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Conclusions on Aluminum Adhesive Bonding Tests

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GESchwarz

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"the metal stretches beyond the ability of the ability of the adhesive to stretch"

Does this make sense?
When the aluminum is bent, the surface on the outside of the bend will stretch and the surface on the inside of the bend will compress. This happens whether the aluminum is bonded or not. If it's bonded at that point and you have stretching at the bond line, because the adhesive is weaker than the aluminum, of course the adhesive is what gives and it gives at the bond line because that is precisely where the greatest strain is taking place.

The adhesive is actually being stretched in two axises: along the direction of stretch and along the direction of peel. So when you look at it that way it's no wonder that the joint will fail early
 

Tom Nalevanko

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I give up. The use of non-standard terminology and haphazard description prevails. Falls under junk science. The conclusion cannot be drawn from the description of the mechanics.

"The lesson learned is to prevent part deformation at bond lines by design. Don't have the joint in peel or tensile. Pure shear is the ideal application." This is true and can be found in a myriad of design books and articles. If this is a quest of personal discovery and it was discovered, then I am all for it.

Blue skies,

Tom
 

BBerson

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In most states, just buy gasoline, it's got 10% ethanol. Just the right mix to test. Denatured alcohol (sold in hardware stores as paint thinner and stove fuel) is ethanol with a small amount of methanol added to make it poisonous so it can be consumed. Everclear is grain alcohol, available in liquor stores, though I believe some states don't allow it.

-Dana

The difference between theory and practice is that, in theory, there is no difference between theory and practice, but in practice, there is.
I am sure you meant "cannot" be consumed. Some people get confused about these different alcohols.
 

Dana

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Oops, yes, "can not", indeed.

-Dana

"An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr
 

toothengr

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Thank you for all of your work on this. I was researching bonding aluminum to aluminum, and found this article. As it happens, my use is not related to aviation, just a small item that I want to fix. In following the Parson adhesive site, I find the MMA adhesives, and the Partite series, one of which has a shear strength of 3,200-3,750 psi range, Product Code is 7300. I did not find a Partite 3750. Is the Partite 7300 the same material that you reference in your article as Partite 3750?

Thanks,
Carter
 

wktaylor

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Are You familiar with...

[Go to https://assist.daps.dla.mil/quicksearch/ and search for documents MIL noted]
MIL-HDBK-691 ADHESIVE BONDING
MIL-HDBK-337 ADHESIVE BONDED AEROSPACE STRUCTURE REPAIR
MIL-HDBK-83377 ADHESIVE BONDING (STRUCTURAL) FOR AEROSPACE AND OTHER SYSTEMS, REQUIREMENTS FOR
MIL-STD-7179 FINISHES, COATINGS, AND SEALANTS, FOR THE PROTECTION OF AEROSPACE WEAPONS SYSTEMS

SAE docments...[go to Sub Topics - SAE Aerospace Standards and search for noted specs]
AIR4844 Composites and Metal Bonding Glossary
AIR3938 Composite and Bonded Structure Technician/Specialist: Training Document
ARP1524 Surface Preparation and Priming of Aluminum Alloy Parts for High Durability Structural Adhesive Bonding
ARP1842 Surface Preparation for Structural Adhesive Bonding Aluminum Alloy and Low Alloy Steel Parts
ARP5256 Mixing Resins Adhesives and potting compounds
 

Geek1945

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Gary;

I forgot to mention, but there are other classes of aluminum adhesives. In particular, the adhesive / caulk that is used in gutter sealing. I believe that this is a butyl rubber material which has superior weather resistance, plus has high peel strength. It is also widely available at most hardware & discount building supply houses at a cost far below most industrial adhesives... plus it comes in a wide range of colors.

I've never tested it, however, I have tried to tear apart old aluminum gutters and found that to be a difficult task. If it can hold up in a gutter, I suspect that it might have an application or two in holding an aircraft together, especially if you intend to use a 'cheater' rivet or two.

Just a thought you might enjoy.

All the best & fly safe,
MalcolmW
I agree using a $3/caulking tube butyl rubber roof sealant I was amazed at the strength it was difficult even to separate two metal roofing steel. Using a sharp knife I was able to pry it up very little removal of the knife returned metal to previous state. It's tough and considering metal roof temperature in Texas summer the temperature doesn't have any effect on its strength.

Another is windshield sealant even after using a hot knife on my windshield the installer almost bent my seat back using it as a brace while using his feet to kick the windshield till the seal finally failed. He said he fixed a leaking plastic mower gas tank with the sealant and it hasn't leaked since the repair. Now poly tanks are very hard to get anything to adhere to them so metal tanks should be a no-brainier. These adhesives and sealants seem to get better every time I use them but, nothing will work given improper use like failing to read the directions or sloppy application.

I believe most failures are the result of not prep-ing the surface before application. The only problem is resealing the tube without plugging the nozzle and removing it from hands takes days to wear off.
 

cheapracer

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I have done some tests with aluminium and epoxys the last few days.

I bought hideously expensive 3M DP460NS, supposed to be great stuff for 380RMB/USD $61 (200ml) and some local Chinese brand named AB, a 50/50 mix of part A and part B for 7RMB/USD $1 (50ml).

I prepared a number of aluminium strips, flappy sand disked a couple and cleaned with alcohol and some just wiped with alcohol. Glued area about 3" x 3" 75mm x 75mm and stuck them each under a workbench leg for 2 days..

Very disappointed with the results of the 3M, was expecting some minor miracles but the non-sanded sample easily pulled apart with my hands leaving zero bond to one side as you can see lower right in the picture and the sanded one took some heavy pulling with 2 hands on pliers with my foot on the sample and suddenly let go with a big snap each time. the epoxy itself broke through the middle leaving a coating on each strip that could be scraped off, upper right in the picture.

However the cheap Chinese crap was quite brilliant in comparison, it had to be chiseled apart with a blade screwdriver until 90% separation before it could be pulled apart by hand and the residual had to be flappy sand disked off.

So I suggest you do a little self research as ever before believing what others say and figure it out for yourselves!
 

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BBerson

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It takes time for bonds to degrade. Usually about a year.
Mike Hoke (world leader in bond experience) told me that he did several tests with aluminum bonds. Just to see what would happen, they wiped the surface with motor first and did the bond. He said these oiled bonds tested stronger than normal bonds the next day.
But fell apart a few months later.
This us the problem of bonding aluminum. ( time degrades the bond)
 

danmoser

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I prepared a number of aluminium strips, flappy sand disked a couple and cleaned with alcohol and some just wiped with alcohol.
There's yer problem !! ;)

Good aluminum bonds depend far more on good surface preparation than anything else.. sand & alcohol wipe is a very poor method indeed!..
The best is Phosphoric Acid Anodizing .. Chromic acid and other types of anodizing or alodine are generally good too.
There is an acid etch product called "Pasa-Jell" .. works very well, though be careful of how you dispose of the rinse water.. might need to be treated as hazardous waste, depending on your local laws.
There are some primers & other products available from Aircraft Spruce & others that do OK.
Seems like the easier it is to use, the worse your results get.

The deterioration of the bond over time is is a function of the surface corrosion of the aluminum, not the adhesive.. large exposed edges with narrow bond areas don't last as long a broad bond areas with fewer exposed edges and/or protectively sealed against environmental exposure.
Well-made, well-protected bonds will last for many decades!
 

BBerson

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My point was that just because the bond tests good the next day is no guarantee it will last. Lots of things can happen in time. Epoxy can shrink and pull loose. It could harden and get more brittle after a few weeks or years. The peel strength needs flexible epoxy. A brittle edge tends to peel. It could be that the test with oil helped for peel strength, it adds some flex.
.... Note.... I am not recommending adding oil....
 

DeepStall

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...and stuck them each under a workbench leg for 2 days.
What temperature? Most of the higher performance epoxy adhesives like to cure at room temperature, if not higher, and can take several weeks to develop full bond strength. I'd imagine if your bench is sitting on a concrete floor, the samples could be too cold to develop a proper cure in 2 days. Second remark: the higher the performance a product is aimed for, the more fussy it tends to be to use. IOW the 460 may be able to develop a better bond, but only if used correctly, whereas the generic stuff is probably formulated to be relatively insensitive to mixing and cure so the typical consumer user can make it work.
 

cheapracer

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There's yer problem !! ;)

Good aluminum bonds depend far more on good surface preparation than anything else.. sand & alcohol wipe is a very poor method indeed!..
Maybe but if you read my post you will notice I mentioned there wasn't an issue with surface bonding, the bond tore apart through the epoxy's own section - except for the unprepared surface test which I did expect but wanted to experience for myself anyway.

Further, this is only an addition to standard riveting method, if the epoxy is cheap and preparation is fast and easy then I will use it to enhance the joint, not to be the joint's sole strength, that is the rivet's job. The structure has a noticeably more solid feel when assembled with the epoxy by the way.


What temperature? Most of the higher performance epoxy adhesives like to cure at room temperature, if not higher, and can take several weeks to develop full bond strength.
I followed 3M's guide. They say 24 hours, I gave it 2 days and within their temp allowance.

whereas the generic stuff is probably formulated to be relatively insensitive to mixing and cure so the typical consumer user can make it work.
Indeed, which is why it is more suitable for my use as "no brainer" enhancer.

Thanks for your inputs :)
 

GESchwarz

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I am supposing that Bonderite is a brand of two-part epoxy? If so, to learn exactly what it is capable of doing, refer to the data sheet that comes with the product, compare it to other epoxies, and finally do your own test samples and see how it performs to your requirements.
 

blane.c

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I am supposing that Bonderite is a brand of two-part epoxy? If so, to learn exactly what it is capable of doing, refer to the data sheet that comes with the product, compare it to other epoxies, and finally do your own test samples and see how it performs to your requirements.
No ... it is a conversion coating.
 
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