Lesson 6/Learning Event 4
(12) As determined in Step 6, Determine the Feeding Rate, the amount of material required
from each bin is:
After the gradation unit has been calibrated, the feeder gates are adjusted until the gate pointer
corresponds to the lbs per rev (on the spring scale, Figure 24) to be used for that bin.
NOTE: The feeder gate setting should always be approached from the lower side.
This removes the backlash from the gate control linkage for greater accuracy.
(13) When all gates have been set to the proper openings, it is important to check the amount
of aggregate actually being fed from each gate. The check is made by following the same
procedure used to calibrate each gate. If a gate is improperly feeding, the gate opening is
adjusted accordingly. If a gate is reset, another check should be made to insure accuracy.
NOTE: Gates feeding coarse aggregate should NOT be set lower than 1 1/2 times the
largest aggregate size. For example, if a gate is feeding 1" material, it must not be set
lower than 1 1/2. The aggregate portion of the continuous plant must be calibrated when
the apron feeder sprockets are changed to increase or decrease the revolutions per minute
of the feeder. Set pounds of aggregate delivered per revolution of the Gradation Unit
Spring Quadrants. Insure that the springs are uniformly stretched across the scale and
lock them in place. Set the indicator at the desired pounds per revolution.
Step 9. Calibrate the Fines Feeder.
If specifications require the addition of mineral filler to the mix, then the fines feeder must be
calibrated. The fines feeder is calibrated in much the same way as the gradation unit feeder
gates. (Refer to Table 17). The results of the calibration tests are graphed on standard graph
paper (Figure 25) having vertical lines representing the adjusting arm setting and horizontal lines
representing the lbs. per rev. delivered. The graph is used to determine the adjusting arm setting
to deliver the required amount of fines.
Example: Required fines feeding rate = 7.3 lbs/rev. The adjusting arm setting (from Figure 25) =
Plot pounds of fines delivered per revolution at the different adjusting arm settings on Fines
Feeder Gate Calibration Graph (Figure 25) and connect points with a straight line.