Aluminothermic welding

Aluminothermic welding

In addition to flow welding, AWEJA Rail Systems can also create aluminothermically welded joints. This welding process uses a very rapid chemical reaction (the thermite reaction) which is highly exothermic. A feature of this welding process is that it can no longer be controlled once it has been initiated.

Aluminothermic welding (also called thermite or exothermic welding) of crane tracks and rails uses a mixture of iron (III) oxide and aluminium powder. Other components can be added depending on the steel grade and the resulting strength required. Extremely high temperatures are reached during welding (between 2000°C and 2500°C, depending on the reactants used). During thermite welding, a ceramic mould is fitted to the two rails that are to be welded together. Inside this mould, the residue from the thermite reaction, consisting mainly of molten steel, mixes with the steel of the rails at a very high temperature. To ensure sufficient depth of fusion, the rails being welded together are preheated with blowtorches until they are red hot.

In order to produce a proper joint, the rails must be properly aligned, the mould must be tightly sealed and the joint must have cooled down sufficiently before it is put under a load.

The welding process can be broken down into the following steps:

  • Alignment of the tracks or rails;
  • Fitting of a ceramic mould around the joint and sealing all cracks and holes with sand or paste to keep the molten steel in place;
  • Preheating the tracks or rails using blowtorches until they are red hot (900°C);
  • Placing the thermite portion in the crucible above the joint;
  • Igniting the thermite portion in the crucible;

The reaction then lasts a few minutes. As the reaction reaches temperatures in excess of 2500°C, the molten steel flows into the joint between the rails in the mould. The aluminium oxide slag remains floating on top of it (this prevents the hot steel from oxidising) and is collected in slag basins positioned on each side of the joint;

  • Once the joint has cooled down, the reaction vessel and mould are removed;
  • The welding burr is cut off and ground down in accordance with the applicable standards.

For further questions or a request for quote, our staff will be happy to assist you.