Mobile flash butt welding

Rail connections are the most critical elements of any railway line. Whether it's technology, equipment, or the professionals behind them, the highest quality is always required. In addition to the stationary services provided at its own plants, Vossloh offers mobile welding solutions for all types of lines and tracks, regions, and customer requirements.

With machines and experts, Vossloh ensures a completely seamless track on construction sites – delivering rail infrastructure where the rails are continuously welded rather than joined with fishplates. Flash butt welding (RA welding) is the most advanced and highest quality rail welding technology. For this purpose, we use mobile butt welding trucks (two-way vehicles) or our mobile welding plant (semi-stationary). Aluminothermic welding is used for turnouts and on special sections of track.

Overview

Flash butt welding (RA welding)

Semi-stationary welding plant (RA welding)

Aluminothermic welding (AT welding)

Mobile flash butt welding

Flash butt welding, also known as RA welding, is the most advanced and highest-quality technique for manufacturing long rails and is used globally in all stationary welding facilities. Vossloh has been using this technology directly on tracks for over 20 years. Mounted on road-rail vehicles, the welding machines deliver maximum quality, cost-effectiveness, and flexibility in the production of seamless tracks. Flash butt welding teams have already been deployed across four continents.

Overview

Reference: Türkiye

Reference: Copenhagen

Reference: Paris

Reference: Türkiye

Reference: Türkiye

Technology: Fully automated process

Mobile flash butt welding is a highly automated process in which rail ends are heated to the required welding temperature by resistance heating using high electrical current and then pressed together under substantial hydraulic pressure – without the addition of any filler material.

And this is how it works: The various steps involved in the RA welding process, taking into account the working direction:

Preparation of rail ends by contact grinding

Clamping & precise alignment of the rail ends

Flash butt welding

Deburring & rough grinding

Fine grinding

Stress equalization is carried out in accordance with specifications, e.g. using a hydraulic pulling device

Certificates

In terms of processes and machinery, Vossloh holds multiple national approvals and has the capacity to complete major construction projects – such as Germany’s high-speed lines and Norway’s Follobanen tunnel – on schedule.

Certificates

Fact check & benefits:

Higher quality & strength (approx. 500 kN greater bending force compared to a thermite weld on a 60E1 rail profile)
Greater process stability & high reproducibility of results in mass production thanks to processor control ¨ Eliminating the need for additional ultrasonic testing in Germany
Efficient for rapid progress: At least four RA welds per hour guaranteed. Under certain conditions, additional welds can be performed – for example, by modifying the site workflow or operating in a semi-stationary mode.)

No filler material -> significantly improved occupational safety and more environmentally friendly:
- significantly less smoke and dust
- significantly less waste, which is also recyclable
- no slag or welding residues
- No mold or casing etc., only the trimmed weld bead
- reduced logistics costs
- Automatic trimming of weld bead
Can be used regardless of weather conditions
Can be used worldwide:
- Ambient temperature from -10 to +55° C
- Maximum operating altitude up to 3,000 m above sea level
Speeds:
- Road (road-rail vehicle): 80 km/h
- Track: 20 km/h
Quick on- and off-tracking

Some reference projects Welding in Norway's longest railway tunnel

The centerpiece of the Follo Line (Follobanen) project is the nearly 20-kilometer-long, twin-tube railway tunnel, which, upon completion at the end of 2021, will be the longest in Scandinavia. The construction of the new 22 km double-track high-speed line between Oslo Central Station and the new station in Ski, south of Oslo, was carried out in several project phases. As part of the final railway infrastructure measures, Vossloh was commissioned to carry out mobile welding operations to produce a seamless track structure. These operations took place between August 23 and September 20, 2021.

Since the track is designed for speeds of up to 250 km/h, the experts opted for flash butt welding. Vossloh is also the only company with machine-based approval for Norway, including fatigue testing of rail joints in accordance with EU standard EN 14587-2:2009-08, serving as a qualitative proof of minimum load capacity and standard deviation – performed using the more demanding step method.

Tunnel length: nearly 20 km long, twin-tube
High-speed line: 250 km/h (connects Oslo with southern Norway)
Number of welds: 694 in just five weeks
Shifts: 25 within the same period

Welding in a Swedish steel mill

1,400 RA welds were carried out at the H2 Green Steel plant on behalf of the client GRK Sverige AB. The work was carried out using 20 m long rails of the R350 LHT and 60E1 profiles. Fourteen shifts were planned for June 2025, but the project was completed three days ahead of schedule. Since welding is not widely used in Sweden, there was a great deal of interest. In addition, grinding was carried out: the turnouts using Flexis, and the new plant track with the HSG-city.

On the main line between Malmö and Stockholm, 11 km of track had to be replaced and traffic was forced to slow down. In just ten days, the team completed 320 RA welds, enabling full resumption of regular operations.

Semi-stationary flash butt welding

To deliver the quality of a stationary welding plant directly on site, Vossloh developed a mobile welding facility for large-scale projects. It has a modular design, including special wagons and a flash butt welding element. This means that many construction sites can be supplied more quickly, easily, and cost-effectively.

In the mobile welding facility, the base rails from the rolling mills are welded into long rails in the immediate vicinity of the construction site. This concept combines the quality of the stationary facility with the logistical advantages of mobile flash butt welding technology.

Benefits at a glance:

Welding of short rails near construction sites
Manufacture of long rails up to 400 m in length directly on special wagons
Cost savings through minimization of transport routes for long rails
Simplified logistics through demand-driven on-site production
Accelerated construction progress through the use of long rails
Own power supply
Suitable for all standard rail profiles and grades

Scenarios: When is a mobile welding facility a good option?

Projects that are particularly extensive or long-term
Long rails cannot be delivered or delivery is too complicated
The route requires high-quality rails and welding.

Reference: Sneltram project in Utrecht, Netherlands

Upgrading the SUNIJ line for the deployment of low-floor vehicles
Due to very tight curve radii – typical for tram lines – construction of three welding depots for long rail production near the construction site
Over 850 welds
Reduced rail transport & welding on the track
Minimized time pressure & increased work safety (fewer people on the tracks)
Highlight: A record-breaking 60 welds in nine hours

Aluminothermic welding

SKV welding (short preheating welding) is carried out on turnouts, level crossings, and as final welds. In this aluminothermic casting-welt process, molten steel is produced from aluminum granulate and iron oxide in an exothermic process and poured into the rail joint, which is surrounded by molds. To verify a secure and defect-free connection, ultrasonic testing must be performed afterwards.