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operating ideas continued The fluxes designed for mining tools are water-based, high-tem- perature brazing paste products, two of which are shown below. Flux Type White Paste Flux Boron-Modified Paste Flux Active Temperature Range 1,400°F/760°C - 2,100°F/1160°C 1,400°F/760°C - 2,250°F/1230°C Both fluxes work exceptionally well in this application, and are per- fectly matched with the filler alloys used. The white flux performs best on smaller tools, while the boron-modified flux works well on larger tools, owing to its ability to withstand higher temperatures and longer heating cycles. Fluxes are essential when joining metals in ambient air. Filler metals only wet clean metallic surfaces, and flux facilitates this. When heated, fluxes perform five critical tasks: 1) Dissolve or react with surface metal oxides; 2) Protect the cleaned surfaces against re-oxidation; 3) Help transfer heat from the heat source to the joint; 4) Lower the surface tension of the filler metals and the joining sur- faces; and 5) Remove surface oxides, allowing the filler metal to flow and wet the joining surfaces. Finally, when all of the parts are properly arranged within the pocket, the tools are set on a conveyor system, which moves them slowly into the heat zone. Induction heating is the preferred method for brazing the mining tools, and is done in ambient air. Brazing temperatures in the range 1,900°F/1,047°C – 2,100°F/1,140°C are used. Various techniques are employed to make sure that optimum bonding occurs between the steel shanks and the carbide bits. Excellent wetting is a necessary pre-requisite Miners also rely heavily on carbide bits for roof drilling. (Photo courtesy of Kennametal) for achieving the tool strength needed for prolonged operation. After heating, the brazed tools are generally quenched in water. Flux residues either come off in the quenching process or when the tools receive their final cleaning. Dr. Baskin is president and technical director for Superior Flux & Mfg., which is based in Cleveland, Ohio. He can be reached at 440- 349-3000 (Email: info@superiorflux.com). Acknowledgment The writer gratefully acknowledges the assistance of Dr. Jonathan Baskin. February 2012 www.coalage.com 47