New sealant for aircraft.Durable seal for aircraft

Citation

(1998), "New sealant for aircraft.Durable seal for aircraft", Aircraft Engineering and Aerospace Technology, Vol. 70 No. 1. https://doi.org/10.1108/aeat.1998.12770aab.008

New sealant for aircraft.Durable seal for aircraft

New sealant for aircraft

There are more than 1.4 million fasteners on the C-17 Globemaster III, the US Air Force's new transport jet. Until recently, they each had to be installed "wet" ­ using a sealant that costs more to dispose of than it does to buy.

McDonnell Douglas, the aircraft manufacturer, working with Hi-Shear Corp. and the Aerospace Rivet Manufacturing Co., has developed a dry pre-coating for the fasteners ­ titanium pins and aluminium rivets ­ that let mechanics work faster and cleaner while getting better results.

The new sealant, an aluminium pigmented resin with corrosion inhibitors, reduces process variability in installing the pins and rivets while ensuring each hole and fastener is protected against corrosion. "We get a better squeeze on the fasteners and avoid problems where the rivets don't fill the hole tightly," says Jose Jimenez, a McDonnell Douglas team leader. "And if you have to remove any of the titanium pins, they don't seize up because there is more lubricity."

McDonnell Douglas expects to save 2.3 million hours using the new sealant, which translates into $2.2 million per plane.

Durable seal for aircraft

McDonnell Douglas's structural test engineering staff in Long Beach, California, have developed a hydraulic airframe test rig for the company's C-17 transport aircraft that required seals with superior wear resistance. Variseals, made by American Variseal in Broomfield, Colorado, were used because they can withstand temperatures of -320°F to 575°F and pressures up to 10,000 lbs per square inch.

The Variseals are made of Turcon compounds, a proprietary material that combines polytetrafluoroethylene resin with a variety of fillers ­ including graphite, carbon, glass fibres, and polyamides ­ to produce such performance properties as wear resistance, extrusion resistance, and lubricity. The seals are machined to form a U-shaped jacket with a cross-section customized for each application. A corrosion resistant stainless-steel spring energizer is inserted into the jacket to provide permanent resilience.

During operation fluid pressure and spring load create a positive seal with minimal friction. In addition, a back-up ring may be located between the seal and gland to prevent extrusion.

In the McDonnell Douglas application, the Variseal was used on hundreds of hydraulic cylinders that were mounted between the airframe and a steel scaffolding surrounding it.