Grain Bulk Properties as Affected by Mechanical Grain Spreaders

ABSTRACT THE use of mechanical grain A spreaders when filling bins with dry shelled corn significantly im-proved the uniformity of distribution of fine and broken material (chi square reduced from 3.0 to 0.3), increased the bulk density of the grain from 766 kg/m3 to 871 kg/m3, and increased the resistance to airflow from 122 Pa/m to 379 Pa/m at an airflow of 4.6 m3/min-m2 as compared with filling from a spout. Aeration systems designed for loosely packed grain may deliver insufficient airflow to grain in a bin filled with a mechanical grain spreader. When a storage bin or other container is filled with a stream of granular material containing a range of particle sizes, the fine material (f.m.) concentrates in an area under the filling point. An article and a film (Van Denburg and Bauer 1964, ca. 1964) vividly demonstrate the segre-gation that takes place and the resultant variation in composition that is observed during unloading. Segregation of fine material is a source of expense and problems to grain handlers. Even though a storage bin may have been filled with grain containing 3 percent f.m. uniformly distributed, if the withdrawal point is under the fill point, the first grain removed will contain considerably higher f.m. levels than will grain that is removed later. The grade may be lowered, reducing the value of the grain, or requiring reloading of the truck or rail car to meet the required grade. Because f.m. has a higher resistanceto airflow than does a mass of whole kernels, concentrations of f.m. cause a wide variation in resistance to airflow within the bin. In a drying bin, the result is inadequate drying of the core of f.m. or overdrying the remainder of the batch. Broken kernels in con-centrated areas are more susceptible to insect invasion and fungal develop-ment (Christensen and Kaufmann 1969). Shotwell et al. (1972) found aflatoxin to be concentrated in damaged kernels and f.m., but not in whole kernels. The time and cost of aerating dry grain is increased by the reduced airflow in areas of high f.m. One approach often used to combat the storage problems created by the concentration of f.m. is the removal of the core of f.m. immediately after filling by partially emptying the bin. In a large bin this may result in 20,000 bu of unused storage space which has an annual cost of 12 cents to 14 cents per bu (Dodds 1972). Even if the bin were refilled, the extra handling of the grain would add to the cost. Several techniques have been developed to combat the nonuniform discharge characteristics of a bin (Van Denburg and Bauer ca. 1964 and 1964; Fisher 1973). These techniques usually involve the provision of internal baffles or multiple discharge points to recombine the segregated materials. However, these techniques do not correct the storage problems which arise from segragation. Mechanical grain spreaders are sometimes used to prevent f.m. segregation, although their primary selling point has been that they provide a level fill without hand labor. Some manufacturers refer to the drying problems caused by fine material segregation. The objectives of this study were: (a) to measure the effectiveness of mechanical grain spreaders in pro-ducing a uniform distribution of fine materials within the grain mass, (b) to measure the in situ bulk density of grain placed in a storage bin with and without the aid of a mechanical grain spreader, and (c) to measure the airflow resistance of grain placed in a bin with and without the aid of a mechanical grain spreader.