Optimization and experiments of the blade group of ditching devices in rapeseed direct seeder

A ditching device has been widely used for rapeseed direct-seeding in the rice-oil rotation areas of the mid-lower reaches of the Yangtze River. However, the high-power consumption and unstable furrow shape cannot fully meet the large-scale production in recent years, when operating at the high speed (≥10 km/h). In this study, a quasi-propeller ditching device was developed with a blade-soil contact surface similar to that of a propeller suitable for high-speed no-tillage rapeseed direct seeder. The ditching blade group was also optimized. A quasi-propeller cutter group consisted of four sets of cutters. The blade layout structure was then determined using kinematics and dynamics. An optimal model of power consumption and soil throwing efficiency was established for the operation of the blade group using dynamic analysis. The key structural parameters and working factors were determined to improve the power saving and soil throwing efficiency in the ranges of parameters. Single-factor tests were conducted on the blade edge type, pitch angle, and bending angle using EDEM software. The results show that the smallest resistance was achieved in the back blade edge type; The blade resistance first decreased and then increased, as the pitch angle increased, whereas, the soil throwing performance decreased significantly; There was a decrease in the overall resistance of the blade group and the soil throwing performance, as the bending angle increased. Once the blade edge structure of the cutter-1, cutter-2, cutter-3, and cutter-4 was the back edge (BE) type, the pitch angles were 7°, 5°, 4°, and 3°, respectively, and the bending angles were 120°, 120°, 90°, and 90°, indicating the relatively small resistance of the cutter group and the better performance of soil throwing. A Box-Behnken simulation test was conducted on the pitch angle, working velocity, and cutter rotary speed, according to a single factor test. A genetic algorithm (GA) was also used for the multi-objective optimization in the power consumption and soil throwing performance. Box-Behnken results showed that the pitch angle, cutter rotary speed, and working velocity greatly contributed to the power consumption. The most significant impact was found on the working velocity, indicating the lower working velocity and the higher cutter rotary speed, while the higher efficiency of soil throwing. After optimization, the optimal pitch angles of cutter-1, cutter-2, cutter-3, and cutter-4 were 6.7°, 4.7°, 3.5°, and 2.5°, respectively; The optimal rotary speeds of the cutter were 540, 620, and 810 r/min, respectively, at the working velocity of 6, 9, and 12 km/h; The power consumption of the optimized blade group was lower than that of the control group and the international IS225 blade group; The total power consumption of the optimized cutter group was reduced by 5.51-28.99 kW, compared with the control group. The higher the working velocity was, the higher the resistance reduction rate was; The reduction rate of resistance was the highest at 12 km/h, about 41%. Field experiments showed that the total power consumption of the optimized ditching device was 15.1-41.8 kW when operating at a speed of 6-12 km/h, with a relative error of less than 10%, compared with the simulation. The width range of the furrow was 421.3-452.7 mm, the depth range was 163.7-178.7 mm, the stability coefficient range of the furrow width was 95.2%-98.6%, and the stability coefficient range of the furrow depth was 93.8%-97.5%. The working velocity also caused the furrow pattern to change from a circular arc to a V-shape. This research can provide a strong reference to improve the high-speed ditching device for the rapeseed direct-seeding in the rice-oil rotation cropping area of the mid-lower reaches of the Yangtze River.