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Thread: best adhesive for aluminum?
11-26-2008, 11:47 AM #1
best adhesive for aluminum?
The aluminum is 1/4" sheet, brushed, it's a custom replacement dash for a truck. The proposed mounting design is threaded rod projecting 90 degrees from the back. TIG welding the rod might create some visible distortion on the face of the dash, so the idea is to glue them on. Problem I see is that the dash will be subject to wide temperature swings in this climate, from sub-freezing to over 100 degrees F in summer, and the aluminum may expand and contract at a different rate than the adhesive, causing failure.
Any auto industry adhesives that address this problem? Of course, the more conservative route is simply to drill through the dash and bolt it in place, using a fastener with an acceptably decorative head.
11-26-2008, 12:11 PM #2
two part acyrlic. Lord makes some excellent ones. A butt joint like this is far from ideal tho. a wide flange would help considerably, if you made the flange big enough then a high bond psa would work , look at 3M's VHB line. proper prep is tantamount.
11-26-2008, 12:22 PM #3
You might also look at high performance tape. They make some specialized tapes that hold engine mounts on aircraft, the sides on emergency response vehicles etc. Not cheap, but good.
11-26-2008, 12:33 PM #4
honestly, for the application i would use plain old contact cement. used in putting on formica, this stuff works well when the wood base expands and contracts from moisture and tht top from heat.
11-26-2008, 01:12 PM #5
Use a aeronautical epoxy adhesive specific for aluminium, what is as important as the adhesive is the preparation,wipe with neat acetone then lightly abrade with 320 water paper and again wipe with acetone and immediately coat with a two part epoxy adhesive. We use this method all the time with our composites and have found the part you stick the aluminuim to breaks away before the adhesive lets go,you still have pieces of it stuck to the epoxy after failure which is about as good as you can get it.
11-26-2008, 01:13 PM #6
I would suggest that this may be a place where solder would be a good choice. As long as the finished part isn't painted or cleared and the finish can be touched up. I would be making my own threaded part with a large flattened head for attachment.
11-26-2008, 01:46 PM #7
You might consider another approach: 1/4 inch thick is enough to put blind tapped holes in from the rear without any problem. 8-32 would do nicely. Loctite studs in the tapped holes and you have a foolproof fastening system.
I've done many aluminum dash inserts where the insert was applied to an ABS plastic dash and have never trusted adhesives. Both the mold release agents used at the factory during manufacture and the silicone based products people use to "shine" up their dashes are the bane of good adhesive bonding to the plastic.
With thin inserts (yours is not) polished stainless steel button heads look good.
11-26-2008, 02:00 PM #8
I also like the blind tapped hole suggestion, adhesives are asking for trouble.
If you have access to a cnc machine, form type taps work really well for blind holes where you have limited depth available. Since they don't make chips you can tap very close to the bottom of the hole.
11-26-2008, 02:07 PM #9
3M 805 epoxy, can be had from McMaster. As mentioned above, Lord also makes some similar products.
11-26-2008, 02:12 PM #10
Why one solid piece? You can do a 3/16 and 1/32 sandwich so you can use swage-in PEM nuts or studs on the structural layer. Top layer can be SS or aluminum or something fancy. I do electronic panels like that all the time. Easier than working with a structural part that also needs to be a cosmetic part. Also allows milling or forming a recess for bezels held captive between the sheets.
11-26-2008, 08:11 PM #11
My suggestion is Plexus. Leave a fat glue line (in fact you will want to put spacers in there to guarantee a fat glue line - like 1/8 inch). Don't every expect to be able to get it out again. A much cheaper alternative would be 3M 5200 polyurethane, again with a fat glue line. Both of these have 100% - 300% elongation before failure, and are somewhat heat resistant. You need the thick bond line to give the adhesive a chance to flex, rather than break the bond.
We use Plexus to mount aluminum fittings, sail track, stuff like that on boats. The differential coefficient of expansion between aluminum and fiberglass will quickly destroy any epoxy bond. But Plexus hangs in there, at 2000 psi or so, in structurally critical applications.
11-26-2008, 08:28 PM #12
Adhesives depend on surface area and shear loading to do their magic. In aircraft uses like bonded aluminum skins, the glue joint might be 2" wide and 10ft long, working totally in shear. You can't butt glue a 1/4" stud to a sheet and expect it to hold. The flange idea is on the right track. A 1" flange only .032 or so thick would make all the difference in the world.
I'd weld short nipples on and use a threaded rod or bolt. If it tries to distort, fire the welder (heheh), grind it smooth and re-texture with scotchbrite. Seriously, you should be able to TIG to 1/4" without any appreciable distortion on the front.
11-27-2008, 11:57 PM #13
I think I mis understood your post. Is this replacement panels on a dash or an entire dashboard?
11-28-2008, 12:34 PM #14
Locktite makes various types of "Speedbonder" structural acrylic adhesives. H8000 is mentioned for aluminum. Several brands of body panel adhesives seem to be two component methacrylate adhesives.
11-28-2008, 06:29 PM #15
Thank you all for your thoughts and suggestions! The owner of the vehicle (not me) likes the idea of one of the aluminum-specific adhesives on a stud with a wide flange. Should be a simple lathe job.
We'll both be looking at the various adhesives, he is exploring one that is used for aluminum building siding and has some expansion/contraction characteristics. It sound similar to 5200.
11-30-2008, 11:07 AM #16
Get the book called, Adhesive Technology.
My suggestion is a semi rigid epoxy. You need to ruff the surface of the aluminum to give the glue better sticking ability. I usually drill a swiss cheese place full of 1/16" holes that are all 1/16" deep as many holes as I can get into a 1/2" circle and I do not debur the holes. Glue sticks better than a weld. Semi rigid epoxy glue has the ability to expand and contract under a wide range of temeratures.