The effect of the disc setup angles and working depth on disc harrow working resistance

Horizontal, longitudinal and vertical components of working resistance of a compact disc harrow (CDH) were investigated in a field experiment. Three values of the attack angle (12°, 16°, 21°) and two of the tilt angle (7°, 15°) of the plane of the front discs were used. The third parameter was the working depth measured at the lowest point of discs circumference edge. The dependent variable was the horizontal and vertical resultant component of forces occurring in the three-point linkage system on a tractor. Statistically significant differences in the resistance components were found depending on the disc set-up. For evaluation of soil reaction forces on harrow discs the above resistance components were transformed into components of the unit resistance relating to the units of actual working width and depth. Their dependence on the CDH setting parameters was next examined using the empirical estimation of the regression equation. Horizontal and vertical components of the bearing and the pressure area of the discs were used as independent variables. Values of the bearing area were close to zero and only the components of pressure were used. This model describes the components of the horizontal and vertical resistance as a function of design parameters and disc settings expressed by means of pressure area. It reflects the empirical results with 99.7% accuracy for the horizontal component and in 99.9% for the vertical component of the resistance.