As stated, bonding helps mitigate electromagnetic interference (EMI) and radio frequency interference (RFI) by providing a common electrical reference point for all bonded components. It reduces the risk of stray currents and minimizes the impact of electromagnetic fields. Bonding also contrib- utes to the mechanical stability and integrity of the aircraft. In an aircraft fuel system, for example, bonding is crucial to prevent static electric- ity buildup and discharge. Metallic components, such as fuel tanks, pipes, and fittings, are bonded together using a process called “faying surface preparation” as well as through the use of auxiliary bonding conductors or straps (flexible junctions made of plated copper braid material). This approach equalizes electrical potential, minimizing the risk of sparks Bonding in AIRCRAFT SYSTEMS
and potential ignition sources in fuel-rich environments. Faying surface preparation for bonding between two metal- lic surface is a labor-intensive process which joins metallic components and structures within the aircraft into a vibration- and movement- resistant network of mechanical and electrical bonds. The process involves remov- ing any protective coatings, paint, or corrosion layers from the mating surfaces to expose bare metal. The surfaces are then cleaned to remove dirt, grease, or other contaminants that could hinder the bonding process. Various methods may be used for faying surface bond preparation, including abrasive cleaning, chemical cleaning, or mechanical methods like scraping or wire brushing. Once the faying surfaces are properly prepared, they are bonded together using fasten- ers, adhesives, as well a surface sealant. This ensures both a strong mechanical connec- tion and a low-resistance electrical bond between the
components, facilitating proper bonding and electrical conti- nuity throughout the aircraft. The sealant used in the faying process serves several purposes, including ensuring a watertight and airtight joint, preventing corrosion, and enhancing the structural integ- rity of the bonded components. Faying process sealants are similar in function to the poly- sulfide sealant used in Glenair Series 440 banding adapters to prevent galvanic corro- sion between the shell and the conductive braid screen. The choice of sealant depends on the specific requirements of the application, such as temperature, pressure, envi- ronmental conditions, and the materials being bonded. It is important to note that while faying surface bonds contrib- ute to electrical continuity, they may not prove sufficient in all cases—particularly in aircraft zones subject to expan- sion and contraction of the fault current ground path. For this reason, auxiliary braided jumper ground straps and studs (flexible joints) are used in addition to faying surfaces to further establish reliable and low-resistance electrical Adhesive and sealant protected faying surface bonding of mechanical structures. Note cable shielding and auxiliary flexible joints (ground straps) used to ensure common electrical potential.
Bonding and grounding involves the use of galvanic finishes, faying surface preparation of mating metallic parts, the use of compatible structural fasteners and sealants, and flexible joints (ground straps).
QwikConnect • July 2023
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