Report of the 8th Technical Seminar
   
   
   

Aluminothermic welding - an old process with the capacity to react to new requirements

Essentially, the 8th Technical Seminar of the IoRW held recently at TWI, Cambridge, chaired by Eur Ing Bob Sawdon of Balfour Beatty Rail, Vice-Chairman of the IoRW Management Committee, was Thermit (GB) Ltd's and Railtech (UK) Ltd's show. These two companies, the only ones approved to supply aluminothermic welding (ATW) equipment and consumables for use on Network Rail's permanent way infrastructure, were set the challenge by the IoRW Management Committee of jointly running an IoRW seminar dedicated to developments in their processes.

A bit of history...

Thermit Ltd started as an independent British company and went through several owners before becoming part of the German based Goldschmidt-Thermit Group in 2000. The company started supplying ATW equipment for dock and crane rail welding in 1905. The Group now operates on a worldwide basis.

Railtech International is part of the Delachaux Group, a French company established in 1902. Railtech UK did not become active in the UK until after the approval of the PLA Process which was launched in 1998. Railtech International is also active on a worldwide basis.

So what's new....?

Richard Johnson and Tim Clifton tracked Thermit (GB)'s process developments. The SkV-F variant has now been in use for over 30 years with two million welds installed. However, there was a need to address occasional imperfections, like black holes, oxidised (or glazed) or distorted weld collars, poor collar edge fusion, and poor surface finish (cavities and pores). The new SkV-E variant has been developed to tackle these problems and a comprehensive development and evaluation programme has been conducted. The main change compared with SkV-F is better control of pre-heat. The SkV-E variant has shown itself to be highly flexible in giving the sought-after improvements.

Network Rail have approved the following SkV-E parameters:

  • 110A, 113A and 60E1 rail sections.
  • Oxy-propane and oxy-acetylene pre-heating.
  • Flame cut, sawn and disc cut rail ends.
  • 220, 260 and 350HT rail grades.
  • 1-3mm step moulds for 110A and 113A rail sections.
  • Sand and paste luting.
  • Welding up to 15mm of similar head wear with full side cutting.
  • Mould adjustment by 'rubbing in'.
8th Technical Seminar

Approval of stepped moulds is expected soon and then Thermit (GB) will be ready to replace the whole of the SkV-F range with SkV-E moulds.

The SkV-E variant also paves the way for zirconium faced moulds to provide the benefits of improved surface finish and easier mould removal.

Thermit (GB)'s current range is based on the re-usable crucible principle but the next steps are to introduce single use crucibles and reduce equipment weight and cost.

Neil Souter of Railtech (UK) confirmed that his company's growth in the UK has been closely linked to achieving the following objectives:

  • Installing predictably good quality PLA welds.
  • Protecting the welder's health.
  • Keeping processes simple and user-friendly.
  • Keeping the product range simple to reduce stock and transport costs.
  • Minimizing the number of weld defects.

This was expanded upon by Neil's colleagues, Steve Kettle and Richard Kyte. Railtech's PLA Process now benefits from a full range of approvals. The technical advances associated with the PLA 'one shot' crucible system are:

  1. 'Hybrid' wear moulds which mean fewer moulds for greater ranges of wear.
  2. VG2 vent riser giving increased size and improved exhausting of gases.
  3. Polystyrene inserts for improved verticality and self-centering.
  4. Zircon faced, felted moulds for good surface finish and weld collar precision.
  5. Felted moulds for bull head rails (also approved by London Underground).
  6. The PLA Ecofilter which reduces the welder's exposure to fumes, for example when welding in tunnels.
  7. The CJ2 one-shot crucible which is used for both wide and standard gap welds.

Tim Clifton of Thermit (GB) and Frédéric Delcroix of Railtech International explained the actions being taken in relation to quality issues and improvements in their respective companies. The continuous improvement ethic was already embedded in both organisations and areas like customer service, traceability, portion control, packaging and identification were under constant review.

Dr Henri Cohrt, Managing Director of Goldschmidt-Thermit GmBH, gave an overview of the structure and activities of the whole Goldschmidt-Thermit Group world-wide. He stressed the need to maintain a balance between centralising some important aspects, like research and development, but providing customers with a convenient local way of getting help from the company.

Hervé Potaux of Railtech International explained that all TGV lines in France (and Eurostar lines in UK) had been welded with the Railtech process and underscored the success of these projects, in which more than 25 000 welds had been individually documented.

Finally, there was a view from a representative of a contractor that makes use of both Thermit and Railtech processes. Philip Instone of Carillion Rail presented data showing how weld failure rates had been reducing in recent years and gave his view on the key aspects:

  • Improved quality and uniformity of welder training which was giving better control.
  • Poor planning often made it difficult for welders. Site Managers need to know more about welding, especially in relation to time constraints.
  • Rail end preparation/gap is critical and more attention should be paid to the method of cutting. Profile grinding to the tighter tolerances for improved quality needs a new generation of grinding machines which also recognises the hand/arm vibration problem.

The overall message was that the industry can move forward more effectively by sharing information.

In conclusion....

The last sentence sums up what IoRW is all about. Suggestions of how sharing of information through IoRW can be improved would be welcome!

Eur Ing Tim Jessop
Executive Officer