Chattanooga Paper - The Hardinge Conical Pebble-Mill

Disregarding for the present the economic side of a new device, let us turn to that feature of the conical pebble-mill which is of interest from a scientific point of view, and consider the device as a puzzle in which the theories of the cylindrical type of mill have been increased. Many articles have been written on the theory of the tube-mill, and explanations have been made which do not explain ; but these have evolved suggestions of practice which have resulted in changes in the tube as to length, diameter, feed, discharge, speed of rotation, rotation on hollow trunnions, rotation on rings, and changes in the operation as to quantity and size of pebbles, charge of load above or below the axis, crushing by causing the larger pieces of the material of the charge to act as grinders, whether crushing is abrasive or impactive, etc. The practical worker in crushing. is first interested in the endeavor to reach an econonlic means of accomplishing a desired end; but the improvements in crushing-practice have been largely left to the manufacturer of machinery, who, as a rule, has little, if any, knowledge of the specific requirements— such as granulation, sizing for concentration without pulverizing the metals, instead of pulverizing the rock or gangue; the metals being the more friable, while the rock is tough and not so easily disintegrated. A reversal of this practice is the aim of sliming direct for cyanidation or pulverizing for cement, etc. In the ordinary cylindrical mill, having a diameter of 4 or