Glueing aluminum to other metals

I gluing 2 pieces of metal together there a 3 things to remember;

#1 surface area If you can use a 1" sq plate with a hole in the corner instead of the standoff it will have 20 times the glue joint area.

#2 tooth Rough up the joint surface with 80 grit sandpaper, it increases the surface area and randomizes the shear angle so it will not pop off easily.

#3 Chemical coupling Epoxies work best when they are able to chemically bond with the metal. This is tough on aluminum because the oxide surface on aluminum is almost completely inert and will form immediately on exposure to air. The solution is to put a drop of epoxy on the area to be glued and rough the surface of both pieces to be glued with sand paper through the epoxy. This protects the surface from exposure to air. Then, wipe off the dirty with epoxy with a DRY paper towel and apply some fresh clean epoxy and bond as usual.

Paul K. Dickman

Many thanks Paul. That all sounds like very solid (sic) advice. I did sand down the surface of the aluminum but not in the way you described. I will try that next time. The plate idea is a good one, so I'm thinking of putting a short countersunk machine screw through a small plate (unfortunately it will have to be more like 3/5" square due to lack of room) and then gluing the plate to the front panel. I can then screw a spacer on to the screw.

Dave

Screw the spacer to the plate before you glue it down. It'll be a lot easier to get tight.

Paul K. Dickman

Dave, If you can, cut a plate the same size as the pcb. Drill and c'sink for the screws you want to use. Use short screws and thread a spacer onto them. Then, wet both surfaces to be bonded with epoxy and use a wire brush to rough up the surfaces through the epoxy. Or, use loctite 330 adhesive. You can get this as a kit for about $20.00. And it sticks very well. Even on oily surfaces. I have personal experience with both methods. Eric

Many thanks Eric. That sounds like great advice. I'm going to give it a try asap.

Dave

I used Tracon 2151 epoxy for aluminum applications a lot. Its CTE is quite decently matched to aluminum, which helps a lot if the assembly sees temperature variations, etc.--C. Hale

Penn Engineering, makers of Pem Nuts, makes just the product you need. They are called concealed head studs. You take an end mill and make a counter bore part way thru your panel. Then you press this stud in. Viola! instant stud with no head or hole visible on the outside.

Erich

Many thanks for the link Erich. I'll take a close look at those.

Dave

Many thanks for the epoxy recommendation. I will give that a try. TBH when I have done testing to breaking point, there is always epoxy left on the aluminum, but never on the screwheads/spacers. So it seems to me that the epoxy is having most difficulty adhering to the nickel plated brass (spacers), or the zinc/stainless steel (screws).

Someone elsewhere suggested anodized aluminum spacers. Maybe they would stick more firmly? (if I can find a source for them).

Dave

On Wed, 9 Jun 2004 15:28:17 +0100, "Dave Marsh" vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

Ideas:

(1) If you placed a panel behind the front panel, stuck to the front panel and made of something eminently glueable, you get a huge area of contact on the front panel aluminium, and an easily-glued surface behind it. On such a large area, even contact cement would hold.

I am thinking of some of the "super cardboard" fibreboards etc, gasket material etc.

OR

(2) If you can place the circuit board closer than 1/4" to the panel that holds it (say 1/8") then you can adhere a standoff panel to the front panel with plenty of area, and bolt the cctbd to the backing panel.

(3) Place spacers _behind_ the cctbd, so that there is no pressure on the panel, except that carried by the back wall of the enclosure or columns from the bottom.

(4) Re-design the project box as many would. Countersink the front "working" panel by pressure, to allow csunk screws. Place a prettypanel in front of that, label and all, held by the edges of the box (if it's one of those slotted things), or again simply held on by contact.

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Sometimes in a workplace you find snot on the wall of the toilet cubicles. You feel "What sort of twisted child would do this?"....the internet seems full of them. It's very sad

That sounds a very good idea, thanks.

For the next design I will definitely rethink it - Many thanks for your suggestions Nick.

Dave

On Thu, 10 Jun 2004 15:31:03 +0100, "Dave Marsh" vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

Think behind the panel you hide behind

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Sometimes in a workplace you find snot on the wall of the toilet cubicles. You feel "What sort of twisted child would do this?"....the internet seems full of them. It's very sad

On Thu, 10 Jun 2004 15:31:03 +0100, "Dave Marsh" vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

BTW. Like the accountant, I trot out that "If only" theory that I _should have_ applied to my last effort....

Signed....boundary umpire....who _sometimes_ got to apply the learning from the last match.

HIH...and all that.

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Sometimes in a workplace you find snot on the wall of the toilet cubicles. You feel "What sort of twisted child would do this?"....the internet seems full of them. It's very sad

How is your front panel held on?

It must be connected to the back somehow - even if it is glued to a chassis then what I'd do would be mount the pcb to whatever the panel mounts to.

I'm thinking you have a box or something with a pretty front panel - well, mount the pcb to the back of the box on some sort of standoff.

I'd rather have dumb users (are ther any other kinds?) push on a structure that is solid than pull on one that is glued.

Dave,

Using glue for your application is messy and unreliable. For your application, as someone mentioned, use:

I have used these at work for electronic enclosures. Give me the height and screw size and I can probably send you some studs free. I just drill and press in using a vise. (Sorry, I can't make that offer to everyone)

Ed Ferguson

Hi Ed,

Thanks for your advice and the very kind offer. I'm after M3 studs height

6mm (panel is 0.06" thick). I'm in the UK and I'm guessing you are in the US? I can get a bag of 50 Penn self-clinching nuts (not studs, but they would be ok) from Rapid Electronics over here for ~$4, so that might be easier and save you overseas postage. But thanks again.

Dave

On Fri, 11 Jun 2004 15:28:15 +0100, "Dave Marsh" vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

oooohhh!

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Sometimes in a workplace you find snot on the wall of the toilet cubicles. You feel "What sort of twisted child would do this?"....the internet seems full of them. It's very sad

That is the result of viewing Hillary Clinton nude.

That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there. - George Orwell