Combine harvester

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A postage stamp of a combine honors Russian agriculture.

The combine harvester, or simply combine, is a machine that harvests, threshes, and cleans grain plants. The desired result is the seed (such as canola or flax) or grain (such as oats, wheat, or rye); a byproduct is loose straw, the remaining husk of the plant with all nutrients removed. A great advance upon the threshing machine and the reaper, the combine was developed by Australian farmer Hugh Victor McKay in 1882. By 1885 the 'Sunshine Harvester' was in full production and by 1891 the units were being exported across the world.

Early combines, some of them quite large, were drawn by horse or mule teams and used a bull wheel to provide mechanical power. Tractor-drawn, PTO ( combines were used for a time. These combines used a shaker to separate the grain from the chaff and straw-walkers (grates with small teeth on an excentric shaft)to eject the straw while retaining the grain. Tractor drawn combines evolved to have separate gas or diesel engines to power the grain separation. Today's combines are self-propelled and use diesel engines for power. A significant advance in the design of combines was the rotary design. Straw and grain were separated by use of a powerfull fan. Rotary combines were introduced in the late 1970's. About this time on-board electronics were introduced to measure threshing efficency. This new instumentation allowed operators to get better grain yields by optimizing ground speed and other operating parameters.


Crop heads

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A John Deere 9410 Combine set to harvest Oats.
A combine harvesting corn
A combine harvesting corn

Combines are equipped with removable heads that are designed for particular crops. The standard head, sometimes called a grain platform, is equipped with a sickle bar mower, and features a revolving reel with metal or plastic teeth to cause the cut crop to fall into the head. A cross auger then pulls the crop into the throat. The grain platform is used for many crops, including grain, legumes, and many seed crops.

Wheat heads are similar except that the reel is not equipped with teeth. Some wheat heads, called "draper" heads, use a fabric or rubber apron instead of a cross auger. Draper heads keep the crop orientation uniform, feeding grain headfirst into the throat, which allows slightly more efficient threshing.

Dummy heads feature spring-tined pickups, usually attached to a heavy rubber belt. They are used for crops that have already been cut and placed in windrows.

While a grain platform can be used for corn, a specialized corn head is ordinarily used instead. The corn head is equipped with snap rolls that strip the stalk and leaf away from the ear, so that only the ear (and husk) enter the throat. This improves efficiency dramatically since so much less material must go through the cylinder. The corn head can be recognized by the presence of points between each row.

Occasionally rowcrop heads are seen that function like a grain platform, but have points between rows like a corn head. These are used to reduce the amount of weed seed picked up when harvesting small grains.

Self propelled Gleaner combines could be fitted with special tracks instead of tires to assist in harvesting rice.

Sidehill levelling

An interesting technology is in use in the Palouse region of the Pacific Northwest in which the combine is retrofitted with a hydraulic sidehill levelling system. This allows the combine to harvest the incredibly steep but fertile soil in the region. Hillsides can be as steep as a 50% slope. Gleaner, Case/International Harvester, John Deere and others all have made combines with this sidehill levelling system and local machine shops have fabricated them as an aftermarket add on. Linked pictures below show the technology.

The first levelling technology was Developed by Holt Co., a California firm, in 1891. Ag Power Mag, Sept 2001 ( Many Years later modern levelling came into being with the invention and patent of a level sensitive mercury switch system invented by Raymond (Haywire) Hanson in 1946., 2005 ( Hanson's company Rahco, Inc. still produces levelling systems exclusively for John Deere combines.

Sidehill levelling has several advantages. Primary among them is an increased threshing efficiency on sidehills. Without levelling grain and chaff slide to one side of separator and come through the machine in a large ball rather than being separated, dumping large amounts of grain on the ground. By keeping the machinery level the straw-walker is able to operate more efficently and this problem is eliminated for more efficient threshing. Case International produced the 453 ( combine which leveled both side-to-side and front-to-back thus enabling efficient threshing whether on a sidehill or climbing a hill head on.

Secondarily, levelling changes a combine's center of gravity relative to the hill and allows the combine to harvest along the contour of a hill without tipping over. The danger is very real on the steeper slopes of the region and it is not uncommon for combines to roll on extremely steep hills. See this picture (

Currently sidehill levelling is on the decline with the advent of huge modern machines which are more stable due to their width. Still, most combines on the Palouse are equipped with dual drive wheels on each side to stabilize the machine.

Maintaining threshing speed

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Claas Lexion 570

Another technology that is sometimes used on combines is a continuously variable transmission. This allows the ground speed of the machine to be varied while maintaining a constant engine and threshing speed. It is desirable to keep the threshing speed since the machine will typically have been adjusted to operate best at a certain speed. As part of the threshing operation for small grains, a fan blows the husks from the grains. If the fan blows too much, some grain is blown out with the chaff and yield is lost. If the fan blows too little, husks remain in with the grain, which also is undesirable.

External link

de:Mähdrescher fr:Moissonneuse-batteuse sv:skördetröska


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