11
coarse end curvature in log-log Schuhmann (1940) and
Rosin-Rammler (1933) plots, and which revealed grain size
grindability effects. This was in order to explain observed
variations in work index with particle size. This “modified
semi-log” plot included the energy input (or “energy regis-
ter,” as he termed it) as a factor in the in the exponent relat-
ing particle size to percent passing, and steps to calculate
the actual (theoretical) “crack length.” While this plot was
mentioned in his subsequent writings, it was not material to
the basic work index calculations as described in his other
key writings like “Crushing and Grinding Calculations,”
Parts l and ll, in British Chemical Engineering, 1961.
Interestingly, this paper also included, in Appendix
D, Bond’s observation on the effect of circulating load on
the 12" laboratory ball mill test results. He said the results
demonstrated “no increase in efficiency of new crack length
production,” i.e., grinding itself. The reduction in calcu-
lated test work index (e.g., from 13.5 to 12.2 kWh/t, or
just under 10%) in going from a circulating load of 150
to 390 percent he attributed to the increase in “the effi-
ciency of grinding to pass a certain size,” and subsequently
provided quite small correction factors for open vs. closed
circuit grinding (BCE, 1961). This did not consider that
plant classifiers impose very different (far less sharp than lab
screening) separation, and worsening, in fact, separation
performance with increasing circulating load, and despite
this worsening classifier performance, overall circuit effi-
ciency increases significantly (Davis, 1925) with increasing
circulating load.
In “Action in a Rod Mill” (E&MJ March, 1960), Bond
used Work Index to show a major loss of rod mill efficiency
with broken rods which create void spaces in the charge. He
introduced the correction factor for excessively high reduc-
tion ratio, and a new (but later amended) recommended
rod sizing equation.
The “Three Principles of Comminution” that Bond
published in Mining Congress Journal in August of 1960
were as follows. First, comminution energy input is the
difference between the energy register (in kWh/t) of the
product minus that of the feed, the “energy register” repre-
senting strain introduced into the particles. Second, energy
register increases as particle size decreases, following some
exponent, valued at one by Rittinger, zero by Kick, and 0.5
by Bond’s Work Index. Thirdly, variations in Work Index
at different product sizes are governed by the flaw struc-
ture of the material. He discussed these in greater detail
in “Principles and Progeny in Comminution,” presented
at the 1961 SME, adding updated (today’s) equations for
calculating work index values from rod and ball mill grind-
ability tests. He also re-presented the above-mentioned
correction factors for P80 less than 70 microns and feed
with fines removed.
As “The Third Theory” became known, Allis-Chalmers
used Bond’s new notoriety to promote its equipment busi-
ness. They hailed him in advertising as “A Living Legend”
(Engineering and Mining Journal, Jan., 1963) which he
found to be quite unsettling. A number of following arti-
cles, besides the “Crushing and Grinding Calculations”
noted above, repeat the “Third Theory” and “Three
Principles” themes of presenting both the work index equa-
tion and its variations due to grain size and certain design
and operating conditions. These include “Principles and
Progeny in Comminution” presented at SME in March,
1961 “Crushing and Grinding with Pyro-Processing,” Pit
and Quarry, January, 1962 “New Ideas Clarify Grinding
Principles,” Chemical Engineering, February 5, 1962
“The Laws of Rock Breakage,” Zerlkeinern Symposium,
Verlag Chemie, Dusseldorf, 1963 “More Accurate
Grinding Calculations,” Cement, Lime and Gravel, March,
1963 “Constant Work Index from The Crack Length,”
Engineering &Mining Journal, March, 1963 “Some
Recent Advances in Grinding Theory and Practice,” British
Chemical Engineering, September, 1963.
In the June, 1963 issue of Canadian Mining Journal,
Bond provided a brief and very general discussion of “Particle
Size Reduction—Theory and Practice.” He broadly covers
types of size reduction machinery, from crushers to rod and
ball mills, impact crushers and vibrating mills, and also
describes autogenous and semi-autogenous primary mills.
He describes his Third Theory, comparing it to Kick’s and
Rittinger’s. He finally notes the modern trends of increas-
ing mill size (up to 4,000 HP) and degree of automation.
He mentions the “lower unit grinding costs of these giant
machines.”
Bond first published on the topic of autogenous mill-
ing in Engineering and Mining Journal, April of 1962, with
“Rock on Rock Grinding—A Growing Technology.” What
he referred to as “rock-pebble” autogenous mills used ore
pieces removed from upstream to grind finely in small diam-
eter to length mills, as practiced widely on South Africa
gold ores and on some Canadian uranium and gold ores.
These of course qualified as “autogenous” mills. He clarified
the terminology and covered the history from the first dry
“Hadsel” mill, which mimicked dropping the ore through
the mine ore passes with a “large-diameter ferris-wheel”
using elevating scoops. These evolved into the “wet primary
autogenous” grinding mills of large diameter to length
ratio (initially motivated to facilitate better air sweeping in
dry grinding) fed by run-of mine or primary crushed ore.
With fully autogenous in mind, he provided many useful
coarse end curvature in log-log Schuhmann (1940) and
Rosin-Rammler (1933) plots, and which revealed grain size
grindability effects. This was in order to explain observed
variations in work index with particle size. This “modified
semi-log” plot included the energy input (or “energy regis-
ter,” as he termed it) as a factor in the in the exponent relat-
ing particle size to percent passing, and steps to calculate
the actual (theoretical) “crack length.” While this plot was
mentioned in his subsequent writings, it was not material to
the basic work index calculations as described in his other
key writings like “Crushing and Grinding Calculations,”
Parts l and ll, in British Chemical Engineering, 1961.
Interestingly, this paper also included, in Appendix
D, Bond’s observation on the effect of circulating load on
the 12" laboratory ball mill test results. He said the results
demonstrated “no increase in efficiency of new crack length
production,” i.e., grinding itself. The reduction in calcu-
lated test work index (e.g., from 13.5 to 12.2 kWh/t, or
just under 10%) in going from a circulating load of 150
to 390 percent he attributed to the increase in “the effi-
ciency of grinding to pass a certain size,” and subsequently
provided quite small correction factors for open vs. closed
circuit grinding (BCE, 1961). This did not consider that
plant classifiers impose very different (far less sharp than lab
screening) separation, and worsening, in fact, separation
performance with increasing circulating load, and despite
this worsening classifier performance, overall circuit effi-
ciency increases significantly (Davis, 1925) with increasing
circulating load.
In “Action in a Rod Mill” (E&MJ March, 1960), Bond
used Work Index to show a major loss of rod mill efficiency
with broken rods which create void spaces in the charge. He
introduced the correction factor for excessively high reduc-
tion ratio, and a new (but later amended) recommended
rod sizing equation.
The “Three Principles of Comminution” that Bond
published in Mining Congress Journal in August of 1960
were as follows. First, comminution energy input is the
difference between the energy register (in kWh/t) of the
product minus that of the feed, the “energy register” repre-
senting strain introduced into the particles. Second, energy
register increases as particle size decreases, following some
exponent, valued at one by Rittinger, zero by Kick, and 0.5
by Bond’s Work Index. Thirdly, variations in Work Index
at different product sizes are governed by the flaw struc-
ture of the material. He discussed these in greater detail
in “Principles and Progeny in Comminution,” presented
at the 1961 SME, adding updated (today’s) equations for
calculating work index values from rod and ball mill grind-
ability tests. He also re-presented the above-mentioned
correction factors for P80 less than 70 microns and feed
with fines removed.
As “The Third Theory” became known, Allis-Chalmers
used Bond’s new notoriety to promote its equipment busi-
ness. They hailed him in advertising as “A Living Legend”
(Engineering and Mining Journal, Jan., 1963) which he
found to be quite unsettling. A number of following arti-
cles, besides the “Crushing and Grinding Calculations”
noted above, repeat the “Third Theory” and “Three
Principles” themes of presenting both the work index equa-
tion and its variations due to grain size and certain design
and operating conditions. These include “Principles and
Progeny in Comminution” presented at SME in March,
1961 “Crushing and Grinding with Pyro-Processing,” Pit
and Quarry, January, 1962 “New Ideas Clarify Grinding
Principles,” Chemical Engineering, February 5, 1962
“The Laws of Rock Breakage,” Zerlkeinern Symposium,
Verlag Chemie, Dusseldorf, 1963 “More Accurate
Grinding Calculations,” Cement, Lime and Gravel, March,
1963 “Constant Work Index from The Crack Length,”
Engineering &Mining Journal, March, 1963 “Some
Recent Advances in Grinding Theory and Practice,” British
Chemical Engineering, September, 1963.
In the June, 1963 issue of Canadian Mining Journal,
Bond provided a brief and very general discussion of “Particle
Size Reduction—Theory and Practice.” He broadly covers
types of size reduction machinery, from crushers to rod and
ball mills, impact crushers and vibrating mills, and also
describes autogenous and semi-autogenous primary mills.
He describes his Third Theory, comparing it to Kick’s and
Rittinger’s. He finally notes the modern trends of increas-
ing mill size (up to 4,000 HP) and degree of automation.
He mentions the “lower unit grinding costs of these giant
machines.”
Bond first published on the topic of autogenous mill-
ing in Engineering and Mining Journal, April of 1962, with
“Rock on Rock Grinding—A Growing Technology.” What
he referred to as “rock-pebble” autogenous mills used ore
pieces removed from upstream to grind finely in small diam-
eter to length mills, as practiced widely on South Africa
gold ores and on some Canadian uranium and gold ores.
These of course qualified as “autogenous” mills. He clarified
the terminology and covered the history from the first dry
“Hadsel” mill, which mimicked dropping the ore through
the mine ore passes with a “large-diameter ferris-wheel”
using elevating scoops. These evolved into the “wet primary
autogenous” grinding mills of large diameter to length
ratio (initially motivated to facilitate better air sweeping in
dry grinding) fed by run-of mine or primary crushed ore.
With fully autogenous in mind, he provided many useful