivenesB with temperature. )r~anics do not have a build-up at end of stops. -" They protect themselves !rom heat damage by fading at ~ i~'h temperatures. 7 :)r~anic linings do not require extremely smooth lining facing ,r d~lm finishes (60-150 micro-inch range permissible an i!"'t. ms) ~ but organic suri"aces are sensitive to moisture and -:ortarr.inants. METALLIC BRAr:E LININGS TI.e ::lthe!" lining compound under wide development is the sintered lIletallic type. ~tal' i'~ 1inings represent the !'lost important new development in brake lining. Me~allic linings are composed at finely powdered iron or copper, graphite and lesser a"lount s .:>f' inorganic fillers and friction modifiers. Tb> drJ powders are accurately we1.ghed, placed 10 a sUter in a specific order, and m-:xed in a tumbling cone type blender for 30 to 50 minutes. A lubricating oil is added to prevent segregation of the individual ingredients which are of di!- reren~ 5i~e~ and denoitie~. 'lbR powders are then put through a briquetting process in which the backing ~nrl frtc~ion material poWders are compressed between a punch and a stripper to form the lining. In the first step, the stripper is lowered slightly and the powder tba t forms the bClck1ilg of the lining is poured into a cavity as shown in the schem- atic drawing in F'1.gure 3. The stripper is lowered again and the lining facing or powder is pOllred into the cavity. Then the powders are cO!IIpacted under high prea- aures. During the briquetting stroke the two layers powder are pressed into an integral lmU with green strength. The briquettes then are automatically conve;yed lnto a furnace a.nd :5intereci in temperaturos well over 11 lOOODF. The furnace cr@ateg exothermic a'tmosphere generated from 1000 BTU natural gas that protects linings from oxidation. :'his heat treatment forms sintered bonds between particles that give linings gT"FUI- sb"ength and durabil1ty The manutacture of metallic linings is highly autom~tic. a fact that will lead to more competitive priCing aa production . increases. 21 . ... w ... C_. ,sw. . 'I 4C5 ;u ;;:0$ 4PP.@ ,.';S , Jj ..<. i ......~ ._ pt . . . . . . . j QC t. Q What's new in brake Iinings_1959_substitutes.max -4- ?resen~ ~ay metallic linL~gs have several distinct and important char- act e-:-ist::..c s : In ccmparison with organic linings. the metallics are relatively hi~:h cost. At present the cost factor is one reason the applicati(>n :)f metallic linings is restricted to the "heat-problem" brcll:e:: ~etallic linings have a low initial friction, and a resultant hard pec~l that lightans with usage. They have reduced effectiveness at low speeds and temperatures. '.. :'hey <ire extremely heat and fade resistant. :)n':'y s:ight roughness is detectable at high speeds with metallics. !-1etill:ics are not affected by wetness. ? ~hF.'J do require D. smooth facing grind and drum finish. The metallic :::"in:.ng brake drum has a mirror-like finish with a uniformity of surfact~ that is required to assure stability of braking. ~~ cOMpcunder must select the exact combination of ingredients from ' :lUndred~ c~ p"5sitilities to pr?duce linings that have all the required characteristi~s. His <:UCCf-SS i:: rr.easured by the manner in which his linings stann up under A battery et' :'t!!ts. - LABORATORY mTING JF BRAKE LININGS To <ornplete the comparison of organic and metallic linings, it is necessar,r to evaluate the performance characteristics of both types as established by the wide range ~f laboratory and road tests heing ~onductQd by the automotive indu~tr.r. Laboratory testi~g provides fast, low-cost evaluation of the wide range of linings developed annual 17. Over l$OO compounds of various metallic combinations already have been developed by Jne manufacturer and organic lininl!: compounds run i.nto the thousands. The :hase machine shown in Fig. h is invaluable in quickly comparing :fric-' tion material:: for d~rability, wear, and the effects of temperature on :friction and wear chAracteristi!s. The Cha~e machine consists ot a heav,r iron brake drum that Is rotated by a v5ria~le speed motor and magnetic clutch assembly. A speci~en of f~c tion material Ls hl~ld against the drum by dead weights. Instruments record all test results. ':,e 'urVE-S in Fig. 5 indicate the basic differences between metallic and .- organic liningn throughout their rise in temperatures caused by their own friction . plus external ~eat applied to the drum within the Chase machine. The friction co-ordinate is showr~ at left, drum temperatul"e at the right and time at the bottom of the. chart. The 0r~anic lining curve shows some increase in friction up to about 850 0 and t.hml a !"llpi:l C:.d~ :ut. The metd::'lll: I1n!ng curve lndicates a constant. lower friction that L~cr~ases at high temperatures~ Metallic lining drum temperature goes highe~ than ~h.c )r~anic. ~ma~o~eT.er~ of the type in Fig. 6 provide an excellent evaluation of a hrake on an ac~~Lp.~~ted laboratory schedule of tests including effectiveness, fade, ~cover-;f, il.:rai-ility. dI"'lm score and odor. The dyr.amometer dupli('ates the energy lJad of th~ 3u~,moril~. What's new in brake Iinings_1959_substitutes.max ~n: r ::'inings that prove worthy in the laboratory receive further testing. ROAD 're3TING JF 21.4 KR ::.rNINGS As is t~e of all automotive development, the vehicle itself must produce t.he !'inai veri;~ication of laboratory brake findings. Large fleets of vehicles and numerous eng~neering personnel are conttnually engaged in brokg dev@lopmAnt and test- ing opera~ions (Fig. 7). Tests of ever" type of Chevrolet brakes totaled 1,ryBo.ooo miles fro~ O~tnber :957 tc October 1955. ~h,- :"esul-:.s o~ brake road tests described herein apply to organic lining bonded tr_ -:h' st.:e5. as ~=,n~ra~ted to the riveted type, both of Which are shown in !i'ig. :": .. -:'ef ts ':-n metallic linings apply to the type shown in Fig. 9. with the ln~g rivet~ tc the shoes in segments. The metallic segments on the shoe are flexible i!"l t~e!.:- ap~li:::ation in that they can be varied in number, position on Rhoe or 'lIatet"ial !',)l""1Ula to produce the braking effort desir~. Th" ultimate str.lcture of all linings is determined by test. A brake ~Jnlng mater~al that has progressed from laboratory to road testing first undergoes a "genera: !'~el" test. Brake development engineers try the facings for an overall itnpr.,,,::! i ~'n I!' tile findings are good, an effectiveness test is made. The 50 and 80 'TIpr :''C'ai{J? :ie'~el-e7"'at1on test results shown in Fig. lQ depict the effectiveness of high speer. el'lerge:lCY atops With organiC and metallic llningl:l. '!'hie t~st requirA!'J the use of a load ap?licitor, decelerometer and reCording unit. Load is applied to the brake peca: aut~matica~ly and the recording unit indicates pedal load, deceleration, pedal travel and t line ':"equ:lred Lo make te;::,t stops. Th@ 50 and 80 mph brake deceleration cu~es show tee ~rake effectiveness of the organic and metallic linings. The rate of load app:icati~n on the brake pedal to obtain the curves is 30 pounds per second and each ::urre :;~prc"ents ::a. singlf' l'Itcp. The curres reveal that the organic material is less speed sensitive and more effective in this te5t. It should be POinted out that the metallic' lir;ing curves are those in which the brakes were cool at the start ot th~ ~~op. ror the organic lining, the pedal load required at a deceleration rate of 2;J feet per seccr!!i per second from 50 mpll is 50 pounus, and from 80 mph ia 118 pmmds. Under the Snme :onditions for metallic lining, the pedal load from 50 mph is 103 pounds, ,md f:")!l ,3'~ rnph is 165 pounds. I-: Lirings perform well in the effectiveness test, they are subjected to th~ fade ted. The chart in Fig. 11 illustrates a brake fade test comparison o~ organi~' cud r.!talJ ic linings. :"inA pressure is indicated by the co-ordinate at the left and st,)P nt;mbers at the bottom of the chart. The stops were lIade from 60 1I1}:h at :5 feet !)er :econd per second deceleration. The i.1'lterval between i"ade stops was L-t~nths ~f a ~:le. or about ~O seconds. Initial feel and recover,y stops were made. f'rr:ll!l i.lC mph &t f-, feet per second per second at one m1le InLerval~. The organiC CUrft stows a sli~btl:r dec!"easing initial to final line pressure during the first three sto~s ~th ~ach successive stop becoming harder. This is indicated by the shaded d:s-:'ancp between the broken and ljolid line eurves. ily' the J,th stop the line pressure u!c~ease~ pr~gr~seively during each stop and the pedal becomes harder. ay the 7th stop, :l!1e ~!""esm~e i.s ov~r 800 psi and fade continues with each stop. Recovery is 5:'QW dll\l r":qui:::-e3 --. 'lIilas to l~vp.l out to r.nthin 20 pounds per aquare inch of the lnitia:. ite toh-=: "1etallic lir.ing curves indicate) the line pressure increaSe5 only ,0 ),,~, pounds ;e!' s::/uare inch during entire test. The line pressure decreases during <;!~c~ ;t'!"(:P i... t.r. :"e~o"ery being required. Tests such as this shoW' the need for ~-sani2 :~:ing~ that ~ave less heat build-up and, thereby. le~3 fade. Therefore, - - .",i ..!NJiMi4ifl. ~~.~~ ~~...._~. i? iif4i' : .., 'NI'.. ...r1!SP:x"owt .oW ~~...*,!W; i~'.,.!IQL ...JiPSs.: '4 IQ .'9:..;~~!'#J:" i What's new in brake Iinings_1959_substitutes.max " so~e ~rgar.i~ ;ini~gs are being grooved down the middle to ventilate the lining and Titiglte ~he ,eat problem. GroovL~ of the linings also reduces heat spotting of the drum. In addition lining areas are betng increased, because for a given rate or veh~c:e oraki~, the pressure per square inch of lining area decreases as total area :'nc:-e!iises. ar-l he~t r:oncentration is reduced. Following the fade test, the brake linings are checked for general durabl:.ity. This b accompli:!hed by installing linings on vp.hi.c1.es scheduled for the 25.0C:J "IIile riurabil:.ty run. Consistency of effectiveness is observed during periodic st3PS whi~h -c~ut about every two miles throughout the 25,000 mile run. Concurrently With the tests described, linings are subjected to a steam !"com humiiit:, test, wet brake tests, grade parking checks and others. :n addi ti)~ to the many standard tests for brak~lj, the urake development '3ng~eers "ora'.lc'!; ,"any special tests to collect performance data. Dnt:" .J th'e mo:;t comp:-ehensivc and r9v9aling special tests of organic and ~eta:lic ~ra~e linings was conducted recent~ on a lOCO mile police vehicle schedule .: Fig. 12; C:-. th~ chart, line pressure is sholr.l at left. and the 5th and 12th stop -!lnd slowdown o~ E-ach t.e!'lt cyc:'e are shown. The length of each arrow indicates the :-ange of Lim pre-ssure during a stop or slowdown. The wide range of line pressures du::-ing st0PS and slJWdowns shows the effectiveness of organic linings to vary IIIQch ~cr~ thar. me+allic linings, especially durir~ the first 200 miles. A much greater --::if :'-f'r~n('e Sf OWl: up on the fadp. stops. Note tnat With organic l1nings, the 35 mph 'It' feet pe!' sec ond per second stop fades fro'l'l 425 psi to lCOO psi. Also during the ~i:-s~ st 'p ai 5J mph at IS feet per second per second" with brakes hot. line pressure ::-eai'hes 12JO psi. '!hi:; fade conditione gradually improves as long ~l't the :ining las~s but is always present. Note the arrows at the end of fade schedules pcL"lt'illg '.!pward :ndicating increasing line pressure during decelerations. With the "'1eta:lic, :~o'" El h a.bsent bet'ansp the a rrows in metallic part of test are pointing downward. Crganics developed ~onsiderable noise, odor, roughness, pulis. and near the last grahbiness. Failure "~curred at 396 miles, while the metallic linings re~ained const~r.t throughout the 1000 mile schedule. The police schedule is extreme~ ~gg~ and s~;ce elllperatures usually- go above 6001" durtng the fade stops. Th! leT.ters PO at the noise test line stand for Itpinch out," a short noisp. at ext ~eme end of stop. WB ~tand~ for "wire bl"Uah," a scraping noise thrr.mgh the p.ntire 1.lSt part of a stop. The length of each noise line indicates intens~ty 01' <;mJnC. 1 ~ght lines are primary shoes, dark lines are secondary shoes. Th:! stabL!.i ty line on the chart indicates vehicle pull to right, light l~r.es, and l~ft, dark lines, during stops. The length of lines indicates amount or pulL Ndi("~ tht~ superior stability of vehicles with metallic lining in this test. It/ear W'iS a.'1other measurable differential between the two linings ind:"C'ated by be police schedule. Notice the extent of organic lining wear shown in Figure L~. L'he :-ight front pr1mary 11ning wore .112 o an inch and the ri.ght ront se~ondarJ li~ing wore .182 of an inch and broke off at 396 miles to end the test. As tl:e ~1.art ShO'lS a maximum wear of only .014 of an inch occurred on the right rear ~~,~~da:j' ~ctal:ic :L~ing at the end o~ a 1~n0 ~iles of high speed stops. The po+iee ::lura::,ilP;,' ~ ~tec l:e e'1lphasize~ the inadequacy of organic linings on heat-problem b~,!lk"!~. - _ _ _ _ _ _ _ _ _~.opo~._.....:..~~ . .- '7"-_ r--'''''~- ,'-"-"1,-.1-- .. .;-I'"':'l.if.~.'I'!iJ I!;~S;;r- What's new in brake linings_1959_sUbstitutes.max - 8- s~ve~e ar.d B~th :hp. policQ p~0ve the value dur3bility and the Pikes Peak brake tests are extremelY of Metallic linings for vehicles that must withstand ab- nOl"'lIlil bl"aki~g r~ql;i.rp.ments. a Il'O~1". F~eld impor:ant testing* of brake linings on police and taxi fleet vehicles is also method o! gathering important test data. Chevrolet has installe 'I1E'ltaJ :'ic linJ.ngs on police vehicles in three different areas of the country. d The. fpaocltisceounl:w:peaarrtm, efn~tesl,pafratdice1pnaotiisneganredpaodrtdeidtioancatul adl aotap,ertaotioCnhaelvrooblesterfviaetlidonsse, rvinicceludenin-g aegnqicnu:~epelirIns'enhtthp. a:;t\V~lj-odnuftiyr~-:e>dPQcto"omtipoannay, Ctehsetvrroelseut lhtas.., rAels~aa5erdesumlettaollfiCthleiinrinsguspearsioorppteiorfnoarlm- CONCLUSION ~a~A for Th~ ?ost-war trend the ~~ak9 engineer. in automobile developments has been a veritable nightAs cars have become heavier and far more powArfnl. hi. working dr~a '!as :Jeen reduced With the size of wheels. ~u13rly his 1 i.nin~s, have proved equal to the t.est. Yet his brakes, and parti- . :and In 'l!Atallic 'omp:;\ring the overall capabilitie5 and weaknesses of today's ~iniIlgs, it has been shown that both have their good and bad organic character- isti~s. ~'Jda~r's organics are more than equal :'he '7letal::'i~s ar'=? equal to the demandl'l of the to the demands IIhlilat-problemn of average braking or daily driving. polLce cars, sports :oa:'."3'. m.:::! "ther vehicles sub~ected to high speed, prolonged dec~lerations:' aroe ::let :-Iow~ver! compl'?tely in striving :or the perfect brake satisfied with either the organic friction material j engineers or metallic linings. In defense of ~~e metalllcs it should ment work :mly in the last be kept in mind that the,r have undergone 3-1/2 years, and great progress has been intensive developmade' in that sh ?9ri')o in Lmp!'ovir.g their object.lonable characteristics. ort On the other hand, organics have been :mdf'r intensive ~iency imp~ov~ment may be development for over 30 years and, although further defiobtained, they have possib~ reached their peak of perfec- -tion with the L'1.gredients to wnir.h theY' are the 'Jrganic and metallic friction materials now reotric::ted. The compet1tion between is a healthy condition that points to rapid ~r015!'esE the :utu!"e .. i...'1. the attainment of the versatile, highly ef.fective brake lining of ~- SCAheEvr~o~p,e~r+ 'sJra:ig.en1e1t F";oeretDinAgfpa.ecttsir- ~tFiieesl.d Testin~, 1958. by Edward Gray described What's new in brake Iinings_1959_substitutes.max.