Bond Laboratory Procedure
The standard Bond test to establish an empirical work index for single stage ball milling, utilized a 12” x 12” ball mill to batch grind a dried sample of the mineral crushed to minus 6 mesh. A ball charge of approximately 20 kg together with a mineral sample of 700 cc are initially run for 100 revolutions. The weight of the sample is recorded before the test begins. The mill speed is 66 RPM. The undersize (i.e.. desired product size) portion of the sample is screened out, and fresh minus 6 mesh mineral added to the original sample’s oversize to bring its weight up to the original weight and the total returned to the mill. The number of revolutions for the second run is determined by a formula dependent upon the net product achieved in the second run is screened out, the sample restored to original size and the revolutions needed for the third run a gain determined by formula. Successive runs are made until the ratio of net product achieved to the number of run revolutions stabilizes. This stabilized ratio then is used in calculating the Bond work index by an empirical formula developed by Mr. Bond.
Limitations of the Bond Procedure
The Bond index is a widely used and respected tool. Experience gathered over many years has assisted mill application engineers in using the Bond index for reliable sizing of mills.
Whenever actual experience with an ore or an ore known to be comparable is not available, the engineer is well advised to keep in perspective:
The empirical nature of the test.
The relatively small splitting techniques and the human factors involve in the multiple steps of testing, and judgment relative to when “stability” has, in fact, been reached.
The possibility that natural grain boundaries may not reconcile with the test procedure. (In such cases it is not uncommon to arrive at an index higher than that needed for production size grinding).
A Bond rod mill test and other refinements are sometimes employed to obtain a better analysis for the expected operating conditions.
Material Size 
80 Percent Passing Equivalent 


Microns (F) or (P) 
formula……. 
99%  1 ½” 
25,000 
158.0 
99%  1” 
18,000 
134.0 
99%  ¾” 
12,000 
109.5 
99%  ½” 
5,500 
92.2 
99%  3/8” 
6,000 
77.4 
99%  3 mesh 
4,200 
64.8 
99%  4 mesh 
3,000 
54.8 
99%  6 mesh 
2,100 
45.8 
99%  8 mesh 
1,500 
38.7 
99%  10 mesh 
1,000 
31.6 
99%  14 mesh 
800 
28.3 
99%  20 mesh 
550 
23.4 
99%  28 mesh 
400 
20.0 
99%  35mesh 
270 
15.4 
99%  48 mesh 
150 
12.25 
99%  65 mesh 
105 
10.25 
99%  100 mesh 
72 
8.48 
99%  150 mesh 
55 
7.42 
99%  200 mesh 
23 
6.00 
99%  325 mesh 
20 
1.47 
Correction Factor to Mathematical Sizing of Mills. 
Reference % Passing 
Correction 
50 
1.035 
CORRECTION FACTOR 3. CF_{3} (diameter) 
CORRECTION FACTOR 4. CF_{4} (oversized feed) 
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