Document MJEjDndEJzvwJ4jKwm2Gd28Rx

FILE NAME: Allied Signal Bendix (ASB) DATE: 1950 June DOC#: ASB206 DOCUMENT DESCRIPTION: Journal Article - Brake Lining Material - Society of Automotive Engineers % c T % V % y/,, 5 5 4 THE varied properties required of a brake lining material calls for careful selection and blending of its ingredients. Lining requirements are: . 1. Correct coefficient of friction, which is influ enced by temperature reaction, aging qualities, water reaction, and oil a n d g rease re a c tio n ; 2. Durability; A utomotive 3. Relative freedom from any tendency to score dr4u.mQs;uietness In operation; and 5. Nonoffensive odor. . Lining friction coefficients generally run between 0.20 and 0.40. Manufacturers usually describe lin ings as having high, medium, and low friction co BASED ON FA.PEP* EV efficients without specifying friction value numeri cally. It's not hard to compound a lining with an initial specific friction coefficient; but to produce a lining with uniform braking performance under various operating conditions takes much compound A. J. Carter Assstant Department Head Poster P.as: :s Laboraron C r r .s e - Corp ing study and laboratory and road testing. The ideal lining would have a constant friction coefficient at high and low tem peratures, under wet and dry conditions, throughout th e lining's life. There is no such lining. All linings disintegrate under high braking temperatures. Cnemical and physical changes either increase' friction coefficient (build-up) or decrease it (fade). With fade, if lriction characteristics return to their initial condition, the lining is said to have good recovery properties. Satisfactory linings fade slightly with each brake application, but recover immediately after cooling Linings producing build up in friction coefficient are not satisfactory Friction coefficient may increase ^r decrease with age When it decreases, it develops a hard pedal. Some linings harden and tend to score drums and be noisy. Other linings are sensitive to water on the fric tion lace, with effects as pronounced ns those from temperature. Moisture alsu causes "morning sick ness. ' Iron oxide forms on the drum and gives high friction reaction during the first two or three stops made after the car has been parked over night. Be cause of contact with oil and grease m service, lin ing.should have some resistance to there materials. Linings also should wear slowly and uniformly. This insures more consistent braking action by con tinually renewing the friction surface. Negligible wear may produce a glased friction surface. Certain ingredients tend to score drums. Steel dru m ; score more readily th a n cast-iron ones. Brake system quietness is a function of the lining as well as other fa c to r1'. Ingredients m ust uci pro duce offensive odors at high braking temperatures. Good compounding ingredients may be di5c.'.rdr d because of this limitation. Brake lining materials derive their properties from fillers, binders, and wear-enhancing ingredi ents, such as those in Table 1. Selection and per centages of ingredients used varies with the type of lining. Chief lining constituent is Chrysotile asbestos, used as the primary reinforcing material. Chemi * Paper "A ,,-rr'or-v" c'-ate L-.:n g Mate - a < ' v..=s r ' : "" . 3 s' Anp_,a' Derrp.t Jan _ e- C (T s paper a ava^b'e ,n fu'l in rr-./'iiithographed fpr-i ren 5.AE Spec* Pl. ' - . - '$ i 4 Pr re 2 ~ i to members, "2d to " o r--.em1. ers ) cally, it is an hydrous m agnesium silicate (H4 Mg, Si: 0 9). The m ineral fibers are ^ to 6 in. long. Under high magnification the fiber looks like many finer crystalline threads bundled together. Diam- Binders Elastomers Rubber OR-S Buna N Neoprene Phenolic resins Oil modified phenolic resins Cashew nut oil resins Drying oils Bulfunzed oils > Reinforcing Chrysotile Asbestos Table 1-- Brake Lining Ingredients Filler* Nonieinforcing Barium sulphate Calcium sulphate White lead Lead carbonate Clay Asbestine Friction Modifying and Wear Enhancing Agents Cashew nut liquid products ipowders' Rubber and synthetic rubber Ground rubber tire scrap Iron oxide Metals--lead. zinc. b"ass Lead salts Tale Graphite Bituminous materials Abrasives Curing Agents ind Accelerators Standard rubber and resin primary and secondary curing agents and accel erators 9 9 20 SAE IOURNAL ( BRAKE LINING MATERIAL Ingredients Hold Key To Service Behavior etcr of the smallest fiber which can be separated is reducing cr inert atmosphere. This prevents oxida about 0.00003 m. tion of the metal to an oxide and permits it to func Asbestos makes a coed friction material because tion as a friction stabilizer. of its heat resistance, chemical resistance, flexibil G raphite in lining compounds im parts a lubricat ity. low therm al conductivity, and hardness. Its ing effect for smoother stopping. It can be incor reaction to heat is particular^- important. porated in the hard rubber or added separately. The asbestos fibers start losing their water of Some compounders see two advantages for graphite crystallization a t about 600 F. The loss rate in- encased in rubber. First, it does not interfere with c f a s e - with tem perature and become rapid a t 1000 flow of the resin binder during curing. Second, F. When the water is driven <,7. asbestos looses its graphite is released for Its lubricating action only ! crystalline properties : nd Incomes a powder. As- a f t i r the rubber Is softened by high braking tem be-'tos fiber breakdown to powder with heat make? perature. p o "ih le rejuvenation of the lining's fru lion surface. Iron oxide in small am ounts sometimes 1 used as Today's brake linings would be impossible it heat a friction-controlling element. It tends to have a generated in braking a car decompesed only organic sclf-poli.shing action which partly controls surface materials and changed asbestos mto a hard, organic frictional properties. fused layer of abra.-ive material. The compound usually requires large amounts of Poc>r heat-conductiip properties of asbestos help inorganic fillers to produce frictional effect.',. This keep heat from penetrating deeply into the lining. necessitates an improved friction stabilizer that Tins would produce civ mica! chance, in binder functions over a wide temperature range. Organic matt rials arc' would harm lining fr.ctinn character- modifier.' such as rubber, ground ruboer scrap, lst ics. pitches, and gilsonite- function besf over narrow Asbestos fabrics have a lra.tion coefficient of tem p eratu re ranges. about 0.35. This is within t h e 0.2 to 0 4 range A powdered product m ade from cashew n u t liquid aiour.d which satisfactory braking systems have is. cue of the bettei friction-stabilizing and w ear bee.-, designed. enhancing agents used today. This material works Brass, lead, or lead alloy wires used in woven m a satisfactorily up to tem peratures of 000 to C50 F. terials strengthen the yarn Some claim lead su r Tire scrap particles function up to about only 500 F. passes other nictal- becam e it stabilizes the friction About G to 8To of dust is needed to improve wearing coefficient, acm as a dry lubricant to prevent drum qualities. scoring, and inhibit.- formation of abrasive particles G round-rubber tire scrap has been, and will con on the friction surface. tinue to be, widely used because it is a cheap raw Metallic powders, sue)', as zinc and lead, improve material. Other friction modifiers--such as pitches, performance at high tem peratures. Limitation gilsonite. coal, and petroleum coke--can be used in with fine ler d is that it oxidizes easily to litharge, limited quantities only because of their low te m which promotes oxidation m unsaturatert organic perature resistance. Braking temperatures destruc compounds. Some believe these powders help tively distill these materials to form tarry or pitchy Lreak the continuity of the friction surface film residues at the friction surface. These increase the during braking action. Larue am ounts of metal friction coefficient a t low tem peratures. But at high (40~i), such as brass chips, are added to linings for tem peratures, volatile m aterials may he driven oft u ry high temperature req lircments. too rapidly before formation of tarry products, los Brake lining compound'rs also add lead to com ing their effectiveness. positions in th e form of organic salt. High t e m Research today is aimed at. getting binding m a perature libe rates it as finely divided 1<ad in a terials with high heat resistance. Currently the U-'NE 195C 21