Stress Analysis and Design Modification of 3-stage Helical Gear Box Casing

the finite element analysis of 3 stage helical gearbox that constitutes the driving mechanism of a double bascule movable bridge was performed. The triple reduction helical gearbox was made of ASTM A36 Steel. The triple reduction helical gearbox was a three stage gearbox transmitting 112.5 H.P. at 174 rpm with a reduction ratio of 71.05:1. The Differential gearbox was a single stage gearbox transmitting 150 H.P. at 870 rpm with reduction ratio of 5:1 The load calculation for helical, herringbone, and bevel gears were performed using the MATHCAD Software package. The reactions were used to apply loads to the finite element model of housing (casing). Geometric model of 3 stage helical gearbox was built using NX-8 and meshed using the ANSYS finite element program. Linear structural analysis was performed using a combination of shell and solid elements to determine the deflection and to estimate the stress distribution in the housing. Nonlinear analysis was later performed using shell, solid, and beam & gap elements to determine if the interface between the two halves of the housing separated and contributed to any undesirable misalignments of the shafts or bearings. In the triple reduction gearbox, the axial forces caused a maximum displacement 0.05588 cm. The location and magnitude of the displacements would not contribute to the undesirable misalignment of the shafts and bearings. The maximum von Misses stress in the triple reduction gearbox was 9000 psi. The minimum factor of safety in the triple reduction gearbox was four. The nonlinear analysis determined that separation did not occur on the interface between the two halves of the gearbox housings.