Untitled Gardening Project #39

[xiphmont]

Deburr and scour each bottom plate using 220 grit silicon carbide sandpaper. The sanding is to remove surface dirt and corrosion, not produce an unblemished surface. Wash and degrease each plate.

Comments

[zkzkz.livejournal.com]

Corrosion? I thought aluminum oxidized so readily that just about any exposed aluminum is covered with a thin layer of aluminum oxide which is very hard and actually protects the aluminum nicely.

[xiphmont.livejournal.com]

"Corrosion is breaking down of essential properties in a material due to reactions with its surroundings." --Wikipedia

The important things that differentiate corrosion from oxidation is that corrosion tends to be ongoing and that it renders the material unsuitable.

So, yes, aluminum oxidizes readily, but the oxide layer is self-sealing against further oxidation (unlike, eg, red rust). It doesn't disrupt or penetrate the substrate, doesn't discolor it, doesn't alter dimensions, and doesn't damange adhesion properties.

Aluminum does react with things other than atmospheric oxygen that would count as corrosion. Soap/detergent has a tendency to discolor and chalk the surface. Plenty of other chemicals will mar it as well. That's what the sandpaper needs to remove. Powdercoat will stick nicely to an oxide layer and the slight roughness will help too.

[thpeech.livejournal.com]

They look like Knights of Templar shields, but somehow I don't think that's an accurate guess as to the final product...

I can't imagine what that grooving is for except for gasketing. Or attaching more pieces. Or just to look pretty. And the cylinders on the corners... Are they going to be coffee tables? Or shelving? But then why would you drill seemingly random holes in them? I'll wait for more clues.

stumped,
Julia

[xiphmont.livejournal.com]

(actually, misread your comment first time; yes, the oxide layer is beneficial, but you can't assume that aluminum straight from the mill has passivated solely from normal atmospheric conditions. Not to mention the cutting oils have all sort of interesting things in them that warn you to wash the part as soon as its tooled....)

[mbrubeck.livejournal.com]

He mentioned gasketing in #33. Some sort of bizarre fountain?

[thpeech.livejournal.com]

You're right; the gasketing *had* been specified. Hmm... these top and bottom plates must have to move, otherwise he would just weld it all together, not bother with gasketing. OR, a different material is supposed to attach there. Glass? Maybe they're going to be fish tanks, with exterior aluminum supporting columns?