In the world of aerospace engineering, ensuring the integrity and reliability of bolted connections is paramount, given the extreme conditions and critical nature of aerospace missions. Secondary retention methods for bolted connections are essential to prevent loosening and potential failure of these connections due to factors such as vibrations, thermal cycling, and microgravity. The primary method for retention is proper joint design and proper tightening technique. Secondary methods provide an additional layer of security, ensuring that bolted joints remain secure throughout the mission.
Mechanical locking features include cotter pins, safety wire, and safety cable. Mechanical features provide a reliable locking method for joints but come with drawbacks and design details that must be considered. Most of these features require additional parts which may increase the design’s complexity and weight. Sharp edge hazards from mechanical locking features are not acceptable for designs in crew translation paths for manned spaceflight vehicles or crew actuated joints. Mechanical locking features posing sharp edge hazards may be mitigated using encapsulation methods with room-temperature vulcanizing silicones or epoxy, however, materials must be compatible with their use environment.
The other methods such as cotter pins and safety wire allow some rotation until abutment. This can lead to loss of preload.
Safety wire involves threading a wire through a hole in the bolt head or nut and twisting it to secure the fastener. This method is highly effective in preventing bolts from backing out, as the wire physically restrains the bolt from turning. Safety wire is particularly useful in high-vibration environments, making it ideal for space applications where mechanical stability is crucial.
Another method widely used across other industries is the application of thread-locking compounds, such as anaerobic adhesives. However, due to the extreme temperatures, these compounds cannot be used in space applications, and a mechanical mechanism is required.
In addition to these techniques, other mechanical devices such as lock washers and locknuts are employed as secondary retention methods. Lock washers and tooth washers create friction between the bolt and the mating surface, preventing the bolt from rotating. Locknuts, which feature deformed threads or nylon inserts, provide resistance to loosening by increasing the friction between the mating threads. These mechanical solutions are particularly beneficial in space applications, where reliability and ease of installation are critical considerations.
Additionally, wedge-locking technology can be a reliable option that secures bolted joints, even when exposed to severe vibration and dynamic loads. The system is composed of a pair of lock washers with cams on one side and radial teeth on the other.
Retention features that rely on friction may not be suitable for highly critical applications and my add complexity to the tightening process.
To sum it up
Secondary retention methods for bolted connections in space are vital for maintaining the integrity and reliability of these connections under challenging conditions. Techniques such as safety wire and mechanical devices like lock washers and locknuts provide additional security, ensuring that bolted joints remain secure throughout space missions. These methods are essential for preventing failures that could jeopardize the success of a mission and the safety of the spacecraft and its crew. As space exploration continues to advance, the importance of robust and reliable secondary retention methods will only grow, underscoring their critical role in aerospace engineering.
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