At the recent South African Heavy Haul Association (SAHHA) conference, industry experts Alberto Ronchi from Lucchini RS S.p.A. and Regan Holland from Lucchini South Africa presented a paper titled “Navigating Heavy Haul Success with Optimised Materials and Smart Designs.” The paper highlighted the importance of understanding the specific needs and goals of the customer when designing wheel and wheelset solutions for heavy haul applications. The presentation showcased three case studies from different parts of the world, illustrating how tailored wheel solutions can address unique operational challenges and enhance performance in heavy haul operations.
Alberto Ronchi highlighted the critical role of normative scenarios in designing wheels for heavy haul applications, which differ primarily between European (EN standards) and North American (AR standards) contexts. These differences include material choices, production processes, design, and validation procedures. For example, European standards permit only forged wheels, while US standards allow both forging and casting, each affecting wheel performance and mechanical characteristics differently. Moreover, while both regions use carbon steel grades, European steel grades such as ER7, typically used for tread-braked wheels in heavy haul applications, are generally softer than their American counterparts. This difference impacts wheel-rail interactions, affecting the wheel’s durability, wear behaviour, and overall service performance.
The design standards also diverge in their approach to thermal inputs from braking. European standards require separate investigations of mechanical and thermo-mechanical behaviours, whereas American standards necessitate both separate and combined evaluations. This distinction means a wheel compliant with one standard is unlikely to meet the requirements of the other, underscoring the importance of tailored designs for each application. Additionally, while some countries adhere strictly to either European or American standards, others, like South Africa, use both depending on the specific requirements of the case.
When designing a wheel for heavy haul applications, the wheel is normally tread-braked. This means that the thermal inputs and loading occurring on the wheel must be considered in the design process to ensure the wheel is suitable for withstanding these loads. The main point is that if you design a wheel according to European standards, it should not be expected to be compliant with American standards, and vice versa.
For heavy haul wheels, as with all railway wheels, material selection is a critical factor because it drives performance, wear behaviour, durability, and service life. The Lucchini RS Group is very proud of its steel production capability and metallurgical expertise. However, customer collaboration is essential; the process cannot be completed solely on paper or in theory. Feedback from service conditions, specificities of maintenance operations, and real-world performance is necessary to develop the best metallurgical solutions tailored to customer needs.
Case Study 1: Northern Europe – LKAB in Sweden
The first case study explored a challenging heavy haul application in Northern Europe, specifically involving LKAB, a Swedish company operating beyond the Arctic Circle. LKAB transports iron ore along a line entirely within this harsh environment. The conditions in this region are characterised by extremely cold temperatures throughout the year, but it’s truly a scenario of “fire and ice” because, despite the cold, the wheels become very hot due to tread braking. The line features severe gradients, including steep track segments with an elevation change of 537 metres and a maximum downhill slope of 1.7%, necessitating constant braking of the wagons.
To address these demanding conditions, Lucchini RS developed a wheel capable of withstanding an axle load of 35 tonnes, using their design solution branded as SURA®35. This is a thermo-stable solution, meaning the wheel is capable of enduring even the most severe thermal loads that occur during service, particularly from braking. A key feature of this design is the wheel’s special shape, which allows it to act like a spring under thermal loads—expanding due to thermal dilation but returning to its original position without excessive distortion.
The wheel was designed according to European standards, but an American steel grade was selected, as mixing standards is permissible. EN-designed wheels can incorporate American steel grades based on factors such as exploitation conditions and rail hardness. Initially, a Class C steel grade was chosen, but after gathering service feedback from the customer, it became clear that there was room for improvement. Lucchini RS is currently testing an enhanced solution using the A.Cl.CS UPLOS® steel grade, an evolution of the Class C steel grade according to AR standards. This ongoing testing aims to further improve the wheel’s wear performance and overall service life.
Case Study 2: South America – Rumo in Brazil
The second case study is from Brazil, where Lucchini RS has been supplying locomotive and freight wagon wheels to Rumo, a major logistics operator, over the past several years. These wheels are designed according to the AR standards. The compliance process for these wheels involved an extensive series of simulations through Finite Element Analysis (FEM) to verify the wheels’ adherence to AR requirements. It is not only about mechanical and thermal loads but also encompasses the stresses caused by fitting the wheel onto the axle, the stresses from the heat treatment applied during production, as well as other specialised analyses specific to locomotive wheels.
For all these wheels, Lucchini RS used the SANDLOS® steel grade, an advanced evolution of the AR steel grades. This material aims to improve rolling contact fatigue, wear behaviour, and performance during braking applications, representing an optimised version of the standard AR materials.
The first wheel supplied to Rumo in this case study is a 36-inch wheel for freight wagons, based on the K36 type as per American standards. While this type is a typical multi-wear freight wagon wheel, Rumo’s requirements exceeded the basic specifications of the standards, prompting Lucchini RS to apply additional design expertise. This enhanced wheel design was developed using CAD models and FEM models, focusing on the main design characteristics to meet the customer’s higher demands. Initial service feedback was highly positive, with the expectation that the wheel life will reach at least 1.5 million kilometres. This represents a significant improvement compared to the previous wheels used by Rumo, which were not supplied by Lucchini RS, particularly in resolving severe rolling contact fatigue (RCF) issues.
Lucchini RS also designed two separate 42-inch locomotive wheels for Rumo, both utilising the SANDLOS® H steel grade. The first wheel type closely aligns with standardised locomotive wheels according to American standards; however, due to Rumo’s specific requirements, a tailored solution was developed to further enhance performance.
The second locomotive wheel case was more distinctive because of unique wheelset interfaces, necessitating a different wheel shape. In both locomotive cases, Lucchini RS is confident that the wheels will outperform those previously used by Rumo. The ongoing service feedback continues to validate these expectations, indicating enhanced durability and operational performance under the demanding conditions of Brazilian railways.
Case Study 3: Africa – Transnet in South Africa
Regan Holland presented the third case study, which focused on Transnet. The wheel was designed specifically for the Heavy Haul line running between Sishen and Saldanha, and also the coal line. These lines operate under extreme conditions, from very hot to very cold, and dusty environments, with demanding axle loads. Lucchini’s approach was twofold: firstly, to increase the tonnage for Transnet and secondly, to enhance the safety conditions of the wheel. This led to the development of a SURA®32.5 wheel, designed according to EN standards but using AR material grades, increasing axle load capacity from 30 to 32.5 tonnes. The development process spanned 5-8 years, culminating in final approval from Transnet at the start of this year. The initial in-service tests demonstrated significantly reduced wear compared to previous wheels, enhancing the overall performance and lifespan of the wheels. The life expectancy or the wear life of the wheel, after two years in service, was significantly improved compared to the normal wear life of other wheels that were previously supplied.
The Future: Condition-Based Maintenance with Smart Solutions
Looking ahead, Alberto Ronchi emphasised the shift towards condition-based maintenance, moving away from standardised, fixed maintenance intervals to more adaptive approaches driven by real-time monitoring. Lucchini RS has developed a suite of condition-based monitoring solutions under the brand Smartset, which measures real stresses on axles during service. By analysing these stresses with advanced algorithms, the optimal inspection intervals can be determined, potentially extending maintenance intervals and reducing costs.
This approach has already been implemented in Europe and China, with one European customer doubling their inspection interval to 500,000 kilometres. Such innovations represent the future of heavy haul operations, aiming to enhance sustainability, vehicle availability, and overall system efficiency.
