Introduction

With more than 31,000 kilometers of track across the country, the railways connect the major mining and steelmaking centers, as well as industrial and agricultural hubs to the main Brazilian ports. Due to the significant load capacity of locomotives, railroads excel in loading large volumes of products and raw materials, which helps to reduce travel and consequently reduce costs for companies and the prices of consumer goods.

With this in mind, the continuous increase in the use of railroads generates wear and tear on assets as a result of use, which can compromise the conservation of their structures and the safety of operations. As an example, it is possible to cite the occurrence of fatigue in rails and components as a result of increased axle loads and/or changes in the speed of locomotive and wagon trains.

Nesse sentido, a adoção de técnicas de instrumentação permite monitorar os efeitos dinâmicos em vagões, locomotivas e vias permanentes. Isso possibilita a aquisição de dados para tomadas de decisões mais assertivas, que asseguram o funcionamento adequado das operações e mitigam os custos com manutenções corretivas – relembre visitando os exemplos apresentados nos artigos Instrumentação Ferroviária e Case de sucesso: Instrumentação de ferrovia.

Sob esse contexto, um de nossos clientes solicitou a análise das condições de um truque ferroviário de um vagão tipo gôndola, frente ao aumento de carga de minério no vagão. Foi requerida uma avaliação dos esforços atuantes no truque por meio de extensometria, assim como o monitoramento do curso das molas de suspensão e da temperatura dos rolamentos.

By way of example, the study in question made it possible to estimate the useful life of the bogie, given the operating conditions of the wagon, by means of fatigue analysis. The information and conclusions of the service carried out by Kot enable the client to carry out a comparative and quantitative study of the costs involved in its logistics process, such as preventive maintenance, freight pricing and other operating costs.

Field instrumentation

Initially, the railway bogie was instrumented - consisting of two sides (Figure 1) and a cross member (Figure 2) - to continuously acquire the required data, according to real working conditions, during three cycles of the wagon's journey. Thirteen strain gauges, 1 GPS, 2 thermocouples and 2 load cells were installed.

The sensors in question were strategically implemented in order to evaluate and monitor, respectively, the stresses acting on the components, the geolocation of the wagon, the temperature of the bearings and the displacement of the suspension system. All of them were connected to an on-board acquisition system and the data obtained in real time was recorded for later processing and correlation with the stages of loading, moving and unloading the wagon. Figures 1 and 2 show the individualized models of the bogie side and cross member, respectively.

Figure 1: Computer model of the side of the bogie. SOURCE: Kot Collection.

Figure 2: Computer model of the bogie crossbar. SOURCE: Kot Collection.

Development and calibration of the computer model

Em seguida, elaborou-se um modelo de elementos finitos (MEF) do truque em um software CAE (Computer Aided Engineering), com base em um levantamento dimensional feito em campo (as built), reproduzindo de forma detalhada a geometria do ativo. O modelo computacional gerado pode ser visto na figura 3 a seguir.

Figure 3: Computer model of the trick. SOURCE: Kot Collection.

To validate the model, the components were analyzed separately based on the stresses collected by the strain gauges during loading of the wagon. Figures 4 and 5 show the strain results obtained during calibration.

Figure 4: Deformations obtained in the bogie beam during model calibration. SOURCE: Kot Collection.

Figure 5: Deformations obtained on the sides of the bogie when calibrating the model. SOURCE: Kot Collection.

With the model calibrated, a structural check was carried out to assess the forces acting on the sensor installation points under three different loading conditions. Once the results had been obtained, the stresses in the bearings were evaluated and the respective equivalent Von Mises stresses were determined.

Analysis of the wagon's operating cycle

Secondly, a static structural analysis was carried out based on the data obtained from strain gauges fixed to the top and inside of the bogie during the wagon's operating cycle. The first sensor was used to identify bending due to vertical loading of the wagon, and the second for bending due to lateral loading. The deformations recorded by the sensors in question are shown in graphs 1 and 2.

Graph 1: Strain values on the strain gauge located at the top of the bogie. SOURCE: Kot Collection.

Graph 2: Strain values on the strain gauge located inside the bogie. SOURCE: Kot Collection.

With this in mind, the peak values were used to quantify the stresses and consequently to determine the stresses in the concentration regions. Figure 6 illustrates the result of this analysis, highlighting the wheel supports in the computer model.

Figure 6: Voltage concentrators in the computer model. SOURCE: Kot Collection.

It was concluded that the lateral load variations on the bogie (graph 2) have a greater amplitude than those of the vertical load (graph 1), which increases the stress in the stressed areas and reduces the useful life of the component due to fatigue.

Analysis of bearing temperatures

The on-board system only recorded variations in the ambient temperature over the three trip cycles. No significant variations were detected in the bearing temperatures monitored by the thermocouples, which remained within the bearings' working temperature range.

Suspension spring travel analysis

With regard to assessing dynamic displacement, the load cells monitored data on the travel of the suspension springs. Some of the values recorded during the journey with the wagon loaded with ore can be seen in Graph 3 below.

Graph 3: Travel of the suspension springs during the journey of the loaded wagon. SOURCE: Kot collection.

The dynamic analysis showed that the loading in question resulted in a displacement of the suspended mass. In general, spring compressions were observed in the sections where the wagon was loaded and no distensions were identified in the unloaded sections, due to load relief. The frequency of the suspension oscillations is shown in graph 4, with 2 Hz being the main frequency during the three cycles monitored.

Graph 4: Suspension oscillation frequency. SOURCE: Kot collection.

Fatigue analysis

As for the fatigue analysis of the bogie, a useful life of 61 years was estimated for a load of 132.9 tons of ore. For loadings of 133.7 and 134.9 tons, reductions of 28% and 44% respectively were observed in the component's useful life when compared to 61 years. The peaks with the greatest influence on the bogie's useful life are highlighted in Graph 5.

Graph 5: Peaks with the greatest influence on bogie service life. SOURCE: Kot Collection.

By excluding the critical peaks from the analysis, the useful life was recalculated as 69, 55 and 42 years for shipments of 132.9, 133.7 and 134.9 tons of ore, respectively.

Conclusion

It is well known that the wear and tear on wagon components and structures is inherent to rail transport operations, a modality that is growing more and more on the national scene. According to ANTF (National Association of Railway Transporters), in 2021, the rail freight sector grew by 506.8 million useful tons (TU), 3.6% compared to 2020.

With this in mind, the instrumentation aims to monitor and detect the areas of the railroad where the most damage to trains occurs, which compromises the safety and logistics of freight transport.

In this regard, we would highlight the service carried out by Kot, in which the monitoring and evaluation of the dynamic effects on the wagon's components was carried out, making it possible to offer the client greater reliability in making data-based decisions, with a view to reducing future costs.

In view of the above, the excessive variations in compression and load relief of the suspension travel and the influence of ore loading on the useful life of the bogie were the highlights of this study. With regard to the variations recorded on various sections of the railroad, the most pronounced occurred in curves and in the areas of the old permanent way yards.

In addition, the main causes of the component's reduced lifespan are the lateral loads imposed on the bogie during journeys. Once identified, the main causes and the data collected on the stretches become fundamental inputs for the client to draw up studies of ideal loads and speeds for transportation, which will be adopted to mitigate premature wear and derailment risks by means of strategic and specific interventions.

Among other gains, the study of the useful life of the components of the wagons, as well as the permanent way, allowed the client to predict expenses with replacements and interventions, resulting in a more assertive forecast of logistics costs.

Percebe-se, portanto, que as técnicas de instrumentação são extremamente relevantes para a gestão e manutenção de integridade dos ativos ferroviários. Nesse sentido, a Kot conta com um time de profissionais qualificados para desenvolver as melhores soluções de engenharia para os desafios intrínsecos ao dia a dia do modal ferroviário. Consulte nossa equipe para mais informações!

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