REMOVING STRAW IMPURITIES FROM GRAIN HEAPS BY CYLINDRICAL SIEVE

Abstract

There is given a brief description, modes of operation and findings of experimental studies on a cylindrical sieve with screw dispenser for  grain pre-cleaning. In a cylindrical sieve without dispenser, a grain heap being moved by the rotating cylindrical surface is  concentrated in a quarter of the circumference of the sieve. When  the dispenser rotating in the opposite direction with respect to the  sieve is installed, the grain heap captured by the screw blades is  distributed over 1/3 to 1/2 of the circumference of the sieve. The  heap is moved by the screw blades in the axial direction, and  distributed over the length of the sieve. Thus, contact area between  the heap and the surface of the cylindrical sieve increases, the grain  heap layer thickness decreases, the probabilities of grains to pass  through the layer thickness and the holes of the sieve increase, and  performance per unit of the working surface area increases. An  inclination of the sieve towards feed makes it possible to control the  speed of the heap movement by means of the dispenser. The screw  dispenser installed in the sieve allows increasing feed of the grain  heap 1.2–1.6 times with the acceptable level of grain losses and  removal of straw impurities up to 70 percent. The dispenser  rotational speed of 30 rpm is preferable to that of 40 rpm because of much lower grain losses at the same grain feed, and of more  complete removal of big impurities at the acceptable grain losses.  The cylindrical sieve, made in such a way that its 75 percent have  the holes of 10 mm in diameter and 25 percent the holes of 6 mm in diameter, contributes to completeness of removing straw impurities by 10.5 percent.