Riveting question - sealer or anti-squeak required?

Just a quick question for you aircraft guys, or any other folks experienced with riveted construction...

Doing some flush riveting on an aluminum roof insert. I have two seams that will be a butt jointed with the supporting structure underneath securing the joint. The rest of the supporting structure riveted in place as well.

What would you guys recommend for a sealer for these butt joints? My first thought is that any old silicone based sealer would keep the weather out, but could create havoc when it comes time for paint if any has squeezed out.

Also, someone mentioned to me about "anti-squeak" or some type of welting to put between the skin and the support structure. Wasn't sure why I needed this or if it's really needed at all. I was just going to lay the skin of the insert on the structure directly, and only seal at the seams.

Any input would be appreciated!

Thanks!

 

Maybe a piece of foam weather strip would work, could be trimmed if any hung out, would eliminate squeak and keep a little tension on the rivetted connection.

 

This is what we use on Airstreams and Avion camping trailers which are all aluminum.
http://www.cadeco.com/productfiles/Tremco-Vulkem116.pdf

Silicone is not recommended for aluminum, though lots of people use it.

 

Is this an off the shelf locally found type of thing, or a specialty sealer? Are you guys just using that for sealer or are you using it between all your panels and support structure?

 

Do Airstream joints on the skin butt or lap? Is this applied between the lap?

 

Sort of a back-woods mechanic type of question, but what about Permatex Form-a-gasket? The black non-hardening stuff? I don't think it's silicone based. Never used it for anything beyond engine applications or tried to paint over it either, but I've got a ton of it and it's readily available.



I'll order something if needed though. I want to do it right...

 

OOO! Just ran across this...

3M 5200. And I can get it at ACE Hardware...

Anyone tried this?

http://www.wholesalemarine.com/p/3-M-05203/3M+5200+Polyurethane+Adhesive+Sealant+3oz+Tube.html

 

Hey Scoot,

I'd go with some "dumb-dumb" (flexable body seam sealer, the rope type" as it will not dry out, and will flex with the panel. Lay out beads of it in the joggle areas, clamp, drill & rivet as necessary. Cut & scrape off anything that seeps out. I don't know of any finish that can't be painted over it, even lacquer!



" Do not reach greedily for the Kool-Aid "

 

Is this what you're talking about, Rex?

Where in the hell do you get that stuff?

 

Scooter couldn't you use seam sealer like they use in a body shop? Just a thought, I don't have a real answer.

I would think that if you had any flex at all you would want something in there if not for anti-squeek then to help where unlike metals rub.

 

I'm thinkin that Airstream stuff. Google the company, maybe there is a distributor nearby.
The 3M marine stuff is more like metal fitting to fiberglass/ wood......? 7 day cure...

 

Putting a barrier such as sealant on the rivet is a good idea for a couple of reasons. First, it'll seal the panel/rivet interface and keep moisture from getting inside. The area will corrode if water gets entrapped and has no way to get out. Secondly, even though the metals can be of similar composition (aluminum), the rivets are softer than the aluminum skin, and they will corrode at different rates.

I would definately use dip primer or a polysulfide based sealant. I work in aircraft, and we use a polysulfide sealant. It is the sealant that we use when we are assembling aircraft skins to longerons and frames. We also use it inside the fuel tanks to make a leakproof seal. The stuff kicks ass. It comes in various types, which determine it's application. It has a good long work-life, which is really important if you're doing a big panel. You do a light coat on the rivet shank, buck the rivet, and wipe the excess squeezeout with a rag soaked with solvent. Here's a link to Aircraft Spruce and the poly sealants they sell:
http://www.aircraftspruce.com/menus/cs/fueltanksealants.html

As far as as using a welting to provide an anti-squeak interface, I wouldn't suggest it. The welting is compressable, and if it's going to be in an area where it's being secured with a row of rivets, it may cause the panel to not lay flat, especially between the rivets. If the panels lay flat to each other, I would suggest a sealant instead. Butter the support that the skin is going to lay on with a nice, even coat using a bondo spreader. Shoot the rivets, and wipe the excess squeezeout. Squeezeout is good, because it's a great indicator that you've got a 100% bond between the panels.

Get LOTS of Clecos with a shank size that is the same as the rivet stem diameter you're shooting. You don't want to be using a #40 Cleco to hold the panel down and shooting a 5/32 rivet because the panel will move all over the place. By the time you get to the end, the holes will not line up and you're drilling new holes, which is bad because you're drilling through your wet sealant putting metal chips in the hole. Metal chips can make the rivet not shoot flush because you're trying to compress the rivet AND the chips.

Also, make sure you have the right rivet set in your gun. If you're shooting button heads make sure you've got the right concave set so you won't score the head of the rivet. Make sure you have a nice flat, solid bucking bar. Do a bunch of practice shots with your buddy because it takes good communication between both of you to do it right. Slow and steady is good. Don't go trigger happy because it'll increase the possibility of bouncing off the rivet head and donkey-tracking the aluminum skin.

 

Flat-n-Low,

We use the "Pro-seal" here at work and keep it in stock:
http://www.aircraftspruce.com/catalog/appages/prosealant.php

I guess I could just use that stuff. Pretty gnarly stuff for sure! We use it in our transformer tanks to seal up any pin-holes that may occur during it's life span. Just thought it was a little bit over-kill for my application and it's SUPER messy to work with. I can't imagine putting that stuff on every little rivet!

I'm all set on tooling. I have TONS of clecos, too! I'm setting flush heads.

I was totally thinking the same thing about the welding. Really seemed like a BAD idea. Didn't understand why it was suggested to me.

Realistically, this car will be stored inside and won't see too many road trips in the rain. The insert is more or less in case I get caught in some rain I wasn't planning for. None the less, I'm going to treat it as if it were any other panel.

 

Hey Scoot,

3M sells/sold? the stuff. Comes in a white & blue box bout the size of a pencil, sold in roll form, too.

 

Okay! Thanks!

 

http://www.aircraftspruce.com/catalo...prosealant.php

That's exactly the stuff we use! Yes, it's super messy, and it stinks bad. But it works great. Just squeeze some into a cup, use a little stick or the end of a small drill bit and do a quick little spin around the rivet shank.

That's great you've got Clecos. The more the better! If you can do Clecos in every hole during the riveting process, it'll keep the panel aligned and nice and tight to the underlying structure during the entire process.

I like the fact that you're using countersunk rivets. Nice touch. A tip: Make sure the shooter (the guy with the rivet gun) stays tight to the rivet head and flush to the panel when he hits the trigger. Don't let the head gap and assume that the rivet will pull itself into the countersink. It'll swell the center of the shank and the rivet won't go flush. That's why I recommended a practice panel. Once you and the guy bucking get on the same page, the job goes much quicker and smoother.

Wear your ear muffs! The sound of a rivet gun on a big panel is deafening.

 

Okay! Well maybe I'll just use that and be done with it, then...

Would you use the sealer on the supports that are NOT part of a seam, or just rivet the two pieces together and go?

I have around 200 clecos and a handful of side type clamping fasteners. I also got a nylon-faced counter-sinking tool to set the depth on the flush rivets as well.

I'll probably assemble 99% of the insert off the car. All the bows and support structure are being formed with it in place, and will probably drill and cleco it on the car so I know it's correct, but it's small enough that I think I can buck most if not all the rivets myself, without a helper. Guess we'll find out.

 

Hey Scott,
I don't have a recommendations for a particular product, but I definitely would use something.
aluminum roof insert on a steel car, several things come to mind. Dissimilar metals is one, the expansion of aluminum is greater than steel is another.


Make sure it stays flexible, and has some anti galvanic response characteristics. I'm sure you are aware of this already, just wanted to make sure.

 

Sneak peek at one of the support ribs...

(these use round, universal type heads since they're not exterior rivets)

 

Oh yeah! The aluminum insert will be completely sealed and galvanically isolated from the steel car. Thought all that through already. It's a VERY good tip, indeed! Thanks man! People don't think about dissimilar metals often enough!

You'll have to wait and see how it'll all work though!

 

I've always wanted to do the top insert for a Model A coupe this way! Can't wait to see how it turns out!

 

25 years of building Airboats we use nothing but Flammable type contact cement, use it with a brush or the way we did and put it in and old mustard bottle and apply it in a few beads, wiping the excess off with mineral spirits after it has squeezed out and set alittle, It'll be there forever.
Reworked a 20 year old boat and had to pry the siderails and stringers off with no corrosion.

 

Either Home Depot or Lows has it. As do a lot of roofing supply places, or on line I use the vulkem 116.

They lap. It is put between the lap and spread over the joint on the inside of the panel where it doesn't show. It does come in colors.

 

Scott-
I'm at work, so I get the dreaded Red X and can't see the pictures. I'm really anxious to see them, and will have to wait until I get home. Sounds like a cool project.

Definately put a fay seal (thin barrier coating between parts) on the parts that are touching each other. 31Vicky is right about galvanic corrosion, especially with aluminum.

 

Okay! Cool! Easy enough!

 

Oh yeah! The aluminum insert will be completely sealed and galvanically isolated from the steel car. Thought all that through already

Are you using something like Mylar tape for this or another sealant?

 

The insert will actually removable and all the edges sit in seals.

 

I've used Pro-Seal (polysulfide) in wet wing aircraft to make the riveted compartment into a fuel tank. Thiokol is the same stuff: http://www.polyspec.com/products/Thiokol.htm

It is messy but Thiokol comes both in open containers that you mix, and in caulking gun tubes with the hardener in the middle of the tube....you have to mix it by pumping a push-rod that comes with the tube. Much easier and they have a cheap caulking gun available.

Try not to get any on your clecos.

Dan

 

That's a good tip. I usually give mine a quick stab into an old can of paste wax if I'm securing a wet panel. Grab the cleco with the pliers, extend them, and stab it into wax, then pop it into the panel. It makes the clean-up a lot easier.

 

YIKES! Good tip! Didn't think of that!! That's a good way to muck up a bunch of cleclos!!!

What are you guys using for solvent to take care of what has squashed out? Lacquer thinner?? MEK?? Something else?? What works?