Seals in the sky for the evolving aerospace industry
03 July 2014
In 1903, Orville Wright took to the sky in the world’s first powered airplane, and aviation was born. Now there is a passenger and freight aircraft fleet of over 16,000 and this is predicted to double by 2032, according to the Airbus Global Market Forecast 2013-2032. This equates to a new plane build of $4.4 trillion over the next twenty years or so.
As the aerospace industry rapidly developed, it needed quality suppliers to support it. For more than 65 years, Trelleborg has partnered with aircraft manufacturers in design of systems containing its seals, bearings and airframe components, as well as evacuation slides.
The company has been a supplier of polymer solutions onboard aircraft for decades. Elastomers are mainly used for airframe seals, O-Rings and custom-designed engineered molded parts, while polytetrafluoroethylene (PTFE) based products are used in slide bearings and seals for hydraulic systems.
“Every time you board an aircraft, it will probably contain numerous Trelleborg solutions,” said Torben Andersen, director of aerospace segment marketing with the company. “Quality, reliable solutions are mandatory as safety is critical in aircraft production. Our solutions feature in various areas of the plane, such as the landing gear. This takes extreme stress, especially when taking off and landing. In such applications, failure is not an option.”
System and functional quality requirements within Trelleborg’s facilities that focus on the aerospace industry, such as the production site in Tewkesbury, England, follow some of the most demanding quality regimes of all. “ISO9001:2008 is an important quality standard but in the aerospace industry, as consequences of failure are high, suppliers need to go beyond that,” according to Chris Busby, aerospace product manager at Tewkesbury.
All Trelleborg facilities supplying to the aerospace industry possess the coveted AS EN9100 accreditation. More stringent than the ISO standard, AS EN9100 focuses on business and product risk, documentation and full product traceability requirements.
“When we receive an aerospace order, we specifically look at how we handle documentation and batch traceability. That may include special part marking or bag and tag, where every individual seal supplied is bagged separately with its own numbering and documentation,” explained Busby. “In the unlikely event of a sealing issue, manufacturing can be traced back to the exact second of production, the machine the part was produced on, the operator and the rest of the batch identified.”
DEVELOPMENTS IN SEALING TECHNOLOGIES
Trelleborg was the first to work with polytetra-fluoroethylene as a material for sealing and its Turcon compounds and proprietary seal designs have become a standard for others to follow. In the aerospace industry, the low friction characteristics of Turcon, wide operating temperature range and resistance to lubricants, make it ideal for hydraulic systems.
“Hydraulic systems are used throughout the plane in controls, brakes, suspension and landing gears; all the control surfaces on the wings and tail of larger planes are hydraulically actuated,” continued Andersen. “These systems require a large number of seals as in most of them there is a configuration of seals, combining different types to exclude media, keep lubricants in and create a back-pumping effect for greater efficiency.”
The center for excellence for PTFE-based sealing technology is in Helsingør, Denmark, where the design and development of Turcon seals for most airliners in the world takes place. Here, and in other Trelleborg PTFE manufacturing sites globally, Turcon is molded into annular or tubular shapes, carefully heated and cooled in a controlled process and subsequently machined to extremely tight tolerances.
“A new airliner takes some five years to develop. Nowadays, we’re part of the design teams of most major aircraft builders right from the first drawings,” Andersen said. “Who we’re working with and where we’re working with them is changing. The big manufacturers, such as Airbus and Boeing – to name just two – are becoming increasingly global, as manufacturing adapts to new passenger trends.
“The US and Europe used to be where most flights were made to and from, but that will not necessarily be the case in the future,” he added.
Asia is predicted to see the biggest growth over the next 20 years. Airbus estimates that Indian air traffic growth, at 9.8 per cent, will be the highest in the world, even higher than China at 7.2 per cent. The Minister for Civil Aviation, Shri Ajit Singh, speaking at a function on Aviation Day earlier this year, said that the country’s airports would be handling 336 million domestic and 85 million international passengers with projected investment to the tune of $120 billion by 2020.
“This is where the issue of globality is vital to our customers,” continued Busby. “Trelleborg has 10 facilities capable of producing seals, bearings and airframe solutions around the world that can offer products to the same standards, drawings and quality regimes. More importantly, wherever the components are manufactured, engineering support is local. One of our US customers, for example, may transfer production of a system to India. We will support design and development in the US and be on hand to support on the production line or in assembly in India.”
TECHNOLOGY DEVELOPMENTS IN AEROSPACE
The long-term, close relationship between Trelleborg and its aerospace customers means that it keeps abreast of the latest technology developments to meet the sealing and bearing challenges they may present.
Andersen gave an example of Fly-by-wire. “This is a fairly recent development in aircraft design. With this technology, aircraft are controlled not directly by the pilot, but rather by onboard computers, dramatically increasing the number of movements of the actuators in flight, meaning that the hydraulics of the control surfaces work much harder than before.
“At the same time, the industry requires ever-extended lifespans and longer maintenance intervals of the actuators. Traditionally, the seals in actuator hydraulics had a service life of 1,500 hours, but thanks to ongoing developments in the manufacture of our bearings and seals, a service life of 85,000 hours for the actuator seals can be guaranteed on a Boeing 787 and even 100,000 hours for those on the new Airbus A350.”
Busby pointed to where advanced elastomers were making a contribution. “Fuel is the second-largest cost of airlines, so ever-leaner engines are a top priority for all aircraft builders and their clients. Generally speaking, the higher an engine’s operating temperature, the more efficiently it runs. And, as temperatures and pressures go up, so do the demands made on all the materials involved.
“Trelleborg’s Isolast is a perfluoroelastomer material combining the chemical inertness of a PTFE with the flexibility of an elastomer,” he explained. “It’s used for seals on the plane’s gearbox and bearing chamber in an increasing number of jet engines around the world because of its stability at high temperatures, coupled with a greater resistance to high thermo-oxidative stability gas turbine lubricating oils.”
How about the space in aerospace? Does Trelleborg also contribute to the conquest of the ‘final frontier’? “Compared with our role in civil aviation,” said Andersen, “our deliveries to space programs at this point are quite small – but there are actually some vehicles with our seals roving around on Mars right now.”http://www.engineersjournal.ie/2014/07/03/seals-in-the-sky-for-the-evolving-aerospace-industry/http://www.engineersjournal.ie/wp-content/uploads/2014/07/aircraft-wheels.gifhttp://www.engineersjournal.ie/wp-content/uploads/2014/07/aircraft-wheels-300x200.gifChemaerospace,aviation,manufacturing