broken steel screws in aluminum casting - the experiment
Grant Erwin
broken screws in the same machine, one I was able to get out with an easyout,
the other not. Last night I made up a small amount (~3 oz.) of hot alum solution
and weighed the piece I got out. It weighed .7 grams at 11:30PM. I dropped it
into the hot alum and it started bubbling. Clearly doing something, I went off
to bed. This morning the piece looked about the same size, no more bubbles,
clearly it had cooled almost immediately, spending the night at ambient (maybe
63°F in my kitchen). I heated it back up in the microwave, ferocious bubbling
again. Cooled, slowed down. As expected. Anyway, at nearly 12 hours I took it
out, washed it off (it had turned a deep velvety black), dried it and weighed it
again. Down to 0.3 grams, clearly it will dissolve at this rate in about a day.
Incidentally, the reason these screws were so tough to drill out is that they
are self-tapping screws, very hard on the tip, also more brittle. Not a real
good choice IMO for running into aluminum, not if getting them out 40 years
later is an issue.
So now I'll go try making a little dam and plug arrangement and try dissolving
out the screw still stuck in the machine. I don't have anything to lose, since
as you guys have pointed out I can obviously work around the stuck part. So this
is all learning at this point.
GWE
Scott
Grant
There is a commercial product for just such thinks called "Tap Out"
It is used to dissolve hss taps that have broken off in aluminum
parts. Try you friendly industial supplier. It may be hard to ship
becuase of the nature of the acitd involved.
Grant Erwin
That's a tough name to google on! I found a dead link:
http://www.internationaltoolsupply.com/tapprices.html
which google still has cached: http://tinyurl.com/d26ze
which appears to refer to such a kit. I'm nowhere near $30 worth of desperate,
especially when a tablespoon of alum is nicely dissolving another screw
identical to the one I've got stuck.
Wish I knew what the chemical reaction is that's taking place. Alum is actually
potassium aluminum sulfate, a double salt of the SO4 ion, which is of course the
same ion in sulfuric acid. Since the screw is bubbling, and it doesn't stink, it
must be bubbling off oxygen, which means what's going into solution is some iron
sodium compound, but what? and why not the aluminum? (anyone?)
Grant
Nick Müller
> Last night I made up a small amount (~3 oz.) of hot alum solution
What is hot? Boiling or just enough that you don't want to put your
finger it it for some seconds?
Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO -> YADRO <- Eigenbau-Digitalanzeige
Grant Erwin
> Grant Erwin <gr...@NOSPAMkirkland.net> wrote:
>
>
>>Last night I made up a small amount (~3 oz.) of hot alum solution
>
>
> What is hot? Boiling or just enough that you don't want to put your
> finger it it for some seconds?
30 seconds in the microwave got it to boiling, but there is so little thermal
capacity there that probably 2 minutes later you could stick your finger in it.
The reaction, whatever it is, goes faster when the solution is hot.
One person knowledgeable on chemistry wrote me that the salt of a strong acid is
a weak base. Another wrote me that AlKSO4 dissolves into K+ and AlS04- ions, not
as I'd suspected into K+, Al+ and SO4-- ions.
The plot thickens.
GWE
Nick Müller
> The reaction, whatever it is, goes faster when the solution is hot.
You can always heat the part.
> One person knowledgeable on chemistry
Can't be me. :-)
> wrote me that the salt of a strong acid is a weak base. Another wrote me
> that AlKSO4 dissolves into K+ and AlS04- ions, not as I'd suspected into
> K+, Al+ and SO4-- ions.
That's quite interesting. Because I remember that someone asked the same
problem in a chemistry-NG and he got no (helpful/right) answer.
Furthermore, I do have some alum (after I found out the translation).
Sadly enough, I don't intend to break a tap in aluminium in the near
future. OTOH, I hope near enough to be able to remember the recipe.
Hope you are making progress.
ph17314
Would you be so kind to share this process start to finish?
I have a similar problem as yours
Thanks Paul
"Grant Erwin" <gr...@NOSPAMkirkland.net> wrote in message
news:11p9gp4...@corp.supernews.com...
drpcfix
70% solution of nitric acid/water - (always add the acid to the water).
I make a dam using modeling clay, flill it with the acid solution and
a few hours later it is gone.
Grant Erwin
metal guards which were badly rusted and which rattled terribly. When I removed
them I discovered two 10-32 screws broken off below flush. As it turned out,
these were self-tapping screws, which have a very hard tip. I tried punching a
hole in a piece of sheet metal about the size of a postage stamp, then I dimpled
the hole out using a punch. Using a small tip on my O/A torch, I tried to weld
the sheet metal to the screw. This simply resulted in welding the hole shut,
with no fusion to the screw at all. Next I tried to heat the screw in situ, to
add weld bead to the top. The aluminum all around it wicked the heat away too
fast. Next I took a 7/64" drill, centerpunched the screws, and drilled them
lengthwise which took a few drill bits because the material was so hard. Then I
tried easyouts, both the left-screw type and the 4-corner type. I was able to
get one screw out, but the other resisted. So I started looking at dissolving it
out. People on this newsgroup were kind enough to share with me that alum, a
common white chemical used in turning cucumbers into pickles, and available at
any grocery store in the spice isle, will dissolve steel much faster than it
dissolves aluminum. Being of an experimental bent, I then took the one screw I
got out, figuring it's essentially identical to the one left in, put a couple of
teaspoons of alum in some water, weighed the screw (0.7 grams at the start) and
dropped it in. In 2½ days very little was left, just a little smudge on the
bottom of the solution. I heated it several times, but it cooled almost
immediately.
My next step is going to be trying to find some nitric acid, and repeating the
experiment with 0.7 grams of the same kind of screw. Whichever works better, I
will then try on my part.
Stay tuned.
GWE
Paul G. Shultz
would dissolve the tap without affecting the brass. I'm building Phil
Duclos' model makers dividing head and it's much too pretty to do
anything other than dissolve the tap. I'm no chemist and I don't know
if nitric acid will affect brass.
Lew Hartswick
I'm no chemist and I don't know
> if nitric acid will affect brass.
Boy, wil it ever. Very fast probably faster than the
steel.
I think your not going to do it chemically.
...lew...
Ken Moffett
@alaska.net:
If I remember correctly, I've used the hot-water/alum soak to dissolve taps
out of copper, so it should be safe for brass. But, try a small piece of
brass first.