Performance analysis of the top rollers in a sugar mill using finite element method

Abstract

Sugar milling is the process of extracting juice from crushed sugarcane fibres for production of sugar crystals. The three-shaft sugar mill set consists of the top roller and two bottom rollers to crush the sugarcane. The top roller shaft is the main crushing shaft of the sugar mill which is directly attached to the prime mover so it rotates and is loaded. Therefore, the top roller shaft in the mill set is subjected to more torsion and bending stresses. This study examined the mechanical performance of four top rollers under dynamic loading in four mill sets 1-4 of the sugar plant. To achieve this, firstly, the forces on the top rollers were determined and stresses on the top rollers were analysed using the maximum shear stress method to determine the unsafe loaded zones of the top rollers. Secondly, camera photos were obtained for visual inspection, detailed micrographs of the failed surfaces were obtained for microstructural examination; and the chemical composition and hardness of the failed components were determined and compared with known material standards for the top roller bare shafts, roller shells and couplings. Thirdly, geometrical models of the top roller were generated using solid works and transferred to ANSYS workbench which was used to analyse the maximum displacement, fatigue sensitivity, safety factor and equivalent alternating stress for the subjected dynamic loading in sugar milling; monotonic and cyclic parameters of forged steel were used for the bare shaft and parameters of ductile cast iron were used for the roller shell. The results of the shear stress analysis, microstructural characterization, and chemical composition and hardness of the failed top rollers showed that material non-conformance contributed to shaft failures. Maximum displacement, fatigue sensitivity and equivalent alternating stress showed that failure occurs at shoulders, key-way and shaft square ends; and top rollers in mill sets 3 and 4 are more susceptible to failure than top rollers in mill sets 1 and 2. The study evaluated the fatigue performance of top rollers in sugar mills. Keywords: Top Roller Shafts, Dynamic loading, Shear Stress, Alternating Stress, Mechanical Performance.