Optimum Profile of Chisel Front Surface

Cultivators for fallow and intertilled crops cultivation have several tipes of chisel. The key design data of a chisel are a tip overhang, radius of curvature of the front surface, an angle between a tangent to the tip and the furrow bottom. The radius of curvature of the front surface consists of two parts. The first one is in the form of a logarithmic spiral, the another is as a straight line. The angle between the tangent to the top and the furrow bottom depends on the angle of internal friction. It is in an interval of 35-40 degrees. The curvature radius and a lateral form of chisel generally depend on the size of an internal angle of friction of the deformable soil. (Purpose of research) To obtain an analytical dependence o of the front surface profile of the chisel working body, which allows to work on soils with different granulometric composition and angle of internal friction. (Materials and methods)The authors assumed that the condition of steady sliding of soil layer with various aggregate-size distribution on the chisel surface is feasible if the product of the projections of the tangential reactions of the elemental area of the surface and projections of the movement trajectory is less than zero. The projection of the tangential reactions of the elemental area of the surface depends on the concordance of the rotation angle to the size of digging-in, also on the deepening of the elementary area, the coefficient of external friction of the soil, and the first derivative of the function curve of the surface. The curve coefficient of a quadratic parabola outlining the surface of a chisel was estimated considering its smoothness and continuity. (Results and discussion) At the same time the current value of vertical coordinate of chisel lateral surface changed when the fixed values of tip overhang and running depth. The lateral profile of the as-designed chisel does not depend on soil characteristics. The size of the initial angle corresponds to the requirement that the deformation does not extend below the tip, and elementary reactions cross the surface of the field. (Summary) The angle of grade of the lateral profile surface of the chisel makes 26 degrees and 50 minutes. The curved surface of the wedge-shaped mouldboard is described by the function square parabola. The coefficient of the curve parabola describing a profile of a chisel surface, being negative, is equal to ratio of chisel overhang to the doubled parameter of the running depth