Filling cavities on a cast alu surface to obtain perfect flateness

Hi, I have an aluminuim surface that is supposed to be planar,
(perfectly flat), but has imperfections, i.e. cavities of 1 to 2 millimeters
deep, of about 1 to 4 centimeters circumference (we're talking
of very irregular puddle shapes here).

The cavities originate from a poor casting technique.

This problem would be easily solved if there existed an epoxy that could
fill the cavities, I could then resand the finished surface and
make it perfectly flat. I have been reading about problems with
bonding to aluminium. So it seems that it might not be easy.

The finished surface need only to withstand mechanical presure
and not break, so there is no tensile strenght required here, only
resistance to compression. I am hoping that this can put less
constraints in the choice of material. The other constraint is that
the filler should not be elastic. Esthetics doesn't matter here,
so I don't care of how the finish looks like.

BTW, the simple solution of just sanding the surface until flat is not
feasable, because the total thikness of the plate needs to remain the
same.


Any advice ?

 

best way would be gouge out and fill with weld

could you attach a sheet of aluminum with fasteners or plug welds?

 

Thanks for the quick answer !
Pardon my poor english but I don't know what gouge means ! I googled
and found that it might be a form of carving, if that's the case, then shoudn't the
gouging be done *after* the welding ?

The sheet is not an option, because the surface is *mostly* correct, so if I add
a sheet it will thicken the whole thing...

 

gouging would be opening up the cavities enough to get a solid weld in

some cavities may be in the form of bubbles with small openings at the surface and difficult to fill with weld

if it was cast in sand there may be sand in the cavities

anyway if the part can stand the heat of welding without deforming that would be best

my opinion

 

Ive used "etch primer" in the past with good results for bonding epoxy to sandblasted and mechanically abraded Aluminum plate.

Aluminum casting is a different alloy...contact an Epoxy manufactures technical department for bonding..etching... advice.

For aluminium plate Ive used ....

West system 860 Aluminum Etch

 

Sand the aluminum then immediately wipe with acetone. When it flashes off (a minute or two), then immediately apply straight epoxy. Some will have you scrub the surface with a wire brush as the epoxy goes on, but if you follow my description you'll get a great bond. If you flood coat the area, you can have a nearly perfect surface before sanding fair.

 

Wrong Par...The original poster is not working with flat surface plate... its a casting, he can not abrade the surface of the pit. READ... the description of his project...he is working with a pitted casting.

 

I'm not going to get into it with you Michael, it's clear you have a limited skill set. Yes, you can abate a pitted surface, once again proving how little you know, in spite of your insistence otherwise. Just because you don't know how to do it, doesn't mean it can't be done, it just means you don't know how, which is like most of your posts here.

 

Par is right, Here is a epoxy material,If you can not sand it clean then sandblast it and use this product:


http://www.devcon.com/products/products.cfm?market=Maintenance & Repair&cat=Metal Repair

 

I would recommend PAR's suggestion too, simple, neat.

I wouldn't recommend welding, especially if you don't know what grade of ally it is. You need to be very careful welding cast ally, such as knowing what grade of ally it is, otherwise you'll cause more problems than you think you're solving.

 

You can also use one of a number of tools, to get down into the pitted areas, such as a needle sander.

Some years ago I played with using uniform length steel filings (1/16") and a magnet to polarize the metal filings as the epoxy setup. Naturally, density issues cropped up and I wasn't interested in experimenting further, but preliminary test results hand some huge material properties changes, over the usual set of filler materials. My intent at the time was two fold, the first to dramatically improve compression strength and secondly as a potential anti fouling coating (of course steel wouldn't be the metal used) with considerable penetration resistance as well.

 

...i would go the Devcon way, have done it before using Devcon on cast iron machinery, and of course we use it for bedding.....it will do the job well..(Note: Devcon is an epoxy product with fine metalic particles, the alloy version will be the one to use).

 

Thank you all for the advices, this is a very helpful cummunity. I will try the epoxy filling,
since I am not equiped for welding, if I get bit by oxidation problem, the fill will just come
off and I'll start over with a more careful surface preparation.
Cheersi !

 

Seconded.
That or just pick up a tube of JB weld at the local hardware store.
Skim it in neat with a pallet knife & there will be hardly any sanding to do.

 

"JB Weld" is metal filled epoxy, Bntii.