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. The combine was patented in 1834 by Hiram Moore, the same year as Cyrus McCormick was granted a patent on the mechanical reaper.
Early combines, some of them quite large, were drawn by horse or mule teams and used a bull wheel to provide mechanical power. Tractorrawn, PTOowered 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 powerful fan. Rotary combines were introduced in the late 1970's. About this time on-board electronics were introduced to measure threshing efficiency. This new instrumentation allowed operators to get better grain yields by optimizing ground speed and other operating parameters.
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Crop heads
A combine harvesting cornCombines are equipped with removable heads (called headers) that are designed for particular crops. The standard head, sometimes called a grain platform (or platform header), 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. On many farms, platform headers are used to cut wheat, instead of seperate wheat headers, so as to reduce overall costs.
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. Rahco.com, 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.
Currently sidehill levelling is on the decline with the advent of huge modern machines which are more stable due to their width. These modern combines use the rotary grain separator which makes leveling less critical. Most combines on the Palouse are equipped with dual drive wheels on each side to stabilize the machine.
Maintaining threshing speed
Claas Lexion 570Another 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.
The Threshing Process
Despite great advances mechanically and in computer control, the basic operation of the combine harvester has remained unchanged almost since it was invented.
First of all the header, described above, cuts the crop and feeds it into the concave. This consists of a series of rasp bars fixed across the path of the crop and in the shape of a quarter cylinder, guiding the crop upwards through a 90 degree turn. Moving rasp bars pull the crop through the concave and separate the grain from the straw. The grain heads fall through the fixed rasp bars onto the sieves. The straw exits the top of the concave onto the straw walkers.
There are usually two sieves, one above the other. Each is a flat metal plate with holes set according to the size of the grain. The holes in the top sieve are set larger than the holes in the bottom sieve. Anything that falls through the bottom sieve is assumed to be grain, and is transported to the grain tank.
The sieves are mounted at a slight incline and shake, further separating the grain. A powerful fan blows from the front of the sives to remove chaff (wheat) or haynes (barley). If the fan is set too high it will blow grain off the back of the sives and out of the combine. If it is set too low then chaff/haynes will be present in the grain.
Heavy material, e.g., unthreashed heads, fall off the front of the sieves and are returned to the concave for re-threshing.
The straw walkers are located above the sieves, and also have holes in them. Any grain remaining attached to the straw is shaken off and falls onto the top sieve.
When the straw reaches the end of the walkers it falls to the floor. A straw chopper may be fitted if the straw is unwanted.
Setting the concave clearance, fan speed, and sieve size is critical to ensure that the crop is threshed properly, the grain is clean of debris, and that all of the grain entering the machine reaches the grain tank. ( Observe, for example, that when travelling uphill the fan speed must be reduced to account for the shallower gradient of the sieves.)
Combine harvesters in popular culture
- British Scrumpy and Western group The Wurzels had a number one hit in 1976 with The Combine Harvester. It takes the form of a love song from the point-of-view of a farmer who proposes marriage to his girlfriend, offering to give her the key to the "brand-new combine harvester" to use on her 43 acres of arable land.
- Grand Theft Auto: San Andreas features combine harvesters. CJ had to use one to bring to his friend on some mission.
- The movie Son In Law features a combine with a fictional joystick control system. Real combines have marked controls, including pedels and a steering wheel.
- Body Harvest features a combine, in the Russia level, which is the only way to kill the zombies for good. The farmer gives you the keys to his combine because the zombies ate all of his shotgun shells.
External links
- Pictures of combines with corn and wheat heads
- History of Sunshine Harvesters - Museum of Victoria, Australia
- The IH 151 an early levelling machine
- Pictures of Gleaner levelling combines
- Excellent picture of a levelling John Deere with the header removed to show the modified undercarriage and extreme leveling ability as well as pictures of the region
