Document peYyY30BeXrjZE35pLqJQRd2D

FILE NAME Brakes BRK DATE 1959 Jan DOC BRK190 DOCUMENT DESCRIPTION Unpublished Conference Presentation What's New in Brake Linings t SOCIETY $ 3 PAPERS PREPRINT Subject to revision Per- mission to publish this paper in full or in part after its presentation and with credit to the author and the Society may be ob tained upon request The Society is not responsible for statements or opinions advanced in papers or discussions at its Meetings Sintered Sintered metallic metallic metallic linings linings WHAT'S NEW IN BRAKE LININGS By NEWELL H. McCUEN Chevrolet Engine Dept. Chevrolet Motor Div General Motors Corp. ee eee eee . FIN - 623.74061 623.74061 623.74061 623.74061 67 623.74061 For presentation at the SAE ANNUAL MEETING Cadillac & Statler Hotels Detroit Michigan January 12-16 1959 Writter discussion of this paper will be accepted by SAE until Feb. 16 1959 Three spaced copies are appreciated _ SOCIETY of AUTOMOTIVE ENGINEERS Inc. 485 Lexington Avenue York 17 N. Y. What's new in brake linings_1959_substitutes.max WHAT'S NEW IN BRAKE LININGS INTRODUCTION The development of brake linings capable of meeting all the requirements of the progressive American passenger cars is one of the most pressing problems of automotive engineering Great effort is expended annually by the automobile industry to develop the most effective braking systems possible It is in the development of improved linings that perhaps the greatest effort is being made Millions of dollars are spent on experimental engineering and millions of miles of brakes tests are made each year to produce efficient dependable brake linings There are numerous brake designs currently being carried on in the indus- try both here and abroad These engineering designs cover disc type band type cooled and immersed brake systems However regardless of the brake design under discussion a review of friction materials today is essentially a study of two linings -therefore the organic to restrict type and the metallic type its subject matter to these It is the intention of this paper two basic lining materialo To be acceptable to the automobile manufacturers present day linings must have the following following characteristics 1. 1. Wearing ability Without sacrificing any other attributes a brake lining must have a low wear rate 2 Minimal friction variations Brake linings must have a high - coefficient of friction that is equal at all four wheels and consistent on all cars to prevent pull grabbiness or other erratic braking conditions 3 Resistance to high temperature and fading Linings must be capable of withstanding and dissipating heat to prevent brake fade which is a temporary reduction of brake effectiveness resulting from heat and linings must have adequate mechanical strength through all operating temperatures 4. Lining surface must be compatible with mating surface to prevent galling excessive wear or heat checking of the drums 5. Consistency of performance in all braking systems The majority of cars are still equipped with unassisted braking systems There- fore brake linings must engage smoothly with low effort and oper- ate effectively with both standard and power brakes 6. Quietness of operation Quietly operating brakes are an important comfort factor in passenger cars therefore lining and drum engage- ment sounds must stay below the audible level 7 Low cost In this era of conscious engineering it is essential that the expenditures for brake lining fabrication and warranty servicing be controlled What's new in brake linings_1959_substitutes.max linings_1959_substitutes.max ns or Pas Ore tes ORES. Seeman ate ee 2 The compounding of friction materials that successfully meet all these requirements is the specialty of some of the anonymous heroes of the automotive industry The uninitiated might think that with a stable brake design and evaluation reduced to simple terms the friction material compounder's job would be routine This is far from the case The many influences on brake performance resulting from variations in vehicle weights climates road conditions vehicle equipment and : driving habits make the engineering of brake lining friction materials a most chal- lenging assignment is the guarded commonly throughout and a highly secretive operation The formula of a brake lining secret of the supplier while other brake components are used the industry - BASIC DRUM AND SHOE BRAKE DESIGNS For purposes of clarity all data presented herein applies to a drum and .. shoe brake of the servo type Fig 1 The two other drum and shoe brake de- signs generally employed are the two leading shoe type and two trailing shoe type Fig 1 There is also a one leading one trailing shoe type in general use which is not shown ORGANIC BRAKE LININGS Al American passenger cars use organic brake linings There are two organic linings which are classified by their method of fabrication Organic dry mix is basically a white compound of asbestos filler materials and powdered resins which is thoroughly mixed preformed to shape and placed under heat andand pressure until it forms a hard slate hoard Then it is cut and bent into in- dividual arcuate segments and attached to the shoe Organic wet mix is a compound of asbestos organic fillers and liquid resins that has a brown color when blended The compound is processed by any of several different methods which include high pressure extruding screw extruding calendering and other processes Figure 2 shows a step in the high pressure extruding process The extruded lining is being removed from a die that has formed it into a long slab that will be compressed to a uniform density under heat and pressure Organic Linings are generally composed of six basic ingredients Asbestos with its high heat resistance and high coefficient of friction in contact with Iron and steel is the basic material Friction modifiers such as the oil of the cashew nut shell give linings desired fiction qualities Fillers are a wide variety of materials such as rubber scrap which are added to linings to control noise wear or other brake characteristics Curing agents and accelerators are added to a lining compound to produce required chemical reactions in the ingredients Materials for special effects are added to compounds to improve overall braking performance They include powdered lead brass chips and aluminum powders Binders which are predominantly phenolic resins hold all the other ingredients together and are selected to govern the physical strength of the material at high temperatures What's new in brake linings_1959_substitutes.max linings_1959_substituteslin.gs_19m5_subastiutxes.max 3 Organic brake linings have several distinct and important characteristics regardless of how they are compounded 1 The fabricating cost is low in general 2. A high initial friction is inherent with organic linings along with a light pedal effort which hardens with usage 3. They vary only slightly in effectiveness with speed 21 They show a moderate change in effectiveness with temperature 5 Organics do not have a build at end of stops They protect themselves from heat damage by fading at high temperatures 7 Organic linings do not require extremely smooth lining facing or drum finishes 60-150 micro range permissible on imms but organic surfaces are sensitive to moisture and cortaminants METALLIC BRAKE LININGS type The other lining compound under wide development is the sintered metallic Metalic Metalic linings represent the most important new development in brake lining and Metallic lesser amounts linings are composed of inorganic fillers of finely powdered iron and friction modifiers or copper graphite order oil is ferent The dry powders are accurately weighed placed in a sifter in and mixed in a tumbling cone type blender for 30 to 50 minutes added to prevent segregation of the individual ingredients which sizes and densities a specific A lubricating are of dif- The powders are then put through a briquetting process in which the backing and friction 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 that forms the backing of the lining is poured into a cavity as shown in the schematic drawing in Figure 3. The stripper is lowered again and the lining facing powder is poured into the cavity Then the powders are compacted under high pressures During the briquetting stroke the two layers of powder are pressed into an integral unit with green strength The briquettes then are automatically conveyed into a furnace and sintered in temperaturos well over a 1000 The furnace creates exothermic atmosphere generated from 1000 BTU natural gas that protects linings from oxidation This heat treatment forms sintered bonds between particles that give linings great strength and durability The manufacture of metallic linings is highly automatic a fact that will lead to more competitive pricing as production increases What's new in brake linings_1959_substitutes.max linings_1959_substituteslin.gs_1m95_suabstiuxtes.max -4- -4Present day metallic linings have several distinct and important char- -- In comparison with organic linings the metallics are relatively high cost At present the cost factor is one reason the application of metallic linings is restricted to the problem brakes . Metallic linings have a low initial friction and a resultant hard pecal that lightens with usage 2. They have reduced effectiveness at low speeds and temperatures '. They are extremely heat and fade resistant 5. Only slight roughness is detectable at high speeds with metallics h Metallics are not affected by wetness ?. They do require a smooth facing grind and drum finish The metallic lining brake drum has a mirror finish with a uniformity of surface that is required to assure stability of braking The compounder must select the exact combination of ingredients from hundreds of possibilities to produce linings that have all the required characteristics His success is measured by the manner in which his linings stand up under a battery of tests LABORATORY TESTING OF BRAKE LININGS To complete the comparison of organic and metallic linings it is necessary to evaluate the performance characteristics of both types as established by the wide range of laboratory and road tests being conducted by the automotive industry La- boratory testing provides fast cost evaluation of the wide range of linings de- veloped annually been developed by Over 1500 compounds one manufacturer and of various metallic combinations already have organic lining compounds run into the thousands The Chase machine shown in Fig 4 is invaluable in quickly comparing friction materials for durability wear and the effects of temperature on friction and wear characteristics The Chase machine consists of a heavy iron brake drum that is rotated by a variable speed motor and magnetic clutch assembly A specimen of friction material is held against the drum by dead weights Instruments record all test results The urves in Fig 5 indicate the basic differences between metallic and - organic linings throughout their rise in temperatures caused by their own friction . plus external heat applied to the drum within the Chase machine The friction or- - dinate is shown at left drum temperature at the right and time at the bottom of the chart then a The organic lining curve shows some rapia fade cut The metallic lining increase in friction up to about 850 and curve indicates a constant lower fric- tion that increases at high temperatures higher than the organic Metallic lining drum temperature goes Dynarometers of the type in Fig 6 provide an excellent evaluation of a brake on an accelerated laboratory schedule of tests including effectiveness fade recovery durability drum score and odor load of the automobile The dynamometer duplicates the energy What's new in brake linings_1959_substitutes.max linings_1959_substituteslin.ings_1m959_suabstituxtes.max 5 Ons linings that prove worthy in the laboratory receive further testing ROAD TESTING OF BRAKE LININGS As is true of all automotive development the vehicle itself must produce the final verification of laboratory brake findings Large fleets of vehicles and numerous engineering personnel are ing operations Fig 7 Tests of miles from October 1957 to October continually engaged in brake development and test- every type of Chevrolet brakes totaled 1,680,000 1958 ; bonded to Fig Fig 5 The the results of brake road tests described herein apply to organic lining shoes as contrasted to the riveted type both of which are shown in Tests on metallic linings apply to the type shown in Fig 9 with Tining riveted to the shoes in segments The metallic segments on the shoe ible in their application in that they can be varied in number position on material formula to produce the braking effort desired the are flexshoe or The ultimate structure of all linings is determined by test A brake lining material that has progressed from laboratory a general feel test Brake development engineers impression to road try the testing facings first undergoes for an overall If the findings are good an effectiveness test is made The 50 and 80 mph brake deceleration test results shown in Fig 10 depict the effectiveness of high speed emergency stops with organic and metallic linings This test requires the use of a load applicator decelerometer and recording unit Load is applied to the brake pedal automatically and the recording unit indicates pedal load deceleration pedal travel and time required to make test stops The 50 and 80 mph brake deceleration curves show the brake effectiveness of the organic and metallic linings The rate of load application on the brake pedal to obtain the curves is 30 pounds per second and each curre represents a single stop The curves reveal that the organic material is less speed sensitive and more effective in this test It should be pointed oul that the metallic lining curves are those in which the brakes were cool at the start of the stop For the organic lining the pedal load required at a deceleration rate of 20 feet per second per second from 50 mph is 80 pounds and from 80 mph is 118 pounds Under the same conditions for metallic lining the pedal load from 50 mph is 103 pounds and from 80 mph is 165 pounds I lirings perform well in the effectiveness test they are subjected to the fade test The chart in Fig 11 illustrates a brake fade test comparison of or- ganic and metallic linings Line pressure is indicated by the ordinate at the left and stop numbers at the bottom of the chart The stops were made from 60 at 15 feet per second per second deceleration The interval between fade mph tenths of a mile or about 40 seconds Initial feel and stops was from 40 mph at & feet per second per second at one mile intreercvoavlesry sTthoepsorwge ar niec mc au dreve shows a slightly decreasing initial to final line pressure during the first three stops with each successive stop becoming harder This is indicated by the shaded distance between the broken and solid line curves By the ith stop the line increases progressively during each stop and the pedal becomes harder pressure By the 7th stop line pressure is over 800 psi and fade continues with each stop Recovery is slow and requirea miles to level out to within 20 pounds per square inch of the initial As the metallic lining curves indicate the line pressure increases only 50 pounds per square inch during entire test The line pressure decreases during each stop with no recovery being required Tests such as this show the need for organic rings that have less heat build and thereby less fade Therefore RT aE RRR Ee nS EET Fgh r What's new in brake linings_1959_substitutes.max linings_1959_substitutes.max lings_195_substiutes.max some organi linings are being grooved down the middle to ventilate the lining and ritigate the neat problem Grooving of the linings also reduces heat the drum spotting of In addition lining areas are being increased because for a given rate of vehicle praking the pressure per square inch of lining area decreases as total area increases ard heat concentration is reduced Following the fade test the brake linings are checked for general durability This is accomplished by installing linings on vehicles scheduled for the 25,000 mile durability run Consistency of effectiveness is observed during periodic stops which cour about every two miles throughout the 25,000 mile run Concurrently with the tests described linings are subjected to a steam room humidity test wet brake tests grade parking checks and others engineers In addition to the many standard tests for brakes the brake development worduct many special tests to collect performance data One of the most comprehensive and revealing special tests of organic and metallic brake linings was conducted recently on a 1000 mile police vehicle schedule Fig 12 On the chart line pressure is shown at left and the 5th and 12th stop and slowdown of each test cycle are shown The length of each arrow indicates the range of line pressure during a stop or slowdown The wide range of line pressures during stops and slowdowns shows the effectiveness of organic linings to vary much more than metallic linings especially during the first 200 miles A much greater difference shows up on the fade stops Note that with organic linings the 35 mph at feet per second per second stop fades from 425 psi to 1000 psi Also during the first st at 50 mph at 15 feet per second per second with brakes hot line pressure reaches lining lasts but 1200 psi is always This fade conditione gradually improves as long as the present Note the arrows at the end of fade schedules pointing upward indicating increasing line pressure during decelerations With the metallic face is absent because the arrows in metallic part of test are downward pointing Organics developed considerable noise odor roughness pulls and near the last grabbiness Failure occurred at 396 miles while the metallic linings re- mained constant throughout the 1000 mile schedule The police schedule is extremely rugged and shice emperatures usually go above 600 during the fade stops intensity The letters PO at the noise test line stand for pinch out a short noise at extreme end of stop WB stands for wire brush a scraping noise through the entire last part of a stop The length of each noise line indicates of sound Ight lines are primary shoes dark lines are secondary shoes lines puil The stability line on the chart indicates vehicle pull to right light and left dark lines during stops The length of lines indicates amount of Notice the superior stability of vehicles with metallic lining in this test Wear was another measurable differential between the two linings indicated by the police schedule Notice the extent of organic lining wear shown in Figure 1. The right front primary lining wore .112 of an inch and the right front secondary lining wore .182 of an inch and broke off at 396 miles to end the test As the chart shows a maximum wear of only .014 of an inch occurred on the right rear secondary metallic lining at the end of a 1000 miles of high speed stops The police durability schedile emphasizes the inadequacy of organic linings on problem brakes What's new in brake linings_1959_substitutes.max linings_1959_substitutes.max lings_195_substiutes.max -8- severe normal Both the police durability and the Pikes Peak brake tests and prove the value of metallic linings for vehicles that must awriethesxttarnedmealbybraking requirements Field testing of brake linings on police and taxi fleet vehicles is also a most important method of gathering important test data Chevrolet has metallic linings on police vehicles in three different areas of the installed police departments participating reported actual operational country The | facts on wear feel fade noise and additional data to Chevroolbesterfviaetlidonsserivniccleudein-ng gineers that confirmed company test results As a result of their ance in heavy operations Chevrolet has released superior perform- equipment . metallic linings as optional ; CONCLUSION mare The post trend for the brake engineer in automobile developments has been a veritable night- As cars have become heavier and far working area has been reduced with the size of wheels Yet his more powerful his cularly his linings have proved equal to the test brakes and parti- . In comparing the overall capabilities and weaknesses of today's organic and metallic linings it has been shown that both have their good and bad character- istics Today's organics are more than equal to the demands of The metallics are equal to the demands of the average daily driving sports cars and other vehicles subjected to hipghro spb eeldepm rolbornagkedingdeocfelpeorlaitcieoncsars However in striving for the perfect brake friction material engineers are not completely satisfied with either the organic or metallic linings In defense of the metallics it should be kept in mind that they have undergone intensive development work only in the last 3-1 years and great progress has been made in that short period in improving their objectionable characteristics On the other hand organics have been under intensive development for over 30 years and although further deficiency improvement may be obtained they have possibly reached their peak of perfec- tion with the ingredients to which they are now restricted The the organic and metallic friction materials is a healthy conditiocnomtpheattiptoiionntsbettwoeen rapid progress in the attainment of the versatile highly effective brake lining of the future .SAE paper Dragnet Chevrolet's field For Defects - Field testing activities Testing 1958 by Edward Gray described os oe oo. Mem ny ates Traeee: OTE eer Sa te ee ee SORTS - ~ What's new in brake linings_1959_substitutes.max