Composite Friction Materials for Brakes and Clutches
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BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX Composite Friction Materials for Brakes and Clutches 1* 2 3 4 R. Biczó , G. Kalácska , Z. Szakál , G. Fledrich Abstract: As a part of a broad tribological research this paper deals with composite friction materials used in brake and clutch applications. Lists their main types searching for similarities and differences in manufacturing, takes into consideration components used for production showing development trends in the past considering material and construction. Finally it shows a glimpse into present and near future investigation and experiments to answer questions and solve problems of the field of frictional material science. Keywords: polymer, composite, frictional material, clutch, brake 1. INTRODUCTION good wear resistance during operation. They should possess the ability to resist heat induced deterioration, Typical components of polymer composite impact and centrifugal force during friction. Tribological friction materials for clutches and brakes can be performances and mechanical properties of the friction classified in the following groups: reinforcements, materials depend on the mentioned components. For binders, friction modifiers and fillers. The friction instance fibers play a critical role in determining the materials are deformable, their task is to maintain a mechanical strength, thermal resistance, and friction and sufficiently high and stable friction coefficient and a wear properties of the materials. [11] Table 1. Manufacturing steps of brake linings Type Brake lining Subtype Linings Segments Disk pad Blocks Preferred application heavy-duty use fibrous for organic blocks: as for fiber, organics: intensive reinforcement, segments, for semimetallic mixing modifiers, dry mixer, semimetallics: friction modifiers, blocks: as for resin less intensive blender liquid resin, 50 °C semimetallic disk pads Heating to 90 °C, 60-90 cm pressed into preforms preforming extrusion at 14-28 preform at 3-4 at room temperature, at 10-17 MPa MPa MPa 28-42 MPa drying 2 h, 80 °C preheating to 90 °C, 15-30 min Manufacturing rolling, partial hot-pressing, 3- hot pressed 5-15 min steps drying, fiber 10-30 min, 130-150 °C, forming 10 min at 140- at 160-180 °C, 28-55 aligning in the 14-21 MPa, 160 °C, cooling MPa tape reheated, hot- pressed slitting to width, grinding cutting to length, sizing preforms cut, of internal and external forming, 150 °C bent at 170- radii 190°C heat curing: 4-8 h, curing: 4-8 h curing: 4-8 h, 220- curing: 5 h, 180 °C or 6 treatment 180-250 °C 220-280 °C 300 °C h, 280 °C grinding a a a a + drilling, chamfering 2. OPERATING CHARACTERISTICS gradually dissipates it into the atmosphere. A brake is a sliding friction couple consisting of a rotor – disk or Requirements of composite friction materials drum – connected to the wheel or machine and a stator derives from the operating characteristics of applications on which is mounted the friction material. [7] they are used in. It demands brake and clutch friction A clutch transfers the kinetic energy of a rotating materials to be separately dealt from this scenario. crankshaft – coupled to a power source – to the A brake converts the kinetic energy of the moving transmission and wheels. Slippage results in the vehicle or machine part into heat, absorbs the heat, and 21 BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX generation of heat, which is absorbed and eventually members. When the application operates in fluid, for dissipated to the atmosphere by the clutch. [7] instance oil, this liquid absorbs the heat and maintains Both applications have dry and wet operation types. If low operating temperatures while trapping the wear the friction couples are dry, heat is removed by debris. [7] conduction to the surrounding air and other assembly Table 2. Manufacturing steps of clutch facings Type Clutch facing Fiber reinforced hybrid matrix composite Sintered cermet Paper based facing Subtype facing segments trucks, heavy off- manual automatic Preferred application road equipment paper-made soaked roll of winding friction material taken up onto a winder weaving forming a reel of wire preforming curable ribbons with preforming preforms designated widths dry: ingredients based dry: fillers, wet: fillers, mixing fillers, on desired modifiers modifiers modifiers properties strand run through premix picks applying adhesive coating up viscous to the core plates mass, ~160 °C molding molding of of mix mix around molding without strand or strands or wire preforms wire Manufacturing cooling and drying steps drying sizing desired shape to a to a specified to a specified weaving specified pattern pattern pattern 4 min, 150- thermal pressure hot-pressing a a 180 °C bonding curing a a 24 h, 210°C compacting a reducing or neutral atmosphere at temperatures sintering high enough so that the metallic ingredients adhere to each other coining or a recompacting grinding a a a a 22 BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX Fig. 2. Typical clutch facing types (from left to right): first row: clutch facings [3]; industrial technical friction materials, clutch segments [3] second row: Schaeffler woven clutch facings; Fig. 1. Typical brake lining types (from left to right):, Schaeffler woven facing with steel carrier plate first row: brake linings; molded brake linings; third row: cermet segmented facing with steel second row: woven brake linings; roll linings; carrier plate by Miba; Schaeffler paper based third row: disc brake pads; brake shoes; friction materials forth row: friction blocks; brake block [3] 4 COMPONENTS AND MATERIALS 3 MANUFACTURING STEPS Components used during the creation process of In spite of different operating characteristics the these materials – as mentioned before – can be fiber components and the manufacturing steps for clutch reinforcements, binders, friction modifiers and fillers. facings and brake linings show some similarities as Typical fibers are aramid, glass, carbon, steel, cellulosic shown in Table 1 and Table 2. By brake friction material fiber, thermoplastic fiber and asbestos in the past. The types – for main types see Figure 1 – the typical latter became popular relatively fast due to it’s high manufacturing steps are mixing of ingredients, strengths and modulus, thermal stability, good wear preforming, forming by hot pressing, sizing to the properties and the fact that this material could be used demanded dimensions, curing at high temperatures, then also as a filler. Regarding strength and modulus aramid, final grinding. [7] glass, carbon and steel can be taken into account as a Clutch facing types – for main types see Figure 2 – have substitution. Aramid also has high thermal stability, more diversities in manufacturing steps – as seen in good wear properties and stable coefficient of friction. Table 2 –which is a result of the fact, that three basic Glass fiber is relatively cheap. In terms of thermal types of clutch facing materials are available on the stability aramid, carbon and steel fibers became popular. market nowadays. They are fiber reinforced woven [3] clutch facings – some subtypes bonded onto a steel carrier plate –, paper based friction materials usually for oil-immersed clutches, and cermet segments for heavy duty and high velocity applications. [7] 23 BULETIN ŞTIINŢIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia Construcţiilor de Maşini SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology, ISSN 1224-3264, Volume 2016 No.XXX Table 3. Issues with fibers Fiber Problems expensive, extra care against pulp on mixing, alone not Aramid adequate, needs other ingredients week heat resistance causes fade, loses fiber form in high shear mixing, molding, springs back, unsteady coefficient Glass of friction, low wear characteristic Carbon expensive, loses fiber form in mixing Steel heavy, corrodes, abrades disc, rotors, noise Cellulosic fiber low strength and modulus, low char temperature Thermoplastic fiber melts causing fade Asbestos health hazard Despite the wide range of advantages, suppliers had to beginning of the twentieth century, only after the take a lot of disadvantages into account when decided to discovery of flexible resins could they spread widely on use these fiber materials. Some of their problems are the market. Another change in trends began in the 60’s shown in Table 3. with the growing number of reports about the hazardous These trends developed throughout the last century and effects of asbestos. Sweeping out the material from all decade showing enormous developments in both main newly developed applications took more than thirty fields of friction materials. Table 4 shows how brake years. friction materials changed since the 1870’s. [4] Although fiber reinforced materials were present since the Table 4. Brake friction materials Year Material Application prior to 1870's cast iron on steel railroad car brake blocks and tires ~1897 hair or cotton belting (max 150°C) wagon wheels and automobiles