Combine harvester

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The combine harvester, or simply combine, is a machine that "combines" the tasks of harvesting, threshing, and cleaning grain plants. The desired result is the seed or grain (including corn, soybeans, flax, oats, wheat, or rye among others); a byproduct is loose straw, the remaining husk of the plant with all nutrients removed.

Contents 1 History 2 Combine Process 2.1 Header 2.2 Conventional combine 2.3 Sidehill levelling 2.4 Maintaining threshing speed 2.5 The Threshing Process 2.6 Rotary vs. Conventional Design 3 Combine harvesters in popular culture 4 Literature 5 See Also 6 External links

History

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 power. Tractor-drawn, PTO-powered 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 eccentric 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 by Case IH in the late 1970s. 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.

Combine Process

Header

Combines 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 separate wheat headers, so as to reduce overall costs.

Dummy heads or pick-up headers 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 or swaths. This is particularly useful in northern climates such as western Canada where swathing kills weeds resulting in a faster dry down.

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. Some combines, particularly pull type, have tires with a diamond tread which prevents sinking in mud.

Conventional combine

The cut crop is sent up the feeder house by a series of chains, then dropped into the threshing cylinder. The cylinder consists of rings to which grooved steel bars are fitted. These bars thresh or separate the grain and chaff from the straw.

Sidehill levelling

An interesting technology is in use in the Palouse region of the Pacific Northwest of the United States 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 efficiently 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

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.

Self-propelled combines started with standard manual transmissions that provided one speed based on input rpm. Deficiencies were noted and in the early 1950's combines were equipped with what John Deere called the "Variable Speed Drive". This was simply a variable width shive controlled by spring and hydraulic pressures. This shive was attached to the input shaft of the transmission. A standard 4 speed manual transmission was still used in this drive system. The operator would select a gear, typically 3rd. An extra control was provided to the operator to allow him to speed up and slow down the machine within the limits provided by the variable speed drive system. By decreasing the width of the shive on the input shaft of the transmission, the belt would ride higher in the groove. This slowed the rotating speed on the input shaft of the transmission, thus slowing the ground speed for that gear. A clutch was still provided to allow the operator to stop the machine and change transmission gears.

Later, as hydraulic technology improved, hydrostatic transmissions were introduced by Versatile Mfg for use on swathers but later this technology was applied to combines as well. This drive retained the 4 speed manual transmission as before, but this time used a system of hydraulic pumps and motors to drive the input shaft of the transmission. This system is called a Hydrostatic drive system. The engine turns the hydraulic pump capable of high flow rates at up to 4000 psi. This pressure is then directed to the hydraulic motor that is connected to the input shaft of the transmission. The operator is provided with a lever in the cab that allows for the control of the hydraulic motors ability to use the energy provided by the pump. By adjusting the swash plate in the motor, the stroke of its pistons are changed. If the swash plate is set to neutral, the pistons do not move in their bores and no rotation is allowed, thus the machine does not move. By moving the lever, the swash plate moves its attached pistons forward, thus allowing them to move within the bore and causing the motor to turn. This provides an infinitely variable speed control from 0 ground speed to what ever the maximum speed is allowed by the gear selection of the transmission. The standard clutch was removed from this drive system as it was no longer needed.

Most if not all modern combines are equipped with hydrostatic drives. These are larger versions of the same system used in consumer and commercial lawn mowers that most are familiar with today. In fact, it was the downsizing of the combine drive system that placed these drive systems into mowers and other machines.

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 threshing cylinder. This consists of a series of horizontalrasp 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 or rub bars pull the crop through concaved grates that separate the grain and chaff from the straw. The grain heads fall through the fixed concaves onto the sieves. The straw exits the top of the concave onto the straw walkers.

Since the International 1440 and 1460 came out in the 1970s, combines have rotors in place of conventional cylinders. A rotor is a long, longitudily mounted rotating cylinder with plates similar to rub bars.

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 mounted at an angle which shakes. The holes in the top sieve are set larger than the holes in the bottom sieve. While straw is carried to the rear, crop and weed seeds, as well as chaff, fall onto the second sieves, where chaff and crop fall though and are blown out by a fan. The crop is carried to the elevator which carries it into the hopper. 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.)

Heavy material, e.g., unthreshed 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 out the rear of the combine. It can then be baled for cattle bedding or spread by two rotating straw spreaders with rubber arms. Most modern combines are equipped with a straw spreader.

Rotary vs. Conventional Design

For a considerable time, combine harvesters used the conventional design, which used a rotating cylinder at the front-end which knocked the seeds out of the heads, and then used the rest of the machine to separate the straw from the chaff, and the chaff from the grain.

In the decades before the widespread adoption of the rotary combine in the late seventies, several inventors had pioneered designs which relied more on centrifugal force for grain separation and less on gravity alone. By the early eighties, most major manufacturers had settled on a "walkerless" design with much larger threshing cylinders to do most of the work. Advantages were faster grain harvesting and gentler treatment of fragile seeds, which were often cracked by the faster rotational speeds of conventional combine threshing cylinders.

It was the disadvantages of the rotary combine (which were increased power requirements and pulverization of the straw by-product) which prompted a resurgence of conventional combines in the late nineties. Perhaps overlooked, but nonetheless true, when the large engines that were utilized to power the rotary machines were employed in conventional machines, the two types of machines delivered similar production capacities. Also, research was beginning to show that incorporating above-ground crop residue (straw) into the soil is less useful for rebuilding soil fertility than previously believed. This meant that working pulverized straw into the soil became more of a hindrance than a benefit. An increase in feedlot beef production also created a higher demand for straw as fodder. Conventional combines, which use straw walkers, preserve the quality of straw and allow it to be baled and removed from the field.

Combine harvesters in popular culture

• British Scrumpy and Western group The Wurzels had a number one hit in 1976 with "The Combine Harvester". A parody of the hit song by Melanie, "Brand New Key", 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.
  • This song was used in soundtrack for British horror movie Evil Aliens, involving plot point of chasing and chopping humanoid aliens through wheat field, with combine harvester.

• The film Twister depicts a typical tornado tearing though a small, American, mid-western town. The tornado picks up and drops an International Harvester (IH) 1688 combine in front of the main characters' pickup truck as they race to gain distance on the tornado.

• The film Son in Law features a combine with a fictional joystick control system. Real combines have marked controls, including pedals (two brake pedals for tighter turning) and a steering wheel, however some earlier models are steered using wheel brakes and a "T" bar.

• The video game Body Harvest features a combine in the Russia level, and is the only way to kill zombies for good. A farmer gives the player the keys to his combine as the zombies ate all of his shotgun shells.

• The video game Grand Theft Auto: San Andreas features a mission ("Body Harvest") in which the player character is required to steal a combine harvester from a farm. Using a combine harvester itself to run over people head-on would, clearly, cut the victims into pieces, and their body parts are deposited at the rear.

• The Disney/Pixar film Cars features an angry anthropomorphized harvester (named Frank) chasing Mater and Lightning after the two were "tractor tipping" (which is similar to cow tipping). The tractors in the film were the film's equivalent of cows, and the harvester is the parallel of an angry bull. Later, in a nightmare that Lightning has after the run-in with Frank, Lightning, The King, and Chick (who gets shredded), are beaten by Frank. The machine featured is red, which is the color code of American manufacturer Case IH; a brand of FIAT's Case-New Holland family.

Literature

• Graeme R. Quick, Wesley F. Buchele: The Grain Harvesters. American Society of Agricultural Engineers, St. Joseph/Michigan 1978, ISBN 0-916150-13-5

See Also

• Museum of Scottish Country Life Largest collection of Combine Harvesters in Europe.

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