DESIGN OF TAPERED AUGERS FOR UNIFORM UNLOADING PARTICULATE MATERIAL FROM RECTANGULAR CROSS-SECTION CONTAINERS

The design equation for an ara:ger to provide uniform unloading of par ticulate material from a container with a rectangular cross-section (J ones and Kocher; 1995) was revised to account for the minimum flightin g height that could effectively unload particles with a known average smallest diameter: A minimum flighting height that was about 64% of th e average smallest diameter of the particles was experimentally determ ined to obtain mean slopes of the top surface of the material not sign ificantly different from zero for screened soybeans. A linear taper th at best fit the square root curve for the inside diameter of the anger was determined by minimizing the integral of the squared area differe nces between the linear taper and the square root curve. The maximum d ifference between the auger radii as determined with the square root c urve and linear taper functions was less than 0.3 mm, significantly le ss than the 4.7 mm average smallest particle diameter for the screened soybeans used. An auger constructed following this design (linear tap ered inside diameter with a minimum flighting height) provided uniform unloading of particulate material from a container with a rectangular cross-section, as evidenced by mean slopes of the top surface of the material being maintained not significantly different from zero, until the top surface dropped to within 30 cm of the top of the auger fight ing.