Oct 14 Thrust Bearing for 750,000 kg Regeneration Rotor on Joint European Torus (JET) Fusion Research Project

The Culham Centre for Fusion Energy (CCFE), which operates the JET experiment in Oxfordshire, UK, on behalf of its European partners, approached KCE to help overcome a problem on a 750,000 kg vertical regeneration rotor. CCFE were having difficulties in starting up the rotor because they could not achieve the break-away torque required to overcomethe friction between the thrust runner and thrust pads, despite the hydrostatic jacking system. In addition, they were also experiencing uneven wear of the thrust pads and therefore shorter life times and potentially unreliable operation. KCE evaluated the design, which consists of a bed of compression springs in a nest, supporting each thrust pad. The pads have a low aspect ratio between the thickness and width and therefore deflect significantly under hydrostatic and hydrodynamic loads. This deflection was postulated to be the root cause of the problems. KCE’s solution was to repair the thrust pads with a spherical crown on the whitemetal face that would counter-act the deflections of the pads and ensure oil is dragged onto the thrust pad surface to enable hydrodynamic lubrication. Spherical crowning is a known design feature of large scale thrust pads. The only difference in this project was the application was far more critical and sensitive than a typical hydro turbine application or vertical mill. CCFE is a world centre for nuclear fusion researchand unsurprisingly – a demanding customer! As KCE were making design proposals and changes to core components of the facility, this meant that a new book was written in machining and inspection techniques to reach the very stringent requirements of CCFE. A large radius spherical surface was to be machined on the thrust pads and this had to be machined to micron precision – something we could not even achieve on CNC machining centres. The innovation of KCE has always been driven by its founder Dr. Keith Chester and again his creativity found an innovative solution in an old 4 axis manual milling machine. The machine was equipped with a custom made tool that allowed very precise adjustment to micron precision using purely mechanical system. The end result was that KCE helped to bring the machine back online in 2013and the company is very proud of the role it has played. More information can be found at www.ccfe.ac.uk and www.bbc.co.uk/news/science-environment-27138087