graphite flakes is harmful because theycause the alloy to be weak in tension and tobe brittle. The machining of gray cast ironsurfaces smears the surfaces with graphite,making it diffïcult to wet the surfaces withbrazing filler metal. During brazing, silverand copper filler metals do not wet thegraphite flakes or nodules. Graphite mustbe removed from the surfaces prior to brazing. Filler metals that contain chromium, titanium, or other carbide formers wilI wetand bond to the graphite. Filler metals suchas BNi-2 can be used without the normalcleaning process to remove the graphite.Some high silicon cast irons may have asilicon oxide on the surface of the castingwhich will also prevent wetting by the fillermetal. These surfaces must be cleaned byone of the methods described below. Whenusing metals that do not contain carbideformers, smeared graphite and graphiteflakes must be removed from the surfaces tobe brazed. There are several processes thatmay be used, depending on the parts application and the cost.
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