COMPACTION BEHAVIOR OF BULK WHOLE CORN KERNEL AT PRESSURES UP TO 34.6 MN/m2

Abstract

ABSTRACTThe compaction behavior of whole corn kernel (1.8–22.0% mc, w. b.) was investigated by axial compression in an 18.5 mm diameter die using the Amatek Universal Testing Machine at 28°C. The maximum applied pressure in each experiment was 34.6 MN/m2 at loading rates of 0.028, 0.28, and 2.8 mm/s. Sample failure due to oil expression or sample extrusion did not occur in any test run. However, extensive physical rupture of corn kernels occurred at 1.8% moisture content and at lesser but significant levels at 6.6 and 9.7% moisture. At 15.9 and 22.0% moisture, samples were plastically deformed but little macroscopic kernel damage was evident. The effectiveness of compaction increased dramatically as moisture content increased up to 22.0% and then appeared to gradually decline with further increase in moisture. The average compression ratio at zero pressure varied from an average low of 1.70 at 1.8% to an average high of 1.92 at 22.0% mc corresponding to reductions in corn volume of 41 and 47%, respectively. In contrast, loading rate had little effect on density‐pressure profiles. The latter were not adequately characterized by powder compaction models reported in the literature. Substantial volumes of internal tissue gas were estimated with an average maximum of 21% in 15.9% moisture corn kernels.The extent of stress relaxation after termination of compaction increased as loading rate increased and was highest in 15.9% moisture corn. The pressures required for the ejection of compacted corn from the 18.5 mm die varied from 0.5 to 2.1 MN/m2 and revealed an average maximum value at 9.7% moisture. Ejection pressures were substantially independent of loading rate. The most stable compacted corn samples were those produced at the 15.9% moisture level although the compact stability in general was very poor indeed.