Theory of Adhesives?

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Well, in the case of pure flex, won't a thicker material flex less, thereby introducing less force? Seems like an optimization problem here..... Also, by definition, distance from the neutral axis would have SOME contribution, no?

Will I get to specify her dimensions?
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EA


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Thinner gives more, so it won't load the aluminum-to-wood bond as much.

Let's not go there. We'd need pictures and I'm not up for it.

And degrees of firmness. Do you prefer inflatable or foam-filled?
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Ed Huntress




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On 07/12/2011 08:14 AM, Ed Huntress wrote:

I dunno -- I was seeing it as the distance from the neutral axis. You can't increase the distance from the neutral axis without increasing volume, so they pretty much go together.
I was saying that if you only put the aluminum on _one side_, _and_ you use something thinner than 1/2 inch, that you should be OK. Basically, the aluminum is going to move a lot less than the wood. Only doing one side gives the wood an opportunity to move (and to bow with humidity), which relieves stress on the glue joint.
Put Al on both sides of the wood and you're right back to gluing a strong thing to a weak thing with stuff of questionable strength -- so if you stress it to breaking, either the glue bond or the underlying wood is going to shear, or the glue on the compression side is going to let the aluminum lift and buckle, or the wood on the compression side is going to let the aluminum dig in and buckle.
But (again) if rigidity is more important than strength, this may not be a bad way to go.
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Tim Wescott
Wescott Design Services
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It's not the neutral axis that's determining the force. It's an integrated value of all of the force exerted by the expanding wood from the bond plane to the plane of the wood panel farthest from the aluminum. And all of that force is applied to the bending resistance of the aluminum, through the glue bond.
Compounding the effect is the greater leverage exerted by any expansion force generated in the wood fibers farthest from the aluminum.

It would be less likely to sheer off.

But the force is applied *to* the glue joint, as the wood tries to expand. More wood, more force.

True, but as others have said, it will be stiffer to begin with, and much less vulnerable to expansion from changes in humidity.

I think EA has a fairly low-tech application here. He can get away with a lot, as long as the plywood is thick enough to provide the stiffness he needs.
'Don't know why he's talking about aluminum, though. That's the biggest bonding problem, and it has little else to offer to the application. It must be something he isn't telling us. d8-)
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Ed Huntress

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Uhhh..... it's SHINY???? :) Well, at least it starts off shiny!! And it's half the price of same-thickness SS.
Not absolutely wedded to any single strategy, as there are no doubt lotsa unforeseen things that will make one strategy more do-able than another. And regardless of what the laminating strategy is, I have the luxury of using no adhesive at all, due to the way the edges are treated.
Lotsa options here, super info, appreciate all the input.
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EA



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Damn. I didn't think about that. d8-)

Sometimes it's good to just fish around like that, to hear some options you might not have considered. But now you can get down to looking at your objectives in light of what's available.
I still think that laminating it yourself is going to be a losing proposition relative to buying overlaid ply, but you can check out those options for yourself.
Let us know how it works out.
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Ed Huntress



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Very inneresting site, lots of upside potential with that site, that I emailed them about.

So it seems!!!
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EA





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Existential Angst wrote:

Contact cement is hard to apply evenly and is messy: plan on throwing away any roller/brush used for application. Porous surfaces will most likely require two coats. Each surface needs to look glossy all over and must be dry enough so your finger doesn't stick.
Others have suggested using paper slip sheets. That will work but the thing about contact cement is, well, it bonds on contact. I prefer to use dowels or sticks to keep the two surfaces well apart from each other until you are ready to bond them. I usually space them (dowels) 12-15" apart, depends on the dowel diameter.
Once you start bonding, start at the center and work out toward the ends to avoid trapping air. Once all is bonded it needs to be *BONDED*. Do that with a J-roller, lots of pressure; again, work from center out to the ends and edges. You can also use a rubber mallet, roller is better.
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dadiOH
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You are also hoping the cheap roller isn't made with pile stuck into an adhesive that the solvent in the contact cement doesn't dissolve. That way the roller itself will unroll, and then you're in trouble.

Nooooo paper slip sheets... they can get caught and tear. Dowels 5/16" or bigger.

J roller indeed. You obviously know your laminating stuff.
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Yes. Many opinions. Just make sure that when laminating dissimilar materials, to do both sides of the substrate, a 'balance' sheet. Trying to get away without one is foolish. In case of laminate, just a cheap discontinued colour will suffice. Also, look into Wilsonart 3000 adhesive. Water based, will stick anything to anything (other than greasy plastics). Lots of open time and a decent roller which will allow your body weight to do the work is all you need. Wilsonart 3000 is NOT contact cement but works a bit like it. One side of the joint has to have minimal porosity.
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wrote:

Yes. Many opinions. Just make sure that when laminating dissimilar materials, to do both sides of the substrate, a 'balance' sheet. ========================================= A very inneresting idea, altho in this case it will likely add substantially to costs. But mebbe a workable compromise is to laminate both sides, but not with identical materials. Proly an ongoing experiment. But I do hear the demands of symmetry.... :)
Trying to get away without one is foolish. In case of laminate, just a cheap discontinued colour will suffice. ========================================== In non-stress situations, like countertops, one-sided lamination seems OK, but mebbe even there, two-sided lamination might help longevity (warping, etc)..
Also, look into Wilsonart 3000 adhesive. Water based, will stick anything to anything (other than greasy plastics). Lots of open time and a decent roller which will allow your body weight to do the work is all you need. Wilsonart 3000 is NOT contact cement but works a bit like it. One side of the joint has to have minimal porosity. ============================================= Will look into Wilsonart.
What does "contact cement" connote, adhesive-wise? Is it a specific genre, or are there a variety of types?
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EA




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wrote:

There are a several types. They have great relative peel and cleavage strength, but they yield a bit in shear. You want that with a countertop or you'd have warping problems.
EA, you've asked a question that could go around in circles for a long time. Why don't you just tell us what it is you're trying to accomplish? That will narrow it down.
As for being complicated, back in '78 or '79 I wrote a 16-page Special Report for _American Machinist_, titled "Adhesives in Metalworking," or something like that. I took four months to research it and I travelled all over the country, visiting engineering companies and suppliers who work at the high-performance end of the business. My report had so many elements in it, it was hard to keep it organized. And it just scratched the surface of the subject.
You're right, it is a very complicated subject. If you've ever read the reports on adhesives from the USDA Forest Products Laboratory, you know they're long -- and excellent. And that's just for wood and wood composites. When you get metal and plastics involved, the complexity compounds.
That is, if you need high performance. The gummy glues, like contact cement and consumer-grade moisture-cure polyurethanes, solve a hundred different problems very neatly. But that's because most applications only require one or two types of strength -- in their case, it's mostly peel and cleavage, which are the toughest kinds of strength to get, usually, when you're bonding dissimilar materials. Contact cement is not a strong adhesive in engineering terms. But it may well be the strongest, and the best, for your application.
So tell us what the application is.
--
Ed Huntress



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Existential Angst wrote:

Keep in mind that any flex means that one sheet has to compress while the other has to elongate. If you could make the base crowned and direct the bending force outward to firmly fixed sides...
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dadiOH
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I can't speak for Tim, but I have laminated elevator panels, restaurant cabinets, bars, floors, walls, tables, countertops in a variety of materials, back splashes, suspended ceiling sections, valences.... I could go on.
The most stable 'packages' do not include MDF or plywood. When you laminate onto plywood, your joint is only going to be as strong as the next ply's adhesion to the ply below. You have no control over that. A quality particle board, and yes there are many, many grades (hardwood, long fibre, different binders, densities etc.), when laminated, will be a far better performer that a regular plywood, again assuming properly laminated. In terms of strength, a proper plywood (and there is a lot of shit out there) will be stronger, but cost and the de-lamination problems which I have encountered over the years doesn't make a plywood an automatic choice over PB. Proper High Density PB is VERY impact resistant especially when clad in a GP grade HPLAM.
I have used sprayed rubber contact cement for years and years and only like the Imperial airless 32 lb cannisters, as the layer of adhesive can be very thin and therefore not give you much slippage relative to the laminate and substrate. Too much rubber contact cement and you 'disconnect' the laminate laterally from the base. It actually slides ever so slightly even after it has cured. Wilsonart 3000 PVA does not allow for slippage which can set up immense tension between the lam and subs to the point that 0.125 acrylic with actually form hairline cracks, so in that app, use rubber contact cement.
People I know are now using an MDF and/or PB which is water resistant, but not as nutso-coo-coo as Extira waterproof... or expensive.
And ALWAYS ALWAYS use a balance sheet even IF you're going to screw the 'half' package to a row of cabinets. For the little time and money involved, it is simply silly NOT to. In two adjoining buildings, I laminated the elevators panels in one building, my way, 15 years ago. The other building's elevator (I didn't bid on that gig) has its panels redone, at contractor's expense, after 2 years, THEN they did use a balance sheet that time but cheaped out on post-form grade laminate, thinking they'd save a few bucks. Within 6 months, they had me do it that time. I billed them for materials only. The building's owner added $ 500.00 for labour. (Not enough, mind you, but I got a lot of referrals over the years from him.)
Shortcuts WILL bite you in the ass......like that time, I....nebber mind...
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On 07/12/2011 10:09 AM, Robatoy wrote:

Like I said, I was specifically addressing the oddball case of laminating aluminum to plywood. It makes a really interesting theoretical problem, and may even be practical for a homebuilt airplane, if you need the strength and you're a hot-shit adhesive engineer, and you keep it dry.
But it's not what EA wants.

Is there a particle board that has the bending strength that he needs for his machine base? Oriented strand board ("chipboard", or "Crudboard (TM)", as my dad used to call it) would -- but I could see it having the same problem as plywood, with glue letting go in shear.
Or to stop looking at trees and to take a look at the forest -- is there a way to start with plywood that has the strength that he wants, and make it look good without laminating?
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Tim Wescott
Wescott Design Services
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Laminating aluminum, clear, brushed, shiny comes in many diffent sheens, and is already prepped for laminating. Just about anybody sells that stuff, Wilsonart, Formica, Arborite, Nevamar.

Yea.... what DOES he want? LOL
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On 07/12/2011 12:08 PM, Robatoy wrote:

But is it load bearing? Can you laminate it onto plywood, then actually use the strength of the aluminum?
Or is it just a way to make it shiny?

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Tim Wescott
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If you want stiffness out of wood construction, look up "torsion box". Can be scaled to whatever size you want. I've seen the technique used for cantilevered shelves coming out of walls with no supports.
Stan
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wrote:

Torsion boxes are great, but if you follow the whole thread, it sounds like he needs something much thinner.
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says...

If he wants something fairly stiff, light, and about a half inch thick, I'd say try bonding some 20" wide flashing to both sides of a piece of 1/2" foam insulation. Use a structural adhesive rated for foam and aluminum. Point of failure will likely be shear in the foam. Same caveats as with all foam core--if you need to put screws or bolts through it, cut out the foam where they go and put in something solid.
And test the Hell out of it before trusting it in a situation in which someone can get hurt.
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