Investigation of grain separation through straw layer over …

Straw walker is a separator that separates grain from straw, and limits the efficiency of combine-harvesters therefore special attention is devoted to the development and improvement of its design and technological parameters. The most important parameter of walker operation is Froude-number k that depends on the amplitude of the straw walker movement in vertical direction, i.e., walker sieve oscillation amplitude r and angular velocity ω. High speed camera used in the investigation tests helped to determine not only the behavior of the straw layers on the oscillating sieve of straw walker but also the duration of grain penetration (separation) through the straw. With estimation of these parameters the rational values of Froude-number k were substantiated. It has been determined that at various ω and r combinations when k=const. sieve vertical accelerations when the crankshaft is rotated at the same angle are equal, but speeds and displacements are varied. For this reason the duration of grain separation is different. The rational angular velocity of the crankshaft is 22.5 s-1 (r=0.05 m), as then the straw layer when the crankshaft is rotated at the angle 2π, raised from the walker surface (sieve) the most early and strokes with it latest, i.e. the duration of free movement of the straw is 1.5 times longer and the grain separation about 15% more intensive than when ω=21.5 s-1. The estimation of grain separation enabled to define critical value of crankshaft angular velocity equal to ω=23.5 s-1. When this value is exceeded the top straw layers receive only one stroke when the crankshaft is rotated at the angle 4π, therefore the increase of crankshaft angular velocity and, simultaneously, sieve oscillation intensity above the critical value is inexpedient.