|Fred Bond, 1972|
Fred Bond’s work on circuit design occurred from the late 1930s to the mid 1960s and it changed the method of design completely. In the pre-Bond era the prediction of the power required per tonne to grind material to a known product size was based on experience and judgment, but in the post Bond era the method of prediction has become engineering practice based on measurement and calculation.
Bond’s work defined the relationship between ore hardness, tonnage processed, size reduction achieved and power required. It set the standard for circuit design in the 1950s and it is widely used today, although modifications have been made to handle the large increases which have occurred in mill sizes, feed sizes and feed rates. The Bond Work Index approach is the standard method of selecting ball mills to grind from about 3 mm to 25 µm provided that correction factors are used if necessary.
A graduate and former professor of the Colorado School of Mines, Bond worked in the mining and ore milling equipment business of Allis-Chalmers from 1930 to 1964, and he knew the limitations of design techniques which were current at the time. During the late 1930s and the 1940s he studied the relationship between energy and size reduction and in 1952 he proposed a “Third” theory of comminution to define this relationship, Rittinger and Kick having proposed the first two. To apply it he defined “Work Index” for an ore as the specific energy (kWh/tonne) required to reduce the ore from infinite grain size to 100 µm and he showed that for any ore the Work Index can be calculated from plant data and determined in a laboratory test in a specified Bond Mill. The power prediction is fairly accurate for devices that produce a product with a size distribution parallel to that of the feed. It does not work well for devices such as the AG/SAG mill and high pressure grinding rolls where the product size distribution is not parallel to that of the feed. For SAG mills methods such as the Starkey SAGDesign mill, the SAG equivalent of the Bond Mill, are used.
Bond, who died in 1977, was inducted with first class into the National Mining Hall of Fame in 1988 and received a Distinguished Achievement Medal by his alma mater, the Colorado School of Mines, in 1952. He received the 1965 AIME Robert H. Richards Award "for major contributions to increased knowledge of crushing and grinding processes and for achievement in industrial application of this knowledge to advancement of the milling industry."