Danger! Hot! The rail welding
The Goldschmidt process, named after its inventor, is used for rail welding between the Rotes Rathaus underground station and the Museum Island underground station. In this process, the respective ends of the rails are welded together with the help of thermite. Thermite is a mixture of iron oxide and aluminum that melts and reacts under high temperatures to form iron and aluminum oxide when ignited. This property is used in rail welding.
After the tracks have been precisely aligned, they are first shortened slightly to create a gap between them. Then a device is fitted to enclose this gap, into which the iron will later flow. After the fixture has been fitted, the ends of the track are preheated so that they will later bond better with the iron. In the next step the thermite is used: it is placed on the device and ignited until the iron melts and flows into the device between the tracks. The aluminium oxide, on the other hand, remains outside and is knocked off with a massive hammer. The welding point is then ground smooth. The welding crews have already completed just under 120 welds; another 120 welds will follow by May. Then the track superstructure between the underground stations Rotes Rathaus and Museumsinsel will be completed.