DonFromTX

DonFromTX

Well Known Member
I need to make the best bond possible between aluminum and a plastic fuel tank, should be fuel proof as well. What would be recommended as an adhesive?
 
Some suggestions

You might find what you need in the Hysol products line.

Another that comes to mind it the stuff some folks are now using to install canopies-----Sikaflex.

Check with local automotive body shops too, lots of parts on new cars are glued on.
 
DonFromTX said:
I need to make the best bond possible between aluminum and a plastic fuel tank, should be fuel proof as well. What would be recommended as an adhesive?
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Cannot help with adhesive but would like to say check the coefficient of expansion of the two dissimilar products. Typically plastic and fiberglass expand a LOT more than aluminum. May be able to get a good bond at a single temperature but the range of temperatures our airplanes see from sitting on the ramp in the sun to high altitude could make the good joint bad.

Just suggesting another potential issue that should be looked at.
 
I'm a Lancair guy, so I did a lot of gluing aluminum to fiberglass. The hardpoints in the fuel tanks come to mind, but you never want to trust the aluminum-to-plastic bond itself; It's crucial to fiberglass over the whole thing when you're done.

First, you need to properly prep both the plastic and the aluminum.
  • 1. Solvent clean both parts
    2. Rough up the plastic with 80 grit
    3. Wet sand the aluminum until it sheds water in a sheet
    4. Etch the aluminum with Alumi-Prep and rinse with copious amounts of water
    5. Bond with structural adhesive (3M or Hysol or ?)
When the structural adhesive has set up, lay fiberglass over the aluminum and plastic to hold the aluminum in place. Use flox around the edges of the aluminum so the fiberglass makes nice, smooth, transitions.
 
For anyone to properly answer, you almost certainly need to specify the type of plastic. (Rotomolded tanks come to mind...) Would also help to know the actual application.

Charlie
 
Sure thing. I am gluing a fitting of aluminum into a Moeller outboard fuel tank cap (to be used as an Aux tank in my RV12). Not sure what the fuel cap is made from exactly.

rv7charlie said:
For anyone to properly answer, you almost certainly need to specify the type of plastic. (Rotomolded tanks come to mind...) Would also help to know the actual application.

Charlie
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Fuel vent? Pressurized feed?

Does it really need to be bonded in, or just sealed?

If not pressurized, have you looked at either the snap-in fittings ('rubber' gasketed) that are fairly common in boat/offroad gas containers? A lot of ultralite guys use them in the bottom of their rotomolded plastic tanks, without any leak issues, and almost all use mogas.

edit:
If it must be bonded, how about TIG-ing it to an aluminum disc cut to the diameter of the filler neck. Drill the cap to let the fitting poke through, insert the disk in the cap, and gasket between the disc & the neck.
 
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I like 2 part urethane structural adhesives for F/G to aluminum. Not sure how they would deal with plastics. Some plastics, like polyporpolene are very problemetic.

Do you know what type of plastic? Lots of automotive structural adhesives for ABS to metal; 3M has several and they are very strong. The old Vette that I restored has several FRP (a type of fiberglass) panels that are held to the steel structure with only adhesive.

Larry
 
fitting

How about tapping some threads or a fitting with a nut on the fitting and a seal.
Bob
 
I never anticipated so much interest - and questions! Here is a photo of what I am doing, actually fitting a vent to an aux fuel tank. I removed the original vent (since I did not want smells inside the cockpit) and have grafted this swivel with quick disconnect, so the cap can be removed for filling the tank. I initially forced this in the old vent hole, but it needs some glue or something to hold it better. I am thinking some devils snot pro seal might well be the best stuff to use, since I already have some of that available.
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I would look at West system G Flex. It is made for dissimilar bonding and I used it on my cowl hinges. Unlike normal west epoxy it willl not crack when one material expands at a different rate. there are two versions , Thickened and un thickened. You want the thickened. Easy to use it comes in two tubes and is a 50 50 mix. The stuff is even able to set up under water. There is a You Tube demonstrating it. I had use HYsol and it does work but a pain to mix. Also expensive. I keep a peace of the RV8 cowl with a hinge attached in my shop. without tearing up the cowl plastic no one are been able to tear it apart. A two tube kit is around 25$. I have used it to bond some non-structural stuff on the RV. with food surface prep its hard to beat.
 
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