This paper presents the systematic mechanical design, finite element analysis (FEA) validation, and iterative structural optimisation of an automated eccentric lift-and-shift rebar handling mechanism for the cooling bed of a hot rolling mill. Motivated by a 32.1% incident rate and a throughput deficit of 50 bars per hour at Steel Brands Zimbabwe, a 7.5 kW eccentric-shaft mechanism was designed to advance 8–25 mm diameter rebars across a 7-metre bed at 30 mm/s. The primary technical contribution is a three-phase FEA study conducted in SolidWorks Simulation 2024, employing curvature-based tetrahedral meshing (137,482 nodes; 89,204 elements) and mesh convergence verification (< 3% stress change between 4 mm and 3 mm element sizes). An initial 50 mm EN8 shaft produced an inadmissible maximum von Mises stress of 540.6 MPa at the keyway root—a safety factor of 0.86—indicating impending plastic deformation. Failure was attributed to a stress concentration factor (Kt) of 3.0 at the standard rectangular keyway. Two corrective iterations were executed: shaft enlargement to 65 mm at the keyway region and transition to a sled-runner keyway profile (Kt = 2.2), reducing peak stress to 214 MPa and raising the safety factor to 2.17. All four structural sub-assemblies—eccentric shaft (SF = 2.17), moving rake (SF = 6.05), stationary rake (SF = 1.32), and support frame (SF = 3.73)—meet the specified threshold of 2.0 for the primary load-bearing shaft and satisfy AISC 2016 intermittent-duty criteria. Cross-validation with closed-form Shigley beam-bending analysis confirms FEA accuracy to within 12%. The study establishes a replicable, low-cost FEA-driven design methodology applicable to eccentric-mechanism equipment in resource-constrained sub-Saharan African manufacturing contexts.

Keywords

Finite element analysis, eccentric shaft, stress concentration, keyway optimisation, cooling bed automation