Using Gravity to Sort Grain

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During harvest, grain and seed product will add in rocks, dirt or low quality seed. It's all mixed together and farmers need a way to separate it out.

At an Iowa State University Workshop, Seed Science Center Seed Conditioning Specialist Alan Gaul leads a class on the century-old technology called a gravity separator.

"A gravity separator is basically a more precise means of density separation." Gaul says, "Basically we have a layer of seed that's at least three to five seeds deep. Air is introduced, it starts to lift the seed. And at that point, the seed is basically floating."

The Gravity separator angles one side up and shakes the grain, "The heavy seed sinks to the bottom and the light seed floats on the top of the layer. The heavy materials make contact with the deck, and the deck is shaking in such a way that anything touching the deck actually works its way up the hill. Since we're at least three seeds deep. The product in the top layer is now more or less isolated from the effect of the shape. and since the deck is sloped it tends to run down the hill pulled down by gravity."

The air pushing light grain down and the machine shaking heavy grain up leads to the grain sorting, Gaul says, "At this point we wind up with a range from the lightest product to the heaviest product. Typically the light is undesirable and the heaviest could potentially have rocks, but typically it's thought to be the better seed. And then the difficult part is deciding what we're going to keep and what we're throwing away."

Gaul says a gravity separator can make three to six fractions of weight measurement depending on the application.

He adds technology like this improves the quality of products farmers and consumers use.