Grain Seprator and Washing

7/31/2019 Grain Seprator and Washing

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Cleaning And Grading

Equipments

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S.K.Engineering & Allied Works, established in 1975, has been engaged in manufacturing &

Export of Cleaning And Grading Equipments, Pea Dehusking & Splitting Plant ( Modern DalMill Plant) and has earned a prominent place in the world market.

Grain Destoner Machine

It is an ideal machine for the removal of stones,

mudballs, glass pieces, metal pieces from Grains,Legumes, Pulses, Coffee beans, Soyabean & Oil seeds

etc. This machine can be used at all such places where

impurities and material are of same sizes but of different

specific gravity. Main advantages of this latest design arehigher capacity, better efficiency, compact design, low

power consumption and dust free run.

Construction : Machine essentially comprises of a

structural frame supporting on an Oscillating deck,exhaust hood and feed control device. Two vibromotors,

adjustable oscillating eccentric rotor type, imparts

vibrating motion to the working deck which features

variable stroke and in line motion. The sieve box

contains two screens one above other and is supported onframe by means of hollow rubber springs. Large glass

window on deck allow proper inner view. Oscillatingdeck with adjustable inclination relative to the vibrating

axis comprising of working deck covered by metal

screen and discharge spouts, with air tight rubber fittings

i.e. for stones and cleaned product ensure best efficiencywith least maintenance.

Operation : The material entering the machine spread

over the entire width of screen and gets stratified in sidedue to the negative pressure created by suitable fan.

Heavy material like stone, metal/glass pieces etc. keepson moving up along with screen deck towards stone-

outlet whereas sound grain get fluidised by air cushion

and start moving down in opposite direction of stonetowards product outlet and gets separated. The machine

is designed two screens in the sieve box which provides
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more area for effective separation of stones. Degree ofstone separation can be optimized by adjusting the deck

inclination, air quantity and plexiglass valve adjustment.

De-Stoner

Separates Stones, Mud pieces, and other Heavy impurities of same size from any Cereal, Pulses,

Paddy, Grains, Corn, Oilseeds and Spices etc. On the basis of difference in Specific gravity and

exposed Surface area. Very useful Machine for Separation of Damaged Seed of Pulses from

Sound Grains. Very useful Machine for Separation of Germs from Ground Corn and lightkernels and ergot from Wheat.

The Dry-destoner is an ideal Machine for the separation of Stones, Mud particles, Glass, and Iron

pieces and other heavy impurities of same size from food grains, pulses, oilseeds, corn and spices

etc. These impurities being of equal size and shape da not separate by seiving. As this machine

works on the difference in specific gravity and exposed surface area of the stocks and thespecific gravity of the impurities, the cleaned material becomes air-borne and travels downward

direction while the impurities on account of oscillating motion of the deck travels in opposite

direction i.e. upward

Features :

Fabricated of Robust steel Construction, compact in design with bestquality components. Easy to transport, easy to install and easy to operate. Multi-purpose operation with High efficiency & low power consumption.

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How Is Wheat Processed?By Julie Elefante, eHow Contributor

How Is Wheat Processed?

Other People Are Reading

How to Plant Bin-Run Wheat

How do I Prepare Whole Grain Wheat? Print this article

1.Reapingo

Wheat farmers reap the wheat of its kernels after they have fully developed andmostly dried out. The farmers know it is ready when the kernels of wheat have a

rich golden brown color. The kernels will contain 15 percent or less moisture at

this point. This usually occurs sometime between July and September, depending
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on the region. In many countries, wheat is still reaped with hand-held instruments

such as scythes or sickles. In industrialized countries, the wheat is usuallyharvested by giant farm machines called combine harvesters, which cut the heads

of the wheat off the stalks. The machine then threshes the wheat, beating it to

remove the chaff. The wheat farmers then ship the wheat to millers.

2.Cleaning and Temperingo The millers clean the wheat kernels with mechanical cleaners using a series of

disks and streams of water to remove any dust, stones, straw and weeds that mighthave come in with the kernels. A final water bath separates any heavy items from

the wheat, because those items will sink while the wheat floats to the top. The

moistened wheat kernels will also toughen the bran coat in a process called

tempering. The toughened bran coat will separate from the wheat's endosperm.The water will also soften the endosperm, which will become flour.

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3.Grindingo

Millers crack and grind the wheat with their mill's grinding stones or steel rollers.

Rollers are the more common way for industrialized countries to grind wheat into

flour. The rollers flatten the wheat germ as the wheat is rolled through, whichhelps the sifters catch the germ. Some millers blow the germ away with streams

of air right after the wheat is cracked and the germ is separated away. The germ is

blown away when millers make white flour. If they're making whole wheat flour,

the bran is ground down with the endosperm. The flour is ground continuously,making it finer and finer. Finally, the flour is passed through sifters, each with

progressively smaller mesh, and sometimes as often as 25 times, to ensure very

fine flour.

4.Enrichingo
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Millers bleach the flour and, if all the bran has been removed, they enrich it with

supplements such as B vitamins (thiamine, niacin, and riboflavin) and iron. Ifbran has been left in the flour, then these vitamins and minerals are already in the

flour.

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Sieve analysisFrom Wikipedia, the free encyclopedia

Jump to:navigation,search

A sieve analysis (or gradation test) is a practice or procedure used (commonly used incivil

engineering) to assess theparticle size distribution(also called gradation) of a granular material.

The size distribution is often of critical importance to the way the material performs in use. A

sieve analysis can be performed on any type of non-organic or organic granular materialsincluding sands, crushed rock, clays, granite, feldspars, coal, soil, a wide range of manufactured

powders, grain and seeds, down to a minimum size depending on the exact method. Being such a

simple technique of particle sizing, it is probably the most common.[1]

Contents 1 Procedure

o 1.1 Preparation 2 Results 3 Methods

o 3.1 Throw-action sievingo 3.2 Horizontal sievingo 3.3 Tapping sievingo 3.4 Sonic sievingo 3.5 Wet sievingo

3.6 Air Jet Sieving 4 Types of gradation 5 Limitations of sieve analysis 6 Properties 7 Engineering applications 8 Forecast

o 8.1 "Sieving" with Digital Image Processing 9 See also 10 References 11 External links

Procedure
http://en.wikipedia.org/wiki/Sieve_analysis#mw-headhttp://en.wikipedia.org/wiki/Sieve_analysis#mw-headhttp://en.wikipedia.org/wiki/Sieve_analysis#mw-headhttp://en.wikipedia.org/wiki/Sieve_analysis#p-searchhttp://en.wikipedia.org/wiki/Sieve_analysis#p-searchhttp://en.wikipedia.org/wiki/Sieve_analysis#p-searchhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Particle_size_distributionhttp://en.wikipedia.org/wiki/Particle_size_distributionhttp://en.wikipedia.org/wiki/Particle_size_distributionhttp://en.wikipedia.org/wiki/Sieve_analysis#cite_note-0http://en.wikipedia.org/wiki/Sieve_analysis#cite_note-0http://en.wikipedia.org/wiki/Sieve_analysis#cite_note-0http://en.wikipedia.org/wiki/Sieve_analysis#Procedurehttp://en.wikipedia.org/wiki/Sieve_analysis#Procedurehttp://en.wikipedia.org/wiki/Sieve_analysis#Preparationhttp://en.wikipedia.org/wiki/Sieve_analysis#Preparationhttp://en.wikipedia.org/wiki/Sieve_analysis#Resultshttp://en.wikipedia.org/wiki/Sieve_analysis#Resultshttp://en.wikipedia.org/wiki/Sieve_analysis#Methodshttp://en.wikipedia.org/wiki/Sieve_analysis#Methodshttp://en.wikipedia.org/wiki/Sieve_analysis#Throw-action_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Throw-action_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Horizontal_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Horizontal_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Tapping_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Tapping_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Sonic_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Sonic_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Wet_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Wet_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Air_Jet_Sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Air_Jet_Sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Types_of_gradationhttp://en.wikipedia.org/wiki/Sieve_analysis#Types_of_gradationhttp://en.wikipedia.org/wiki/Sieve_analysis#Limitations_of_sieve_analysishttp://en.wikipedia.org/wiki/Sieve_analysis#Limitations_of_sieve_analysishttp://en.wikipedia.org/wiki/Sieve_analysis#Propertieshttp://en.wikipedia.org/wiki/Sieve_analysis#Propertieshttp://en.wikipedia.org/wiki/Sieve_analysis#Engineering_applicationshttp://en.wikipedia.org/wiki/Sieve_analysis#Engineering_applicationshttp://en.wikipedia.org/wiki/Sieve_analysis#Forecasthttp://en.wikipedia.org/wiki/Sieve_analysis#Forecasthttp://en.wikipedia.org/wiki/Sieve_analysis#.22Sieving.22_with_Digital_Image_Processinghttp://en.wikipedia.org/wiki/Sieve_analysis#.22Sieving.22_with_Digital_Image_Processinghttp://en.wikipedia.org/wiki/Sieve_analysis#See_alsohttp://en.wikipedia.org/wiki/Sieve_analysis#See_alsohttp://en.wikipedia.org/wiki/Sieve_analysis#Referenceshttp://en.wikipedia.org/wiki/Sieve_analysis#Referenceshttp://en.wikipedia.org/wiki/Sieve_analysis#External_linkshttp://en.wikipedia.org/wiki/Sieve_analysis#External_linkshttp://en.wikipedia.org/wiki/Sieve_analysis#External_linkshttp://en.wikipedia.org/wiki/Sieve_analysis#Referenceshttp://en.wikipedia.org/wiki/Sieve_analysis#See_alsohttp://en.wikipedia.org/wiki/Sieve_analysis#.22Sieving.22_with_Digital_Image_Processinghttp://en.wikipedia.org/wiki/Sieve_analysis#Forecasthttp://en.wikipedia.org/wiki/Sieve_analysis#Engineering_applicationshttp://en.wikipedia.org/wiki/Sieve_analysis#Propertieshttp://en.wikipedia.org/wiki/Sieve_analysis#Limitations_of_sieve_analysishttp://en.wikipedia.org/wiki/Sieve_analysis#Types_of_gradationhttp://en.wikipedia.org/wiki/Sieve_analysis#Air_Jet_Sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Wet_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Sonic_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Tapping_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Horizontal_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Throw-action_sievinghttp://en.wikipedia.org/wiki/Sieve_analysis#Methodshttp://en.wikipedia.org/wiki/Sieve_analysis#Resultshttp://en.wikipedia.org/wiki/Sieve_analysis#Preparationhttp://en.wikipedia.org/wiki/Sieve_analysis#Procedurehttp://en.wikipedia.org/wiki/Sieve_analysis#cite_note-0http://en.wikipedia.org/wiki/Particle_size_distributionhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Sieve_analysis#p-searchhttp://en.wikipedia.org/wiki/Sieve_analysis#mw-head


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Sieves used for gradation test.

A mechanical shaker used for sieve analysis.

A gradation test is performed on a sample of aggregate in a laboratory. A typical sieve analysisinvolves a nested column ofsieveswith wire mesh cloth (screen). See the separateMesh (scale)

page for details of sieve sizing.

A representative weighed sample is poured into the top sieve which has the largest screen

openings. Each lower sieve in the column has smaller openings than the one above. At the baseis a round pan, called the receiver.

The column is typically placed in a mechanical shaker. The shaker shakes the column, usually

for some fixed amount of time. After the shaking is complete the material on each sieve is

weighed. The weight of the sample of each sieve is then divided by the total weight to give apercentage retained on each sieve.
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The size of the average particle on each sieve is then analysed to get a cut-off point or specific

size range, which is then captured on a screen.

The results of this test are used to describe the properties of the aggregate and to see if it is

appropriate for various civil engineering purposes such as selecting the appropriate aggregate for

concrete mixes and asphalt mixes as well as sizing of water production well screens.

The results of this test are provided in graphical form to identify the type of gradation of the

aggregate. The complete procedure for this test is outlined in the American Society for Testing

and Materials (ASTM) C 136[2]

and the American Association and State Highway and

Transportation Officials (AASHTO) T 27[3]

A suitable sieve size for the aggregate should be selected and placed in order of decreasing size,

from top to bottom, in a mechanical sieve shaker. A pan should be placed underneath the nest ofsieves to collect the aggregate that passes through the smallest. The entire nest is then agitated,

and the material whose diameter is smaller than the mesh opening pass through the sieves. After

the aggregate reaches the pan, the amount of material retained in each sieve is then weighed .

[4]

Preparation

In order to perform the test, a sample of the aggregate must be obtained from the source. Toprepare the sample, the aggregate should be mixed thoroughly and be reduced to a suitable sizefor testing. The total weight of the sample is also required.[4]

Results

The results are presented in a graph of percent passing versus the sieve size. On the graph thesieve size scale is logarithmic. To find the percent of aggregate passing through each sieve, first

find the percent retained in each sieve. To do so, the following equation is used,

%Retained = 100%

where WSieve is the weight of aggregate in the sieve and WTotal is the total weight of the

aggregate. The next step is to find the cumulative percent of aggregate retained in each sieve. To

do so, add up the total amount of aggregate that is retained in each sieve and the amount in the

previous sieves. The cumulative percent passing of the aggregate is found by subtracting thepercent retained from 100%.

%Cumulative Passing = 100% - %Cumulative Retained.

The values are then plotted on a graph with cumulative percent passing on the y axis andlogarithmic sieve size on the x axis.[4]
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There are two versions of the %Passing equations. the .45 power formula is presented on .45power gradation chart, whereas the more simple %Passing is presented on a semi-log gradation

chart. version of the percent passing graph is shown on .45 power chart and by using the .45

passing formula.

.45 power Percent Passing Formula:

% Passing = Pi = x100%

Where:

SieveLargest - Largest diameter sieve used in (mm).

Aggregatemax_size - Largest piece of aggregate in the sample in (mm).

Percent Passing Formula:

%Passing = x100%

Where:

WBelow - The total mass of the aggregate within the sieves below the current sieve, not includingthe current sieve's aggregate.

WTotal - The total mass of all of the aggregate in the sample.

Methods

There are different methods for carrying out sieve analyses, depending on the material to bemeasured.


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Throw-action sieving

Throw-Action Sieving

Here a throwing motion acts on the sample. The vertical throwing motion is overlaid with a

slight circular motion which results in distribution of the sample amount over the whole sieving

surface. The particles are accelerated in the vertical direction (are thrown upwards). In the airthey carry out free rotations and interact with the openings in the mesh of the sieve when they

fall back. If the particles are smaller than the openings, they pass through the sieve. If they are

larger, they are thrown upwards again. The rotating motion while suspended increases the

probability that the particles present a different orientation to the mesh when they fall back again,and thus might eventually pass through the mesh.

Modern sieve shakers work with an electro-magnetic drive which moves a spring-mass systemand transfers the resulting oscillation to the sieve stack. Amplitude and sieving time are set

digitally and are continuously observed by an integrated control-unit. Therefore sieving results

are reproducible and precise (an important precondition for a significant analysis). Adjustment of

parameters like amplitude and sieving time serves to optimize the sieving for different types ofmaterial. This method is the most common in the laboratory sector [citation needed].

Horizontal sieving

Horizontal Sieving

In a horizontal sieve shaker the sieve stack moves in horizontal circles in a plane. Horizontalsieve shakers are preferably used for needle-shaped, flat, long or fibrous samples, as their

horizontal orientation means that only a few disoriented particles enter the mesh and the sieve is

not blocked so quickly. The large sieving area enables the sieving of large amounts of sample,for example as encountered in the particle-size analysis of construction materials and aggregates.
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Tapping sieving

Tapping Sieving

A horizontal circular motion overlies a vertical motion which is created by a tapping impulse.

These motional processes are characteristic of hand sieving and produce a higher degree of

sieving for denser particles (e.g. abrasives) than throw-action sieve shakers.

Sonic sieving

The particles are lifted and forcibly dropped in a column of oscillating air at a frequency ofthousands of cycles per minute. Sonic sievers are able to handle much finer dry powders than

woven mesh screens.

Wet sieving

Most sieve analyses are carried out dry. But there are some applications which can only becarried out by wet sieving. This is the case when the sample which has to be analysed is e.g. a

suspension which must not be dried; or when the sample is a very fine powder which tends toagglomerate (mostly < 45 m)in a dry sieving process this tendency would lead to a clogging

of the sieve meshes and this would make a further sieving process impossible. A wet sieving

process is set up like a dry process: the sieve stack is clamped onto the sieve shaker and the

sample is placed on the top sieve. Above the top sieve a water-spray nozzle is placed whichsupports the sieving process additionally to the sieving motion. The rinsing is carried out until

the liquid which is discharged through the receiver is clear. Sample residues on the sieves have

to be dried and weighed. When it comes to wet sieving it is very important not to change tosample in its volume (no swelling, dissolving or reaction with the liquid).

Air Jet Sieving

Air jet sieving machines are ideally suited for very fine powders which tend to agglomerate andcannot be separated by vibrational sieving. The reason for the effectiveness of this sieving

method is based on two components: A rotating slotted nozzle inside the sieving chamber and a

powerful industrial vacuum cleaner which is connected to the chamber. The vacuum cleanergenerates a vacuum inside the sieving chamber and sucks in fresh air through the slotted nozzle.

When passing the narrow slit of the nozzle the air stream is accelerated and blown against the

sieve mesh, dispersing the particles. Above the mesh, the air jet is distributed over the complete
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sieve surface and is sucked in with low speed through the sieve mesh. Thus the finer particles are

transported through the mesh openings into the vacuum cleaner.

Air jet sieving machine

Types of gradation

Dense gradation

A dense gradation refers to a sample that is approximately of equal amounts of various

sizes of aggregate. By having a dense gradation, most of the air voids between thematerial are filled with particles. A dense gradation will result in an even curve on the

gradation graph.[5]

Narrow gradationAlso known as uniform gradation, a narrow gradation is a sample that has aggregate of

approximately the same size. The curve on the gradation graph is very steep, and

occupies a small range of the aggregate.[4]

Gap gradationA gap gradation refers to a sample with very little aggregate in the medium size range.

This results in only coarse and fine aggregate. The curve is horizontal in the medium size

range on the gradation graph.[4]

Open gradationAn open gradation refers an aggregate sample with very little fine aggregate particles.

This results in many air voids, because there are no fine particles to fill them. On the

gradation graph, it appears as a curve that is horizontal in the small size range.[4]

Rich gradation

A rich gradation refers to a sample of aggregate with a high proportion of particles of

small sizes.[5]

Limitations of sieve analysis
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Sieve analysis has, in general, been used for decades to monitor material quality based on

particle size. For coarse material, sizes that range down to #100 mesh (150m), a sieve analysisand particle size distribution is accurate and consistent.

However, for material that is finer than 100 mesh, dry sieving can be significantly less accurate.

This is because the mechanical energy required to make particles pass through an opening andthe surface attraction effects between the particles themselves and between particles and the

screen increase as the particle size decreases. Wet sieve analysis can be utilized where thematerial analyzed is not affected by the liquid - except to disperse it. Suspending the particles in

a suitable liquid transports fine material through the sieve much more efficiently than shaking the

dry material.

Sieve analysis assumes that all particle will be round (spherical) or nearly so and will pass

through the square openings when the particle diameter is less than the size of the square opening

in the screen. For elongated and flat particles a sieve analysis will not yield reliable mass-basedresults, as the particle size reported will assume that the particles are spherical, where in fact an

elongated particle might pass through the screen end-on, but would be prevented from doing so ifit presented itself side-on.

Properties

Gradation affects many properties of an aggregate. It affects bulk density, physical stability and

permeability. With careful selection of the gradation, it is possible to achieve high bulk density,

high physical stability, and low permeability. This is important because in pavement design, a

workable, stable mix with resistance to water is important. With an open gradation, the bulkdensity is relatively low, due to the lack of fine particles, the physical stability is moderate, and

the permeability is quite high. With a rich gradation, the bulk density will also be low, the

physical stability is low, and the permeability is also low. The gradation can be affected toachieve the desired properties for the particular engineering application.[5]

Engineering applications

Gradation is usually specified for each engineering application it is used for. For example,

foundations might only call for coarse aggregates, and therefore an open gradation is needed.

Gradation is a primary concern in pavement mix design.Concretecould call for both coarse andfine particles and a dense graded aggregate would be needed.Asphaltdesign also calls for a

dense graded aggregate. Gradation also applies to subgrades in paving, which is the material that

a road is paved on. Gradation, in this case, depends on the type of road (i.e. highway, rural,

suburban) that is being paved.

Forecast

Within the last years[when?] some methods for particle size distribution measurement were

developed which work by means of laser diffraction or digital image processing.
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"Sieving" with Digital Image Processing

The scope of information conveyed by sieve analysis is relatively small. It does not allow for a

clear statement concerning the exact size of a single particle it is just classified within a sizerange which is determined by two sieve sizes ("a particle is < than sieve size x and > than sieve

size y"). And there is no additional information concerning other relevant properties like opacityor shape available. Devices which work with digital image processing enable to recall even thisinformation and a lot more (surface analysis, etc.). The results can be fitted to sieve analysis so

that a comparison between measurement results obtained with different methods is possible.Digital image processingis being used to sieve materials in mining, agriculture, and forestry

industries on a regul

Mechanical screeningFrom Wikipedia, the free encyclopedia

Jump to:navigation,search

Mechanical screening, often just called screening, is the practice of taking granulated orematerial and separating it into multiple grades by particle size.

This practice occurs in a variety of industries such as mining and mineral processing, agriculture,

pharmaceutical, food, plastics, and recycling.[1]
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Contents

1 General categories 2 Applications 3 Process 4 Physical principles 5 Screening terminology 6 Types of mechanical screening

o 6.1 Circle-throw vibrating equipmento 6.2 High frequency vibrating equipmento 6.3 Gyratory equipment

7 References

General categories

Screening falls under two general categories: dry screening and wet screening. From these

categories, screening separates a flow of material into grades, these grades are then either furtherprocessed to an intermediary product or a finished product. Additionally the machines can be

categorised into moving screen and static screen machines, as well as by whether the screens are

horizontal or inclined.

Applications

The mining and mineral processing industry uses screening for a variety of processingapplications. For example, after mining the minerals, the material is transported to a primary

crusher. Before crushing large boulder are scalped on a shaker with 0.25 in (6.4 mm) thick

shielding screening. Further down stream after crushing the material can pass through screenswith openings or slots that continue to become smaller. Finally, screening is used to make a final

separation to produce salable product based on a grade or a size range.

Process

A screening machine consist of a drive that induces vibration, a screen cloth that causes particleseparation, and a deck which holds the screen cloth and the drive and is the mode of transport for

the vibration.

There are physical factors that makes screening practical. For example, vibration,g force, beddensity, and material shape all facilitate the rate or cut.Electrostatic forcescan also hinder

screening efficiency in way of water attraction causing sticking or plugging, or very dry material

generate a charge that causes it to attract to the screen itself.

As with any industrial process there is a group of terms that identify and define what screening

is. Terms like blinding, contamination, frequency, amplitude, and others describe the basic
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characteristics of screening, and those characteristics in turn shape the overall method of dry or

wet screening.

In addition, the way a deck is vibrated differentiates screens. Different types of motion have their

advantages and disadvantages. In addition cloth types also have their different properties that

lead to advantages and disadvantages.

Finally, there are issues and problems associated with screening. Screen tearing, contamination,

blinding, and dampening all affect screening efficiency.

Physical principles

Vibration - eithersinusoidalvibration or gyratory vibration.o Sinusoidal Vibration occurs at an angled plane relative to the horizontal. The

vibration is in a wave pattern determined by frequency and amplitude.

o Gyratory Vibration occurs at near level plane at low angles in a reciprocating sideto side motion.

Gravity - This physical interaction is after material is thrown from the screen causing it tofall to a lower level. Gravity also pulls the particles through the screen cloth.

Density - The density of the material relates to material stratification. Electrostatic Force - This force applies to screening when particles are extremely dry or is

wet.

Screening terminology

Like any mechanical and physical entity there are scientific, industrial, and layman terminology.

The following is a partial list of terms that are associated with mechanical screening.

Amplitude - This is a measurement of the screen cloth as it vertically peaks to its tallestheight and troughs to its lowest point. Measured in multiples of the acceleration constant

g(g-force).

Acceleration - Applied Acceleration to the screen mesh in order to overcome the van derwaal forces

Blinding - When material plugs into the open slots of the screen cloth and inhibitsoverflowing material from falling through.[2]

Brushing - This procedure is performed by an operator who uses a brush to brush over thescreen cloth to dislodged blinded opening.

Cloth, screening cloth - it is the material defined by mesh size, which can be made of anytype of material such steel, stainless steel, rubber compounds, brass, etc.[3]

Contamination - This is unwanted material in a given grade. This occurs when there isoversize or fine size material relative to the cut or grade. Another type of contamination

is foreign body contamination.

o Oversize contamination occurs when there is a hole in the screen such that thehole is larger than the mesh size of the screen. Other instances where oversize
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occurs is material overflow falling into the grade from overhead, or there is the

wrong mesh size screen in place.

o Fines contamination is when large sections of the screen cloth is blinded over, andmaterial flowing over the screen does not fall through. The fines are then retained

in the grade.

oForeign body contamination is unwanted material that differs from the virginmaterial going over and through the screen. It can be anything ranging from tree

twigs, grass, metal slag to other mineral types and composition. This

contamination occurs when there is a hole in the scalping screen or a foreignmaterial's mineralogy or chemical composition differs from the virgin material.

Deck - a deck is frame or apparatus that holds the screen cloth in place. It also containsthe screening drive. It can contain multiple sections as the material travels from the feedend to the discharge end. Multiple decks are screen decks placed in a configuration where

there are a series of decks attached vertically and lean at the same angle as it preceding

and exceeding decks. Multiple decks are often referred to as single deck, double deck,

triple deck, etc.

Frequency - Measured inhertz(Hz) or revolutions per minute (RPM). Frequency is thenumber of times the screen cloth sinusoidally peaks and troughs within a second. As for a

gyratory screening motion it is the number of revolutions the screens or screen deck takesin a time interval, such as revolution per minute (RPM).

Gradation, grading - Also called "cut" or "cutting." Given a feed material in an initialstate, the material can be defined to a have a particle size distribution. Grading isremoving the maximum size material and minimum size material by way of mesh

selection.[4]

Shaker - A generic term that refers to the whole assembly of any type mechanicalscreening machine.

Stratification - This phenomenon occurs as vibration is passed through a bed of material.This causes coarse (larger) material to rise and finer (smaller) material to descend within

the bed. The material in contact with screen cloth either falls through a slot or blinds the

slot or contacts the cloth material and is thrown from the cloth to fall to the next lowerlevel.[5]

Mesh - Mesh refers to the number of open slots per linear inch. Mesh is arranged inmultiple configuration. Mesh can be a square pattern, long-slotted rectangular pattern,circular pattern, or diamond pattern.[6]

Scalp, scalping - this is the very first cut of the incoming material with the sum of all itsgrades. Scalping refers to removing the largest size particles. This includes enormouslylarge particles relative to the other particle's sizes. Scalping also cleans the incoming

material from foreign body contamination such as twigs, trash, glass, or other unwanted

oversize material.

Types of mechanical screening

There are generally three types of mechanical screening equipment that cause segregation. These

types are based on the motion of the machine through its motor drive.
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Circle-throw vibrating equipment - This type of equipment has an eccentric shaft thatcauses the frame of the shaker to lurch at a given angle. This lurching action literallythrows the material forward and up. As the machine returns to its base state the material

falls by gravity to physically lower level. This type of screening is used also in mining

operations for large material with sizes that range from six inches to +20 mesh.[7]

High frequency vibrating equipment - This type of equipment drives the screen clothonly. Unlike above the frame of the equipment is fixed and only the screen vibrates.

However, this equipment is similar to the above such that it still throws material off of it

and allows the particles to cascade down the screen cloth. These screens are for sizessmaller than 1/8 of an inch to +150 mesh.[8]

Gyratory equipment - This type of equipment differs from the above two such that themachine gyrates in a circular motion at a near level plane at low angles. The drive is aneccentric gear box or eccentric weights.[9][10]

Circle-throw vibrating equipment

Circle-throw vibrating equipment is a shaker or a series of shakers as to where the drive causesthe whole structure to move. The structure extends to a maximum throw or length and then

contracts to a base state. A pattern of springs are situated below the structure to where there is

vibration and shock absorption as the structure returns to the base state.

This type of equipment is used for very large particles, sizes that range from pebble size on up to

boulder size material. It is also designed for high volume output. As a scalper, this shaker willallow oversize material to pass over and fall into a crusher such a cone crusher, jaw crusher, or

hammer mill. The material that passes the screen by-passes the crusher and is conveyed and

combined with the crush material.

Also this equipment is used in washing processes, as material passes under spray bars, finer

material and foreign material is washed through the screen. This is one example of wet

screening.

High frequency vibrating equipment

High frequency vibrating equipment is a shaker whose frame is fixed and the drive vibrates onlythe screen cloth. High frequency vibration equipment is for particles that are in this particle size

range of an 1/8 in (3 mm) down to a +150 mesh.

These shakers usually make a secondary cut for further processing or make a finished product

cut.

These shakers are usually set at a steep angle relative to the horizontal level plane. Angles range

from 25 to 45 degrees relative to the horizontal level plane.
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Gyratory equipment

This type of equipment has an eccentric drive or weights that causes the shaker to travel in an

orbital path. The material rolls over the screen and falls with the induction of gravity and

directional shifts. Rubber balls and trays provide an additional mechanical means to cause thematerial to fall through. The balls also provide a throwing action for the material to find an open

slot to fall through.

The shaker is set a shallow angle relative to the horizontal level plane. Usually, no more than 2 to

5 degrees relative to the horizontal level plane.

These types of shakers are used for very clean cuts. Generally, a final material cut will not

contain any oversize or any fines contamination.

These shakers are designed for the highest attainable quality at the cost of a reduced feed rate.

Documents

Grain Seprator and Washing