Document npNKzQJEyE8RjJMYDRGkvYB12

FILE NAME: General Motors (GM) DATE: 1959 DOC#: GM085 DOCUMENT DESCRIPTION: Unpublished Conference Presentation - W hat1 New in Brake Linings  SOCITX A PEB Sf PREPRINT: Subject to rovision. Per* mtnion to pubfeh this paper, In full or in pert, after He presentation and with credit to the author and the Society may bo ob tained upon request. The Society not re sponsible for statements or opinions advanced in pa pers or discussions a t H i Meetings. rts. r MAR lf> ip'i y 4. 14T / WHAT' S NEW I N BRAKE L I N I N G S BJT NEWELL H. McCUEN Chevrolet Erigine Dept. Chevrolet Motor Div. General Motors Corp. '""'O- ^ / v "`"'C; . t-f rNi'i4!^-?^1, ' For presentation at the SAE ANNUAL MEETING Sheraton-Cadillac & Statler Hotels Detroit, Michigan January 12-16, 1959 Written discussion of this paper w ill 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. W hat's new in brake linings_1959_substitutes.m ax 628-74062 S 67 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, water-cooled and oil-immersed brake systems. However, regardless of the brake design under discussion, a review of friction materials today is essentially a study of two linings -- trie organic type and the metallic type. It is the intention of this paper, therefore, to restrict its subject matter to these two basic lining materials. Tc be acceptable to the automobile manufacturers, present day linings must have the following characteristics: 1. Wearing ability. Without sacrificing any other attributes, a hr ike 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, "gi-abbiness" or other erratic braking conditions. 3- Resistance to high temperature and fading. Linings must be caoable 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. U. 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. ? Lew cost. In this era of cost-conscious engineering, it is essen tial that the expenditures fer brake lining fabrication and warranty servicing be controlled. W hat's new in brake linings_1959_substitutes.m ax - 2- T V 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 evalua tion reduced to simple terms, the friction material compounder's job would be routine. This is far -`rom the case. The many influences on brake performance, resulting from variations in vehicle weights, climates, road conditions, vehicle equipment and , driving habits, irake the engineering of brake lining friction materials a most chal lenging assignment, and a highly secretive operation. The formula of a brake lining is the well-guarced secret of the supplier, while other brake components are used commonly throughcut the industry. - BASIC DRUM AND SHOE BRAKE DESIGNS For purposes of clarity, all data presented herein applies to a drum and . shoe brake o-' the duo-servo type. (Pig. l) The two other drum and shoe brake de- . Signs genera-ly employed are the two leading shoe type and two trailing shoe type. (Fig. 1. There _s also a one leading one trailing shoe type in general use which is not shown. ORGANIC 3RAKE LININGS A l - American passenger cars use organic brake linings. There are two organic linings -duch are classified by their method of fabrication. Organic dry mix is basic illy a gray-white compound of asbestos, filler materials and powdered resins which is thoroughly mixed, preformed to shape, and placed under heat and' pressure until it forme a hard, slate-like 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 re sins that has a gray-brown color when blended. The compound is processed by any of several different methods tdiich include high pressure extruding, screw extruding, calendering and ether processes. Figure 2 shows a step in the high pressure extrud ing 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 liningo ore 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 ?-i< tior. qualities. Fillers are a wide variety of materials, such as rubber scrap, which are added tc linings to control noise, wear or other brake characteristics. Ci.ring agents and/or accelerators are added to a lining compound to pro duce recuird chemical reactions in the ingredients. Materials for special effects are added to compounds to improve overall brakins performance. They include powdered lead, brass chips and aluminum powders. Binders, which are predominantly phenolic resins, hold all the other ingreriienis tigether and are selected to govern the physical strength of the material at high temoeratures. W hat's new in brake linings_1959_substitutes.m ax - 3- Organic Drake linings have several distinct and important characteristics, regardless o1'hov 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. u. They show a moderate change In effectiveness with temperature. 0. Organics do not have a build-up 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 (60-100 micro-inch range permissible on Irvins), but organic surfaces are sensitive to moisture and cortarrinants. METALLIC BRAKE LININGS . 12.e other lining compound under wide development is the sintered metallic type. Metal ic linings represent the most important new development in brake lining. Metallic linings are composed of finely powdered iron or copper, graphite and lesser amounts of inorganic fillers and friction modifiers. Th*1 dry powders are accurately weighed, placed in a sifter in a specific order, and mixed in a tumbling cone type blender for 30 to 00 minutes. A lubricating oil is added to prevent segregation of the individual ingredients which are of dif ferent sizes and densities. The powders are then put through a briquetting process in which the back ing 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 schem atic 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 pres sures. 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 arid sintered in temperaturoa veil over a 1Q00F. 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 grea- strength and durability. The manufacture of metallic linings i3 highly automatic. a fact that will lead to more competitive pricing as production increases. IBUUVLM < .lS l.l.JM lN r**m p N P 4 p | *9U !'k|l.*IIU piipM W hat's new in brake linings_1959_substitutes.m ax - a - Present day metallic linings have several distinct and important char- . acteristics; _. In comparison with organic linings, the metallica are relatively high cost. At present the cost factor is one reason the applica tion of metallic linings is restricted to the "heat-problem" brekes. ?. Metallic linings have a low initial friction, and a resultant hard pecal that lightens with usage. }. 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 metal lies, b. Met allies are not affected by wetness. 7. '"hey do require a smooth facing grind and drum finish. The metallic lining brake drum has a mirror-like finish with a uniformity of sur face that is required to assure stability of braking. . The compounder must select the exact combination of ingredients from - Hundreds cf possibilities to produce linings that have all the required character istics. Kis success is measured by the manner in which his linings stand up under a battery cf te: ts. LABORATORY TESTING 0? 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 heing conducted by tho automotive industry. La boratory testing provides fast, low-cost evaluation of the wide range of linings de veloped annually. Over VyQ0 compounds of various metallic combinations already have been developed by one manufacturer and organic lining compounds run into the thousands. The Chase machine shown in Fig. 1 is invaluable in quickly comparing fric-` tion 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 fric tion 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 co-or dinate is shown at left, drum temperature at the right and time at the bottom of the chart. The organic lining curve shows some increase in friction up to about 850 and then a rapio fado :ut. The metallic lining curve indicates a constant, lower fric tion that increases at high temperatures. Metallic lining drum temperature goes higher than th organic. Dynamometers 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, dram score and odor. The dynamometer duplicates the energy load of the automobile. W hat's new in brake linings_1959_substitutes.m ax > 1 r linings that prove worthy in the laboratory receive further testing. 30AD TESTING IF 39AXF 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 continually engaged in brake development and test ing operations (Fig. 7). Tests of every type of Chevrolet brakes totaled 1,680,000 miles from October l5?!?? tc October 1958. ' fh* results of brake road tests described herein apply to organic lining bonded tc th* shces. as contrasted to the riveted type, both of which are shown in <r ** , . - Tef-ts :n metallic linings apply to the type shown in Fig. 9. with the "ining riveted tc the shoes in segments. The metallic segments on the shoe are flex ible in their application in that they can be varied in number, position on shoe or material formula to produce the braking effort desired. Th-J ultimate structure of all linings is determined by test. A brake lining material that has progressed from laboratoiy to road testing first undergoes a "general f?ei" test. Brake development engineers try the facings for an overall impressicn. If the findings are good, an effectiveness test is made. The 0 and 80 mph crake deceleration test results shown in Fig. 10 depict the effectiveness of high speed emergency ;;tops with organic and metallic linings. This test requires the use of a load applic itor, decelerometer and recording unit. Load is applied to the brake pecal automatically and the recording unit indicates pedal load, deceleration, pedal travel and time required to make test stops. The and 80 mph brake deceleration curves show the crake 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 c u r r e p r e s e n t s a single stop. The curves reveal that the organic material is less speed sensitive and more effective in this test. It should be pointed out that the metallic lining curves are those in which the brakes were cool at the start of th^ atop. For the organic lining, the pedal load required at a deceleration rate of 20 feet per seccnd per second from 50 mph is 90 pounds, and from 80 mph is 12.8 pounds. Under the same tondttions for metallic lining, the pedal load from 50 mph is 103 pounds, and fro." 50 mph is 165 pounds. I.' firings 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 co-ordinate at the left and stop numbers at the bottom of the chart. The stops were made from 60 mph at 15 feet per second per second deceleration. The interval between fade stops was 1-tenths nf a mile, or about uO seconds. Initial feel and recovery stops were made from UG mph at 6 feet per second per second at one mile intervals. The organic curve sr.ow3 a slightly decreasing initial to final line pressure during the first three slops with each successive stop becoming harder. This is indicated by the shaded distance between the broken and solid line curves. By the Jj+.h stop the line pressure increases progressively during each stop and the pedal becomes harder. By the 7th stop, line pressure is over 800 psi and fade continues with each stop. Recovery is slow anti requires ^ 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 5r- pounds per square inch during entire test. The line pressure decreases during eacr. stop with to recovery being required. Tests such as this show the need for i"ganic lirings that have less heat build-up and, thereby, less fade. Therefore, . INI , m. . -------------r-- TT ----------------T l I ' mil W h ats new in brake Iinings_1959_substitutes.m ax 11 '! HM M M 3<5De srgari- linings are being grooved down the middle to ventilate the lining and Itigate the neat problem. Grooving of the linings also reduces heat spotting or the drum. In addition lining areas are being increased, because for a given rate of veniele orate!ng, 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 dur ability. This Ls accomplished by installing linings an vehicles scheduled for the 25,000 mile durability run. Consistency of effectiveness is observed during periodic stops which ~ccur about every two miles throughout the 25,000 mile run. Concurrently with the tests described, linings are subjected to a steam room humid it; test, wet brake tests, grade parking checks and others. In addition to the many standard tests for brakes, the brake development engineers -orduct many special tests to collect performance data. Onr o f the most comprehensive and revealing special tests of organic and metallic oral-e linings was conducted recently on a 10C0 mile police vehicle schedule. ;?ig. 12; Or. 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 atop or slowdown. The wide range of line pressures d u rin g stops and slowdowns shows the effectiveness of organic linings to vary much mere than metallic Linings, especially during the first 200 miles. A much greater d iffe r e n c e slows up on the fade stops. Note tnat with organic linings, the 35 mph at ' fe e t per second per second stop fades from 1*25 psi to 1C00 psi. Also during the first st -p at 50 mph at 15 feet per second per second' with brakes hot. line pressure reaches 1200 psi. This fade conditions gradually improves as long as the lining lasts but is always present. Note the arrows at the end of fade schedules pointing upward indicating increasing line pressure during decelerations. With the metallic, face it absent because the arrows in metallic part of test are pointing downward. Organics developed considerable noise, odor, roughness, pulls, and near the last grahbiness. Failure occurred at 396 miles, while the metallic linings re mained constant throughout the 1000 mile schedule. The police schedule is extremely rugged and sice -emperatures usually go above 600'K during the fade stops. Thu letters ?0 at the noise test line stand for "pinch out," a short noise at extreme end of stop. WB stands for "wire bruoh," a scraping noise through the entire last part of a stop. The length of each noise line indicates intensity of sound. L ^ght lines are primary shoes, dark lines are secondary shoes. Ihe stability line on the chart indicates vehicle pull to right, light lur.es, and left, dark lines, during stops. The length of lines indicates amount of pull. Notice the superior stability of vehicles with metallic lining in this test. Wear was another measurable differential between the two linings in dicated by tne police schedule. Notice the extent of organic lining wear shown in Figure ip. Lhe 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 .011* of an inch occurred on the right rear secondary metallic lining at the end of a 1.000 miles of high speed stops. The police durability seri lie emphasizes the inadequacy of organic linings on heat-problem " brakes. W hat's new in brake Iinings_l959_substitutes.m ax - 8- t>-,+h -he- police durability and the Pikes Peak brake tests are extremely severe and prove the value of metallic linings for vehicles that must withstand ab normal braking requirements. F_eld testing* of brake linings on police and taxi fleet vehicles is also a most important method of gathering important test data. Chevrolet has installed metallic linings on police vehicles in three different areas of the country. The . police departments participating reported actual operational observations, including facts on wear, feel, fade noise and additional data, to Chevrolet field service en gineers that confirmed company test results. As a result of their superior perform ance in npavy-duty operationo, Chevrolet haa released metallic linings as optional equipment. CONCLUSION The post-war trend in automobile developments has been a veritable night mare for the orake engineer. As cars have become heavier and far more powerful, his working area has seen reduced with the size of wheels. Yet his brakes, and parti- . rularly his linings, have proved equal to the test. In -omp.iring the overall capabilities and weaknesses of today's organic and metallic minings, it has been shown that both have their good and bad character istics. Today's organics are more than equal to the demands of average daily driving, "he metafiles are equal to the demands of the heat-problem" braking of polLce cars, sports cars, ir.d -ther vehicles subjected to high speed, prolonged decelerations? However, in striving for the perfect brake friction material, engineers are net 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 develop ment work only in the last 3-1/2 years, and great progress has been madef 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 defi ciency improvement may be obtained, they have possibly reached their peak of perfec tion with the ingredients to which they are now restricted. The competition between the organic and metallic friction materials is a healthy condition that points to rapid progress in the attainment of the versatile, highly effective brake lining of the future.. SAB oape: Chevro`-5' T "' ' Dragnet 's field For Defects - Field Testing, 1958, by Edward testing activities. ------ -XT- r W hat's new in brake iinings_1959_.substitutes.max Gray described