"glues" for structural bonding of aluminum?

[Tom W2ILA]

Does anyone have any experience with bonding aluminum that is part of an aircraft or boat structure?

I dumpster dove for a 17' Grumman aluminum canoe made pre-'52 in the USA by the same American labor that built the F6F Hellcat.  It's all constructed using flush rivits.
The center rib is cracked, new ribs are available ($20 by Grumman-boats of Marathon NY).   I'm thinking of sistering the new rib immediately next to the existing rib and fastening it with an aluminum adhesive instead of rivets.  Research on the aircraft boards seems to show that it can be done.

The Pearson Adhesives Partite 7350 2-part methaclryte has been used in experimental aircraft builds.  Anyone tried it? 

Tom
W2ILA 

       

[Opcom]

There are "aluminum welding sticks" that might do the job. Use a mapp gas torch. They melt before the aluminum and bond with it. I don't know how it works but have used them to fix cracked variac frames.

[Ed/KB1HYS]

Scotchweld 2216 adhesive is pretty good.  It will bond aluminum and when it cures it retains some flexibility. Very strong stuff, and it's used in Aerospace applications. With any adhesive surface prep will determine the strength of the bond.

[W3RSW]

Boy, that brings back memories. I 'tended' a 17 footer when I was a kid on the West Fork of the Mon. for a coal baron.   I can still see that Grumman name plate.

Good find.

I think I'd go ahead and use stainless nuts and screws, and get a good caulking or glue to handle water tightness if necessary.  Add to the patina and give the algae something to cling to.

Stuff like that never bothered us back then ; we always had an official bailer and, come to think of it, rarely went out without rolling it, mostly on purpose.  . Mostly my brother, I and Chomondely (Chumly), our dog , were captain and crew.  We tried several times to get Uncle Bill Purseglove to buy the lateen sail, lee boards and rudder kit for it.

After one flood and mud filled canoe, that was that. He gave it to a kid in town to take care of.

[K5WLF]

You can get countersunk head, closed-end aluminum POP rivets. If it were mine, I'd change out the rib, rather than sistering up, just to maintain as close as possible to the original look of that classic canoe.

If you are going to sister the ribs up, the aluminum "welding" rods that Patrick mentioned do work well, as does MIG welding with Al wire, and of course, TIG welding. And, with the various adhesives that have been mentioned, you do have a lot of options.

[k7yoo]

I do not recommend welding. One screw up and you have an ugly looking mess. It will also create a stress area at the welded area and be a potential point for cracking. "Glue" is standard assembly on most new cars and auto parts stores that specialize in bodywork supplies are carrying the it. Removing the rib and using pop rivets would be fine along with the glue. It would look better and the rivets would hold the rib in place while the glue sets. Drilling out the old rivets shouldn't be a big deal. I have used a small center/countersink drill for this.

[K1JJ]

I just love the old Grumman aluminum canoes.  Built a sailboat with outriggers out of one and still use it.


They built it like an airplane in an era of quality.

T

[K5WLF]

Nice work on the canoe there, Tom. And Yaz looks like he's right at home aboard. With the mast that far forward, is that the canoe version of a cat rig?

[ve6pg]

  DEVCON is a better choice than 2216...these are 2 part expoxys...

..sk..

[KL7OF]

Let us know what you do and how it works out.....I vote for rivets.....

[Tom W2ILA]

Update:
Thanks all for the input.  Pulling the original and riviting in a replacement was out due to the holes not aligning. Also, none of the vo-techs were intrested in having their airframe students work on a boat.
Welding was out because heat would have damaged the seal under the keel.
A call to 3M yielded the recommendation of DP460 2-part 'toughened' epoxy for an aluminum to aluminum structural bond.  Prep with 80grit on a random orbital sander, cleaning with MEK etc etc was followed with application and plenty of bracing for the cure time.  The new center rib is sistered adjacent to the cracked original.
The boat was originally a "3-rib" but I also added 2 intermediate ribs from a "5-rib" configuration.  The 5 and 7 rib boats are designed to take a bit more abuse.  In this case I just figured adding the two additional ribs would assure that any loads were more distributed.

The repair came out great!  Everything is now coated with zinc chromate primer and matching paint.  The canoe should be good to go for another 60 years.

When speaking to the techs to get the replacement ribs we talked about the epoxy repair and they also have used it.  Turns out that 3M approached them to start building with glues instead of rivets but thus far it is not cost effective for a complete boat build. 

73

[KL7OF]

I'm glad that your repairs worked out...Sounds like a great little classic Grumman....As an old sheet metal worker, riveter, A and P mechanic, and aluminum boat welder....I had my doubts about gluing a rib in an aluminum canoe...that adhesive must be OK...How was the fit of the replacement ribs to the contour of the boat?  Is the adhesive thick enough to fill small gaps?...Does the adhesive set up hard or have some flex to it when set up?  I'm considering using adhesive on a similar but top secret project of my own, so your results are encouraging...Have you done sea trials on the Grumman yet?  Thanks for the report....Steve

[Tom W2ILA]

Steve,
I also had doubts about using glues.  But my welding experience is only with steel so this aluminum was a new world.  The skin of the boat is .050 and the new rib fit the contour perfectly. A set of wood braces was set to put pressure on the rib during the cure.  Also the hull is lightly rock dented so some outside pressure points were set up for the cure as well. The epoxy is thick enough to fill voids but it is viscous and will flow. Working time was less than an hour.  It was then not touched for a few days afterward.  The rib was predrilled for riviting so the finishing touch was to put small dabs of epoxy on each of the holes and with the paint and future abuse the dabs will look like peened rivit heads.   
The turning point for me using epoxy came after reading more of the new Lotus frame that has some glued joints (albeit done with much higher QC).
During the seatrials the floor no longer bulges up towards the sky and worry of the keel breaking is gone.  But so far it has not been given any proper abuse.  The epoxy is a "toughened" version which in epoxy marketing seems to mean it can take some flex rather than just be solid and rigid then snap under load.
I'd be curious of any comparisons you make vs welding etc.   
Tom 

[KL7OF]

The epoxy has some "flex" and is not so hard that it will crack...That is what will make it work in an application like yours... Riveting is solid at the rivet point but the metal can flex between the rivets allowing for some movement....If the rib was welded in, with stitch welds, the metal can flex between the welds... 
   I had a job assembling /rebuilding an old steel frame roller coaster ...The old experienced man on the job taught me a lot about how to weld all types of steel joints together to make them strong but still have enough flex so that they wouldn't crack under the movement of the roller coaster....A lot of those principles have served me well in the boat/ship business as well.....Sounds like you are all set for fun on the water...Thanks for the postings