| Rotary Tilling is an important means of returning straw to the field in Yangtze Plain rice fields,the whole straw was directly buried and returned to the field by rotary tiller.However,it is difficult to cut the length of straw effectively under one round of cultivation,a large number of straw is located on the surface of the soil and the location of shallow soil,straw distribution in the soil is not uniform.It is easy to affect the decomposition rate of straw.It needs repeated tillage to achieve the required targets,but repeated tillage is easy to cause soil compaction problems,reducing the soil’s ability to store water and retain moisture,thus affecting the subsequent planting of the growth of crops.A series of studies have been carried out to improve the effect of straw chopping and straw covering,the straw crushing-rotary burying combined machine is designed.The main research contents and conclusions are as follows:(1)The experiment of rice cutting was carried out.The rice straw was sampled and divided into three sections according to the position of the straw.The results: in the process of cutting straw,the force of straight cutter has a large change trend,while the force of circular cutter and slide cutter has a stable change trend;the maximum shear stress of the upper section is always greater than that of the lower section;it takes longer to cut the thick-walled middle and lower stover with the slide cutter than with the straight cutter and the arc cutter,but the force needed by the slide cutter is much less than with the straight cutter and the arc cutter.(2)A discrete element model of straw-cutter-soil was established to simulate the interaction of straw,soil,rotary blade and spiral transverse blade.Among them,the use of rigid straw straw,soil contact model using JKR model.The soil tank is divided into several grids,and the straw quality in each grid is counted,and the variation coefficient of straw quality is taken as an index,the effects of the serrated angle of the spiral transverse cutter,the rotation speed of the cutter roller and the advance speed of the cutter roller on the covering effect of the straw were studied.The results: under the condition of 70.40 ° sawtooth angle,0.48 m/s forward speed and 213.25 rpm rotational speed,the coefficient of variation of straw quality was the smallest,which was 55.11%;The effect of blade roll advance speed on the straw covering effect is very significant,the effect of rotation speed on the straw covering effect is significant,the effect of serrated angle on the straw covering effect is not significant.(3)In order to improve the spatial distribution uniformity of rice straw,a straw crushing-rotary burying combined machine was designed.In order to ensure that the machine works in a relatively stable state,and reduce the volume and weight of the machine,the vertical height difference of the grinding knife roller,the pressing roller and the rotary burying knife roller is determined,the crushing roller is fixed between the grinding roller and the rotary burying roller by the barycenter principle.The arrangement of tillage cutters on the axes was determined to improve the quality of tillage.The action force of moving blade on straw was analyzed,and the moving blade was determined to be y-shaped flick blade.In order to reduce the vibration of the roller and improve the crushing efficiency,the milling cutter is arranged in double spiral shape on the cutter shaft and comminuted with the combination of moving and fixing cutter.The range of rotation speed and the range of tillage depth were determined after analyzing the movement track of the pulverized cutter roller and the rotary cutter roller.(4)To conduct field trials,to cultivate(a combined operation)with a combine,and first to crush straw with a grinder,the effects of straw burying were compared between rotary tiller and rotary tiller in three different tillage methods,namely,rotary burying(powder first,rotary tiller later)and direct burying(Rotary Tiller Direct).The results: It is difficult to cut straw effectively by rotary tillage and direct rotation,Most of the stalks are longer than 15 cm after tillage,And nearly 60% of the straw is located in the 0～5 cm plough layer.And the combined operation and the first grinding and the second spinning can effectively crush the straw,Most of the stalks are about5～10 cm in length,It can meet the requirement of the length of straw in the range of5～15cm after crushing,Moreover,the combined tillage and the first-powder-andlater-rotation tillage can make the straw burying and mulching more even. |
