Optimising the performance of shallow, high-speed mouldboard ploughs

Abstract

The aim of the project was to undertake experimental and theoretical research, to enable a better understanding of the design of modem mouldboard ploughs. Using this knowledge to optimise the performance in terms of width, depth and speed of operation to enable a more efficient cost saving operation. This would strengthen the presence of the mouldboard plough in the modem primary tillage machinery line-up and make it more competitive against other tillage systems. Soil bin and field studies were undertaken to determine the effect of operating depth, width and speed on the forces and movement of the soil. This was to determine if manufactures, especially Kvemeland; had followed the suggestions of previous researchers with the design of their number 8 mouldboard or an improvement in design was needed to enable high-speed operation. Not only was the design found to operate well at over a range of speed up to 10km/h but also provided good inversion at width/depth ratios up to 4:1. The experiments showed that depth had the greatest effect on the horizontal forces, followed by the width. Speed had the least affect on the draught force with only a 7.0% increase when increasing from 4.5 km/h to 10 km/h. This is very significant in improving the operation of and cost saving associated with high-speed plough operations. These studies indicated two critical issues that face manufactures i) The difficulty of increasing the furrow bottom width to accept wider tractor tyres. This problem was tackled with a re-design of the mouldboard assembly and further testing proved successful. The experiments showed that the actual furrow bottom width produced by the mouldboard could be increased for no additional increase in the horizontal force, both under controlled soil bin and field conditions. ii) The ability of the skimmer to operate at increased ploughing speeds. This problem was addressed by conducting soil bin and field studies on the standard manure skimmer. The forces were measured for a range of depths, speeds, rake angles and approach angles allowing an understanding of how pitch and yaw of the skimmer body affect the forces and the soil flow. The horizontal force studies were conducted under soil bin conditions and showed that both a reduction in the horizontal force and a better control of the soil flow could be achieved with the modification of the skimmers operating configuration. The skimmer field studies used a modified skimmer to investigate the improved soil and trash flow characteristics at higher speeds. Mathematical models have been developed to predict both the horizontal forces on the mouldboard assembly as a whole, the isolated horizontal mouldboard forces and also the horizontal force of the standard manure skimmer. The prediction was based on Mohr-Coulomb soil theory and inertia effects, with the ability to predict geometrical change for the skimmer as well as depth and speed effects. Both the mouldboard and the skimmer prediction show a good representation of the measured horizontal forces with R-squared values of 97.2% and 65.4% respectively. Finally the work rate of different size mouldboard ploughs was examined and the cost of operation investigated. Methods to reduce the cost of operation were highlighted and the overall cost compared to other tillage systems for a given working period and worked area. The increase in speed was seen as the most beneficial way of increasing the work rate and reducing the cost associated with the ploughing operation. Mouldboard ploughing was shown to be cheaper than minimum tillage up to 125ha (hectares) and cheaper than discing up to 275ha, whereas shallow high-speed ploughing was cheaper than minimum tillage up to 225ha and always cheaper than discing up to a limit depending on workdays.