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Post casting process


#1

Hello All: I have been casting for 20 years now and I have always
quenched the flask about 2-3 minutes after it is shot.Allowing
the button to stop glowing.I have noticed that sometimes my
castings are more brittle than others.Is there a annealing that
should take place after the cast? Am I quenching to soon?Is there
a differance in the quenche time of differant metals?

Michael Mathews Victoria,Texas USA


#2

Hi,

I think that the problem is that you are quenching too early.
I had experienced the same difficulty with a palladium alloy.
The metal has not had the chance to assume its final molecular
state. Trust me.:slight_smile: You are quenching too soon.

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                01/14/9814:33:28

#3

way too soon let flasks cool at least 12-15 min before quenching


#4

need more info for an accurate answer…centrifical or vaccum?
What’s your flask temp? how fast are you melting the silver?
more info please and we can probably solve this…


#5

Michael,

That brittleness you’re descibing can have many causes. Question
#1 What alloy are you casting and what percentage is fresh grain?
#2 Are you Vac or Centrifugaly casting? #3 Are you torch melting
and with what kind of fuel? #4 What is your flask temp at cast?
#5 Is your crucible new or has it been cleaned? #6 What does the
metal look like just before cast? #7 Does it make a difference if
you let it cool a few minutes more? The answers to these
questions should help pin point the problem. At our production
casting facility we cast just about every alloy and have made
many observations on them over the years. We have cast pieces
ranging in size from a pin head to small sculptures. Some of your
post casting problems could be pre or at cast as well. J.A.


#6
    What alloy are you casting and what percentage is fresh
grain?

14 or 18 karat gold anywhere from 50% to 100% fresh grain

    Are you Vac or Centrifugaly casting?

Vacuum.

   Are you torch melting and with what kind of fuel?

Yes a torch and I use acetelene and oxy.for casting

   What is your flask temp at cast?

I use the recommended cast temps per Murry Bovin’s book"Jewelery
Casting" yellow gold thick=800-850 deg. thin 900-1000 deg.
white gold thick 900-1000 deg. thin 1050-1150 deg. I always cast
my white items first

    #5 Is your crucible new or has it been cleaned?

The crucible is not new.

 What does the metal look like just before cast?

mirror, and I am keeping the bushy flame covering the melt so as
not to let it absorbe oxygen,Thanks to advise from this forum.

 Does it make a difference if you let it cool a few minutes
more?

I don’t know,I have always quenched within 5 minutes because
that is the way I was taught.The problem with waiting to long is
that the investment stays stuck in the flask.

thanks for your reply,

michael mathews Victoria,Texas USA


#7

Hi Michael, As to alloy, Silicon in the mix can cause the
symptoms you’re describing. A dirty crucible can add to this
problem as well. When I’m not flush enough to spring for some new
crucibles I use a mizzy wheel to grind out the built up gunk. You
can grind right down to the ceramic and re-flux. Make sure the
crucible is strong enough to re-use (no cracks or thin walls).
I’m assuming you use a different crucible for each alloy you use.
There is not a problem with acet. gas, but propane is cleaner. I
torch melt with propane and a rosebud tip. Mine burns blue but
when you push it deep into the crucible it flashes yellow. I cast
the flasks about 100 F hotter than you do. I have a water blast
cabinet so I let things cool much longer, but I used to quench
when the glow was off and had no problem (except for wt gold
which I let cool to touch) I hope some of this helps. You can
e-mail me off line for more info if you like. J.A.


#8
I'm assuming you use a different crucible for each alloy you use.

I use a different crucible for gold and silver,but not every
alloy of gold.Is that really important?

Michael Mathews USA


#9
     I have been casting for 20 years now and I have always
quenched the flask about 2-3 minutes after it is shot.Allowing
the button to stop glowing.I have noticed that sometimes my
castings are more brittle than others.Is there a annealing that
should take place after the cast? Am I quenching to soon?Is
there a differance in the quenche time of differant metals?

hi michael,

the red glow shouldn’t be apparent in a dark room. that would
take a little longer than 2-3 minutes.

refiners reccomend letting the flask cool completely, but i’ve
yet to meet anyone who actually waits that long with yellow
gold. i use a spit test. i spit on my finger and if it barely
boils the spit it is cool enough. if my finger sticks and burns
meat, it is too hot. i do wait longer for white gold. until it
will barely bubble when i ‘quench’ it. i usually dislodge the
casting by hitting the flask on the concrete outside, button
towards the concrete. as i learned on this forum, vinegar makes
a great investment remover.

the longer cooling time lets the casting xtal structure to set
up better by coolin more evenly thruout. though brittleness can
also be caused by contaminated or old metal as well. but i bet
you know that already.

best regards,

geo fox


#10

I don’t know,I have always quenched within 5 minutes because
that is the way I was taught.The problem with waiting to long is
that the investment stays stuck in the flask.

Michael,

Next time yo cast, try letting the flask cool so you can easily
handle it. Then use a plastic or rawhide mallet and give the
flask numerous medium hard blows (dont dent it or make it oval)
until the investment and cast pieces come loose and fall out.
You can hit the cast button carefully too. Once the casting is
out, hold the button between your index and middle finget of the
hand you don’t hammer well with, and really smack the button with
the hammer a couple of times. I then clean off the remaining
investment in the bead blast cabinate but a high pressure washer
works well too.

You may change methods of investment removal, but
then again you may not. It does work for me though!

John

John and Cynthia/MidLife Crisis Enterprises
Maiden Metals/C. T. Designs/ Bloomin’ Wax Works. etc.

PO Bx 44, Philo
CA 95466
Ph 707-895-2635 FAX 707-895-9332

The playfulness of the Universe
is reflected in the dance of the stars!


#11

Michael, Absolutly! Have a designated crucible for each of your
alloys. You can get away with not doing this sometimes, but it
will definatly cause problems eventualy. Silicon residues from
certain alloys will transfer through the crucible and cause a
silicon eutectic in the crystal interfrices. What that means is
that you will have a beautiful casting that will be brittle right
at the crystal junctions. Do your breaks have a crystaline look?
J.A.


#12
   I use a different crucible for gold and silver,but not
every alloy of gold.Is that really important?

hi michael,

it can be crucial, depending on what you’re doing. small traces
of nickel can cause mottled color if contaminated with yellow
gold (or visa versa). there is a small chance that underkarating
can occur. another consideration would be if one requires a zinc
free alloy. in fusing, mokume, and granulation it is pretty darn
important to have zinc free alloy.

best regards,

geo fox


#13
   I want to thank you guys for the help. So, I got a brittle
casting.How do I fix it? anneal it?or redo it?

hi michael,

if it is just quenching too quickly, annealing should take care
of the problem. if it is contamination like john is talking
about, a redo ( i don’t like that word much) may be in order.

best regards,

geo fox


#14
 I use a different crucible for gold and silver,but not every
alloy of gold.Is that really important?

I use a different crucible for white gold and yellow gold, and
I’m sure you do too. I don’t have a separate one for 14k and 18k
of the same color, but I do keep them clean. I have accidentally
in the past used the white gold flask for yellow gold casting and
had little “lilly pads” of white gold in the yellow gold surface.
Really a bummer, you usually don’t notice them until you have
finished the piece, then have to remove them or start over.

Mark P.


#15

WARNING! If you are going to remove investment by knocking it out
dry, as suggested above, please do it only with a proper
respirator (not a cheap dust mask) rated for silica flour and
similar dangerous fine dusts. Knocking out the investment will
raise a pretty good sized cloud of visible dust. Even more
dangerous is the liberal amounts of dust too fine to see that
this procedure will create. You are working here with a procedure
that generates very significant amounts of silica dusts in
exactly the dangerous sizes. In some cases, the amounts of this
sized material lifted into the air this way can exceed by quite
a margin the amounts you generate when you initially mix the
investment.

Bottom line here, folks, is that this is a rather dangerous way
to remove investment. Don’t do it casually. Silicosis is not a
nice or pleasant disease. By the way, this statement is even more
true for platinum investments, which are often difficult to
remove by other means. Most commercial casters will use a wet
blaster, with water and compressed air creating the jet,
removing the investment wet, or better yet, with the newer
cabinets that simply use a very high pressure water pump, no air
needed… Smaller casters traditionally quench the flask in a
bucket, while the flask is still hot enough to boil the
investment off nicely. If your metal and flask have cooled to
below about 5-600 degrees F, it’s unlikely that you will be
harming the metal in any way by quenching the flask. But keep in
mind that investment is a quite good insulator. Even with small
2 1/2 inch flasks, it can easily take five minutes cooling time
for the flask to cool to these safe-for-the-metal temps. And
importantly, you should note that even with the quenching in a
bucket method of investment removal, some silica is carried into
the air, along with the steam. Though the exposure levels here
are much lower than dry removal, you should still wear a
respirator.

Hope this helps.

Peter Rowe


#16

Peter,

I might also add that a cooled casting may be soaked in water
for a short time, say 5 min or so, and then with a few light taps
with a tack hammer on the button right at the surface of the
water with the button slightly awash
, the button will fall out
and into the water. Once the investment is soaked it is safe to
handle without a respirator AS LONG AS IT IS WET!

You can lightly tap the button to remove the remaining
investment to put into your reclamation barrel for the refinery.

A trick used in many dental labs is to mix the investment while
the exhaust fan in the burnout room is going full tilt. You
incorporate the powder into the liquid right at the exhaust fan
hood.

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                01/23/9800:12:35

#17

Skip:

“to remove the remaining investment to put into the reclamation
barrel for the refinery”

Do you send off the investment to the gold refiner?

Roy (Jess)


#18

Hi Roy, (Jess)

Yes! Of course. I store it in fiber drums, and when I get a
bunch and have a quantity of metallic scrap, I include the
investment.

If you think that this is foolish, the next time you cast, weigh
the button and the new metal. Make your casting. Clean it up
and weigh the casting. Multiply this loss by the number of
castings you have made and you will know how much gold you have
thrown away.

It isn’t a dramatic amount but over the years it adds up.

Regards,

Skip

                                  Skip Meister
                                NRA Endowment and
                                   Instructor
                                @Skip_Meister
                                01/24/9800:40:17

#19

if it is just quenching too quickly, annealing should take care
of the problem. if it is contamination like john is talking
about, a redo ( i don’t like that word much) may be in order.

Annealing as cast silver will not soften it. Quenching sterling
silver at a high temperature (over 1100 degrees F ) actually will
produce the softest sterling silver it also risks cracking of the
silver due to the thermal shock. As cast metal is brittle because
the grain structure is very large and the spaces between the
crystals are larger this is due to the slow cooling rate of the
metal in the mold. To restore the soft working properties to cast
metal it must be worked with hammers or rolling mills to break up
the crystals into smaller pieces and to fill the voids between the
crystals with these smaller crystals. This breaking up also
creates stress that must be relived by annealing. After a couple of
these cycles of working and annealing the metal will be at its most
malleable state. But this hammering or rolling is not generally
what you want to do with the piece you just cast. Unfortunately
there is not really a way to make as cast metal less brittle. If
you really need malleable metal on a cast object it is probably
best to add that material after casting by soldering or some other
means of mechanical attachment.

Jim


@jbin
James Binnion Metal Arts
2916 Chapman St
Oakland, CA 94601
510-436-3552


#20
   Annealing as cast silver will not soften it.  Quenching
sterling silver at a high temperature (over 1100 degrees F )
actually will produce the softest sterling silver it also risks
cracking of the silver due to the thermal shock.  As cast metal
is brittle because the grain structure is very large and the
spaces between the crystals are larger this is due to the slow
cooling rate of the metal in the mold. 

hi jim,

if a ring is broken near or at the sprue, this a sure sign of
dousing too quickly. as i understand my casting, the breakage is
due to uneven cooling, causing contraction at different rates
because of the differences in mass of ring shank and sprue, which
does not usually occur in a poured ingot. this stress caused by
the different rates of contraction can be relieved by annealing,
as one can relieve the stress or spring from hammering by
annealing. so, if one were to anneal the broken ring, and solder
it, this would correct the uneven cooling problem. softening the
metal isn’t the only consideration here, but making the temper (or
lack of it) of the ring uniform throughout.

best regards,

geo fox