Aircraft engines seals are a hot topic
Paul Jones has been involved in aerospace engineering for the last 12 years, and for the past 18 months, he’s been responsible for putting together the Trelleborg Sealing Solutions global strategy for business development of aero engine sealing systems. Here he gives his views on the trends and opportunities in this challenging market.
“Last year the number of aircraft manufactured remained steady,” says Paul Jones, Global Segment Manager Aero Engines. “Build schedules were already set based on past orders, so the fact that order intake was badly hit in 2009 had little effect on production. The exception was the business jet sector, which went down by a massive 33 percent.”
Investment continues in the aerospace industry
Despite the difficult economy, prospects in the aerospace industry look good and real growth in the civil market is expected in 2012. “While other industries may have backed off on new product development, aircraft manufacturers have continued their innovations. It’s been quite exciting recently. We saw the first flights of the 787, A400M and Gulf Stream 650. The A350 is under development, and we are expecting the engine for this to be flown in 2011, not on the model itself but bolted onto an A380 flying test bed.”
Reduction of fuel consumption a main driver
When asked what has been driving new platform development, Paul says the biggest focus is on reduction of fuel consumption. “Everyone is looking at greening their fleets. For every ton of fuel burnt, three tons of CO2 are produced. So obviously the less fuel burnt, the less CO2. However, the emission of carbon dioxide is not regulated, and up until now what has really motivated aircraft operators to reduce consumption is the need for profitability.
The lowering of fuel burn therefore has double drivers: a green one and a monetary one. “So we are seeing great emphasis being placed on developments to meet this objective. Composites are coming to the forefront as a means of making planes lighter. And on the engine side we’re seeing a move from traditional design to advanced turbo fan models and eventually to integrated propulsion systems. The advanced turbo fan models can give around 15 percent better performance.”
New engine designs bring greater efficiency
According to Paul, while integrated propulsion designs are still on the drawing board, advanced turbo technology will be available in the near term and is being considered for upgraded and redesigned single aisle planes. The Bombardier C-Series fitted with the advanced turbo engine is expected to be in service in 2013. “Single aisle planes such as Boeing’s 737 and the Airbus A320 are by far the most popular aircraft.
The 737 had its first flight in 1967 and the A320, 20 years later, so they are considered aging platforms. There’s only so much that can be done to improve fuel economy before a new start in aircraft design is required. Modifying the engine and lightweighting the wing of the existing planes may bring savings of around 20 percent. But the next generation aircraft could see an improved performance of 30 or 40 percent.”
Hotter engines make sealing more challenging
The latest engine technologies present greater challenges for seal and airframe suppliers. “The new engine designs push at the limits of material technology to achieve the maximum efficiency gains and reduce maintenance requirements,” says Paul. “Seals therefore have to be stable at extreme temperatures. To cope with these we’ve developed special Isolast® perfluoroelastomers that can operate up to +325°C/ +617°F. Lubricants are also an issue. For these hotter engines High Thermal Stability (HTS) oils are used. These are aggressive and can degrade seal materials. We have developed and tested high-temperature sealing materials for these lubricants. Fluorocarbons with enhanced chemical resistance can operate in temperatures from -40°C/ -40°F up to +200°C/ +392°F.”
Optimized sealing materials for synthetic fuels and biofuels
Environmental pressure to reduce consumption of fossil fuels has led the aircraft industry to look to synthetic fuels and biofuels. Extensive testing of sealing materials has also been undertaken in these. “Airlines are serious about investing in alternative fuels,” continues Paul. “This is shown by the announcement from British Airways that it’s struck a deal to build the first plant in Europe to produce jet fuel from waste matter.
“Synthetic fuels and biofuels are potentially difficult media to operate in for seals. These fuels are characterized by their lack of aromatic hydrocarbons, and if a sealing material is wrongly specified, degradation can occur, causing shrinkage and potential leakage. We’ve tested a selection of our materials with Synthetic Paraffinic Kerosene (Bio-SPK) and variants so we can recommend the optimum performers to our customers.”
Making the best of what we do well globally
In terms of the strategy, Paul says that Trelleborg’s pedigree in aero engines is not only its biggest opportunity, but also its greatest challenge. “Trelleborg has been supplying the aerospace industry for over 50 years. A natural consequence of how we have grown through acquisition is that different parts of our business are stronger in a one region than another, or with a particular customer.
Though we may have leading positions in the supply of aero engine components, we have never really consolidated these. “For instance, we are strong through our Northborough, U.S. facility in fire seals in the U.S., through Cadley, England on nacelle air frames in Europe and through Condé, France, we are a leader in O-Rings, again primarily in Europe. Also, in Tewkesbury, England, we specialize in the development of Isolast® sealing materials for aerospace applications. “We will capitalize on these leading positions to enable us to provide a complete product offering to our customers. This will expand our sales and make Trelleborg a more attractive partner. Our strategy is to make the best of what we do well globally.”
A broad range and global reach are advantageous
The breadth of Trelleborg Sealing Solutions range for aero engines meets another growing trend within the industry, as customers move towards supply chain reduction. “We are in a prime position, as engine manufacturers look to lessen the number of suppliers they have. Trelleborg Sealing Solutions is respected within the industry, and there is no other supplier who can offer the breadth of range we can.
“Our global reach is also proving an advantage. The move to Asia Pacific has been less rapid than in other industries, and aerospace is still primarily centered in the U.S. and Europe. There are some joint ventures and partnerships, but Rolls Royce is the first engine builder to have its own Asian facility in Singapore. We have existing manufacturing sites throughout Asia and expect that our existing relationships will make us a first choice for supply. This is also the case as U.S. manufacturers move into Mexico and the Western European ones into Eastern Europe.”
Future aircraft will look totally different
Asked about how aircraft engine technology will develop in the future, Paul says that future planes could look totally different from now. “The buzz around the industry is about completely integrated propulsion systems. This manages the aircraft’s energy demands while minimizing the weight and drag of engine related components. It involves matching the engine to the airframe and systems. There will be an increase in the use of electric actuation rather than hydraulic or pneumatic; engineers are moving toward weight-savings through increased composites and better harmonization of the wing, pylon, nacelle and engine combination.
“The concept designs for planes with this technology appear very odd. They have a primarily composite body with forward swept thin wings and unducted fan engines at the rear. Whether these ideas will become reality, we do not know. What I am sure of, though, is that Trelleborg seals will be specified on aero engines in the future, whatever they may look like.”
Anatomy of an aero engine
Seals and airframe components from Trelleborg Sealing Solutions are used throughout the aero engine. Airframe components are featured in the nacelle, the visible part of the engine, which consists of the inlet cowl, fan cowl and thrust reverser. As well as these, we supply annulus filler seals that bridge the gap between two adjacent blades in the main fan and the fire-resistant ducting that surrounds the engine.
Less visible are the seals that Trelleborg Sealing Solutions provides for the internal workings of the engine. Seals such as O-Rings, Wills Rings®, Turcon® Variseal® and Turcon® Varilip® PDR are in the internal gearboxes and associated bearing chambers, oil and fuel systems including the pumps, metering units and filters. In addition, we provide clamp blocks and glass braided shielding to hold pipes, ducting and wires in place.
Aero engine product range from Trelleborg Sealing Solutions
Turcon® Varilip® PDR
Ideal for dynamic applications within the aero engine, Turcon® Varilip® PDR rotary shaft seals are constructed from a precision manufactured metal body and a mechanically retained Turcon® sealing element. They offer improved media resistance and operating temperature range over seals with pressed cases that require a gasket. Turcon® Varilip® PDR has low friction and stick-slip-free running, reducing temperature generation and permitting higher peripheral speeds.
Glass braided shielding
Used around steel clips on fuel line pipes, glass braided shielding is made from filament glass yarn impregnated with PTFE. It is resistant to a wide range of media and unaffected by lubricants, hydraulic fluids, fuels and atmospheric conditions. In addition it withstands abrasion, shearing and mechanical damage.
For static and dynamic applications in the aero engine, Turcon® Variseal® is selected for Applications where elevated temperatures, high pressure and potential contamination create an extremely demanding environment for sealing elements. Turcon®, the Trelleborg Sealing Solutions proprietary PTFE based sealing material, is resistant to virtually all media and can operate in temperatures up to +260°C/ +500°F.
O-Rings and gaskets
Used for static sealing in various parts of the aero engine including the gearbox, air, oil and fuel systems, O-Rings and specially molded gaskets are available in media and temperature optimized sealing materials. These include Fluorocarbon (FKM) as well as the Trelleborg Sealing Solutions proprietary Perfluoroelastomer (FFKM) Isolast®, which has superior thermal stability at extremes and is resistant to virtually all media.
Throughout the engine, seals from Trelleborg Sealing Solutions perform in elevated temperatures, aggressive media and high pressures. These range from O-Rings and gaskets used in static applications in fuel metering units, filters and connectors to dynamic seals such as Turcon® CX Seals, Turcon® VL Seal®, Turcon® Variseal® used in linear actuators and valves and Turcon® Varilip® PDR used in rotary applications.
Used throughout the aero engine in ducting, fire seals are the ultimate in safety-critical sealing components. Manufactured from proprietary polymers and fabrics, they are compliant with international standards ISO2685 and AC20-135. To meet the requirements of these standards they are capable of withstanding a +1,100°C / +2,012°F flame for 15 minutes
The nacelle allows the smooth flow of air into the engine, reducing noise, and in the event of blade failure it protects the aircraft from debris. Trelleborg Sealing Solutions provides fire seals in the fire wall of the thruster reverser, vital for safe landings. There are also aerodynamic seals on the translating sleeve and blocker doors and custom-designed components such as pressure-relief doors and hinge covers.
Annulus filler seals
Specialized airframe seals, precisionfabricated annulus filler seals are manufactured from advanced materials developed to withstand their difficult environment. Designed to bridge the gap between two adjacent blades in the main fan, the seals smooth air flow and improve engine efficiency.
Produced from fire-resistant materials, Silicone or Fluorosilicone, pipe clamps are molded blocks that hold pipes, ducting and wires in place within the aero engine. Appearing to be simple, they do a vital safety-critical job, ensuring pipes, ducting and wires are not damaged or disconnected by the high vibrations within the engine.
The original metal seals, Wills Rings® are engineered for use in demanding situations where the capabilities of polymeric seals are exceeded. Operating in temperatures from cryogenic up to +850°C/+1,562°F, they withstand pressures from hard vacuum up to 1,000 MPa / 145,038 psi. These seals can be specified close to the combustion and exhaust section of the engine where the conditions are extreme.
Further information on Aerospace Sealing Solutions
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