Seizure on A286 bolt/nutplate combination 1

[Joel Stampfli]

Hi,
due to environmental regulations we have recently started banning cad-plated hardware on new products.
The choice has been made to go for A-286 hardware.

The issue we now observe on a specific batch of nutplates (NAS1791C..) in combination with screw NAS1802 is seizure / high friction during first installation. This seems to be related to a too tight crimping of the nutelement in this batch, since the running torque is over-spec. The screw threads are deformed/worn and some debris/chips are visible.
Similar but less severe behavior is observed on other batches of screw and nutplate. I'm concerned that this combination will not take installation/removal cycles as cad-plated hardware does.

Nut elements are dry-film lubricated.
Thread type is .1900-32 UNJF-3A/B.

Did some of you guys make similar experiences?

Kind regards
Joel

 

[3DDave]

In small threads it is easy to go from too little to too much deformation, so if the torque is too high, reject the parts back to the supplier and get new ones. Also, use anti-seize on the screws. Dry-film is good for only a few times, less if there is any roughness in the mating thread. I've never seen benefit from it and those who say it bakes into the pores of the metal are wishing. It also reduces clearance in the threads, which makes binding more likely in conjunction with class 3 threads.

 

[jaceb]

confirmed - i had similar experience with test hardware i've build - if it is problematic for CRES/CRES type fasteners for CRES/Ti or CRES/Al effect is disaster - 65-80% of such fasteners are totally single use, with high probability of structural elements damage during disassembly.

 

[Sparweb]

I would suggest LPS lubricants. There are a variety of them, different formulations to spray-on or brush-on, so choose wisely and you should be able to improve the installation process.
The disassembly, however, will still be nasty. Maybe "not as" nasty. Maybe

 

[Joel Stampfli]

Thanks 3DDave, jaceb and SparWeb for your replies. This does not sound too promising to get away without additional lubrication.
I'll give it a try.

regards
Joel

 

[WKTaylor]

JS...

Odd bolt/NP combination.

Did You verify bolt [hex-head screw NAS1802] threads by running on a 'plain' UNJF nut... and have You verified the assembly/torque-fit of these bolts with common all-metal/hex SL nuts, such as MS21042 or NAS1291?

The replaceable nut barrel-elements are made per procurements spec NASM25027... which demands high QC/QA for thread-locking... what is the manufacturer's trademark code for these parts [based on stamped code per MIL-HDBK-57]? Likewise the NAS1802 Hex-head screw is made per NAS4003 with rigorous QA/QC.

Are there any industry [FAA] or DoD [GIDEP] complaints regarding quality of either of these parts... OR similar parts made-by either of these OEMs?

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[WKTaylor]

Also... at trick taught me by structural mechanic-equipment specialist...

In installations where galling or corrosion may be a problem... especially with mix of CRES and/or low alloy steel threaded parts...

Most mechanics/structural-techs have access to epoxy primer kits.
Example... MIL-PRF-23377 epoxy primer, Type * Class C1, C2 or N...
Part A ~= Pigmented resin [can]
Part B ~= Catalyst [can]
[Part C is usually thinner, supplied by shop].

Simply 'dip' the cleaned bolt threads in 'Part A' to lightly-wet the threads... then install the bolt 'to-torque' using value for 'lubricated threads'.

Ta-Da... the thin-film of non-curing 'Part A' tends to coat the nut threads and provides surprisingly long-term corrosion protection... IE: is a lot easier to disassemble years later, even with crusting rust [unless of course the head drive-recess is corroded-out].

NOTE1. IF the bolt threads and shank are coated with 'Part A' during installs, then mating aluminum and steel structure holes and countersinks or head/washer-contact surfaces tend to be very well protected by the non-curing squeeze-out!


Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]