I. J. Ross

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.

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.

Asymmetry of Bin Loads Induced by Eccentric Discharge

A series of tests involving eccentric discharge from a model bin were conducted using bin wall surfaces of smooth galvanized steel, corrugated galvanized steel, and abrasive paper simulating a concrete bin wall. Bin load asymmetry resulting from eccentric discharge was found to decrease with increasing value of friction coefficient of the bin wall.

COMPARISON OF LOAD DISTRIBUTION IN Two SIMILAR GRAIN BINS

Wall and bottom loads and the resultant moment of force have been compared for two similar model bins. Corrugated wall bins of 0.6 and 1.2 m in diameter with height-to-diameter ratios of 4 were used in the experiments. The wall and flat bottom of the bins were each supported independently on three load cells to isolate wall and bottom loads. Center and off-center discharge of the bins was tested. The vertical wall load to total grain load and the dimensionless moment found during eccentric discharge were strongly influenced by the difference in the wall friction coefficient resulting from different size corrugations and different kinds of grain. The maximum moment was found for an orifice eccentricity ratio of 0.67 for both bins.

LOADS CAUSED BY BOTTOM UNLOADINGWALL FLUMES IN A MODEL GRAIN BIN

Wall loads were measured in a model bin 2.44 m in diameter and 7.3 m tall equipped with a bottom unloading wall flume. The results were then compared to the wall loads measured during unloading of this same bin without the flume. During most of unloading the wall loads measured when using the flume were smaller than those during filling. However, at the onset of discharge a load spike was observed prior to the formation of the funnel-flow discharge pattern. Wall moments in the direction of the flume were observed to occur which were three times as large as those measured during centric unloading.