Document zQd0KpOjvmNYwkNVLrZkgokZ6

United States Patent 4,217,255 Page 3 of 9 r The friction material of claim 11, wherein the synthetic fiber is polyester fiber 13 An asbestos-free and lead-free composition friction material, comprising, by weight, 1 4-3 5% synthetic fiber, 74-82% filler and 16-21% organic binder 14 The friction matenal of claim 13, wherein the synthetic fiber is glass fiber 15 The asbestos-free and lead-free composition friction material, comprising, by weight, 2 7-3 5% synthetic fiber, 74-82% filler and 16-19% organic binder 16 The friction matenal of claim 15, wherein the synthetic fiber is glass fiber Description This invention relates generally to composition type railroad friction matenals and, more particularly, to such matenals which feature the use of synthetic fibers and the absence of asbestos and lead BACKGROUND OF THE INVENTION Most of the composition type railroad friction matenals m use today include asbestos and lead An example of this type of matenal is shown in U S Pat No 3,168,487--Spokes et al Some Kivironmentalists have warned of possible problems caused by the use of lead in friction matenals As a suit, demand has developed for a lead-free friction matenal Examples of some composition fnction matenals which exclude lead are U S Pat Nos 3,492,262--Gnffith and 3,959,194--Adelmann The former patent discloses a composition which has no lead and includes up to 16 5% by weight asbestos fiber, while the latter patent discloses some compositions which delete lead and have up to 11 1 % by weight asbestos fiber More recently, certain environmentalists have pointed out that possible problems may be caused by the use of asbestos fiber in fnction matenals Thus, it may be desirable to eliminate asbestos as well as lead from composition friction materials US Pat No 3,959,194 has some examples which utilize cellulosic fiber in a range of 3 5-8 0% by weight as a substitute for asbestos, although the patent is not concerned with eliminating asbestos in friction matenals Asbestos has traditionally been used in friction matenals because of its high heat resistance and strength and its low cost. A direct substitution of other types of fiber for asbestos is expensive, since other fibers cost much more than asbestos, and difficult, since no known fiber combines all of the desirable qualities of asbestos noted above It is known to use high-content carbonized or graphitized fibers in aircraft fnction matenals, as shown in U S Pat No 3,552,533--Nitz The use of glass fiber in friction materials is disclosed m several patents U S Pat No 3,743,069--Barnett relates a clutch facing consisting almost entirely of bundles of continuous glass filaments US Pat No 3,627,606--Bentz teaches a glassfilament-reinforced fabnc clutch facing impregnated with a cement containing lead (litharge) U S Pat No 3,713,934--Morton discloses a clutch facing composed of glass and asbestos None of these friction matenals would be suitable for railroad brake shoe use, since they are either too expensive and/or Kontain lead or asbestos It is, therefore, an object of this invention to provide lead-free, asbestos-free, high coefficient of friction, composition friction matenals which feature a low fiber content including synthetic fiber and low wear http //patft uspto gov/netacgi/nph-Parser?Sectl=PT02&Sect2=HITOFF&u=/netahtml/sea 10/18/2003