Working an issue in which design engineering applies MMM-A-132 Type I Class 3 aircraft structural adhesive across bolt heads as a torque stripe. The bolts are NAS1351N3, 10-32 UNJF-3A, in case it matters. At one point, another stripe (F900 Torque Seal) was added to a derived overhaul publication via the assertion that color media was no longer available in the material but the original compound, deemed inadequately visible, needed to be retained for its 'staking' function. Thread locking compound such as Loctite C is used in this application. Some research findings have suggested that similar bolt head striping is used in other designs, but it is not entirely clear what is the intent or effectiveness other than visible indication that the bolt position is disturbed. My initial impression has been that with conditions capable of backing bolts out against thread locking compounds, any ‘staking’ applied short of welding the bolt heads in place will not have any appreciable effect.
Is this bolt ‘staking’ concept valid, or is the MMM-A-132 material applied really only a torque stripe?
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I would follow the overhaul publication suggestions if for no other reason than to protect yourself if anything happened. If the procedure complicated anythign then consider asking the pnverhaul publication to be changed. I do not think that the new application enhances the resistance to backing off much but the color will probably be useful
Just to clarify, I am actually in a position to have the manual edited. Not inclined to alter the configuration without sufficient reason, but the issue arose over a -40°F storage requirement for the original material. I do not find the visibility aspect very compelling. It apparently was not for the original designers, since among four selections of the adhesive, only one has tint media added. If the MMM-A-132 adhesive is actually only a torque stripe as originally characterized, then the arguably frivolous green (F900) substance could replace it with substantial benefit to the shop. The 'staking' concept was applied to justify using both.
Looked more into this recently and found some application notes in the system designer's adhesive process. That segment actually makes a distinction between torque striping and staking, and the recommended method of application differs between the two. In the original design, torque stripes are applied. The 'improvement' to the manual added the green stripe for visibility, arguing that the original stripe function was partly 'staking', despite not being applied or characterized that way. Also re-checked and found that no thread locking is applied. I am converting the original torque stripe to the staking form (surrounding the bolt skirt) and retaining the added green torque stripe.
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by: grg99Posted on 2005-02-09 at 13:19:25ID: 13269281
I'm not a ME either, but as a guess:
Adhesives are usually rated for bond strength, so many PSI normal to the plane of application at a certain adhesive thickness range.
But applying an adhesive across a bolt head onto adjoining surfaces is going to give a very small effective area of adhesion, not to mention the adhesive forces are going to be parallel instead of normal to the surfaces. It seems unlikely that any adhesive would be rated for or could be depended on for this kind of application.