Hello all you very smart folks:
Using some clean scrap 18K, I melted it in charcoal with the
addition of a little flux, then rolled wire which was then pulled
through a star shaped drawplate. The wire had some “slivers” that
stuck out from it. Can anyone shed some light on why this might
have happened so that I might avoid this problem in the future? I
haven’t much experience with this drawplate because it is new.
Thanx everso…
Susan Ronan
Coronado, CA and back from a break!
Susan,
Did you anneal, pickle and wash the metal after you created the wire
and before you ran it through the draw plate? Using scrap gold to
roll and draw requires extra care.
Your metal either became to hard or it was contaminated.
Another problem may have been the alloy that was used. Some alloys
are designed for rolling and others for casting.
After reducing the metal by approximately 50% you should anneal and
quench the metal.
Good Luck
Greg DeMark
email: greg@demarkjewelry.com
Website: www.demarkjewelry.com
Link Exchanges Welcomed
The wire had some "slivers" that stuck out from it.
This might have been caused by squeezing the wire too tightly as it
passes through the rolling mill during the process of rolling the
ingot down. If the reduction is overly aggressive using the square
wire grooves in the rolling mill the corners of the wire will develop
thin fins of excess metal. If this excess metal isn’t removed it
will be rolled back into the wire stock as the reduction continues.
The wire often appears to be smooth, but when it begins to change
shape by drawing through a drawplate these slivers of metal will
re-appear. The same thing occurs if the ingot itself has any
flashing on the edges or corners after pouring which are not removed
prior to rolling.
I saw a well illustrated article about this exact problem in one of
the trade magazines within the past few years. I can’t recall which
publication it was, it might have been either AJM or Professional
Jeweler.
Michael David Sturlin
Hi Susan,
That’s a pretty classic problem that is the result, in my experience,
of rolling too far without annealing. The metal begins to get a bit
“crispy” and too stressed. Another problem might be that when you
rolled the initial ‘blank’ wire, prior to drawing the star, you had
some fins on the points – corners-- of the square wire. This is the
result of stepping down too quickly in the square rollers. These fins
may appear to roll back into the metal and the wire, in the case of
round wire, for example, may look pretty good. When you bend it
however, even after annealing, these fins peel back as flakes.
Remember to anneal when necessary and be careful not to step down
too quickly from one square groove to the next.
Hope this helps.
Take care, Andy Cooperman
coopermanjewelry.com
Susan,
Think of the metal distorting along the length of the wire as it
passes through the plate as being similar to a wave on the surface
of a body of water. As long as it’s a very tiny wave and there’s
plenty of depth, i.e., a very small difference in diameter change
with respect to the overall diameter, the wave moves along nicely,
but if the change is too large, the wave “crests” and “breaks”, like
an ocean wave approaching a beach. Those slivers are the result.
When I get them, drawing round wire, I stop and clean up the ratty
places before going through again, and I always pull from
alternating ends, never twice the same way. I’ve never used a
star-shaped drawplate, so I can’t cast any light on that part.
Loren
Hi Susan,
You said you used clean 18kt scrap. I will bet that some of the
scrape you used was from old castings. The alloys used for sheet and
wire are different then the alloys used for casting grain. Casting
grain usually contains some type of degasser, typically zinc. Its
purpose in a casting grain alloy is to help control porosity and
reduce oxidation. However, it is not good in sheet and wire because
it tends to migrate to the grain boundaries which results in stress
cracking. I suspect the “slivers” you describe are a result of using
cast scrape in your melt.
The slivers could also be caused by not annealing often enough when
rolling or drawing your wire. A good rule of thumb is to anneal after
not more then a 10% reduction in thickness. You can not anneal too
often. When in doubt anneal again. Also never quench any hot metal in
pickle. Always quench in clean water first and then place the metal
into hot pickle. It is complicated but quenching in hot pickle can
lead to stress corrosion under certain conductions. So why take the
chance when it is so simple to avoid?
All that said, it is possible to use casting scrape for sheet and
wire if you anneal even more frequently. My own experience with using
casting scrape for this purpose is mixed. It is rarely worth the
extra effort required because I never seem to get enough usable
material for the job at hand.
Good Luck
Jim Miller
Susan,
The star shaped draw plates do have their limitations. It’s best to
roll the metal carefully, looking for any cracks or distortions, and
then to draw the wire down in a regular round drawplate until you
reach a size just above the ultimate size of wire you need before
moving to the star shaped drawplate. If you go directly from a
squared shape to the star shape, a lot of stress will be placed on
thickest part of the metal and none on the thinnest parts. The
slightest misalignment will break off the points. If the star has
deep grooves, like say a traditional pentagram, you will need to be
very careful in your alignment so as to keep the grooves lined up as
well as possible. I hope that helps.
Larry