. Graphite. otyping, and boiler graphite, and is inspecial demand for pencil manufacture. In Fig. 10 is shown a grinding installation specially designed for thefine grinding of graphite (Raymond Bros., Chicago). FLAKE GRAPHITE. The extraction of flake graphite from its ores, and its preparation forthe market—more particularly the crucible trade—has always been aproblem presenting considerable difficulties from both the technical andthe economic side. This is due in the first place to the fact that the prin- 1 Dammer und Tietze, Die Nutzbaren Mineralien, Vol. I, p. 65. 65 cipal minerals with wh
. Graphite. otyping, and boiler graphite, and is inspecial demand for pencil manufacture. In Fig. 10 is shown a grinding installation specially designed for thefine grinding of graphite (Raymond Bros., Chicago). FLAKE GRAPHITE. The extraction of flake graphite from its ores, and its preparation forthe market—more particularly the crucible trade—has always been aproblem presenting considerable difficulties from both the technical andthe economic side. This is due in the first place to the fact that the prin- 1 Dammer und Tietze, Die Nutzbaren Mineralien, Vol. I, p. 65. 65 cipal minerals with which flake graphite is usually associated, (quartz,calcite, feldspar, and mica), and which commonly form from 75 to 95 percent of the ore, possess specific gravities varying but little from that ofgraphite itself; added to which, one of the most common impurities—mica—is of more or less identical form, hardness and toughness, andbehaves in much the same fashion as the graphite particles at practically. mjr XTU- Fig. 10. Installation of Raymond high-side roller-mill equipment for grinding graphite. all the stages of mechanical treatment, such as grinding, jigging, tabling,screening, etc. Owing to this latter fact, mica is one of the most difficultminerals to eliminate by any of the straight mechanical processes; and,being a mineral that fuses readily at the temperatures to which cruciblesare subjected, its presence even in minor amount is highly prejudicial ingraphite intended for the crucible trade. The principal difficulty, however, in connexion with the concentratingand refining of flake graphites, is due to the fact that the crucible trade,which uses probably about three-fourths of the worlds output of graphite,demands the best quality, and pays the highest prices, specifier that whatis known as No. 1 crucible flake shall not only possess a high carboncontent (90 per cent or better), but, in addition, must not exceed a certaindegree of fineness. The limits usually set
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Keywords: ., bookauthorcanadami, bookcentury1900, bookdecade1920, bookyear1920
