Oscillating slide-cutting blade in shovel-type seedbed preparation machine for rapeseed direct seeding

A large amount of straw and high stubble can often be remained after rice harvest in the rice-rapeseed rotation areas of the mid-lower Yangtze River. It is very necessary to enhance the straw cutting for the high consistency of straw-soil mixing. In this study, an oscillating slide-cutting blade was developed in the shovel-type plowing device. The uniform vertical distribution of straw was also realized within the plow layer for the shovel-type seedbed preparation machine during rapeseed mechanical direct seeding. This blade was used to pre-disturb the soil surface, and then cut the straw before the shovel operation. Thereby the frequency of straw cutting was improved during operation. The structure and working parameters were then optimized in the shovel-type seedbed preparation machine. The edge curve of oscillating slide-cutting blade was then proposed, according to the principle of slide cutting. The dynamic model of straw cutting was also constructed for the oscillating slide-cutting blade. The slide-cutting angles were determined to be 31° to 59°, fully meeting the operational requirements. A kinematic model was also established for the oscillating operation of the blade. A systematic analysis was implemented to clarify the relationship between the dynamic and static slide-cutting angles, crank rotational speed, and forward speed. The angular velocity was finally derived for the oscillating slide-cutting blade in the shovel-type plowing device. Taking the high forward speed (0.9 m/s) and low crank rotational speed (240 r/min) as the critical parameters, the blade edge curve was designed, according to the Archimedean spiral. A simulation was performed on the oscillating slide-cutting blade that installed on the shovel-type tillage device using discrete element method (EDEM) software and multibody dynamics software (ADAMS). Crank rotational speed, forward speed, and blade edge angle were selected as the experimental factors, while the effectiveness of straw cutting and average working resistance were used as the evaluation indicators. Single-factor and three-factor, three-level orthogonal experiments were conducted to analyze the influence of each factor on the test indicators. The optimal combination of parameters was obtained using range and variance analysis. Field experiments were conducted at the rice-rapeseed rotation test base of Huazhong Agricultural University in western China. The experimental conditions were set as the surface after rice harvest, and the soil type was the clay soil. The average content of soil moisture before the test was 26.75%, the bulk density was 1.76 g/mm³, and the average soil cone index at a depth of 0-200 mm was 1 225.3 kPa. The average height of rice straw stubble was 405 mm, with a straw coverage of 1 558 g/m². Field experiment results indicated that all quality indicators of the shovel-type seedbed preparation machine reached the optimal levels after operation. The straw burial rate increased by 3.71 percental points using oscillating slide-cutting blade. There was no significant impact on the tillage depth, seedbed surface, and soil fragmentation rate. In the case of oscillating slide-cutting blade, the proportion of straw shorter than 100 mm increased by 17.09 percental points, while the proportion of straw longer than 200 mm decreased by 20.75%, and the uniformity of vertical straw distribution within the soil was improved by 39.68 percental points. This finding can provide a strong reference for the key components in the tillage machinery.