Materials

7-2000

It's so simple

Crazed windows cured by sealing

PROBLEM Aircraft windows suffer from arrays of very fine scratches, which form on their outsides. The only way to get rid of them is to remove and polish the windows at regular intervals. The scratches are no threat to passenger safety but are a major cost to aircraft owners. A similar hazing problem is also well known to owners of plastic greenhouses and sea-going boats.

Research by CSIRO in Australia, working in conjunction with Australian company Aeroclear, has established that the culprit is water. Geoff Thomas of Aeroclear says: "The water content of the windows varies with altitude. At sea level, it is about 2 per cent. As an aircraft climbs to its cruising altitude, the water in the plastic is forced out, as it descends the window takes up water again." The frequent change in water content is enough to cause stresses which cannot evenly dissipate and the window water in the plastic is forced out. This frequent change in the water content is enough to cause stresses that cannot evenly dissipate, hence the window crazes.

SOLUTION The project team has developed a process for coating the windows with a water repellent polymer, flexible enough to accommodate the changes in shape undertaken by the window without itself crazing or coming unstuck.

BUFFING WINDOW.jpg (23598 bytes)

Aeroclear, which specialises in refurbishing aircraft windows, CSIRO and Belgian company Europlasma have developed a specially designed plasma reactor to apply the coating to passenger windows. The process has been successfully trialed and is covered by patents.

APPLICATIONS Dr Hans Griesser at CSIRO says: "This treatment should result in massive cost saving for the aero industry. The time between refurbishments is trebled and the need for replacement windows reduced accordingly. In addition, other industries that need to eliminate crazing of windows or transparent plastic sheets should likewise benefit from this invention. For example, boat windows become hazy from exposure to salt water and a protective coating could eliminate this." TS

Back to Materials