Optimization of process parameters for multi-frequency rapid compression molding of corn stalk silk used for forage

Abstract: In order to obtain the best process parameters of compression molding with corn straw after silking, corn stalk collected from the test field of Land and Environment College, Shenyang Agricultural University was studied by using the WDW-200 testing machine controlled by computer and the cylinder sleeve from a six-cylinder engine as the mould. In consideration of physical characteristics of the compressed briquettes used for forage, the relaxation ratio of the briquettes was taken as objective function. The key experimental factors included the moisture content of the materials, the maximum pressure (namely the minimum pressure for compression molding), the frequency of compression and the velocity of compression, and the quadratic regression rotary combination test of relaxation ratio of the compressed briquettes with the corn stalk after silking was performed. At the same time, the regression model between the relaxation ratio and the 4 factors was established. The experimental results indicated that the materials moisture content ranging from 7.8% to 18.3%, the minimum pressure 6.22 MPa for compression molding, compression for 2-6 times and the velocity of compression ranging from 128 to 337 mm/min were the optimum technological conditions for the compression molding. Then the validation test under the optimum technological conditions was carried out and the results indicated that the relaxation ratio of the briquettes was from 1.2 to 1.5, which could satisfy the request of the lower energy consumption and the stable shape. As to the established regression equation, the relative error between the predicted value and the measured value was 2.87% under the optimal condition. Additionally, the influences of the moisture content of the materials, the minimum pressure for compression molding, the frequency of compression and the velocity of compression on the slack ratios of the compressed briquettes were analyzed. The influence of the moisture content of material was obvious, and the higher moisture content of material made corn straw hard to mold even compressed with higher pressure, but the compressed briquette with too low moisture content of material maybe took off the dreg. To ensure the relaxation ratio of the compressed briquettes is less than 1.5, the moisture content of the corn straw after silking must be lower than 20%, and to obtain the better compression molding effect, the moisture content of corn straw after silking should be maintained above 10%. When the relaxation ratio reaches a certain value, the increasing of the maximum pressure is useless, thus the appropriate compressive force not only reduces the energy consumption and improves the efficiency, but also reduces the damage to the equipment. The compression frequency and the compression velocity had linear relationship with the relaxation ratio of the briquette, and they had also certain interactions on the relaxation ratio of the briquette; the lower compressive force with high-frequency fast compression can get a similar compression molding effect with the single higher compressive force. The experiment is significant for the optimization of the compression process of corn straw used for forage. The experimental results provide an important reference for the development of compression equipment and the understanding of compression molding product characteristics.