Aluminum Adhesives 4

[podum]

I need to reassemble a Bonanza gear door. The doors are spot welded.

I drilled and broke all spot welds in the door. Material is 2024-T3.

I would like to use an aluminum adhesive instead on spot welding.

Can anyone recommend the proper aluminum adhesive to use ?

 

[IRstuff]

It's probably spot welded for a reason.

TTFN

 

[CoryPad]

Go to 3M's and Loctite's Internet sites. They have a lot of technical information to help you choose the proper adhesive.

http://www.loctite.com

http://www.3m.com/us/mfg_industrial/adhesives/

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[WKTaylor]

podum...

CAUTION: ANY modification to a type certificated aircraft [or any repair NOT that is NOT an approved repair technique in aircraft manuals] requires FAA certification to insure legal airworthieness.

NOTE: Surface preparation and finishing, detail design/fit-up and good adhesive selection are all critical for "anticipated" bonding performance!!!

EXAMPLE of "fly-by-night practices": I used to work for a GA manufacturer in California in the early 1980s. The M&P engineers got GREAT life performance [fatigue durability] from a few adhesive-bonded gear-doors THEY prepared and assembled for testing [production doors were primarily riveted, then later spot-welded and had lousy fatigue lives]. As the engr liaison, I wanted to add adhesive bonding to the drawing in-lieu-of riveting or spot-welding. Their answer was, and I quote: "our experience with the really poor back-shop practices here (couldn't consistently control alodine bath chemistry), made us realise that high quality production adhesive-bonded doors were not possible to assemble [consistently] in this facility."

Regards, Wil Taylor

 

[Stache]

Will is right, if you change the spot wells to something else it is a alteration in accordance with FAR 21.303 and will require a field approval. Us FAA Inspectors are required to to send all materail changes to the FAA ACO engineering for review/buy off, before we can field approve the change.

Stache

 

[podum]

Gentlemen,

I am talking with some of the adhesive MFG's about the materials available.

I have specifically asked for engineering data on the materials that are currently utilized for bonding airliner skins. I have asked for suggestions on my writeup for continued airworthiness when the Form 337 is submitted.

The processes used to bond 2024-T3 require careful measurement and controlled environmental conditions. Both are easily duplicated in my shop at home. The materials are nasty and dangerous. Being a chemist in one of my past lives I appreciate sticking to processes. Ever seen permanent wave power a rocket ?

I agree that a Form 337 will be required. I don't see a problem with ACO approval. The FAA folks down at the LB ACO will have to be dragged kicking and screaming into the 20th Century but they should come around given acceptable documentation.

I would like to use this process on other parts of the aircraft such as flaps and ailerons when the gear doors win FAA approval. Just think of the improvements we could make on older airplanes.

I appreciate all of the input. Some specific sggestions on the bonding process would be appreciated. This is fairly old science at this point. All of the airplanes we hop into these days are "glued" together, not riveted or spot welded.

Spot welding was a common process in the 20's, 30's, 40's 50's, 60's and 70's. I believe that in the 80's the aircraft industry has largely migrated away from spot welding parts together in favor of aluminum bonding.

Thanks again for all of your input.

One more question. If I bond these gear doors together I wonder if they will be repairable ? Can the adhesive bond be broken once the adhesive cures ? I highly doubt it based on my research. That is another MFG question.

Paul

 

[WKTaylor]

podum... again, CAUTION...

Conventional sheet metal dimensions, parts "fit-up" and assembly tooling will NOT [likely] work with parts [same configuration] fastened by adhesive bond methods. There are LOTS of issues to be considered that we have NOT discussed.

Also... the processes [and the environmental factors associated with them] and the the new configuration parts will likely required "full-blown" FAA approval [analytical and testing]. I think the FAA guys you said neede to be brought into the 21st Century "kicking and screaming" may really know what You don't know.

Suggestion: start "simpler". Try rivet-bonding methods first. In this process the configuration remains the same, EXCEPT the faying surfaces are filed with adhesive during assembly [thick film or paste with bond-line thickness control, 180F-to-250F MAX cure]. Obviously parts will have to have finishes designed for adhesive bonding [Phos acid anodize & adhesive-bond primers].

Assemble all parts using "clean" [not dirty] gloves, tables, drill-bits, tooling and fasteners. Deburring and proper fit-up up parts is essentail. Caution: parts MUST be clamped tightly together before fastening to isure tight joints [minimum gapping].

After fastening, "cook the assembly" [hot-cure the adhesive] in an air-circulating oven environment. NO bond-tooling is [usually] required... just racks for spacing the assembled parts to insure even heating and adhesive flow [with gravity and/or cappillary force].

After bonding, grind-off adhesive flash... touch-up any bare metal, prime and topcoat.

Advantages of rivet bonding.
a. Part looks, and is, essentially unchanged [for FAA certification purposes].
b. The adhesives fill-solid/hard all micro-gaps between parts. This improves vibration resistance and minimizes inter-fastener strain-deflection [buckling or flexing]. The part narural frequency(s) 1st, 2nd, 3rd etc.. orders] tend to increase as a result of the dampening affect of the adhesive [vibration an/or flight testing may be required to insure natural frequencies are still OK]. NOTE: sheet metal parts usually see dramatically higher dampening-of [resistance-to] "sonic vibrations" [very high frequency & high Db].
c. Usually, the corrosion durability of the of joints increases [CAUTION: YOU must insure adequate water-drainage holes/paths].
d. For general fatigue purposes, rivet bonding generally inproves thin sheet metal part lives from +25% to +250%... depending on base alloys/tempers of aluminum, quality of fastening methods [amaturis or very professions]... detail/assy fit-up and general configurations.

Regards, Wil Taylor