Gary Katsanis wrote:
> I have a heavily rusted piece of what was high-strength steel in the
> 1800's. I want to restore the mechanism to functioning condition.
> Penalty for failure is severe and messy.
> Would electrolysis be an unacceptable method of dealing with the
> rust? I've heard of hydrogen embrittlement, but I don't know if it
> is a serious issue.
The metallurgist replies:
Hydrogen embrittlement occurs when an acid (or electrolysis) liberates
hydrogen atoms at the surface of the steel, whereupon they are driven
into the metal by chemical forces. Any stressed areas of the steel
promote the recombination of the dissolved hydrogen atoms to generate
hydrogen gas, which pries apart the grain boundaries in the steel so
that the resulting fracture surfaces have a "rock candy" appearance.
Experienced non-metallurgists say that their steel whatsis broke because
it "crystallized."
Saws curled up for electrolysis in a bucket will demonstrate this very
nicely, if you don't mind the noise.
The critical hardness is 300 Brinell. Saws, chisels, plane blades,
springs and the like fall in the susceptible category. Don't try
electrolysis or acid treatments on those unless you know that they
have been stress relieved (e.g., tempered) beforehand. I don't
remove rust from such gadgets with either method, as I think that
even when they don't break, they look awful afterwards.
Weldable steels are OK, as welding often causes hydrogen to enter
them, and they don't crack afterwards, unless the steel was air-arc
gouged beforehand with a carbon electrode, which carburizes the
prepared surfaces, so some parts of the subsequent weld get too hard.
How do I remove rust ? With a dull chisel or scraper and a lot of
elbow grease. The red rust is what gets removed, leaving the black
rust behind, which is much harder. That also leaves a passably
smooth surface which is sufficiently porous to hold some protective
oil. The scraper (made from an old triangular file) is less likely
to dig in, because you're pushing it with your fingers, not with
your entire upper body. Still, it's gotta be dull or it will scratch
the steel. It also has to be quite hard ... like a file.
If you're really determined to use acid, the method I have used in
my consulting work combines dilute hydrochloric acid (ten percent,
what they sell for etching concrete at the hardware store) with
about four grams of hexamethylenetetramine (a.k.a. hexamine) per
liter. The hexamine inhibits attack of the steel by the acid. Rinse
and dry thoroughly afterwards. All of the rust, even the black stuff,
is removed in a few hours at room temperature. You can get hexamine
as those heating tablets that one uses on camping trips. The spent
acid can be neutralized after use by adding crushed limestone
(agricultural lime) until it no longer sizzles.
On the topic of spring-making:
Chuck springs have two problems: Too loose a fit, and they buckle
and get squashed between the jaws when the chuck is tightened; too
tight, and they hang up on the corners of the hole with the same
result.
Solution: Wind your own springs. Hjorth invented a very nice spring-
winding tool which can be found every so often. There are two sizes,
one which is about the size of a small pipe wrench and no good for
chuck springs, the other is about three inches long, which is perfect.
I learned a long time ago that the ideal spring for this purpose
crams the most and largest wire that will fit into the holes of the
chuck jaws when the chuck is fully closed. That produces a pretty
stiff chuck spring, but it's less vulnerable than a fashion-model
spring.
Also long ago, I cornered the market on spring wire, as I went to
MSCDirect.com and cleaned 'em out of all the available sizes. Then
I got a couple of sets of wire-gauge drill blanks. That leaves
georgesbasement.com as the go-to place for replacement chuck springs.
They aren't intended to fool the judges at the oldtools _concours
d'elegance_, but your chuck will work a lot better afterwards.
This will entail your sending me all three jaws so I can hand fit
the new springs. Cost is five bucks plus postage ... galoot terms.
See my methodology here:
..../mfno2typestudy/MakingChuckSprings/MakingChuckSprings.htm
I can also make oddball springs with a pair of needlenose pliers,
but so can you, if you have an old spring to use as a pattern.
George Langford, trying to consolidate thirty years of metallurgy
reports in SE PA.
http://www.georgesbasement.com/
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