Steel grinding rods with good surface for rod mill. Mill (grinding) Wikipedia. A rotating drum causes friction and attrition between steel rods and ore particles. Rod mills are less common than ball mills for grinding FL - Rod Mills. FL Rod Mills are able to grind coarser material than ball mills. Grinding Rod manufacturers suppliers.Grinding Rod. Gerdau's N90 grade Grinding Rods are high carbon, micro-alloyed steel bars in sizes 2 through 4' in diameter. The non-heat treated hot-rolled process is controlled to provide hard (208-350 BHN) yet tough bar products for application as the grinding media for Mineral Processors to use in their rod mills to crush and grind ores, such as iron, copper and gold, for further processing.