Document v1w79Yp4qNZL9da0J0OnenzBR

FILE NAME Allied Signal Bendix ASB DATE 1950 June DOC ASB206 DOCUMENT DESCRIPTION Journal Article - Brake Lining Material - Society of Automotive Engineers op ek sr SAFE SAFE SAFE SAFE 13 JUN 1950 _ toes wr a OL ake. ne le anmeas'sch8ronaareeesmae HE 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 and grease reaction 2. Durability 3. Relative freedom from any tendency to score drums 4. Quietness in operation and 5. Nonofensive odor Lining friction coeficients generally run between 0.20 and 0.40 Manufacturers usually describe lin- ings as having high medium and low friction coefficients 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 compounding study and laboratory and road testing The ideal lining would have a constant friction coefficient at high and low temperatures under wet and dry conditions throughout the lining's life There is no such lining All linings disintegrate under high braking temperatures Chemical and physical changes either increase friction coefficient build or decrease it fade With fade if triction characteristics return to their initial condition the lining is said to have good recovery properties Satisfactory Imings fade slightly with each brake immediately after cooling application but recover Linings producing build- up in friction coefficient are not satisfactory Friction coefficient may increase or 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 face with effects as pronounced as those from temperature Moisture also causes morning sickness 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- 7 Materias Paper Automotive Brake Lining Materias Annual Meaning Detroit Jan 10 1910 This in multilithographed form from Price 256 to members 50 to Spect S8 normembers normembers ) WAS PRE tg OE available avail ble paper paper ete fu'l in r natty AUTOMOTIVE BASED ON PAPER BY A. J. Carter Assistant Department Head Pubber & Plastics Laborator Chrisler Corp cause of contact with oil and grease in service lin- ings should have some resistance to these materials Linings also should wear slowly and uniformly This insures more consistent braking action by continually renewing the friction surface Negligible wear may produce a glazed friction surface Certain ingredients tend to score drums Steel drams score more readily than cast ones Brake system quietness is a function of the lining as well as other factors Ingredients must not produce offensive odors at high braking temperatures Good compounding ingredients may be discarded because of this limitation Brake lining materials derive their properties from Allers binders and enhancing ingredi- ents such as those in Table 1. Selection and percentages of ingredients used varies with the type of lining Chief lining constituent is Chrysotile asbestos used as the primary reinforcing material Chemically it is an hydrous magnesium silicate H. Mg Si O The mineral fibers are 4 to 6 in long Under high magnification the fiber looks like many finer crystalline threads bundled together Diam- Binders Elastomers Rubber GR Buna N Neoprene Phenolic resins O^,,modified phenolic resins Cashew nut oil resins Drying oils Bulfurized oils ? Table Brake Lining Ingredients Fillers Reinforcing Chrysotile Asbestos Nonreinforcing Bariem sulphate Calcium sulphate White lead Lead carbonate Clay Asbestine Friction Modifying and Wear Enhancing Agents Curing Agents and Accelerators Cashew nut liquid products powders Rubber and synthetic rubber Ground rubber tire scrap Iron oxide Metals zinc brass Lead salts Tale Graphite Bituminous materials Abrasives Standard rubber and resin primary and secondary curing agents and accel- erators ~ - - _ --- 20 SAE JOURNAL | anewiag os ^'e i BRAKE LINING MATERIAL Ingredients Hold Key To Service Behavior eter of the smallest fiber which can be separated is about 0.00003 in Asbestos makes a good friction material because of its heat resistance chemical resistance flexibil- ity low thermal conductivity and hardness Its reaction to heat is particularly important The asbestos fibers start losing their water of ee crystallization at about 600 F. The loss rate in- creases with temperature and become rapid at 1000 AM F. When the water is driven o7 asbestos looses its ee crystalline properties and becomes a powder Asvt a bestos fiber breakdown to powder with heat makes Ses possible rejuvenation of the lining's friction friction surface Mage Today's brake linings would be impossible if heat generated in braking a car decomposed only organise het materials and changed asbestos asbestos into a hard organic L fused layer of abrasive material 7s Poor cunducting properties of asbestos help keep heat from penetrating deeply into the lining This would produce chemical changes in binder TE materials and would harm liming friction friction characteristics Asbestos fabrics have a ination coefficient of about 0.35 This is within the 0.2 to 04 range around which satisfactory been designed braking systems have Brass lead or lead alloy wires used in woven ma- temals strengthen the yarn Some claim lead sur- passes other metal because it stabilizes the friction coefficient acts as a dry lubricant to prevent drum scoring and inhibite formation of abrasive particles on the friction surface Metallic powders such as zinc and lead improve performance at high temperatures Limitation with fiue lerdlerd is that it oxidizes easily to litharge which promotes oxidation in unsaturated organic compounds Son believe these powders help break the continuity of the friction surface film during braking action Large amounts of metal 40 such as brass chips are added to linings for very high tenperature requirements requirements Brake lining compounders also add lead to compositions in the form of organic salt High teniperature liberates it as finely divided had in a reducing or inert atmosphere This prevents oxidation of the metal to an oxide and permits it to func- tion as a friction stabilizer Graphite Graphite in lining compounds imparts a lubricating effect for smoother stopping It can be incorporated in the hard rubber or added separately Some compounders see two advantages for graphite encased in rubber First it does not interfere with flow of the resin binder during curing Second graphite is released for its lubricating action only after the rubber is softened by high braking tem- perature Iron oxide in small amounts sometimes is used as a controlling element It tends to have a polishing action which partly controls surface frictional properties The compound usually requires large amounts of inorganic fillers to produce frictional effects This necessitates an improved friction stabilizer that functions over a wide temperature range Organic modifiers as rubber ground rubber scrap pitches and gilsonite- function best over narrow temperature ranges A powdered product made from cashew nut liquid is one of the better stabilizing and wearenhancing agents used today This material works satisfactorily up to temperatures of 600 to 050 F. Tire scrap particles function up to about only 509 F. About 6 to 80 of dust is needed to improve wearing qualities Ground tire scrap has been and will continue to be widely used because it is a cheap raw material Other friction modifiers as pitches gilsonite coal and petroleum coke be used in limited quantities only because of their low temperature resistance Braking temperatures destruc- tively distill these materials to form tarry or pitchy residues at the friction surface These increase the friction coemcient at low temperatures But at high temperatures volatile materials may be driver off too rapidly before formation of tarry products losing their effectiveness Research today is aimed at getting binding materials with high heat resistance Currently the JUNE 1950 21