a little aluminum advice please!

[hidefxj]

Greetings everyone! I am doing a build (that I will share soon enough with everyone) and the roof/front of the trailer exterior are a single sheet of 4x8 aluminum bent to 90 degrees and placed on a 2x2 square steel frame.

My question is, how should I secure the aluminum to the steel?
Rivets, epoxy etc....
I am aware of the corrosion issues when combining the two but I will be coating them before mating them together.
I am mostly concerned about the expansion/contraction of the aluminum with the temperature and possible rippling and tearing due to the method I will be selecting to affix it to the frame.
Oh, it is about 16ga. Aluminum.
Suggestions?

Thanks everyone!

 

[Rbertalotto]

Lots of builders use a 3M super adhesive double sided tape. Keeps the two alloys apart and cuts down on condensation transfering to the metal frame.

 

[hidefxj]

Lots of builders use a 3M super adhesive double sided tape. Keeps the two alloys apart and cuts down on condensation transfering to the metal frame.

I really thought about that! I was just concerned with the one piece aluminum flying off while on the interstate when the tape reaches the end of its life.

 

[Kiddmen57]

Check out 3M 8115 panel adhesive. It's available on amazon and is an epoxy adhesive used extensively on the collision repair industry to adhere body panels instead of spot welds.

 

[hidefxj]

Check out 3M 8115 panel adhesive. It's available on amazon and is an epoxy adhesive used extensively on the collision repair industry to adhere body panels instead of spot welds.

Any thoughts on the performance of this product?
What about the aluminum expanding and contracting from the heat? If all 4 sides of the sheet are bonded to the frame, how will the aluminum sheet react?
Thanks

 

[hidefxj]

Flat aluminum will ripple & warp. In my case(BW RadioBox from a 404 UNIMOG)
Not entirely pretty, I known it would be a concern, I just live with it. Its perimeter is secured well with rivets & a good bed or urethane caulk. The middle is attached but a couple locations. I foresaw the expansion problem and was careful to not create a 'trap' where expansion would have no where to go but to break something.
In all, No problems with joint pulling loose, cracks or leaking. Just in hot weather it shows up.

Commercial RVs are made of a corrugated skin to alleviate the expansion problem, hide imperfections, etc.

Damn.....such a shame. It's nice, looks good and is light weight but the down side is warping.
I guess I can add another support down the center so it is attached on the perimeter as well as the center. Maybe put rivets every 8 to 10 inches. I will eventually put a RTT on so it will cover up the aluminum and provide some shade.
I was just hoping someone could suggest a method that would alleviate the warping or at least minimize it. Grrrr....

 

[jwiereng]

From the website of 3M. The makers of Very High Bonding (VHB) tape.

Bonding side panels to metal frame posts to build smooth-sided trailers, truck cabs and other vehicle exterior applications with 3M™ VHB™ Tape.
Designing unconstrained smooth-sided design solution in which the exterior walls are attached to the posts using 3M™ VHB™ Tape, and the top and bottom of the panels are left to “float” in a notch-like component designed into the extrusions. This unconstrained design allows the panel to expand vertically when exposed to heat. The differential expansion of 0.120 inches experienced on a 96-inch unconstrained panel to post application is within the design parameters of 3M™ VHB™ Tape. The same expansion of 0.120 inches on a constrained design that utilizes mechanical fasteners at the top and bottom extrusions could cause the exterior skin to buckle. 3M found that a design that leaves only one end of the panel to float – top or bottom – will also allow the panel to expand on an even plane, which helps to prevent delamination.



Seems to me that warping and oil canning can be avoided if one does not use mechanical fasteners on the sheet metal

 

[protohyp]

I'm using 3M VHB on my off road trailer and coming from refurbing and rebuilding Airstreams which are mostly buck and pop riveted I would go 3M every day all day. Waterproof and adhere panels in one shot? what's not to like...maybe just the price but check google for 3M VHB 4941 tape. They have two thicknesses...one for bonding panel to panel and one for panel to support member. the stuff is EXPENSIVE but doing labor on rivets and sealing and hoping it doesn't leak is way worth the money

 

[hidefxj]

I am absolutely pro "less work" I am just worried about the panel flying off without any fasteners, just adhesive tape securing it on. Can you imagine a 3 1/2' x 8' piece of aluminum taking flight off of a trailer that is in front of you at 70 mph?
Maybe I will use the bonding tape and figure out a way to put a couple of 1" wide aluminum straps across it as an extra precaution.

Thanks for the 3m VHB tape suggestion.......definitely looking into that one!

 

[eggman918]

I just thinking out loud but what if you preheat the aluminum to ~175* before securing the edges so that it is in tension at room temp.
That way you are using the aluminum's thermal properties to your advantage.
Steve.

 

[eggman918]

I am absolutely pro "less work" I am just worried about the panel flying off without any fasteners, just adhesive tape securing it on. Can you imagine a 3 1/2' x 8' piece of aluminum taking flight off of a trailer that is in front of you at 70 mph?
Maybe I will use the bonding tape and figure out a way to put a couple of 1" wide aluminum straps across it as an extra precaution.

Thanks for the 3m VHB tape suggestion.......definitely looking into that one!

I've used that tape a few times and it is much stronger than you would think,before using I did a little destructive testing and if you do the same your confidence in it will grow.

 

[protohyp]

Maybe this will help your decision

http://youtu.be/ZllHVGPXLGQ


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[hidefxj]

I just thinking out loud but what if you preheat the aluminum to ~175* before securing the edges so that it is in tension at room temp.
That way you are using the aluminum's thermal properties to your advantage.
Steve.

I was thinking about just letting it bake in the sun before I secured it.
But it seems like either way, there are 2 states for the aluminum to be in, expanded or contracted. Which ever way I choose will only be acceptable 50% of the time.

I really do appreciate the VHB suggestion. The video is promising too! Now i'm off to check out the prices on the stuff!

 

[gatorgrizz27]

I doubted the tape too but it seems to be holding. Possibly use tape on every stud/crossmember and secure the corners with rivets and silicone bonded angle on too for peace of mind?

 

[protohyp]

It really isn't a fair assessment of the rivets and tape honestly. Rivets in strength are a calculation for it to be as strong as a weld if not stronger. Look at airplanes and the amount of rivets per panel. The video above shows rivets almost every 3-4" where an airplane or airstream trailer is almost every inch. Plus they are typically buck riveted for external panels vs pop riveted. Two different strengths there with buck rivets being the strongest. But again the amount of work needed to water proof rivets can be more of a headachee than anything. If you use the tape just be aware that once it touches and adheres there is no turning back. A 36 yard role of 4941 will run you more than 100.00 in 1" width just to give you an idea how much it costs


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