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a machine for separating seeds from the ears, tassels, heads, and cobs of agricultural plants.
The introduction of threshers began in the 17th century. The first threshing device in Russia was developed by the artisans Andrei Terent’ev and Moisei Krik in 1655. A rotating threshing drum with three-sided beaters that was partially encircled by a cylindrical casing was manufactured in Scotland in the late 18th century. The threshing device and beater drum were further refined and later used in threshers and grain-harvesting combines. In the first half of the 19th century a threshing device with a toothed drum and concave was proposed. This combination was the basis for creation of the thresher and later was used in combines with toothed drums. All the parts of the thresher except the drum were made of wood. The first threshers were operated manually. The production of threshers powered by horses began in Moscow in 1809. The first threshers only threshed the crop; they did not separate the grain from the chaff. With the introduction of the straw separator, which divided the products of threshing into straw and grain, semicompound threshers were created; with the installation of cleaners, they became finisher threshers, or separators. The latter produce high-quality market grain and are driven by steam or internal-combustion engines or electric motors.
The production of grain separators in the USSR began in 1924. The separators had a beater threshing device, a straw separator, three grain cleaners, and additional devices to feed the crop to the threshing device and remove the products. With the transition to combine harvesting in the USSR in 1950–54, the production of grain separators was stopped. Corn shellers and flax, hemp, kenaf, vegetable, and stalk threshers are used in the USSR to thresh other crops.
A corn sheller (Figure 1) threshes the ears, separates the cobs, and cleans light impurities from the grain. The working parts of the thresher are driven by a 7.5-kilowatt (kW) electric motor. The loading elevator feeds ears from the receiving bin into the threshing device, which consists of a toothed drum and a cylindrical grate concave. The threshed grain passes through the holes of the concave and falls onto the cleaning screen, where a ventilator blows light impurities out of the material. The cleaned grain is transferred to containers by an elevator. An ear conveyor throws the cobs to the side of the sheller. The productivity of the machine is up to 3 tons per hr.
Flax, hemp, and kenaf threshers are similar in their functional diagrams but differ somewhat in design. These types of threshers comb and thresh sheaves of bast crops, grind the heap, and clean the seeds. To perform these operations, the threshers have a gripping conveyor with platforms for feeding and removing the combed sheaves, combing and rubbing devices, a screen (a sieve pan with sieves and a ventilator), a seed elevator, and transmission mechanisms. The threshers are driven by power takeoff shafts from the tractor engine. Their productivity for bulk sheaf hemp is up to 1.4 tons per hr; for kenaf, up to 2.3 tons per hr.
A vegetable thresher (see Figure 2) is designed to thresh seed-bearing plants and partially remove the seeds of vegetable crops. It can thresh grain crops and thresh and remove seeds from grasses. During threshing, the seed-bearing plants are placed manually on the feed conveyor, which carries them to the blades of the grader, and then the beater drives the heap into the threshing apparatus, which consists of a beater drum and a grate concave. After threshing, the heap passes into the straw separator. Some of the seeds and their shells, after passing through the openings of the concave and straw separator, reach the rubbing device, which rubs out the shells and throws the threshed
material onto the sorter screens, where a stream of air from the ventilator separates waste material from the seeds. The clean seeds pass through the openings of the screens and fall onto a conveyor, which drops them into containers. For threshing grain crops, a shaking board and oscillating feeder are used instead of the blade grader, and the grate-type straw separator is replaced by an oscillating separator. Threshers produced in the USSR are driven by a 10-kW electric motor and have a productivity up to 500 kg/hr for threshing seed-bearing vegetable crops and up to 3,000 kg/hr for threshing grain crops.
Stalk threshers (see Figure 3) are designed to produce undamaged threshed stalks of ear grain crops for use in making mats to cover hothouses and clamps for sugar beets, potatoes, and table root crops. The main parts of such threshers are a gripping conveyor, a stripping cylinder, a mobile frame with six beater drums, a conveyor for threshed material, and a 4.5-kW electric motor. The gripping conveyor feeds a hand-graded layer of stalks into the threshing chamber. The frame, together with the rotating beater drums, moves back and forth and threshes the ears. The length of the stroke of the frame and the distance between the upper and lower drums can be regulated. The strip-ping cylinder removes the tangled stalks from the thick ends of the plants. The productivity of this type of machine is up to 1.2 tons per hr.