CE 3220 13-2 aggregate Production.pdf
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Transcript of CE 3220 13-2 aggregate Production.pdf
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Aggregate Production
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SCREENING
Screens are use to:
Separate material into
particle size ranges.
To scalp off oversize rock
To screen out fines.
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SCREENING
The screening process is based
upon the premise that:
Particle sizes smaller than
the screen cloth opening size will
pass through the screen.
Oversize pieces will be
retained on the screen.
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SCREENING
Screens consists of 2, 3, or 4 decks
(layers) of open mesh screen wire cloth mounted one above the other in a rectangular box.
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MESH
The term “mesh”
refers to the number
of openings per lineal
inch. To count the
number of openings
to an inch, measure
from the center of a
wire to a point one
inch distance.
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MESH
The term “mesh” refers to the
number of openings per lineal in.
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CLEAR OPENING
Clear opening
or “space” is the
distance
between the
inside edges of
two parallel
wires.
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CLEAR SQUARE &
MESH OPENING
These screen openings are the
most commonly accepted in the
industry.
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FLAT TOP SQUARE
OPENING
Flat top cloth is used as a subscreen
which supports a finer wire cloth.
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SCREEN CAPACITY
Capacity is the rate in tons per hr
that 1 sf of screen produces
(passes) of the desired size.
Capacity varies with many factors.
Desired efficiency
Deck
Aggregate-size
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SCREEN CAPACITY
Capacity, Fig. 14.18.
Efficiency, Table 14.7
Deck, Table 14.8
Aggregate-size, Table 14.9
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SCREEN CAPACITY
The minimum screen
area to provide a
given capacity is
determined by
Equation 14.5, page 436.
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SCREENING
EXAMPLE
The product from a 36- by
42-in. jaw crusher is
passed over a 2½ and a
1½ in. opening vibrating
screen.
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CAPACITY OF
CRUSHER
42- by 48-in jaw crusher
Closed setting of 3 in.
Capacity of crusher
Table 14. 3, page 413
190 tph
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CAPACITY ADJUSTED
Capacity of crusher 190 tph
Stone unit weight of 110 lb/cf
11cflb100
cflb110AdjustmentWeightUnit .
/
/
190 tph 1.1 = 209 tph
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Fig. 14.5, read down the 3” line to the size.
SIZE DISTRIBUTION
Percent
passing
is on
the left
side of
the
figure.
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QUANTITY
Output of crusher, 209 tph
Size,
in.
%
passing
% in
range
Total
output
Produced
tph
Over 2½ 100-73 27 209 56.4
2½- 1½ 73-46 27 209 56.4
1½- 0 46-0 46 209 96.2
Total 100 209
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SCREENING EXAMPLE
Output of 42 X 48-in. jaw crusher.
Size,
in.
Produced
tph
Over 2_ 56.4
2_- 1_ 56.4
1_- 0 96.2
209
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SCREENING EXAMPLE
The permissible screen
efficiency is 85%. Determine
the minimum-size screen, in
sq ft, required to handle the
crusher output. The screening
unit is 4 ft wide.
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SCREEN WIDTH
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STEP 1. QUANTITY
The quantity that will strike the 2 1/2 in. screen is the total output of the crusher:
209 tph
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STEP 1. QUANTITY
If the 2½ in. screen was 100%
efficient (56.4 + 96.2) 152.6 tph would pass through to the 1½ in. screen.
Size,
in.
Produced
tph
21/2 - 11/2 56.4
11/2 - 0 96.2
152.6
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STEP 1. QUANTITY
But the 2½ in. screen has an 85% efficient,
therefore only 129.7 tph strike the 1½ in. screen.
tph7129856152 .%.
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STEP 2. SCREEN
CAPACITY
Screen capacity, Fig. 14.18
2½ inch -
4.2×1.1= 4.6 tph per sf
1½ inch -
3.4×1.1= 3.7 tph per sf
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STEP 3. EFFICIENCY
Efficiency factors, Table
14.7
The permissible screen
efficiency is 85%.
Efficiency factor - 1.5
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STEP 4. DECK
Deck factors, Table 14.8
2½ inch - Deck 1
Deck factor 1.00
1½ inch - Deck 2
Deck factor 0.90
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STEP 4 -
AGGREGATE-SIZE
Aggregate-size factors, Table 14.9
Need % of aggregate less than 1/2
the size of the screen opening.
One-half size for 2 1/2 inch screen:
...
in12
openingscreenin524
1
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STEP 4.
AGGREGATE-SIZE
One-half size for 2½ inch
screen is 1¼ in.
Figure 14.5 percent passing
1¼ in., for 3 in. closed
setting:
= 39%
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STEP 4.
AGGREGATE-SIZE
Percent passing 1¼ in.,
39%
Quantity less than 1¼ in.:
209 tph 0.39 = 81.51 tph
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STEP 4.
AGGREGATE-SIZE
%..
390tph209
tph5181
Percent of aggregate less
than one-half size for 2½ in.
screen.
In this case it was obvious, lets go on to the 1½ in. screen.
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STEP 4.
AGGREGATE-SIZE
Aggregate size factor for
2½ inch screen with 39%
passing 1¼ in. Table 14.9
980910
200800 .
..
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STEP 4.
AGGREGATE-SIZE
One-half size for 1½ inch screen:
...
in2
openingscreenin514
3
Figure 14.5, percent passing ¾ in., for 3 in. closed setting:
26%
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STEP 4.
AGGREGATE-SIZE
Percent passing ¾ in., 26%
Quantity: 209 tph 0.26 = 54.3
However, this must be adjusted
because of the 85% efficiency of
the 2½ in. screen.
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STEP 4.
AGGREGATE-SIZE
Adjusted because of 2½ in. screen 85% efficiency, the
one-half size for 1½ inch screen is:
54.3 tph 0.85 = 46.2 tph
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STEP 4.
AGGREGATE-SIZE
%..
.350
tph7129
tph246
Percent of aggregate less
than one-half size for 1½
in. screen.
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STEP 4.
AGGREGATE-SIZE
Aggregate size factor for
1½ inch screen with 35%
passing ¾ in. Table 14.9
900510
200800 .
..
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STEP 5. NET SCREEN
SIZE
Formula 14.5, p. 436
2½ in. screen Q = 209 tph C = 4.6 tph/sf D = 1.0 E = 1.5 G = 0.98
sf9309800151sftph64
tph209A .
.../.
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STEP 5. NET SCREEN
SIZE
Formula 14.5
1½ in. screen Q = 129.7 tph C = 3.7 tph/sf D = 0.90 E = 1.5 G = 0.90
sf92890090051sftph73
tph7129A .
.../.
.
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STEP 6. GROSS
SCREEN SIZE
Prudent (p. 434) to have gross capacity 10 - 25% greater than net capacity.
2½ in. screen 30.9 1.1 = 34.0 sf minimum
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STEP 6. GROSS
SCREEN SIZE
Gross capacity 10 - 25% greater than net capacity.
1½ in. screen 28.9 1.1 = 31.8 sf minimum
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STEP 7. SCREEN SIZE
ft 8.5=
widthft4
sf34
Therefore, a 4 X 8.5 screen
Screen size must match
screening unit box width.
2½ in. screen
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STEP 7. SCREEN SIZE
ft 8.0=
widthft4
sf831.
Therefore, a 4 X 8 screen
Screen size must match
screening unit box width.
1½ in. screen
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SCREENING
How about that stone!