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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.
Metso Minerals' bulk materials handling solutions specialises in equipment for loading, unloading and storing bulk products such as coal, iron ore, limestone, wood chips, potash, grain, fertilizer and other bulk materials. The railcar dumpers are one type of bulk material handling equipment.
The Metso Minerals railcar dumpers have set industry standards worldwide since 1905, with the most technologically advanced list of standard features for system dependability, efficient operation and long service life. Single, tandem and triple dumpers are engineered to provide long life and low maintenance service in dumping coal, ores, sulphur, phosphates, wood chips and other bulk materials. The Metso Minerals complete railcar dumper/positioner system provides fast dependable train turnaround requiring only one operator.
For each individual application, the railcar unloading system is custom-configured and built with the site specifics and customer needs in mind. The graphic below shows a tandem barrel configuration, which allows double unloading capacity.
Designing dumper barrels with finite element analysis (FEA) software allows Metso Minerals engineers to evaluate high-stress areas prior to manufacture for optimum fatigue life. CADFEM UK CAE Ltd. was approached 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.
The dumper assemblies were supplied to CADFEM UK CAE Ltd. 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. The graphic above depicts the basic FE mesh as created within 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 have 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 (as shown in the graphics below) 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.
CADFEM UK CAE Ltd. have carried out 3 such analyses for Metso Minerals with each subsequent analysis taking less 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 ANSYS Workbench. These new solid shell elements reduce the requirement for creating mid-planes and take advantage of surface to surface contact defined between the original solids parts in the CAD model. Further to this, the use of macros for carrying out fatigue and weld assessments also gave substantial time savings.
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