con expo 2008 screening eff101

8/4/2019 Con Expo 2008 Screening Eff101

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SCREENING EFFICIENCY 101

Joe Schlabach, Deister Machine CompanyJim Merritt, Vulcan Materials Company

Brian Barlow, Major Wire


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WHAT IS A VIBRATING

SCREEN?


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WHAT IS A VIBRATING

SCREEN? A machine tool to separate aggregates by

particle size by means of an exciting force

applied to the machine causing it tovibrate.


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+


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IT IS A MACHINE USED TO:

Separate aggregates

Wash aggregates


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HOW DOES IT SEPARATE? It agitates the material causing the

material to stratify allowing the smaller

material to fall through the openings of

the screening surface.


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HOW DOES IT SEPARATE? It agitates the material causing the

material to stratify allowing the smaller

material to fall through the openings of

the screening surface.


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HOW DOES IT WASH?


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HOW DOES IT WASH?

By adding water during the agitation

process.


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TYPES OF VIBRATING

SCREENS


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INCLINED SCREEN


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HORIZONTAL SCREEN


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TRIPLE-SHAFTED

HORIZONTAL SCREEN


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HIGH SPEED


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DEWATERING


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QUALITY AND

CONSISTANCY Determined by:

Proper Screen Selection


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INCLINED SCREENS


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HORIZONTAL SCREEN


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QUALITY AND



Proper Operating Parameters


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OPERATING PARAMETERS

To effectively separate the materials, the

proper operating parameters are applied

to the vibrating screen. Speed

Stroke

Direction of rotation

Angle of inclination


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SPEED READINGS


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SPEED READINGS


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Screen Strokes

StraightLine Motion

Circular

Motion


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How can you measure stroke?


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STROKE


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VIBRATION ANALYZER


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CHECKING STROKE


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How can you change thestroke?


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COARSE SEPARATION

LOW SPEED AND LARGE STROKE

FINE SEPARATION

HIGH SPEED AND SMALL STROKE

SCREEN SETUP


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G-Force

Formula

G-FORCE = 0.051 x(REVOLUTIONS PER

SECOND)2 x THROW IN

INCHESOR

(RPM2 X THROW)

70418

G-Force Formula


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Setup #1

Stroke 0.38 Inches

Speed 850 RPM

G Force 3.85

Setup #2 - Increase Speed 10%

Stroke 0.38 Inches

Speed 935 RPM

G Force 4.66% Increase 21%

Setup #3 - Increase Stroke 10%Stroke 0.41 Inches

Speed 850 RPM

G Force 4.23%Increase 10 %

G-Force Example


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DETERMINING FACTORS

Feed volume

(TPH)

Size of deckopenings

Largest particle

size

Particle shape


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DETERMINING FACTORS

Feed volume

(TPH)


Largest particle

size

Particle shape

Type of screen

media


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DETERMINING FACTORS

Feed volume

(TPH)


Largest particle

size

Particle shape

Type of screen

media

Size and type ofmachine


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DETERMINING FACTORS

Feed volume

(TPH)


Largest particle

size

Particle shape

Type of screen

media


Size of screen

bearings


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DETERMINING FACTORS

Feed volume

(TPH)


Largest particle

size

Particle shape

Type of screen

media


Size of screen

bearings

Wet or dry

screening


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QUALITY AND



Proper Operating Parameters

Proper Screening Media


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SCREEN MEDIA

Screen Cloth

Screen Plate

Polyurethane

Screens

Rubber Screens


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SCREEN MEDIA

Screen Cloth with:

Square openings

Rectangular openings

Slotted openings

Zig-Zag openings

Proper Wire Diameter

Proper Grade of Wire


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Efficiency =

% undersize in feed that actually passes an opening

% undersize in feed

SCREEN EFFICIENCY


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Screen Efficiency

Feed OversizeTPH 860 382

3" 100 100

2" 94.4 87.3

1 1/2" 83.6 63.1

1 1/4" 73.2 39.8

1" 64.3 30.2

3/4" 52.3 20.21/2" 32.5 8.4

3/8" 22.5 4.3

1/4" 13.5 1.6


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Calculating Screen Efficiency

Step #1 Calculate oversize in feed

860 TPH Feed x 73% passing 1 = 630TPH undersize in feed

Step #2 Calculate TPH undersize in deck oversize

382 TPH Oversize x 40% passing 1 = 152 TPH undersize in overs

Step #3 Calculate TPH undersize that passes the deck

630 TPH 152 TPH = 477 TPH undersize that passes deck

Step #4 Calculate Efficiency

477 TPH / 630 TPH = .76 or 76% Efficient


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Screen Efficiency Problem


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Screen Feed

What is the proper way to feed ascreen?


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Basic Rules for Proper Screen Feed

Feed material to the screen opposite the directionof flow down the screen

Present the material to the screen in the screenfeed box

Feed box should be screen width -12

Spread the material in the feed chute

Minimize segregation in the feed chuteThe feed conveyor should be in line with the

centerline of the screen


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Typical Feed Box Arrangement

T i l F d B A


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Typical Feed Box Arrangement


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Screen Feed Distribution9"

311

16"

Poor Feed Distribution:Heavy Bed Depth at Middle

Proper Feed Distribution:Even Bed Depth AcrossWidth


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Narrow Screen Feed Chute


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Eff f P S F d


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Effect of Poor Screen Feed

Sieve % Passing

Feed Oversize

3 1/2" 86%

3" 86% 92%

2 1/2" 84% 86%

2" 75% 76%1 1/2" 64% 45%

1 1/4" 60% 30%

1" 56% 16%

3/4" 49% 4%

1/2" 32% 1%

3/8" 25% 1%#4 16% 1%

#8 11% 1%

1527 TPH

606 TPH

1 , 0.375 Dia.

TPH1 in Feed = 916 TPHTPH1 in Oversize = 182 TPH

Screen Efficiency= 1 (182/916)= 80%

(2) 8x20 TD Screens


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APPLICATION PROBLEMS


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Plugging

Near size particles which become lodged in

the openings blocking the openings


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Material Plugging


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Material Plugging

M i l Pl i


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Material Plugging



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Plugging



Blinding

Fine particles which stick to the surfacemedia due to moisture gradually blanking

over the openings

M t i l Bli di


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Material Blinding

Material Blinding


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Material Blinding



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Plugging



Blinding

Fine particles which stick to the surfacemedia due to moisture gradually blanking

over the openings

Carryover or dirty material Excessive undersize particles failing to pass

through the openings


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PLUGGING SOLUTIONS

More stroke

More speed

Smaller wire diameter

Change hole shape (slotted or

rectangular openings)

Different surface media

Adjust crusher setting

BLINDING SOLUTIONS


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BLINDING SOLUTIONS

Increase speed

Change stroke

Smaller wire diameter

Different surface media Ball trays

Heated decks

Add water

CARRYOVER SOLUTIONS


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CARRYOVER SOLUTIONS

Change stroke

Change speed

Reverse screen rotation

Change wire diameter or shape of openingto increase open area

Change angle of inclination

Feed centered/uniformly distributed Control feed segregation

Change feed tonnage


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CRUSHING AND SCREENING

OBJECTIVE Crushers Produce Material

Screens Separate Material

Screening Efficiency Affects Efficiency of

Crushers

con expo 2008 screening eff101

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