The empirical model of grain separation on straw walker

Abstract

Straw walker is used in modern combine-harvesters because they are universal and maintain grain and straw quality but they are sensitive to combine inclinations and to uneven MOG (material other than grain) feedrate and their moisture. The objective of the present work was to investigate grain separation through the straw and the screens of four straw walkers. Three walker screens of various designs and active separation area have been used during the tests. The inclination angle of walker screens (from 6° to 36°), the straw feedrate onto the straw walker (from 0.5 to 4.0 kg s-1), and the crankshafts rotation speed (from 185 to 245 min-1) have been changed during the tests. In addition, the grain separation has been investigated by introducing various amount of chaff into the straw layers with different moisture content. The empirical grain separation model has been made. The optimum rotation speed of the crankshafts is 195 min-1 when the straw moved over the surface of the straw walker without steps (į1= į2= į3= 0°), the crankshaft rotation speed is 205 min-1 when the straw moved over the surface of the control walkers (į1= į2= į3= 11°), and the crankshaft rotation speed is 215 min-1 when the straw moved over the surface of the experimental walkers (į1= 22°, į2= 10°, į3= 18°). The screens inclination angle is related with the crankshaft rotation speed, i.e., the straw movement speed over the walker surface. The optimum MOG throughput of the experimental straw walker is 3 kg s-1 m-1, when the crankshaft rotation speed is 215 min-1. The grain separation intensity through the changing thickness of the straw layer of different moisture and the straw walker screens may be almost constant when the inclination angle of the walker and the rotation speed of the crankshafts are changed after estimating the grain loss level of the straw walker.