4/6/2023 0 Comments Blisk fatigue blade failure![]() ![]() The gases, fresh from combustion, are at around 1,700☌ and the shaft spins at speeds in excess of 12,000rpm. The combustion chamber is annular, with an exit ring at the back controlling the flow of exhaust gases, and it’s here where the single-crystal blades are found. ![]() Outside this is the high-pressure shaft, which runs the compressor that forces air into the combustion chamber itself. This shaft runs through the middle of the shorter, wider intermediate pressure (IP) shaft, which again has turbine blades at the back and compressor blades at the front. So at the back of the engine, the low-pressure turbine blades, which operate in a gas stream that has cooled down somewhat, are on the same shaft as the large fan blades at the front of the engine, which accelerate air to generate the engine’s thrust. Jet engines work by positioning turbine blades, which spin in the current of hot gases expanding out of the combustion chamber, on the same shaft as the compressor blades that force air into the engine at high pressure. “Nickel alloys retain their strength up to 85 per cent of the melting point.Īnd engine manufacturers make full use of this property. “In steel or even titanium, the strength rapidly drops off as you reach 40–50 per cent of the melting point,” Glover said. Even more important is its ability to form alloys, and the particular property of one of those alloys, a compound known as gamma-prime in which nickel combines with aluminium, to retain its strength at high temperatures. Relatively abundant, with large deposits in Australia, and low in price, nickel melts at 1,728K (1,455☌) and is resistant to corrosion – both valuable properties for components that function inside a jet engine. Its unsuitability led to a search for a more temperature-resistant material, and jet makers turned to nickel alloys. “Steel is great for strength and surface hardness, but if you need high-temperature performance it isn’t actually very good 450–500☌ is about its limit.” Rolls-Royce chief of materials Neil Glover, with a Trent XWB engine on the test rig “Back at the birth of the jet engine, Sir Frank Whittle’s prototypes were made entirely of steel,” said Rolls-Royce chief of materials Neil Glover. Far from the decorative brilliance of Greek bronzes, they combine a utilitarian appearance with complexity of form and function and a jewel-like internal perfection: weighing only about 300g and small enough to fit in the palm of a hand, they are in fact perfect single crystals of a metal alloy whose composition has been fine-tuned over many years to operate in the hellish conditions of the fastest-moving part of a jet engine. The components the ABCF is producing are not ones that most people ever see: they are the turbine blades that are hidden away in the hottest part of jet engines. It is to be found in the UK’s historic centre of metalworking, Sheffield, at the Rolls-Royce Advanced Blade Casting Facility (ABCF), a facility purpose built near Sheffield University’s Advanced Manufacturing Research Centre in Rotherham. Its most recent incarnation is arguably the most advanced procedure that has ever been undertaken in metals, and is vital for one of the emblematic activities of the modern world: routine air travel. Yet this most ancient of skills is still in use today, and indeed is still being developed. The single-crystal turbine blade's small size belies its complexity Many of the gleaming marble sculptures of Ancient Greece are in fact more recent Roman copies of originals that had been cast in bronze: the few surviving originals, such as the Riace Bronzes of Greek warriors found in the sea off Sicily, show the incredible sophistication and level of detail achieved by these long-dead masters of metals. The oldest-known casting is a copper frog made 6,000 years ago in Mesopotamia. If you can make a fire hot enough to melt a metal, and manufacture a crucible to melt it in and a mould that can withstand the heat, you can cast complex metal forms and we’ve been doing it for millennia. An ancient form of metalworking is being used by Rolls-Royce to create a single-crystal turbine blade for jet enginesĬasting is one of the oldest and most basic methods of metalworking. ![]()
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