Title: Boiling a broken fastener out of an Al casting with Alum
Owner: Andrew Waugh , added Oct 03 2013 16:02:34
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1024x768 102kb(If the image has failed to load, click on it to view large version) Description: Happens to everybody sooner or later, I should have used heat before even trying, but was trying to save the Otter switch.
1024x768 75kb(If the image has failed to load, click on it to view large version) Description: Broken off flush with surface.
1024x768 78kb(If the image has failed to load, click on it to view large version) Description: Drilled. It was one of those days... the bolt extracter broke off (also flush), in spite of having used Penetrating oil for 48 hour AND heat.
1024x768 82kb(If the image has failed to load, click on it to view large version) Description: So I resorted to a trick from my other hobby (Horology). Alum from a pharmacy, you don't really need distilled water.
1024x768 101kb(If the image has failed to load, click on it to view large version) Description: Double boiler using a deep fat fryer, Just below boiling would be best, but the tstat on the fryer is shot. Add Alum until no more will dissolve (about 200g/l)
1024x768 75kb(If the image has failed to load, click on it to view large version) Description: You can just see it gassing as the Alum attacks the Iron. Arrange the piece so that the gas doesn't get trapped in the hole. Interestingly the Alum attacked the tool steel of the extractor _much_ faster than the vestigial remains of the screw - it was gone in about 10h.
1024x768 125kb(If the image has failed to load, click on it to view large version) Description: Not wanting to leave it unattended overnight, I unplugged the fryer. Next morning the Alum had formed crystals.
1024x768 62kb(If the image has failed to load, click on it to view large version) Description: After about 3o hours boiling in total, it had almost completely stopped outgassing, and I could feel the threads all the way down the hole with a dentists probe. Note how the Al has turned black where it was in the Alum. I _Think_ this is Iron(2) Oxide deposited on the Al at the molecular level.
1024x768 90kb(If the image has failed to load, click on it to view large version) Description: So I tried a tap. I chose to use a bottoming tap, ran it with lots of cutting oil. I used only the lightest of effort, backing out at the slightest resistance, cleaning the hole and tap, and starting again.
1024x768 96kb(If the image has failed to load, click on it to view large version) Description: Getting the black smut off was a bother. In the end I used abraisive pads and, W&D (800) and polish. The pits and impossible fillets are still black. Glass beading would probably have taken it off, but I haven't got the kit.
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