Hello all,I just got a new rolling mill at work and it seems
that I just started having trouble with my gold square stock
cracking as I roll it smaller. I thought at first that it was the
gold so I alloyed a fresh few grams and tried it and it cracked.
I thought maybey I was going down to fast so I went to .025mm
smaller each pass.I even started anieling it every mm or so and I
still get cracks. Has anyone had this problem? The mill we got is
a Durston.
Michael Mathews Victoria,Texas USA
Hi MichaelâŚ
Yeah I have noticed that the gold has benn more tempramental(?)
since my boss bought a new set of Durston rollers⌠Canât work
out whyâŚMy theory is that the truncated corners are too sharp
and it stresses the metal too muchâŚDonât know if I am right but
it sounds good to meâŚ
RayâŚ
Hi Michael - you may well be rolling too small too fast, or not
annealing enough. Every mm in reduction would not really seem
like enough. One thing you might try is compressing your ingot
BEFORE rolling. By this I mean take a hammer on an anvil and
smack the heck out of your ingot - reducing it by 15% or so.
This reduces all molecules in the metal to the same size and
prevents the bending and cracking from rolling. If you do this,
you may not have to anneal at all. I imagine this method is
explained better and in more detail somewhere here on the list by
Charles Lewton-Brain, from whom I learned it. Good luck, Mike
Michael -
I am not sure from your discription, just how your gold is
cracking.
I have had a Durston Mill for almost 10 years and am very
pleased with it. I roll rod ingots thru the lower square wire
rolls and have no problem with cracking. When going from one
groove to the next, I loosen the rolls, put the wire thru,
tighten a bit, put it thru the same groove again, etc. This way,
I do not get those fins out the sides which can get pressed into
the wire and then flake off later.
The Dinkle(sp?)mills I have seen do not have one wheel for
adjusting the wire rolls, but two nobs - not nearly as
convienent. You should not have to anneal very often. I go from
an ingot down to the smallest groove on my mill without
annealing(with 18 and 22 Karat yellow). In fact, I believe it is
better not to anneal before the material has been worked quite a
bit.
Mary
I too have had problems with cracking gold. I even use a Durston
mill too. The metal that sometimes cracks is 9ct, when I melt
down clients gold. I started a thread some months ago about
exactly the same subject. Check it out in the archives for the
replies. People were saying that it was due to the composition of
the melt. Hope this helps.
Andrew
Hello - Well I have also had this problem - my first work in 18k
and I assumed it was something I was doing, so I actually had
the refiner make my plate for me - so I never figured out why my
ingots were cracking- I have only had this problem in silver
once, when I was trying to roll plate with a new fire scale
proof alloy, which cracked quite nicely - I went back to my
supplier who said that the alloy was better suited to casting -
and this doesnâe address the gold cracking. My mill is a
Cavallin, and seems to work fine on Sterling.
Cheers
Douglas
Perhaps the cause of the cracking gold is the alloy. Are you
trying to make wire from un-refined scrap? Oxidized alloy
components can dramatically change the working properties. Virgin
golds always give the finest working results, and the time saved
is worth the small extra expense. Bucky
If you wear cubic zirconia, God will know.
@Bucky
Minutes off I-95 in sunny central SC, USA
Not being an expert on gold, and only a user of a mill once on
silver . . . Iâm wondering if youâre not trying to reduce your
stock TOO quickly (Rolling it too small would result in problems
as would trying to hammer it too much without softening between
reductions.) I can only assume that youâre not anneling enough
and that you need to gradually reduce rather than trying to take
a BIG BITE (big bite being that .025!) : ) I may be totally
wrong!
There are several things that could cause the gold to crack. The
primary one is oxygen built in during melting. The second thing
is not compressing it properly and annealing it after casting
before rolling to create a small crystal structure. Also, if
there are indentations in the sides of the ingot these may foster
cracks as well.
Silver and gold alloys containing silver love to absorb oxygen
while at high temperatures, where it is dissolved just like CO2
in soda pop-you canât see it until you change the pressure
conditions when the gas comes out of solution like when you take
the top off the soda bottle. (in Lab conditions 1 kg of fine
silver can dissolve 20kg of Oxygen by weight-luckily once you add
copper in the mix it is not as bad.
If you have allowed oxygen to be dissolved in the metal while
molten then it comes out as the temperature drops and the metal
solidifies, tending to occur and be sqeezed towards the
gate/sprue button area of the model or ingot thus resulting in
pits there.
The other thing that happens is that dissolved oxygen bonds with
copper contained in the alloy and forms brittle compounds that
are deposited at the grain boundaries. When you roll these they
try and slide past each other and can cause cracks. Large
crystals are worst. Large crystals are made by heating too high
when annealing, not compressing heavily and annealing after
making an ingot, air cooling and so on.
Avoidance: in industry melts are done in vacuums, under ammonia
atmospheres and so on. Sometimes an induction melting crucible
is used, load the crucible, put a thin layer of charcoal powder
over the metal (eats oxygen), put a lid on it until molten. In a
small studio one has to use other methods.
Do all you can to limit oxygen access at high temperatures to
your metal. Keep the time it is hot/molten and able to absorb
oxygen to a minimum. Preheat the crucible intensely (like a long
long time) and use a slightly gassy flame-note the slightly-if
you are leaving black soots around you need way more oxygen in
the flame, what you are looking for is a slightly yellowish
flicker at the end of the inner blue cone-assuming an
oxy-acetyelen or oxy-propane rig.
Watch the edges of the crucible, they should glow evenly, if it
darkens in one spot then oxygen is sliding into the crucible.
Use a bushy, large flame and slant it towards the crucible so it
makes a lid to protect the melt, a sheet of flame as a shield. In
Germany the actual cast is sometimes done through a pure (yellow)
gas flame as well.
Roll your metal that you are going to melt out as thin as it
will get and roll it up into coils like mini rolled rugs for
melting. This increases the surface area and reduces the melting
time dramatically (the time your metal is hot and exposed to
oxygen). Keep the melt covered by the gassy flame at all times
and consider adding a chunk of charcoal to the crucible to
consume oxygen. The shorter the melting time the less oxygen can
be absorbed by the metal. Do not add to much oxygen to the flame
to shorten melting time-it is counterproductive-you need that
reducing flame.
Do not remove the flame to add flux, if you have to add flux
then insert an iron or graphite rod into the flame to warm, dip
it into powdered flux and then insert the rod through the flame
to add flux-do not remove the flame which is protecting the melt.
If you have melted very well you may not need to make any flux
additions, the melt will be smooth and shiny like a mirror-in
that case you did well and just cast with it.
Scrap cast metal may have dissolved oxygen locked into it from
previous exposure at high temperatures, it seems to be
cumulative.
Some people add a âfluxâ to the melt, ammominum chloride and so
on to âdegasâ it, I feel this is not useful. In refineries they
sometimes add the teeniest smidgion of zinc to a melt just before
casting to âdegasâ it, often with silver alloys.
After casting an ingot which you are going to work you need to
recrystalize it for best results, to make a lot of fine crystals
or grains in the metal. To do this compress (do not forge out,
but compress) the ingot with the flat side of a forging hammer.
Compress up to 15% to 40% or so thinner than when you started.
Then anneal (but not too high! Just when the flame leaving the
metal turns orange, if your metal is glowing red you are too
hot!), then quench it (everything except nickel white gold).
This resets the crystal structure. Then file and sand (I like a
small belt sander called the âZippeeâ) so that the sides of the
ingot are smooth, any small indentation can turn into a crack.
Roll until you have reduced the thickness by at least 30% (there
are actual percentages for each alloy, perhaps Marcus and Peter
Rowe can enlighten us, examples are sterling is 45%, 18 k gold
can be 75% reduction before annealing). If you do all this then
this should reduce the cracking problem.
Lets say you did all this and your gold is still cracking
(probably oxygen built in-made brittle copper oxides at the grain
boundaries) then you could try a remelt to fix it. You need very
good ventilation for this fix-the fumes are dangerous. Melt the
metal. Add a heaping tablespoonful of potassium nitrate
(saltpeter), this will foan up and make a spongly mass which then
collapses down to a pool of metal again. Pour this as an ingot
and it often fixes the problem. You amy expereice some loss of
weight in the ingot.
When melting metal: Oxygen is your enemy.
best
Charles
Brain Press
Box 1624, Ste M, Calgary, Alberta, T2P 2L7, Canada
Tel: 403-263-3955 Fax: 403-283-9053 Email: @Charles_Lewton-Brain
Metals info download web site: Learning Center - Ganoksin Jewelry Making Community
Product descriptions: http://www.ganoksin.com/kosana/brain/brain.htm
Links list hosted at the Metal Web News:
http://www.mindspring.com/~wgray1/jewelry/
Howdy, I donât have any answers on this topic, but I do have
questions on this subject. I have noticed from reading threads on
this list, that if you donât mix new metal with old when you do a
melt, that you will not have good results with the finished
product. Why ? What happens with the old metal when it is
re-melted that causes the need to add new metal to the mix ? If
new metal is not added to the mix, what will be the results? What
is the raito of old to new for the best results? Dose this apply
to all metals or only gold? Is recovered gold worth less than new
gold? How can you make sure the gold you buy is new? Having never
cast anything but fish weights, Iâm not familiar with the details
of precious metals. thanks jerry
I did just start a new lot of alloy. and today I tried a batch
of 14K green and had no cracks. I also used info from Brain and
reduced my heat and oxydation when I aneal. Thanks so much I
think you are right about the alloy.
Michael Mathews Victoria,Texas USA
Michael One possibility maybe you are using gold with oxidizers
in it. If this is case thats where you may have problems, gold
w/oxidizers dont prefrom as well when you try to mill it. The
silicon or boron used to prevent firescale prevent it from
reducing as easily as gold without. I know i have to specifically
ask for casting grain without these oxidizers if I am going to
use it in a mill project. Michael
The metal that sometimes cracks is 9ct, when I melt down clients gold.
Howdy, The problem is probably the alloy. Especially if you are
melting class rings. If you didnât take out that little white
metal symbol under the stone, it has contaminated the gold,
making it brittle. There are rolling alloys, and there are
casting alloys. If you tried to roll an ingot made out of a cast
ring, you probably have the wrong alloy. Stuller Settings can
help with the proper alloys, and help on the metallurgy.
Hope this helps. Duane
I think maybe you misunderstand, at .025mm per pass it would
take 40 passes to reduce the stock by 1mm. Hardly âa BIG BITEâ. I
only tried that on one piece of stock as an experiment, but I
think Charles lewton-Brain answered most of my problem. It is
always refreshing (and depressing) to realize that even if I have
been doing one sort or another of jewelery for the last 20 years
that there is so much to learn.So much of the time we get away
with doing things the way we always do them because it works OK.
But when we change maybe one variable it stops working and we
scratch our heads.Well at least with a forum we can scratch our
collective heads and find answers. Continued learning is GREAT.
Thank you
Michael Mathews Victoria , Texas USA
Hello all,I just got a new rolling mill at work and it seems that I just started having trouble with my gold square stock cracking as I roll it smaller. I thought at first that it was the gold so I alloyed a fresh few grams and tried it and it cracked. I tholler each pass.I even started anieling it every mm or so and I still get cracks. Has anyone had this problem? The mill we got is a Durston.
Micheal, It isnât your new rolling mill. One problem with
alloying gold (and it sounds like your doing it yourself) is that
the temperature needed to thoroughly mix and melt your metals
together is too hot for casting, whether into an ingot or lost
wax (pure gold melts at 1981 deg. and overheats the alloy). The
crystal structure is just too big and doesnât have the strength
to withstand rolling, hammering, bending or anything else.
Annealing will do no good since that takes small tightly grained
crystals (which in this case arenât there yet) and rearranges
them in a less orderly structure. However when you do anneal
make sure you arenât overheating the metal (espesially with white
gold). Overheating causes a large grain to form as well and will
make your gold âbrittleâ.
So, either let your melted, alloyed gold solidify and then
remelt it after quenching(the melt will occur at a much lower
temp. not that it is alloyed) or if your doing a large batch dump
your gold into a large bucket of cold water and remelt the
âshotâ.
If this doesnât fix your problem check for contamination.
Either the 24K you are using isnât pure, the alloy is bad or the
crucibles are contaminated. But rest assuredâŚit isnât your
rolling mill!
Larry Seiger
JA certified master bench jeweler
Hartford usa
Michael One possibility maybe you are using gold with oxidizers in it. If this is case thats where you may have problems, gold w/oxidizers dont prefrom as well when you try to mill it.
I think what is meant here is deoxidizers (silicon copper, zinc,
etc.). I used to have MAJOR problems with gold cracking while
rolling until I learned a few tricks. The first thing to remember
is to roll the metal (after pouring the ingot) before annealing
it to at least 50%. This allows the grain structure to compress
and reduce in size. One of the main causes of cracks in gold is
the grain size. Thats also why one shouldnât use an alloy
containing deoxidizers. The grain size of these alloys are huge!
After casting, you can actually see the grain structure of the
gold. Ideally, one should use an alloy made specifically for
rolling (more silver content). Second, if possible use a
controlled atmosphere to anneal the gold with. You will get a
much more even distribution of heat and less oxidation etcâŚ
After annealing, quench the metal (yellow gold only)
immediately. If rolling white gold, wait until all the visible
heat has disappeared before quenching. I anneal gold in a muffle
furnace at 1250 F for 30 mins. after cold working to at least
50%. This is what is called âdead softâ. It amazes me how
malleable it is after I quench it. Third, and probably the most
important, roll the metal in ONE direction only. If you need to
even out the stresses, you can flip the piece over, but Never
reverse the direction. I usually cut a line or file a small
groove in the top portion of the stock so I can remember which
side goes in the mill first. Lastly, if you do happen to see a
crack forming, immediately file or grind away the area with the
crack (it will only worsen if you donât). Hope this helps, Ken
Mike,
Handy and Harmon, in their precious metals "handy book"
publication, suggest that 14 and 18K yellow golds can be rolled
to a 90% reduction between anneals, and white golds to about a
40% reduction between anneals. If you reduce the metal too
little between anneals, youâll get uneven grain sizes from the
outside to the inside of the metal, especially if youâre too hot
with the annealing temp.
Personally, I cannot see how the mill itself could be causing
cracking with one exception. There is a little flat surface at
the bottom of each V groove. A square mill is designed so that
with the mill screwed down tight, the distance from flat to flat
(vertically) is equal or less than the distance side to side (the
square diagonal without the flat) on the next smaller groove.
This is done so that you can turn the wire 90 degrees, and it
will then be thicker than the next groove, but not wider. This
is supposed to prevent forming a flashing along the sides.
Occasionally, one or more groves may be slightly off in this
regard, allowing a slight ridge or flashing to form. If you
then turn the wire and as usual roll that ridge back down, youâll
be starting a hairline crack at that tiny fold. Every time.
Softer metals may not visibly crack, but chances are, youâll find
that defect again if you then try to draw the square wire down,
or bend it later, etc.
If, on inspection, you cannot find any such defect forming as
you roll, then the mill is not likely to be the culprit. If it
IS doing this, then you need, when you get to that groove, to
start with the rolls opened up, and do that groove in several
passes to prevent forming that step/flange. It is possible,
perhaps, to slightly widen a groove in the mill that is doing
this, so it includes the entire width of the stock fed in, thus
not forming that sharp flange. But this is often difficult to
do, and can then mess up the progression to the next groove down.
Also, if your new mill has a better reduction gear ratio than
the old one, you may not realize that youâre moving the metal
faster than you are used to. But normally, if the mill is
working well and youâre not getting flanges, then this isnât the
problem.
Other things that can do this are of course contaminants in the
alloy. They may be coming from unexpected sources, such as
contaminated fuel in your torch (not likely, but it can happen),
or the wrong flame. To soft, for example, can give you carbide
inclusions in the metal. Even traces of iron can make gold
alloys brittle, as can tin or lead. Iâve now and then for one
reason or another attempted to reuse scrap white golds, and
found even traces of some solders can make the alloy so hard that
it work hardens way too fast to be useable. White gold can be
tricky too. It usually cannot be quenched from above about 900
F, so you have to wait for the red to dissappear after annealing,
or it can form cracks that will show up when you roll. But if
you wait too long, it can start to age harden again as well in
some cases. 18K rose golds are very touchy. They MUST be
quenched from about 1000 F or above or they can form brittle
ordered structures on slow cooling. Cracks which form in such
metals donât heal, even after subsequent proper annealing and
proper quenching, so even one improper anneal can ruin the metal.
Be sure youâre either preventing fire scale when you anneal, or
abrading (sanding/scraping, etc.) it off again after annealing,
so youâre only rolling clean metal, not oxides, into the
surface. Check your alloying/melting setup. Is it about time to
break in a new crucible perhaps? Are you stirring the melt with
something improper? is the ingot mold in need of a good
cleaning? Did your flux somehow get contaminated with something?
The answer is there somewhere. Keep looking.
Hope this helps.
Peter Rowe
MICHAEL, I had the same problem once. turned out to be lead
contamination in my pure gold. check out your gold source perhaps
it needs rerefining. Frank
Thats also why one shouldn't use an alloy containing deoxidizers. The grain size of these alloys are huge! After casting, you can actually see the grain structure of the gold.
hi ken and all,
the deoxidisers you mention silicon and zinc are also grain
refiners (i wouldnât bet that copper would be called a
deoxidiser). they are designed to make grain smaller in cast
items. refiners put them in there because the goldsmith (us) is
unable to reduce a cast item (the cast item is usually the final
form) like he/she can with rolling down or compressing grain
structure. the large xtal in the castings you describe are more
likely to come from premature quenching. but there is the
question how big is big? you probobly already know that any cast
article, whether it has grain refiners or not, will not have the
fine grain structure that a fabricated ring has. a demonstration
of this would include stretching a die struck ring one size up.
the grain boundaries are barely visible. take the ssame ring
that is cast and stretch it up one size, iâll garantee youâll
see a lot of big grain boundaries and one ugly ring.
it is possible to cast and roll with the same alloys. i use
casting type alloy for everything for the sake of color. the
casting alloy grains compress just like the rolling alloys do.
there is a difference, but it is not a major one. i wouldnât be
adverse to cast and fabricate with all rolling alloy either. the
method for pouring ingots and rolling iâve been using is more or
less what charles has described in his post. i push the metal
more than he suggests and when i get lazy iâll roll both
directions. iâve even read refiners lit that instruct to do
this.
please donât think in posting this iâm trying to be
contradictory or antagonistic, iâm not. what iâm trying to say
that these things are not as vital as some think. please donât
mistake me, i know they help. i believe the vital things are
good mixing/pouring, reduced atmosphere (charles battle cry "
oxygen is the enemy!"), clean metal, and adherance to annealing
temps, intervals between anneal, and quenching.
my 2 cents worth.
best regards,
geo fox
the deoxidisers you mention silicon and zinc are also grain refiners (i wouldn't bet that copper would be called a deoxidiser). they are designed to make grain smaller in cast items. refiners put them in there because the goldsmith (us) is unable to reduce a cast item (the cast item is usually the final form) like he/she can with rolling down or compressing grain structure. <snip>
Silicon and zinc are not grain refiners. Silicon causes larger
grain sizes. Refiners add silicon to deoxidize and zinc to
increase fluidity and to a lesser extent deoxidize. Several
elements can be added to reduce grain size Ir, Co, Rh, Ru, Zr, B
come to mind. Boron is often used in silicon deox alloys as Si
does not mix well with the other grain refiners. Youâre right
about copper, itâs there for hardness not as a deoxidizer.
Brett