REG NASA-LLIS-0524-1994 Lessons Learned Torque Value on Screws After Repeated Applications of a Thread-locking Compound.pdf

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1、Lessons Learned Entry: 0524Lesson Info:a71 Lesson Number: 0524a71 Lesson Date: 1994-08-23a71 Submitting Organization: LARCa71 Submitted by: Bernard LewisSubject: Torque Value on Screws After Repeated Applications of a Thread-locking Compound Description of Driving Event: On 1-15-91 a failure occurre

2、d in the 8 Transonic pressure tunnel during testing of a model wing with attached flap. During the test run, the flap peeled away from the wing, broke free, and proceeded down the tunnel. Extensive damage resulted.It is hypothesized that reuse of screws having repeated applications of a thread-locki

3、ng compound caused the east most flap bracket screws to either lose or never obtain proper preload. Under test conditions the screws loosened, then the east most flap bracket was lost, load was shifted to the flap fitting, the flap fitting sheared, and failure occurred.Of special significance is the

4、 fact that a thread-locking compound is always used on the screws that attach the flap brackets to the wing. These screws were reused for all tests and no special effort was made to clean them. The flap bracket screws had received an application of a thread-locking compound approximately thirty minu

5、tes prior to final installation in the wing, resulting in dried, but undisturbed, thread-locking compound on the screw threads. Further, an additional coating of a thread-locking compound was applied to the flap bracket screw threads just prior to their actual installation. Torque values shown on dr

6、awings were given for a preload of 50% or proof load based on dry threads. It is impossible to predict the actual torque on the bracket under the conditions indicated.The thread-locking compound corporation has provided conflicting information. One individual stated that screws should not be reused

7、after having a thread-locking compound applied; further, a tap should be run into the female threads to clean them prior to a new screw being installed. Other representatives said they had no information about reusing screws. To achieve prescribed torque values, however, prudence would seem to dicta

8、te a more conservative approach to the use of a thread-locking compound as well as to the cleaning of threads.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Lesson(s) Learned: It is impossible to predict torque value on screws after repeated applica

9、tions of “a thread-locking compound“.Recommendation(s): The “thread-locking compound“ Corporation has provided information that screws should not be reused after having “a thread-locking compound“ applied; further, a tap should be run into the female threads to clean them prior to a new screw being

10、installed.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Parts Materials & Processesa71 Test ArticleAdditional Info: Approval Info: a71 Approval Date: 1997-04-02a71 Approval Name: Elijah C. Kenta71 Approval Organization: 421a71 Approval Phone Number: 757-864-3345Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-