What are the premium requirements of gaskets for flange-to-flange aerospace assemblies such as antennas, access panels, radars and lighting? Electrical conductivity? EMI (electromagnetic interference) shielding? Fluid and pressure sealing? Galvanic corrosion mitigation? In short, the answer is all of these things and more.
For this reason, designers choosing fully-cured, urethane-filled expanded aluminium gaskets will not only find a solution that meets all of these criteria, but one that offers numerous performance improvements when compared with alternative sealing solutions. In fact, users can expect a 33% lower total cost of ownership (TCO) resulting from the avoidance of assembly rework and material replacement.
What's the secret?
The gasket material! Impressive levels of electrical through-resistance, shielding effectiveness, corrosion resistance and fluid resistance, as well as an extensive temperature operating range are all attributes of the latest urethane-filled expanded aluminum gaskets.
For any design engineer, the foremost consideration of a gasket is sealing performance. Here, the high conformability of low-modulus urethane binder systems adapts to surface irregularities to ensure leak-path elimination and efﬁcient sealing characteristics.
Gasket materials must also perform well in terms of both atmospheric pressure and fluid sealing, and again urethane-filled expanded aluminium gaskets perform well. The high surface afﬁnity and conformance associated with urethane binder systems creates an efﬁcient sealing solution in variable applications such as those found between externally mounted aircraft devices and the fuselage. When subjected to speciﬁed torque values for such devices, pressure sealing of circa 2.8 bar should result, while also providing sealing capabilities and chemical resistance against common aviation ﬂuids.
Among other major gasket functions is electrical conductivity, as lightning strike survivability and EMI shielding (to avoid antenna signal interruption) are paramount. Expanded aluminium improves upon electrical performance compared to particle-ﬁlled or woven mesh alternatives by eliminating the electrical contact resistance associated with point-to-point conductance requirements. The homogenous nature of expanded metal results in a highly efﬁcient electrical system which optimizes attenuation and electrical grounding performance.
So what of airframe pitting? Clearly, it is vital to avoid the surface pitting of airframes and any associated stress fatigue and cracking. Here, 3000 series aluminium alloys offer a notable advantage. When these materials act as the gasket’s conductive medium, they become the sacriﬁcial entity of the assembly when interfaced with harder aluminium components. Expanded aluminium also promotes an even distribution of interfacing surface load, resulting in the elimination of concentrated stress points that can increase pitting occurrence. Microscopic inspection of substrates after gasket deﬂection shows no negative interaction with expanded metal-based gaskets. Conversely, woven-wire based solutions can create stress points at wire-overlap locations that cause surface pitting.
With regard to minimizing aircraft TCO, the mitigation of corrosion is a significant contributor. Using urethane-filled expanded aluminium gaskets, moisture ingress, and the resulting electrolytic environment, can be minimized through increased sealing performance. Additionally, as aluminium is the typical base material for substrate design, deploying 3003 expanded aluminium as the gasket’s conductive medium galvanically matches the sealing solution with the mating assembly. In these two ways, aircraft owners can expect signiﬁcant reductions in rework and component replacement requirements commonly associated with corrosion.
Finally, installation is straightforward thanks to a symmetrical gasket cross section. This allows for gasket installation without consideration of Z-axis orientation, thus allowing process yields to improve.
For more information pertaining to urethane-filled expanded aluminum gaskets, please contact the Chomerics Division.
This article was contributed by Jarrod Cohen, marketing communications manager, Parker Chomerics Division.