5
shapes. He concluded that Rittinger’s law, which states that
the useful work done in crushing is proportional to new
surface area produced, is only valid for particles of the same
relative shape (height to width to thickness ratios).
Bond’s 1937 article in AIME’S Mining and Metallurgy,
“Determination of the Circulating Load in a Wet Closed-
Circuit Grinding System,” presented use of the two-product
formula to calculate classifier solids split from the percent
solids of the classifier streams, or the circuit feed tonnage
from the water dilution rate. He stated that this was better
than using individual screen sizes, which, even with small
measurement errors, gave highly variable results with dif-
ferent mesh sizes. In 1950 Bond updated the method. As
an alternative to using the stream percent solids, error was
reduced by using graphed size distributions, and, perhaps
most significantly, “the suggestion by Professor Taggart
(1941), … the size which 80% passes.”
In the 1938 Engineering &Mining Journal article,
“Reduction Ratio Curves for Crushing and Grinding,”
Bond showed that the amount of size reduction measured
by certain cumulative size passing ratios between the feed
and product could be related to energy consumption. This
was suggested at the time to hold potential promise for
comminution machine power specification.
Presented at SME in 1938 and published in 1939, Bond
and Maxson’s “Grindability and Grinding Characteristics
of Ores” firstly expanded the ball mill grindability tables
given in 1933. It followed with a method of calculating
surface area from screen analysis, and subsequently, the
new surface generated on ten-gram samples with the net
energy (work) input from an Amsler pendulum impact
testing machine. They proposed this method of generating
new surface area to be “absolutely efficient.” Comparison of
test results on several ores ground with the Allis-Chalmers
grindability test ball mill (estimated energy input of 85.7
joules per revolution) put its relative efficiency at close to
60%. Commercial, wet closed-circuit ball mills, they said,
produced relative efficiencies averaging 63.5%, but that
these were affected by circulating load. They finally con-
cluded that new surface area generated per revolution of the
test mill is constant for any given ore ground to different
finesses, in agreement with Rittinger’s law.
Bond’s paper on the sedimentation balance (a precision
balance pan suspended in liquid that collects and weighs
settling particles with time) for measuring fine particle
size distribution was published in 1939 and presented to
the AIME in 1940. It covers a lengthy, extremely detailed
description of the equipment and procedure from an inten-
sive investigation carried out at the Allis-Chalmer’s labora-
tory. He also provided a table to convert size fractions into
surface area, again to be able to interpret grinding results
in terms of Rittinger’s law. Numerous complexities and
assumptions meant that it did not develop into a practical
tool for his, or plant operators’ purposes, as he had hoped.
Up to this time Bond’s theoretical work results largely
supported Rittinger’s law. The difficulties in putting this to
practical use for equipment design, in particular the specific
energy needed for a given amount of size reduction, were
significant. Surface area of ground materials was difficult
to measure. Screen analyses were used in industry as grind-
ing liberation proxies, and did not convert readily to sur-
face area. The finest fractions dominated surface area, and
did not reflect useful grinding, but rather over-grinding in
terms of mineral liberation and often downstream recov-
ery. And different machines clearly displayed different size
reduction “efficiencies,” depending on the means by which
they applied their energies. Classification in closed circuit
systems added to the complexities. Theoretical size reduc-
tion efficiency versus practical terms for machine, or cir-
cuit, relative comminution “efficiency” was recognized, but
the two were not reconcilable.
Bond presented and published “Wear and Size
Distribution of Grinding Balls” in 1940. He starts by refer-
ring to the above Bond and Maxson (1938–39) work which
showed that Rittinger’s law of surface area creation is pro-
portional to the work input holds with different ball sizing,
even though the resulting distribution by size class varies.
He then discusses ball wear from over nine years of con-
tinuous records of rates of wear of each ball size using their
standard laboratory dry testing ball charge. They concluded
that larger balls wear slightly faster than smaller ones, as
would be expected due to impact forces. Equilibrium ball
charges were so calculated, from charging a single size,
from 5" downward. From this the total surface area of an
equilibrium charge is calculated, as are relative total ball
consumption rates. Bond follows with a theoretical discus-
sion of matching mill feed size distribution with the best
suited ball size distribution to maximize production rate
through a given screen size, the most common objective in
ore grinding. In passing, he notes that “the use of a circula-
tion load and short detention time in the mill,” are also best
for this objective. He concludes that “rationing” (addition
of a second smaller size) would be beneficial in most cases.
But, as noted, the relevant discussion in the paper on the
best suited ball sizing for grinding a given grinding circuit
or mill feed is strictly theoretical, and no practical guide-
lines are provided.
In 1940 Bond also co-authored “Deleterious Coating
of the Media in Dry Milling” with F.T. Agthe for AIME,
which was also published in Rock Products (1941) and
shapes. He concluded that Rittinger’s law, which states that
the useful work done in crushing is proportional to new
surface area produced, is only valid for particles of the same
relative shape (height to width to thickness ratios).
Bond’s 1937 article in AIME’S Mining and Metallurgy,
“Determination of the Circulating Load in a Wet Closed-
Circuit Grinding System,” presented use of the two-product
formula to calculate classifier solids split from the percent
solids of the classifier streams, or the circuit feed tonnage
from the water dilution rate. He stated that this was better
than using individual screen sizes, which, even with small
measurement errors, gave highly variable results with dif-
ferent mesh sizes. In 1950 Bond updated the method. As
an alternative to using the stream percent solids, error was
reduced by using graphed size distributions, and, perhaps
most significantly, “the suggestion by Professor Taggart
(1941), … the size which 80% passes.”
In the 1938 Engineering &Mining Journal article,
“Reduction Ratio Curves for Crushing and Grinding,”
Bond showed that the amount of size reduction measured
by certain cumulative size passing ratios between the feed
and product could be related to energy consumption. This
was suggested at the time to hold potential promise for
comminution machine power specification.
Presented at SME in 1938 and published in 1939, Bond
and Maxson’s “Grindability and Grinding Characteristics
of Ores” firstly expanded the ball mill grindability tables
given in 1933. It followed with a method of calculating
surface area from screen analysis, and subsequently, the
new surface generated on ten-gram samples with the net
energy (work) input from an Amsler pendulum impact
testing machine. They proposed this method of generating
new surface area to be “absolutely efficient.” Comparison of
test results on several ores ground with the Allis-Chalmers
grindability test ball mill (estimated energy input of 85.7
joules per revolution) put its relative efficiency at close to
60%. Commercial, wet closed-circuit ball mills, they said,
produced relative efficiencies averaging 63.5%, but that
these were affected by circulating load. They finally con-
cluded that new surface area generated per revolution of the
test mill is constant for any given ore ground to different
finesses, in agreement with Rittinger’s law.
Bond’s paper on the sedimentation balance (a precision
balance pan suspended in liquid that collects and weighs
settling particles with time) for measuring fine particle
size distribution was published in 1939 and presented to
the AIME in 1940. It covers a lengthy, extremely detailed
description of the equipment and procedure from an inten-
sive investigation carried out at the Allis-Chalmer’s labora-
tory. He also provided a table to convert size fractions into
surface area, again to be able to interpret grinding results
in terms of Rittinger’s law. Numerous complexities and
assumptions meant that it did not develop into a practical
tool for his, or plant operators’ purposes, as he had hoped.
Up to this time Bond’s theoretical work results largely
supported Rittinger’s law. The difficulties in putting this to
practical use for equipment design, in particular the specific
energy needed for a given amount of size reduction, were
significant. Surface area of ground materials was difficult
to measure. Screen analyses were used in industry as grind-
ing liberation proxies, and did not convert readily to sur-
face area. The finest fractions dominated surface area, and
did not reflect useful grinding, but rather over-grinding in
terms of mineral liberation and often downstream recov-
ery. And different machines clearly displayed different size
reduction “efficiencies,” depending on the means by which
they applied their energies. Classification in closed circuit
systems added to the complexities. Theoretical size reduc-
tion efficiency versus practical terms for machine, or cir-
cuit, relative comminution “efficiency” was recognized, but
the two were not reconcilable.
Bond presented and published “Wear and Size
Distribution of Grinding Balls” in 1940. He starts by refer-
ring to the above Bond and Maxson (1938–39) work which
showed that Rittinger’s law of surface area creation is pro-
portional to the work input holds with different ball sizing,
even though the resulting distribution by size class varies.
He then discusses ball wear from over nine years of con-
tinuous records of rates of wear of each ball size using their
standard laboratory dry testing ball charge. They concluded
that larger balls wear slightly faster than smaller ones, as
would be expected due to impact forces. Equilibrium ball
charges were so calculated, from charging a single size,
from 5" downward. From this the total surface area of an
equilibrium charge is calculated, as are relative total ball
consumption rates. Bond follows with a theoretical discus-
sion of matching mill feed size distribution with the best
suited ball size distribution to maximize production rate
through a given screen size, the most common objective in
ore grinding. In passing, he notes that “the use of a circula-
tion load and short detention time in the mill,” are also best
for this objective. He concludes that “rationing” (addition
of a second smaller size) would be beneficial in most cases.
But, as noted, the relevant discussion in the paper on the
best suited ball sizing for grinding a given grinding circuit
or mill feed is strictly theoretical, and no practical guide-
lines are provided.
In 1940 Bond also co-authored “Deleterious Coating
of the Media in Dry Milling” with F.T. Agthe for AIME,
which was also published in Rock Products (1941) and