A GEOMETRICAL ANALYSIS OF INCLINED AND TILTED SPHERICAL PLOW 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 dis c 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 d eep disc concavities are considered. A presentation is made of formula e derived for disc critical angle and depth and for bearing and pressu re areas of contact with the soil on vertical and horizontal planes. I n 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 degrees t o 25 degrees) and disc angle (35 degrees to 55 degrees) it is shown th at the bearing area of the rear spherical area of discs is zero, so th ere 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 li ttle difference for the two disc concavities. Disc angle and working d epth have significant effects on this area. The horizontal presssure a rea is not affected by disc angle over its practical range. It has lar ger values for the 81 mm concavity than for the 51 mm concavity and is significantly influenced by tilt angle and working depth. Discs worki ng in a gang, have overlapping of the areas of soil cut for disc angle s 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 ou tside sharpening does not significantly affect the overall findings co ncerning critical disc parameters. The flat bevelled surface formed by outside sharpening will generally be in contact with soil over the pr actical range of tilt and disc angles. (C) 1996 Silsoe Research Instit ute