Situation
• An aircraft structures manufacturing company was encountering galling when installing titanium bolts (type NAS1581) to threaded stainless steel nut-plates (type MS21060L6). The fastener system is used to attach a large exterior communications structure to the airframe.
• The end customer set a specification of 5 installation/removal cycles with no galling for maintenance purposes. While the manufacture could achieve this at times during pre-production testing, the results were not reliable and required careful manual installation.
Results:
• A set of Dicronite dry lubricated bolts and nut-plates were prepared for testing.
• Manual Installation: As shown in Figure 1, the run-in torque was low and decreased with every installation/removal cycle. No evidence of galling was noted and the coating was found to be in good condition throughout the test.
• Automated Installation: The run-in torque measured after the 5th cycle was 32 in-pounds and no evidence of galling or coating loss was noted. The data from the subsequent five cycles (#s 6-10) is shown in Figure 2. Interestingly the 6th cycle run-in torque was higher but then consistently decreased with each cycle. No evidence of galling was noted throughout; minimal coating degradation
was observed.
• Dicronite dry lubrication was recommended for the final design, as it eliminated the galling problem and enabled automation during production. In addition, the design