A Geometrical Analysis of Inclined and Tilted Spherical Plough Discs

An analysis is presented of the effect of disc geometry in relation to its areas of contact with soil at the working depth, treating the disc as a segment of a thin spherical shell. In addition, the effects of the disc angle of tilt, the disc angle of inclination to its direction of motion and the working depth are examined in detail. Shallow and deep disc concavities are considered. A presentation is made of formulae derived for disc critical angle and depth and for bearing and pressure areas of contact with the soil on vertical and horizontal planes. In addition, a study was made of the overlapping of soil working areas when adjacent discs are working in a gang arrangement. The effects of inside and outside sharpening of the circumferential edge of the disc are also examined.For the practical range of tilt angle (15° to 25°) and disc angle (35° to 55°) it is shown that the bearing area of the rear spherical area of discs is zero, so there is no soil contact with the rear surface of the disc. The vertical pressure area is only slightly affected by tilt angle and there is little difference for the two disc concavities. Disc angle and working depth have significant effects on this area. The horizontal presssure area is not affected by disc angle over its practical range. It has larger values for the 81 mm concavity than for the 51 mm concavity and is significantly influenced by tilt angle and working depth. Discs working in a gang, have overlapping of the areas of soil cut for disc angles and spacings (180 to 300 mm) adopted in practice. The area cut by an individual disc is not markedly affected by disc angle. Inside and outside sharpening does not significantly affect the overall findings concerning critical disc parameters. The flat bevelled surface formed by outside sharpening will generally be in contact with soil over the practical range of tilt and disc angles.