Document pmxzX1OEM6VnJBb8ernNypb8w

1 It in important to note that one major purpose of the reconditioning Agents lo to retard the formation of foraterite (a mineral not originally present in the brake material, but created by dchydroxylotion and re- crystallisation of chrysotile asbestos at high temperatures) which may V y' accumulate on the surface of the brake lining. The hardness of the for6torite (Mohs, 6.5-7.0) is such that it tends to score end gouge brake ^ ''y.1 ^^linings (hardness degrading them prematurely. Therefore, re- /S \/ crystallisation of chrysotile to forsterite is an unwanted effect, ty y .i* hindered insofar as possible by the modifiers present in the matrix. f'iV e' -,* Materials of biological interest Asbettoa, quart?, and heavy metals arc constituents of automotive brake linings, each warranting special consideration from the viewpoint of biological activity. The focus of this report is limited to the problem of chrysotile asbestos exposure. Mechanisms of degradation of brake linings during use brake wear is dependent upon many factors, such ns the temperature goner ated at the surface of the brake shoe during braking operations. At any one time, only a small percentage of the rubbing area is in contact with the Wheel, with "hot spots" generated, ranging up to 600 to 1,000C (Carroll, 196?; Anderson, 1969). It is not uncommon during aioderate hinting action, to attain temperatures as high as (M0vC (Anderson, 1969) Some investigators have suggested that, in addition to binder pyrolysis, chrysotile completely dehydroxylates under these conditions and "reduces to powder" where it is swept off the brake facing (Carroll, 1962). how ever, this hypothesis is oversimplified, in that other important pio- ccrses, besides thermal wear, contribute to shoe breakdown, and brake shoe degradation. PQ6005 1871, .y PRODUCED BY FORD