Abstract
In a threshing device, identifying the optimum balance between grain damage and grain loss during threshing is highly relevant while harvesting high-moisture corn ears. The qualitative performance indicators of a threshing device depend on the corn ear properties and process parameters as well as the device's design. Comparative experimental trials of two concaves (control and experimental) of a tangential threshing device were conducted under laboratory conditions by threshing high-moisture corn ears. The control concave's surface line corresponded to a circular arc, whereas that of the experimental concave corresponded to a portion of Archimedes' spiral. The clearance between the crossbars and cylinder rasp bars in the first section of the control concave length increased, whereas in the second section, it decreased. For the experimental concave, the clearance along the entire concave length consistently decreased. The experimental concave yielded approximately half the grain loss of the control during separation in the concave. A rational clearance between the experimental concave crossbars was validated because the portion of damaged grain did not exceed 3% at that point. With clearance l equal to 62.5 mm in the control concave, the grain threshing loss was 2.2%, whereas for the experimental concave, the loss was virtually independent of q and did not exceed the acceptable 0.3% limit. In general, the trials demonstrated that for high-moisture corn ear threshing, the surface line of the concave should correspond to a portion of Archimedes' spiral and the clearances between adjacent crossbars should be 62.5 mm. DOI: http://dx.doi.org/10.5755/j01.mech.24.1.18345
Highlights
The varieties of corn grown in recent times can be classified into two groups: corn for silage and corn for grain
The axial threshing device has a greater throughput compared with a tangential device [2, 3] and is characterised by less damage to the grain [4], combine harvesters with a tangential threshing device tend to be common in more humid climate zones [3]
Our results demonstrated that in view of the shape of the experimental concave, about 2 kW of additional power is required, irrespective of the corn ear feed rate (Fig. 10a)
Summary
The varieties of corn grown in recent times can be classified into two groups: corn for silage and corn for grain. The axial threshing device has a greater throughput compared with a tangential device [2, 3] and is characterised by less damage to the grain [4], combine harvesters with a tangential threshing device tend to be common in more humid climate zones [3]. In countries with a more humid climate, including the Baltic States, corn ears are harvested in the second half of October and sometimes as late as after the first frost, when grain dry matter content is lower than 65% [7]. Mechanical damage to grain at harvest is mostly caused by field threshing, which is largely due to a high moisture content. Studies have shown that minimum grain damage during corn ear threshing is registered at moisture contents between 20% and 22% [10]
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