A roller-type device was developed by the Bureau of Mines that promises to effectively sample coal mine float dust. Float dust is the air-entrainable layer of fine coal that settles on the rock dust substrate in coal mine airways. Evaluating the potential hazard of float dust requires accurate sampling of this thin--approximately 1/64 inch--layer of coal dust, which is equivalent to 0.03 Ounce of float dust per cubic foot of entryway. The prototype sampler is constructed from 40-mesh stainless steel screen formed into a cylinder 6 1/4 inches long by 3 7/8 inches in diameter. Seventeen 6- inch-long by 1/4-inch-wide flights are soldered inside the screen with about 1/2 inch of open screen between the flights. A dust- collection tray is suspended from the central axle of the cylinder so that the open side of the tray always remains upright. In laboratory tests, the rolling screen sampler made minimal impression in the dust surface and, therefore, removed a representative layer of re-entrainable solids. Extensive areas could also be rapidly covered by the sampler, thus increasing the recovery of sample material typical of the surface.
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