Document 2qorgGVR2dyXe59pZpGO1L57L

United States Patent 4,217,255 Page 4 of 9 rates. UMMARY OF THE INVENTION I have discovered that railroad brake shoes that meet AAR (Association of American Railroads) standards for brake shoes can be made from compositions having a low, non-asbestos fiber content which includes synthetic fiber The friction matenals according to this invention compnse, by weight, 0 5-11 0% non-asbestos fiber, including at least 0 5% synthetic fiber, 66-81% filler and 14-21% organic binder A preferred embodiment of this composition friction material for railroad car use contains 2 73 5% synthetic fiber, 74-82% filler and 16-19% organic binder DETAILED DESCRIPTION OF THE INVENTION The criterion for suitability of a composition friction material for railroad car brake shoe use is the ability of the friction material to pass the standards set forth in the A A R Specification M-926-72, Feb 13, 1973 Revision Some of the pertinent dynamometer performance test criteria called for m this AAR Specification are as follows. 1 Instantaneous Retarding Force During 45 Minute Dynamometer Drag Test Drag Heavy load Light load Retarding Force 400 lbs min 300 lbs mm 2 Static Coefficient of Friction 9 Test Average--0 38 mm 3 Stop Distances From 90, 70, 50, 30, 10 mph Under Light and Heavy Brake Shoe Loads (all stop distances must be within varying tolerances) 4 Wear Loss Drag Tests (total)-O 60 in sup 3 max Test Stops (total per sequence)--1 20 in sup 3 max As used herein, the term "synthetic fiber" means fiber made from a substance which does not naturally occur in a fibrous state and includes glass, polyester and kaowool The term "synthetic fiber" excludes all forms of cellulose, which naturally occurs in a fibrous state, but which can also be processed into a different fibrous form (e g , rayon) Some example mixes used a single type of synthetic fiber, while others used several types of synthetic fibers in combination Other example mixes contained a mixture of synthetic and cellulose fibers All mixes were totally free of asbestos and lead Organic binders, such as styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR) and modified phenolic and cashew resins were used Cunng agents for the organic binders included sulfur, zinc oxide and hexamethylene tetramine http //patft uspto gov/netacgi/nph-Parser9Sectl=PT02&Sect2=HITOFF&u=/netahtml/sea 10/18/2003