2,500-Year-Old Blacksmithing Techniques Revive China’s Giant Machine

China: An ancient technique, used 2,500 years ago to make swords for a great Chinese king, has now been used for a tunnel boring machine known as the “king of construction machinery.” While trying to build the world’s largest piece of equipment for tunnel construction, the scientists and engineers working on the project had to overcome a major obstacle: no country was able to make steel strong enough for such a huge machine. The tunnel boring machine (TBM) has a main bearing with a diameter of 8.61 m (28 ft) – as high as a three-story building. This bearing drives the giant machine weighing more than 10,000 tons – almost as heavy as the Eiffel Tower. All this weight is carried by the surface layer of the bearing that is less than 1 cm (0.4 in) thick. The main problem in manufacturing bearings of that size is that the temperature of different areas changes at different speeds during the process, and a lack of uniformity can weaken the steel. For an answer to this modern problem, the project team had to look to the past. The technique used to make the 2,500-year-old “Sword of Goujian” offered a solution, the state-run Science and Technology Daily reported Tuesday.