An investigation into wear characteristics of a direct drilling coulter (opener) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Agricultural Mechanisation at Massey University
Wear on a promising chisel coulter, developed at Massey University, was considered to be marginally unacceptable. A functional lifespan of approximately 20 hectares for non-rolling blade components necessitated relatively frequent coulter replacement, and thereby incurred increased costs for components and machine downtime. Three experiments were carried out with an improved version of the Massey University chisel coulter concept. The respective objectives were as follows: 1. To determine whether soil particles were passing between the rotating disc and stationary coulter blade components during normal field machine operation. 2. To determine the patterns of coulter blade wear. 3. To compare several selected blade treatments in their abilities to prolong functional coulter blade life. In the first (laboratory) experiment, a stationary test rig was constructed. This closely simulated coulter assembly operation in the field. Measurements of changes in soil particle size with time for "soil" and "no soil" introduction to the disc/blade interface did not detect any soil breakdown which might have indicated a soil "lubrication" effect at that interface. However, observations of the patterns of abrasion and of photographs did indicate that some form of soil "lubrication" had occurred. In the second experiment, a hard-facing welded (Hardcraft 700 over mild steel) and a control treatment (mild steel) were evaluated to establish patterns of wear on a three row field-operating test rig. The former treatment displayed potential for resisting dimensional changes at various stages throughout blade life. The rotating action of the disc against the inner shank of the blade was responsible, in the prevailing conditions, for wear at the inside lower leading edge/wing intersection of the blade. This action eventually accelerated wing wear. The weld bead pattern was modified for use in Run A of Experiment 3 (top pattern); and another pattern (bottom pattern) was designed to prevent possible increased penetration forces associated with the original weld pattern. The third experiment involved evaluation of selected treatments during routine field drilling operations, using a pre-production prototype direct drill. Carbonitrided mild steel blades offered an almost three-fold increase in relative wear resistance (in terms of metal weightloss per hectare) compared to the standard mild steel blades. The carbonitrided treatment also resisted dimensional changes more effectively, and was more cost effective than all other treatments. The influence on wing and shank dimensions exerted by left and right side blade positioning on each coulter assembly, appeared to reflect continual anti-clockwise machine cornering during operation and seed/fertiliser dispersal differences. Coulter wings on the outside of field turns were subjected to greatest wear, as were the shank regions of blades dispersing fertiliser. Lateral and fore/aft positioning of coulter assemblies appeared to have no effects on blade life.