Lesson 2/Learning Event 3
Material larger than the roll top product size must be considered. This material must go to the roll crusher, so its
capacity must be checked against the input rate. The amount of material is found by using Table 8, Open Circuit
Production, since the material comes from the jaw crusher.
Table 8 is used when crushing is being done in an open circuit system such as the jaw crusher. Table 9 is used
with a closed circuit system, such as a roll crusher, where the material is being screened prior to crushing and then
recirculated back to the screens after it is crushed in the roll crusher. Figures in the left hand column of the charts
indicate size ranges. Figures across the top of the charts represent crusher settings. To read the chart, locate the
size range to be considered, and then locate the crusher setting column. Intersect the size range row with the
crusher setting column to find the percentage of material that will fall in that size range due to the crushing action
at that particular crusher setting.
Example: Intersect the row and column marked with an asterisk on Table 8. With a 1 1/4 inch setting, 12 percent
of the crushed product will be in the 1 1/4 inch to 1 inch size range. Table 9 is read and used in the same way as
Remember, you set the Jaw crusher at 2 1/4 inches and specified the, top product size at 3/4 inch. To find the
percentage of oversize particles add up all decimal fractions in the 2 1/4 inch crusher setting column, of Table 8,
which are greater than 3/4 inch in size (under size range locate the 7/8 inch to 3/4 inch row). Intersect the crusher
setting column and the size range row. Add up the percentages in each size range above and including the 7/8
inch to 3/4 inch size range as follows:
1" - 7/8"
1 1/4"- 1"
1 1/2" - 1 1/4"
1 3/4"- 1 1/2"
2" - 1 3/4"
2 1/4" - 2"
(NOTE: + means "greater than.")
This means that 65% of the production from the jaw crusher, which you calculated at 60 tons per hour, must go to
the roll crusher for further processing. Thus: 0.65 x 60 tph = 39 tph. This means that 39 tons per hour produced
by the jaw crusher will be larger than 3/4 inch and must be sent to the roll crusher for further processing.
Continuing to use Table 8, 11%