Division of Information Technology, Engineering and the Environment
School of Advanced Manufacturing and Mechanical Engineering
School of Advanced Manufacturing and Mechanical Engineering
Thesis Abstract
The interactions between soil, a disc blade opener and its accompanying gauge wheel - as used on zero-till disc seeders - are poorly understood. Single flat disc blades are often combined with a side gauge wheel to control the operating depth and reduce the soil throw. Available soil force prediction models have considered either concave blade as used on disc ploughs and harrows, which are not suitable for the flat disc blade openers and gauge wheel combinations used on zero-till seeders. The objectives of this study is develop and validate an analytical force prediction model to suit a single flat disc opener and side gauge wheel system and validate the model’s ability to simulate sticky soil conditions. This study will provide recommendations for reducing soil forces, increasing disc speed ratio and improving disc seeder component performance with particular considerations to sticky soil conditions.
The passive earth pressure theory is used to analyze the soil reactions to a flat disc blade operating under both tilt and sweep angles. Hence, a number of measurements of soil failure and 3D force components were performed under controlled soil conditions, in particular to determine the critical disc angle and quantify the contact area of scrubbing under different sweep and tilt angles. The effect of blade shape (circular vs square) and disc rotation on soil force components and soil failure characteristics were also evaluated in a process of linking the actual blade system to that assumed in a basic model. Results showed that, soil failure is generated by the front quadrant of the disc blade, particularly at low sweep angles. The exact proportion of the disc chord at the soil surface that is actively involved in generating soil failure was quantified. In addition, a field test was performed to evaluate the force and soil build up characteristics of a disc blade with gauge wheel system in sticky soil conditions. Results showed that both the presence of the gauge wheel and greater down force loading applied onto the disc + gauge wheel system significantly increases the soil build up. A UHMW polymer coated disc demonstrated less soil build up compared to a common steel disc. The results were in agreement with the findings of a laboratory test which showed decreased soil adhesion under lower normal loads and with the polymer material. The results to date highlight a possible avenue to develop a useful soil/disc force prediction model based on classical soil-mechanics theory.
