Combine

A combine is a large, self-propelled agricultural machine used to harvest grain crops such as wheat, corn, soybeans, milo, rape-seed, and rice. As its name suggests, the combine performs two, and sometimes more, basic functions of harvesting: first it reaps (cuts) the crop, and then it threshes it, separating the kernels of grain from the seed coverings and other debris(chaff). Some combines may also bale the straw that remains after threshing; the machines can also be equipped to pick cotton.

Combines are very large pieces of equipment. The operator sits atop the machine in a high cab with full-length windows for a good view. A long, square body, topped with a grain tank and a chute through which the threshed grain can be removed from it, rides on huge, front-mounted drive wheels and smaller, skinnier rear steering wheels. A turbo-charged diesel engine propels the combine and provides power for the header, threshing cylinder, cleaning system, and augers that move the grain from the header through the threshing cylinder to the grain tank and then out to a waiting truck.

As a combine progresses along rows of grain, its front component—the reel, a large, hexagonal metal piece set parallel to the ground—rotates, sweeping the grain stalks up into the machine. Different reel designs are required to harvest different crops. For example, while a wheat reel shunts the stalks into a cutting bar that slices them just below the heads of ripe grain, a corn reel strips the ears of corn from the stalks, leaving them flattened against the ground. Today, farmers can choose from many different types and sizes of header models. The explanation below describes the progress of wheat through a combine.

Once inside the body of the combine, the stalks are thrust against the cutter bar, a component that looks something like a comb. With the "tines" of the comb catching the stalks, a knife-like implement slices them near ground level. The stalks are then transported up onto an elevator by means of a stalk auger. Large metal cylinders, augurs feature screw-like projections that trap the grain so that it can be transported. The stalk augur, set parallel to the ground, sweeps the cut stalks onto the elevator—a pair of rollers fitted with conveyor belts that carry the grain upwards into the heart of the combine, the threshing cylinder. This cylinder is a large roller with protuberances. Rotating at high speed over a slitted, half-moon-shaped trough (the concave), the cylinder separates the kernels of grain from the heads of the stalks.

Once separated from the kernels, the stalks are swept up by the bars of the threshing cylinder, which deposit them on the first of a series of straw walkers. These are large, slightly overlapping, square platforms that gradually descend toward the rear of the combine. Vibrating slightly, the first walker causes the straw to drop onto the second, and the second shakes until the straw drops onto the third and lowest, at which point it is either dropped through a chute onto the ground or, in a baling machine, packed into bales. Unlike the stalks of grain, the kernels are small enough to fall through the slits in the concave and are caught in the grain pan that lies beneath it. The grain pan vibrates, shaking the kernels, the chaff, and some heads that made it through the threshing cylinder intact into a set of vibrating sieves.

The vibrations cause the kernels to fall through the sieves, while the unthreshed heads are trapped. A fan adjacent to the sieves blows air across them, causing the chaff (which is very light) to blow backwards out the rear of the combine. The unthreshed heads are then routed, via another auger, into the tailings elevator, which transports them back into the threshing cylinder. Meanwhile, the kernels fall into the grain augur and are transported up into the grain elevator, which deposits them in the grain tank. Yet another augur, the unloading augur, is inserted into the grain tank, and grain can be removed from the tank through it.

The combine was developed during the 1800s, when many agricultural processes were being automated. Beginning as early as 1826, individual inventors and businessmen turned out hundreds of contraptions to aid farmers in harvesting grains. However, these early machines performed only one of two important functions: they were either reapers, which cut the stalks of grain, or threshers, which separated the grain from the chaff.

The first reaper was designed by a Scottish minister, Patrick Bell, in 1826. Of the many others developed during the mid-1800s, the most successful machine was created by an American, Robert McCormick, and perfected by his more famous son, Cyrus. Robert McCormick worked on various reaper designs from 1809 until 1831, and Cyrus McCormick, continuing his father's work, sold the first McCormick Reaper in 1839.

Threshing machines, to separate and clean the kernels of grain, were first assembled in the late 1700s and were in widespread use in England and Scotland by the 1830s. Over the next two decades, several Americans invented threshing machines. The most successful were Hiram and John Pitts, brothers who sold the first "Chicago Pitts" thresher in 1852. Jerome Increase Case also produced an enduringly popular thresher: founded in 1844, the company that bears his name continues to thrive today.

The first farm machine that could do the work of both a reaper and a thresher was patented in 1828, although the first model was not sold until 1838. Both huge and cumbersome, the machine required twenty horses to pull it. For this reason, combines were not used in large numbers until the early twentieth century, when refinements had rendered them easier to use.

Today, modern combines are the most complicated machines produced on an assembly line. While a passenger automobile is made up of 6,000 parts, a combine comprises over 17,000. This complexity is reflected in the price: a single combine can cost as much as $100,000. Today, there are two major combine manufacturers in the United States. Both firms, John Deere and J. I. Case, have large, modern manufacturing plants that sit next to one another along the Mississippi River in East Moline, Illinois, and in 1990, they sold about 11,500 combines in the United States and Canada.