Mechanical Properties of Granular Feed Ingredients

Abstract

Ground corn and soybean meal are common feed premix carriers. The knowledge oftheir mechanical properties is important to the feed manufacturer and consumer. Changes inthese properties may lead to abnormally high or low levels of active ingredients in finished feedthus decreasing its quality. Mechanical properties of wheat, ground corn and soybean mealwere investigated using a modified direct shear apparatus. The moisture content (wet basis),uncompacted bulk density and multipycnometer density were: 10.4%, 733 kg/m3and 1.41 g/cm3for wheat; 11.4%, 583 kg/m3and 1.35 g/cm3for soybean meal; and 11.7%, 595 kg/m3and 1.41g/cm3for ground corn, respectively. A relatively long sliding path of 60 mm was utilized toaccount for the high compressibility of the materials and minimize boundary effects. Thecompressibility of the materials was determined at a maximum vertical pressure of 34.4 kPa thatcaused a density increase of 21% for ground corn while the density of wheat and soybean mealincreased by approximately 5%. Frictional properties were tested for seven levels of verticalconsolidation pressures ranging from 4.1 to 20.7 kPa. The high compressibility of ground corn resulted in severe stick-slip vibrations of frictional forcedisplacement relationships compared tothe typical behavior of cohesion-less granular materials such as wheat. The angles of internalfriction of wheat, soybean meal and ground corn were found to be 26.30.3, 33.90.9 and30.71.4, respectively. Cohesion of soybean meal and ground corn was approximately 0.7kPa without a clear relation to consolidation stress, while for wheat it was approximately 0.3kPa. With cohesion lower than 4 kPa all three materials should be treated as free-flowing.