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

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]

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 woven asbestos reinforced with brass or other ~1908 automobiles and trucks wires Molded linings with shorter chrysotile fibers, ~1926 automobiles and trucks brass particles and low ash bituminous coal ~1930 dry mix molded material London underground 1930's flexible resin binders brake drum linings 1950's resin bonded metallic brake linings industrial and aircraft applications Glass fibers, mineral fibers, metal fibers, carbon 1960's automotive and trucks and synthetic fibers (instead of asbestos) 1980's NAO: non asbestos (fiberglass) reinforcement brake drums on original equipment cars 1990's carbon fibers automotive brakes

Taking a look at the development which went through in early, but only the availability of new materials and the field of clutches regarding constructions along with machining methods allowed them to be realized. friction materials in use, – see Table 5 – one can find some similar dates assuming a common influence 5 DEVELOPMENT TRENDS compared to brake materials – for instance efforts to replace asbestos – that affected the goals of the whole Working with polymer composites opens a wide friction material industry. The table also shows that the range of opportunities to develop new or better materials construction and material development trends regarding experimenting with amounts of ingredients, untested, clutches became parallel only with single clutch discs new components or expanding or narrowing down going through milestones in fields like lubrication manufacturing steps. For instance Table 6 shows how improving possibilities and utilization of newly one of the suppliers, FCC examined the sensitivity of discovered friction material components, then taking some product characteristics to the different steps of healthcare and environmental protection into production in order to better understand how to consideration. Most of the basic designs were developed manipulate the characteristics of the final product from the beginning steps of the whole process. [5]

Table 5. Clutch friction materials vs constructions 1889 - 1918 - ('04) Year 1886 1920's 1920's -1920's 1900 - 1918 1900's - 1920's - Type of clutch friction clutch transmission cone/bevel Daimler/Mer- Weston NAG Daimler single belt clutch friction cedes spring multidisc cone Al-cone clutch disk Year Friction material clutch band clutch oiled/dry 1886 leather belts x 1889 camel hair x x after leather belt soaked x 1889 into castor oil after spring loaded pins/ x 1889 leaf spring + leather 1918 metal x x 1918 - oiled aluminium x oiled bronze and 1900's - x steel 1900's - riveted friction lining x 1920's - graphite lubricated x 1920's - ferodo asbestos x asbestos free (NAO) 1990's - x linings

Today’s development and experimental trends vary materials. [8] Investigating further it came out, that among studying uncertain tribological phenomena, copper powder is very effective to reduce the sensitivity effects of different fillers, the role of copper, solving of the friction coefficient to dynamic variations in production induced problems or searching for pressure and speed. [9] These studies led to the possibilities to use bio materials taking environmental conclusion, that inclusion of copper improves all major protection into consideration. Basavarajappa et al properties of frictional materials also at production scale. examined dry sliding characteristics of glass-epoxy [10] Bakry et al investigated the effect of agriculture composite with various volume percentage of filler fibre wastes – corn, sugar bars and palms fibres – on materials finding their contribution significant in early friction coefficient and wear. The aim of the work was to stage of wear. [2] Gurunath et al experimented replace composite components with environmentally successfully with a newly developed resin in order to friendly friction material for brake linings and clutch avoid shrinkage, a major problem that occurs at the end facings. It turned out, that they are capable of increasing of the production of friction materials using phenolic friction coefficient and decreasing wear. [1] resin as binder. [6] Kumar et al focused on metallic fillers, especially copper, which was found best performer regarding friction and wear of brake frictional

Table 6. F.C.C. sensitivity analysis – production steps affecting product features Step Affected item thermal resistance, friction Composition characteristic Bending of raw materials Density friction characteristic Strength peeling resistance Resin impregnation, hardening peeling and abrasion resistance thermal, peeling and abrasion Density resistance Bonding onto core plates Bonding/ peeling and abrasion resistance Strength

6. CONCLUSIONS [7] Jacko, M. G. and Rhee, S. K. (2000). Brake Linings and Clutch Facings. Kirk-Othmer Encyclopedia of Composite friction materials’ history developed Chemical Technology, Online ISBN: alongside with the evolution of brake, clutch and 9780471238966, p144-154, industrial application construction. Milestones that [8] Kumar, M., Bijwe, J., (2010). Role of different pushed it forward were the discovery and utilization of metallic fillers in non-asbestos organic (NAO) flexible resins, the growing popularity then the banning friction composites for controlling sensitivity of of asbestos considering healthcare. Nowadays trends coefficient of friction to load and speed, Tribology turn in the direction of environmental protection International vol. 43, experimenting with environmental friendly components doi:10.1016/j.triboint.2009.12.062, p. 965–974 such as plant fibers and fillers or bio-degradable friction [9] Kumar, M., Bijwe, J., (2011) Composite friction materials. materials based on metallic fillers: Sensitivity of µ There are still open questions about friction behavior to operating variables, Tribology International vol. under different conditions, wear characteristic 44, doi:10.1016/j.triboint.2010.09.013, p. 106–113 sensitivity, thermal loads and responses, manufacturing [10] Kumar, M., Bijwe, J., (2011) Non-asbestos organic steps etc. The field of composite frictional materials is so (NAO) friction composites: Role of copper; its wide-spread and still an undeveloped land, that it grants shape and amount, Wear vol. 270, a wide range of research opportunities for present and doi:10.1016/j.wear.2010.10.068, p. 269–280 future investigations, experiments and studies. [11] Zhang, X., Li K.-Z., Li, H.-J., Fu, Y.-W., Fei, J. (2014). Tribological and mechanical properties of REFERENCES glass fiber reinforced paper-based composite friction material, Tribology International, vol. 69, [1] Bakry, M., Mousa, M. O., Ali, W. Y. (2013). doi:10.1016/j.triboint.2013.08.003, p. 156–167 Friction and wear of friction composites reinforced by natural fibres. Mat.-wiss. u. Werkstofftech., vol. Authors addresses 44, Issue 1, doi: 10.1002/mawe.201300962, p. 21- 28 1Roland, Biczó, PhD student, Institute for Mechanical [2] Basavarajappa, S., Ellangovan, S. (2012). Dry Engineering Technology, Szent István University, Páter sliding wear characteristics of glass–epoxy Károly u.1, Gödöllő, Hungary, [email protected] composite filled with silicon carbide and graphite particles, Wear, vol. 296, 2Gábor, Kalácska, DSc, professor, Institute for doi:10.1016/j.wear.2012.08.001, p. 491–496 Mechanical Engineering Technology, Szent István [3] Bijwe, J. (1997). Composites as friction materials: University, Páter Károly u.1, Gödöllő, Hungary Recent developments in non-asbestos fiber [email protected] reinforced friction materials—a review, Polymer Composites, vol 18, Issue 3, doi: 10.1002/pc.10289, 3Zoltán,Szakál,PhD, lecturer Institute for Mechanical p. 378–396 Engineering Technology, Szent István University, Páter [4] Blau, P. J. (2001). Compositions, Functions, and Károly u.1, Gödöllő, Hungary, Testing of Friction Brake Materials and Their [email protected] Additives, Oak Ridge National Laboratory, Metals and Ceramics Division, 4Gellért, Fledrich, PhD, associate professor, Institute for https://www.ornl.gov/ Mechanical Engineering Technology, Szent István [5] F.C.C. Co. Ltd. Technical Information, Segment University, Páter Károly u.1, Gödöllő, Hungary, Disc Manufacturing Process http://www.fcc- [email protected] net.co.jp/en/technical/segmentdisk.html [6] Gurunath, P.V., Bijwe, J., (2007). Friction and wear Contact person studies on brake-pad materials based on newly * Roland, Biczó, PhD student, [email protected] developed resin, Wear, vol. 263, doi:10.1016/j.wear.2006.12.050, p. 1212–1219