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Sizing a Vibratory Screen

Sizing a Vibratory Screen

 

A separate calculation is required for each deck of a multiple deck screen, although the same formula is utilized for each calculation.                       

Screening Area =              _______U________          = Square Feet

                                                AxBxCxDxExFxGxHxJ     

Were:                  

Factor "U" - Undersize : Amount in STPH of material feed to deck that is smaller than a specified aperture.                       

Factor "A" - Basic Capacity: Predetermined rate of material STPH through a square foot of a specified opening when feed to deck contains 25% oversize (Factor "B") and 40% halfsize (Factor "C").            

Screen Surface Square Opening

% of Open Area

STPH Passing Per Sq ft

4

0.75

7.69

3.5

0.77

7.03

3

0.74

6.17

2.75

0.74

5.85

2.5

0.72

5.52

2

0.71

4.90

1.75

0.68

4.51

1.5

0.69

4.20

1.25

0.66

3.89

1

0.64

3.56

0.875

0.63

3.38

0.75

0.61

3.08

0.625

0.59

2.82

0.5

0.54

2.47

0.375

0.51

2.08

0.25

0.46

1.60

0.1875

0.45

1.27

0.125

0.40

0.95

0.09375

0.45

0.76

0.0625

0.37

0.58

0.03125

0.41

0.39

 

Factor "B" - Oversize : Actual % of material in feed to deck that is larger than a specified aperture. (Adjusts Factor "A" to suit conditions)               

% Oversize

Factor "B"

5%

1.21

10%

1.13

15%

1.08

20%

1.02

25%

1.00

30%

0.96

35%

0.92

40%

0.88

45%

0.84

50%

0.79

55%

0.75

60%

0.70

65%

0.66

70%

0.62

75%

0.58

80%

0.53

85%

0.50

90%

0.46

95%

0.33

 Factor "C" - Halfsize: Actual % of material in feed to the deck that is one-half the size of a specified aperture. (Adjusts Factor "A" to suit conditions).   

% Halfsize

Factor "C"

0%

0.40

5%

0.45

10%

0.50

15%

0.55

20%

0.60

25%

0.70

30%

0.80

35%

0.90

40%

1.00

45%

1.10

50%

1.20

55%

1.30

60%

1.40

65%

1.55

70%

1.70

75%

1.85

80%

2.00

85%

2.20

90%

2.40

Factor "D" - Deck Location: Applies for multiple deck screens. Total screening area is available for top deck separation. Time delay for material to pass top deck and 2nd or 3rd decks leaves less effective area available. This factor is expressed as a percentage of the top deck effective area.                

Deck

Factor "D"

Top

1

Second

0.9

Third

0.8

 Factor "E" - Wet Screening: Applies when water is sprayed on the material as it moves down the screening deck. Generally, about 5 to 7 GPM of water is used per STPH of solids fed to the screen. The volume of water required should be supplied so that a portion is combined with the solids into a feed box to prepare a slurry feed to the screen. The balance of water is added through a series of spray bars located over the screening deck.                          

Opening

Factor "E"

0.03125

1.00

0.0625

1.25

0.125

2.00

0.1875

2.50

0.25

2.00

0.375

1.75

0.5

1.40

0.75

1.30

1

1.25

 Factor "F" - Material Weight: Applies for weights other than 100 lbs. per cubic foot. If bulk density of one cubic foot of material weighs ± 100 lbs. cu.ft. .                            

Factor "F"=          lbs. per cu. ft.   

                                       100 

Lbs./cu. ft.

Factor "F"

150

1.50

125

1.25

100

1.00

90

0.90

80

0.80

75

0.75

70

0.70

60

0.60

50

0.50

40

0.40

30

0.30

 Factor "G" - Screen Surface Open Area: Applies when open area of screening surface is less than the open area shown in the Factor "A" capacity chart.                    

Factor "G" =        % open area of screen surface being used          

                                % open area indicated in capacity chart               

Screen Surface Square Opening

% of Open Area

4

0.75

3.5

0.77

3

0.74

2.75

0.74

2.5

0.72

2

0.71

1.75

0.68

1.5

0.69

1.25

0.66

1

0.64

0.875

0.63

0.75

0.61

0.625

0.59

0.5

0.54

0.375

0.51

0.25

0.46

0.1875

0.45

0.125

0.40

0.09375

0.45

0.0625

0.37

0.03125

0.41

 

Factor "H" - Shape of Opening : Applies when rectangular openings are used. Slotted or oblong openings will pass more material per square foot than square openings.                              

Shape

Factor "H"

Square

1.00

Short Slot (3 to 4 x Width)

1.15

Long Slot (More than 4 x Width)

1.20

 

Factor "J" - Efficiency : Applies when objective screening efficiency is less than 95%.                   

Factor "J"  =        % of undersize in feed which actually passes    

                                % of undersize in feed (should pass)     

Efficiency

Objective

Factor "J"

95%

1.00

90%

1.15

85%

1.35

80%

1.50

75%

1.70

70%

1.90

 

 

MIke Albrecht, P.E.

o   40+ years’ experience in the mining industry with strong mineral processing experience in Precious metals, copper, industrial minerals, coal, and phosphate

o   Operational experience in precious metals, coal, and phosphate plus in petrochemicals.

o   Extensive experience studies and feasibility in the US and international (United States, Canada, Mexico, Ecuador, Columbia, Venezuela, Chile, China, India, Indonesia, and Greece).