Member of GOLDSCHMIDT Thermit Group

SKV technology (rail track welding)

SkV technology is applied for welding of rail tracks of R65 and R50 types. This technology is characterized by a swift (2 min max) pre-heating and possibility to carry out welding works at the ambient temperature of minus 5°С.


The sequence of operations is as follows: 


1. Preparation of a gap and rails in the joint

Latches are removed from the joint, while the rails are cleared of dirt and rust. Rail fastenings are loosened at three cross sleepers on the right and on the left of the joint, whereas they are completely removed at the cross sleepers close to the joint.

The rail ends are cut with a rail saw, abrasive cutting-off disc in a way that the gap is equal to 24-26 mm.

In case of a certain approval, the cutting of rail ends might be carried out with the use of a burning torch, propane and oxygen mixture in accordance with a template.


2. Alignment of rail ends

The alignment of rail ends is carried out with the use of grip wedges and metric ruler, with a special measuring wedge.

The rails are aligned in two planes. In the vertical plane, the rails are purposefully set up in excess to compensate for joint thermal setting and to create an allowance for further polishing.

The final step in this process is pre-heating of rail ends at the joint up to the temperature of 50°С to eliminate moist.


3. Setting up casting molds

A special retaining clamp is fixated on the rail, the casting molds are set up in the metal mold frames and fixated at the joint with the use of mounting brackets.

Molds are then filled with fire sand mixture along the rail outline, while slag cups are hung along the mold frames.

Finally, protective caps are put along the molds, on the railhead.


4. Mounting of crucible

Crucible is attached to a special mounting bracket. Crucible plug is mounted inside the crucible and thermite portion is spread.

Crucible can be both reusable (as shown on the photo), and disposable. Smoke filter (not shown on the photo) can be installed on top of the crucible in a steel cone shaped case. It significantly reduces smoke spread in the work area and prevents the spread of sparks.


5. Quick pre-heating

Prior to thermite reaction, a quick pre-heating of rail ends is carried out. This procedure is carried out with the use of propane and oxygen mixture and a special burner. At that, the pre-heating time depends on the rail profile:

- for R50 type rails, it equals 1.5 to 2 minutes;

- for R65 type rails, it equals 2 to 2.5 minutes.


6. Thermite reaction and mold casting

Immediately after the pre-heating, the burner is removed from the mold, and the thermite mixture is ignited with a special lighter.

After the thermite reaction (within 20-25 seconds), the crucible plug automatically opens up at the bottom of the crucible and the liquid thermite steel is poured into the mold.

While the molten thermite steel is poured into the open joint, the rail ends are burned through and welded.


7. Burr removal

After the pouring is completed, the steel is to be matured within 3.5 to 4 minutes until completion of crystallization process.

After the specified time is over, the mold frames and retaining clamp are removed, as well as the top of the mold, while burr is cut along the running surface of railhead and its side with the use of a weld trimmer and a set of special knives.


8. Joint polishing

Joint polishing along the roll surface and sides of the railhead is carried out using a polishing machine in two stages:

- rough polishing, which is performed right after the burr removal*;

- fine polishing, which is performed after the joint and rail fastenings tightening cool off.

* Railway operation at a speed of 25 km/h is allowed after the rough polishing of the joint.


9. Ultrasonic examination

After the fine polishing and complete cool-down of the joint, the quality control of the welded joint is performed with the use of ultrasonic inspection equipment according to the existing rules PR 07.41-2006.

  Features of the aluminothermic welding in the underground tunnels


The SkV technology used by us makes it possible to produce termite welding of rails in metro tunnels and fully complies with the requirements of the Technical Guidelines "Aluminothermic welding of subway rails", "Safety instructions for the production of rail welding work by the aluminothermite method in metro tunnels" No. 18-03.00-04 and PSPO 147 " Rules of fire safety on metro. "

To meet the requirements set forth in these documents, the technology provides for the use of a special smoke filter in a steel conical casing, which can be used both with a disposable crucible (see photo) and with a reusable crucible. The filter significantly reduces the smoke content of the working area and does not allow sparks to fly apart during the thermite reaction.

Otherwise, the technological process of aluminothermic welding of rails in metro tunnels is identical to the above process for railways.


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