^^"^ MECHANICAL SEED

CLEANING

AND HANDLING

Agriculture Handbook No. 354

Agricultural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE

in cooperation with

Oregon Agricultural Experiment Station
CONTENTS

Page

Introduction 1

Seed cleaners and separators 1

Air-screen cleaner 2

Grader 7

Horizontal screen cylinder 9

Vertical screen cylinder 9

Indent disk separator 10

Indent cylinder separator 12

Special indent cylinder 14

Screen selection according to seed

measurement 16

Specific gravity separator 16

Air separator 18

Velvet roll separator 21

Spiral separator 28

Inclined draper separator 24

Horizontal disk separator 25

Magnetic separator 26

Bumper mill 28

Vibrator separator 29

Electrostatic separator 30

Page

Color separator .. 83

Resilience separator 84

Other separators 35

Seed conditioning and treating 36

Scalper 36

Debearder 37

Hammermill 37

Huller-scarifier ^ 33

Treater 33

Seed handling and storing 39

Handling 39

Storing 43

Related operations 45

Plant layout 46

Types of layouts ..^ 47

Dust elimination ._ 49

Waste disposal . 50

Flow diagrams 51

References 53

Appendix 54

Decimal equivalent tables 54

Glossary 55

This handbook supersedes Agriculture Handbook No. 179,

"Seed Cleaning and Handling."

Washington, D.C. Issued October 1968

For sale by the Superintendent of Documenta, U.S. Government Printing Office Washington, D.C. 20402—Price 55 cents
MECHANICAL SEED CLEANING

AND HANDLING

By JESSE E. HARMOND, N. ROBERT BRANDENBURG, and LEONARD M. KLEIN, agricultural engineers, Small Seed

Harvesting and Processing Investigations, Agricultural Engineering Research Division, Agricultural Research

Service

INTRODUCTION

Agriculture is the largest single industry in

the world, and seed production is an important

segment of this industry. Grass and legume

seed production in the United States alone is

valued at more than $250 million annually,

and imports represent another $15 million.

When the production of vegetable, grain, and

flower seed is included, the total annual value

climbs to $750 million. Seed is important not

only as planting stock but also as a source of

basic raw material for many manufacturing

processes.

Seed, as it comes from the ñeld, contains

various contaminants like weed seeds, other

crop seeds, and such inert material as stems,

leaves, broken seed, and dirt. These contaminants must be removed, and the clean seed

properly handled and stored to provide a highquality planting seed that will increase farm

production and supply uniform raw material

for industry. The procedures used to meet

present quality standards result in a loss of

up to 50 percent of the good seed even though

many special machines and techniques are

used for seed cleaning and handling.

Attempts are being made to reduce seed

losses by developing equipment and methods

to improve efficiency in cleaning, treating, handling, and storing of seed. Although the research is concerned mainly with grass and

small legume seeds, the techniques and equipment involved are generally applicable to all

types of seed—^forage, grain, vegetable, flower,

tree, and industrial oil seed.

Manufacturers of seed machinery have done

an outstanding job in developing processing

equipment. 1 Some of the present seed-cleaning

machines make extraordinary separations of

small crop and weed seeds; however, the entire seed-cleaning problem is very complex,

and improvements are still needed in methods

and equipment to reduce the heavy seed losses.

This handbook was prepared as a guide in

understanding, selecting, arranging, and operating seed processing equipment. Various

types of seed cleaners and related machinery

are described; principles of separation for

both commercial and experimental developments are discussed; and basic concepts of

seed handling, storage, and plant layout are

presented.

There are many other related factors, not

discussed here, which are important in any

consideration of efficient seed production.

Some of these are improved seed varieties,

good cultural practices, effective seed harvesting techniques, accurate seed testing, and economic aspects of seed processing.

This publication is not intended to replace

manufacturers' instruction manuals or the

knowledge and experience of operators—

rather, it is meant to supplement them.

Acknowledgment is made to Hilmer E.

Carlson, Agricultural Engineering Department, Oregon State University, for the use of

his diagrams and sketches.

SEED CLEANERS AND SEPARATORS

Much seed cleaning is or should be done in

the field before the crop is harvested. Good

cultural practices like spray programs, crop

rotation, and roguing can minimize many

serious weed and contaminant problems.

When a seed lot enters the processing plant

for cleaning, contaminants are removed by the

use of special equipment that takes advantage

of differences in physical characteristics of

various components in the mixture. The chief

^ A list of manufacturers of seed processing machinery is available by writing to the Agricultural Engineering Research Division, Agricultural Research

Service, Beltsville, Md.
AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

characteristics used in making separations are

size, shape, density, surface texture, terminal

velocity, electrical conductivity, color, and resilience.

Many types of seed-cleaning machines are

available that exploit the above physical properties of seed, either singly or in some combination. There are air-screen cleaners, specific

gravity separators, pneumatic separators, velvet roils, spirals, indent cylinders, indent disks,

magnetic separators, electrostatic separators,

vibrator separators, and others. Of these, the

most v^idely used machine is the air-screen

unit; it is common to all seed-cleaning plants

from the small farm operation to the largest

commercial installation. All the other separators can be considered secondary machines

v^hich follov^ the air-screen unit in the processing sequence.

The choice of machines used and their arrangement in a processing line depends primarily on the seed being cleaned, the quantity

of v^eed seeds and other contaminants in the

mixture, and the purity requirements that

must be met. Seed for planting is of little

value unless it reaches the farmer in a viable

condition, essentially free of contaminants,

and at a price he can afford. The degree to

which these requirements are satisfied is related to the equipment used, its arrangement

in the processing plant, and the knowledge

and skill of the man operating the machine.

Air-Screen 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

air-screen cleaners ranginer from the small,

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

multiple-fan, six- or eight-screen machine with

several air columns. Screens are manufactured

with many sizes and shapes of openings. There

are more than 200 screen types available, and

with a four-screen 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 figures 1 and 2. Seed flows by gravity

from the hopper into a feeder that meters the

seed mixture into an airstream, which removes light, chaffy material so that the remaining seed can be distributed uniformly

over the top screen. The top screen scalps or

removes large material, the second screen

grades or sizes the seed, the third screen

scalps the seed more closely, and the fourth

screen performs a final grading. The finely

graded seed is then passed through an airstream, which drops the plump, heavy seed,

but lifts and blows light seed and chaff into

the trash bin.

The arrangement described above uses two

screens as top screens and two as bottom

screens. Other arrangements possible with a

four-screen machine are three top and one

bottom, or one top and three bottom.

Screen Numbering System

The size of a round-hole screen is indicated

by the diameter of its perforations. Perforations larger than 5V2/64ths of an inch are

measured in 64ths. Therefore, a 1-inch roundhole screen is called a No. 64, a 1/2-inch screen

is a No. 32, and so forth. Screens smaller than

5i/2/64ths of an inch are measured in fractions

of "an inch. Therefore, the next size smaller

than 51/) is l/12th; then, in descending order,

l/13th, l/14th, and so forth.^

The smallest round-hole perforation commonly used in air-screen machines is a l/25th

which has a hole diameter of 0.040 inch. However, for special cleaning requirements, roundhole screen in smaller sizes (down to 0.016

inch) can be obtained from manufacturers of

perforated metal. These special screens use a

different numbering system and must be

mounted on frames to fit air-screen machines.

Swedish and other foreign manufacturers use

the metric system in designating sizes of

screen openings.

Oblong-hole screens are measured in the

same manner as round-hole screens except that

two dimensions must be given. In laree oblonghole or slotted screens, the hole width is indicated in 64ths of an inch; for example,

11 X % means an opening ll/64ths of an inch

wide and %ths of an inch lone. In slotted

screens smaller than 5V2/M x %, width is

generally indicated in fractions of an inch;

for example, 1/12 x 1/2- There are some exceptions to this latter desiornation in that such

sizes as 5/64 x %, 47/8/64 x %, 3/64 x 5/16,

and others, use the large-screen numberm^

system with hole widths indicated in 64ths of

an inch. In all cases, the final number is the

length of slot.

' A table of decimal equivalents for various designations of round holes in screens is shown in the Appendix. This table is useful in comparing hole sizes of

screens with different number designations.
MECHANICAL SEED CLEANING AND HANDLING 8

FIGURE 1.—Air-screen cleaner.

S-205-6-B9

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 twentytwo 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-mesh

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

ll/64ths of an inch long. Another system used

by perforators is to designate the triangular

opening as the diameter of the largest circle

that can be inscribed in the triangle.

Table 1 shows screens in sizes and shapes

commonly stocked by manufacturers of seedcleaning machinery.

Selecting Screens

The two basic screens for cleaning roundshaped 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, which 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 round-hole 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 bot-
AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

Light

Trash

|:'^^-^i Clean Graded Seed

FIGURE 2.—Schematic view of air-screen cleaner.

torn screen. These shapes allow the best cleaning possible when a machine is equipped with

only one top and one bottom screen. The lensshaped seeds tend to turn on edge and drop

through a slotted top screen but lie flat and

travel over a round-hole bottom screen, which

will pass most other crop and weed seeds.

Since most air-screen 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, this system assures the most thorough seed separation.

One of the lens-shaped seeds commonly

cleaned with an oblong-perforated top screen

and a round-hole bottom screen is flax. This

slick, shiny seed must turn on edge to drop

through the oblong holes. If the top screen

is a perforated-metal type, some of the seeds

will slide over the screen without turning on

edge, thus reducing capacities and increasing

seed loss. When a wire-mesh screen with rectangular openings is used in place of the oblongperforated screen, greater capacities and accuracy can be achieved for two reasons: The

roughness of the wire 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.

Many seed shapes cannot be neatly classified

as round, elongated, or lenslike. For example,

timothy is shaped like a football, vetchling

like a cube, and dock or sorrel like a pyramid.

Corn occurs in many irregular shapes, and

sudangrass falls in an intermediate classification between round and elongated. Consequently, when screen types are selected for

specific seeds, the choice depends largely upon

what must be removed from that mixture.

When sudangrass is cleaned in a multiplescreen unit, the top screens usually will be a

round-hole and an oblong, and the bottom

screens also a round-hole and an oblong.

Special Separations

After seeds have been *'sized" with a roundhole screen, further separation can be made

with other hole shapes. One of the earliest

used screens for special separations was the

"dock'' screen, 3/64 x 5/16, devised mainly to

remove dock, mustard, ragweed, and other
MECHANICAL SEED CLEANING AND HANDLING 5

TABLE 1.—Sizes and shapes of screens commonly stocked by seed machinery manufacturers

PERFORATED METAL SHEET WIRE CLOTH

Round holes Oblong holes

Triangles

Oblong

cross slot

Roundhole

half

sizes

Oblong

half sizes

Square

Frac- openings

tions 64ths Fractions ^ 64ths 64ths

Oblong openings

Inches Inches Inches Inches

6 24 V24X1/2

1/^5 7 25 V22 X 1/2

V?A 8 26 2/64 X 5/16

V?.^ 9 27 V20 X 1/2

y?.?. 10 28 1/18X1/4

i/i>i 11 29 1/18 X 1/2

y?.o 12 30 1/18 X %

i/io 13 31 V16 X 1/4

Vl8 14 32 1/16 X 1/2

Vl7 15 34 Vl5 X 1/2

I/16 16 36 Vl4 X 1/4

Vl5 17 38 1/14 X 1/2

Vu 18 40 Vl3 X 1/2

V18 19 42 1/12 X 1/2

V12 20 44

21 48

22 56

23 64

72

80

478 X %

5x%

5y2 X %

6x %

61/2 X %

7x%

8x%

9x%

10 x%

11 X %

12 x%

13 x%

14 x%

15 x%

16 x%

17x3^

18 x%

19 x%

20 x%

21 x%

22 X %

24 X %-L

32x1

Inches Inches

6 X %

7x%

8x%

9x %

10 x%

11 X %

12 X %

13 x%

14 X %

15 X %

16 X %

18 x%

111/2X3/^

9

10

11

12

Inches

51/2

61/2

71/4

71/2

81/2

91/2

101/2

111/2

121/2

131/2

141/2

151/2

161/2

171/2

I81/2

191/2

201/2

211/2

221/2

Inches

71/2 x%

81/2X3^

91/2 X 3/4

101/2 X 3/4

111/2 X %

121/2 X %

131/2 X3^

141/2 X %

Inches

3x3

4x4

5x5

7x7

8x8

9x9

10x10

12x12

14x14

15x15

16x16

17x17

18x18

20x20

22x22

24x24

26x26

28x28

30x30

32x32

34x34

36x36

38x38

40x40

45x45

50x50

60x60

Inches

2x8

2x9

2x10

2x11

2x12

3 X 14 sp.

3x16

3 X 16 sp.

3 X 17 sp.

3x20

3x21

Inches

4x15

4x16

4x18

4x19

4x20

4x22

4x24

4 X 24 sp.

4x26

4x28

4x30

4x32

4x34

4x36

Inches

6x14

6x15

6x16

6x18

6x19

6x20

6x21

6x22

6x23

6x24

6x25

6x26

6x28

6x30

6x32

6x34

6x36

6x38

6x40

6x42

6x50

6x60

11/22 X ^ diagonal.

plump or round weed seed from thinner clover

seed.

Bottom screens with triangular openings are

being used for separating wild buckwheat and

field bindweed from small grains, and dock

and sorrel from fescue. These triangularshaped weed seeds can be dropped throuth the

openings, while longer crop seeds will **float"

over them.

Triangular openings in screens do not become plugged as readily as round holes. For

this reason, bottom screens with slotted or triangular holes are also used in some cases to

separate round seed from elongated seed, such

as mustard from oats. A 6 x 15 wire-mesh

bottom screen will remove burclover from subterranean clover even though both have been

screened to the same size with a round-hole

screen. The subterranean clover is round and

will not go through the narrow slot, while the

thin burclover will.

Since seed shape and size are so important

in screening operations, seed measuring has

been investigated as a basis for selecting

optimum shape and size of screen holes. This

research is discussed in a later section.

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 highcapacity screening than is possible with perforated-metal screens. Comparing a perforatedmetal screen to an equivalent wire-mesh screen,

the perforated screen has only a fraction of

the total number of openings per square inch

that are available in the wire-mesh screen,

and consequently would reduce capacity if

used.
6 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

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. Perforatedmetal screens have smooth surfaces and seeds

may lie flat and "float" over the openings.

Bottom screens may take advantage of this

flotation. 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 v^ith the contaminants.

Length of Slot

Slotted screens are perforated in different

lengths, such as the sizes 1/14 x 14 ^i^d

1/14 X 1/1,. Seed processors use the half-inch

length to drop hulled oats when they are cleaning seed oats. Cleaners of market grain want

to hold the hulled oats but drop small weed

seed. In this case, the shorter slotted hole is

desirable because it will float the long seed

(oats) over the screen but drop the weed

seeds. Processors of Korean and Kobe lespedeza

find that the 1/18 x 14 slot is fine for Korean

but a longer slot, size 1/18 x V2 or 1/18 x %,

is needed for Kobe, which is a flatter, wider

seed, and will not pass rapidly enough through

the 1/18 X l^ slot. For the same reason, a

three-quarter-inch long slot is good in a bottom screen for cleaning seed wheat because

it effectively drops wild oats, quackgrass, or

cheat without 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 short enough to prevent 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 separations of small round seed. For example, dodder can be removed from Korean lespedeza

with a one sixteenth 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 a quarter

of an inch high and 2 inches wide. When fastened over the cross braces of the screen with

nails or screws, the dams are positioned crosswise to 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.

Dams also can be used to cause elongated

seeds to upend and drop vertically through a

round or slotted hole. For example, screen

dams are effective in separating ryegrass and

flaxseed. When this mixture is passed over a

one-twelfth 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 causes the seed to pass

through the screen endwise, making the separation. Also, rattail fescue can be dropped from

fine fescue using a 6 x 26 slotted wire screen

fitted with dams.

When screen dams are used on round-holebottom screens, the accuracy of sifting is increased so that a heavier layer of seed may be

carried on the screen, with a resultant increase

in capacity.

Except when a screen is being used for grading, dams are generally used 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

flow over the screen to stand on end and drop

through with good seed.

Because of the close sizing and upending of

seeds that dams encourage, there is a tendency

for screen holes to plug more readily than in

conventional screening. This means that more

attention must be paid to keeping the screens

clean.

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. Rollers or flat wipers also

may be used under screens instead of brushes.

Mechanical hammers or bumpers are sometimes used to assist brushes in dislodging seed

by striking the screen ribs periodically at top

center, bouncing seed free of the openings.
MECHANICAL SEED CLEANING AND HANDLING

Clod-crushing rolls are another air-screen

attachment. These usually consist of two

spring-loaded, 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.

An attachment that can be used to improve

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 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.

In some cases, it is a good practice to blank

off the lower section of a top screen. Once a

line has been determined where all the good

seeds have dropped through, the screen can be

blanked off from that line to its discharge edge

with paper, plastic, sheet metal, or other suitable material. Then, any undesirable material

that has passed over the upper section of open

perforations will flow onto the blanked-off portion and have no further chance to stand on

end and drop through with good product.

Adjustments

Feed rate can be adjusted by increasing and

decreasing the speed of the metering roller,

or by varying the opening 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 separated. If it is

too slow, the seeds have a tendency to glide

across the screen with the larger material and

not sift through.

The pitch can be adjusted for each screen individually in most air-screen machines. The

steeper the screen, the faster will be the flow

of seed across it, and the more likely a long

seed is to stand on end and go through. 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 the best chance for a long seed to stay

in the horizontal position and slide over the

screen in lieu of through it.

Capacities

Capacities for air-screen machines vary considerably depending on the machine size, the

crop seed being processed, and the amount

and type of contaminant to be removed. Approximate rates listed by manufacturers for

a four-screen machine (screen size: 42 inches

wide and 44 inches long) are 75-125 bu./hr. for

seeds, 100-175 bu./hr. for cereal grains, and

200-350 bu./hr. for beans.

Further Cleaning

After seed is cleaned on the air-screen

machine, it is inspected to determine if further

separating is needed, and, if so, what special

machines are required to make the specific

separations.

Subsequent cleaning may be done with additional units that again use size properties. Or,

machines may be employed that exploit other

physical properties of seed like density, surface

texture, or terminal velocity. The characteristic differences in the physical makeup of the

seed and its remaining contaminants will

dictate the equipment to be used next. The

many types of machines used to make these

further separations will be discussed in following sections.

Grader

The grader is a size separator that classifies

seed either by width or thickness. It employs

cylindrical screens or '^shells" that are mounted

horizontally and have slotted or round perforations as shown in figure 3. In operation, the seed

lot to be separated is fed into one end of the

rotating shell where it tumbles and migrates

toward the tail end. Longitudinal movement

is caused by a continuous spiral channel and

a slight incline of the cylinder. During the

transit, seeds or particles smaller than the perforation drop through the shell while larger

material is retained and discharged out the

tail end. The dropped material may be directed

to a vibrating conveyor, screw auger, chute,

or other means of removing it from the

machine
AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

The

saddle dividing the channels or

grooves up-edges grain or other

material to proper thickness sizing

position.

View at end of cylinder

showing round recessed perforations

used for width sizing.

Cross-sectional view from section of cylinder with round recessed perforations which are used for width sizing. The perforation at the bottom of the

recess causes the grain or other material to be up-ended and positively presented

to the perforation.

FIGURE 3.—Slotted and round perforations in grader shells.

Three types of perforations (one slotted and

two round) are used in the cylinder shells. The

slotted perforations are available in widths

from 3/64 to 24/64 inch and are located at the

bottom of a corrugated groove having steeply

slanted sides. The corrugation acts to tip the

seeds or particles on edge so that the crosssectional dimensions can be sensed. In this

case, thickness of the particle determines

whether it can drop through the slotted hole.

Round perforations are available in two

styles. Large holes, from 13/64- through 26/64-

inch diameter, are perforated at the bottom

of a deep indentation. This construction tends

to upend particles so that widths can be

sensed. Large particles like oats, peanuts, and

certain grass seeds can be upended readily to

drop through the hole if their widths permit.

Smaller holes, from 4/64- through 12/64-inch

diameter are not indented. With these perforations, bars running the length of the shells

introduce a periodic tumbling action which

again encourages upending and width-sizing

of the particles. Small round holes can do a

good job of dropping bluegrass singles from

doubles.

The various perforations are kept free of

plugged particles by a soft, rotating rubberblade cleaner located outside the shell at the

top. The cleaner runs the full length of the

shell and taps or pushes wedged particles free

of the holes. A unique feature of this cleaning

action is that it occurs when the perforation

is inverted, and gravity therefore helps remove

the plugged material. In contrast, cleaning

mechanisms on conventional flat screens must

work against the force of gravity in performing their function.

Various model arrangements are available

containing from one to six shells per machine.

Capacity will vary greatly depending on the

product being processed and the percentage of

the total lot that passes through the perforations. With hybrid seed corn, for example, from
MECHANICAL SEED CLEANING AND HANDLING

25 to 80 bu./hr. can be sized per shell. The

largest single use of the grader is sizing corn

to fit planter plates.

Horizontal Screen Cylinder

The horizontal screen cylinder sizes products

by width or by thickness and is similar to the

grader in many respects. Material introduced

to the rotating cylinder either passes through

the perforations or is discharged from the tail

end.

The cylindrical screens or "reels" contain

slotted perforations, round perforations, or

both. The slotted screens are made from stainless steel wire. This construction provides a

great deal of open area in a given surface and

encourages good capacities. The round perforations are deeply indented as in the grader

shells to upend particles for width sizing. The

cylinder frame is constructed so that one, two,

or three different lengths of screen can be used

in one machine. Also, round-hole, slotted, or

both types of screen can be assembled on one

reel. This means that up to four different size

fractions can be produced in one pass through

the same reel.

Special lifter bars in the reel act to feed

particles to the screen even when the screen

surface is nearly vertical. This tends to use

more of the surface in a given revolution and

increase capacity.

Screen cleaning is accomplished with resilient rubber rollers mounted over the top of

the reels. Lodged particles are pushed back

into the cylinder with gravity aiding in the

process. As in the grader, the cleaning takes

place when the cylinder is free of its bed of

material.

The machines are available in single and

multiple reel combinations, and capacities

vary with the product and the separation involved. These cylinders have many uses but

primarily are used to size-grade corn.

Vertical Screen Cylinder

The vertical screen cylinder is an experimental development that is aimed at performing the same function as a conventional, reciprocating, flat screen but in a more efficient

manner.

The unit shown in figure 4 employs a round

or slotted-hole screen rolled into a cylinder of

8-inch diameter. In operation, the cylindrical

screen is rotated about its vertical axis and

also reciprocated vertically.

S-401-8-64

FIGURE 4.—Vertical screen cylinder with one-half of

cover removed.

Seeds to be separated are fed into the top

of the cylinder to a feed cone seen in figure 5.

The cone starts seeds into a rotary motion and

directs them against the rotating screen.

Centrifugal force holds the seeds against the

screen, and the vertical reciprocation, along

with the pull of gravity, causes the seeds to

move downward. Small seeds go through the

screen and into a center discharge collecting

shell, while large seeds slide down the inside

of the screen to a separate discharge.

The vertical cylinder unit has several advantages compared to a conventional flat
10 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

BALL

BEARING (6)

FLEXIBLE

DRIVE SHAFTC4)

BALL

BEARING

(7)

ECCENTRIC

YOKE (5)

BEARINGS (9)

FEED CON¿

(3)

COLLECTING

SHELL FOR

SMALL SEED

(2)

BELT SHEAVE

(8)

COLLECTING FUNNEL

FOR LARGE SEED

LARGE SEED

SMALL SEED

FIGURE 5.—Schematic diagram of vertical screen

cylinder.

screen. It shows higher capacity per unit area

of screen surface because centrifugal force

acting on the seed is greater than the force of

gravity, and this speeds up passage of seed

through the screen. The seed layer is more

uniformly distributed over the vertical screen

than on flat screens. Screen cleaning is accomplished readily with a resilient roller which

rolls against the screen.

Other desirable features are simple feeding

by pouring seed into the top of the machine,

small floorspace requirement, and an ability

to operate satisfactorily when tilted. Tilting

has relatively little effect on the separating

action because centrifugal forces acting on the

seeds are several times that of gravity.

Efficiency of separation is affected by screen

revolutions per minute, frequency of vibration,

amplitude of vibration, feed rate, and screen

size. Optimum adjustments have been determined by tests with a mixture of wheat and

clover. Separating efficiencies were determined

by weighing the clover left in the wheat after

a given run. At comparable separating efficiencies, the vertical screen showed more than

twice the capacity of a flat screen.

Other tests have included the separating of

rattail fescue from fine fescue, and crotalaria

from corn, as well as the sizing of sunflower

seed—all with good results at greater capacities than those obtained with a flat screen.

Indent Disk Separator

Seeds that have been size-graded by width

and thickness can be further separated on the

basis of length differences. Length separators

are of two general types—the indent disk and

the indent cylinder—but both use 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 disk separator consists of a

series of indented disks which revolve together

on a horizontal shaft. Each disk contains numerous undercut recesses on each face. (See figs.

6 and 7.) As the disks revolve, the recessed

pockets lift out the short seeds and reject the

longer seeds; for example, vetch can be lifted,

leaving oats, ryegrass, and other elongated

seeds, and crimson clover can be lifted, leaving

ryegrass and fescue seeds.

If the contaminants in a mixture are longer

than the seed being cleaned, a pocket is chosen

that will lift the good seed. When several sizes

of short contaminants are to be removed, the

disks are located so that disk pocket size increases progressively from intake to discharge

end of the machine. Short seeds are removed

first, with longer seeds being lifted as the seed

mass moves toward the discharge point. When

there is only one separation to be made, many

disks of the same size and shape are incorporated in a machine, or several machines, to

increase capacity. (See fig. 6.)

Seed Travel

Seed travel from intake end of the machine

to discharge end is provided by vanes attached

to spokes of the disks. The removable vanes

operate like a screw conveyor to move the seed

mass slowly through open portions of the disk.

In addition to conveying, this operation brings

the seed mass in contact with each disk 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 disks, but there is sufficient clearance to prevent the crushing of seed.

This favors seed travel through the center and

open portions of the disks.
MECHANICAL SEED CLEANING AND HANDLING 11

S-194-6-69

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

Disk Pocket Design

The disk pocket functions like an elevator

bucket. As the disk passes through the reservoir of seed at the bottom of the machine,

short seed will be held in the pocket by the

ability of the seed to become seated on the

pocket bottom. Whether 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 leaves the pocket in the same

manner that an elevator bucket discharges its

load.

Disk pockets are made in three basic shapes,

and each shape is available in several sizes.

In any one disk, the length or height of a

pocket is essentially the same as the width,

and depth is about one-half the width. The

undercut part of the pocket is referred to as

the bottom.

The "R" pocket.—This pocket or, indent was

designed to remove broken rice grains from

whole grains. The lifting edge is flat, while

the leading edge is round. Pocket design is

such that it will reject round seeds, but will

lift out cross-broken grain or elongated seeds

on the flat surface.

The "V" pocket.—This pocket was 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 flat surface to bear on. These seeds tip out

of the pockets as the disk revolves.

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

in the smaller sizes, usually 21/2 mm. to 6 mm.

in pocket width measured on a line from the

center of the disk. These disks are designed

primarily for removing small materials from

a mixture, such as dodder, dock, sorrel, or

plantain from fescues and ryegrass. Both types
12 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

Lifts Short

Seeds

Rejects Longer

Seeds

FIGURE 7.—Cross section of an indent disk separator.

of pockets are designed lo 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 pocket size in millimeters. For example, an R5 pocket has a flat lifting edge

and a radial width of 5 mm.

The square pocket.—Some disks are made

with pockets designated solely by letter. They

carry no numeral to indicate width, and are

available in larger sizes than the '*R" and "V

pockets. Normally these pockets are squarefaced.

Disk pocket selection.—^When several different pocket sizes and types are used in one

machine, the disks are grouped into sections,

with the smaller-sized pocket disks installed

near the seed intake. In this arrangement,

material shorter than the crop seed can be

lifted and discharged first, then the crop seed

will be lifted and the long contaminants rejected. The selection of "R^', ''Y'\ or other

pockets, (or a combination of these) depends

on the shape characteristics of the seed and

the separation desired.

Reject and rerun.—Adjustments in the machine make it possible for liftings from various

disks to be either discharged or returned to

the feed end for recleaning.

Seed travel adjustment.—Conveyor vanes

may be added or removed as desired to move

the seed mass through the machine at a rate

giving best separation. Capacity and efficiency

of separation will be influenced by the number

of short particles to be removed compared to

the number of pocket recesses needed to remove

them. The travel speed of the mass therefore

may need to be varied. Raising the tailings

gate tends to keep seed in the machine longer

and gives the disks more time to lift out short

particles.

Combination units.—Single rotor disk machines may be combined in various arrangements. One typical setup employs a largepocket unit mounted over a small-pocket unit.

When a seed lot is fed into the top unit, the

large pockets lift the main mass of seed and

reject long unwanted material. Liftings of the

top unit then are delivered to the bottom machine where two or three pocket sizes may be

in use. Each pocket size will lift a different

length fraction, and depending upon the composition of the seed lot, pocket size and disk

arrangement can be chosen to either lift the

clean seed or discharge it as tailings.

Indent Cylinder Separator

Operation

Disk rotational velocity.—The rotating speed

of the disks should be held nearly constant

since variations of only a few revolutions per

minute affect the efficiency of disk operation.

Too great a velocity prevents the material from

becoming seated in the pocket bottom, or prevents the disks from discharging seed properly.

Low velocity will reduce capacity.

Indent cylinders use centrifugal force and

length differences to lift material from a seed

mass, making a length-sizing separation; for

example, sloughgrass can be lifted, rejecting

meadow foxtail.

The indent-cylinder separator, shown as the

bottom unit in figure 6, consists of a rotating,

horizontal cylinder and a movable, horizontal

separating trough. The inside surface of the

cylinder has small, closely spaced, semispherical indentations. In operation, the seed mass
MECHANICAL SEED CLEANING AND HANDLING 13

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 numerous indents. At some

point before reaching the top of the rotation,

the seeds drop from the indents and are received by an adjustable trough or vibrating

tray. (See fig. 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 cone-shaped sides was best for the

removal of seeds which would not roll readily.

A cylinder having spherical-shaped indents

drawn slightly shallower than their diameter

was better for removal of round seeds, such

as crimson clover or soybeans. Indents with

straight, vertical sides showed good lifting

ability, but they became plugged more readily

than indents with tapered or curved sides.

In the conventional indent cylinder, a compromise in pocket design was reached where

side slope, depth, width, and shape provided the

best results for the most seeds normally encountered. The indent is hemispherical and its

size is described by a number which indicates

its diameter, expressed in 64ths of an inch.

For example, a No. 4 indent cylinder has

pockets 4/64ths of an inch in diameter. Indent sizes available range from No. 2 to No.

32. This numbering scheme does not indicate

depth, and depths vary somewhat in the same

size indent made by different companies.

Selecting the indent.—Good selection involves the use of the smallest size indent that

will satisfactorily lift all material to be removed. The combination of centrifugal force

and indent size lifts short particles and carries

them the highest out of the main seed mass.

Next to fall from the indent are intermediatesize seeds. The longest seeds fall free of the

indent only a short distance above the seed

mass, or are not lifted at all.

Some materials are too long 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 inside the separator agitate the seed.

This also tends to level the seed mass in the

machine and prevent buildup at the feed end.

Too much buildup would let material enter 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. As these sizes are depleted and the mass works toward the center

of the cylinder, the intermediate-size material

is removed. At the tail end of the machine,

the final and closest length-sizing is accomplished. There usually is a retarder at the tail

end to act as a dam and maintain a satisfactory depth of material in the cylinder. If the

cylinder is ^'starved" at this point, the indents

ADJUSTABLE

TROUGH

AUGER OR VIBRATI1SJG

TRAY MOVES LIFTED

SEED OUT OF MACHINE

DISTRIBUTING

AUGER

SHORT SEED BEING LIFTED

& DROPPED INTO TROUGH

LONG SEED

REJECTED

BEING

FIGURE 8.—Cross section of an indent cylinder separator.
14 AGRICULTURE HANDBOOK 854, U.S. DEPT, OF AGRICULTURE

will lift longer particles than desired. Material

flows through the cylinder from feed to tail

end by gravity or by an open conveyor running in the mass of material.

Operation

The indent cylinder generally shows its

greatest efficiency when lifting dense material.

For this reason, the unit finds much use with

small grains and legumes. Although not as extensive, its use with grass seed is increasing.

Unlike the disk separator, seedcoat texture,

density, and moisture content of the seed do

affect separation in an indent cylinder. Friction of the seed slipping out of the indent affects

the distance it will travel in the pocket before

being dropped. Hence, a rough or wet seed

will be lifted and carried from the seed mass

more readily than a slick, dry one. The following two adjustments, together with the variations in physical properties of seed, provide a

wide range of separation response in this machine.

Speed of cylinder.—A seed is held in the indent recess by centrifugal force sufficient to

lift it from the seed mass and to retain it until

some determined point of the travel arc is

reached. Adjustment for cylinder speed is

therefore provided on this machine. Speed

should not be increased beyond 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 hand, speed must be

great enough to lift seed from 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 mass. Combination

of these variables gives considerable flexibility

in operation.

Methods of Use

Single unit.—Where only one length separation is needed, a single unit is used in the processing plant.

Multiple units.—For more than one length

separation, a useful multiple-cylinder unit can

be arranged wherein the cylinders are grouped

vertically, with the top cylinder having a

medium-size indent. Liftings of the top cylinder

are sent to a lower cylinder fitted with a small

indent. Tailings of the top cylinder are sent

to another lower cylinder fitted with a largesize 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 offering several mediums of seed processing. For example, equipment is manufactured which provides for scalping, aspiration,

disk separation, and cylinder separation all in

one machine.

Special Indent Cylinder

Microscopic measurements of seeds lifted by

commercial indents have shown that in many

cases there is enough length difference to

salvage a high percentage of the crop seeds

removed with the contaminants. Special experimental cylinders designed according to

seed measurements were found effective in

making these separations.

Seed Measuring

Specific seed types and their contaminants

were measured microscopically to determine

length, width, and thickness for each component. This was done with the equipment shown

in figure 9, using a scale in the microscope

eyepiece to read dimensions to the nearest

thousandths of an inch.

An analysis of plotted measurement data

provided the following information: (1) The

differences, if any, in the ranges of length,

width, and thickness dimensions of crop seed

and contaminant; (2) the optimum diameter

and depth of an indent to exploit length difference; (3) the optimum type and size of

screen hole to exploit width or thickness difference; and (4) a basis for predicting yield

and purity of final '*clean" product.

Seed measurements have indicated consistently that alfalfa and pigweed, for example,

are very similar in width and thickness, but

that most alfalfa seeds are longer than pigweed. Likewise, measurements of bentgrass

and its frequent contaminants show that the

bentgrass is significantly longer.

Special Indent Design

Capitalizing on existing length differences,

indents were designed from seed measurements

to remove short contaminants from bentgrass,

pigweed from alfalfa, and many other weed

seeds from crop seeds. For bentgrass mixtures,

a straight-side indent 0.032 inch in diameter
MECHANICAL SEED CLEANING AND HANDLING 15

S-300-6-62

FIGURE 9.—Equipment for measuring seed microscopically.

and 0.012 inch in depth was constructed and

used successfully to remove such contaminants

as Western yellowcress, red sandspurry, toad

rush, path rush, mouse-ear, big mouse-ear,

shepherds-purse, and small dirt clods.

To remove pigweed from alfalfa, a straightside indent was designed and tested that has

a hole depth approximately one-half that of the

No. 4 commercial indent generally used. Although it made a good separation, this indent

was abandoned because short alfalfa seeds

lodged crosswise in the holes. To overcome the

lodging, a shallow hemispherical indent was

produced (0.065 inch in diameter and 0.025 inch

in depth) that performed satisfactorily.

Processor Trials

Farm and commercial seed processors have

had special indent cylinders constructed for

cleaning bentgrass, alfalfa, and other seeds.

In processing bentgrass, the straight-side indent has shown favorable performance—contaminant removal is good, crop shrinkage is

small, and indent plugging is negligible. Inplant operation has shown that care must be

taken not to flood the "bentgrass" cylinder

since this deprives some contaminant of the

chance to encounter an indent and be lifted

out.

Another important factor in processing

small seeds like bentgrass is cylinder speed.

Tests have shown that slow speeds must be used

to permit small seeds to nest in the indents.

Best results were obtained with a peripheral

speed of 30 feet per minute which is equivalent

to 5 revolutions per minute in a cylinder of

23-inch diameter. At these low speeds, centrifugal force has little to do with the lifting of

a seed; instead, the relationship of seed length

to indent size is the controlling factor.

To minimize plugging, a brush can be

mounted at top-dead-center which will help

free lodged seeds. Capacities are relatively low
16 AGRICULTURE HANDBOOK 354, U.S. DEPT. OP AGRICULTURE

with bentgrass—from 30 to 100 pounds per

hour—but this rate may be tolerable if the

separation cannot be made otherwise.

The straight-side indent has not been successful with alfalfa in full-scale operation.

Even though pigweed removal was good with

little crop loss, the indent plugging was prohibitive. However, good performance was

obtained with the special, shallow, hemispherical indent.

Several manufacturers of commercial indent

separators will now construct special cylinders

on request with a greater choice in depth and

diameter of indents.

for predicting the purity and lot shrinkage resulting from use of a given screen.

Depending upon the actual distribution of

seed measurements in overlapping ranges, it

may be possible to exploit width differences

with one screen (round-hole) and thickness

differences with another screen (slotted-hole).

This possibility, as well as the hole size to

use, will be indicated by the plotted data.

The seed measuring technique described here

can be used as an aid in determining proper

screens or indents for any of the seed separators discussed so far—all of which are size

sensitive.

Screen Selection According to

Seed Measurement

The practice of seed measuring, described

earlier, has proven very helpful in selecting

screens for a size separation. When seed measurements from representative samples of crop

and contaminant are tallied on a common

scale, the comparison shows immediately If

there is a usable difference in width or thickness dimensions.

For example, the range of width measurements for the contaminant may be lower on

the scale or higher than the width range for

the crop. This indicates three things: (1)

Width differences can be used to separate crop

and contaminant; (2) a round-hole screen

should be used because a round hole senses

width and separates particles on this basis;

and (3) the ideal hole diameter of the screen

can be picked from the scale at a value between the two width ranges.

Another approach is indicated if the range

of thickness measurements for the contaminant should fall in a different region of the

scale than thickness measurements for the

crop. A slotted-hole screen (perforated or wire

mesh) should be used here because a slot

senses thickness and separates on this basis.

Again, a scale value that falls between the

thickness ranges will determine the optimum

hole size. In this case, the important hole dimension is the minimum opening in the slots.

Frequently, the ranges of width or thickness

measurements for crop and contaminant will

overlap, particularly if the seed lot has been

through a preliminary sizing operation. When

there is some overlap, the plotted data may

indicate a particular hole size that can make

a partial separation or a complete separation

but with some crop loss. From representative

samples, the measurement data provide a basis

Specific Gravity Separator

The specific gravity separator classifies material according to density or specific gravity.

This unit was originally developed 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 the separating of crop

seed and contaminants. (See fig. 10.)

S-489-3-67

FIGURE 10.—Specific gravity separator.
MECHANICAL SEED CLEANING AND HANDLING 17

There are three basic rules that apply to

gravity separation:

1. Particles of the same size but different

ties 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 be separated.

Component parts of the gravity separator

are an airblast fan, an air-equalizing chamber,

a perforated deck, a variable-speed eccentric,

deck rocker arms, a feeding or metering device,

a deck end-raise adjustment, and a deck sidetilt adjustment. The end-raise adjustment

varies the inclination of the discharge edge.

The side-tilt adjusts the deck so that the back

is higher 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 deck and its oscillating motion move

the seed over the deck. Air forced up through

the porous deck from the equalizing chamber

forms thousands of small jets v^hich cause the

material to stratify into layers of different

densities in much the same manner as water

stratifies ground cork and sand. Cork floats on

the surface of v^ater, and sand will form a

layer 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 11. The oscillating motion of the deck

''walks'' the heavy material uphill nearly

parallel to the discharge edge, and the air

''floats'' the light material downhill. As the

material travels from the feed point on the

deck to the discharge edge, a gradation of material takes place ranging from 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.

^ To illustrate the machine's capability, consider a seed lot made UD of crimson clover,

wild geranium, dirt clods, and rocks. When

this mixture is passed over a properly adjusted

gravity separator, the geranium seed and immature clover seed will be discharged at the

low side of the deck, the rock and heavy dirt

clods at the upper side, and the good crimson

clover seed in the middle.

The Deck

The deck can be called the "heart" of the

gravity machine, and deck covering plays an

important role. Separation efficiency is dependent on air distribution through the deck, and

on inclination and movement of the deck.

SEED

HOPPER Q LIGHT SEED

<^ MED. SEED

» HEAVY SEED

DECK

FIGURE 11.—Cross section of specific gravity separator.

About three or four types of deck coverings

are needed to handle a range of seed crops

varying in size from small grasses to beans.

Coverings that have veen used satisfactorily

are linen, other cloth of various weaves, smallhole perforated metal, plastic, and wire mesh.

The main job of the deck covering is to help

stratify seed material above the deck, yet

adequately restrict airflow to build up static

pressure within the air chamber and insure

uniform air distribution. A closely woven covering gives best results for small seed, while

a coarser weave is required for large seed. It

is imperative that the deck covering be made

from material that will withstand abrasion

and is free of lint, which would collect dust

particles and clog openings, that would prevent uniform air distribution.

Adjustments

Feed rate adjustment.—The rate of material

entering the gravity deck is important and

greatly affects operation efficiency. Optimum

rates vary according to the difference in density or specific gravity of the mixture components. The greater the difference, the more

rapid will be the travel of light material to

the low side of the deck and the subsequent

moving of heavy material to the high rail.

Greater feed rates are 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
18 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

the deck may be "starved." For satisfactory

separations, the deck surface should be covered at all times. An excessive feed rate v^ill

flood the deck, prevent proper stratification

of the material, and cause good seeds to be discharged v^ith the middlings or rejects.

Air adjustment.—The airstream 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 the deck imparts an uphill direction to the

heavy seed.

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

case, the intense airstream 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 airstream

still must be maintained at a degree suflScient

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 particles

to the low side of the deck and heavier particles

to the high side begins to appear. The separation becomes complete when the vertical stratification has dissipated and given 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 uncovered areas at the upper rail. Insufficient air rate shifts the seed material to the

high 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 usual slope of the discharge edge is 2° -

6° from the horizontal, although greater slopes

may be required for some seed lots.

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 seedbed 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 are closely interrelated.

They must be matched properly to obtain efficient operation of a gravity separator. Figure

12 illustrates typical deck patterns for normal

operation and for unbalanced conditions resulting from faulty adjustments.

Air Separator

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.
MECHANICAL SEED CLEANING AND HANDLING 19

GRAVITY ADJUSTMENT CHECK CHART

FIG. 5 A

INSUFFICIENT

SIDE ^RAISE

FIG. 2 B

EXCESSIVE

AIR

FIG. 4 A

INSUFFICIE

END RAi:

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

A. START THE SEPARATION AND WAIT FOR THE

MATERIAL TO DEFINE A CONSTANT PATTERN OF

DISTRIBUTION.

B. COMPARE EACH PATTERN OF MATERIAL DISTRIBUTION WITH FIG. I FOR IDEAL OR OPTIMUM

ADJUSTMENTS.

C. CORRECT ERRORS OF ADJUSTMENT IN THE

FOLLOWING ORDER.

I.AIR ADJUSTMENT FIG. 2 A OR 2B

2. ECCENTRIC SPEED FIG. 3A OR 3B

3. END RAISE SLOPE FIG. 4A OR 4B

4. SIDE RAISE SLOPE FIG. 5A OR 5B

FIGURE 12.—Check chart for adjustment of specific gravity separator.
20 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

Terminal velocity can be thought of as the

velocity of a rising air current that v^ill suspend a given particle. Although terminal velocity of a particle is a single characteristic,

it is dependent on other properties—shape,

size, surface texture, and density—all of v^hich

influence the particle's aerodynamic behavior

in the airstream. If two different particles are

fed into a rising airstream vahóse velocity is

midway between the terminal velocities of the

particles, one particle will rise and one will

drop. This, essentially, is the basis for air

separation.

In classifying types of air separators, one

primary difference is location of the air-moving unit. In the aspirator, a fan is placed at

the discharge end of the air column where it

induces a partial vacuum so that atmospheric

pressure can force air through the system. In

the pneumatic separator, the fan is at the intake end of the air column where it creates a

pressure greater than atmospheric, which

again forces air through the system. Airflow

characteristics and theory of separation are

the same for each system. Regardless of how

the air movement is induced, it is the velocity

of air moving through the system from a high

pressure region to a low pressure region that

is important in conveying the material and

making the separation.

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. Materials with the same

terminal velocity as the air will float, and objects with a higher terminal velocity will fall

against the airflow.

There are several forms of aspirators. Figure 13 is a cross section view of a scalping

aspirator. A seed mixture is fed from the hopper, "A'', to the rotating scalping screen, "C,

which allows seed to pass to the aspirating

chamber, "E'\ Sticks, straw, leaves, and other

large roughage components are carried over

the rotating screen into section ^^B". With a

suction or negative pressure at ''W\ air passes

through the aspirating chamber, ''E'\ at a velocity slightly below the terminal velocity of

the heavy, plump seed. Shriveled or weevileaten seeds, light 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 ''0'\

^ Figure 14 is a cross section view of a fractionating aspirator. When seed is metered into

SCAllPINGS _. SCREENINGS

L.d^DISGHARGE

FIGURE 13.—Cross section of scalping aspirator: A,

Feed hopper; B, section into which large trash is

thrown off as it passes over the rotating scalping

screen; D, reclaimer for any seed that may have

passed over the scalping screen; E, aspirating chamber; 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 through 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.

the air column, '*B'', the heavy seed falls

against the airflow and out the air inlet,

whereas the lighter seed, shriveled seed, weed

seed, and chaff are lifted. By adjusting the

movable air vane in column **C'\ which is controlled by the air lever indicated, the air velocity can be decreased below the terminal velocity of those components that one wishes to

drop. Column *'D'' will receive the heaviest of

the lifted fraction, which usually consists of

good seed but of lesser quality than that at

"B'\ Column "E'' will catch lighter seed and

broken pieces, while chaff, dust, 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",
MECHANICAL SEED CLEANING AND HANDLING 21

AIR CONTROL

LEVER AIR CONTROL

DAMPER

FIGURE 14.—Cross section of fractionating aspirator :

A, Feed hopper; B, air column through which heavy

seeds fall against the airflow; C, column into which

lighter seeds and chaff are lifted; D, column which

receives the heavier liftings; E, column which

catches salvage grass seed, broken seed, or light and

unusable seed; F, column into which extremely light

waste materials are delivered.

can be 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 four fractions in a continuous operation.

Figure 15 is a cross section view of a

pneumatic separator. When seed enters the

feed chute, the light seed, splits, broken seed,

chaff, and straw are lifted by the airflow up

through the column and are deflected by an

inverted cone to a discharge pan. Heavy seed

falls against the airflow until it is diverted by

an inclined screen to the heavy seed outlet. In

principle, this separator is much like the

blowers used extensively by seed analysts in

seed-testing laboratories. An essential difference, however, is the continuous feed-discharge

feature of the pneumatic separator as contrasted to the batch operation of the seedtesting blowers.

With adequate control of airflow and feed

rate, many precise separations can be made

with air separators. Examples are removing

rattail fescue and quackgrass from meadow

foxtail, empty tree seed from full seed, sunflower hulls from the meats, broken and immature sorghum seed from good sorghum seed,

halfbeans from whole beans, and cone parts

and trash from various flower seeds.

Velvet Roll Separator

The velvet roll separator is a special seedcleaning machine that divides material by

differences in surface texture and shape. It

consists primarily of pairs of velvet-covered

rollers placed 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 16 and 17 show, respectively, a velvet roll separator and the basic principle of

operation. A seed mixture to be separated is

fed onto the rolls at the upper end so that

seed travels down the incline formed by the

rolls. Rough-coated seeds, sharp-pointed 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. Smooth-coated

seeds spin and work their way down the incline and are discharged from the lower end of

the rollers. The separation is a graduated one

with rougher seed being thrown out first ; then

progressively smoother material is thrown out

as seeds approach the discharge or lower end

of the rollers.

The velvet roll machine, like other seedcleaning equipment, needs balanced adjustments to give best performance. The speed of

the rolls, angle of incline, clearance between

shield and rolls, and rate of feed are all adjusted according to the particular seed mixture

requirements. The clearance between rollers

and shield should be great enough so that seed

can turn freely 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 comes

in contact with the roller. If the clearance is

too great, many rough seeds will fall back into

the smooth-seed stream. When the clearance is

too little, smooth seed will be pressed against

the roller and rolled out with the roughsurfaced seed.

The rate of feed is important on a velvet

roll machine. If too great, many seeds will not

come in contact with the rollers, and therefore will not have the chance to be separated.

The rate of feed and angle of incline of the

rollers can be increased as the differences in

surface texture of the seeds in a mixture increase. The speed of the rolls is another important factor, and should be adjusted as

required to make the separation. The faster the

roll speed, the greater the ''throwout." If too

much good seed is being thrown out, the roll

speed should be decreased. When too much
22 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

DEFLECTOR

CON'E

DISCHARGE

PAN

FEED CHUTE

AIR CONTROL

LEVER

MOTOR

FAN

a

FIGURE 15.—Cross section of pneumatic separator.

rough seed is discharged with the clean seed,

the roll speed should be increased.

Since the effects of machine adjustments are

sometimes difficult to see, the following practice is recommended in adjusting the velvet

roll separator. Make only one change at a time ;

operate the machine 5 minutes after each

change, and then observe the results. If roughcoated seed is found in the smooth-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

rough seed, the rolls are running too fast.

The velvet roll machine is not complicated,

and once set in operation, can run continuously

with little attention. It is used to finish many

seed separations where capacity requirements

are not too high. The name '^dodder rolF' is

sometimes assigned to this unit as it is used to

remove rough-coated dodder weed seed from

smooth legume seed. Other possible separations

are dirt clods from beans, dock from clovers,
MECHANICAL SEED CLEANING AND HANDLING 23

FIGURE 16.—Velvet roll separator.

S-193-5-B9

cocklebur from sunflower seed, unhulled from

hulled lespedeza, and many rough weed seeds

from smooth crop seeds.

Spiral Separator

The spiral separator classifies seed according

to shape and ability to roll or slide. It is a simple machine that has no moving parts and

requires very little floorspace. After it is placed

under a feed hopper and the feed rate regulated, the spiral will operate steadily

with little or no care, and with no power cost.

It is light and relatively easy to move into or

out of the processing line as needed. It may

readily be taken to the seed location rather

than moving the seed lot to it. Some separations can be made with this unit that 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 open screw conveyor standing in a vertical position. (See ñg. 18.)

\

Feed /

Hopper

Rough

Seed Rough a

Some Smooth

Seed

Velvet Covered

Rollers

Smooth a Some

Rough Seed

Smooth

Seed

Metal

Shield

Rough

Seed

SECTION A~A'

FIGURE 17.—Side view and cross section of velvet roll separator.
24 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

S-192-5-59

FIGURE 18.—Spiral separator.

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

smooth, round seeds on the outer flight.

The spiral is used to separate round seeds,

such as rape, vetch, and soybeans, from irregularly shaped seeds like wheat, oats, and ryegrass. It can also separate whole vetch seed

from broken vetch, crimson clover from rape

or mustard seed, and morning-glory from

soybean seed. Large 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 ranges from 200 to

700 pounds an hour, depending upon the seed

being separated.

Inclined Draper Separator

Like the spiral, the inclined draper also

separates seeds on the basis of their ability to

roll or slide. The rolling or sliding properties

are governed by the shape and texture of the

seeds, and by the frictional characteristics of

the draper surface they are contacting.

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 ñgure 19. Round or smooth seeds,

like vetch, will roll and slide down the draper

faster than the draper is traveling up the incline. In contrast, flat, rough, or elongated

seeds, like oats, will be carried to the top of the

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 seeds, having greater velocity, make

a wider circle than the irregularly shaped

seeds, and the original mixture can then be

divided into fractions by splitters at the discharge end of the flight.

Spiral separators sometimes have multiple

flights arranged in order of increasing size,

with each flight having a separate discharge

chute. Seeds that roll well because of their

roundness travel downward in a spiral path of

increasing diameter. These seeds will flow over

the edge of one flight to another until they

SEED HOPPER

FLAT

ROUG

CANVAS OR

PLASTIC DRAPER

FIGURE 19.—Cross section of inclined draper seed

separator.
MECHANICAL SEED CLEANING AND HANDLING 25

incline, thereby making the separation. The

seeds dropping off the draper at its lower end

are gathered in one chute, and the seeds reaching the upper end are dropped into a second

chute.

To gain capacity in commercial operation,

multiple draper belts can be used in a single

machine. (See fig. 20.) The rate of feed to the

draper may be varied. The rate should be slow

enough to allow each seed to act individually

and not be hindered from rolling or sliding by

those that are stationary. Also, a seed should

not be forced to move by those that are

traveling.

The angle of incline may be varied according to 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 draper. A relatively rough canvas belt may be employed

when rolling tendencies are predominant in

seed of the lower fraction, while a smooth belt

is more useful if a sliding action is wanted for

the lower fraction.

In many cases, a smooth belt can do all that

a canvas belt does, and in addition, can provide

a means of making a more precise separation.

This is particularly true with small seeds of

different shape or texture, like timothy and

dogfennel. Even though there is a shape difS-196-6-B9

FIGURE 20.—Commercial inclined draper equipped with

multiple draper belts.

ference in these seeds, the protruding fibers in

a canvas belt will prevent small seeds from

rolling or sliding. A smoother surface can detect the differences in shape or texture of these

small seeds and let one roll or slide downhill,

thereby making a separation.

In adjusting the machine to perform a given

separation, start with a very low rate of feed,

a slow draper speed, and a flat draper slope.

Increase the angle of slope until none of the

rolling or sliding fraction of the mixture is

being carried to the top. Increase the draper

speed until none of the flat or elongated seed

is falling off the lower end. Increase the rate

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 buckhorn plantain from red clover,

oats from vetch, grass seed from crimson

clover, and other flat, rough, or elongated seeds

from round, smooth seeds. This machine is also

used extensively for removing trash and weed

seed from garden beet seed.

Horizontal Disk Separator

The horizontal disk separator (fig. 21) is a

special machine that divides seeds by their relative abilites to roll or slide over a horizontal

surface when acted on by varying amounts of

centrifugal force. Physical factors affecting

this separation are shape, weight, and surface

texture of the seeds. The unit is used primarily

to salvage rejected seeds from other cleaning

equipment. It can separate mixtures where one

seed type rolls or slides more readily than

another.

The separating action of the horizontal disk

is similar to that of the spiral and can be more

selective. The disk machine has an adjustable

speed control which varies the centrifugal

force acting on the seeds and therefore changes

the proportions of the mixture retained on the

disk or rejected.

The disks are mounted at regular space intervals, one above another, on a hollow vertical

shaft. The seed mixture is fed from a hopper

into the hollow shaft which meters seed to

each disk through variable orifices. A plastic

fence with two adjustable outlets confines

seed in the center of the disk, discharging two

single seed rows, spaced 180° apart, to the

outer portion of the disk, as shown in figure

22. Centrifugal force causes round or smooth

seeds to roll or slide off into either of two discharge areas, while irregularly-shaped seeds

remain on the disk until they are raked off at
26 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

S-89-4-B6

FIGURE 21.—Horizontal disk seed separator.

two points. The outer region of each disk 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 the disk

rotation.

The 16-disk machine pictured in figure 21

has a capacity ranging from 300 to 500 pounds

per hour, depending upon the seed being

cleaned.

Magnetic Separator

The magnetic separator takes advantage of

differences in seedcoat characteristics. Generally, the crop seed will have a smooth coat,

like legumes, while the seed or material to be

removed will have a rough coat or sticky

surface that can pick up and retain a fine iron

powder when pretreated with water or a combination of water and oil.

Several different makes of magnetic separators are used in the seed industry representing

American, German, and English developments.

Some employ permanent magnets and others

use electromagnets in their operation. All are

considered finishing machines and are becoming increasingly popular as seed standards

grow more exacting.

The operating principle of a single-drum

magnetic separator is shown in figure 23. The

seed mixture is fed into a screw conveyor

that tumbles and mixes the seed with a proportioned water spray and a finely ground iron

powder. The powder will adhere to rough seedcoats, cracks in a seedcoat, dirt clods, chaff,

or seeds with a sticky residue on the surface.

The mixture is then discharged from the mixing screw onto the revolving drum, which has

a high-intensity magnetic field. The roughtextured or sticky seeds, which are now coated

with iron powder, are attracted to the magnetic drum, but smooth good seeds (free of iron

powder) flow off the drum in a regular manner, thereby making the separation. If a permanent magnet is used to provide the

magnetic field, the seeds adhering to the drum

fall by gravity when they reach an unmagnetized area on the bottom or back side of the

drum. With electromagnetic drums, a rotating

brush at the back of the drum surface removes

the iron-coated seeds and inert material as well

as free iron powder.

The efficiency of the magnetic cleaning

process depends largely upon the components

of the seed lot, the water and iron

powder used, and the mixing or treating operation. The greater the difference in surface

characteristics of the components to be separated, the more effective the separation will be.

Best use is made of existing differences when

proper amounts of water and powder are

thoroughly mixed with the seed lot.

The water and powder dosages will vary according to the amount of contaminant to be

removed, roughness and water-absorbing

character of the contaminant, and the surface

texture of the desirable crop seed. Too little

water or powder prevents proper coating of the

contaminant. Too much water can cause clus-
MECHANICAL SEED CLEANING AND HANDLING 27

Flat Seed

Disch. Spout

Feed Port

Rotating Table

Spheroidal Seed

Disch. Spout ^

Spheroidal Seed

Disch. Spout

Feed Port

Flat Seed

Disch. Spout

FIGURE 22.—Cross section of horizontal disk separator: A, Hollow vertical shaft which meters seed to the disks;

B, inner portion of disk; C, adjustable outlets; D, plastic fence; E, outer area of disk; F, discharge for round

seed; G, rakeoffs for flat seed.

tering of seeds, discoloration, excessive crop

loss, and poor pickup of powder. Enough

powder should be used to insure that the

amount needed is available. Greater amounts

are wasteful if not reclaimed but not

particularly harmful. Seeds with hard, smooth

coats (like sericea lespedeza) tend to take up

less powder than seeds with rougher coats

(like sweetclover).

Various iron powders are available for use

in magnetic separation. They all contain a

high percentage of pure iron, but they differ

in particle size and shape, apparent density,

and presence of other elements. Generally,

separation efficiency is best with powders of

fine particle size. Practice varies in the salvage

and reuse of iron powder. There is some evidence that the powder changes with use and

becomes less effective; even so, some cleaning

plants reuse the same powder or blend salvaged

powder with new stock and achieve good performance in their magnetic operations. Other

plants use the powder only once.

After the proper amounts of water and

powder have been established, it is extremely

important to mix them well with the seed lot.

Successful magnetic cleaning requires that all

of the contaminant, but none of the desirable

seed, be coated with powder. Properly operated

screw conveyors, augers, and batch units can

do an effective job of mixing.

Magnetic separators are effectively used in

cleaning clover, alfalfa, lespedeza, trefoil, and

other seeds to remove dodder, buckhorn plantain, wild geranium, sorrel, dock, inert matter,

and other contaminants. It is claimed that

separation of some mixtures is improved by

adding a soluble oil to the moistening water.

Hulled Johnsongrass, for example, reportedly

can be removed more effectively from sudangrass by this treatment because the oil helps

the iron powder cling to the johnsongrass

seed. A light scarification of this seed mixture

also helps the johnsongrass to hold powder.

In addition to removing impurities, magnetic separators can be effective in raising germination of clean seed lots. The cracked,

broken seeds and some of the immature, misshapen seeds of a clean lot will pick up iron

powder and be removed, leaving good, whole

seed.

Both the permanent magnet and the electromagnet have performed well as energizing

units. The machines using permanent magnets
28 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

IRON POWDER SUPPLY

MIXING CHAMBER

MAGNET

DRUM

/'I

WEED a

CRACKED SEED

FIGURE 23.—Cross section of a single drum, magnetic separator.

CLEAN

SEED

usually cost less than those with electromagnets. On the other hand, the magnetic field can

be varied in electromagnetic machines, and

this offers the possibility of greater precision

in separating certain lots. Regardless of

magnet type, most machines use two or more

energized drums in series. The clean fraction

from the first drum passes over the next drum

so that any iron-coated seeds missed by one

drum will contact the next and be removed.

Multiple drums permit capacities to be increased without sacrificing purity. Capacities

of magnetic separators range from 200 to

2,000 pounds per hour, depending on machine

size and the seed lot being cleaned.

Bumper Mill

The bumper mill was originally developed to

remove weed seeds from timothy. It makes

separations by exploiting differences in shape,

surface texture, and—to a lesser degree—

weight of seeds.

The unit consists of two sets of identical

superimposed decks suspended in a rigid frame

and connected by a linkage. (See fig. 24.) A

small 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
MECHANICAL SEED CLEANING AND HANDLING 29

S-197-5-Ba

FIGURE 24.—Bumper mill.

batteries of decks. All decks of a battery are

at the same inclination at any one time, and

this inclination within the suspended frame

can be varied by adjustment screws. Each deck

is divided into 3- x 9-inch smooth metal

plates, and a feeder is positioned to supply seed

continuously to each plate.

As the rocking deck battery bumps the

rubber 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 move from the feed end to the discharge end of the metal plate, the seed types

have migrated far enough apart to be discharged into separate spouts.

When this machine is properly adjusted in

deck angle, feed rate, stroke length, and stroke

frequency, it can separate alsike clover,

Canada thistle, sorrel, ryegrass, quackgrass,

buckhorn, and other contaminants from timothy and similar rounded seed.

Vibrator Separator

The vibrator separator is designed to separate seeds by their differences in shape and

surface texture. This is an experimental development that has progressed through several

stages—it has been constructed as a singledeck laboratory model, as a 30-deck pilot plant

prototype, and as a 500-deck full-scale machine.

The vibrator separator is similar to the

bumper mill and the gravity separator in that

all three machines perform their separations

on inclined reciprocating decks. However, the

vibrator separator is different from the

gravity separator since it uses a solid-textured

deck and does not employ air stratification of

a seed mass in its operation. Another important difference is that the stroke of the

vibrator separator is much faster and shorter

than that of the other two machines.

Basically, the vibrator separator consists of

an inclined textured deck which is activated

by an electromagnetic vibrator whose stroke is

adjustable. (See fig. 25.) The whole assembly

can be tilted sideways and forward to provide a

wide range of deck slopes.

Multiple decks may be mounted in a rigid

frame so that one or two vibrators will power

the whole assembly. The decks can be of varying textures, as needed, ranging from smooth

metal or plastic laminates to rough sandpaper

depending upon the seed components being

separated. However, a fine-textured sandpaper

deck works satisfactorily for most separations

and is used on the multideck machines. The

vibration can be regulated by a rheostat controller in the electrical circuit which governs

the length of stroke.

In operation, a seed mixture is introduced

near the center of the upper edge of the inclined deck. The action and direction of vibration causes all seeds to try to climb the incline,

but flat, rough, or hairy seeds climb more

readily than the rounded or smooth seeds. On

each stroke the round, smooth seeds will travel

a shorter distance up the incline and may roll

or slide to the low side of the deck. The forward deck tilt causes gradually widening

bands of different seed fractions to travel

over the deck from the feed to the discharge

edge, where dividers isolate these fractions.

With a suitable deck surface, inclination,

and vibration, the unit can make many separations which are difficult or impossible with

conventional seed cleaners. It will remove silverhair and rough bluegrass from bentgrass,

mustard and pigweed from alfalfa, barnyardgrass and dodder from carrot, morning-glory

from sorghum and soybeans, vernalgrass from

ryegrass, stems from flax, watergrass from

onionseed, clods and leaves from various flower

seeds, and many other contaminants from desirable seed.

The single-deck unit has been successfully

adapted for mechanized purity analyses in

seed-testing laboratories where it is used primarily to concentrate quackgrass and Canada

thistle in test lots of tall fescue, orchardgrass,
30 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

S-419-11-64

FIGURE 26.—Vibrator separator (single-deck).

fine fescue, and ryegrass. The machine also

can be used to make many other complete or

partial separations that may aid the seed

analyst, plant breeder, weed researcher, or

seedsman who need to process a small quantity

of high-value seed.

A 30-deck model was built to test the feasibility of multideck construction in larger-scale

operation. It performed well in salvaging good

ladino clover from clover-pigweed screenings

and in removing silverhair from bentgrass. A

seed processor has built and operated a 500-

deck unit (shown in fig. 26) based on the same

design. The decks are about 4 x 10 inches and

are covered with a fine-grade sandpaper (80

grit). The complete assembly is energized with

two matched electromagnetic vibrators. Capacity ranges around 200 pounds per hour in salvaging certified ladino clover from screenings.

Electrostatic Separator

Electrostatic seed cleaners take advantage of

differences in electrical characteristics of seed

to make many separations that cannot be made

with conventional seed-cleaning equipment.

The degree of separation possible depends upon the relative abilities of seeds in a mixture

to conduct electricity or to hold a surface

charge.

Electrostatic separations have been practiced extensively in the mineral industry for

many years. To a lesser degree, various agricultural foodstuffs also have been cleaned electrostatically. Examples are removing leaf and

stem material from raisins, watercress seed

from rice, chaff from flour, and contaminants

from coffee. Recently, this principle of separation has been applied to seed mixtures, and

several makes of electrostatic separators are

receiving limited use by the seed industry.

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 will attract lightweight objects like bits of paper. This attraction occurs because the electric charge on the

comb is now different from that on the paper.

Basically, the same principle is used in elec-
MECHANICAL SEED CLEANING AND HANDLING 31

8-475-2-67

FIGURE 26.—Vibrator separator (500 deck).

trostatic cleaning where seeds are separated

according to how well they retain or lose an

electric charge.

The usual arrangement of an electrostatic

seed separator consists of a feed hopper, a conveyor belt or cylinder, a high-voltage power

unit and electrode, and adjustable dividers and

containers. (See fig. 27.) In operation, seeds

are metered from the hopper to the belt or

cylinder and conveyed into an electric field

surrounding the electrode where they become

charged. A given seed will tend to hold or lose

charge according to its electrical conductivity.

Depending on field characteristics, some seeds

are repelled by the electrode and attracted by

the moving belt. With another field arrangement, the opposite is true and seeds are attracted by the electrode. These attractions or

repulsions cause deflections in the paths taken

by seeds as they leave the belt or cylinder.

Dividers in the drop paths then can be positioned to collect any desired fraction of the

distribution.

Field characteristics are dependent on the

high-voltage electrode. One position of the

electrode will provide a discharging or "pinning" field. Seeds passing through this field are

sprayed with electrons and become negatively

charged by conduction. The better conductors

of the seed mixture will lose this charge and

fall in a normal discharge pattern from the

belt. Seeds that are relatively poor conductors

will adhere to the belt until their charge is

neutralized.

A different electrode position can produce a

static or "lifting" field. When seeds pass

through this field, they receive a positive

charge by induction. With seeds that are good

conductors, the positive and negative charges

already present tend to migrate on the seed

surface. Positive charges assume a position

nearest the negative electrode, and negative

charges (electrons) accumulate at or near the

seed surface contacting the belt. Free electrons

of the seed move to the belt, leaving the seed

with a net positive charge. A force of attrac-
32 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

Feed

Hopper

Seed Conveyor Belt

W...... /.

^/^ Electrode

-5 p y V J t \f . V V ! Adjustable

V' Dividers

;• . •• /-^

FIGURE 27.—Schematic drawing of an electrostatic seed separator.

tion then exists between the seed and electrode

causing the trajectory of the seed to be shifted

toward the electrode. Poor conductors, because

they resist the charge migration, are relatively

unaffected and drop normally from the belt.

The best combination of field characteristics,

voltage setting, and divider positions for a

given separation depend upon the seed mixture

and surrounding atmospheric conditions and

are best determined by trial and error.

An experimental unit developed for electrostatic separation is shown in figure 28. Main

objectives of research conducted with this unit

have been to learn what seed mixtures can be

separated, the effects of seed moisture content

on separating efficiency, and the inñuence of

high-voltage exposure on the germination of

seed.

Moisture content was found to play an important role in separation, stemming from the

fact that a seed's ability to conduct electricity

is influenced by seed moisture. Changes of 2 to

3 percent in moisture were great enough to

impair separation. However, variations in seed

moisture can be compensated for, to some degree, by changes in machine settings.

Another factor influencing separation efiiciency is uniformity of voltage. Uncontrolled

voltage variations in the supply line are magnified in the power unit and appear as wide

fluctuations at the electrode. Since these fluctuations will distort the seed trajectories, it is

important to employ a constant-voltage transformer or other means of regulating the

voltage supply.

High-voltage exposure was studied by subjecting Chewings fescue, ryegrass, and

subterranean clover to voltages ranging from

10,000 to 45,000 volts in increments of 5,000

volts. In another test, the following seed types

were exposed 50 or more times to voltages up

to 25,000 volts : ladino clover, red clover, Dutch

white clover, alfalfa, common ryegrass, perennial ryegrass, creeping red fescue, and alta

fescue. All exposed lots and untreated control

samples were germinated in an official seed

testing laboratory, and no significant differences were found in germination.

Many seed mixtures have been separated

electrostatically in the research program.

Some of these are curly dock from red clover,

bachelors-button and chervil from common

and perennial ryegrass, sheep sorrel from alsike clover, wild radish from crimson clover,

red clover from lotus, watergrass and trash

from onion, morning-glory from asparagus,

trash from bluegrass, whitetop from alfalfa,

pigweed from snapdragon, and hulled

bermudagrass from white clover.

Acceptance of electrostatic separation in the

seed industry has been varied, due in part to

operation in uncontrolled climatic conditions. However, research studies indicate that

separating efficiency can be improved when
MECHANICAL SEED CLEANING AND HANDLING 33

*±.*£Eí44-üS-15B-1-69

FIGURE 28.—Electrostatic seed separator developed cooperatively at Oregon State University.

seed moisture and voltage supply are regulated.

This means that best results will be obtained

when the electrostatic separator is operated in

a controlled atmosphere and with a constant

voltage supply.

Color Separator

The color separator is an electronic machine

that sorts materials according to color or

light-dark characteristics. Some of the agricultural products now being color separated

are lemons, peanuts, walnuts, coffee beans,

peas, garden beans, rice, and raisins.

Several manufacturers produce color separators which vary somewhat in mechanical operation, but are similar in basic concept. (See

fig. 29.) The objects to be sorted are passed

through a brightly illuminated viewing area

where light reflected from the object is compared with light reflected from a standard

background surface previously chosen as acceptable. When the light reflection is different.

a signal is generated, amplified, and used to

eject the off-color object from the mixture,

leaving a product of fairly uniform color and

shade.

The objects may be conveyed into the viewing area on the ends of suction ferrules, or they

may enter by gravity flow. In one type of

gravity flow, the objects fall from the periphery of a cone; in another, they are discharged single-file from a horizontal belt so

that their trajectory passes through the view

area. In all cases, the objects are scanned individually by one or more photocells, any of

which can trigger the reject command and remove the unwanted object mechanically or

pneumatically.

In a sense, the color separator functions like

a human inspector. The photocell is the eye,

the electronic circuits are nerves, the amplifier

is the brain, and the air ejector is the hand.

However, the similarity ends there because the

color separator can sense differences not detected by the eye; it can view an object from

four sides simultaneously; and it can be set
34 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

' 1 • • #

FIGURE 29.—Color separator.

S-421-11-64

to produce an end product whose color or

shade is essentially constant over any given

time period.

Both light-dark separation and true color

separation can be accomplished in the same

pass through some machines. For example, a

machine may be equipped with four viewing

stations where each contains a photocell that

is light-dark sensitive. In addition, two of the

stations may have color-sensitive photocells.

This means that six separate optical circuits

are at work comparing the light reflectivity of

the object with that of the standard background. The separator circuits can be adjusted

to reject objects lighter than the background,

objects darker than the background, or both.

Also, the amplifier can be set so that two different color separations are made at the same

time as the light-dark separations. Such versatility lets this type of unit perform some

very difficult separations, like the sorting of

peas that are discolored in varying degrees and

hues from frost damage, weevil attack, bleach,

or mold.

Most of the color separations being practiced

in seed processing are with relatively large

seeds ranging in size from rice to lima beans.

Recently, however, special interest has been

paid to smaller seeds like sesame, onion, beet,

mustard, tomato, and flower seeds. Although

small seeds can be separated, capacities usually

are low—for example, about 40 pounds per

hour with mustard seed. In contrast, peas and

corn can be processed at rates up to 500

pounds per hour.

Present techniques in color separation evaluate every seed singly. Although this practice

tends to limit capacities, it offers the advantage of extremely accurate and consistent results.

Resilience Separator

The resilience separator is an experimental

development designed to separate seeds on the

basis of difference in resilience or bounce

properties. In its simplest form this machine

consists of a feeding device that drops seeds

onto an inclined hard surface, and several

pans located to catch seeds from different

trajectories as they bounce after impact.

One test model consists of a long inclined

plane interrupted with several bounce plates.

As a seed mixture slides down the plane and

impacts on the plates, seeds that bounce farthest from the plane are trapped and others

continue down the plane to another plate. In

this way, one seed gets several chances to

bounce out of the mixture during one continuous pass. Relatively poor bouncers tend to miss

each trapping point and are discharged into a

collector at the bottom of the plane. A full-size

unit of this design was constructed by a seed

processor and used to remove ryegrass from

orchardgrass.

Another test unit employs glass plates inclined at 45° and arranged generally one above

another with alternating slopes. (See fig. 30.)

As a seed mixture impacts on the top plate,

resilient seeds bounce far enough to clear the

second plate while poor bouncers travel only to

the plate or perhaps not that far. Seeds that

go over or under the second plate are caught

separately in "good bounce" or "poor bounce"

fractions, respectively, and seeds impacting on

the second plate are provided another chance

to bounce and be classified. The cycle can be

repeated as many times as desired in one pass

through the separator by adding plates.
MECHANICAL SEED CLEANING AND HANDLING 35

S-431-4-65

FIGURE 30.—Resilience separator with glass bounce

plates.

The glass plates of the unit shown in figure

30 are equipped with pins and supported by

pegboard panels to make for easy adjustments.

With this arrangement, individual plates can

be added, removed, rotated, and moved horizontally or vertically as needed.

Limited tests with the multiple-plate model

have shown encouraging results in removing

white clover from bluegrass, ryegrass from

orchardgrass, asparagus from beet seed, and

dirt clods from ladino clover.

Other Separators

In addition to the conventional and experimental separators already described, there are

other separators and related equipment used

in seed processing which are peculiar to certain crops or find limited use for some reason.

Scalpers, debearders, hammermills, and hullerscarifiers fall in this category and are discussed

in a later section. Other examples are the

stoner, reverse roll, diverging rolls, inside velvet roll, cocklebur roll, buckhorn machine, and

polishers.

Stoner

The stoner is a type of specific gravity

machine, but it produces only two fractions

on a sloping deck—heavies at the high end and

lights at the low end. It will remove rocks from

beans, sand from clover, or other heavy components from light ones. Generally, the stoner

can show greater capacities than the gravity

machine but cannot make as fine a separation.

Reverse Roll

The reverse roll is used mainly to remove

dirt clods or other rough material from beans.

Rubber wipers contact a rough-surfaced roll

and travel around it in a direction opposite to

the roll rotation. When a mixture is fed to the

machine, the wipers take beans to their direction while the roll takes dirt and rough material with it.

Diverging Rolls

The diverging rolls are somewhat like the

velvet roll machine except that the fabriccovered rolls diverge and form a space that

gradually widens toward the discharge end.

Dirt clods, rocks, and other rough material

can be removed from beans, and the variable

space serves to size the crop, dropping out

small beans first.

Inside Velvet Roll

The inside velvet roll also is used mainly to

remove rough material from beans. This machine is similar to an indent cylinder with

fabric lining the inner surface. Rough material tends to cling to the fabric and be lifted

away from the smooth beans.

Cocklebur Roll

The cocklebur roll is an experimental device

developed to remove thorny seeds from

smooth ones, like cocklebur from sunflower
36 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

seed. The unit employs a conveyor belt and a

pressure roll covered with polyurethane foam.

When a mixture is conveyed under the rotating

roll, thorny seeds will adhere to the foam

covering and be raised from the belt where a

doffing roll can remove them.

Buckhorn Machine

The buckhorn machine is used primarily to

prepare buckhorn plantain seed so it can be

removed from legume seed such as alfalfa and

the clovers. Often, these seeds are so similar

in size, density, and surface texture that they

cannot be separated readily. However, the

buckhorn seed has a mucilaginous coating

that becomes sticky when dampened and will

pick up fine sawdust forming a larger seed unit

with lower density and rougher texture. Sawdust does not adhere to the smooth legume

seed. After small amounts of water and sawdust are mixed with a seed lot, as shown in

figure 31, the coated buckhorn seeds can be

removed with screens or the specific gravity

machine.

Polishers

Various types of polishers may be used to

clean and brighten the surface of beans, peas,

and grains. Some units agitate the products

with a compound like sawdust or bran in

either a wet or dry process to accomplish the

cleaning. Other polishers use a revolving brush

to scour the grain against a rubber or screen

surface.

SEED CONDITIONING AND TREATING

Many seed lots are conditioned or precleaned

before they enter the usual seed processing sequence. This frequently is necessary to permit

safe storing, efficient drying, ready handling,

or proper cleaning. The major machines used

for conditioning or precleaning are scalpers,

debearders, hammermills, and huller-scarifiers.

Scalper

Scalping is a rough cleaning operation,

usually performed at high capacity, that

screens off foreign material larger than the

crop seed. The scalped material typically contains stems, green leaves, weed seeds, insects,

and trash, and it may represent half or more

of the total lot. Removing this large bulk of

waste early will reduce later handling and

storing requirements, as well as improve cleaning efficiencies. Also, the removal of trash and

high-moisture green material will lower drying

costs and permit safer storage.

There are many types and sizes of scalpers

available. One is a reel of perforated metal

screen which turns on a central shaft and is

inclined slightly from the horizontal. Material

fed into the higher end tumbles inside the reel

until the crop seeds drop through the perforations. Large trash stays in the reel and is discharged separately. Another type of scalper

Seed Feed

Water Sproy

Sowdust Feed

Conveyor ^

Mixing Chamber Clover a Sowdust y^;

Covered Buckhorn

Seed

FIGURE 31.—Cross section of buckhorn machine.
MECHANICAL SEED CLEANING AND HANDLING 37

makes the same kind of separation with a

single, flat, perforated screen which is mechanically shaken.

Some seedsmen prefer a more complete precleaner than the basic scalpers just described.

Such units are available with several flat

screens or reels and may include air separation

features. One model is essentially a simple airscreen separator that lifts light chaff and dust

with a controlled air current, scalps large

trash over a large-hole screen, and drops small

contaminants through a small-hole screen. Another style using a screen reel and air separation is the scalping aspirator illustrated in

figure 13.

For greatest benefits from a scalper, it

should be the first equipment used when seed

comes in from the field. Consequently, scalpers

may be installed to advantage ahead of the

main receiving elevator in cleaning plants,

dryers, or storage facilities.

Debearder

Many seed lots can be cleaned directly after

scalping, but others may require further conditioning. In some cases, a lot may contain

unthreshed seed in the form of pods, heads,

clusters, or doubles. Also, some seeds like barley have awns or beards. To minimize seed loss,

these unthreshed units must be broken down

to single seeds, and awns should be removed

for proper separation. Debearding machines

are commonly used to perform these functions

and, in effect, to complete the threshing

process.

The debearder consists of a horizontal beater

assembly that rotates inside a steel drum. The

beater is made up of a shaft with projecting

arms which are pitched to move the seed mass

through the drum. Stationary posts, adjustable

for clearance with the arms, protrude inward

from the drum and prevent the mass from rotating with the beater. In operation, this

machine causes a vigorous rubbing of seeds,

pods, heads, and doubles against the arms,

posts, and each other. The time that seeds remain in the unit is varied by regulating a

v^eighted discharge gate. The severity of action is controlled by the exposure time, beater

speed, and clearance between beater arms and

posts.

The debearder is used extensively to remove

awns and hairs from certain grains, native

grasses, and other seeds. Seeds with appendages like these are difficult to handle, clean,

and plant because they tend to interlock and

cause undesirable clustering. A properly adjusted debearder can greatly improve flow

properties of such difficult-to-handle seed.

Some of the jobs performed by this machine

are debearding barley, clipping seed oats,

threshing whitecaps in wheat, defringing

carrot seed, decorticating sugar beet seed, subdividing fescue doubles, and removing fuzz

from bluegrass.

Other equipment sometimes used to remove

awns and appendages includes farm hammermills and, to a lesser extent, threshers operating at high speed, and tumbling pebble mills.

Since all of these units, as well as debearders,

rely on rubbing and abrasion to accomplish

their purpose, they should be operated carefully to prevent seed damage.

Hammermill

The hammermill employs many fingerlike

hammers rotating inside a section of

perforated metal cylinder. Seeds processed in

the mill are subjected to a vigorous beating,

or rolling action between the hammers and

perforated screen which removes appendages

and forces the seeds through the screen holes.

Results with the hammermill depend on

hammer speed, size of screen openings, feed

rate, and crop condition. The screen should

have an opening slightly larger than the deawned seed. If too large a screen is chosen,

there will be an excess quantity of inert matter and a high percentages 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 partly

full, there will be more seed damage and a

higher percentage of awns not removed.

A good speed for the hammermill is about

50 percent of that used in a normal grinding

operation; however, this can vary slightly according 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 effectively. Seeds of

the following species have been successfully

treated in a hammermill operation: bluegrass,

bluebunch wheatgrass, blue wildrye, Canada

wildrye, Siberian wildrye, tall oatgrass, bulbous barley, squirreltail, alfileria, and virginsbower,

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 airblast. However,
38 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

moisture content at time of threshing is quite

influential in this process.

Some seeds like black grama have fine, flexible awns that do not break off in hammermills

or debearders, but which bnd themselves to

differential burning. The seeds are dropped

through a flame where an instant flashing of

the hairlike awns takes place. The flame exposure must be short to avoid damaging the

seed by excessive heat.

Seeds of some native grasses of the Great

Plains receive little intermediate processing

between harvest and planing. Arizona cottontop, for example, is harvested by heading and

then is fine-chopped in a hammermill or similar

unit. Special equipment then plants the seed

material without removal of the fuzz or additional cleaning. Other grasses like tanglehead

and cane bluestem are handled the same way.

A green-forage harvester is used in Texas

wintergrass to harvest and chop the seed material in one operation for later planting. With

grasses such as bie: cenchrus and Argentine

wintergrass, both of which require precleaning

to remove süines and awns, the forage harvester is used for the harvest and does part

of the job otherwise performed by the hammermill.

Some seeds with cottonlike stylets, such as

Texas bluegrass, defy conditioning with debeaiders or hammermills and cannot be

planted readily with regular grass drills. An

experimental solution to this nroblem is pelleting. All plant material, including seeds, stems,

and leaves, is mixed with a binder like cornstarch, silvicon, or krilium and extruded

throueh a quarter-inch hole in a die.

Cornstarch-binder pellets can be planted with

a corn nlanter or cotton planter. Pellets made

with silvicon (from Douglas-fir tree bark)

form a coarse granule which can be planted

with a conventional grain drill or range seeder.

Huller-Scarîfier

After scalping and sometimes debearding,

many kinds of seeds can be cleaned without

further conditioning. However, certain legumes

and grasses may require hulling, scarifying, or

both. Hulling is the removal of an outer coat

or husk to improve the seed's cleaning characteristics or its planting qualities. With the

husk removed, the seed is more readily

handled in both cleaning and planting

equipment, and, in some cases, the husks are

impermeable to water and thus prevent termination. In scarification, the seedcoat itself is

scratched or ruptured. Scarifying is practiced

with "hard'' seeds which otherwise will not

absorb water and germinate promptly.

Hullers and scarifiers usually abrade the

seeds between two rubber-faced surfaces or impel seeds against roughened surfaces like sandpaper or carborundum stone. The severity of

abrasion or impact must be controlled

accurately to prevent seed damage. Seeds of

high moisture content are harder to hull or

scarify than seeds with less moisture, and

clean seed scarifies more uniformly and with

less damage than dirty seed.

Some kinds of seed lose viability quickly

after being hulled or scarified, so these processes should be delayed for such seed until

shortly before planting time. Other seeds that

maintain viability well after being hulled and

scarified can be processed soon after harvest

and stored safely until the following season.

Hulling and scarifying may be performed

separately or jointly, depending on the presence of unhulled seed, hard seed, or both.

Some seeds that may require hulling are

bermudagrass, bahiagrass, buffalograss, lespedeza (Korean, Kobe, common, and bicolor).

Some seeds that may require scarification are

alfalfa, subclover, white clover, suckling clover,

hairy indigo, crotalaria, and wild winter peas.

Some seeds that may require both hulling and

scarification are sweetclover, sourclover, sericea lespedeza, crownvetch, and black medic.

Treater

The scientist, the 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 plantborne 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 stimulating the use of treating

machines in processing plants.

Seed treaters may be divided into three

categories: dry-powder applicators, slurry applicators, and liquid applicators. The drypowder applicators were 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 effects of breathing chemical dust, and the

diflSculty of controlling chemical dosage in the

dry-powder units.

The introduction of wettable powders and

the development of the slurry treater came

next. This was considered a major step forward in seed treating, since it made possible
MECHANICAL SEED CLEANING AND HANDLING 39

the metering of chemicals needed to treat a

given seed quantity, while at the same t e

confining the chemical to the seed. The slurry

is a versatile treater that will handle many

different commodities. However, it is not suitable for applying low dosages of the more potent chemicals. This failing led to the development of the liquid applicator.

The liquid applicator has several advantages.

With it, as little as half an ounce of mercury

will treat a bushel of seed without the necessity

of adding water, and the treatment can be performed in temperatures as low as —20° F.

The seed does not have to be completely covered to give the desire protection. Unfortunately, this technique cannot be used with

vegetable or other food-crop seeds. These are

still treated by the slurry method.

There are two types of liquid treaters in

general use. In one type, a seed mass is tumbled

in a rotating drum, and liquid is applied in

small drops by a number of fingerlike tubes.

The drum is set on an incline so that the seed

travels from inlet to discharge as the drum

rotates. The other liquid treater consists of a

chemical pump and tank, an electrical motor.

seed feed control, seed-weighing pan, chemical

measuring cups, a seed-dispersion cone, and a

rotary disk. (See ñg. 32.) 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

falls on a high-speed revolving disk 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 treater is satisfactory for applying very small amounts of chemical to seed,

and can be easily and quickly adapted for

treating a wide range of sizes and types of

seed.

A further development in seed treating is

a machine that employs principles of both the

liquid and slurry treaters. This combination

unit was developed for corn but has many

other applications.

SEED HANDLING AND STORING

Effective seed handling and storing are important in the economy of seed processing.

Seed lots are handled many times in receiving,

drying, cleaning, and bagging, and they may

be stored before, during, or after cleaning. If

care is not exercised in these operations, processing efficiency will be reduced by seed damage, contamination, and handling costs.

Handling

Generally speaking, methods of handling

seed in the processing plant can be classified

in two major divisions—mechanical and pneumatic. Mechanical systems include various

types of conveyors, elevators, vibrators, and

bulk-handling schemes, while pneumatic systems employ air flow and may operate above

or below atmospheric pressure.

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 trousrh. Little or no seed

damage takes place in this type of conveyor,

but contamination or intermixing of bulk seed

lots is possible when the belt travels in a

trough. In contrast, trough-forming belts supported by inclined rollers are self-cleaning and

find extensive use in corn and grain handling.

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

housings for the lift 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 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 discharge velocity may cause excessive damage to injurysensitive seed. Slow-speed units are better for

easily damaged or slow-flowing materials. Another limitation of bucket elevators is that

they are difficult to clean. Small seeds tend to

lodge in hard-to-clean areas throughout the

elevator and remain there to contaminate subsequent lots.

A different type of bucket elevator that is

becoming popular in seed handling is a slow-
-?*!!

40 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

FIGURE 32.—Liquid seed treater.
MECHANICAL SEED CLEANING AND HANDLING 41

speed, high-capacity, multisection conveyor

that operates without a filler boot or enclosed

housing. The bucket assembly can be supplied

in as many compartments as desired, and in a

three-compartment unit, for example, three

different seed types can be lifted separately

in adjacent compartments of buckets. Individual, timed rotary feeders load the compartments of each bucket section at the bottom of

the elevator.

The buckets gradually turn upside down as

they follow a horizontal path at the top of

the conveyor and gently discharge the seed

load by gravity. Because of the open-type construction, any seed dislodged from a bucket

will fall in catch pans or on the floor free of

the system. Since there is neither high-speed

discharge to cause damage, nor boot or housing

to act as a source of contamination, 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 U-shaped trough, with or without a cover.

As the element rotates, seed fed to it is moved

forward to the discharge end of the trough.

Since this conveyor agitates or tumbles the

product handled, it does considerable mixing.

It can also function as a feeding or metering

device.

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, some may remain

in the system and contaminate subsequent

lots.

Vibrating conveyor.—The vibrating conveyor transports material by ''bouncing'' it

along a tray that has a reciprocating stroke

produced by electromagnetic, mechanical,

pneumatic, or hydraulic action. Depending on

the type of action, flow rates may be changed

by varying the length or frequency of stroke.

Little or no seed damage occurs in this conveyor, and it tends to be self-cleaning. One

limitation, however, is that seed transport is

restricted to horizontal or near-horizontal

paths. Vibrating conveyors are frequently

used as feeding or metering devices because

they are easily adjusted for a wide range of

flow rates. With proper attention, they also

offer a convenient means of controlling feed

rates at desired levels.

In electromagnetic units, the conveying

tray is pulled sharply downward and backward by magnetic attraction and then returned upward and forward to its original position by springs. This action is modified in

some designs so that electromagnets, supplemented by spring, alternately attract and repel the tray to impart the reciprocating motion. Flow rates are changed by adjusting a

rheostat which regulates the power input to

the electromagnet. Although frequency remains fixed at 3,600 or 7,200 cycles per minute,

the stroke length of the tray is changed and

this alters the conveying rate.

In experimental tests of different vibrating

feeders, those powered electromagnetically

showed smooth changes in flow rate as rheostat setting was varied. There was a tendency

for flow rate to drift considerable over an extended period of time at a fixed rheostat setting, particularly when handling grass seed

and if air temperatures fluctuated around the

vibrator. However, when checked periodically

and readjusted if needed, electromagnetic

feeders can provide a convenient, dependable

method of regulating feed rates.

Vibrating conveyors may achieve their motion mechanically in several different ways. In

the positive-drive unit, the vibrations are produced by an eccentric mounted on a shaft so

that its throw causes movement of an attached

trough mounted in a special suspension. The

trough action is similar to that of the conventional strawwalker in a combine. 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 an 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.

Another mechanical action used to produce

vibration is that of an unbalanced rotating

mass. Offcenter weights are added either to

the shaft of an electric motor or to a pulley

driven by a motor. The vibration generated

by this unbalanced condition is transmitted

to an attached trough which is supported so

that its movement is essentially forward and

backward in repeated cylces. Feed rates can

be regulated with the use of resilient material forced against the trough or suspension

to dampen the vibration as desired.

Vibrating conveyors also can be powered

pneumatically or hydraulically. One type of
42 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

pneumatic drive uses high-pressure air and

suitable valving to actuate a reciprocating

piston and produce vibration which is transmitted to a trough. In another design, compressed air forces a steel ball around a closed

circular race at high speed to generate the

vibration. With both arrangements, feed rates

can be controlled to some extent by regulating

pressure of the supply air and thereby frequency of vibration. In a test of the two systems, the steel ball unit showed much better

control. Hydraulic and pneumatic drives are

basically similar except that the working

medium of one is liquid and the other, gas. In

the hydraulic system, a pump produces a flow

of liquid through piping and pressure control

valves to a cylinder where straight-line motion

is generated. With appropriate high-speed

valve action, this motion is made reciprocating

and is transmitted to a conveying trough.

Aside from its use in conveyors and feeders,

vibration also can be employed to improve the

flow characteristics and handling of some

seeds. Unit vibrators are mounted on bins,

hoppers, or chutes to improve the flow of material that tends to "bridge'' or cling to the

sides.

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 truck bed. At the plant, the

seed is either processed directly or stored in

sacks, boxes, or bulk. Sacks can be handled

singly by special elevators and conveyers, or

in loads stacked on pallets and moved by forklift trucks. Boxes, also, are handled by lift

truck, or sometimes with a box elevator which

can grasp a large box, elevate it to a point

where the load is dumped, and return the box

to floor level. Advantages of the box method

are reduced labor requirements, less chance of

seed contamination, and ease of maintaining

seed-lot identity.

In bulk storage, 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 open-end bins.

Pneumatic Methods

Pneumatic systems transport material by

air and have the advantages of good cleanout

characteristics, flexible horizontal and vertical

operation, and mechanical simplicity. In order

to transport material in conventional pneurnatic conveyors, certain minimum air velocities are required, as shown in the tabulation

below. Once this condition is achieved, a ruleof-thumb method for supplying air-volume requirements is to provide 40 cubic feet per minute under average atmospheric conditions for

each pound of material to be moved per minute.

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.

Air velocities needed for typical pneumatic

conveying of materials at 70"" F. and 70 percent relative humidity

Approximate duct

velocity in lineal Material to be conveyed

feet per minute

2,500 . Dry dust and light fluffy seed

(bluegrass, meadow foxtail)

3,000 Ryegrass, fescue, and similar

grass seed

3,500 to 4,000 Alfalfa, crimson clover

4,000 to 5,000 Heavy oats and cottonseed

5,000 to 6,000 Wheat, corn

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 trucks, freight cars, and ships. Other

successful applications are in short runs where

seed is conveyed and removed from the system

before it reaches a velocity that may be damaging. The vacuum system is particularly effective if material is to be collected from several points and conveyed to a single discharge.

Low-pressure system.—Low-pressure systems operate above atmospheric pressure in a

range of approximately 10 to 15 inches of

water (about one-half pound per square inch),

and require a fan, conveying line, cyclone,

and a means of introducing seed into the airstream. Generally speaking, conveyors of this

type employ centrifugal fans and conveying

lines ranging from 6 to 24 inches in diameter.

Depending upon actual system pressures, seed

can be introduced by injector or auger feeders,

or if a better air seal is needed, by using a

rotary airlock (also called a star feeder or

bucket wheel). The low-pressure and vacuum

systems are the most common types of pneumatic conveyors used in seed processing.

Medium-pressure system.—Svstems operaing at pressures from about 15 to 50 inches

of water are classified as medium-pressure conveyors. The greater pressure requirements usually result from longer runs, more elbows, or

greater conveying rates. Special centrifugal
MECHANICAL SEED CLEANING AND HANDLING 43

fans act as the air source, and common conveying pipe sizes are 4 to 8 inches in diameter.

Rotary airlock units are needed to supply seed

to the airstream for this type of conveyor.

High-pressure system.—These systems operate at pressures of about 2 to 15 pounds per

square inch with relatively low air volumes,

and generally use small conveying pipe, about

1 to 4 inches in diameter. Positive-displacement air sources are employed in the form of

rotary blowers or reciprocating piston pumps.

Seed introduction to the high-pressure airstream is accomplished satisfactorily up to

about 10 p.s.i with rotary airlocks, but operation at higher pressures requires special locks

or air-sealing mechanisms.

Several characteristics of high-pressure systems in seed conveying are flexibility of smallsize pipe runs, high solid-air ratios, and relatively low seed velocity—therefore, low seed

damage. Also, with low air volumes, there is

little or no dust problem, and cyclones or collectors generally may not be needed.

An experimental pneumatic conveyor of the

high-pressure type has been developed that

employs principles of "fluidized" flow. (See

fig. 33.) Seed movement through the system

takes place in the form of aerated slugs that

show a high degree of mobility or fluidity.

Tests were conducted with a 56-foot run of

1%-inch diameter tubing that included a 30-

foot vertical lift and four elbows. Performance

results with freeflowing seed like crimson

clover showed that seed velocities were low,

seed damage was negligible, and cleanout was

good. Conveying rates could be varied from

600 to 1,800 pounds per hour while retaining

a low seed velocity and a high solid-to-air ratio.

Greater capacities—up to 6,000 pounds per

hour—were achieved in the 1%-inch line but,

necessarily, at higher seed velocities. Operating levels for this conveyor can be regulated

according to the capacities required and the

damage susceptibility of the seed being handled.

Storing

Almost all seed lots must be stored some

time during their processing. They may be

stored as brought in from the field, after a

preliminary scalping operation, between later

cleaning sequences, after cleaning, or after

bagging. Bulk storage in the form of boxes

and bins is used extensively during cleaning,

and cleaned seed may be stored in bags, cartons, or bulk.

S-226-a-60

FIGURE 33.—Fluidized conveyor.

Regardless of storage method, certain requirements must be met for proper storing of

seed. (1) The seed should be dry so that it will

not heat or lose viability; (2) temperature

and humidity of the storage atmosphere should

be kept relatively low to minimize seed deterioration, especially in long-term storage;

(3) seed should be handled in storage operations without producing mechanical damage;

(4) physical arrangement of the storage facility should be conducive to eificient handling;

and (5) good housekeeping practices should

be observed.

Drying

Seeds must be stored dry if they are to retain their ability to germinate when planted.

High moisture content tends to shorten seed

life by increasing respiration rate, encouraging mold growth and insect attack, and increasing the danger of injury during fumigation.
44 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

Drying may be classed as natural or artificial. Natural drying takes place with atmospheric air moving naturally around damp seed

spread on trays, canvas, floors, or fields. Artificial drying uses heated or unheated air that

is mechanically forced through or over the

seed mass. Too-high temperatures or too-fast

drying may injure moist seed, so temperatures

of drying air usually should not exceed 90°-

100° F.

Safe moisture levels for seed storage vary

considerably depending on the seed type, temperature and humidity of the storage atmosphere, the type of seed container, and the

length of storage period desired.

Storage Atmosphere

Once seeds are dried and placed in storage,

moisture content still may change. Seeds absorb or give up moisture until they are in

equilibrium with the surrounding air. If temperature and relative humidity of the air

fluctuate, so will the moisture content of the

stored seed.

Proper storage conditions will depend on the

seed itself and the length of storage required.

For a short storage period, say several months,

it is usually sufficient to place dry seed in

moisture-resistant containers like multiwall

bags. For bulk seed storage, it is desirable to

make provisions for aerating the seed mass to

help maintain its temperature and moisture

content at safe levels. During longer storage

periods, dried seed can be placed in sealed cans

or in humidity-controlled, vapor-sealed rooms.

For extended storage, it may be necessary to

control temperature as well as humidity in the

storage area.

The best storage atmosphere is dry and

cold—this helps retain the viability and vigor

of many seed types. Several ''rules of thumb*'

are used to help determine safe storage atmospheres. One is that seed life is doubled for

every drop in seed moisture content of 1 percent or for each drop in air temperature of

10° F. Another rule suggests that the numerical sum of air temperature (in degrees F.)

and the relative humidity (in percent) should

not exceed 100.

Mechanical Damage

Seeds can suffer mechanical injury in any

handling operation that provides a chance for

abrasion or impact to occur. The injury may

not be evident immediately, either visually or

by germination tests, but may appear later in

the form of reduced storage life and poor field

germination.

Probably the greatest single source of mechanical injury is the threshing operation.

Within the processing plant, however, the

main potential offenders are conveyors, debearders, huller-scarifiers, polishers, and unbroken drops. Of these, drops are frequently

overlooked as a source of seed damage. However, research studies have shown that some

seeds like beans show reduced germination

after only a single drop from a height of a

few feet.

Several devices have been developed experimentally to minimize free drops of seed. One

of these is a spiral tubing arranged with its

axis vertical so that seed introduced at the top

is delivered gently at the bottom. Another is

a series of short inclined chutes arranged generally one above another with alternating

slopes. Seed fed to the top chute slides down

to the second chute where it changes direction

and is delivered to the third, and so on. If

desired, these chutes can be made from sections of automobile tire casings. A third type

of **letdown'' can be constructed with a hollow

tube perforated at intervals throughout the

tube length, fitted with inclined baffles, and

mounted vertically in a bin to be filled. When

seed is delivered to the top, it drops through the

tube from one baffle to another until the seed

level in the tube reaches the lowest perforated

hole. Then the seed flows out the hole into the

bin until the seed level in the bin reaches the

hole. Incoming seed then fills the tube to the

next hole, and again flows into the bin. The

proper arrangement of baffles and holes will

slow the seed movement and create a series of

short drops rather than one long one.

Physical Layout

The physical arrangement of a storage facility contributes a great deal to overall efficiency. For example, fork trucks can be used

effectively to handle bagged seed or tote bins

if the warehouse floor and column positions

are suitable. Floors and runways should be

smooth, level, and firm, and spacing of columns and posts should be great enough to permit easy maneuvering of trucks. Aisles at

least 10 feet wide are needed to handle loads

into and out of stacks, and main aisles should

be about 20 feet wide.

If the atmosphere of the storage space is to

be controlled, much care must be taken with

such construction details as insulation, vapor

sealing, and door design.

Housekeeping

Many advantages can be claimed for good

housekeeping practices in storage areas. Clean-
MECHANICAL SEED CLEANING AND HANDLING 45

Imess pays dividends in reduced contamination of seed lots, better control of insects and

rodents, and less fire hazard.

Related Operations

Several other operations closely related to

seed handling and storing are blending, sampling, bagging, and packaging.

Blending

There are many methods used to blend seed

after cleaning in the attempt to produce a

uniform, well-mixed lot. Methods range from

simple hand operations to elaborate electronic

setups with pushbutton controls. In typical

hand blending, seeds are dumped from sacks

into a pile and mixed manually with shovels.

In the automatic setups, an operator can dial

the desired proportions of seed for the mix

and the electronic system will meter the seed

from different tanks, as needed, and deliver

it to a rotating drum mixer. Other blending

methods fall between these extremes.

Blenders may be batch-type or continuous.

Some use varipitch vertical screws or horizontal agitators to mix seed from different

parts of a tank. Others use metering augers

to proportion seed from several tanks to a

conveyor belt that feeds a bagger. Still others

use calibrated vibrator feeders to meter seed

from tanks to the conveyor belt. Some seed

lots are blended by passing them one or more

times over an air-screen machine.

All of these efforts improve the uniformity

of seed lots, but most blenders still leave much

to be desired. It has been reported that over

half of the samples investigated by seed control officials are not uniform.

The whole problem of uniformity in seed

lots is a difficult one—even the filling and

emptying of a tank tends to stratify seeds

that are different in physical properties like

size, shape, and density. When a tank is filled,

heavy seeds tend to penetrate the middle of

the pile and force lighter seeds toward the

sides. Fines or very small seeds also tend to

penetrate the center. When a tank is emptied,

seeds flow out in a funnel-shaped pattern with

a small opening through the center of the discharge. Most of the initial seed flow is from

the gradually dropping top surface and from

the central core of the seed mass. Most of the

final flow is from the seeds originally at the

outer edge of the tank load. As a tank is

emptied, the bushel-weight figures for the seed

tend to gradually decrease from the first bag

to the last. A new approach that offers promise

in minimizing this flow-out condition is the

use of several small outlets at the bottom of a

tank that take seed from six or eight points

and deliver it to one vibrator feeder.

An experimental blender that has shown

good results is pictured in figure 34. Seed from

four tanks is metered by vibrator feeders at

controlled rates to a common trough that delivers the combined amount to a mixing cone.

Several commercial units of this arrangement

have been installed in processing plants and

have proven successful.

Sampling

Since entire seed lots cannot be analyzed,

they must be sampled to obtain small fractions which the seed analyst can then subS-1B4-1-B9

FIGURE 34.—Seed blender.
46 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

sample and test for purity, germination, and

other quality factors. These fractions should

be as representative as possible of the entire

lot. Sampling methods vary considerably, and

research is being done to compare different

methods.

One of the oldest sampling methods is to

take small handfuls of seed from many different bags or sources and mix them together.

A device that also finds much use is the "trier"

—a slotted tube that can be inserted in a bag

or bin to extract a small quantity of seed

from many points along the tube length.

Mechanized samplers are also available. Some

v^ithdrav^ samples periodically from a dropping seed stream while others sample the

stream continuously but at a very lov^ rate.

Sampling, like blending, is a complex and

important process. The economic value of a

seed lot is determined, to a large extent, by

the purity and germination analyses of the

sample tested. Careful sampling helps insure

that the sample tested represents the original

lot as nearly as possible.

Bagging

Processed seeds may be handled either in

bags or in the bulk. Most farm seed cleaners

use burlap bags. In some plants, the seeds are

discharged directly from the final cleaning

machine into the bag. Other plants may elevate the seeds to bins or tanks where they

are stored and sacked off periodically.

When seed is being bagged, a small platform

scale is commonly used to weigh the filled bags

which are then sewn closed by hand or portable

machines. Identifying tags may be stitched to

the bags by the sewing machine, or they may

be attached by wire.

Some bagging procedures are mechanized.

One type of semiautomatic bagger is located

under the bin and will receive seed, weigh it,

and fill the bag. An inlet valve is automatically

closed when the seed in the bag reaches a

predetermined weight. The operator removes

the filled bag and guides it into a combination

conveyor and bag closer, after which he places

an empty sack on the bagger while the unit is

weighing out the next batch of seed.

A recent bagging development is an automatic unit that receives seed from an overhead bin, weighs it, fills the bag, checks the

weight, and, by electronic feedback, adjusts

the scales to discharge the correct weight of

seed. This system will handle burlap, paper,

cotton, or plastic bags ranging in size from 5

to 100 pounds capacity and at rates of 20 or

more bags per minute. In some cases, the information usually found on tags is automatically printed directly on paper bags. This

eliminates the need for tags while still providing such required information as lot number, variety, purity analysis, germination percent, and date.

Packaging

Seed is packaged for the retail trade in

many forms of containers. It appears in cardboard boxes, vacuum-sealed cans, and bags

made of plastic, paper, cotton, or burlap.

Probably the most popular packaging system is the semiautomatic type. Seed to be packaged flows by gravity from an overhead tank

into scales that weigh and discharge at adjustable time intervals. In a typical operation,

a box is removed from a pile, glue is applied

to the flaps of one end, and the box is placed

in position to receive the seed. At the end of

the time interval, the seed is automatically

discharged into the box, after which the operator removes the filled box and applies glue to

flaps of the other end. The box is then fed

into a special conveyor that applies pressure

to the glued flaps. The weights of filled boxes

are checked periodically as a control measure.

In the final step, individual boxes are placed in

cartons for shipping.

Fully automatic packaging systems perform

the same operation described above, but at accelerated rates. The only manual operations

are supplying collapsed boxes to the magazine

that feeds the packaging machine, and placing

filled boxes in the shipping cartons.

PLANT LAYOUT

In laying out a seed processing plant, many

factors should be considered such as the kinds

of seed to be cleaned and the contaminating

crop, weed, and inert matter; the volume of

seed to be processed; the type of separators

to be used; the method of handling (bulk or

sacks, and, if sacks, whether they will be

moved by hand, roller conveyor, or forklift

trucks) ; the conveyor system to be used (pneumatic or mechanical) ; and the location of receiving, storing, and shipping facilities.

The plant should be laid out so that seed is

received, cleaned, and shipped without mixing

or damaging the lots and with a minimum

of time, equipment, and personnel. The seed

separators, conveying system, and storage bins
MECHANICAL SEED CLEANING AND HANDLING 47

should be arranged so 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. Accumulating tanks

should be considered for use above the separators so that a machine can be stopped

briefly, if needed, v^ithout stopping the entire

processing line. Separators should be located

so they are accessible for inspection, cleanout,

and adjustment. It is desirable to allow room

for future expansion of the plant as well as

possible rearrangement of equipment to accommodate new machines in the processing

line. Provision also should be made for dust

elimination and an adequate waste-handling

system to dispose of discard material from

the various cleaners.

To conserve floorspace and minimize the

handling of materials, seed processing

machines are sometimes placed one above another, or arranged in series so that the discharge of one unit flows into another unit.

Debearders are often found above air-screen

cleaners, and indent disk separators are frequently mounted above indent cylinder machines.

Where a plant operation must be flexible

enough to permit processing of various grass

seed, legume seed, grain, corn, or other products, floorspace can be saved by mounting the

processing equipment on rollers or mobile

frames. Then, depending upon given cleaning

requirements, the necessary machines can be

rolled or moved by forklift truck into the

processing line, or into storage until needed.

Types of Layouts

There are about as many different plant

layouts as there are seed processing plants.

However, most plants can be classified into

four general types of building arrangement.

These are the grain elevator, converted barn,

single story, and single story with half balcony

types of structures. Figure 35 illustrates these

arrangements.

(A) GRAIN ELEVATOR

MCHY. FLOOR

i"U^

MCHY FLOOR

ip'-^iyi \/^''^ vu*'///\i"^-"-^--v\\^^^^'\u\\'<i^^>v\\

© SINGLE STORY WITH BALCONY

/\

MCHY FLOOR

U

MCHY FLOOR

SINGLE STORY L_r ^^~^^=TFIGURE 35.—Types of building arrangements used for seed processing plants.
48 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

Grain Elevator

In the grain elevator type of arrangement,

elevated bins are grouped around a conveyor

that lifts seed high enough to spout it into

the bins. Processing machines are located beneath the bins so that seed can flow into them

by gravity. This arrangement reduces the

number of elevators required to handle the

crop but requires a high, reinforced structure

to support the heavy vibrating machinery on

the upper floors. Also, workers are needed on

each floor to operate and maintain the equipment.

Converted Barn

In the converted barn arrangement, cleaning machines are located on the original haymow, and the main floor is used to weigh, sack

off, and store seed. This layout makes good

use of a less expensive building, but frequently

requires strengthening the structure, adding

elevators, and does not always lend itself to

best arrangement of equipment.

Single Story

In the single-story structure, the seed

cleaners are arranged in series on the main

floor, and the seed is re-elevated between passes

through the machines. The present day emphasis on varietal purity and the special processing requirements for certified seeds are

causing a shift toward pure seed handling, and

the single-story layout is well adapted to this

process. It requires an elevator for each machine but has the advantage that one man can

supervise the entire processing line from one

floor. (See fig. 36.) In many cases, the reduced

cost of a single-story building compared with

the cost of a reinforced, multistory structure

will offset the expense of an elevator for each

cleaning machine.

Single Story With Half Balcony

A fourth plant arrangement uses a building

having one story and a half balcony. In this

layout, the machines requiring frequent observation and adjustment (air-screen, gravity,

" l" iiiiMl***''"''*^ ''

" ' pi;

^\.'±^*i

^"^^TAZ-^ 4i|i mr

J'^IPE': ^^H.'-^^ 1 ^llliTI

^ NuiN.' ,.^ a

^^^^H^KJl^ lili ^..

SH^^^^^^^^I^ 9JIS9ÄN ñiZ

I^Hpi. j„,_„„< ' '

1 nil vHV^ ^^^VJL <w|^mi

ih^

^^^^

jC^^ii:

1^lMí¿

éi^

S-186-5-S9

FIGURE 36.—Single-story processing plant. Interior view.
MECHANICAL SEED CLEANING AND HANDLING 49

and so on) are placed on the ground floor

but on raised stands so the operation can be

inspected easily and seed can be sacked off

readily. Other equipment requiring less attention (hullers, scarifiers, debearders, and length

separators) are located on the half balcony.

The airlift or elevator discharge can be above

the roof and directed to storage bins that feed

the balcony machines. Seed flows by gravity

from the balcony units to the ground floor

units.

Experimental Setup

An experimental plant developed for investigation and demonstration is an example of

the single-story layout. (See fig. 37.) It consists of an air-screen cleaner, a gravity separator, an indent disk separator, a velvet roll

machine, three 30-bushel storage bins, and a

self-cleaning elevating and conveying system

that will handle seed without mixing or damaging. The arrangement provides a flexible operating sequence and is located in a floorspace

measuring 20 x 30 feet, as shown in figure 38.

The ceiling height is 13 feet.

Dust Elimination

A dust elimination system can add materially to the comfort, health, safety, and efficiency of personnel in a seed processing plant,

as well as improve the appearance of the plant.

In many cases a dust system will reduce the

insurance rate on the plant and equipment.

Without such a system, dust will contaminate

the air; settle on rafters, walls, and machinery; and bother the workers. Dust in buildings has been blamed for explosions and fires

that can result in injury or death to personnel

and damage to the building and equipment.

Dusty plant conditions can cause lung disease,

eye discomfort, and allergic reactions in

workers. It also causes excessive wear in bearings and other moving parts of machinery.

Many farm seed processing plants do not

have dust systems; however, they are becomFiGUBE 37.—Experimental single-story seed-cleaning plant at Corvallis, Oreg.

S-161-1-69
50 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

EXPERIMENTAL SINGLE STORY SEED GLEANING PLANT

so BUSHEL

STORAGE BINS

VELVET ROLL SEPARATOR

8 Roll»

22 INDENT DISC

SEPARATOR

4 BUCKET

SELF- CLEANING

OPEN-TYPE

BUCKET ELEVATOR

HORIZONTAL VIBRATOR CONVEYORS

4 above —returning from

elevator

SACK

PUMP

DIMENSIONS^ (Approx.)

ROOM-20' X 30'X 13'

AISLE- 4' WIDE

SPECIFIC GRAViTY

SEPARATOR

32"« 56" Trlwiçlf Deck

AIR-SCREEN

CLEANER

4 Screen— 54" Wide

FLOOR PLAN

#- -v^^ vV- Vf

S-487-3-67

FIGURE 38.—Floor plan of the experimental single-story seed-cleaning plant at Corvallis, Oreg.

ing increasingly popular and are being added

to existing plants. Types of dust elimination

systems vary considerably. Probably the simplest is a fan that draws air from the sack

dump and discharges it outside. More extensive is a multifan system with many air inlets

that take air from strategic points throughout

the plant. The inlets are located in such

places as the top of a bin, the sack dump, the

debearder housing, or at other machines

where dusty conditions prevail. The dust fans

can discharge into cyclones or a dust room for

concentration of the airborne material.

The cost of a dust elimination system will

vary with the installation, but, in general,

will be cheaper and more satisfactory if installed with the initial processing machinery

instead of being added after the plant is in

operation. If the system is planned early

enough, the pipe can be run in a floor tunnel

or in a wall or attic where it will be out of

sight and not occupy space in the processing

area. Once the system is installed, it requires

little attention other than periodic maintenance. A single fan can be used satisfactorily

to collect dust from many points, provided a

balanced system is designed that will maintain an air movement in each branch that is

above the conveying velocity of the particles

concerned. Air velocities around 2,000 feet

per minute will convey dust ; whereas air velocities needed to convey most seeds range from

about 3,000 to 5,000 feet per minute.

Waste Disposal

Waste disposal is an important feature of

plant layout that is often overlooked in planning. The waste material from a seed processing plant is composed of leaves, stems, weed

seeds, dirt, and other contaminants that have

been separated from the crop seed. Waste can

be a problem of considerable magnitude if

proper means are not provided to handle it.

With light, chaffy grass seeds such as bluegrass, the weight and volume of the waste will

often exceed that of the crop seeds.

The most common methods of waste dis-
MECHANICAL SEED CLEANING AND HANDLING 51

posai are burning the material or trucking it

to a dump pile located on the banks of a gully

or stream. Burning the waste tends to contaminate the atmosphere, and dumping over

banks also is unsatisfactory. One disadvantage

of this dumping location is that during periods

of high water the weed seeds float downstream

and contaminate other banks and flooded

fields. There is an ever increasing effort to

clean up both our air and streams, and this

increases the importance of proper waste disposal from seed plants. In large operations

where the volume of material is sufficient to

interest feed processors, seed waste sometimes

is purchased and blended with other ingredients to be made into pellets for animal feed.

If a waste disposal system is properly

planned, material from various processing machines and floor **sweeps" can be spouted directly into a waste conveyor and delivered automatically to an incinerator for complete

burning or to a loading hopper for trucking to

an approved disposal area.

Dust elimination and waste disposal can be

incorporated into a single system that collects

dust and waste products from throughout the

plant and conveys them to a collection chamber.

Flow Diagrams

The particular combination of machines

forming a seed processing line will be determined by the seed crops handled and their

contaminants. Figure 39 illustrates general

sequences of operation in processing several

different crop seeds including legumes, grains,

bluegrass, and corn. The flow diagram for bluegrass can be used also to process other grass

seeds by omitting those machines not required.

For example, the machines usually used in

processing ryegrass and fine fescue are the

air-screen cleaner and the length separator.

Depending on the contaminants, the gravity

separator may or may not be used.

A typical machinery arrangement for a

single-story farm seed-cleaning plant handling

grass seed is shown in figure 40.

FIGURE 39.—Flow diagrams for processing seed.
52 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

TRUCK

C5UMP

DISTRIBUTOR

HEAD

AIR

SCREEN

S

SURGE

TANK

DISCO O

O

SURGE

TANK

GRAV/Ty

SCALE

SINGLE STORY FARM SEED CLLA-NiMi P1.ANT_

MECHANICAL CONVEYING

FIGURE 40.—Single-story farm seed-cleaning plant for grasses.
MECHANICAL SEED CLEANING AND HANDLING

REFERENCES

53

BRANDENBURG, N. ROBERT, and HARMOND, JESSE E.

1964. FLUIDIZED CONVEYING OF SEED. U.S.

Dept. of Agr. Tech. Bui. 1315, 41 pp.

and HARMOND, JESSE E.

1966. SEPARATING SEEDS BY LENGTH WITH SPECIAL INDENT CYLINDERS. Oreg. Agr.

Expt. Sta. Tech. Bui. 88, 20 pp.

CHING, TE MAY.

1958. SAFER SEED STORAGE. Crops and Soils

11(3): 16-17.

COOPER, H. W., SMITH, JAMES E., JR., and ATKINS, M.D.

1957. PRODUCING AND HARVESTING GRASS SEED

IN THE GREAT PLAINS. U.S. Dept. Agr.

Farmers' Bui. 2112, pp. 1-30.

HALL, CARL W.

1957. DRYING FARM CROPS. Agricultural Consulting Associates, Inc., 336 pp.

HARMOND, JESSE E.

1961. A PRACTICAL EVALUATION OF PNEUMATIC

CONVEYING. West. Feed and Seed, vol.

16, pp. 31-33.

1966. AUTOMATIC PICKUP FOR BAGS, TAGS, AND

CARTONS IN PACKAGING AND LABELING

AGRICULTURAL PRODUCTS. U.S. Dept.

Agr. ARS 42-117, 6 pp. February.

and BRANDENBURG, N. R.

1961. A VELVET-ROLL SEPARATOR FOR SEED TESTING. U.S. Dept. Agr. ARS 42-53, 12

pp. July.

and KLEIN, L. M.

1961. VIBRATOR SEED SEPARATOR. U.S. Dept.

Agr. ARS 42-50, 5 pp. February.

BRANDENBURG, N. R., and BOOSTER, D. E.

1961. SEED CLEANING BY ELECTROSTATIC SEPARATION. Agr. Engin., pp. 22-25. January.

BRANDENBURG, N. R., and JENSEN, LOUISA A.

1965. PHYSICAL PROPERTIES OF SEED. Trans.

Amer. Soc. Agr. Engr. 8(1): 30-32.

HARRINGTON, JAMES F.

1963. THE VALUE OF MOISTURE—RESISTANT CONTAINERS IN VEGETABLE SEED PACKAGING.

Calif. Agr. Expt. Sta. Bui. 792, pp. 1-23.

February.

HAWTHORN, LESLIE R., and POLLARD, LEONARD H.

1954. VEGETABLE AND FLOWER SEED PRODUCTION.

The Blakiston, Co., Inc., 626 pp. New

York.

HENDERSON, S. M., and PERRY, R. L.

1955. AGRICULTURAL PROCESS ENGINEERING.

John Wiley and Sons, Inc., 402 pp. New

York.

HUDSON, WILBUR G.

1949. CONVEYORS AND RELATED EQUIPMENT.

John Wiley and Sons, Inc., 468 pp. New

York.

HURST, W. M., HUMPHRIES, W. R., and MCKEE, ROLAND.

1935. BARREL AND DISK SEED SCARIFIERS. U.S.

Dept. Agr. Cir. 345, 24 pp. March.

MOORE, JAMES M.

1962. PLANT LAYOUT AND DESIGN. The Macmillan Co., 566 pp. New York.

MusiL, ALBINA F.

1963. IDENTIFICATION OF CROP AND WEED SEEDS.

U.S. Dept. Agr. Handb. 219, 171 pp.

PARK, JOSEPH K., and HARMOND, JESSE E.

1967. A VERTICAL ROTATING SCREEN SEPARATOR.

Agr. Engin. 48(5): 275-277. May.

SCHWENDIMAN, JOHN L., SACKMAN, ROLAND R., and

HAFENRICHTER, A. L.

1940. PROCESSING SEED OF GRASSES AND OTHER

PLANTS TO REMOVE AWNS AND APPENDAGES. U.S. Dept. Agr. Cir. 558., 15 pp.

SPRAGUE, GEORGE F.

1955. CORN AND CORN IMPROVEMENT. Academic Press, Inc., 699 pp. New York.

STEFFERUD, ALFRED, ed.

1961. SEEDS. U.S. Dept. Agr. Yearbook, 784

pp.

UNITED STATES PRODUCTION and MARKETING ADMINISTRATION.

1952. TESTING AGRICULTURAL AND VEGETABLE

SEEDS. U.S. Dept. Agr. Handb. 30, 440

pp.

VAUGHAN, C. E., GREGG, B. R., and DELOUCHE, J. C, eds.

1967. SEED PROCESSING AND HANDLING. Miss.

Agr. Expt. Sta. Handb. 1. March.

WELCH, G. BURNS.

1954. SEED PROCESSING EQUIPMENT. Miss. Agr.

Expt. Sta. Bui. 520, 22 pp. December.

WHEELER, W. A., and HILL, D. D.

1957. GRASSLAND SEEDS. D. Van Nostrand Co.,

Inc., 734 pp. New Jersey.
54 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

APPENDIX

Decimal Equivalents of Screen Hole Designations

[Figures shown under "Decimal Equivalents" are equivalents of figures in other columns and are not

arranged as a uniform linear scale. Millimeter screens are available in 0.05 mm. graduations from 0.40

mm. to 25.40 mm. (1 inch)]

Decimal

equivalents

Screen hole designation

Fractions 64ths Millimeters

Decimal Screen hole designation

equivalents Fractions 64ths Millimeters

1.0000

.9844

.9688

.9531

.9375

.9219

.9063

.8906

.8750

.8594

.8438

.8281

.8125

.7969

.7874

.7813

.7656

.7500

.7480

.7344

.7188

.7087

.7031

.6875

.6719

.6693

.6563

.6406

.6299

.6250

.6094

.5938

.5906

.5781

.5625

.5512

.5469

.5313

.5156

.5118

.5000

.4844

.4724

.4688

.4531

.4375

.4331

.4219

.4063

.3937

%

64

63

62

61

60

59

58

57

56

55

54

53

52

51

50

49

48

47'

46

45'

44

43

42

41

40

39

38

37

36

35

34

33

32

31

30

29

28

27'

26

25.40

20.00

19.00

18.00

17.00

16.00

ís'.óó

14.00

13.00

12.00

11.00

10.00

.3906

.3750

.3672

.3594

.3543

.3516

.3438

.3333

.3281

.3203

.3150

.3125

.3047

.2969

.2891

.2852

.2813

.2756

.2734

.2656

.2578

.2500

.2422

.2362

.2344

.2266

.2188

.2165

.2109

.2031

.2000

.1969

.1953

.1875

.1797

.1772

.1719

.1667

.1641

.1575

.1563

.1496

.1484

.1429

.1417

.1406

.1339

.1328

.1260

.1250

i/è

Vè

1/6

1/7

%

25

24

23 ¥2

23

22%

22

21

20%

20

19%

19

18%

18%

18

17%

17

16%

16

15%

Í5'

14%

14

Í3%

13

12%

12

11%

11

10%

10

9

8%

8

9.00

8.00

7.00

6.00

5.50

5.00

4.50

4.00

3.80

3.60

3.40

3.20
MECHANICAL SEED CLEANING AND HANDLING 55

Decimal Screen hole designation

equivalents Fractions 64ths Millimeters

Decimal Screen hole designation

equivalents Fractions 64ths Millimeters

.1181

.1172

.1142

.1133

.1110 %

.1102

.1094

.1063

.1055

.1024 —

.1016

.1000 "i/io

.0984

.0977

.0945 —

.0937

.0909 Vii

.0906

.0898

.0866

.0859

.0833 'i/l2

.0827

.0820

.0787

.0781

.0769 î/is

.0768

.0762

.0748

.0742

.0728

.0714 "i/l4

.0709

.0703

.0689

.0669

.0667 'Vl6

.0664

.0650

.0630

.0625 Vl6

.0610

.0591

.0588 Vl7

7y2

7^4 '

6%

6^

6

'5%

m~

5

'478

^%

'4y2

3.00 .0586

.0571

2.90 ,0556

.0551

.0547

2.80 .0531

.0526

2.70 .0512

.0508

2.60 .0500

.0492

.0476

2.50 .0472

.0469

2.40 0455

.0453

.0435

2.30 .0433

.0430

2.20 .0417

.0413

.0400

2.10 .0394

.0390 2.ÓÓ .0374

.0354

.0352

1.95 .0335

.0315

1.90 .0313

1.85 .0295

.0276

1.80 .0273

.0256

.0236

1.75

1.70 .0234

.0217

.0197

1.65 .0195

.0177

1.60

.0157

1.55 .0156

1.50 .0117

.0078

3%

1/18

Vl9

'1/20

'1/21

'i/22

'1/23

"i/24

25

1/32

— 1.45

3^

Ï.40

1.35

s% 1.30

1.25

3

1.20

1.15

2%

i.io

1.05

21/2

Ï.00

.95

2V^

2

.90

".85

.80

1%

.75

.70

.65

.60

iy2

11/4

.55

.50

.45

1

%

V2

.40
56 AGRICULTURE HANDBOOK 354, U.S. DEPT. OF AGRICULTURE

Glossary

(Names of seeds referred to in this publication)

Common Botanical

Alfalfa Medicago sativa

Alfileria Erodium, cicutarium

Alsike clover Trifolium hybridum

Alta fescue Festuca arundinacea

American sloughgrass Beckmannia syzigachne

Argentine wintergrass __ Stipa spp.

Arizona cottontop Trichachne californica

Asparagus Asparagus officinalis

Bachelors-button Centaurea cyanus

Bahiagrass Paspalum notatum

Barley Hordeum spp.

Barnyardgrass Echinochloa crusgalli

Beans Phaseolus spp.

Beet (garden) Beta vulgaris

Bentgrass Agrostis spp.

Bermudagrass Cynodon dactylon

Bicolor lespedeza Lespedeza bicolor

Big mouse-ear Cerastium vulgatum

Black bindweed (wind

buckwheat) Polygonum convolvulus

Black grama Bouteloua eriopoda

Black medic Medicago lupulina

Bluebunch wheatgrass Agropyron spicatum

Bluegrass Poa

Buckhorn plantain Plantago lanceolata

Buffalograss Buchloe dactyloides

Bulbous barley Hordeum bulbosum

Burclover Medicago hispida

Canada thistle Cirsium arvense

Canada wildrye Elymus canadensis

Cane bluestem Andropogon spp.

Cenchrus (sandbur) Cenchrus pauciflorus

Carrot Daucus carota

Cheat Bromus spp.

Chervil Chaerophyllum spp.

Chewings fescue Festuca rubra var.

commutata

Clover Trifolium spp.

Cocklebur Xanthium pennsylvanicum

Common lespedeza Lespedeza striata

Corn Zea mays

Crimson clover Trifolium incarnatum

Crotalaría Crotalaria spp.

Crownvetch Coronilla varia

Dock Rumex spp.

Dodder Cuscuta spp.

Dogfennel Anthémis cotula

Dutch white clover Trifolium repens

Fescue Festuca spp.

Field bindweed Convolvulus arvensis

Flax Linum usitatissimum

Hairy indigo Indigofera hirsuta

Johnsongrass Sorghum halepense

Kobe lespedeza Lespedeza striata *Kobe'

Korean lespedeza Lespedeza stipulaces

Ladino clover Trifolium repens

Lentils Lens culinaris (Ervum lens)

Lima beans Phaseolus lunatus

Meadow foxtail Alopecurus pratensis

Morning-glory (common) _ Ipomoea purpurea

Mouse-ear (chickweed) __ Stellaria media

Mustard Brassica spp.

Common Botanical

Oats Avena spp.

Onion Allium cepa

Orchardgrass Dactylis glomerata

Path rush Juncus tennis

Peas Pisum sativum

Perennial ryegrass Lolium perenne

Pigweed Amaranthus graecizans

Plantain Plantago spp.

Quackgrass Agropyron repens

Ragweed Ambrosia spp.

Rape Brassica spp.

Rattail fescue Festuca myuros

Red clover Trifolium pratense

Red fescue Festuca rubra

Red sandspurry Spergularia rubra

Rice Oryza sativa

Rough bluegrass Poa trivialis

Ryegrass Lolium spp.

Sericea lespedeza Lespedeza cuneata

Sesame Sesamum indicum (S.

orientale)

Sheep sorrel Rumex acetosella

Shepherds-purse Capsella bursa-pastoris

Siberian wildrye Elymus sibiricus

Silverhair Aira caryophyllea

Snapdragon Anterrhinum spp.

Sorghum Sorghum vutgare

Sorrel Rumex spp.

Sourclover Melilotus indica

Soybeans Glycine max

Squirreltail Sitanion hystrix

Subclover Trifolium subterraneum

Suckling clover Trifolium dubium

Subterranean clover Trifolium subterraneum

Sudangrass Sorghum sudanense

Sugar beet Beta vulgaris var.

saccharifera

Sunflower Helianthus annuus

Sweetclover Melilotus alba

Tall oatgrass Arrhenatherum elatius

Tanglehead Heteropogon contortus

Texas bluegrass Poa arachnifera

Texas wintergrass Stipa leucotricha

Timothy Phleum pratense

Toad rush Juncus bufonius

Tomato Lycopersicon esculentum

Terfoil Lotus

Vernalgrass Anthoxanthum aristatum

Vetch Vicia spp.

Vetchling Lathyrus

Virgins-bower Clematis ligusticifolia

Watercress Rorippa nasturtiumaquaticum (Nasturtium

officinale)

Watergrass Echinochloa crusgalli

Western yellowcress Rorippa sylvestris

Wheat Triticum spp.

White clover Trifolium repens

Whitetop Cardaría

Wild geranium

(cranesbill) Geranium spp.

Wild radish Raphanus raphanistrum

Wild winter peas Lathapus hirsutus

ir U.S. GOVERNMENT PRINTING OFFICE: 0-298-341