Field experiments to study the performance of toothed disc mowing mechanisms

Abstract

Extensive experiments were conducted in the field to examine the performance of toothed discs when mowing a wide range of grass crops. The work was performed using (1) a modular rig fitted with six discs, (2) a two-drum mower fitted with toothed annuli and (3) a five-disc mower-conditioner modified to accommodate toothed discs. Mowing performance was studied over a range of forward speeds from 2 to 12 km/h and at tooth tip speeds up to 80 m/s. Tooth pitch was varied over a range up to 25 mm. Performance was compared with that of commercial drum and disc mowers using conventional blades. The efficacy of mowing was measured by samples of the length of stubble produced and the power consumption of the mowers. Studies were also made of the wear of the disc teeth during mowing. The work has shown that tooth pitch should be between 8 and 10 mm for minimum stubblelength and power consumption, at a typical mowing forward speed of 9 km/h. This results in a bite length for each tooth of 0·5 to 0·6 mm. The optimum tooth form was a 0° rake angle and a 30† clearance angle. The critical speed was in the range of 25 to 35 m/s and that for minimum power was in the range 25 to 30 m/s. A speed of 40 m/s is suggested, however, to achieve effective cutting over a range of crop conditions. Sharp-toothed discs required 65% of the total power of sharp conventional blades and 50% of that with blunt conventional blades. Worn-toothed discs required about 60% of the power of worn conventional blades. Stubble length increased, however, for worn teeth, particularly in laid crops. For stainless and high carbon steel discs a tangential wear volume of 3·6% of the toothvolume was indicated when cutting 10 t (d.b.) of crop. To achieve a minimum wear rate, a tooth hardness of 550 HV is likely to be required. Further development of the toothed-disc mower is required to overcome some problems of soil and crop accumulation at the intersection of co-rotating discs which can cause long stubble at these points.