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The Advanced Thread Locking Mechanism
Technical Paper
2006-01-3165
ISSN: 0148-7191, e-ISSN: 2688-3627
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English
Abstract
Locking of threaded members is accomplished by a wide variety of engineering solutions. Generally, in terms of separate locking devices or by built-in locking features such as friction generating means.
In regard of space flight vehicles, threaded joints are subject to severe vibration loads during launch, maneuvering, and reentry. This requires fastening systems which are capable to join structural members and attach accessories or equipment in a secure manner. However, manned spacecraft and especially payload components will be subject to installation activity during orbital or interstellar flight maintenance, repair, or mission modification. This, in turn, requires fast separation and engaging of the concerned fasteners, yet providing performance characteristics for high reliable and safe joints.
The further described Advanced Thread Locking Mechanism (ATLM) has been developed to combine the merits of both, safe joining technique and a fast installation process. The ATLM uses a freewheel which is securely installed in one part of the threaded member and releasable coupled with the engaged counterpart. While screwing the threaded members together, once coupled, the freewheel will allow free mating of the threaded members including torquing to the desired value. The moment, the pair of threaded fasteners is forced to unscrew (by intended or unintended occurrence of torque in the undoing direction) the freewheel does lock instantly. Disengaging the coupling between the members of the threaded joint takes a separate release action.
Owing to the nature of the ATLM, there are a number of design variants ready for implementation.
Threaded fasteners in ATLM design are highly recommended for mechanical joints subject to fastening and unfastening during Extra Vehicular Activity (EVA) in course of space flight operations. This is justified through:
- 1Threaded members mate free running, thus, torque values preset at the wrenching tool are not influenced by varying prevailing (a.k.a. self-locking, running) torque.
- 2No extra locking hardware or retaining compounds are required.
- 3ATLM fasteners produce stable retention (locking) torque with no limitation for the number of screw cycles; i.e., unlimited use of fastener in respect of the self-locking capability.
- 4Anti friction coatings on threads have no influence on locking torque.
- 5Locking of the threaded members takes place automatically - no assembly errors possible.
- 6Integrated tool design for installation / torquing and unlocking / removal of the fastener.
- 7Capture of unscrewed fastener by the tool - no inadvertent loss of hardware resulting in space debris.
- 8Relative to screw locking, no assembly inspection procedures are required.
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