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IDAC was approached by Metso Minerals to carry out the finite element analysis work using ANSYS for three separate design projects of rotary railcar dumpers to evaluate the stress and displacement levels at different operational and extreme positions and conditions, as well as evaluating the natural frequencies of the main structure.
Metso Minerals is a leading global supplier of equipment, services and process solutions to industries, including quarrying and aggregates production, mining and minerals processing, construction and civil engineering, and recycling and waste management.
Designing dumper barrels with finite element analysis (FEA) software allowed Metso Minerals engineers to evaluate high-stress areas prior to manufacture for optimum fatigue life.
The dumper assemblies were supplied to IDAC in Autodesk Inventor format. The Inventor model was imported into ANSYS Workbench DesignModeler where mid-plane extraction was conducted to reduce most solid plates into 3D surfaces. Some components such as the side pad, non-tip brackets, non-tip vibrator and the dumper buffer were represented with simple solids. The model was then transferred the finite element (FE) module, workbench design simulation (WBDS) where the FE model was prepared.
A three-dimensional, structural analysis was carried out. Shell, brick and beam elements were used to mesh the dumper barrel and the car geometry in WBDS.
Beam and link elements were added to represent the clamp system and a simple framework was added to represent the rollers and the support framework. Coal was added to the car as a concentrated mass element at the appropriate location depending on the tip angle and load case being run, as specified by Metso Minerals.
The different components of the dumper barrel assembly were connected using standard ANSYS contact elements and beam elements. All materials were assumed to behave elastically and homogeneously for the purpose of the design evaluation.
A total of 22 load cases were analysed which included 12 different orientations of the dumper car, modal analyses to compare natural frequencies to those of the motor and a ‘frozen load’ load case to simulate the effect of having a complete load in the car at the different orientations.
The structure was supported on six rollers at each ring, with three on the tip side and another three symmetrically on the non-tip side. The three rollers on either side on the rings were mounted on a pivoting framework modelled as simple beam elements with translational and rotational degrees of freedom.
The results requested for each load case were stresses and displacements of the main dumper barrel structure. Metso Minerals required equivalent stress, principal stresses, normal and shear stress, and displacements in the three global directions. The results were reported at mid-plane and at the centroid of the shell elements.
Fatigue and weld assessments were also carried out in accordance with BS2573 and BS2573 Part 1 respectively. Macros were written to carry out the checks automatically on an element-by-element basis.
IDAC have carried out three such analyses for Metso Minerals with each subsequent analysis taking a fraction of the time of the previous one. This was largely due to the creation of macros to run the analysis and improvements made in the model preparation for the analysis. It is now envisaged that time will be further reduced for future projects by making use of the new solid shell element within WBDS.
The solid shell elements are able to handle moments and as such this reduces the requirement for creating mid-planes and surface to surface contact can be used rather than edge to surface contact.
The use of macros for carrying out fatigue and weld assessments also gave substantial time savings.
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