Lesson 2/Learning Event 3
A = Area of screen deck in square feet. Table 11 gives square footage measurements on various military
crushing plants.
TABLE 11. SCREEN SIZE CHART, A (in square feet)
D = Deck position factor (Table 12). The lower a screen is in a deck of screens, the lower the capacity of that
screen will be. This is because the aggregate going across the first deck of a set of screens works down the
total length of the screen. But as the aggregate passes through the top screen and down to the second screen,
it does not fall on the leading end of the second screen, but rather part way down from the leading end. As a
result the aggregate failing on the second screen does not travel across the total length of the screen.
Therefore, the capacity of the second screen is reduced. The same holds true for the third and fourth screens
of a deck of screens.
H = Halfsize material. This is the aggregate in the feed that is half the top size of the aggregate that the
screen is supposed to pass (Table 12). For example, if a screen is installed to screen out a maximum size
aggregate of 10 inches, then all material in the feed 5 inches or less is 1/2 size ag-
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