A combine harvester is a machine used to harvest grains like wheat, rye, barley, oats, corn, flax and soybeans. Instead of using separate machines for reaping, threshing and winnowing the grain, the harvester combines all these functions into one machine.
The wide header at the front of the harvester gathers the grain into the combine. The reel moves it towards the cutter bar, where it is sliced off at the base. The grain then travels up a conveyor to the threshing drum, where the grains are separated from the stalks. A collecting tank gathers the grain as it falls through sieves, and straw walkers carry the chaff towards the back of the harvester. As the grain tank fills, it must be emptied into a trailer through a side pipe called an unloader. The chaff is either spread out over the field or baled up for later use.
Different removable heads are designed for the various types of crops. Standard grain platforms are generally used for wheat, while flex platforms that can cut closer to the ground are used for soybeans. Corn heads have snap rolls that remove the ear from the stalk and leaves. Dummy heads pick up crops that have already been cut. Special combines with mud tracks are able to harvest rice. For hillsides, combines are fitted with special hydraulic systems that enable them to level out while they are harvesting.