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WELDING PROCESS TRACK MAINTENANCE TRACK TECHNOLOGY TECHNICAL SUPPORT TRACK EQUIPMENT PRODUCT INFORMATION
THE BEGINNING
In 1837 Theodore Goldschmidt founded the Goldschmidt Company in Berlin to supply chemicals to the textile
industry, and established a research and development facility investigating processes for refining metals and
their oxides. In March 1895, Dr Hans Goldschmidt was granted German Patent #96317 for a "process to
manufacture metals and alloys" based upon the reduction of heavy metal oxides by a more reactive metal such
as aluminium.
THE THERMIT ® WELDING PROCESSES
When applied to the reduction of Iron oxides, the exothermic reaction generates sufficient energy to raise the
reaction product temperature to in excess of 3,000°C at which both the metal and aluminium oxide are both
liquid:
Iron Oxide + Aluminium > Aluminium Oxide + Iron + Heat
3FeO + 2Al > Al2O3 + 3Fe + 880 kJ
Fe2O3 + 2Al > Al2O3 + 2Fe + 850 kJ
The process was first used to provide the thermal energy for a method for forge welding rails in 1899, when a
number of welded joints were installed in the Essen Tramway. The process was first used in the UK to weld
tram rails installed in Leeds in 1904.
Further development leading to the addition of alloying elements to the basic Aluminothermic reaction produced
a steel with a compatible metallurgy to the parent rails, thus enabling a full fusion welding process to be
developed. While early welds were produced by casting the Thermit steel into hand produced moulds
encompassing the two rails to be joined together, subsequent development lead to the introduction of pre
formed refractory moulds designed to fit specific rail profiles.
While the basic Aluminothermic process still forms the heart of the Thermit welding processes, continuous
development coupled with modern production technology, statistical process control and quality assurance, has
resulted in processes which more than match the service demands of modern high speed, high axle load
railway systems.
Conventional "Flat bottom" or "Vignole" Rails
Special Section Railway rails
Grooved Tram Rails
Heavy Section Crane Rails
Electrical Conductor Rails
In addition, products are available to suit special types of track support, confines spaces, environmental
restrictions, and for joining rails of differing types or with differing degrees of wear.
THERMIT WELDING PROCESS
ESTABLISHED WORLDWIDE
TECHNICAL INFORMATION
LATEST NEWS
Brochures and Prices for SmartWeld
Control and Rail Setter now available
View full news list
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In each case, should products not be available from our own manufactured stock, we will either design and
manufacture the products to suit, or call on the extensive range available from within the Thermit Group.
THE PRINCIPLE OF THERMIT WELDING
Thermit welding is an effective, highly mobile, method of joining heavy section steel structures such as rails.
Essentially a casting process, the high heat input and metallurgical properties of the Thermit steel make the
process ideal for welding high strength, high hardness steels such as those used for modern rails.
Thermit Welding is a skilled welding process and must not be undertaken by anyone who has not been trained
and certificated to use it.
Detailed operating instructions are provided for each of our processes, but the welding methods all comprise of
6 main elements:
1.
A carefully prepared gap must be produced
between the two rails, which must then be
accurately aligned by means of straightedges
to ensure the finished joint is perfectly
straight and flat.
2.
Pre-formed refractory moulds which are
manufactured to accurately fit around the
specific rail profile are clamped around the
rail gap, and then sealed in position.
Equipment for locating the preheating burner,
and the Thermit container is then
assembled.
3.
The weld cavity formed inside the mould is
preheated using an oxy fuel gas burner withaccurately set gas pressures for a prescribed
time. The quality of the finished weld willdepend upon the precision of this preheating
process.
4.
The Thermit® Portion is manufactured to
produce a steel with a metallurgy compatiblewith the specific type of rail to be welded. On
completion of the preheating, the container isfitted to the top of the moulds, the portion is
ignited and the subsequent exothermicreaction produces the molten Thermit Steel.
The container incorporates an automatictapping system enabling the liquid steel -
which is at a temperature in excess of2,500°C - to discharge directly into the weld
cavity.
5.
The welded joint is allowed to cool for a
predetermined time before the excess steeland the mould material is removed from
around the top of the rail with the aid of ahydraulic trimming device.
6.
When cold the joint is cleaned of all debris,
and the rail running surfaces are precisionground the profile. The finished weld must
then be inspected before it is passed asready for service.
Once correctly installed, the finished weld is expected to last the life of therail, with no further maintenance.
It is estimated that over 100,000 Aluminothermic welds are manufactured in track each year, with a total
population in excess of 1.8 million. The processes are used throughout the year on site with no heavyequipment other than that which may be carried to site by the two man welding team. All the equipment, ancillary
tools such as lighting, gases and consumables can be transported to site by small commercial vehicles.
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WELD TYPES
SkV-E SkV-L SkS SrZ CRW
Joining of New andworn flat bottom rail
Replacement ofstandard welds,
removal of raildefects. Compositejoints between
different rail profiles
Joining of heavysection crane rails
Installation ofgrooved tram rails
and joining them toconventional rails
Joining of lowresistance electrical
conductor rails
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