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SIEVE SHAKERINSTRUCTION MANUAL

EXPERIMENTATION

SIEVE SHAKER

INTRODUCTION

SIEVE SHAKERS are used for mechanical separation of dry, hard grains ordinarily pass without

trouble through screens. Screens, which are rapidly vibrated with small amplitude, are less

likely to blind (a screen plugged with solid is said to be blinded.) than are gyrating screen.

Mechanical vibrations are usually transmitted from high –speed eccentrics to the casing of the

unit and from there to screens. Ordinarily no more than three decks are used in vibrating

screens.

The objective is if screen is to accept mixture of particles of various sizes and separate it into

two fractions, an underflow that is passes through screen and an overflow that is rejected by

screen. Either one or both of these streams may be a product.

THEORY:

Screening is a method of separating particles

AIM:

To determine the screen effectiveness of screens.

P ROCEDURE:

1. Start SIEVE SHAKER and set for a known time.

2. Weigh sample accurately.

3. Pour sample on screen and allow the sample to screen thoroughly.

4. Remove screens from unit carefully.

5. Weigh sample retained on each screen.

6. Calculate weight fraction of each sample retained on every screen.

7. Calculate screen effectiveness.

Material balances over screen:

Simple material balances can be written over a screen, which are useful in calculating the ratios

of feed, oversize and underflow from the screen analyses of the three streams and knowledge of

the desired cut dia.

F = Mass flow rate of the feed.

D = Mass flow rate of overflow.

B = Mass flow rate of under flow.

Xf = Mass fraction of material A in feed.

XD = Mass fraction of material A in overflow.

Xb = Mass fraction of material A in underflow.

The mass fraction material B in feed, overflow, and underflow are 1- Xf, 1-Xd and 1-Xb. Since

the total material feed to the screen must leave it either as overflow or as underflow.

F = D + B -------------------------------- ( 1 )

The material A in the feed must also leave in the streams and

FXf = DXd = BXb -------------------------------- ( 2 )

Elimination of B from equations ( 1) and ( 2 ) gives.

D = Xf - Xb

F = Xd – Xb

Elimination of D gives,

BF

=Xd−¿X f

Xd−Xb¿

Screen effectiveness of a screen (often called as a screen efficiency) is a measure of the success

of a screen in closely separating material A & B. If a screen functioned perfectly. All material

should be in overflow and all of the material B would be in underflow. A common measure of

screen effectiveness is the ratio of oversize material A that is actually in the overflow to the

amount of a entering with the feed. These quantities are DXd and FXf respectively. Thus,

Ea=D X dF X f

Where Ea is the screen effectiveness based on the oversize. Similarly an effectiveness Eb based

on the undersize material is given by

Eb=B(1−xb)F (1−X f )

A combined overall effectiveness can be defined as the product of the two individual ratios and

denoted by E,

E=Ea .Eb=D .B Xd (1−X b)F2X f (1−X f )

Substituting D/F and B/F from equations (3) and (4),

E=(X f−Xb)(Xd−X f )Xd (1−Xb)

(X ¿¿d−Xb)2(1−X f )X f ¿

Screen

No.

Size in

M.M.

Mass of particle

Retained on screen gms.

A B C

Mass fraction

A B C

Cumulative mass

Fraction of oversize

A B C

Here A = feed. B = Overflow, c = underflowPlot a graph of screen size v/s cumulative mass fraction.