Brush seals World class sealing technology
MTU brush seal team High-tech from a technology leader The MTU brush seal team is a highly specialized center of expertise of MTU Aero Engines, Germany s leading aero engine manufacturer. Its specialists have been developing innovative turbomachine seals for over thirty years. Their specialized dedication has its origins in military engine construction. Until recently, dynamic components were sealed off from the engine gas flow with the aid of labyrinth-type seals, which were embarrassed by relatively high leakage rates. That is why in 1983, MTU Aero Engines began experimenting with brush seals and soon, in 1985, filed a patent for its new technology. Today, the company is a global leader in this area. One-stop source Meanwhile, MTU has expanded its brush seal activities far beyond the engine domain, finding customers in diverse industries. Brush seals are increasingly being used also in industrial gas and steam turbines, as well as in compressors and for mechanical engineering applications. To fulfil the needs of all the various applications and meet the high demands on technology, the company has pulled the necessary know-how and specialty expertise together in a brush seal team, so that design and development, production, sales and marketing and support are all under one roof. Its experts are closely cooperating with customers at the various sites to introduce this technology in the most diverse industries. They also directly benefit from MTU s engine manufacturing background, having access to the company s advanced test rigs and participating in significant research and development programs. In the process, they have achieved a number of innovations in this field, such as Kevlar brush seals and seal housings produced using additive techniques. And brush seals are now finding their way into a host of new applications, such as sub-sea compressors. More efficiency at less volume The technology behind MTU brush seals is as simple as it is brilliant. Thousands of wires or bristles are safely fixed via a clamping tube, using a core wire, to form a flexible seal. Incoming gases press the wire pack against a supporting ring, compressing it still further and so minimizing the seal s permeability to gas. Compared with conventional labyrinth seals, then, losses are reduced to almost nothing. If you take a medium-haul aircraft consuming 20,000 tons of fuel a year, you easily save one percent fuel, which equates to an amount carried by a fleet of ten 20-ton fuel trucks.* Another advantage is that for given tightness requirements MTU brush seals need less space. This permits much more compact designs and substantially reduces the weight and size of turbomachines. * Source: NASA TM-1998-206961 MTU brush seals enhance the efficiency of: aircraft engines industrial gas turbines steam turbines industrial compressors many mechanical engineering applications 2
The new Airbus A320neo powered by PW1100G-JM engines. Brush seal technology milestones 1983 MTU begins experimenting with brush seal manufacturing processes 1985 First patent application for MTU brush seal 1986 Test stand trials 1992 First flight tests 1996 Testing in industrial turbomachines 1998 Production release for aero engine applications 1999 Production launch for industrial compressors and turbines 2000 First use as semi-static brush seal 2002 Testing of Kevlar brush seals 2003 Testing of semi-static brush seals in industrial gas turbines 2005 Production launch of semi-static brush seals 2006 Production launch of Kevlar brush seals 2007 Development and market launch of new brush seal variants 2008 Testing of new sealing positions in the Geared Turbofan demonstrator engine 2012 Application of brush seals in organic Rankine cycle (ORC) steam turbines 2013 Certification of the PW1500G (engine for the Bombardier CSeries), equipped with MTU brush seals 2013 Expansion into new business areas: Sub-sea compressors and coal pulverizers 2014 Testing of additive techniques for brush seal housing production 3
The advantages at a glance Simple concept big effect MTU brush seals comprise a sealing element and a housing. The sealing element includes a core wire, a wire or bristle pack and a clamping tube. This design ensures safe positive retention and permits the use of non-metallic bristles. The housing comprises a cover ring to protect the wires or bristles and a support ring to prop them up when under gas pressure. Operating conditions Operating media: gas/gas or gas/liquid Differential pressure per sealing element: up to 2,000 kpa Temperature: up to 700 C Sliding speed: up to 500 m/s Design of the MTU brush seal Compact design Brush seals are compact and need appreciably less space than labyrinth seals. That provides additional options for the design of rotors and casings. Housing The outer housing contour may be designed freely, allowing MTU brush seals to be optimally adapted to suit given installation environments. Cover ring The cover ring serves to largely eliminate the adverse effects of the gas flow on the front bristle rows. Sealing element The sealing element is designed to reliably seal off circular as well as any other two- or three-dimensional geometries. Clamping The wires are mechanically clamped in position, eliminating the need to weld them. This produces a perfectly safe and long-lived positive connection. Support ring The support ring prevents bending of the bristle pack in axial direction. Materials Apart from metallic wires like Haynes 25, use can be made also of bristles like Aramid or Polymer. Their sealing effect is even better than that of metallic wires. Pressure relief chamber The pressure inside the pressure relief chamber is nearly the same as that upstream of the seal. This relieves the pressure acting on the upper portion of the bristle pack and in turn enhances the function and service life of the seal. Rotor to be sealed Angular orientation The wires or bristles are normally arranged at an angle of 45 or 20 with the rotor s direction of rotation. With their elasticity, they compensate for all rotor excursions, invariably returning to their original position. 4
Patented design advantages of the MTU brush seal The design of the MTU brush seal ensures secure retention of wires or bristles since each individual bristle is bent around the core wire and positively fixed in place by means of the clamping tube. This prevents bristle loss during operation. The compact design provides additional options for the design of rotors and casings. MTU brush seals are characterized by enhanced radial flexibility. Due to its high elasticity the sealing element is extremely resistant to wear over a long time. The cover ring, which is integrated in the housing, protects the bristle pack from turbulences and makes it tolerant to swirls in the gas flow which are typical in turbomachines. Another important advantage afforded by the MTU brush seal is that it allows the use of various metallic wires and also of non-metallic bristles. These are all produced by the same method which ensures high process stability. Since the housing design is not dictated by the sealing element design both constituents can be separately optimized to suit any given sealing environment. Reduced height Brush seals stand out for: leakage rate reduction by up to 80% optimum preservation of clearance compensation of axial and radial movements ease of replacement at overhaul compact design stable operating behavior long service life Conventional design MTU design Leakage reduction by MTU brush seals 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Three-fin straight labyrinth seal 30% Three-fin stepped labyrinth seal up to 80% less leakage 80% MTU brush seal Compared with conventional labyrinth seals, MTU brush seals reduce leakage rates in engines, gas turbines, steam turbines and compressors by up to 80%. 5
Portfolio of MTU brush seals Individual solutions to suit every requirement MTU s approach to design the sealing element and the seal housing separately permits the seals to be optimally adapted to the specific conditions at a particular seal location. The sealing elements can be combined with any form of housing or be integrated in a housing provided by the customer which is a particularly cost-effective solution. This approach results in a variety of design options for each type of seal. A selection of seals from MTU s product portfolio is shown in the table below. Brush seals sealing elements Sealing element type: Haynes 25 Wire diameter 0.07 mm: 100 Bpmm/200 Bpmm Wire diameter 0.10 mm: 140 Bpmm Wire diameter 0.15 mm: 50 Bpmm Design features: angular orientation optional (radial/axial) sealing element form optional (also threedimensional) no limitation as to size Sealing element type: Aramid (Kevlar) Bristle diameter 0.012 mm: 4,000 Fpmm/6,350 Fpmm In the next step, these two sealing element types are fitted in housings to produce the various MTU brush seal types. Brush seals product portfolio of MTU brush seals Housing Design Size Illustration sheet-metal part <Ø 300mm turned part <Ø 650mm injection molded part <Ø 250mm sheet-metal part >Ø 300mm without housing optional Customers can choose from a variety of brush seal designs or have the brush seal tailored to their individual needs. 6
MTU brush seals are successfully being used on: Potential applications Purpose Aircraft engines and stationary gas turbines bearing chamber seals shaft seals interstage seals static seals reduction of fuel consumption reduction of size and weight Steam turbines/orc balance piston seals shaft end seals interstage seals efficiency improvement improvement of rotor dynamics reduction of cost by shorter length MTU brush seals are used in new installations and in retrofits. Compressors shaft seals interstage seals impeller seals reduction of leakage improvement of rotor dynamics efficiency improvement Mechanical engineering applications machine tools pumps ship building special machinery coal pulverizers efficiency improvement ensuring machine serviceability omission of sealing air system improvement of rotor dynamics MTU offers a suitable brush seal for any application. 7
Aviation well proven in practice MTU brush seals replace labyrinth seals MTU brush seals are highly efficient and particularly easy to install. This warrants retrofitting them on entire engine production runs. A prime retrofit example are the RB199 jet engines that have been powering the Tornado multi-role combat aircraft since 1969. To further improve the operational safety and performance of the engine, MTU in 1995 began developing brush seals tailored to the specific needs of the Tornado. The new system went into production as early as in 1999. MTU brush seals are successfully employed also in the Eurofighter s EJ200 engine. On each engine, six MTU brush seals make sure the high-tech fighter achieves its rated performance. Standard in next-generation aircraft engines MTU brush seals have widely proved their worth, being superior to labyrinth seals from various aspects. This is why the technology is finding a home on practically every engine in the pipeline worldwide. MTU s brush seals are indeed proving their worth in operation, having accumulated well over 7.5 million running cycles in advanced aircraft engines. MTU s innovative seals have likewise found a home in next-generation Geared Turbofan engines of Pratt & Whitney: All PurePower PW1000G family engines will come equipped with brush seals made by MTU. The PW1100G-JM engine to power the Airbus A320neo alone will incorporate MTU s seals at four locations. Compared with labyrinth seals, MTU s brush seals have halved the cooling air losses at all installation positions in the engine. As a result, efficiency is improved while fuel burn and carbon dioxide emissions are reduced. The seal s triumph is bound to continue, considering the enormous application potential of MTU brush seals. Secondary air system seal Bearing chamber seal MTU brush seals in the EJ200 engine powering the Eurofighter. MTU brush seals as semi-static seals One innovation developed by the MTU experts is the semi-static brush seal. In this field of application, MTU brush seals are used to seal off non-rotating or stationary parts of a machine in operation by compensating movements of several millimeters in a mostly hot environment of up to 700 degrees Celcius. This innovation has already proved its worth on several occasions. Fit for the future: MTU s brush seals are now being used also on the new PurePower PW1100G-JM Geared Turbofan, which will power the Airbus A320neo. 8
In use far and wide also in industrial applications MTU s brush seals lend themselves to use in a wide variety of industrial applications and provide excellent sealing solutions at various installation positions. These benefits are winning over more and more machine operators, with MTU s technology already having chalked up well over 10.5 million running hours in stationary turbomachinery. Steam turbines In our times of relentlessly rising energy costs, efficient sealing systems are needed more than ever, considering that they significantly boost the efficiency of quite a few systems. For example, one third of the performance losses of steam turbines is attributable to leakage.* MTU brush seals considerably reduce these losses, enhancing efficiency by as much as two percent. For a 20-MW steam turbine, for instance, they boost power generation by about 400 kw, enough to cover the power requirement of over 900 private households. * Source: GE Power Systems Industrial gas turbines For industrial gas turbines, too, enhancing efficiency has taken on additional significance as primary energy sources are drying up and the need to relieve the impact of NO X and CO 2 emissions on the environment is becoming ever more evident. In this context, improvement of sealing systems holds the greatest short-term potential. MTU here provides tailormade sealing solutions to reduce operating costs and improve efficiency as well as system reliability to benefit customers and the environment alike. Compressors The use of MTU brush seals in industrial compressors drastically reduces leakage losses. That in turn reduces the compressor s energy demand while increasing its product throughput. On a 590-kW geared air separation compressor, for instance, about 500 kg/h in product loss can be prevented. The compressor s energy consumption is reduced by 60 kw. Additionally, the overall length of the shaft can be reduced to improve rotor dynamics. While owing to natural wear by rubbing or erosion, labyrinth seals need replacing regularly, the use of brush seals appreciably boosts the life of the sealing system. General mechanical engineering In mechanical engineering, the use of MTU brush seals is recommended at all sealing positions requiring high sealing efficiency and reliability. The function and design of MTU brush seals permit their use at high temperatures, high pressure differentials and high peripheral speeds. The use of MTU brush seals also often permits the seal environment to be simplified; in part, the need for sealing positions may even be obviated, allowing for instance drive shafts to be shortened. MTU brush seals permit solutions to be implemented that for practical sealing purposes had so far been impossible to realize. Siemens AG Assembly of a 375-MW industrial gas turbine. 9
Always one step ahead MTU s brush seal expertise MTU has developed a unique manufacturing method for brush seals. The highest of quality standards As Germany s leading engine manufacturer and an established global player in the industry, MTU sets high standards when it comes to its products, procedures and processes. These quality and safety standards also apply to brush seals, which are manufactured using a unique wire looping and clamping method. Once the production process is complete, every individual brush seal undergoes careful testing and inspection using sophisticated methods to detect any non-conformances. The stiffness of the brush seals, for example, is measured using two different methods: either on a compression-tension testing machine or on a rotable. MTU has developed an optical measurement technique for the inspection of the inner diameter of the seal (bristle pack), for which a camera is used to take measurements with utmost precision. This ensures the highest component quality, right down to the smallest detail. Further development of proven technology MTU is working relentlessly to further improve its brush seals, the aim being for them to replace as many conventional seals in aircraft engines and industrial gas turbines as possible to yet further improve their efficiency. Under national and international research projects, and in cooperation with prestigious universities, MTU is currently investigating alternative designs, as well as potential new bristle materials and fibers. MTU is exploring ways to use brush seals in more sealing positions and more applications. The potential is there, considering the vast range of possible applications. MTU s brush seal team is comprised of specialists with a wealth of experience in techno- logical research and development. They benefit from having direct access to MTU s expertise in aircraft engine development and production and to the company s advanced test cells, and use rig set-ups at MTU for brush seal validation. Work is now underway for the planning, design, production, and commissioning of a dedicated test cell for brush seals, which is slated to be up and running sometime in 2015 or 2016 and will be the only one of its kind worldwide. New materials capable of withstanding even higher temperatures are already under development. These materials will make it possible for MTU s brush seals to be used at high temperatures well over 650 degrees Celsius, in the hot gas duct of an aircraft engine, for example. In addition, seals with an even more flexible design are being tested that better accommodates axial and radial rotor expansion. The seals resistance to wear and tear is thus improved. MTU has achieved a milestone in alternative production concepts for brush seals. New additive processes, in which components are made directly from 3D CAD model data by depositing molten metal powder layer by layer using a laser, are particularly cost effective and are currently being tested by the brush seal experts for production of the seal housing. The first prototypes have already been manufactured successfully using these additive techniques. Utmost precision: Instead of a tactile inspection method, an optical technique with a camera is used to measure the inner diameter of the brush seal. 10
Measuring of the stiffness of a brush seal. 11
MTU Aero Engines AG Dachauer Straße 665 80995 Munich Germany Tel. +49 89 1489-0 Fax +49 89 1489-5500 www.mtu.de Brush seal team Tel. +49 89 1489-5597 Fax +49 89 1489-4540 www.mtu.de/brushseals GER 04/14/MUC/01000/DE/EB/E