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 Main subject - july/aug 2003
Harvesting machines with longitudinal separation
Antônio Lilles T. Machado
Professor UFPel
lilles@ufpel.tche.br
Since harvesting is the last stage in the growing process, in this phase all the investments and efforts to reach a good income of farming were executed, except the product retreat. Undoubtedly harvesting machines are very important in the execution of the product retreating task. In this operation, a proper and careful planning, is necessary, but also a deep knowledge on the characteristics of the product to be harvested, and on the machine to be used. Factors such as seed moisture, landscape, and the ability of the operator, are of great importance for the proper losses control , which may occur during the harvesting operation, guaranteeing the success of this phase.
Seed moisture influences, directly, threshing operation, because each crop presents a moisture range in which the operation is better done. As it is impossible to accomplish the whole harvest with seeds in the ideal threshing moisture, after seeing the occurrence of limitation, as much of economical order as of operational capacity of the machines' fleet, usually, the harvest begins with the seeds presenting moisture above the levels considered ideals. But, we also should take into account that seed moisture decreases along the day, having as a consequence, the need to establish new adjustments.
In order to avoid losses during harvesting, many aspects must be considered, as maturation uniformity, plant size, defoliation and land declivity. The success begins with the choice of the variety that will be cultivated, passing through important operations, such as systematization of the land, preparation of the soil, sowing and crop treatments.
Modern harvesting machines demand ability of the operators, machines are complex and the operators must be qualified to carry out several tasks, which are: machine conduction, their adjustments, verification of possible flaws, maintenance and control of electronic equipment. Such factors evidence the need of a calm and observer operator and, at the same time, dynamic and qualified.
Therefore, to obtain a correct regulation of the harvesting machine, what will certainly lead to a low level of harvesting losses, it is important that the operator and even the farming administrator have a deep knowledge on the constructive characteristics, their different systems and ways to adapt its regulation to the crop that will be harvested.
Until the IX century, the harvest was done manually and threshing used to be executed with manual flails or by animal trampling. In the half of the last century, the first cutter was invented, pulled by horses and the first threshing factory was settled in the USA. In 1930, appeared the combined machines that cut and threshed at the same time. In the year 1938, self-driven harvesting machines started being used in the same way we do nowadays, in other words, doing the 5 basic operations: the cut, threshing, separation, cleaning, and storage. Until 1977, the threshing system of the harvest machines remained the same (transversal flow), but that year with the harvesting machine model 1440 from International Harvester, a new concept was introduced, called longitudinal flow system, popularly known as axial flow, in which the cylinder and the concave are usually positioned longitudinally to the machine, so that the material to be threshed moves in parallel direction to the axis of the threshing cylinder (usually nominated as rotor).
During mechanical harvesting, the operations developed in the threshing and in the separation unit, have the function of hulling the grains from the plant parts, separating them from the rest of the crop (stem, ears, green beans, panicles and leaves). The separation percentage in this unit is usually between 60% and 90%, meaning that almost all grains are separated from remains of the crop in the threshing and separation unit.
In the system of longitudinal flow, the rotor - one or two, according to the manufacturer - provided with fins in its periphery, forming a type of helicoids (snail). The concave is composed by a fixed cylinder, or half of this, of perforated foil, which surrounds the rotor, total or partially. As the material (grain + straw) is being moved inside the system, the grains are separated from the straw passing through the holes of the concave. The straw is kept for a longer period than the grains, being released to the exterior of the machine in the opposite extremity of the feeding.
After leaving the system, the grains are released in a column of air and/or on sieves, for final cleaning. Machines endowed with these systems do not possess separation units (bag-straws), because the mechanism accomplishes the threshing operation, separation and unloading of the straw at the same time. This fact, by itself, already provides a reduction of grain losses, when compared to the conventional system. In addition, it provides the construction of machines with less movable pieces, therefore simpler, lighter and shorter.
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