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Casting investment absorbed moisture


#1

I have done casting only intermittently in the last 10 years. Before
this I could count on 99% of my castings being fine. I always
weighed investment, measured H2O, used vacufilm, and burned out
slowly. Last year I had so many problems that I bought a new vacuum
table. Things got a little better. However I have Satin Cast that is
a couple of years old. I have it sealed tightly, but suspect that it
has still absorbed moisture. I ended up with fins on edges of
casting. I never had this unless not measuring H2O and weighing
investment. I am pretty sure the issue is not metal or alloy. I’m
stumped and fearful to resume casting. Would new investment and
debubbler help? Losing a wax original hasn’t happened yet, but I can
put a major amount of time on delicate waxes even when not original.
I have not been afraid of casting before!

Thanks, Jay


#2

New investment. Small packages

To say that my studio has moisture issues is an understatement. Too
much investment trashed. Investment and any thing the least bit
hydroscopic is stored upstairs in my living room now. And still has a
finite shelf life

Bad investment handles just about the same as new stuff, it just
produces bad castings.

jeffD, from the vertical swamps of Vermont
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand


#3
I have it sealed tightly, but suspect that it has still absorbed
moisture. I ended up with fins on edges of casting. I never had
this unless not measuring H2O and weighing investment. I am pretty
sure the issue is not metal or alloy. I'm stumped 

It it sets up properly and solidly, in an appropriate amount of
time, then likely the investment is still OK. You might try to seal
the container, and roll it around a bit, to make sure the mix of
componants is still uniform. Investment can sometimes settle out
unevenly (especially in shipping, I was told), so rolling it around
to make sure it’s a uniform mix, can help.

Also, I prefer to weigh both the investment AND the water, rather
than measuring the water in some graduated container. Weighing is
more accurate. Pay attention to water temperature, and how it relates
to gloss off time. If it sets more slowly than it should, then
perhaps the investment isn’t so good any more.

Also, I’d suggest allowing the invested flask to set, quietly, for
at least two hours or more, before starting the burnout. That allows
it to reach full strength.

And skip the debubblizer. It can cause as many, if not more,
problems than it claims to solve. Also take care if using those
"orange oil" wax cleaners. If not totally dry and clean, those can
really screw up some investments. Personally, I don’t take a chance
with them any more. The platinum investments seem especially weakened
by that stuff, causing very rough surfaces if it’s at all still wet,
or even if there’s too much and fully dry.

And try to use a slow temperature rise during at least the first 400
degrees F of the burnout cycle. If you don’t have a programmable
burnout controller, set the furnace so it takes at least an hour or
so to get those first 400 degrees. Crystobalite undergoes a
structural change within that temperature range that causes an
expansion to take place. If the flask is rising in temp too fast,
this can be uneven, resulting in increased risk of cracking, which is
what it sounds like you’re getting. Also, don’t use a larger flask
size than you need. Smaller flasks are more forgiving of overly rapid
temperature changes.

And finally, if you’re still unsure whether the investment is good
or not, and don’t have the time or energy to fuss with
troubleshooting it, there’s the other simple solution. Get a new
container. fortunately, the stuff isn’t as pricey as metals have
become. Use the new for “important” flasks, and save the old stuff
for things that might not be as important to have them come out
perfect. In my shop, that might include things straight from rubber
molds, with little labor in the wax, so if it doesn’t cast, one just
shoots another wax from the mold and does it over…

Hope that helps.

Peter Rowe


#4

One of the reasons for getting fins is that the investment has
absorbed moisture. Even in tightly sealed containers, this is still
a problem. Another thing that can happen is the particles can settle
and separate even if the investment is not moved. Try mixing the
powder before your next casting.

The only other likely reason would have to do with heating the flask.
If it was heated to quickly or burned out then let cool before
casting without wetting it again, can cause fins. Investment is like
cheese: Before you eat it make sure to… On second thought, it
isn’t like cheese.

John V


#5

That has happened to me before when the investment went bad. I now
buy smaller amounts and keep it in the house, not the garage. I
suspect that is theproblem.

Good luck and happy casting. Janine in Redding CA, where it is still
too hot.


#6

I have a new Programmable Paragon Kiln for burnout. When setting it
for a 9 hour burnout, I have the choice of the rate of heating-(-how
fast it will heat up.) Is it better to set it for a low rate of
burnout for the first 3 hours, and then ramp it up to full, or should
I start the burnout with it ramped up to full. I did check with the
manufacturer and they suggested full (fast heating), however, I have
been told that I should start at a slower rate.

The kiln is easy to program, except that I am bewildered as to how
fast I should be heating it.

I will be casting silver, and am following the directions given for
using Kerr investment, except they the instructions do not mention
the speed of heating–just the temperatures for the various steps.

Thank you for your help. Alma


#7

Hi Jay

This is almost certainly an issue of bad investment — it readily
absorbs atmospheric moisture, Once it goes off even further you will
have the metal breaking through the bottom of the flask. I try to buy
no more investment than I can use in a year and I only open the bag
of powder to transfer some to a plastic storage bucket with a sealed
clip on lid which I only otherwise open when weighing out the powder
and immediately reseal.

All the best
Jenny


#8

I start my burnout slowly — up to 200C and hold for 2 hours to dry
out moisture then slowly up to 650-700 soak for at least 2 hours and
slowly back to 450 for casting. I try to get rid of all moisture
before burning the wax and minimise the risks of thermal shock. I
mostly use 95mm diameter flasks. You can use a faster pace with
smaller flasks.

All the best
Jenny


#9
Also, I prefer to weigh both the investment AND the water, rather
than measuring the water in some graduated container. 

Weighing is ore accurate. Pay attention to water temperature, and
how it relates o gloss off time…and rightly so. In the Kerr labs,
we didn’t weigh the water, but we used only distilled water from a
closed system, maintained at lab conditions: standard temperature
and pressure. I don’t think our customers did so – but they were
going through inveswtment by the tons daily, leaving little time for
sucking up moisture!

Blessed be…


#10

Alma,

I use Ultra-Vest from Ransom and Randolph.

The flyer that was stuck in the box defines the following burnout
schedule for up to 4" X 6" flasks:

Hold at 300F for 2 hours
Elevate to 700F over the next 2.5 hours
Hold at 700F for 2 hours
Elevate to 1350 over the next 3.5 hours
Hold at 1350F for 3 hours

reduce to casting temperature and hold for 1 hour before casting.
For larger hold at casting temperature for up to 2 hours.

I fill my 12? by 12? by 8? burnout oven with as many flasks as I can
fit into it. It holds sixteen 2.5? flasks on the first level. If I
have a bunch of flasks 3? or shorter I can stack them up two high.

My programmer controller is set to the following:
Hold at 300F for 3 hours
Increase 150F every hour until 1350F
I do not hold any temperature for an amount of time.

I leave it at burnout temperature for around 8 hours. That works
best for me.

I start the process around 3 O’clock in the afternoon and turn the
oven down to casting temperature around 8 the next morning. I find
the 8 hours at burnout temperature gives me the best clean flasks.

NOTE: Fire scale on sterling castings is a problem because the
casting is held above 1000F for some time. Darning that time fire
scale is forming on the casting.

If you are vacuum casting be sure to read my no Fire Scale casting
procedure which is in the Orchid Archives.

The process is VERY simple and will prevent fire scale from forming
on your castings.

The process is a bunch less expensive than buying anti fire scale
metals.

Check out the following blog
http://lees-papers.blogspot.com/

Good luck,
Lee Epperson


#11

I feel like I may jinx myself, but I have not had firescale problems
with silver?


#12

I measure water by volume. I usually just go to a standard mark I
put on the measuring cylinder for each size of flask I use. I weigh
the investment powder on digital scales accurate to 1 gram. I use
rainwater from a tank.

Jenny


#13
I feel like I may jinx myself, but I have not had firescale
problems with silver? 

If you cast sterling silver and do not use one of the exotic
machines that provides a completely oxygen free environment or use
Lee Epperson’s technique you have firescale on your castings. You
just may not see it if you don’t remove enough metal in finishing to
cut into the clean metal below the firescale but it is there. The
sterling absorbs oxygen during the cooling in the investment and has
a very even layer of firescale on the whole piece.

James Binnion
James Binnion Metal Arts


#14

MIXING INVESTMENT

I weigh out 5 pounds of investment and measure the correct amount of
purified water. The investment is poured into the water in a large
rubber mixing bowl.

I set a count down timer for 7 minutes.

I mix for 1 minute 15 seconds minutes with a electric mixer.

The bowl with investment is placed under a bell jar and a vacuum is
pulled until 1 minute after the investment pancakes.

I pour the investment through a strainer into the number of flasks
that will fit under my bell jar. Usually five 2.5 inch flasks.

I then vacuum for around 1 minute after the first bubble appears.

If everything goes correctly I can run a second bunch of flasks
until the 5 pounds of investment is used up and the timer goes off.

I have been following this procedure for 30 years.

FIRE SCALE

Jay,

James is correct. Sterling forms fire scale as it cools down after
being melted.

You may not realize you have fire scale. Polishing small castings
with convex curves surfaces will rapidly abrade fire scale away. If
you have large flat surfaces you will spend a lot of time abrading
fire scale away or you will end up with jewelry that is dull.

When I polished my first casting I realized I was not getting a
bright finish. The casting was a small pendant with a relief
portrait of an Indian on the front. I polished that face with Tripoli
until a bright spot of silver appeared on the cheek of the Indian.

The instructor explained that apparently some fine silver had
migrated to the cheek and that was why it was so shiny. My
instructor, who had been teaching casting for many years did not know
about fire scale.

From that point on I designed all my castings with the design on
flat convex surfaces.

That way I could remove fire scale by sanding the surface with wet
600 grit sandpaper on an expandable rubber wheel on my rock
polisher.

The flat back surfaces were a pain. It took a long time on the
polishing wheel to remove fire scale there.

That was the way it went until I stumbles on a way to prevent fire
scale from forming when vacuum casting. Now I can do three
dimensional sculptures in sterling.

James, thanks for the mention.

Lee Epperson


#15

Re: keeping investment dry. I keep mine in a dry environment in my
studio, in tightly sealed plastic bags. So far no problems. I have
also been following the advice made on Orchid to make sure that I get
the investment really mixed well, while still in the bag, so that all
the ingredients are in proper proportion. Some of it is several years
old, and I have been wondering about its shelf life.

Given that I have kept it in a dry environment, and mix it well to
assure that some of the ingredients have not settled to the bottom,
should it still be safe to use it?

As an aside, and not intending to hijack this thread, I have been
casting with de-ox silver which I got in exchange for a batch of
scrap silver. I love the way it casts, and it is free of any fire
scale. Best of all, it takes a patina (good old liver of sulphur),
beautifully.

I knew nothing about de-ox, and when I traded my sterling scrap at a
local refinery that was all they had, so I took it. I am glad that I
did, as it is easy to work with. The only thing I had to be aware of
is that after casting, wait about 20 minutes, more or less, before
quenching.


#16

I live in a very wet place (southeast alaska) and i’ve found that
putting a container of damp rid, also known as calcium chloride and
used to absorb moisture in damp places, on top of the investment and
then keeping it sealed can extend the life of investment greatly.
I’ve had investment stored in an unheated storage space that would
regularly flood for two years stored this way with no noticeable
difference in the investment. I put it in a plastic container with
some holes punched in the top and then just set it on top of the
investment before sealing the bucket. of course do not spill damp
rid into your investment, i don’t know what it would it do but i
doubt it would be good. I suspect that this stuff has a greater
affinity for water than investment which means that it might actually
pull the water out of your old investment if left sealed in the
bucket long enough. not sure about that but it might be worth a try.
get some new investment anyway though.

good luck, dd