A debearding machine has been used to remove cotton webbing from Merion bluegrass, which was 98 percent pure when it was cleaned properly. The debearder also is used to clip seed oats, debeard barley, thresh whitecaps in wheat, break apart grass seed doubles, remove awns and beards, hull some grass seeds, and polish seeds.

Another precleaning unit that is effective in removing seed hairs and fuzz is the tumbling pebble mill. It has a drum rotating about a shaft inserted off center at opposite ends. The mill is loaded with seed and smooth, half-inch pebbles and turned at a slow speed until the rubbing action of the pebbles rolls the fuzz from the seeds into small, round balls. The mixture of pebbles, seeds, and matted fuzz is then run over a scalper to remove the pebbles. The pebble mill is used for removing cobwebby hairs from bluegrass and similar seeds.

Some seeds like black grama, which have fine, flexible, hairlike awns that do not break off when run through a hammermill or debearder, lend themselves to differential burning. The seeds are dropped through a flame, and an instant flashing of awns takes place. The burn exposure must be short to avoid damaging the seeds by excessive heat. Seeds of black grama that were deawned in this way were cleaned and seeded easily.

SEEDS of some native grasses of the Great Plains need little processing.

Arizona cottontop, for example, is harvested by heading and then is fine chopped in a hammermill or similar unit. The seed material is reduced in size, and special planting equipment can distribute it without removal of the fuzz or additional cleaning. The same treatment is given other grasses, such as tanglehead, Trichloris species, and cane bluestem.

A green forage harvester is used in Texas wintergrass to harvest and chop the seed material for planting in one operation. With grasses such as big cenchrus and Argentine wintergrass, both of which require precleaning to remove spines and awns, the forage harvester is used for the harvest and does part of the job otherwise required of the hammermill in processing.

Some seeds with cottonlike stylets, such as Texas bluegrass, defy processing with hammermills, debearders, and similar devices or planting with regular grass drills. A new development is pelleting. All plant material, including seeds, stems, leaves, and trash, are mixed with a binder, like cornstarch, silvicon, or krilium, and water and extruded through a quarter-inch hole in a die. Pellets made with cornstarch can be planted easily with a corn planter or cotton planter. Silvicon-binder pellets crumble and can be planted easily with a range seeder.

ALMOST EVERY KIND of seed must be cleaned over an air-screen cleaner before any other separations can be attempted. Many kinds can be cleaned completely on this machine and made into a finished product. The air-screen cleaner therefore is known as the basic equipment in cleaning plants. In this unit, screens take advantage of a difference in size and shape, and moving air senses a difference in surface area and density in seeds so that a separation can be made.

A seed mixture, directly from the combine or from any of the precleaning units, flows by gravity from a hopper to the feeder, which meters it into an airstream. Light, chaffy material is blown out, and the remaining seeds are distributed uniformly over the top screen. In a typical operation of a four-screen machine, the top screen scalps or removes large material. The second screen sizes or drops particles smaller than the seeds. The third screen scalps the seeds more closely. The fourth performs a final grading. The graded seeds then pass through a second airstream, which lifts light seeds and chaff into the trash bin while dropping the plump, heavy, crop seeds into a clean chute.

Top screens have openings larger than the seeds to be cleaned. Bottom screens have openings smaller than the seeds. The size of air-screen cleaners varies from the small, two-screen farm model to the modern precision unit, which is so arranged that several top and several bottom screens can be used in one cleaning operation.

Large cleaners, used in commercial seed-cleaning plants, subject seeds to as many as seven screens and three air separations in one pass through the machine and have capacities up to 6 thousand pounds of seeds an hour.

The air-screen cleaner uses perforated metal or wire mesh screens. The perforated metal screens are available with round, slotted, or triangular openings. Round-hole sizes range from 0.039 to 1.250 inches in diameter; slotted holes, from 0.039 by 0.500 to 0.375 by 0.750 inch; and triangular, from 0.078 to 0.187 inch in length of each side.

Screens of wire mesh are woven with square or rectangular openings in sizes that range from 0.0117 to 0.286 inch.

Air-screen cleaners with two top screens generally have one round-hole screen and one slotted. The first bottom screen should be slotted; the second should have round, square, or triangular holes.

Each screen is slanted at a slight angle to cause the seeds to roll or slide downward over the openings. The pitch of each screen is adjustable to facilitate accurate separations.

The mechanism that shakes the screens can be adjusted to shake them slowly or rapidly. The experienced operator can adjust the screen shake so the seeds will slide smoothly over the screen or be agitated by the screen motion, as may be required.

The rate of feed can be adjusted to keep the screens operating at nearly full capacity. The airflow in each air separation is usually regulated by means of dampers in the air ducts.

Commercial cleaners have cleaning brushes that travel under the screens to prevent seed from lodging in its openings. Some have mechanical screen bumpers to assist in dislodging seed.