Effect of Soil Resistance and Gear Composition on Surface Wear and Fatigue of Worm Gear on Locally Made Self-Propelled Rotary Hoe

Abstract

Rotary hoe is a handheld self propelled inter-tillage machine for row crops. The machine had problem with its gearbox, which consists of a worm gear-set. Frequent failures of the worm gear restricted the widespread adoption of the machine. The main purpose of the study was to overcome the problem by analyzing the effect of soil resistance and gear composition on the surface wear and fatigue of the worm gear. Three different gear compositions i.e.: 1. Commercial gun metal (Gear-1), 2. Gun metal (Gear-2) and 3. Gear bronze (Gear-3) were tested against the soil penetration resistance in a controlled soil bin conditions. The bin filled with sandy clay loam soil of 15m x 45m x 0.76m size was constructed and used for testing the above gears. Five soil resistances were created with different five soil moisture conditions (3, 6, 9, 12, and 15% of moisture contents). Hand-held cone penetrometer was used to calculate soil resistance. Undisturbed soil samples were randomly collected from the bin for all five different moisture conditions to determine moisture contents. The same experiments were extended to the field conditions at two different locations having silty and sandy loam soils testing Gear-1 and Gear-3 for surface wear. The gear composition Gear-1 used by the manufacturer had significantly high surface wear and fatigue as compared to the other two gear compositions in the soil bin experiments. Gear bronze (Gear-3) showed significantly lower surface wear and fatigue among the other gear compositions. Gear-3 exhibited minimum surface wear as compared to Gear-1 in the field experiments. Composition of Gear-3 showed the lowest wear among all the three gears in both soil bin and field experiments which may be used in the machine transmission for its longer service and durability.