Mathematical modeling and analysis of helical blade for stubble burying rotary tiller

Abstract: Tillage practice shows that it is feasible to bury high stubble remains through rotary tillage in paddy field. The 1GMC-70 boat-type high stubble burying rotary tiller is widely used in paddy field. This machine is suitable for plowing paddy field of muddy depth less than 350 mm with high stubble less than 700 mm. However, most study on the paddy tillage focused on prototype production and field testing. In order to probe the mechanism of high stubble burying rotary tillage in paddy field, a mathematical model was built for the helical blade of 1GMC-70. Through equations of the helical blade edges, curves were plotted between main tillage parameters and positional angle of helical blade, such as dynamic sliding cutting angle, dynamic cutting angle, and so on. Theoretical factors were discussed for high stability of tillage depth above 90%. The fluctuation for dynamic sliding cutting angle of helical blade ranges from 25° to 25.3°, which is less than 0.3°. Each helical blade cuts into soil in turns. When the latter helical blade begins to cut soil, the former blade is still in soil with the whole length rate 10/46. This makes the continuous procedure of cutting soil. Reasons were analyzed for high stubble burying rate above 94.6% and for high soil broken rate above 90%. Compared with traditional rotary blade, the sliding cutting angle of helical blade is smaller, while the cutting angle, clearance angle and edge angle are greater, which static value is 25.3°, 71.7°, 36.2° and 35.5° respectively. The main function of helical blade is not soil-cutting, but stubble-burying. The rotary tiller rotates at high speed of 380 r/min, while the rotary speed of traditional rotary tiller ranges from 150 to 350 r/min. When the machine of 1GMC-70 works in paddy field, the inner surface of helical blade casts plowed soil backward fiercely. All those factors contribute to stubble burying and soil breaking.