Soil forces on deep tillage tools
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The force performance of different tillage tools was investigated in sandy loam and clay loam fields at a working depth of 18 cm and at three operating speeds. The tools included four cutting edges: flat, 90°, 40°, and elliptical with rake angles of 20° and 33°. Draft, vertical, and side forces were measured using six loadcells in a three directional arrangement such that two loadcells measured draft, three measured vertical force, and one measured the side force. All the variables were combined to form a 2x3x4 factorial experiment with three replicates. The force data were analyzed using balanced analysis of variance with a Mini tab statistical package. The instrumentation included an accelerometer to investigate the movement of the shank, a potentiometer to determine working depth, and a magnetic pickup to indicate operating speed. The draft measurements for all tools were compared to the values generated using a prediction equation from an ASAE standard. Results indicated that two of the modified tools had lower draft than the predicted values. Draft increased from a minimum for the flat cutting edge to a maximum for the elliptical shape in the sandy loam and clay loam soils. There was no significant difference in draft with respect to the rake angle, but there was a significant increase in draft due to higher operating speeds in sandy loam and clay loam soils. The clay loam field had draft values lower than those of the sandy loam field. Similar trend was observed for the vertical force. Due to tool symmetry, the side force was insignificant. A linear relationship existed between resultant force and operating speed in both soil types. The accelerometer data showed that there was vibration of the shank during tillage. The results were similar to the ones reported by Zhang (1997) and indicated an increase in vibration frequency of the shank with an increase in resultant force.