Over the years, railways throughout the world have been confronted with a growth in passenger numbers, increased train speeds, higher traction and braking forces and an overall rise in gross tonnage passing over their tracks.
Although, in many cases, rail maintenance regimes have been adapted to manage these increases via improvements in inspection, lubrication and rail grinding, rolling contact fatigue (RCF) damage is still a serious problem encountered by a number of railways.
Rail grinding has proved to be an excellent tool for controlling rail wear damage and preventing certain types of RCF development. However, some types of RCF, such as squats, studs and other surface-initiated rail defects, remain a serious problem. Factors such as rail steel quality, poor wheel-rail interaction, not enough (or in some cases too much) lubrication, track geometry faults, vehicle characteristics and even climatic conditions can contribute to the occurrence of RCF, and rail defects up to 5mm deep are not uncommon these days.
Since RCF can significantly reduce rail service life and is a serious safety hazard, new methods of dealing with the worst rail defects have been sought. Over the last decade, rail milling has been identified and introduced by railways throughout Europe as an essential treatment technique to increase rail service life, thereby significantly reducing rail replacement requirements and capital expenditure.
Innovative rail treatment
For decades, Germany’s Schweerbau, operating from its base in Stadthagen near Hanover, has been one of the main service providers for mobile rail treatment throughout Europe. Providing rail profile planing and oscillating grinding services since the late eighties, during the mid-nineties the company introduced the world’s first mobile rail milling train.
Over the following years, Schweerbau has developed and introduced further highly innovative technologies including rail milling machines for underground operations and rail rotational planing machines (DHOB technology) suitable for the productive, high accuracy and clean machining of rails in turnouts. Its most recent development has been the HSM high-speed mobile rail treatment train, again setting new standards in terms of output, quality and, last but not least, safety.
Today, Schweerbau operates the world’s largest fleet of diverse mobile rail treatment trains for both main line and urban railway systems. Its portfolio of rail treatment trains includes planing, oscillating grinding, milling, rotational grinding, rotational planing and high-speed milling systems. In fact, when it comes to bringing rails back to shape or keeping rails in shape, Schweerbau has all the tools in the box.
A three-car diesel-electric powered machine, the HSM high-speed rail milling train was built by Schweerbau in 2015. It was based on experiences with earlier rail milling trains, all of which had certain limitations, and also on the demands from the industry for more-productive machines with higher metal-removal rates as a result of reductions in track possession times combined with a need for improved safety and availability.
The HSM is fitted with four high-output 1440mm milling wheels, fitted with up to 720 cutters each, rotating around horizontal shafts perpendicular to the rails. This so-called ‘climb’ milling process, where the milling wheels turn in the same direction as the machine’s working direction, combined with the large diameter milling wheels (and number of cutters), allows for faster machining speeds with higher metal removal capabilities when compared to previous milling trains which were fitted with 600mm diameter milling wheels.
In addition, the HSM milling technology allows for the treatment of up to 5,000 metres of track before the milling cutters have to be replaced. This eliminates the need for technicians to go trackside, thereby improving both safety as well as total output per shift.
Where longer track possession times are available, the innovative ‘segmented’ design of the large diameter milling wheels fitted on the HSM, in combination with an on-board automated segment change system, allows for renewing all milling cutters on the milling wheels rapidly without the need to get off the train and work trackside.
From an environmental point of view, the HSM is capable of collecting 99 per cent of the recyclable metal residue (swarf) it produces and, due to the low noise emissions produced and the single pass operation capability, noise nuisance during operation is significantly reduced compared to other mobile rail treatment machinery.
The HSM was fully approved and introduced on the German rail network by Deutsche Bahn in 2016, where it proved its capabilities in terms of output, quality and safety.
In 2017, Schweerbau was awarded a service contract to provide rail milling services on Network Rail infrastructure. The company chose to work with Derby-based Aegis Engineering Systems to manage the approvals process for the HSM for operation in the UK. Aegis is an independent engineering consultancy with an in-depth knowledge of and experience in gaining approvals for a wide range of rolling stock and infrastructure projects.
The HSM provided an interesting twist on the approvals process, being a train developed by Schweerbau for future UK operations but one that was approved by the German authorities for use on Deutsche Bahn infrastructure.
Aegis developed an approvals procedure that worked from the existing German design and compliance documentation, to create a suite of work packs that demonstrated compliance with the mandated standards, chief amongst these being RIS-1702, GM/RT2400 and EN14033.
In parallel with this, Aegis ran a safety assurance process on behalf of Schweerbau which was compliant with the Common Safety Method – although the project was deemed non-significant, the process applied ensured that best practice was followed. Aegis also managed the process for achieving Network Rail product acceptance, by demonstrating achievement of the requirements in terms of purpose and safety of operation.
Aegis Certification Services provided the independent assessment (NoBo/DeBo and PAB – Notified Body/Designated Body and Plant Assessment Body) services to ensure that ORR (Office of Rail and Road) authorisation was achieved in the most efficient manner, allowing Schweerbau to begin bringing the benefits of its rail treatment services to the UK railway.
Although Network Rail owns and operates quite a large fleet of rail grinding trains, keeping the rails in tracks and switches throughout the network in shape, there are still certain parts of the network that require a more corrective approach. These are areas that suffer from particular RCF problems, areas that cannot regularly be addressed by grinding trains or simply areas where it’s more suitable and economical to use alternative methods of treatment due to issues such as access, environmental requirements or fire risk. This is where the HSM will have its primary role on the Network Rail infrastructure over the next few years.
Although Schweerbau has been a track and rail maintenance ‘service provider’ from origin, the increasing worldwide demands to purchase specialist mobile rail treatment machines has recently led to the founding of an affiliate company, Schweerbau International, which is also based in Stadthagen, Germany.
By taking full advantage of the experience and know-how gathered in railhead treatment over the past 30 years, Schweerbau International focusses on the design, manufacture and supply of specialised high-technology maintenance machines such as rail milling trains, rail grinding trains and specialist maintenance trains.
The next generation in mobile rail milling trains – the highly innovative CM42 series – is due for arrival in 2020.
This article was written by Maurice Verheijen, director of Schweerbau International.
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