Document Type : Research Article
Authors
Department of Biosystems Engineering, College of Agriculture, Shiraz University, Shiraz, Iran
Abstract
Introduction
The dynamic response of soil on tillage tools, is an important factor in determining their performance. For a tractor with a certain size, a reduction in draft force, the working width and speed of tools can rise and result in increasing performance and reduce costs. Researches carried out in order to reduce the draft force led to design and build new tillage tools called Bent Leg and Parra plows. The dual bent blade sub-surface tillage tool was built and examined inspired by the shape of a bent leg. The researches indicated that the combination of a dual bent blade sub-surface tillage tool and chisel plow could be used in order to reduce draft force, loosen the seed bed by the chisel plow and wings, increase in soil disturbance area by the wings, and create a suitable space for root growth by chisel plow. Since the fuel consumption and traction power of tractor are the limiting factors for pulling tools in the soil. The rake angle of tillage tools is the penetration factor of the tools to the soil. It is necessary to determine the optimized rake and bend angles according to their effect on draft force and better penetration in soil. In this research, the Response Surface Methodology (RSM) was utilized to determine the optimized points of wing geometry of winged chisel plow in order to minimize the draft and vertical forces of tillage tool.
Materials and Methods
Using the properties of dual bent blade subsurface tillage implement and chisel plow, the winged chisel plow was designed by Catia V5R20 software and was built in the workshop of mechanics of biosystems engineering department at Shiraz University. The effect of three factors of working depth of wing (5, 10, and 15 cm), bend angle (10, 20, and 30 degree), and rake angle (7.5, 15, and 22.5 degree) were analyzed on draft and vertical forces of wined chisel plow in soil bin of Karaj Agricultural Engineering Research Institute. The length, width, and depth of the soil bin were 24 m, 1.7 m, and 1 m, respectively. The most important issue was to study the main effects and interactions of factors. So, the Response Surface Methodology was selected. With the help of this statistical design, the numbers of experiments were reduced and all coefficients of quadratic regression and interaction factors were estimated. The experiments were conducted based on the central composite design considering three main surface including central and axial points for each factors. For each response the quadratic polynomial models were obtained using the multiple linear regression.
Results and Discussion
The results indicated that fitted quadratic model for draft force corresponded with the experimental data by determination coefficient of up to 94% (R2 ˃ 0.94). Increasing the depth of wing, the contact with loosened soil decreased that led to failure in unloosened soil around the chisel blade and increase in pressure to the blade. The results showed that the effect of bend angle was significant on draft force and increasing the bend angle, the tip of wing located in deeper place so, the draft force was increased that was in line with previous researches. The effect of rake angle was not significant on the draft force and its effect on the model was positive and negligible which was reported positive and significant in previous works. The fitted quadratic model for vertical force corresponded with the test data by determination coefficient of up to 93% (R2 ˃ 0.93). The effects of wing depth and bend angle were positively significant on the vertical force of the tool but the effect of rake angle was negligible. The increase in vertical force with increasing bend angle was further in deeper wing position. However, the impact of rake angle was seen in vertical force and the effect of bend angle was not significant in vertical force in rake angles of 7.5° and 15°, but it was significant in rake angle of 22.5°.
Conclusion
The draft and vertical forces were determined 3.43 and 1.31 kN, respectively, at optimum condition (wing depth of 5cm, bend angle of 11.1°, and rake angle of 19.46°). The proposed model to predict the dependent variables were very close to the results of obtained experimental findings. The wing depth and bend angle had positive and significant effects on draft and vertical forces but the effect of rake angle was positive and insignificant on both measured traits.
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