Back to Ganoksin | FAQ | Contact

Casting procedures


#1

Hello All: I have been trying to come up with the best method of
investing, Burn out and Casting over the last several years and I
think I got it now so I thought I would share it with Ya’ll. I
consistently invest as per the advice of Eddie Bell at Rio Grande
(http://www.riogrande.com/) thru and article in the summer 2003
edition of “Bench magazine”(http://www.bwsimon.com/bench/). I almost
exclusively cast hard green carving wax models using 2.5X2 inch
flasks. I use R&R (http://www.ransom-randolph.com/index.html) SJ-27
investment with a 38 ml. to 100 gr. mixing ratio. I use room
temperature distilled water and weigh out the investment carefully
every time to ensure consistency. I do however stray from common
practice by adding the water to the investment for mixing but I have
found that this keeps the dust down more than the other way around. I
have been consistently getting a 13 minute gloss off on this 100 lb.
keg of investment so I mix for 6 minutes,vacuum for 1.5 minutes,pour
and vacuum for 1.5 minutes and then let the flasks sit on the
investing table for 1 hour before numbering the flasks and putting
them in the over to sit overnight until my programmable thermominder
starts the burnout cycle. Using this investing process has eliminated
water marks on my castings and reduced my clean up time and wasted
metal. I am using an Ashurst Designs model 4 kilnminder programmed to
start the cycle at 5:30 am for a cast time of 4:30 pm. A total of 11
hours consisting of 300 F in 20 minutes with a 1.5 hour dwell. 400 F
in 20 minutes with a 1.5 hour dwell. 1250 F in 3 hours with a 2.5
hour dwell. 1000 F in 1 hour with at least a 1 hour dwell until I
cast.If you are using larger flasks the set time of the investment
will take longer of course and the dwell time before casting will be
longer. I added the extra 400 F dwell in the burnout on the advise
of JACMBJ Shannon Calloway, Instructor at the Texas Institute of
Jewelry Technology, Paris Texas because I cast hard carving wax
almost exclusively. Other advise from Shannon was to never invest
injected models and carving wax models in the same flask as the
difference in expansion in the two can damage the mold. I reduced the
maximum temperature of my cycle from 1350 F to 1250 F on the
suggestion of research presented to the Santa Fe Symposium that 1350
F is too hot as brought to my attention by James Binion of this
forum.

I preheat my crucible until it glows red, I then pull my flask out
of the oven and set it on my vacuum caster. I add the metal to the
crucible and melt with a bushy flame. I stir in flux, if required, by
dipping the heated quartz stir rod in the flux and adding it to the
melt without removing the flame from the melt. This reduces the
amount of Oxygen that can be absorbed by the melt by removing the
flame to add flux. Once the metal is completely melted with no more
solids I count to 10 and turn on the caster and pour while holding
the flame on the melt the entire time. I run the vacuum until the
sprue button solidifies and then remove the flask and set it aside
until the sprue stops glowing red and then quench immediately as
recommended by Hoover and Strong (http://www.hooverandstrong.com/)
for metals other than rose golds. I hope this helps someone out there
with water mark problems as I was having. Michael R. Mathews Sr.
Victoria,Texas Usa JACMBJ www.geocities.com/waxcarver


#2

Michael, Thanks for your casting schedule. Its very similar to what
I follow. Probably the most important detail is following the same
procedure every time. Then a single deviation, deliberate or
accidental, will have more understandable consequences and probably
be survivable. The only details I’d add is to control the water
temperature, ‘room temperature’ variations can significantly change
gloss off times. And flask casting temperature can be adjusted to
match the thickness of the waxes, heavy sections will have fewer
shrinkage problems with lower flask temperatures.

What worked yesterday will usually appease the casting gods today.

Jeff


#3

I guess lost wax casting is a process that varies from person to
person.

I discovered the water marks you refer to were caused by too much
water in t he investment. That seems counter intuitive. One would
think that lines on th e casting would be caused by bubbles moving
upward in too thick investment. I use two waxes. Ferris blue for my
originals and Rio Grande pink buckle wax for my reproductions.

I use Ransom and Randolpf investment and mix 5 pounds at a time. I
mix fo r 1.25 minutes with an electric mixer then vacuum for 1 minute
after the investment pancakes . I pour the investment through a
strainer and vacuum t he flasks for 1 minute after the first bubble
appears. I can vacuum 5-2.5 inch flasks at a time. I set the first
flasks aside and invest a second batch. The whole process takes 7
minutes or less.

I have a controlled electric oven that is 12" by 12" by 9 inches
high. I dont cast until I have enough flasks to fill the oven . I
can burn out 16-2.5 inch flasks. I have cut cardboard circles to
represent the various s ized of flasks. I use them to pre-plan the
placement of the flasks in the burnout oven. If the flasks are
short I will stack additional flasks over the spac e between the
lower flasks. There are times when I will burn out 6 inch flask s 7
inches tall. One precaution. The larger flasks should be placed in
the center of the oven. If they are place on the edge next to the
coils the tra pped heat can melt the coil. I have never monitored
the temperature gradient at various places in the oven. I would
imagine that those flasks next to the c oils will heat up faster.

I invest around noon and start the burn out cycle at 2:00 pm.

I usually reach 1300 degrees around midnight and maintain that
temperatur e until around 8:00 AM. When silver casting I cool the
flasks for an hour at 860 degrees before pouring any metal…

I use the large controlled electric melt furnace and melt to 1870
degrees . One caution when using a electric melt furnace. Allow an
additional 5 minutes of heat after the set temperature is reached.
It will allow the gra phite crucible ring to heat up thereby
preventing chilling of the pour.

I vacuum cast all my work. I have poured up to about 35 ounces of
silver in one pour. After pouring I use a process that prevents fire
scale. I immediately put the hot flask on about a teaspoon of wax
that is on a solder pad. I immediately place a larger flask around
the casting flask, throw about a teaspoon of wax on the sprue button
then place a solder pad on the cover fla sk. The wax, as it attempts
to burn, produces a reducing atmosphere around the casting flask
preventing oxygen from joining with the copper in the metal to form
fire scale (cuprous oxide) and the black oxide (cupric oxide). I
quench abo ut 1 to 3 minutes later then I normally would to allow for
the extra cooling time caused by the cover flask. My castings come
out of the quench water so clean I do not have to pickle them. I
have even taken some castings and pol ished them with rouge right out
of the quench water.

The large melt furnace allows me to pour additional flasks around 5
minutes after the previous pour. I wait for 5 minutes between pours
to allo w the crucible ring to regain heat and prevent chilled metal.

I have put together documentation on the anti-fire scale casting
process. I will send a copy, free of charge, to anyone who sends me
their snail mail address.

Lee Epperson


#4

If you have any questions on casting… you are welcome to contact
Greg Gilman at Stuller ext 4300 or Dennis busy at ext 259. Dennis is
head of the casting team at Stuller as well the head of technical
for Stuller

Andy “The Tool Guy” Kroungold


#5

Water marks are most often caused by long set up times in investment
to “gloss-off”. This is where “free water” flows between the pattern
and the investment. The temperature of the water used in the mix can
be a cause of this. 12 minutes is the standard for set-up and
gloss-off. Anything over 15 minutes usually leads to water marks.
These problems generally occur in winter months, when tap water goes
cold. Try storing water in a large covered container to achieve room
temperature.

However, if the problem persists, and you have followed the vendors
instructions for 38/100 or 42/100 water to powder ratios and using
room temperature water (70F to 74F), the investment chemistry has
gone south. The best way to combat bad chemistry is water
temperature. If you have a “bad” batch of investment and cannot
dispose of it by returning it to the vendor, try heating the water to
78F or 80F.

I would mix investment for at least 4 minutes to insure homogenity
between powder and water.


#6

Thank you so much for your write up Michael. I am thrilled to find
someone else commiting the “heresy” of adding water to powder. It
truly works just fine and is sooo much safer and cleaner. Doing it in
reverse, the way most are taught, is actually unnecessary and is, in
fact, unsafe . I teach at a facility where another instructor casts
and measures out investment in a huge-bin balance scale. By the time
quantities of investment are taken from the drum, measured, put in
the mixing bowl and stirred powder to water, every surface has been
contaminated. Most distressing to me.

So, am looking forward to hearing from others who use this method
successfully. I’ve been doing it for over twenty years, without a
failure. We are using Satin Cast 20 still, and that works for us.
Keep up the good work, and thanks for sharing.

Pat


#7
I discovered the water marks you refer to were caused by too much
water in t he investment.  That seems counter intuitive.  One
would think that lines on th e casting would be caused by bubbles
moving upward in too thick investment. 

In too thick an investment, the bubbles wouldn’t move up so well…

Water marks are sometimes caused by too much water, but the most
common culprit is actually one of timing. When you mix investment
and vac and pour it, etc, it then sits in the flask for some period
of time before it becomes sufficiently set up so nothing moves or
changes any more. Normally, one wants to know the overall working
time of the investment, that is the time between when the water and
powder meet, and the time it starts to set up. The latter point is
usually measured at the point where water is absorbed from the wet
surface of the investment, back into the investment, easily visible
by the fact that it stops looking glossy and wet, and becomes
matte/dull. This overall time is known as the 'gloss off time", and
it’s important. You want to optimize the working and mixing of the
investment so you finish the pouring and topping off of the flasks
while the investment is still fully liquid and pourable, but also
as short a time remaining till gloss off. Water marks are a bit
part of the reason. If the flasks sit for too long with fully liquid
investment before that investment starts to thicken and set up, the
investment and water can start to seperate. Until they fully react
chemically, the powder and water are just a suspension, and it can
settle out. This settling, coupled with the surface tension
differences of the wax surface, causes these seperation marks on the
wax. Those are the water marks. it’s not rising air bubbles. You got
rid of those when you vacuumed the flask. It’s just water and
investment seperating slightly at the wax surface.

The keys to preventing this type of problem are first, test each
batch of investment both when you open it, and periodically as you
use it if the container is sitting around for a long time, so you’ll
know the gloss off time. it can change dramatically sometimes, due, I
think, to absorbtion of humidity. We recently threw out a half used
drum of Satin Cast because the stuff was reaching gloss off stage in
under five minutes, instead of the 12 or 13 it should take. So
measure that time, and arrange to be topping off your flasks only
about 2.5 to 3 minutes or so before that time. Then the investment
won’t have time to settle out like that, and you’ll not get the
marks.

Also, pay attention to not just the timing, and water/powder ratios,
but also to the temperature of the water. It makes a big difference
in the time it takes investment to reach the gloss off stage. Cooler
water slows down the reaction, while hotter water speeds it up.
Optimum is generally room temp.

And while this is the party line from the investment makers, it’s
not carved in stone (or investment). A check in the orchid archives
will, I think, find posts from a well experienced and known caster
who uses hot water, but more of it, to invest. The larger quantity
of water slows the gloss off time, and thins the investment so it
flows easier and boils in the vacuum easier, so getting rid of
bubbles is easier. But then the hot water speeds the setting time
again, so it compensates for the slower setting you’d expect from more
water. Plus, a warm investment mix will boil faster in your vacuum
setup. The main end difference is more porous and perhaps weaker,
investment. The more porous investment would mean easier elimination
of air in the mold, both for vacuum casting or centrifuge. Weaker,
on the other hand, might be a problem with some models needing the
investment to hold strength in thin sections, but even then, likely
as not, it would be strong enough.

Note, this is from memory of those posts. I’ve not tried it, as
frankly, I have never had enough trouble with the factory spec
instructions to need to rock the boat.

cheers
Peter


#8
    And while this is the party line from the investment makers,
it's not carved in stone (or investment).  A check in the orchid
archives will, I think, find posts from a well experienced and
known caster who uses hot water, but more of it, to invest.  The
larger quantity of water slows the gloss off time,  and thins the
investment so it flows easier and boils in the vacuum easier, so
getting rid of bubbles is easier.  But then the hot water speeds
the setting time again, so it compensates for the slower setting
you'd expect from more water.  Plus, a warm investment mix will
boil faster in your vacuum setup.  The main end difference is more
porous and perhaps weaker, investment.  The more porous investment
would mean easier elimination of air in the mold, both for vacuum
casting or centrifuge.  Weaker, on the other hand, might be a
problem with some models needing the investment to hold strength in
thin sections,  but even then, likely as not, it would be strong
enough. 

I don’t know about using more water but hot water investing with
standard ratios of water to investment will make for a more fluid
while liquid and harder final set investment. The drawback is hot
water speeds up the the setting time so it is a real trick to get it
all done before it sets. Hot water investing of this type works
best for single flask investing. Try it you may like it it produces
very high detail. Water temps of 100-110 degrees 4 min set up times.
Test it first to get right time for your particular investment
before trying on a actual wax.

Jim Binnion

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160


@James_Binnion
Member of the Better Business Bureau


#9

We have a hot water investment recipe written by Marc Robinson on
our web page, and it has been standard procedure at our place for
fifteen years. We vacuum cast gold and silver with a hydrogen torch.
Not high volume but usually difficult designs

Daniel Ballard
WWW.Pmwest.us


#10

Speaking of mixing…Do any of you ever use a hand mixer? The sort
one uses in the kitchen? It sure would be easier than by hand!


#11

Hello Daniel: So let me get this straight. You increased the amount
of water and it’s temp. I figure from your web site that you used 44
ml of water per 100 grams investment “I mix 1,020 cwt. of powder to
700 ml. of water at 110 F.” . Is this correct? I am eager to try this
Michael R. Mathews, Sr.


#12
    Speaking of mixing...Do any of you ever use a hand mixer? The
sort one uses in the kitchen? It sure would be easier than by hand! 

That’s exactly what I use for mixing investment, an old kitchen hand
mixer. When I’m through, I dip it into the quench bucket to rinse off
the beaters, and hang it back on the wall until the next time.

–Kathy Johnson
Feathered Gems Pet Motif Jewelry
http://www.featheredgems.com