Marek Molenda

Mechanical properties of corn and soybean meal

Ground corn and soybean meal are common ingredients in feed mixes. The knowledge of their mechanical properties is important to the feed manufacturer and consumer. Changes in these properties can lead to abnormally high or low levels of active ingredients in finished feed, thus decreasing its quality. Mechanical properties of wheat, corn meal, and soybean meal were investigated using a modified direct shear apparatus. The moisture content (wet basis), uncompacted bulk density, and particle density were: 10.4%, 733 kg/m 3 , and 1410 kg/m 3 for soft red winter wheat; 11.4%, 583 kg/m 3 , and 1350 kg/m 3 for soybean meal; and 11.7%, 595 kg/m 3 , and 1410 kg/m 3 for corn meal, respectively. A relatively long sliding path of 60 mm was utilized in shear testing to account for the high compressibility of the materials and minimize boundary effects. The compressibility of the materials was determined at a maximum vertical pressure of 34.4 kPa, which caused a density increase of 21% for corn meal while the density of wheat and soybean meal increased by approximately 5%. Frictional properties were tested for seven levels of vertical consolidation pressures ranging from 4.1 to 20.7 kPa. The high compressibility of corn meal resulted in severe stick-slip behavior of the frictional force-displacement relationships. The angles of internal friction of wheat, soybean meal, and corn meal were found to be 26.3° ±0.3°, 33.9° ±0.9°, and 30.7° ±1.4°, respectively. Cohesion of soybean meal and corn meal was approximately 0.7 kPa without a clear relation to consolidation stress and approximately 0.3 kPa for wheat. With cohesion values lower than 4 kPa, all three materials should be treated as free-flowing in terms of Eurocode 1. Corn and soybean meals are known to cause flow problems in practice that were not confirmed during testing. In practical storage conditions, materials undergo a longer consolidation period. Our tests have shown that with processes that have a short duration and low consolidation pressures, these materials should be treated as free-flowing.

BIN LOADS INDUCED BY ECCENTRIC FILLING AND DISCHARGE OF GRAIN

Wall loads were measured in a corrugated–wall model grain bin 2.44 m in diameter and 7.3 m high filled with wheat to a H/D ratio equal to 2.0. The model bin was filled either centrally or eccentrically through a chute located along a radial line, coinciding with one of the major axis of the bin, at eccentricity ratios of 0, 0.5, or 0.75. The eccentricity ratio (ER) is defined as the ratio of the distance from the center of the bin to either the filling location or the discharge gate divided by the radius of the bin. The model bin was unloaded either centrally or eccentrically through discharge gates located at ERs of 0, µ 0.5, or µ 0.7. For both an ER of 0.5 and 0.7, two different eccentric discharge gates were used, located on opposite (plus or minus) sides of the bin on a major axis that was parallel to the filling axis. For experiments involving centric filling followed by eccentric unloading, a maximum wall moment of 11.2 kN–m was measured. For experiments involving eccentric filling followed by eccentric unloading, the mutual location of the filling and discharge gates either magnified or reduced the variation in stress within the bin and the resulting moment carried by the walls. For experiments in which the location of both the filling and discharge gates were on the same side of bin, a maximum wall moment of 17.5 kN–m was measured. For tests in which the filling chute was located on the opposite side of the bin from the discharge gate, a maximum wall moment of 3.2 kN–m was measured.

EFFECT OF FILLING METHOD ON LOAD DISTRIBUTION IN MODEL GRAIN BINS

The spatial arrangement of individual grains forming a bed of granular solids influences the mechanical behavior of the granular material. This article summarizes the effects of the spatial arrangement of wheat in bulk on the angle of internal friction determined in triaxial test and on the load shift in a model bin. In addition, it shows the influence of the bedding structure generated by three filling methods on the radial distribution of vertical pressure on the bottom of a cylindrical flat-floor bin and the resultant lateral to vertical pressure ratio (k). The filling method significantly (a = 5%) influenced the radial distribution of vertical pressure on the floor of the bin. This variation in pressure distribution was reflected in the estimated values of k. An increase of stress ratio was observed after the start of discharge.

Wear-in Effects on Loads and Flow in a Smooth-wall Bin

The wall and floor loads exerted by wheat on a smooth-wall, flat-bottom bin 2.44 m in diameter and 7.3 m high were determined as a function of the number of fill and unload cycles [loading cycle (LC)]. The vertical wall load to total grain load ratio decreased from 52.7% for the first loading cycle to 28.3% for the 10th LC. The dynamic-to-static wall load ratio increased from 1.08 to 1.24 during 10 LCs. The grain height-to-bin diameter ratio at which grain flow changed from plug to funnel flow decreased from approximately 1.75 for the first LC to 1.6 for the 10th LC.

Loads in Model Grain Bins as Affected by Filling Methods

Measurements of wall and bottom loads in flat-bottom model bins have shown the influence of filling methods and wall surface on wall loads and the static-to-dynamic load shift. Four spout-filling methods, at center and eccentric locations, sprinkle filling, and uniformly filling through an annular ring near the bin wall, were evaluated. Three types of bin walls were tested for each filling method: smooth galvanized steel, corrugated galvanized steel, and smooth steel covered with abrasive cloth. Soft and hard winter wheats were used in the experiments. The static wall load to total grain load ratio (SWL/TGL) and the dynamic-to-static wall load ratio (DSR) were found to be influenced by the filling method. In general, a higher SWL/TGL resulted in a lower DSR. Sprinkle filling produced lower SWL/TGL values on the smooth wall and higher values on the rough and corrugated walls. The ratio of the wall to total grain load at the start of discharge was highest for the first opening of the discharge gate as compared to two successive gate openings (each after 30 min of rest). The filling method and the type of wheat significantly influenced the negative friction force on the smooth wall bin. Negative friction force values were highest for the top filling methods. A negative friction force was not observed for corrugated and rough wall bins.

Mechanical properties of potato starch modified by moisture content and addition of lubricant

Abstract Laboratory testing was conducted to deliver a set of characteristics of structure and mechanical properties of pure starch and starch with an addition of a lubricant - magnesium stearate. Considerable influence of moisture content of potato starch was found in the case of density, parameters of internal friction, coefficients of wall friction and flowability. Elasticity was found to be strongly influenced by water content of the material. Addition of magnesium stearate affected density and parameters of flowability, internal friction and elasticity. Bulk density increased from 604 to 774 kg m-3 with decrease in moisture content of potato starch from 17 to for 6%. Addition of magnesium stearate resulted in approximately 10% decrease in bulk density. Angle of internal friction obtained for 10 kPa of consolidation stress decreased from 33 to 24º with increase in moisture content, and to approximately 22º with addition of the lubricant. With an increase of moisture content from 6 to 18% and with addition of the lubricant, the modulus of elasticity during loading decreased from approximately 1.0 to 0.1 MPa. Modulus of elasticity during unloading was found in the range from 19 to 42 MPa and increased with increase of moisture content and amount of lubricant.

Asymmetry of Model Bin Wall Loads and Lateral Pressure Induced from Two- and Three-Dimensional Obstructions Attached to the Wall

An obstruction attached to the wall of a bin produced by cohesive, moldy grain has been reported as a source of failure in steel bins. A study was conducted to estimate the effect of two-dimensional (plane) and three-dimensional (block) obstructions attached to the corrugated wall in a flat-floor model bin where the lateral wall pressure and vertical wall loads were measured. The model bin was 1.83 m in diameter, 5.75 m high, and filled with soft red winter wheat to a depth of 5.0 m (height-to-diameter ratio h/d of 2.75). The plane obstruction had the form of an annulus segment spanning 60° of the bin wall and a width of 0.154 m (surface area of 7.2% of the bin floor area). A three-dimensional obstruction was shaped as a block with two bases identical to the plane obstruction and a height of 0.5 m. The plane obstruction and the upper base of the block obstruction were attached to the wall at h/d ratios of 1.26, 0.81, and 0.38. Even in conditions of near symmetry during centric loading, wall overturning moments of approximately 1 kNm were observed. The highest wall moment measured was 2.7 kNm at the end of filling with the block attached at h/d of 0.38; the moment with a plane obstruction in the same position was 2.1 kNm. Without an obstruction attached to the wall, the maximum lateral pressure increased 2.5 times relative to the static pressuer compared to an increase of 4 times with an obstruction. The data collected indicated that there are considerable additional loads imposed on a bin due to obstructions that may form during storage that are not considered in the design codes and could approach levels observed during eccentric discharge.

AIRFLOW RESISTANCE OF SEEDS AT DIFFERENT BULK DENSITIES USING ERGUN’S EQUATION

Airflow resistance of grains and oilseeds has been extensively studied. Traditionally the data has been presented using Shedd’s curves. However, this assumes that airflow resistance is independent of grain depth. Grain undergoes compaction during storage that changes the bulk density, porosity, and therefore the airflow resistance. Ergun’s equation is a function of particle size and porosity of the granular material. Airflow resistance by Ergun’s equation was used to predict the pressure drop across a column of corn, soft white winter wheat, soft red winter wheat, and soybeans at three moisture content levels and two bulk densities. The maximum root mean square error when predicting airflow resistance using Ergun’s equation was less than 23 Pa/m when the pressure drop was less than 500 Pa/m. If all data was included up to a pressure drop of 1800 Pa/m, the average root mean square error for calculating airflow resistance was 76 Pa/m. The effect of grain orientation that would be typical in storage bins was negligible, less than a 10% increase in airflow resistance over a range of kernel orientations that varied between -10°, +10°, and 20° from the angle of repose. However, the fill method and resulting bulk density increased the airflow resistance by an order of magnitude. Ergun’s equation, with an appropriate model of porosity variation within a storage bin, could be utilized for the design and analysis of grain aeration systems.

Wall loads in a model grain bin during fill and unload cycles

Grain storage structures in their normal use are filled and unloaded in many different ways. This study was conducted to determine how several filling and unloading procedures affected wall loads. The vertical wall loads exerted by soft red winter wheat on a smooth-wall, flat-floor bin 2.44 m in diameter and 7.3 m high were determined as a function of fill height for different fill and unload cycles. The protocols used in the experiments of partially unloading and refilling the test bin clearly reflected the elasto-plastic hysteresis of grain inside the bin.

DYNAMIC LOAD RESPONSE IN A MODEL BIN AT THE START OF GRAIN DISCHARGE

The dynamic response of the vertical wall and bottom loads at the start of grain discharge was influenced by wall configuration and filling method for model bins in plug flow. Experiments were conducted with wheat in cylindrical smooth wall and corrugated bins which were 0.6 m in diameter and 2.4 m high. Central spout and sprinkle filling methods were tested. The highest wall load increase was observed for the smooth wall bin when centrally filled. The corrugated wall and sprinkle filling method produced the smallest wall load increase. A peaked response of the dynamic wall load was observed for both bin wall surfaces which were center filled. Two steps of wall load increase after the start of discharge were observed for sprinkle filling of the smooth wall bin, one occurred immediately after orifice opening and the second occurred after 1 to 2 min of discharge.