Text 8. Combine harvesters

Practically all grain and seed crops are now harvested with combined harvest-threshers, commonly known as combines. The greatest applications of combines are in harvesting the small grains, soybeans, and corn, but these machines are also used for a wide variety of small acreage or specialty seed crops. The corn is cut by a cutter bar, which differs from that of a mower.

The cutter bar is attached to the table, which carries a pick-up reel to lay the corn on the cutter bar. There are several adjustments, which can be made to the reel relative to the tables speed and position, both vertical and horizontal. After the crop is cut, it is raised by an elevator to the threshing mechanism on the main chassis of the combine.

The thrashing mechanism consists of a large cylinder or drums, heavily constructed and carefully balanced. The cylinder operates in conjunction with the concave. This is a series of curved wires in a frame, fitted below the cylinder. The feeding drum controls the flow of material from the elevator to the cylinder. Any tendency for the straw to wrap round the drum is avoided by the spring-loaded stripper bar, which is set as close as possible to the cylinder.

A stripper drum, mounted just behind the stripper bar, deflects the straw and some grain on to the walkers. These are four long narrow open grids which have raised saw teeth on the edges to grip the straw. They are driven by a pair of crankshafts, one at each end.

The grain with chaff and other impurities is separated by a combination of air blast and sieving. The grain falls through a series of reciprocating sieves and is subject to ft controlled air flow during this. The material which has passed through the concave and that from the straw walkers first move over the chaffer sieve. The size of the openings in this sieve can be adjusted.

The grain sieve and small weed seeds pass through this sieve and are collected by a horizontal grain auger which takes them to a vertical elevator and finally to the tank or bagging unit.