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harvester,farm machine that mechanically harvests a crop. Small-grain harvesting has been mechanized to a certain extent since early times. In the modern period the first harvester to gain general acceptance was made by Cyrus McCormick in 1831 (see reaperreaper,
early farm machine drawn by draft animals or tractor and used to harvest grain. Its historical predecessors were the sickle and the cradle scythe, which are still used in some parts of the world.
..... Click the link for more information. ). More recently the combinecombine
, agricultural machine that performs both harvesting and threshing operations. Although it was not widely used until the 1930s, the combine was in existence as early as 1830.
..... Click the link for more information. has been developed for small-grain harvesting. The first mechanical cotton picker was patented in 1850, but, due to the supply of cheap labor, cotton harvesters did not gain acceptance until after World War II. Labor shortages have led to the development of a variety of harvesters adapted for almost every kind of agricultural crop, including tomatoes, grapes, nuts, cucumbers, and root crops, e.g., beets and potatoes. The most common exceptions are certain tree fruits. Nuts and some fruits, such as figs, are allowed to mature and fall to the ground where they are mechanically picked up. Hydraulic shakers have also been developed so that nuts and fruits, such as apricots, grapes, and plums, can be shaken from the tree or vine onto the ground or onto nets or belts. With some plants, such as tomatoes, special varieties have had to be developed that can withstand mechanical contact. The culinary quality of crops developed for mechanical harvesting is presently the cause of concern by consumer groups.
See C. Culpin, Farm Machinery (11th ed. 1986).
(reaper), a machine for mowing agricultural crops and gathering and hauling the cut material to other working elements (combine harvester) or stacking it in the field (a reaper for two-phase harvesting). The first mention of harvesters dates back to Pliny, in the first century A.D.; the development of harvester design dates to the 17th century. According to Academician V. F. Zuev, the Tula armorer Bobrin in 1781 invented a reaper that cut ears and left the straw in the field. In 1833, Zhegalov invented an “ear-reaping machine” that became widely known. Harvesters appeared in England and the USA in the early 19th century. The designers of harvesters continued their efforts to reduce as much as possible the share of manual labor in the harvesting process. A reaper without self-throwing was developed; it cut the grain and placed it on a platform, and a workman then threw it to the ground from time to time. A reaper with a rake mechanism, which automatically threw sacks of grain to the ground, was built in 1856. A binder that automatically tied the cut grain into sheaves was first used in 1867. Windrowers, which cut the stalks, gather them on a platform, and toss them into the field in rows, are in predominant use in the USSR. The USSR is now the world leader in harvester production (in quantity and total swath width). More than 50,000 windrowers and 125,000 harvesters for combines were produced in 1970. In 1973, Soviet agriculture received 63,300 windrowers.
Harvesters for combines are subdivided into platform and screw types. Platform harvesters are used for crops with long stalks. The platform of such a harvester is equipped with a belt or chain-and-cleat conveyor; the conveyor mechanism of a screw harvester is a screw. All modern Soviet and foreign grain-harvesting combines have harvesters with screw conveyors. The screw harvester of a combine can be adapted to harvest various crops (cereals and beans, lupine, and the castor-oil plant), as well as to gather cut stalks from wind-rows by means of a pickup attachment.
Windrowers are tractor-mounted, although trailer wind-rowers also exist. Tractor-mounted harvesters rest on guide shoes in the form of runners, which make the machine readily adaptable to irregularities of terrain and ensure proper cutting height. The purpose, operation, and design of the basic units of a harvester of a combine and a windrower are the same; the difference lies in the arrangement and purpose of the transporting members. The main working parts of a harvester are the dividers, the cutting device, the reel, and the conveyors. A distinction is made between field and internal dividers, as well as dividers for standing and downed plants. A field divider is intended to separate the cut and uncut stalks. An internal divider is usually used as a reference point to steer the unit for maximum use of its swath. To harvest standing crops, harvesters are equipped with rigidly mounted wedge-shaped dividers. For downed crops, a rod-shaped divider is rigidly fastened to the reaper to press the stalks against the ground, or an active divider in the form of a moving knife is used. Harvesters with torpedo-shaped dividers that follow the contour of the terrain and have adjustable stalk deflectors are used for grain with long stalks. The cutting
|Table 1. Main specifications of Soviet harvesters|
|1 Instead of a reel, a cylinder is mounted over the cutting device; it rotates in the opposite direction and has fingers for grasping the flattened stalks from the ground and throwing them onto a cross-mounted conveyor|
|Purpose||For grain||For rice||For seed plants of sugar beet and vegetable crops||For peas|
|Type||Mounted on combine or self-propelled chassis||High-speed trailer type for wheeled tractor||Mounted on caterpillar tractor||Semimounted on wheeled tractor||Mounted on reversible wheeled tractor|
|Width of swath (m)||6||10||4.9||4||4.2||2.1|
|Type of conveyor||Beltless strap-and-cleat||Cleated canvas with straps|
|Operating personnel||Combine||or chassis operator||Tractor driver||Combine operator and tractor driver||Tractor driver||Tractor driver|
|Dimensions in transportation position (m):|
|Output (ha/hr)||up to 4||up to 7||up to 4.15||up to 1.5||up to 1.7||up to 1.2|
device of a harvester cuts the stalks on the scissors principle. Its stationary part consists of cast-iron or steel fingers with opposed plate inserts. The movable part (the knife) is a steel band with attached trapezoidal knife segments. The knife moves back and forth, and the sharp edges of the segments cut the stalks. Stalk lifters are used to raise flattened stalks.
The reel, which is used on most reapers, is intended for guiding the stalks to the cutting device, holding them as they are being cut, cleaning the cutting device, and throwing the stalks onto the platform. A reel with fixed blades is used to harvest standing crops. For operations at more than 10 km/hr the reel is removed, and a cable is stretched over the entire length of the cutting device. When the cut stalks strike the cable, they fall onto the conveyor. A harvester with an eccentric rake reel is used for harvesting flattened grain crops. Instead of wooden cleats it has tubes with spring fingers, which move into the flattened stalks and hold them up until they are cut.
The transporting members of a harvester are the screw and the inclined conveyor (harvester of a combine) or a canvas belt or strap-and-plank conveyor (windrower). In the middle part of the screw or spiral there is a clip mechanism, which takes the cut stalks delivered by the screw and throws them onto the inclined conveyor. The inclined conveyor consists of a chain-and-plank belt. The cleats of the belt take the stalks and force them to the bottom of a chamber and then move them up the inclined plane. A cleated canvas conveyor is used in windrowers to move cut stalks to the discard opening. Wide use is made of beltless conveyors, which consist of several series of straps and cross-mounted short cleats that move the cut stalks along a shaped sheet.
The positions of the working parts in all modern harvesters are controlled hydraulically or, less frequently, mechanically or by other means. The technical specifications of Soviet harvesters are given in Table 1.
The main trends in the advancement of harvester design are an increase in the productivity of the working parts and in the reliability of units and parts, as well as a reduction of expenditures on maintenance.
REFERENCESIzakson, Kh. I. Samokhodnye kombainy SK-3 i SK4, 3rd ed. Moscow, 1963.
Spravochnik konstruktora sel’skokhoziaistvennykh mashin, 2nd ed., vol. 2. Moscow, 1967.
Karpenko, A. N., and A. A. Zelenev. Sel’skokhoziaistvennye mashiny, 2nd ed. Moscow, 1968.
V. I. ZENIKOV