Torque Requirement Analysis and Design of Edge-cell Type Metering Device for Corn Fertilizer Applicator

Abstract

A prototype of integrated machine for planting, fertilizer applicator, and soil tillage for corn cultivation has been developed in 2009. It still had many lacks such as non-uniform seed spacing, unadjusted fertilizer discharge, the level of jamming in driving wheel was 38%, quite high to cause metering device stopped working. Afer being modified, planting and fertilizing performance showed improvement. However, the level of jamming was still high at about 31% which caused inappropriate seed and fertilizer discharge. Due to the excessive friction and fertilizer clogging, the metering rotor often stopped working. Therefore, an optimum design of metering device is needed to overcome the problems. The objectives of the research were: 1) to analyze torque requirement of edge-cell type metering device and 2) to design an edge-cell type metering device for corn fertilizer applicator with lower torque requirement and high accuracy. Metering device used in this research was an edge-cell type rotor, optimally designed to minimize the friction between fertilizer and the rotor tips, produce uniform seed spacing, and require lower torque. The rotor diameter is 40 mm with 6 grooves, its diameter is 4.5 mm each, and rotor length is 80 mm. It was equipped with rotor casing for discharge controlling. For performance test, the hopper and a variable speed electric motor were attached to the metering device in a set of experiments in the laboratory. The rotor shaft was equipped with strain gage to measure the torque requirement. The tests included: accuracy test, uniformity test, torque requirement analysis, and model validation of metering device. The fertilizers used in the research were urea, TSP, and a mixture of TSP and KCl. The rotor rotation speed was varied: 15, 25, and 35 RPM, and fertilizer volume was: 25, 50, and 100%. For comparison, a conventional (prototype-2) metering device was also tested. For torque requirement analysis, a mathematical model to estimate torque requirement of prototype-2 and edge-cell type (prototype-3) metering device was developed. The accuracy test of prototype-3 metering device showed satisfying results. For test on urea, at 50, 75, and 100% rotor opening, the average fertilizer discharge rate was 20.76 g/rotation, 26.00 g/rotation, and 33.56 g/rotation, respectively. It was slightly smaller than teoritical discharge rate. The rotor rotational speed at 15, 25, and 35 RPM gave no significant effect to discharge rate. For test on TSP, at 50, 75, and 100% rotor opening, the average fertilizer discharge rate was 39.81 g/rotation, 50.92 g/rotation, and 62.72 g/rotation, respectively. For test on TSP-KCl mixture, at 50, 75, and 100% rotor opening, the average fertilizer discharge rate was 32.82 g/rotation, 45.83 g/rotation, and 54.58 g/rotation, respectively. The uniformity test also performed satisfying results and the change of fertilizer volume did not affect the discharge rate. For test on urea, at 25, 50, and 100% fertilizer volume, the discharge rate was 33.36 g/rotation, 33.90 g/rotation, and 33.56 g/rotation, respectively. For test on TSP, at 25, 50, and 100% fertilizer volume, the discharge rate was 60.96 g/rotation, 61.03 g/rotation, and 62.72 g/rotation, respectively. For test on TSP-KCl mixture, at 25, 50, and 100% fertilizer volume, the discharge rate was 55.96 g/rotation, 55.59 g/rotation, and 54.58 g/rotation, respectively. From the torque requirement test, it was concluded that the torque requirement of edge-cell type metering device was lower than the conventional type. For comparison, torque requirement at 100% rotor opening tested on urea was 0.13 N·m (prototype-3) and 0.20 N·m (prototype-2). At 75% rotor opening, the torque requirement was 0.12 N·m (prototype-3) and 0.20 N·m (prototype-2). At 50% rotor opening, the torque requirement was 0.19 N·m (prototype-3) and 0.27 N·m (prototype-2). When tested on TSP, the results were 0.27 N·m (prototype-3) and 0.54 N·m (prototype- 2). The torque requirement of edge-cell type metering device was lower than prototype-2 up to 68% (tested on urea) and 80% (tested on TSP). The validation results showed that the mathematical model could predict accurately the torque requirement of the rotor only on the lower volume of fertilizer in the hopper (25%). While the mathematical model to estimate the torque requirement for TSP needed improvement to predict more accurately.