Document ppgdRGZdxg6aKpQDLdKJdGDXX

r emitted from brake drums, disc crakes and clutches of vehicles operating under real conditions. Hopefully the situation will be more clearly understood at the end of those studies. Emission Control Techniques Emission at Overhaul - To avoid blowing the accumulated dust into the atmosphere at the time of overhaul devices have been suggested for extraction of the dust from brake and/or clutch housings by suction. Of the devices tried, a simple hand-held vacuum cleaner has proven to be the most flexible unit. Changes to the original-design have been limited to the addition of a disposable paper bag inserted in the original cloth bag. The paper bag may be easily sealed before removal to prevent emission. I Substitution - Beyond the adaptation of better cleaning practices during brake and clutch maintenance, as mentioned above, additional controls seem to be limited to improve design of brake- and clutch assemblies and/or .substitution of other materials for asbestos. The high temperature properties and exceptional tensile strength of asbestos have resulted in very compact and economi cal design. These.same unique properties which make asbestos applicable to friction materials also make' the application of substitute materials very difficult. The tensile strength and modules of rigidity of asbestos as compared to several candidate substitute materials follows:* Tensile Strength lb/in.2 Asbestos Fiber yarns Steel wool .Mineral wool 550,000 180,000 50,000 25,000 2 Modulus of r.ioiditv Ib/in. .30 000,000 .3 000,000 100.000 60.000 There is no doubt that. substitution of other materials for t asbestos, is possible, but the design changes required to accom modate the stresses and temperatures involved would result in* IT RESEARCH INSTITUTE 27