/WAR3-Í96I

2

SEED CLEANING AND HANDLING

II'

By; JESSE E. HARMOND, LEONARD M. KLEIN, AND N. ROBERT BRANDENBURG /

_ Agricultural Research Service

UmTK) STATES DEPAffFM-ENT, OF AGRICULTURE .

Agriculture Handbook No, 179'

Growth Through Agricultural Progress
PREFACE

Seed proressing is an iii(e<i-i-:il purl of tlie large, agi-icullural ¡iidiistry, wliich has the important

task of feedino- and dothino; the expaiuliii,«' world popidatioii. This handhook has been prepared as a

o-uide in the selection, operation, and ari-ani-einent of seed-cleaniufi eqni]>meiit Ijest suited for particular

processino- needs. Various types of seed cleaner-s are described, principles of separation for both commercial and experimental equipment are discussed, and typical process flow charts are presented for

several seed crops.

Related factors, which are not discussed but which are imjjortant in any considei-ation of efficient

seed production, include improved seed varieties, good cultural practices, and etfective seed-harvesting

techniques.

It is ]iot the hitent that this publication shall replace manufacturers" instruction manuals or the

knowledge and experience of operators, but rather supplement them.

Acknowleda-ment is made to the manufacturers of seed-processing and handling equipment whose

literature and diagrams formed the basis for some of the material presented here; to seed processors who

gave time and assistance in taking photographs of commercial equipment; and to Mr. Hilmer E. Carlson,

Agricultural Engineering Department, Oregon State College, for diagrams and sketches.

CONTENTS

Page

Seed-cleaning Equipment 1

Air-screen wSeed Cleaner 1

Specific Gravity Separator 7

Indent Disc Separator 11

Indent Cylinder Separator 13

Pneumatic Separators 15

Velvet Roll Seed Separator 17

Spiral Separator 19

Inclined Draper Separator 19

Horizontal Disc Seed Separator 21

Electronic Seed Separator 22

Magnetic Seed Separator 24

Buckhorn Machine 24

Timothy Bumper Mill 25

Vibrator Seed Separator 26

Other Equipment 26

Seed Handling and Treating 27

Conveying S,ystems 27

Processing Difficult-to-handle Seed 29

Seed Treating 33

Plant Layout 33

Glossary 38

Washington, D.C. 1//
> SEED CLEANING AND HANDLING

Jesse EiJIarmond, head, Leonard M. Klein, and N. Robert Brandenburg, agricultural engineers,

Small Seed Harvesting and Processing Section, Agr/cultund Engineering Research Dii

Agricultural Research Service

vviston^

Tlie annual production of grass and legume seed

in the United States is valued at more than %-im

million, and imports represent another $15 million. Agriculture constitutes the largest single industry in the world, and man}' American manufacturers depend upon seed and its products as a

source of basic raw material.

To obtain high-quality seed that will increase

farm production and provide uniform raw nuiterial for industry, efficient seed-cleaning practices

are necessary. Even though many types of machines are used for special seed separations, it is

estimated that at least 50 percent of good seed is

lost in cleaning and handling because it is damaged, or not sufficiently cleaned to meet quality

standards set by State seed laws, or certiñcation

requirements.

To assist in reducing these gigantic losses, seedcleaning research is being conducted jointly at

Oregon State College, Corvallis, Oreg., by the

Small Seed Harvesting and Processing Section of

the Agricultural Engineering Research Division,

Agricultural Eesearch Service, U.S. Department

of Agriculture, and the Oregon Agricultural Experiment Station.

Attempts are being made to reduce seed losses

by developing methods and equipment to improve

efficiency in handling, treating, and separating

crop seeds from weeds and inert matter.

Seed separation is accomplished by the use of

special equipment that utilizes differences in physical characteristics of various components in the

mixtures. The chief characteristics by which separations are made are size, shape, density, surface

texture, color, and electrical properties.

Seed-machinery manufacturers have done an

outstanding job in developing separation equipment. Some of the present machines make extraordinary separations of small crop and weed

seeds; however, the entire seed-cleaning problem

is very complex, and much improvement is still

needed in methods and equipment to reduce the

heavy seed losses.

There are many types of seed-cleaning macliines,

such as air-screen cleaners, speciñc gravity se])arators, pneumatic separators, velvet rolls, si)irals,

indent cylinders, indent discs, magnetic separators,

electronic separators, debearders, and others. One

machhie basic to all seed-cleaning plants, from the

small farm operation to the largest commercial

plant, is the air-screen cleaner. A^irtually all

other separators are finishing machines, and follow

the air-screen unit in the pi-ocessing line.

The choice of macliines used in a seed-processing

line depends primarily on the crop being cleaned,

the presence of other crop and weed seeds, and the

quantity of each in the mixture. Seed is of little

value unless it reaches the farmer in a viable condition, essentially free of noxious weeds, and at a

price he can afford to pay. The degree to which

this can be accomplished is related to the equipment used, its arrangement in the processing plant,

and the knowledge and skill of the man operating

the cleaning machine.

SEED-CLEANING EQUIPMENT

AIR-SCREEN SEED CLEANER

The air-screen cleaner is the basic machine in a

seed-cleaning plant. It makes seed separations

mainly on the basis of three physical properties—

size, shape, and density.

There are many makes, sizes, and models of airscreen cleaners ranging from the small, one-fan,

single-screen machine to the large, multiple-fan,

six- or eight-screen machine Avith several air

columns. Screens are manufactured with many

sizes and shapes of openings. There are more

than 200 screen types available, and with a fourscreen machine, more than 30 thousand screen

combinations are possible.

The typical air-screen cleaner now found in a

farm seed-cleaning plant is a four-screen machine

located beneath a seed hopper, as shown in figm-es

1 and 2. Seed flows by gravity from the hopper

1
FIGURE 1.—Air-screen seed cleaner.

S-205-6-59

into a feeder tluit meters the seed mixture into an

air stream, which removes light, chari'y material

so that the remaining seed can be distiibuted uniformly over the top screen. Tlie top screen scalps

or removes large material, the second screen

grades or sizes the seed, the third screen scalps

tlie seed more closely, and the fourth screen performs a final grading. The finel}- graded seed is

then passed through an air stream, which drops

the plump, heavy seed, but lifts and blows light

seed and chaff into the trash bin.

Screen Numbering System

The size of a round-hole screen is indicated by

the diameter of its perforations. Perforations

larger than size 51/^ are measured in 64:ths of an

inch. Therefore, a 1-inch round-hole screen is

called a No. 64; a i^-inch screen is a No. 32, et

cetera. Screens smaller than 514/64 are measured in fractions of an inch. The next size

smaller than .51/^ is a Vioth; then, in descending

order, i/isth, yi4tli, et cetera.

Oblong-hole screens are measured in the same

manner as round-hole screens except that two dimensions must be given. In large oblong-hole or

slotted screens the hole width is indicated in 64ths

of an inch; for example, 11 x % means an opening

i%4ths of an inch wide and %ths of an inch long.

In slotted screens smaller than 514/64 x % width

is generally indicated in fractions of an inch; for

example, y^o x %. There are some exceptions to

this latter designation in that such sizes as %4 x

34, 47/s/64 X %, %4 X 5/16, imd others, use the

large-screen numbering system with hole widths

indicated in 64ths of an inch. In all cases, the

final number is the length of slot.

Wire-mesh screens are designated according to

the number of openings per inch in each direction.

A 10 X 10 screen has ten openings per inch across,

and ten openings per inch down the screen. The

size 6 X 22 has twenty-two openings per inch across

the screen, and six openings per inch down the

screen. Such screens as 6 x 22 have openings

which are rectangular in shape, and are the wire-
ngs

r Rough Kn

<h Graded

Seed

Light

Trash

Clean Graded Seed

FiGUBE 2.—Schematic view of air-screen seed cleaner.

mesli equivalents of oblong-perforated or slotted

screens.

Triangular screens may be measured in two

ways. The system most commonly used in the

seed industry indicates length of each side of the

triangle in 64ths of an inch. The sides of the hole

in a No. 11 triangular screen are i^^ths of an

inch long. Another system used by perforators is

to designate the triangle as the diameter of the

largest circle that can be inscribed in the triangle.

Table 1 shows manufacturers' screens in sizes

and shapes commonly stocked.

Selecting Screens

The two basic screens for cleaning round-shaped

seed are a round-hole top screen and a slotted bottom screen. The round-hole top screen should be

selected so as to drop the round seed through the

smallest hole possible, and retain anything larger.

The seed drops through the top screen onto the

slotted bottom screen, wliich takes advantage of

seed shape and retains the round, good seed while

dropping broken crop seed and many weed seed.

The basic screens for cleaning elongated seed

(oats, fescues) are a slotted top screen and a

slotted bottom screen. In special separations it

may be necessary to pass such seed through roundhole top screens or over some screen other than a

slotted bottom screen, but generally, slotted top

and bottom screens are used.

The basic screens for lens-shaped seed ( lentils,

flax, and Korean lespedeza) are usually a slotted

top screen and a round-hole bottom screen. These

shapes allow the best cleaning possible when a

machine is equipped with only one top and one

bottom screen. The lens-shaped seeds tend to turn

on edge and drop throngli a slotted top screen but

lie flat and travel over a large round-hole bottom

screen, which will pass most other crop and weed

seeds.

Since most air-sci-een cleaners have more than

two screens, the general rule is to equip the cleaner

with oblong- and round-hole top screens, and

oblong- and round-, square-, or triangular-hole

bottom screens. With few exceptions, tliis system

assures the most thorough seed separation.
TABIJí 1.—S/zrs idtd .^hajir.s of scrceriM commonly xforlxd Ijy mamtifo/'turers

I'ElíFORATlín MK'I AL SilICÍCr WIRE CLOTH

Roiiiicl li( los Ohli.Tii; ll"ll>S

Triant-'lrs

Ol.loni;

(TOSS S)()(

UíMlllil

lililí' hiilf

siZl'S

OhllItlR

linll si/.i'S

,Sï|lj:ir<'

ofii'llint'S Oblorifr openings

FrLictions

641 h s Fr;icti(iTis a4tlis (Mlhy

Firilslicil siT

¡nul "X"

slZI'S 'Jl!" X

•cus niüili

llllilcl w

411/' iiii.

iirilv In "«"

illlis. Shri'l

1 2fi" X MJi"

3 X 3

4x4

5 X 5

2x8

2x9

2 X 10

4 X 15

4 X 16

4x18

6 X 14

6 X 15

6 X 16

;í5 6 24 Yi X Y 4% X % 5 6 X ^/í 5^2 7''2 X y. 7x7 2 X 1 1 4x19 6 X 18

ÍÍ4 7 25 '•Ji; X ^í 5 X 34 8 7 X M 6;í 8''2 X % 8x8 2x12 4 X 20 6 X 19

^'23 8 26 H-1 X y,,; 512 X 3/4 9 8 X % l'A 9!.2 X -V, 9 X 9 3 X 14 4 X 22 6 X 20

Yl2 9 27 ' -0 X Y 6 X )-j 10 9 X % IVi 10'/. X y¡ 10 X 10 3 x 10 4 X 24 6 X 21

Yn 10 28 M. X M OH X % 11 10 X 'Vj 8]'2 ivAx% 12 X 12 3 X 16 sp. 4 X 24 sp. 6 X 22

Ho 11 29 Msx M 7xM 11 X J-i 9U V2A X ^i 14 X 14 3x17 sp. 4 X 26 6 X 23

'.9 12 30 •iKX y 8 X M-D 12 X % 10'2 13'!: X y 15 X 15 3 X 20 4 X 28 6 X 24

'is 13 31 Mr, X i;,-A 9 X •!:, 13 X % IVA u;/ X y 10 X 16 3 X 21 4 X 30 6 X 25

'l7 14 32 ]u:X Y 10 X %-VJ 14 X :K, V2'A 17 X 17 4 X 32 6 X 26

}U 15 34 Yr. X K 11 X -í'^-F 15 X % 13/2 18 X IS 4 X 34 6 X 28

Ms 16 36 'H X ;4-B 12 X 3j-ü K) X % 14'/. 20 X 20 4 X 36 6x30

}íl 17 38 M4X >í 13 X ?j-n 18 X >, 15'2 22 X 22 6 X 32

h3 IS 40 '.3 X U 14 X 3',-I 10 "2 X % 16U 24 X 24 6x34

M 2 19 42 ',.>x lí-O 15 X fj-J IVA X 3/ 17H 26 X 26 6x36

20 44 16 X 3/i-K 12 M X M 18'2 28 X 28 6x38

21

22

23

48

56

64

72

SO

'-2 X M diag. 17 X %

18 X %

19 X 3,i

20 X %

21 X ^4

22 X y

24 X %-L

32 X 1

19;4

20}i

21K

22}á

30 X 30

32 X 32

34 X 34

36 X 36

38 X 38

40 X 40

45 X 45

50 X 50

6 X 40

6x 42

6x 50

6x60

18 X 20

20 X 22

60 X 60

One of the lens-shaped seeds commonly cleaned

with an oblong-perforated top screen and a roundhole bottom screen is ñax. This slick, shiny seed

must turn on edge to drop through the oblong

holes. If tlie top screen is a perforated-metal

type, some of the seeds will slide over the screen

without turning on edge, tlius reducing capacities.

When a Avire-mesh screen with rectangular openings is used in place of the oblong-perforated

screen, much greater capacities can be achieved for

two reasons: The roughness of the Avire surface

encourages the flax to turn on edge more readily

and drop through the openings, and the wire mesh

presents many more openings per square inch of

screen area.

Some seed shapes fall between the classifications

of round, elongated, or lenslike. For example,

Sudan grass seed is not exactly round, nor is it an

elongated seed. Consequently, when screens are

selected for such seed, the choice depends upon

what must be removed from the specific mixture.

Generally, when cleaning Sudan grass seed in a

multiple-screen unit, the top screens will be a

round-hole and an oblong, and the bottom screens

will be a round-hole and an oblong.

Special Separations

After seeds have been screened to the same size,

further separations are made on the basis of shape

différences. One of the earliest-used screens for

special separations is the "dock" screen, size %4 x

^165 especially devised for separating dock, mustard, ragweed, and other plump or round weed

seed from thinner clover seed.

Bottom screens with triangular openings are

being used for separating Avikl buckwheat and

field bindweed from small grains, and dock and

sorrel from fescue. TriangTilar-shaped weed seed

can be dropped through these openings, while the

longer crop seed will "float'" over them.

Triangular holes are preferred to round holes

in bottom screens when elongated crop seed is
being cleaned because the openings do not become

plugged with seed as quickly as in round-Iiole

screens. Elongated seed sometimes wedge so

tightly in round holes that screen-cleaning brushes

will not sweep the openings clean, and the bottom

screens become matted and useless. Screens with

triangular openings do not mat or plug as readily,

and screen-cleaning brushes can keep the holes

open. For this reason, bottom screens with triang-ular holes are sometimes used for making separations of round seed from elongated seed, such as

mustard from oats.

A 6 X 15 wire-mesh bottom screen will separate

burclox'er from subterranean clo^'er e^'en though

both crops have been screened to the same size with

a round-hole screen. The subterranean clo\'er is

round and will not go through the narrow slot,

while the thin burclover will.

Percentage of Open Area

In selecting screens, another point to be considered is the percentage of open area. A good

screen must have openings as close together as

possible without impairing the structural strength

of the material. Wire-mesh screens have more

openings per square inch than perforated-metal

screens. For this reason, they are excellent bottom screens for small seeds, and they permit a

more accurate high-capacity screening than is possible with perforated-metal screens. Comparing

a perforated-metal screen to an equivalent wiremesh screen, the perforated screen has only a fraction of the total ntunber of openings per square

inch that are available in the wire-mesh screen, and

consequently would reduce capacity if used.

Another reason that wire-mesh screens serve better as bottom screens is that their surfaces are

rough and seeds passing over them are caused to

turn, tumble, and present all sides to the openings.

As a result, if the seeds are small enough in one

dimension, they have every chance to drop

through. Perforated-metal screens have smooth

surfaces and seeds may lie flat and "float" over

the openings.

Bottom screens may take advantage of this

floatation. In this case, it is desirable for the good

seed to lie flat and float over the perforations

rather than turn on edge and drop through the

screen along with the Aveed seed.

Length of Slot

Slotted screens are perforated in different

lengths because there is a need for longer and

shorter slots. The sizes 1/14 x 1/2 and 1/14 x 14 illustrate these special needs. Seed processors need

the i/o-inch length to drop hulled oats wlien they

are cleaning seed oats. Cleaners of market grain

do not want to drop the bulled oats but should

drop the small weed seed, and thus require the

shorter 1/14 x y^ slot. Processors of Korean and

Kobe lespedeza hnd tliat tlie i/ig x 14 slot is fine for

Korean but a longer slot, size i/^g x I/2 oi' Vis ^ '^i

is needed for Kobe, which is a flatter, wider seed,

and will not pass rapidly enough through the Vif, x

14 slot. For the same reason, a 3/^-inch long slot

is good in a bottom screen for cleaning seed wheat

because it effectively drops wild oats, quackgrass,

or cheat, witliout losing any more good wheat than

would be dropped with a shorter slot.

The length of slot should be carefully considered

when selecting a slotted screen. For a top screen,

the slot must be long enough to pass good seed

freely and give adequate capacity. In a bottom

screen, the slot should be long enough to give weed

seed every chance to engage the perforation and

drop through, yet not long enough to allow excessive loss of crop seed.

Screen Dams

Screen dams are objects fastened to a screen to

make it sift more completely than normal. They

are used for very close and accurate sepai'ations

of small round seed. For example, dodder can

be removed from Korean lespedeza with a YIQ

round-hole bottom screen equipped with dams.

Operators of flat-screen corn graders frequently

use dams on all screens to insure maximum accuracy of grade. Dams may be constructed of any

material, but commonly are strips of wood lath

about 14-inch high and 2 inches wide. When

fastened over the cross braces of the screen with

nails or screws, the dams interrupt the smooth

flow of seeds down the screen, causing them to stop

momentarily and be thoroughly sifted. This provides ample opportunity for all seeds to contact

the perforations and to drop through the screen

if size and shape of the openings permit.

Screen dams are effective in separating ryegrass

seed and flax seed. When this mixture is passed

over a 1/12 round-hole screen with dams, the seed

flow across the screen is retarded and seeds collect

behind the dams. As the ryegrass attempts to

work its way over the dam, it approaches an upright position and the oscillation of the screen
canses the seed to pass thi'ougli the screen endwise,

mukino- the séparation.

When screen dams ai'e nsed on round-liole bottom screens, the accnracy of sifting is increased so

that a heavier layer of seed may he cari'ied on the

screen, witli a resuhant increase in capacity.

lixcept when a screen is being- nsed for grading,

dams are generally nsed only on bottom screens.

Ordinarily, top screens drop their good seed

quickly enough, and dams on a top screen would

cause some weed seeds that normally iiow over the

screen to stand on end and drop through with

good seed.

A device that can be used to improx-e the separating action of a top screen is a piece of oilcloth

lying flat on the screen with the slick side down.

The seed mixture flows between the cloth and the

screen, and the weight of the cloth tends to keep

long pieces of straw and stems flat on the screen

so that they do not stand on end and pass through

the openings with good seed.

It is good practice to blank off the lower section

of a top screen. Once the point where all of the

good seeds ha\-e dropped through has been determined, the screen, from that point to its discharge

edge, can be blanked off with paper, plastic, or

other suitable material. Any foreign material

that has passed over the first section of open perforations will then flow onto the blanked-off portion and have no further chance to stand on end

and pass through with the good product.

Adjustments

Feed rate can be adjusted by increasing and decreasing the speed of the metering roller, or by

varying the oj^ening of the metering gate located

in the bottom of the feed hopper. The feed rate

should be regulated to keep the final grading

screen about seven-eighths full. It is better to

have a small section of the screen uncovered part

of the time than to flood the screen occasionally.

Airflow is usually regulated by means of baffles

in the air ducts. The top air is adjusted to blow

out light chaffy material and dust. The bottom

air is regulated to a higher blast than the top air

so that it will blow out light seed and heavier

trash.

Oscillation of the screens is controlled by means

of variable-speed pulleys and should be adjusted

to keep the seed action "alive" over the screen.

The greater the oscillation, the faster the seed

movement over the screens. If this movement is

too fast, the seeds hop across the screen and will

not be sejiai'ated properly. If it is too slow, the

seeds have a tendency to glide across the screen

with the larger material and not .sift through.

The ])itch can be adjusted for each screen individually. The .steeper the sci'een, the fa.ster will

be the flow of seed across it, and the more likely a

long seed is to .stand on end and go through. The

more the tilt, the smaller tlie size of the particle

that will pass through the screen. The smaller

the pitch angle, the longer the material takes to

pass over the screen. This gives more time and a

better chance for seed to line up with a hole and

pass through the screen, as well as tlie best chance

for a long seed to stay in the horizoiital position

and slide over the screen in lieu of through it.

Screen Attachments

Most air-screen cleaners are equipped with

traveling brushes beneath the screens that move

from side to side sweeping lodged seed from the

openings. The two materials used for brush

bristles are hair and nylon. It is the general

opinion that nylon, although more expensive

initially, will last considerably longer, and do a

more effective job of dislodging seed than the hair

bristles, which tend to be limber.

Mechanical hammers or bumpers are sometimes

used to assist brushes in dislodging seed by striking the screen periodically at top center, bouncing

seed free of the openings. -^.

Clod-crushing rolls are another air-screen attachment. These usually consist of two springloaded, rubber-covered rolls mounted so that material passing through the first grading screen is

fed between the rolls where dirt clods are crushed

without damaging seed. The second, or fine-grading, screen drops the crushed dirt and retains the

seed.

After seed is cleaned on the air-screen machine,

it is inspected to determine whether or not it needs

further processing, and if so, what special machine

or machines will be required to make the specific

separations.

If further cleaning is required, it is done by

taking advantage of some other difference in

physical makeup of the seeds, such as length, surface texture, electrical property, or specific gravity. The characteristic differences will dictate the

special equipment to be used in further processing.

The many types of machines used to make these

special separations will be discussed in following

sections.
SPECIFIC GRAVITY SEPARATOR

The specific gi'uvity sepai-ator classifies material

accordiiiii- to density or specific gravity. Tliis unit

was originally develoj)ed by the mineral industry

to separate ore from clay or dirt and to grade ore

in mining districts. The gravity separator, as it

is commonly called, has been adapted by the seed

industry for the grading of seed and tlie separating of seed and inert matter. (See figui'e ' '>.)

There are three cardinal rules that ai)ply to

gravity separation:

1. Particles of the same size but different densities can be separated.

2. Different-size particles of the same density

can be separated.

3. A mixture of particles of different sizes and

densities cannot l)e sepaiuted.

Component parts of the gravity separator are

an air-blast fan, an air-equalizing cliamber, a perforated deck, a variable-speed eccentric, deck

rocker arms, a feeding or metering device, a deck

end-raise adjustment, and a deck side-tilt adjustment. The end-raise adjustment varies the inclination of the discharge edge. The side-tilt adjusts

the deck so that the back is higlier than the front.

One end of the deck is the discharge edge and the

sides are the banking rails.

A mixture to be separated is metered at a uniform rate to the back of the deck. The slant of

the declv and its oscillating motion move the seed

over the deck. Air forced tlirougli the i)orous

deck from the equalizing chamber forms thousands

of small jets which cause the material to stratify

into layers of d i Itèrent densities in much the same

mamier as water stratifies ground cork and sand,

(^ork floats on the surface of water, and sand will

form a la^-er on the bottom. In the air-stratified

material, the light material floats and the heavy

material is in contact with the deck, as shown in

figure 4. The oscillating motion of the deck

"walks" the heavy material uphill nearly ])arallel

to the discharge edge, and tlie air "floats" the light

material downhill. As the material travels from

the feed i)oint on the deck to the discharge edge,

a gi-adation of material takes place ranging from

FiGUKE .3.—Siiei UK !,ii\iU sciiarutur.

s-u'ju-ii-ia

548373°—61 3
SEED

HOPPER

In

Q LIGHT SEED

<^> MED. SEED

» HEAVY SEED

SEED

a^=^ ji=^ Cr>^ C3 c:^-«:::^ <=> ^

DECK

FiGUEE 4.—Section view of specific gravity separator.

light material on the lower side of the deck to

heavy material on the upper side. By means of

movable splitters, the discharge can be divided

into any number of density fractions.

When a sized mixture of dirt, wild geranium,

crimson clover, and gravel is passed over the gravity separator, the geranium and weevil-eaten crimson clover will be discharged at the low side of the

deck, the rocks and lieavy dirt clods at the upper

side, and the good crimson clover in the middle.

This separation is shown in figure 3.

The Deck

The deck can be called the "heart" of the gravity machine. Deck covering plays an important

role. Separation eíñciency is dependent on air

movement through the deck, and inclination and

movement of the deck. About three or four types

of deck coverings are needed to handle seed crops

ranging in size from small grasses to beans.

8

The main job of the deck covering is to help

stratify seed material above the deck, yet adequately restrict air flow to build up static pressure

within the air-chamber and insure uniform air

distribution. A closelj' woven covering gives best

results for small seed, while a coarser weave is required for large seed. Linen, plastic, and wire

coverings have been satisfactorily used. It is

imperative that the deck covering be made from

material that will stand abrasion and is free of

lint, which would collect dust particles and clog

openings, thus preventing uniform air distribution.

Adjustments

Feed-rate adjustment.—The rate of material

entering tlie gravity deck is important and greatly

affects operation efficiency. Optimum rates vary

according to the différence in density or specific

gravity of the mixture components. The greater
the difference, the more rapid will be the traA-el

of light material to the low side of the deck and

the subsequent reporting of hea\y material to the

high rail. Greater feed rates are then possible

with this type of mixture. Conversely, when separating a mixture with small differences in specific

gravity, seed-travel toward the sides is not as pronounced, and feed rate must be reduced.

Insufficient feed rate causes seed to travel across

the deck in a thin bed, and portions of the deck

will be blank. For satisfactory separations, the

deck surface should be covered at all times. An

excess rate of feed will "rush" the procedure, and

too many good seeds will be discharged with the

middlings or rejects.

Air adjustment.—The air stream through the

porous deck prevents light seed from touching the

deck while it "floats"' to the low side. The air is

regulated to permit heavy seed to contact the oscillating deck. The sideways motion of this deck

imparts an uphill direction to the seed.

A common error in adjustment is an oversupply of air through the deck. If this is the case,

the intense air stream acts as a mixing agent

rather than a separating means, and formation of

horizontal layers or strata does not take place.

The basic principle of successful gravity operation

consists of stratifying the particles into layers of

different densities through the use of air, and separating the layers by a combination of eccentric

motion and inclination of the deck. These actions

take place in two zones on the deck—the stratifying area, and the separating area.

The size of the stratifying area at the rear of the

deck depends on existing differences in specific

gravity of the seed particles. The greater the difference in specific gravity, the smaller will be the

area required for stratification. Seed particle motion in the stratifying area can be considered essentially vertical, and results in a stratified seed mass,

with light material "floating" on top and heavy

material partially suspended just above the deck

surface.

The remaining portion of the deck is the separating area. Here, motion of the seed particles is

confined generally to certain layers, the direction

of motion being essentially horizontal. The lifting action of the air stream still must be maintained at a degree sufficient to retain the formerly

established stratification. However, as the seed

particles proceed on their journey to the front, or

discharge edge, of the machine, the stratification

becomes less pronounced. Movement of the

lighter i)articles to tlie low side of the deck and

heavier particles to the liigli side begins lo api)ear.

The separation becomes complete when the vertical stratification has dissipated and gi\-en way to

a horizontal gradation of material as it flows off

the deck.

Excessive air rate tends to shift the seed material on the deck to the low rail and produce uncoA-ered areas at the upper rail. Insufñcient air

rate shifts the seed material to the liigh rail with

uncovered areas appearing at the lower rail. Satisfactory operation requires uniform coverage of

the deck at all times.

Side-tilt adjustment of the deck.—The sidetilt adjustment (back to front) depends upon the

area required for stratifying. The greater the

difference in specific gravity of the seed components, the smaller will be the required stratification

area, and the steeper may be the side tilt of the

deck. Conversely, a flatter tilt is required for seed

mixtures having more similar specific gravities.

Capacity of the gravity machine is directly related

to the side tilt; therefore, the most efficient operation involves the maximum side-tilt setting that

still gives the mixture enough time on the deck to

become separated.

End-raise adjustment of the deck.—Increasing the end-raise inclination of the discharge edge

causes more material to flow toward the low side

of the discharge edge, and flattening the raise

moves material to the high side. The maximum

slope of the discharge edge is usually about 6°

from horizontal, but a 2° slope is most common for

the average seed mixture.

Eccentric thrust adjustment.—Heavier materials of the seed mixture are forced to travel uphill

due to motion induced by the eccentrics. This

uphill travel is caused by the inclination of the

toggles supporting the deck, which are activated

by the eccentric thrust. The deck is given a horizontal motion as well as an upward and downward

motion, which moves seed in the direction of the

deck travel. The deck surface then drops from

the seed bed and again contacts it on the next

forward stroke. Heavy seed particles "hop"

across the surface of the deck at a rate governed by

the various machine adjustments. The faster the

motion, the faster the movement of material across

the deck to the upper side. Slowing the motion

tends to shift seed toward the low side of the deck.

All five of these machine adjustments are of
critical importance and closely inteiielaled. They

must be blended properly to obtain eflicient operation of a gravity se[)arator. Fi<iure 5 illusti'ates

ty])ica] deck pattei-ns for normal operation and for

unbalanced conditions resulting from faulty adjustments.

FIG. 5 A

INSUFFICIENT

SIDE ^RAISE

IG. 2 B

XGESSIVE

R

FIG. 4 A

INSUFFICIENT

END RAISE FIG. 3 B

EXCESSIVE

SPEED

FIG. 4 B

EXCESSIVE

END RAISE

FIG. 3 A

INSUFFICIENT

SPEED

FIG. 2 A

INSUFFICIENT

FIG. 5 B

EXCESSIVE

SIDE RAISE

AIR

A. START THE SEPARATION AND WAIT FOR THE

MATERIAL TO DEFINE A CONSTANT PATTERN OF

DISTRIBUTION.

PATTERN OF MATERIAL DISTRIBU

FOR IDEAL OR OPTIMUM

B. COMPARE EACH

TIOKI WITH FIG. I

ADJUSTMENTS.

C. CORRECT ERRORS OF ADJUSTMENT IN THE

FOLLOWING ORDER.

I.AIR ADJUSTMENT FIG

2. ECCENTRIC SPEED

3. END RAISE SLOPE

4. SIDE RAISE SLOPE

2 A OR 2B

FIG. 3A OR

FIG. 4A OR

FIG. 5A OR

3B

4B

5B

FIGURE 5.—Check chart for adjustment of siieeiflc gravity separator.

10
INDENT DISC SEPARATOR

Seeds of the same width or thickness can be

separated on the basis of length differences.

Length separators are of tAvo general types—the

indent disc and the indent cylinder—bnt both nse

the principle of lifting short seeds from a mixture

with a given pocket, or indentation, which is too

shallow to accommodate long seeds.

The indent disc separator consists of a series of

indented discs which revolve together on a horizontal shaft. Each disc contains numerous undercut recesses on each face (see ñgnre 6). As the

discs revoh-e, the recessed pockets lift out the short

seeds and reject the longer seeds; for example,

vetch can be lifted, leaving oats, rj-egrass, and

other elongated seeds; and crimson clover can be

lifted, leaving ryegrass and fescue seeds.

Normally, when several sizes of contaminants

are to be removed, the discs are located so that

disc-pocket size increases progressively from intake to discharge end of the machine. Small

seeds are removed first, the larger seeds being

lifted as the seed mass moves toward the dischai's-e

point. When there is only one separation to be

made, many discs of the same size and shape are

incorporated in a machine, or several machines, to

increase capacity. (See figures 6 and 7.)

Seed Travel

Seed travel from intake end of the machine to

dischai'ge end is provided by vanes attached to

spokes of the discs. The removable vanes operate

like a screw conveyor to move the seed mass slowly

through open portions of the discs. In addition to

conveying, this operation brings the seed mass

in contact with each disc and facilitates separation. The vanes and spokes also agitate the seed

mixture, thus minimizing stratification.

The housing of the machine closely fits the rims

of the revolving discs, but there is suiRcient clearance to prevent the crushing of seed. This favors

seed travel through the center and open portions

of the discs.

FIGURE 6.—Indent disc separator above an indent cylinder separator.

11
edge is flat

Lifts Short

Seeds

Rejects Longer

Seeds

FIGURE 7.—Cross-section view of an indent disc separator.

Disc Pocket Design

The disc pocket functions like an elevator

bucket. As the disc passes throu<--h the reservoir

of seed at the bottom of tlie machine, short seed

will be held in the pocket by a combination of centrifugal force and capacity of the seed to become

seated on the pocket bottom. ^Vhether a seed is

lifted or rejected depends upon its length and

position of center of gravity. If the center of

gravity extends beyond the pocket lip, the seed is

rejected. Seed is discharged from the pocket in

the same manner that an elevator bucket relieves

its load.

Disc pockets are made in two basic shapes, and

each shape is available in a number of sizes.

Pocket size is indicated by its width in millimeters,

measured radially from the center of the disc.

Length or height of the pocket is essentially the

same as the width. Depth is usually one-half tlie

M'idth. The undei'cut part of the pocket is referred to as the bottom.

The "R" pocket.—This pocket or indent derives

its name from "rice." It was designed to remove

broken rice grains from whole grains. The lifting

while the leading edge is round.

Pod<et design is such that it will reject round

seeds, but will lift out cross-l>roken grain or elongated seeds on the flat surface.

The "V" pocket.—This i>ocket derives its name

from "vetch," and is designed to remove roundshaped seeds. The pocket has a round lifting

edge. "V" pockets tend to reject tubular, or elongated seeds, as they have no fl:it surface to bear

on. These seeds tip out of the pockets as the disc

revolves.

Both the "V" and "R" pockets are made only in

the smaller sizes, usually ¿i/o mm. to 6 mm. These

discs are designed primarily for removing small

materials from a mixture, such as dodder, dock,

sorrel, or plantain from fescues and ryegrass.

Both types of pockets are designed to give the

maximum contact surface according to the shape

of the material being lifted. The letters "V" and

"R" are always followed by a number, which indicates the size in millimeters. For example, an

R5 pocket has a flat lifting edge and a radial

width of 5 mm.

Other designations.—Some discs are made with

pockets designated solely by letter. They carry

no numeral to indicate width, and usually are

made in sizes exceeding i/4 inch in radial width.

Normally, these pockets are square-faced and are

used in specialized separations or splittings.

Operation

Disc rotational velocity.—The rotating speed

of the discs should be held nearly constant since

variations of only a few r.p.m. affect the efficiency

of disc operation. Too great a velocity prevents

the material from becoming seated in the pocket

bottom, or prevents the discs from discharging

seed properly. Low velocity may not provide

sufficient centrifugal force to hold seed in the

pocket.

Disc-pocket size.—A^Hiether the disc separator

operates with all discs of the same size pocket, or

with a combination of pocket sizes and types, depends upon how closely the seed mixture has been

graded. In a combination type of arrangement,

the discs are grouped into sections, Avith the

smaller-sized pocket discs installed near the seed

intake. In this arrangement, material both shorter

and longer than seed being cleaned can be removed.

The selection of "V" pockets, "R" pockets, or a

combination of both, depends upon the shape characteristics of the seed, and the grading desired.

12
Reject and re-run.—Flexibility of operation

can be achieved by provision for re-run or removal

of such fractions as may be desired.

Seed travel adjustment.—Conveyor vanes may

be removed or added as desired to move the seed

mass through the machine at a rate gi\in<i- best

separation. Capacity and efficiency of separation

are determined by tlie ratio of the number of small

particles to be removed to the numljer of pocket

recesses needed to remove the material. Tlie

travel speed of the seed mass may be controlled

accordino-ly. Raising the tailings gate tends to

keep the seed in the madiine longer, and gives the

discs more time to clean the se«d thoroughly.

INDENT CYLiNDER SEPARATOR

Short Seed

dt Dropped

AdjustOb le Trough

Seed Conveying

Augers

Being Lifted

Into Trough

Long Seed Being

Rejected

FiGTJEE 8.—Cross-sec-tion view of an indent cylinder separator.

Indent cylinders perform separations on the

same basis as the disc separator. Both use centrifugal force and length dilferences to lift material from a seed mass, making a lengtli-sizing

separation ; for example, sloughgrass can be lifted,

rejecting meadow foxtail.

The indent-cylinder separator, as shown in figure 6, page 11, consists of a rotating, horizontal

cylinder and a movable, horizontal separating

trough. The inside surface of th«>. cylinder has

small, closely spaced, semi-spherical indentations.

In operation, the seed mass to be separated lies

on the bottom of the cylinder. As the cylinder

rotates on its axis, the short seeds in the mass are

lifted from the mixture by the nmnerous indents.

At some jîoint before reaching the top of the rotation, the seeds drop from the indents and are recei\'ed by an adjustable trough. See figure 8.

Indent Pocket Design

Shapes.—Various shapes of indents have been

tested. The shapes of bottoms and sides, the slope

angle of the sides, and the indent depth in relation

to width provide a wide range of separation characteristics. For example, an indent with coneshaped sides was best for the removal of seeds

wliich would not roll readily. A cylinder lia\ing

spherical-shaped indents drawn slightly shallower

than tJieir diameter was better for removal of

round seeds, such as crimson clo\-er or soybeans.

13
Indents with sti'aight, \erli<-al sides wei'e best for

liftin«:-, but were limited in (lexibilily of opera! ion.

It is not praclical to inslall more than one size

or shai)e of indent in any one cylinder. Nor is it

practical for the operator to change indent cylinders to take out each shape or size of seed separately. A compromise in pocket desi<;n was reached

Avhere side slope, depth, width, and shajie provided

the best resvdts for the most seeds normally encountered. Indent size is indicated by mmierical

notation, the number indicatinii' indent size in

( )4-ths of an inch. For example, a No. 4 indent

cylinder lias pockets 4/(;4ths of an inch in

diameter.

Selecting the indent.—Good selection involves

the use of the snn\llest size indent that will satisfactorily lift all nn\terial to be removed. The

combination of centrifugal force and indent size

lifts short particles and carries them the highest

ont of the main seed mass. Next to fall from the

indent are intermediate-size seeds. The longest

seeds fall free of the indent oidy a short distance

above the seed mass, or are not lifted at all.

Some materials are too large to lift, and may roll

along the bottom of the cylinder causing a stratification of the seed mass. To prevent this stratification, screw conveyors or similar devices are

located inside the separator to agitate the seed.

This also tends to level the .seed mass in the machine and prevent build-up at the feed end. Too

much build-up would let material fall into the

separating trough without having been lifted by

the indents.

At the feed end of the cylinder there are many

undersize particles in the seed mass. These quickly

find their way into indent pockets and are lifted

out singly and by multiples. As these sizes are

depleted and the nuiss works toward the center of

the cylinder, the intermediate-size material is removed. At the tail end of the machine, the final

and closest grading by the indent is accomplished.

The cylinder is set on a slight incline so that material flows by gravity from the feed end to the

discharge end of the nuichine.

Operation

The indent cylinder lifts particles from the seed

mass by a combination of centrifugal force and

the retention of material in the indent. This unit

shows its greatest efficiency when lifting nuiterial

that weighs in excess of 4.5 pounds per bushel.

For this reason, the cylinder is more practical with

small grains and legumes than it is with grasses.

Unlike the disc separator, seed coat texture, density, and moisture content of the seed do affect

.se])aratif)n in an indent cylinder. Friction of the

seed slipping out of tlie indent allects the distance

it will ti'avel in the pocket before being dropped.

Hence, a rough or wet seed will be lifted and carried fi-om the seed mass more leadily than a slick,

di-y one. The following two adjustments, together

with the valuations in physical properties of seed,

pi'ovide a wide range of separation response in this

machine.

Speed of cylinder.—A seed is held in tlie iiident

i-ecess by centrifugal force sufficient to lift it from

the seecl mass and to retain it until some determined point of the travel arc is reached. Adjustment for cylinder sjteed is tlierefore pi'ovided on

this machine. Speed sliould not be increased Iteyond the amount required to carry the seed to a

point directly over the cylinder axis. Speeds in

excess of this amount will not allow the seed to

drop from the indent. On the other liand, speed

nuist be great enough to lift seed fi-om the mass.

Between these two extremes, maximum separation

efficiency can be obtained.

Adjustment of separating trough.—The edge

of the separating trough can be set at any position

giving best separation. Trough position for any

given seed mixture will be dictated by the speed

of the cylinder, indent size and shape, and level

of the seed )nass. Combination of these variables

gives considerable flexibility in operation.

Methods of Use

Single unit.—The cylinder separator is most

commonly used as a single unit in seed processing.

Multiple units.—A useful multiple-cylinder

unit can be arranged wherein the cylinders are

grouped vertically, with the top cylinder having

a middle-size indent. Liftings of the top cylinder

are sent to a lower cylinder provided with a small

indent. Tailings of the top cylinder are sent to

another lower cylinder fitted with the largest size

indent. The top cylinder acts as a "splitter," and

the final separations of each fraction are made in

the two bottom cylinders.

Combination.—The indent cylinder also can be

employed as one component of a single assembly

ofl'ering several mediums of seed processing. For

example, equipment is manufactured which provides for scalping, aspiration, disc separation, and

cylinder separation, all in one machine.

14
PNEUMATIC SEPARATORS

Many different types of air separators are manufactured for seed processing. Some are called aspirators and others, pneumatic separators, but all

use the movement of air to divide materials according to their terminal velocities. Terminal velocity

refers to the air velocity required to suspend particles in a confined, rising air current, and takes

into account such characteristics as shape, surface

texture, and specific gravity, all of which alîect a

particle's resistance to air fio\v.

The primary diiterence in the two types of separators is the location of the air source. In the

aspirator, a fan is placed at the discharge where it

induces a vacuum so that atmospheric pressure can

force air through the separator. In the pneumatic unit, the fan is at the intake where it creates

a pi'essure greater than atmospheric, which again

forces air through the separator.

In both cases, air velocity through the machines

can be adjusted by regulating the fan air intake.

All products with a terminal velocity less than the

air velocity through the units will be lifted. Material with a higher terminal velocity will fall

against the air flow.

There are several forms of aspirators. Figure 9

is a cross-section view of a scalping aspirator. A

''M^SCREENINGS

^DISCHARGE

m

seed mixture is fed froui the hopper "A" to the

rotating scal])ing screen "(V' whicli allows seed to

]iass to the asi)iratiug cluunber "E." Sticks, straw,

lea\-es, and other large roughage components are

carried over tlie revolving screen into section "B."

With a suction or negative pressure at "H," air

passes through the aspirating cluunber "E" at a

velocity slightly below the terminal velocity of the

heavy, phnnp seed. Shriveled or weevil-eaten

seeds, liglit trash, and weed seeds are lifted and

deposited in chamber "F,'" and the conveying air

escapes through chamber "H." Heavy, plump

seeds fall through the incoming air and out the

inlet to a conveyor or receiving bin. The air

velocity, through the aspirator, is controlled by

regulating bypass air through "M" with adjustable gate "O."

Figure 10 is a cross-section view of a fractionating aspirator. When seed is metered into the air

column "B," tlie heavy seed falls against the air

flow and out the air inlet, whereas the lighter seed,

shriveled seed, weed seed, grass seed, and chafl' are

lifted. By adjusting the movable air vane in

column "C," the air velocity can be decreased to

drop out au}? components traveling below their

terminal velocities. Column "D'' will receive the

heavier liftings, which are usually good seed but

not of the highest quality. Column "E" will catch

salvage grass seed, broken seed, or light and unusable seed. The light chaff, dust, rodent filth,

and other extremely light material will be

delivered to the "F" chamber.

The total air volume flowing through the system, and therefore the air velocity at "B,'' is

regulated by the air-control damper in the fan discharge pipe and by a variable-speed electric motor

driving the fan. This separating unit can provide

graded fractions in a continuous operation.

Figure 11 is a cross-section view of a pneimiatic

separator. When seed enters the feed chute, the

light seed, splits, broken seed, chaff, and straw

FIGURE 9.—Scalping aspirator, cross-section view. A, Feed

hopper ; B, section into which large tra.sh is thrown off as

it passes over the revolving scalping screen; C, rotating

scalping- screen : D, reclaimer for any seed that may have

passed over the scalping screen : B, aspirating chamlier ;

F, area into which shriveled or weevil-eaten seeds, light

trash, and weed seeds are conveyed with the exhausting

air; G, discharge valve; H, suction or negative pressure

chamber thr<nigh which conveying air escapes ; L, same

as F except that air velocity is higher in L ; M, chamber

where bypass air enters; O, adjustable gate.

15

548375°—61 3
AIR CONTROL

LEVER AIR CONTROL

DAMPER

FIGURE 10.—Fractionating aspirator, cross-section view.

A, Fe(Hl hopper; B, air column through which heavy

seeds fall a;;ainst the air flow: C, column into which

lifibler seeds and cliaff are lifted: I), column which

receives tlie lieavier liftings: F, column which catches

sahajie grass seed, broken seed, or light and unusable

seed: F, <-olunjn into which extremely light waste

matei-ials are delivei-ed.

are lifted by the air flow up tlirough the column

and are deflected by an inverted cone to a discharoe pan. Heavy seed fall.s against the air floAV

until it is diverted by an inclined screen to the

heavy seed outlet. With adequate air control,

many precise separations can be made \YÍth pneumatic separators, such as lifting meadow foxtail

and rejecting Alta fescue, cheat, and light

material.

DEFLECTOR

CONIE

DISCHARGE

PAN

FEED CHUTE

AIR CONTROL

LEVER

MOTOR a

FAN

FIGURE 11.—Pneumatic separator, cross-section view.
VELVET ROLL SEED SEPARATOR

The velvet roll separator is a special seed-cleaning machine that divides material by diilerenres

in surface texture and shape. It consists primarily of two velvet-covered rollers ])laced side by

side in contact with one another, and set at an

angle. The rolls, when viewed from the top, rotate outwardly in opposite directions, and have

an adjustable shield above them.

Figures 12 and 13 show, respectively, a velvet

roll separator and the basic principle of operation.

being thrown out lii'st ; then a progressive reduction ill roMglmess of throw-out material takes ])lace

as seeds approach (lie discliarge or lower end of

the rollers.

The vel\-et roll macliine, like other seed-cleaning e(|nipmeiil, needs balancing adjustments to

give best performance. The speed of the rolls,

angle of incline, clearance l)etween shield and i-olls,

and rate of feed are all adjusted according to the

particular seed mixture requirements. Tlie clearFiGur-.E 12.—Velvet roll seed seiiarator.

A seed mixture to be se^^arated is fed onto the rolls

at the upper end so that seed travels down the incline formed by the rolls. Rough-coated seeds,

sharp-2)ointed seeds, and broken seeds catch in the

velvet and are thrown against the shield, which

deflects them back to the roll. They bounce back

and forth in this manner until they are worked

over the roll and out of the mixture. Smoothcoated seeds slide down the incline and are discharged from the lower end of the rollers. The

sejjaration is a graduated one with rougher seed

anee between rollers and shield should be great

enough so that seed can turn freelj- without touching both shield and roller at the same time, but

small enough so that rough-surfaced seeds will

be thrown repeatedly against the shield as the seed

conies in contact with the roller. If the clearance

is too great, many rough seeds will spin and slide

back between the rollers into the smootli-seed

stream. When the clearance is too little, smooth

seed will be pressed against the roller and rolled

out with the rough-surfaced seed.

17
Tlie rate of feed is important on a \'e]\'et roll

machine. If too o-reat, many seeds will not come

in contact with tlie rollers, and Iherefore will not

have the chance to be separated. The rate of feed

and ano'le of incline of the rollers can he increased

as the différences in surface texture of the seeds

in a mixture increase, and \'ice versa. The speed

of the rolls is another important factor, and should

he adjusted as reipiired to nnike the separation.

The faster the roll speed, the greater the "thi'owout." If too much good seed is being- throAvn out,

the roll speed should be decreasecL When too

much rougli seed is discharged with the clean seed,

the roll speed should be increased.

Since the ett'eets of machine adju-stnients are

sometimes diflicult to see, the following practice is

recommended in adjusting the \'elvet roll separator. Make only one change at a time; operate

the machine 5 minutes after each change, and then

ol)ser\'e the results. If rough-coated seed is found

in the smootli-seed discharge, the rolls are running

too slow, or the machine is being fed too heavily.

If too much smooth seed is being thrown out with

the i-ough seed, the rolls are rumiing too fast.

The velvet-roll machine is simple, and one« set

in oi)eration, can run contii]Uously with little attention. It is used to finish many seed separations

where capacity requirements are not too high.

The mime "dodder mill" is sometimes assigned to

this unit as it is used to remo\-e rough-coated dodder weed seed fi-om smooth legume seed. Other

common separations are dirt clods from beans,

thnothy from alsike clover, unhulled from hulled

lespedeza, and many rough weed seeds from

smooth crop seeds.

\

Feed /

Hopper

Velvet Rolls

Rough

Seed qSÜ?J^ <?m««*K "-Smooth a Some" Smooth Some Smooth p^.g^, seed ^--^Seed Seed

Velvet Covered

Rollers Metal

Shield

Rough

Seed

SECTION A-A'

FIGURE 13.—Side and cross-section views of velvet roll separator.

18
SPIRAL SEPARATOR

The spiral separator classifies seed accordiiiiï to

shape, density, and ability to roll. It is a simple

machine with no moving parts, and requires very

little floor space. Once it is placed under a storage,

bin and the feed rate is regulated, the spiral will

operate continuously with little or no attention.

Some separations can be made with tliis unit tliat

are not possible with air-screen machines, length

separators, and other seed cleaners.

Basically, this separator consists of one or more

sheet-metal flights wound on a central tube in the

form of a spiral. The unit resembles an ojjen

screw conveyor standing in a vertical position.

(Seefigure li.)

In operation, a seed mixture is introduced at the

top of the inner spiral. Round seeds roll down the

inclined flight while irregularly shaped seeds tend

to slide. The faster the seed travels down the

flight, the larger the arc of travel becomes because

of centrifugal force. The round seed.s havinogreater velocity, make a wider circle than the

irregularly shaped seeds, and the original mixture

can then be divided into fractions by splitters

(dividing boards) at the bottom or discharge end

of the flight.

Spiral separators sometimes have multiple

fliglits arranged in order of increasing size, with

each flight having a separate discharge chute.

Seeds that roll well because of their density and

roundness travel downward in a spiral path of increasing diameter. These seeds will flow over the

edge of one flight to another until tliey reach one of

sufficient diameter to coincide with the seed-travel

path. Such a separator, with flights of several

widths, will produce gradations of a seed mixture

ranging from flat seeds at the small-diameter,

inner flight to high-density, round seeds on the

outer flight.

The spiral is used to sepaiate round seeds, such

as rape, vetch, and soybeans, from irregularly

FiGlMiE 14.—Spiral separator.

shaped seeds like wheat, oats, and ryegrass. It

can also separate whole vetch seed from broken

vetch, and crimson clover from rape or mustard

seed. Laige seeds require a different size of flight

from that of small seeds; therefore, several spiral

designs may be needed to process a range of seed

sizes.

The chief disadvantages of the spiral are lack

of flexibility in adjustment, and a relatively low

capacity, which may range from 200 to 700 pounds

an hour, dejjending upon the seed being separated.

INCLINED DRAPER SEPARATOR

The inclined draper separates seeds on the basis

of a difference in ability to roll or slide down an

inclined surface. The rolling or sliding characteristics of seeds are governed by their shape and

seed-coat texture.

A seed mixture to be separated is metered from

a hopper to the center of an inclined draper belt

traveling in an uphill direction, as shown in figure

15. Eound or smooth seeds, like vetch, will roll

and slide down the draper faster than the draper

is tra veling up the incline. In contrast, flat, rough,

or elongated seeds, like oats, will be carried to the

top of the incline, thereby making the separation.

The seeds dropping otí' the draper at its lower end

are gathered in one chute, and the seeds reacliing

the upper end are dropped into a second chute.

To gain capacity in commercial operation, nniltiple draper belts can be used in a single machine.

19
FLAT OR

ROUGH SEED

SEED HOPPER

ROUND OR

SMOOTH SEED

FIGURE 15.—Inclined draper seed separator, section view.

(See figure Iß.) The rate of feed to the draper

may be varied. The rate should be slow enough

to alloAY each seed to act individually and not be

hindered from rolling or sliding by those that are

stationary. Also, it should not be forced to move

by those that are traveling.

The angle of incline maj^ be varied to match the

rolling or sliding characteristics of the seed mixture. The speed of the draper may be varied to

simulate a shorter or longer length of incline, and

belts with different degrees of roughness may be

used as the di'aper. A relatively rough canvas

belt may be employed when rolling tendencies are

predominant in seed of the lower fraction, while a

smooth plastic belt is moi'e useful if a sliding action

is wanted for the lowei' fraction. In many cases,

the smooth belt can do all that a canvas belt does,

and in addition, can provide a means of making a

more precise separation.

In adjusting tlie machine to perform a given

separation, start with a very low rate of feed, a

slow drajter speed, and a flat draper slope. Increase the angle of slope initil none of the rolling

or sliding fraction of the mixtuie is being carried

to the top. Increase the draper speed until none

of the flat or elongated seed is falling oti' the lower

end. Increase the I'ate of feed until it becomes

obvious that quantity is interfering with individual seed action and changing previously set conditions; then reduce the feed rate a small amount.

Typical separations made by the inclined draper

are crimson clover from grass seed, vetch from

oats, and other spherical seed from flat, rough, or

elongated seed.

20 FiGUKE 16.—Commercial inclined draper, equipped with multiple draper belts. S-106-5-59
HORIZONTAL DISC SEED SEPARATOR

The horizontal disc sepiinitor (fig. IT) is a

special machine designed to divide seeds hy difference in abilit}^ to roll or slide when subjected

to centrifugal force. Physical factors alfecting

FIGURE 17.

S~8Ö—4—56

-Horizontal disc seed seijarator.

this separation are shape, density, and sui'face

te.\tui'6 of the seeds. Tliis unit is considered a finishing machine, and is used to salvage rejected

seed from otlier cleaning eiiuipment. It will separate dodder from alfalfa., curly dock from red

clover, and other mixtures where one seed has a

greater tendency to roll or slide than another.

The separation made by tlie horizontal disc is

similar to that made with a spiral, but is more

selective since the disc macliine lias a variable

speed control which can change the proportions of

a seed mixture retained or rejected.

The discs are mounted at regular space intervals, one above another, on a hollow vertical shaft.

The seed mixture is fed from a hopper into the

top of tlie hollow shaft which meters seed to

each disc through variable orifices. A plastic

fence with two adjustable outlets confines seed

in the center of the disc, discharging two single

seed rows, spaced 180° apart, to the outer portion

of the disc, as shown in figure. 18. Centrifugal

force causes the round seeds to roll off, while

irregularly shaped seeds remain on the disc and

are raked off at each half-rotation, resulting in

four separations per disc. The outer area of each

disc is banked like a highway curve to offset, partially, the increased rolling tendency due to increased centrifugal force that is present as a seed

moves away from the center of disc rotation.

The 16-disc machine pictured in figure 17 has

a capacity ranging from 300 to 500 pounds per

hour, depending upon the seed being cleaned.

Flat Seed

Disch. Spout

Feed Port

Rotating Table

Spheroidal See^

Disch. Spout

Spheroidal Seed

Disch. Spout

Feed Port

Flat Seed

Disch. Spout

FiGUBE 18.-Cross section of horizontal disc- separator. A, Hollow vertical shaft .;lneh -:^f^^^!^^i;'^^^l;2

inner portion of disc; C. adjustable outlets; D, plastic fence; E, outer area of disc; 1, diseluuge foi rot;nd seed,

G, discharge for flat seed.

21
ELECTRONIC SEED SEPARATOR

Electronic seed cleanere take adviintage of differences in electrical characteristics of seed fo

malie many separations that cannot he made witli

conventional seed-cleaning- eqnijiinent. The degree of separation possible depends npon tlie relative abilities of seeds in a mixtnre to conduct

electricity or to hold a snrface charge.

Electronic, or electrostatic, separations have

been practiced for many years in the mineral indnstries, but the principle has been applied to

seed separation only recently in a few connnercial installations. Some of the separations that

liave been I'eported are watercress seed from rice,

best are attracted most strongly to the electrode;

tlins, a sepai'ation of seed can be made.

In the general ari-angement of an electronic seed

separator, a ho]>pei' feeds the mixture to a belt or

cylinder, which discliarges tlie seed into a highvoltage held. A suitable power unit and electrode

assembly can pi'o\'ide Held strengths up to 45,000

volts, J)C. As the seeds pass tiirough the field,

they ar-e attracted oi' repelled according to the

cliai-ge they j^ossess, and tliis charge determines

the ]3ath that will be taken as the seeds fall from

the belt or cylinder. Dividers in the drop path

can be positioned to collect any fraction of the

Feed

Hopper

Seed Conveyor Belt r /

T «—Tr~r—r- V J i V . a V %

>-

^//^/ Electrode

Adjustable

•1' Dividers

TiGURE 19.—Schematic drawing of an electronic seed separator.

ergot from bentgrass, and Johnson grass from

sesame.

It has long been known that substances can be

"electrified" or charged with static electricity.

For example, a comb which has been passed

through hair is capable of attfacting lightweight

objects such as bits of paper. This attraction

takes place because the electric charge on the comb

is now difterent from that on the paper. In an

electronic separator, seeds are given a surface

charge of static electricity by passing them

through a high-voltage electi'ical field. Some

seeds lose their charge faster than others, depending upon their conducting properties. The

charged seeds tend to move toward an electrode of

opposite polarity. The seeds that hold a charge

distribution desired. Figure 19 is a schematic

sketch of an electrostatic separator.

Three différent field conditions can be provided

according to the position of the high-voltage electrode. One is a static or non-discharging field,

whicli produces a "lifting" effect where seeds of a

particular charge are attracted to an electrode of

opposite polarity. This is a direct example of

the phenomenon of static electricity, and little or

no current flow takes place. Another is a discharging field, which produces a "pinning" effectSeeds passing through this field receive a spray

charge of electricity from the electrode, which

causes some seeds to be repelled from the electrode

and pinned to a grounded belt or roller. A combination lifting and pinning effect is also possible.

22
The proper iiekl conditions for a given separation

depend upon the seed mixture, and are best determined by exi)eriment.

Encourao-ing results iiave been shown l)y a

separator developed at Oreiron State College

through the cooperation of the Agricultural Engineering Research Division of the U. S. De[)artment of Agriculture, and the Agricultural

Engineering Department, Oregon State College.

Preliminar}^ research has been conducted with this

However, changes in moisture content can be coml)ensated for, to s(jme degree, by proper adjustmenlof voltage, held condition, and other machine

l)ink and cornñower) was successfully removed

from Alta fescue and ryegrass. Also, curly dock

was separated effectively from red clover.

To determine the effects of high-voltage exposure u}wn germination, extensive tests were conducted with common ryegrass. After rei^eated

exposure to 25,U(J() volts, seed lots were germinated

FicuuE 20.—Electronic seed .seijaratur developed ccxjiieralively at Oi'egoii State College. ¡5-155-1-59

unit, shown in figure 20, to detei'inine what seed

mixtures could be separated, the effects of seed

moisture content on separating ellicieney, and tlie

influence of high-voltage exposure upon the germination of seed.

oMoisture cf)utent Avas found to play an important ])art in electi'onic separation of cro]) seeds,

which stems from the fact that a seed's ability to

conduct electricity is affected by changes in seed

moisture, ("banges of -2 to ;! percent in moisture

content were great eiujugii to im[)air separation.

a( iiiter\'als o\'er a period of 0 months and showed

no signilicaiff change in germination. Other seeds

that showed no change in gerndnation were alseltings. Bachelor's button (also called Erein'h

faifa, red chixcr, alsil<e clover. Aha fescue, and

])e.reiniial i-ycgrass. Addilional lests wei't' condueled at liigher Aoltages with subterranean

( l()\ei', i-yegiass, and ("hewings fescue, .\tlere\-

])osure to 14,DIM) \-olts, these lois also showed unchanged germinal ion \abies.

Allhouiih eleclronic séparai ion is n(.)l a new

.^4s:iT (;i 4 23
development, it is a useful tool wlieu propei-ly fereiices of seed, it offers the possibility of making

adapted to tlie seed-cleaning industry. Since separations that are now difficult or impossible

this separation is not based upon physical dif- with conventional seed-cleaning equipment.

MAGNETIC SEED SEPARATOR

At least six different makes of magnetic separators are used in the seed industry, representing

German, English, and United States developments. Some employ permanent magnets and

others use electi-omagnets in their opei'ation. All

are considered finisliing machines and are becoming increasingly popular as seed standards

grow nioi-e exacting.

The operating principle is shown in figure 21,

Avhich is a section view of a single-drum, magnetic

separator. Most magnetic cleaners have two

IRON POWDER SUPPLY

WEED a

CRACKED SEED

FiGUKE 21.—Section view of a single drum, magnetic seed

separator.

drums in seiies and subject seed to two magnetic fields, thereby increasing tlie efficiency of

separations.

The seed mixture is fed into a screw conveyor

that tumbles and niixes the seed with a pi'oportioned water spray and a finely ground iron powder. The powder will adhere to rough seed coats,

cracks in a seed coat, dirt clods, chaff, or seeds

with a sticky residue on the surface. The mixture is then discharged from the mixing screw

onto tlie revolving drum, which has a high-intensity magnetic field. The rough-textured or sticky

seeds, which are now coated with iron powder,

adhere to the magnetic drum until they are removed with a i-otaiy brush. The good seeds,

being smoother, are relatively free of powder and

are not attracted by the magnetic field. They

will fall from the drum in a normal manner thus

making the separation.

The magnetic cleaner is excellent for removing

rough-coated seeds like dodder, or mucilaginous,

coated seeds like buckhoni plantain, from smooth

legume or flax seed. Hulled Johnson grass can

be removed from alfalfa by using an emulsified

oil along with water to help the grass seed pick up

and hold the poAvder.

Capacities of magnetic separators range from

200 to 2,000 pounds of seed per hour, depending

upon machine size and the seed being- cleaned.

BUCKHORN MACHINE ¿i

The buckhorn machine is a special unit designed primarily to remove buckhorn plantain

from legume seed, such as crimson clover, alfalfa,

and red clover. Normally, the buckhorn plantain

and the legume seeds are so similar in size, shape,

and weight that many of the buckhorn seeds cannot be removed by the air-screen machine,

the gravity separator, or other seed-cleaning

efjuipment.

Plowever, the buckhoni seed has a mucilaginous

substance on its surface tliat becomes stick-y when

dampened and will pick up finely ground sawdust, thereby formiii

24

a larger seed miit with

lower density. Since the legume seed is smooth,

the sawdust does not adhere to it.

After a seed lot is mixed with a small amount

of water and sawdust, as shown in figure 22, the

Sawdust Feed

Mixing Ctixinnber-^ Clover a Sawdust'

Covered Buckhorn^

Seed —¡—-»

FiGUKE 22.—Buckliorn machine, section view.
enlarged buckhom seeds can be removed with an

air-screen cleaner. If small buckhorn seeds drop

through the screen along with legume seeds, the

gravity machine may be employed to separate

tiiese components on the basis of density

ditl'erencos.

TIMOTHY BUMPER MILL

The bumper mill is a special machine de\eloped

to remove weed seeds from timothy. It makes

separations by exploiting dirt'erences in shape, surface texture, and weight of seeds.

The unit consists of two sets of identical, superimposed decks suspended in a rigid frame and

connected by a linkage. (See figure 23.) A small

and a feeder is positioned to supply seed continuously to each plate.

As the rocking deck battery bumps tlie niblter

cushion, all seeds are given an uphill motion. The

plump timothy seed has a tendency to roll downhill between each bumping cycle, and will travel a

shorter distance uphill than the irregularly shaped

seed. By the time the seeds mo\-e from "the feed

FIGURE 23.—Tiinoth.v bninper mill.

S-107-5-59

electric motor drives a cam that rocks the decks

back and forth and bumps them simultaneously

against adjustable rubber stops mounted on the

rigid frame between the two batteries of decks.

All decks of a battery are at the same inclination

at any one time, and this inclination witliin the

suspended frame can be \-aried by adjustment

screws. Each deck is divided into 3" x 9" plates,

end to the discharge end of the metal i:)late, the

seed types have migrated far enough ajjart to be

discharged into separate spouts.

"Wlien this machine is proi)er]y adjusted in deck

angle, rate of feed, and intensity of sti'oke, it will

separate alsike clover. Canada thistle, sorrel, ryegrass, quackgrass, buckhorn, and other seeds from

timothy seed.

25
VIBRATOR SEED SEPARATOR

Tlie vihrutor sopuralor is a sporinl liiiisliiiig

machine desio-ned to separate seeds \<y iheir contrasts in shape and surface texture. liasicall}', the

unit consists of an inclined deck, which is activated by an electromagnetic \-il)i'alor, the stroke of

which is adjustal)le. (See H<>-ure '24:.) The whole

assembly can be tilted sideways and forward to

provide a wide ranae of deck inclinations.

incbnation causes «rradually widening bands of

dilferent seed fractions to tra\'el over the deck

from the feed to the discbarge edge, where dividers isolate these fractions.

With the ])i-oper deck surface, inclination, and

vibration intensity, the vibr'ator cleaner can make

many difficult separations. It will remove curly

dock from crimson clo\e)-, dogfennel and hedgeFiGUiiE 24.—Vibrator seed separator.

Multiple decks may be mounted in a rigid frame

so that a single vibrator will power the whole battery. The decks can be of varying textures ranging from smooth metal to rough sandpaper

depending upon the seed components being separated, and the vibration intensity can be regidated

by means of a rheostat controller in the electrical

circuit.

In operation, a seed mixture is introduced near

the center of the upper edge of the inclined deck.

The action of the vibrator causes flat or i-ough

seeds to climb the incline, while the more spherical

seeds travel a shorter distance up the incline or

roll to the low side of the deck. The forward deck

mustard from timothy, and rippleseed plantain

and ergot from bentgrass.

OTHER EQUIPMENT

Special items of equipment are found in seedprocessing plants that are not disciissed in this

handbook. Debeardere, for example, remove awns

and separate doubles so that seed can be cleaned

more effectively. Hullers and scarifiers remove

hulls and roughen seed coats to reduce seed loss

and hard seed. Other items found useful in seed

processing are bagging scales, seed blenders, bag

closers, moisture testers, seed samplers, and similar

devices.

26
SEED HAKDLING AND TREATING

CONVEYING SYSTEMS

EfFective handling of materials is important in

the economy of any industry, and seed processinois no exception. Seed lots are transported many

times throughont various operations of hauling,

cleaning, storing, and shipping, and if care is not

exercised, processing efficiency AYíH be reduced by

seed damage, contamination, and handling costs.

Generally speaking, seed-conveying methods

can be classified in two major divisions—mechanical and pneumatic. Mechanical systems include various tj'pes of conveyors, elevators, vibrators, and bulk-handling schemes, while pneumatic

systems entail the use of air, and may operate

above or below atmospheric pressiu-e.

Mechanical Methods

Belt conveyor.—The belt conveyor is an endless

moving belt that can transport material horizontally and at an incline. The belt may be supported

by idler rolls, or it may slide in the bottom of an

open trough. Little or no seed damage takes place

in this type of conve3'or, but contamination or intermixing of seed lots is possible when the belt

travels in a trough.

Bucket elevator.—The bucket elevator consists

of buckets attached to an endless chain or belt

which runs along a vertical or steeply inclined

path. The system may be enclosed in a single

housing called a "leg,'' or separate hou.sings for

the elevator leg and return leg. The buckets load

themselves as they pass through a seed hopper or

"boot" at the bottom of the run, and, depending

upon elevator type, the load is discharged by centrifugal force and/or gravity as the buckets round

the top section of the assembly.

The centrifugal-discharge elevator is commonly

operated at high speeds to obtain high capacities,

and the resultant discliarge velocity may cause

excessive damage to injury-sensitive seed. Slowspeed, high-capacity units are better for easily

damaged or slow-ñowing materials. Another

limitation of bucket elevators is that they are difficult to clean. Small seeds tend to lodge in liardto-clean areas throughout the elevator and remain

there to contaminate subsequent lots.

A different type of bucket elevator that is becoming increasingly popular in seed handling is

a slow-speed, multi-section conveyor, that operates

without a filler boot or enclosed housing. In a

four-section unit, four kinds of seed can be

handled separately in adjacent strands of buckets.

Buckets of each section are loaded at the bottom

of the run by individual, timed, rotary feeders.

The buckets turn upside down as they follow a

horizontal path at the top of the conveyor and

gently discharge the seed. Because of the opentype construction, any seed that is dislodged from

a bucket will fall free of the system. Since there

is no boot, housing, or high-speed discharge to be

a source of contamination or damage, this elevator

is well adapted to handling certified, registered,

and other pure seeds.

Screw conveyor.—The screw conveyor usually

consists of a long-pitch helix mounted in a Ushaped trougli, with or without a cover. As the

element rotates, seed fed to it is thrust forward

and discharged through openings at the end of

the trough. Since this conveyor agitates or

tumbles the product handled, it can be used to

good advantage as a seed blender in batch and

continuous operations. It can also function as a

feeding or metering device where fairly accurate

control is needed.

Screw conveyors may operate in horizontal,

vertical, or inclined paths, but capacity drops as

inclination increases. A cylindrical housing

surrounding the helix is commonly used when

elevating at a steep incline.

This conveyor is simple but seed damage can

result from the sliding, squeezing, tumbling movement provided by the screw action. Also, the

unit is not self-cleaning. If the seeds being

handled are smaller than the clearance between

helix and housing, they may remain in the system

and contaminate subsequent lots.

Vibrating conveyor.—The vibrating conveyor

transports material by "bouncing" it along a metal

tray that has a short, reciprocating stroke of high

frequency. The tray motion can be accomplished

by electromagnetic or mechanical means. No apparent seed damage occurs in this conveyor, and

it tends to be self-cleaning. One limitation, however, is that it is restricted to horizontal or nearhorizontal transport paths. A special application

of this imit is as a metering device where good

control of feed rate is necessary.

17
In electroiiiapiK'tic units, the conveyiiiíí ti-:iy is

pulled down and buck sluirply l»y mao-nelic atf ractiou and then returned up and forward to its

orijiinul position by springs. Tliis action is modiñed in some desi<>ns so that electromagnets, (o-

<l-e(her with spring's, alternately attract and repel

the tray to impart the reciprocating motion. As

the tray drops backward, the material beiny conveyed falls perpendicularly to a new position forward in the tray and is then carried up and forward to have the cycle repeated at high sjieed.

Excellent features of electromagnetic conveyors

are convenient control of feed rate and a wide

range of conveying capacities in a single unit.

The flow rate is simply conti-olled by a voltage

rheostat, which varies the vibration of the tray.

Although fairly costly, the electromagnetic unit

has several other advantages. There are few moving parts that require maintenance, and power re-

({uirements are relatively low.

Another aiiplication of this vibration principle

in seed handling is the mounting of unit vibrators

on bins or hoppers to improve the flow of material

that tends to "bridge" or cling to the sides.

When vibrating conveyors achieve their motion mechanically rather than electromagnetically,

they are sometimes called reciprocating or oscillating convevors. There are several methods of

obtaining the required movement. In the positive-drive unit the vibrations ar'e produced by

an eccentric mounted on a shaft so that its throw

causes movement of an attached trough that pivots from special hangars. The geared-weight

method uses two unbalanced pulleys mounted in

a housing and geared together to revolve toward

each other. "When the two centers of gravity

move in parallel in the same direction, an impulse

is communicated to the housing and to the attached

conveying trough. Since the impulse will be neutralized when the centers of gravity move in opposite directions, a straight-line vibration may be

obtained.

In general, mechanical vibrators can do the

same conveying job as electromagnetic units.

They show no seed damage, and have good selfcleaning characteristics.

Bulk-handling schemes.—In some cases, seed

lots are handled by bulk or unit-load methods.

The seed may be transported from field to processing plant in sacks, unit boxes, or as a bulk load

in the tinick bed. At the plant, the seed is either

processed directly or stored, in sacks, boxes, or

bnik. Sacks can be handled singly by special

elevators and conveyors, or in loads stacked on

¡)allets and moved by forklift trucks. Boxes,

also, are handled by lift truck, or sometimes

with a box elevatoi- which can grasp a large box,

elevate it to a point whei-e the load is dumped,

and return the box to floor level. Advantages

of the box method are reduced labor re(piirements,

less chance of seed contamination, and ease of

maintaining seed-lot identity.

In bulk stoi'age, loose seed is delivered to bins

by various forms of elevators, conveyors, and

pneumatic systems. Scoop attachments fitted on

forklift trucks are also used for handling bulk

seed in oi)en-end bins.

Pneumatic Methods

Pneumatic systems transport material by air

and have the advantages of good clean-out characteristics, flexible horizontal and vertical operation, and mechanical simplicity. In order to

transport material in conventiomd pneumatic

conveyors, certain minimum air velocities are required, as shown in the tabulation below. Once

this condition is achieved, a rule-of-thumb method

for supplying air-volume requirements is to proA'ide 40 cubic feet per minute under average atmospheric conditions for each pound of material to

be moved. Limitations of these conveyors are

(1) possible damage to the seed because of high

velocities, and (2) greater power requirements

than in mechanical handling methods.

Vacuum system.—The vacuum system operates

below atmospheric pressure and usually includes

a conveying pipe, a suction fan, a cyclone or settling chamber to drop seed from the air stream,

and an airlock to discharge seed from the cyclone

while retaining the vacuum. This system finds

considerable use in unloading tracks, freight cars,

and ships. Other successful applications are in

short runs whei-e seed is conveyed and removed

from the system before it reaches a velocity that

may be damaging.

Low-pressure system.—Low-pressure systems

operate above atmospheric pressure in a range of

approximately 10-15 inches of water (about 1/2

pound per square inch), and require a fan, conveying line, cyclone, and a means of introducing

seed into the air stream. Generally speaking,

conveyors of this type employ centrifugal fans

and conveying lines ranging from 6 inches to 24

inches in diameter. Depending upon actual sys28
tem pressures, seed can be introduced by injector

or auger feeders, or if a better air seal is needed,

by using a rotaiy airlociv (also called a star feeder

or bucket wbeel). The low-pressure and vacuum

systems are the most connnon types of pneumatic

conveyors used in seed processing.

Air velocities needed for typical pneumatic conveijing of materiah at 70° F. a7ui 70 percent

relative humidity

Approj-iiiiatc (hict vrlocitii in

liiieaJ feet per iiiiinitc Material to he eiwrcyed

2,ri00 Dry dust and li.siht fluffy seed

(bluegrass, nieadcjw foxtail)

3,000 Ryegrass. fescue, and similar

grass seed

3.500 t(i 4,000 Alfalfa, eriuison clover

4,000 to ."p.OOO Heavy oats and cottonseed

r.,000 to 0,000 Wheat, corn

Medium-pressure system.—Systems operating

at pressures up to about 40 inches of ^vater are

classified as medium-pressure conveyors. The

greater pressure requirements usually result from

longer runs, more elbows, or greater conveying

rates. Special centrifugal fans act as the air

source, and common conveying pipe sizes are -t

inches to 8 inches in diameter. Rotary airlock

units are needed to supply seed to the air stream

for this type of convej'or.

High-pressure system.—These sy.stems operate

at ]n'essures of about ,", to 15 i>ouii(ls ])er square

nicli, widi relatively low air volumes, and generally u.se small conveying pipe, about 1 to 4 indies

in diameter. Positive-displacement air sources

are employed in Die foi-m of rotaiy blowers or i-eciprorating piston ])mnps. Seed inti-oduction to

the high-pressure air stream is accomplished satisfactorily up to about 10 p.s.i. with rotary airlocks,

Init operation at higlier ju'essures requires si)ecial

locks or air-sealing ineclianisms.

Several chai'arteristics of high-pressure systems

in seed conveying are flexibility of small-size pipe

runs, high solid-air ratios, and I'elatively low seed

\elocity—therefore, low seed damage. Also, with

low air A-olumes, there is little or no dust problem,

and cyclones or collectors generally are not needed.

Recent experimental work with high-pressure

seed conveying has shown several types of massflow patterns, all taking place at low velocities.

For example, wJien crimson clover was transported in a li/^-inch con\eying run that included a

30-foot vertical lift, the seed flowed in a dense

phase at the bottom of the run, and completely

filled the pipe with a continuously moving seed

ma.ss. At higher elevations in the lift, the seed

mo\ement took place in a fluidized state, and at

the top of the run the flow consisted of intermittent surges of seed, discharged at low velocity into

an open bin. Conve3nng capacities ranged from

3,000 to 6,000 pounds per hour.

PROCESSING DIFFICULT-TO-HANDLE SEED

Certain tyjoes of seed, particidarly natiA'e

grasses of the Great Plains area, prove very difficult to handle throughout ¡processing and planting

operations. In some cases the difficulty is due to

seed appendages, such as awns, beards, or fuzz

that tend to interlock and cause undesirable clustering. In other seeds, the presence of multiple

florets or "doubles" prevents uniform handling and

metering. Still another problem is posed by light,

chafí'y seeds which bridge easily and fail to flow

properly from a gravity-fed hopper. Seed characteristics like these make a preconditioning treatment necessary to imi:)rove flow properties before

such seed can be cleaned and planted with conventional machinery.

Several mechanical tmits have been investigated

as a means of removing awns and appendages.

These include the hammer mill, a thresher operating at high speed, a tmnljling pebble mill, and a

debearding machine. Since all these units employ

a vigorous abrading action, care is needed in their

operation to insiu-e maximum awn removal with

mininnnn seed damage.

Feed rate, hammer speed, screen selection, and

crop condition are all very important in operation

of the hammer mill. The screen should liave an

opening slightly larger than the de-awned seed.

If too large a screen is chosen, there will be an

excess quantity of inert matter and a high percentage of awns not removed from the seed. If

the screen is too small, the seed will show excess

damage and the capacity will be decreased. The

feed should be regulated so that the mill is approximately full at all times. If the mill is operated only i)artly full, there will be more seed

dannxge and a higher percentage of awns not

removed.

29
The speed of the luminiei' mill best suiled for

preireatiiio- seed for cleaiiiiiji- is iiboiit 50 perceiil

of that used in a normal ^-rindiii«;- operation ; however, this can vary sli<ihtly accordino; to individual

cases. If the speed of the hammers is too fast, the

seed will be mutilated, cracked, or groated. If

the speed is too low, awns will not be removed

eiïectively. With a properly adjusted and operated hammer mill, most seed can be conditioned

so that an air-screen machine can be used for

cleanino-. Seeds of the following species have

been successfully treated in a hammer mill operation : bhiebunch wheatgrass, blue wildrye, Canada

wildrye, Siberian wildrye, tall oatgrass, bulbous

barley, squirreltail, alfileria, and virgins-bower.

Canada wildrye has also been de-awned in a

threshing operation by speeding up the cylinder,

setting concaves to a minimum clearance, and reducing the air blast. However, moisture content

at time of threshing is quite influential in this

process. Another precleaning treatment that is

effective in removing seed hairs and fuzz is the

tumbling of a seed lot in a container with smooth

pebbles. A sample of Merion Kentucky bluegrass,

tumbled in this type of unit and then processed in

pneumatic and air-screen separators, responded

very well and showed imj^roved flow properties.

Debearding machines are also used as j^reconditioners. There ai'e at least two available types.

One is approximately 5 feet in length with a circular ci'oss-section, and has a rotating member

with rectangular beater arms set on it at a slight

angle. Stationary bars mounted on the sides and

protruding toward the center keep the seed mass

from rotating with the beaters. The seed is fed

at one end and conveyed through the unit by the

pitch of the beater arms.

Pressure or density of the seed in the debearder

is regulated by a weighted outlet door at the end

opposite from tlie feed, and a variable-speed pulley permits a selection of beater speeds. When

these adjustments are set according to the peculiarities of the seed being processed, many of the

range grasses can be preconditioned. However,

a high beater speed Avill cause seed damage, and

some groating. Too much weight on the outlet

door will reduce machine capacity, whereas too

little weight will allow seed to escape early and

reduce the percentage of seed de-awned.

The second type of debearder is somewliat similar in operation to the unit just discussed, but uses

li/o-iiT-ch pipe beater arms in place of rectangular

bars. The shape of the debearder housing tends to

reduce i-olling of the seed mass, and de-awning is

accomidished by the seeds rubbing against each

other. In limited preliminary tests, this type of

debearder appeal's to be doing a more efficient and

less damaging job of removing awns and breaking

up doubles than either the hammer mill or the debearder discussed pre\iously. Also, it requires

less horsepower to operate. However, awns that

are not stiff enough to In-eak, but are small and

limber, like the awns of black grama, cannot be

removed completely by this machine. Even after

a lot is processed in debearders, hairlike awns often

keep this seed from flowing over .screens, and further treatment may be required.

As a unique approach to the problem of awn

removal, differential burning has some pos.sibilities. This technique is somewhat similar to flaming grass out of cotton. In a laboratory experiment, the fine awns of black grama seed were

burned off by dropping the seed through a blowtorch flame where an instant flashing of awns

took place. No scorching of the paperlike lemma

and palea was evident, and no increase in seed temperature could Iw detected by feeling the seed.

Conventional air-screen seed cleaners, with alteration, may satisfactorily handle some of these

range grass seeds. To move seed over the screen,

it may be necessarv to mount the screens on arms

so that the cam will give the screen a straw-walker

action rather than a straight reciprocating motion

all in one plane. To prevent choking or lodging

of seed in screen openings, a knocker that periodically taps the screen may be required in addition

to traveling brushes on the underside of the screen.

The aspirator cleaner can l)e used to good advantage both before and after an air-screen cleaning operation. Plere, the air adjustment is veiy

accurate and close separations of a mixture may

be made. This unit was used to process a sample

of meadow foxtail containing sloughgrass, chess,

ryegrass, and rattail fescue. On one pass through

the aspirator, the meadow foxtail and sloughgrass

were lifted and the remainder of the contamination was discharged from the bottom chute. A

Xo. 8 indent cylinder was then used to remove the

sloughgrass leaving clean meadow foxtail.

Älany schemes have been used to obtain seed flow

through planters. Mechanical agitators, brushes

to clean the seeder disc, and free-flowing additives,

such as sawdust, sand, cracked grain, plastic shavings, and rice hulls have been used. Heavy ma30
terials like sand (which is abrasive and should

not be used) and cracked grain have a tendency

to settle below the light seed, resulting in uneven

seeding. Sawdust and rice hulls are better additives, the latter being more desirable. The luills

are light and form a natural pocket to hold (lie

seed. One rule-of-thumb for seeding is to set a

planter for 160 pounds of barley per acre. At

were groated and would not gei'minale, but the

seed mass still contained (angled siems, leaves, and

fuzzy seed.

The need for Texas bluegrass seed to plant in

the (ireat Plains area prompted further effort to

condiiion the seed so that it could be handled and

seeded with a mechanical planier. This conditioning was accomplished by spraying the seeds, stems.

„'v. .1 '.¿zy^ii

FIGURE 25.—Texas bluegrass consolidated for planting : A, Original seed mass ; B, granular product made with a Silvicon

binder ; C, dense pellets made with a starch binder.

this setting it will deliver about 16 pounds of rice

hulls per acre. The desired amount of seed can

then be mixed with the hulls, and the mixture will

flow through the planter.

Texas bluegrass is one of the most difficult seeds

to process. Its cottonlike appendages interlock

the light chaify seeds so that the seed, entangled

stems, and trash are nearly inseparable. Both

conventional and special type cleaning equipment

were used in attempts to clean this seed, but with

little success. The seed was processed until some

leaves, and other plant residue with a binder, and

compressing the whole mass in an extrusion press.

When starch was used as the binder, pellets of seed

were extruded that could be seeded with a conventional cotton or corn planter. When Silvicon

(a powder fraction of Douglas fir tree bark) was

used as a binder, a coarse granule was formed that

could be planted with a conventional grain drill.

(See figure 25.)

The material presented here represents attempts

to process diflicult-to-handle seed.

31
FIGURE 20.—Cut-away of liquid seed treater.

32
SEED TREATING

Tlie scientist, tiie farmer, and the seedsman are

all becoming more aware of the necessity for treating seed. The use of seed treaters to protect seed

from soil- and plant-borne fungi and from insects

in the warehouse and the soil has been known to

double the field stand in infested areas. The increased production resulting from the use of

treated seed is stimulatiuc' the use of treatingmachines in processing plants.

Seed treaters may be divided into three categories: dry-powder applicators, slurry applicators, and liquid applicators. The dry-powder

applicators Avere the first type used. They do a

thorough job of coating the seed, but many of

these units have been replaced by slurry or liquid

types because of the harmful eft'ects of breathing

chemical dust, and the difficulty of controllingchemical dosage in the dry-powder units.

The introduction of wettable powdere and the

development of the slurry treater came next. This

was considered a major step forward in seed treating, since it made possible the metering of chemicals needed to treat a given seed quantity, while at

the same time confining the chemical to the seed.

The slurry is a versatile treater that will handle

many différent commodities. However, it is not

suitable for applying low dosages of the more potent chemicals developed in the past few j^ears.

This failing led to the development of the liquid

applicator.

The liquid applicator has several advantages.

With it, as little as 14 ounce of mercury will treat

a bushel of seed without the necessity of adding

water, and the treatment can ))e performed in

tein])eratures as low as -20° F. Tlie seed does not

ha\-e to 1)6 completely co\-ered to give the desired

protection. Unfortunately, this teclmique cannot

be used with vegetable or other food-crop seeds.

These are still treated l)y the slurry method.

There are two types of liquid ti'eaters in general use. In one type, a seed mass is tumbled

in a rotating drum, and liquid is applied in small

di-ops by a number of fingerlike tubes. The

drum is set on an incline so that the seed travels

from inlet to discharge as the dram rotates. The

other liquid treater consists of a chemical pump

and tank, an electrical motor, seed feed control,

seed-Aveighing pan, chemical measuring cups, a

seed-dispersion cone, and a rotary disc. (See

figure 26.) In this unit, seed is fed to the top

of the machine where it is accurately measured

in the weighing pan while the chemical is measured in metering cups. The exact proportions of

seed and chemical are then dumped simultaneously. The seed falls on a dispersion cone, which

spreads it to form a hollow cylinder, the wall

thickness of which is equivalent to one layer of

seed. The chemical drops on a high-speed revolving disc that breaks up the liquid into a fine,

penetrating mist, which sprays the seed from the

interior of the cylinder as the seed falls from the

dispersion cone into a sacking bin.

This spray ti-eater is satisfactory not only for

applying very small amounts of chemical to seed,

but can be easily and quickly adapted for treating

a wide range of sizes and types of seed.

PLANT LAYOUT

Many factors should be considered in laying out

a seed plant. It should be planned so that seed

is received, cleaned, and shipped without mixing

or damaging the lots, and with a minimum requirement of time, equipment, and personnel.

The seed separators, elevating and conveying

system, and storage bins should be so arranged

that the seed flow can be continuous from the

receiving bin to the shipping point, yet flexible

enough to bypass a machine or return part of the

seed for recleaning, if necessary. An adequate

waste-handling system to convey discarded material from various cleaners is essential but sometimes overlooked in seed-processing plans.

Other factors that should be considered in the

plant layout are: the kinds of seed to be cleaned

and the contaminating crop, weed, and inert matter; the volume of seed to be handled, and the

method of handling (bulk or sacks, and if sacks,

whether they are to be handled by hand, roller

conveyor, or forklift trucks) ; the conveyor system to be used (pneumatic or mechanical) ; and

the location of receiving and shipping facilities.

Also, room should be allowed for future expansion of the seed plant, and possible rearrangement

of equipment to accommodate additional machines

in the processing line.

About as many different plant layouts can be

found as there are seed processing plants. Multistory plants that use enclosed bucket elevators

to convey seed to the top floor are the most common, and usually have cleaning machines placed

33
FIGURE 27.—Exteridi- view of iimlti-story processing iilant. S-187-5-59

34

FiGUßE 28.—Siugle-.story proces.smg plant, exter:lor view. S-134-D-59
in a vertical processing line so that the seed flows

by gravity from one machine to another on a

lower level. This arrangement reduces the number of elevators required to handle the crop but

requires a high, reinforced structure to support

the heavy machinery on the upper floors. (See

figure 27.) Also, workers are needed on each

floor to care for and operate the equipment.

Single-story plants, as shown in figure 28, have

macliinery placed on only one level, and are increasing in number because of the present-day emphasis on varietal purity and the special procsei)arator, u velvet roU seed separator, tlu'ee ;'>0-

busliel storage bins, and a self-cleaning, elevating

and conveying .system. The arrangement prc>

vides a nexi))Ie operating sequence, and is located

in a space 20' x ;](J' x VV, as shown in figures :iO

and ;51.

Other plant layouts iise a modification of the

multi-story and single-story arrangements. For

example, seed nuiy be elevated to an overhead storage bin and fed by gravity to an air-screen cleaner

located on a balcony. The remaining machines

will be placed on the ground floor so that seed

FIGURE 29.—Single-story processing plant, interior view. S-1S5—5-59

essing requirements for certain grass, legume, and

vegetable seeds. This arrangement requires an

elevator for each machine, but has the advantage

that one man can supervise the entire processing

line from one floor. (See figure 29.) In many

cases, the reduced cost of a single-story building

compared with the cost of a reinforced, multistory structure more than oifsets the expense of an

elevator for each cleaning machine.

The experimental ¡jlant at Corvallis, Oreg., set

up on a cooperative basis for investigation and

demonstration purposes, is a complete single-story

seed-cleaning plant. It consists of an air-screen

seed cleaner, a gravity separator, an indent disc

from the air-screen cleaner can be spouted to them

for finishing operations.

Another j)liiiit arrangement that has proven

eifective is a single-storj' structure with a high

ceiling, a half-balcony, and small pits for airlifts

or elevators. In this arrangement, the airlift or

elevator discharge can be above the roof and directed to storage bins that feed machines located

on the balcony, which require little attention. Examples of these machines are hullers, scarifiei-s,

debearders, indent disc and cylinder separators,

and seed treaters, all of which need regulation at

the beginning of a seed-lot operation but require

few adjustments thereafter. Seed from the bal35
cony machines flows by gravity to air-screen

cleaners, gravity separators, and other units

located on the ground floor, which recluiré frequent observation and adjustment.

To conserA^e floor space and minimize the handling of materials, seed-processing machines are

sometimes placed one aboA^e anotlier, or arranged

in series so that the discliarge of one imit flows

into another unit. Debearders are often fomid

above air-screen cleaners, and indent disc separators are frequently mounted above indent cylinder

machines, as shown in flgure G, page 11.

Where a plant operation must be flexiljle enough

to permit processing of grass seed, legume seed,

and grain, floor space can be saved by mounting

the processing equipment on rollers or mobile

frames. Then, depending upon given cleaning requirements, the special machines can be rolled or

moved by forklift truck into the processing line,

or into storage imtil needed.

The particular combination of machines forming a seed-processing line will be determined by

the seed crops and contaminants being handled.

Figure 32 represents the general sequence of

operation in cleaning several different crops.

Figure 33 is a typical flow diagram for processing

bluegrass, and figure 34 is a flow diagram for processmg corn.

Xpeceiving Hopper /

i

Air

2

Screen

Screens

i

Debearder

i

^

Air

4

Screen

Screens

o' *

li.

c

a»

c

c

Length Separator

3

o *

CE rr

Gravity Separator

*

Light Seed

Straw a Chaff Hea

' , Roc

Clean Seed

Sack a Sewino

FIGURE 33.—Flow diagram of bluegrass processing.

WHEAT m^E BARLEY

OATS AND VETCH

V////,<WA GRASS AND LEGUME

\RECEIVING HOPPER

DEBEARDER

AIR SCREEN

CLEANER

-?77r

VELVET

ROLL

^

LENGTH

SEPARATOR

GRAVITY

SEPARATOR SEED TREATER

\SACKING HOPPER /

FIGURE 32.—Flow diagram showing steps in the cleaning

of wheat, barley, oats and vetch, grass and legume

seed.

DRYER

SHELLER

AIR SCREEN

CLEANER

RING GRADER

WIDTH AND THICKNESS

SEPARATOR V

SEED

TREATER

LENGTH

SEPARATOR

GRAVITY

gEPARATOR

SACKING

a SEWING

STORAGE

FIGURE 34—Flow diagram of corn processing.

37
GLOSSARY

(Names of seeds i-eferred to in this publication)

Common

Alfalfa

AlHleria

Alsike clover

Alta fescue

American slonsligrass

Baclielor's button

Barley

Beans

Bentgrass

Black grama

Black bindweed (wild buckwlieat)

Bluebuncli wbeatgrass

Blue wildrye

Buckhorn plantain

Bulbous barley

Burclover

Canada thistle

Canada wàldrye

Cheat

Chess

Chewings fescue

Clover

Corn

Crimson clover

Curly or yellow dock

Dock

Dodder

Dogfennel

Fescue

Field bindweed

Flax

Hedgemustard

Italian ryegrass

Johnson grass

Kobe lespedeza

Bdtiiiiiral

l\ic<lica<j() nativa

Erad i II III cieiitarliim

Triflili II in. Injhriiliim

PentIIca (IninOiiuicea

Bcckiiiannia siizigueline

Centaurea eyuniis

Horden III spp.

Pliaseohis spp.

Ar/rontis spp.

Boiiteloiia eriopoda

Po IIIg 0 n II in eon v olvu lus

Agrrjpyron spicatum

Ely inns glaiieiis

Plantago lanceoJata

Horde urn biitbosum

Medioago hispida

Cirsium arvcnse

Elijinus canadcnsis

Bromiis spp.

BromIIs seealinus

Festuca rubra var. commiitata

TrifoUum. spp.

Zea mays

TrifoUum incarnattim

lîumejf erispus

Rurncx spp.

Cuscuta spp.

Anthémis cotilla

Festuca spp.

Convolvulus arvensis

Linum usitatissimum

Sisynihriurn offlcinale

Lolium multiflorum

Sorghum halepense

Lespedeza striata 'Kobe'

Common

Korean lespedeza

Lentils

Merion Kentucky bluegrass

Meadow- foxtail

Mustard

Oats

Perennial ryegrass

Plantain

Quackgrass

RagN-ieed

Rape

Rattail fescue

Red clover

Rice

Rippleseed plantain

Ryegrass

Sesame

Siberian wildrye

Sorrel

Soybeans

Squirreltall

Subterranean clover

Sudan grass

Tall oatgrass

Texas bluegrass

Timothy

Vetch

Virgins-bower

Watercress

Wheat

Wild geranium (cranesbill)

Wild oats

Botanical

Lespedeza stipulacea

Lens culinariH {Ervum

lens)

Poa pratensis

Alopeeitrus pratensis

Brassicu spp.

Avena spp.

Lejliiim perenne

Plantago slip.

Agropyron repens

Ambrosia spp.

Brassiea spp.

Festuca myuros

TrifoUum, pratense

Oryza sativa

Plantago major

Lolium spp.

Sesamum indicum, {S.

orientale)

Elymus Sibiriens

liume.x- spp.

Glycine maa;

Sitanion hystrix

TrifoUum subterraneum

Sorghum sudanense

Arrhenatheriim elatius

Poa arachnifera

Phleum pratense

Vicia spp.

Clematis ligusticifoUa

Rorippa nastnrtimn-aquatieum (Nasturtium officinale)

Triticum spp.

O cranium spp.

Avena fatua

;b

GOVBiíííiHBNT PRINT-öfG OFFÏ^

WASHINGTON// 1961

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington 25 D.C. Price 30 cents

38