Ever asked what size/length rods (bars) you need for charging your rod mill?  It depends on the rod mill diameter itself.

Rod_Mill_Bar_Length_To prevent most conditions leading to rod charge tangling, the generally recommended relationship of rod length to mill diameter Inside liners is 1.4 to 1.6. When this ratio becomes less than 1.25 the risk of tangling Increases rapidly. For rod mills larger than 3.8 meters (12.5 feet) in diameter rod availability and quality have to be considered. Table II gives rod length to mill diameter ratios for the larger diameter rod mills.

6.8 meters (20 feet) Is a practical limit on the length of good quality rods (that is rods that will stay straight in the mill and will break in to pieces that will discharge from the mill when worn). This length is a function of rod quality and production limits imposed by the suppliers. The mill length inside end liners measured along the surface of the shell liners should be 0.1 to 0.15 meters (4″ to 6“) longer than the rods so that the rods will fit in the length of the grinding chamber without tipping or laying across the charge. A slope as steep as possible should be used for rod mill head (end) liners to prevent unsupported ends of rods from protruding from the charge and being broken under impact from other rods.