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[Casting] investment secrets


#1

Dear Casters,

An easy way to vent flasks for casting is to simply melt some wax
spru wires onto the inside of your flask. Melt it right at the top on
the inside. The position should start about 1/2 to 1 inch above the
bottom of the flask. I have used about 4 or 5 of them. You can look
down into the flask to determine the locations. The spru wax wires
should touch the inside wall of your flask and can be close to any
object to help air flow. Be careful not to have the wire touch any of
your wax items or you will have this wire cast with your object. Your
object will also be ruined. This process is fast and fairly
inexpensive if you buy the spru wax by the larger box.

I rarely use any vent system. At school we cast hundreds of dwt of
model metal brass every semester and at my own shop I cast about 25 to
50 oz of sterling and about 200 dwt of gold per week. I don’t use any
venting. And here is one reason why. This is one of the lessons in our
casting class here in Minneapolis. Casting investment is like a big
bag of cement. If you put the bag on the ground in your garage and let
it set, in a few months the ingredients start to separate. Without
touching it, the gravel, sand and concrete start to separate because
their specific gravities are very different. Just think of why a
cement mixer goes down the street and mixes so that all the
ingredients are well blended. Casting investment has some of the same
properties. Now add the truck transport of investment to your shop and
you have a vibratory method of investment separation. A barrel
sitting has the same thing happen. The investment powder looks all the
same, but believe me it is not!

When the investment comes to you it is designed to breath. Molten
metal goes in air flows out. It would be like a mouth full of smoke
going through a sponge. Now I would bet that if some of you had
problems casting on occasion and couldn’t figure out why, this may be
one reason. Are you towards the bottom of your barrell of investment?
Is your investment old? Has there been any moisture allowed to get
into the bag? Investment doesn’t come with a “use by” date you know.
And there is no manual on how to take care of the stuff. If you just
leave it alone I can guarantee you will eventually have problems.

As a caster, one of the jobs I did every week was to put a mask on
and shove my arm into the invest ment and mix it up. BY HAND! By doing
this I confirmed my suspicions about what happens. You can FEEL the
proper consistancy of the powdered investment. The bottom of the
barrel shold be just a fluffy as the top. When these ingredients are
mixed properly the investment will breath properly and your castings
turn out great. When doing this I have felt hard chunks of investment
towards the bottom of the barrel.

Now I hated to do this job. It was a mess and my arm was full of
investment. When I pulled my arm out there was powder everywhere.
Worse yet investment got under my fingernails. I hate stuff under my
fingernails. You can tell how much I live auto mechanics by that one.
So I thought all I needed was a small cement mixer. Well I found one
and hooked it up in my shop. We have one at school also. Harbour
Freight sells one for about $200.00. The only problem is that there
was no cover for it. I found a cardboard scrap recycling barrel with a
clamp on top that fit the cement mixer opening. After puting a strip
of edge protector on the metal edge of the clamp for a tight seal
(this was the stuff you put on your car door edge to keep it from
being damaged by bumping into another car when opening the door)., I
had my mixer and tight cover. EVERY TIME I mix investment, I stir the
whole supply. No more investment breathing problems. My castings turn
out great. Both spin and vacuum.

Vacuum casters have less of a problem if they have a super heavy duty
pump. The vac does not give the investment a choice. And it you
increase the size of the whole under the flask it works even better. I
never use the perferated flasks. With my investment preparation I
don’t feel I have to. And those perferated flasks a spendy.

One additional story. Back in 1979 I got 1500 pounds of investment
free. The casting foreman at the company I worked at said it was bad.
He taught me the same arm in investment method I described above. The
investment was going into landfill so I took it home. It didn’t seem
to be bad until one day in my arm mixing duties I pulled a mulched up
piece of a cardboard barrel out of the investment. An additional
ingredient! What some of you don’t know is that there have been
investment recalls in the past that most people don’t ever hear of.
Apparently a barrel had fallen into the mixing hopper and just been
mulched up and added to the batch. I used this investment for a few
years and gave quite a bit of it away to others casting buddies. But
from that time I alway mix my investment as soon as it arrives in my
shop. That way I kwow that this component of my process is consistent
and not a potential problem. Any change can create a big problem. By
doing this investment is never a problem.

All the Best,
TR the Teacher & Student


#2

Thanks for the suggestion. Bet not many folks would have thought of
particle seperation in the investment as a potential source of
casting problems.

Guess the moral of the story is ‘Keep the pot well stirred.’

Dave


#3

Thanks for the suggestion. Bet not many folks would have thought of
particle separation in the investment as a potential source of
casting problems.

That is one reason why I buy mine prepackaged. The second reason is
that it is easy to get the investment screwed up because of ambient
moisture in the air combining with the investment.

Regards,
Skip

Skip Meister
@Skip_Meister
Orchid Jewelry Listserve Member
N.R.A. Endowment
"No man’s life, liberty or fortune is safe…while our legislature is in session."
Benjamin Franklin


#4

We use both Kerr and R&R investment and we have found that the
easiest way to stir the investment prior to using it is to roll the
barel back and forth on the floor. This gets rid of any potential
settling problem without getting your hands dirty… just make sure
the top is on securely and that the plastic bag inside is closed or
you will have dirty hands !!! This was a recomendation from the
Kerr company that i received in 1968 and seems to have worked. Most
investment related problems can be atributed to human or mechanical
error from weak vacuum pumps to incorect weights and
measurements.Weighing Scales can and will go out of calibration which
has caused a number of problems to both large and small scale
casters.So a good recomendation is to periodically check your
equipment. Occasionaly, a bad batch of investment might come your
way… you can most likely still use it if you experiment to find
out at what point the material " glosses over". Most investments
Gloss off at around 10.5 minutes from the pouring of the investment
into the water …till the material absorbs all the water and the
gloss disapears. We have had materials gloss off in 6 minutes and
still managed to use it by shortning other parts of the timing cycle
and using various aquired tricks. We have found that adding a cap full
of liquid soap to the water (of an aprox 15 lbs mix of investment)
will help to eliminate bubbles in Kerr & RR investment. It does not
work on other brands .This was a recomendation from the technical
people at R&R and has worked well. If the investment really boils a
lot harder than you have ever seen it do… welll… you might have
added a tad too much Soap!!! Hope this helps someone . Daniel Grandi
Http://www.racecarjewelry.com Visit the "workshop"on the site.


#5

Dear JAGMAN,

I also rolled my barrels up and down the isles for mixing. Only it
really doesn’t shift the settling and separation of the components. I
also flipped the barrels on a monthly basis to reverse the settling
direction. You can’t take my cement mixer away from me. Kerr
investment doesn’t breath as well as R&R so if you spin cast you’ll
have more problems with Satin Cast than with Ultra Vest.

Again if you use a strong enough vacuum with a large one inch hole
under a nonperforated flask or the perforated flasks you probably
won’t notice much of a problem.

If your shop casts smaller numbers of flasks and uses spin casting
you have to be even more careful with your investment.

All the best,
TR the Teacher & Student


#6
You can't take my cement mixer away from me 

Hi “Tr the teacher and student” I certainly made no mention of taking
away your cement mixer. I merely made the suggestion to roll the
barels which has worked fine for my 31 years of lost wax
casting.Every caster has their own ideas as to what works best for
them and what doesn’t. Personaly, I atribute the high success rate of
my casting company to the fact that our timers,vacuum pumps and
tables ,and oven controls are kept calibrated and in excellent shape.
We use a digital scale to weigh our water and our investment.The
mechanical postal scales that are usually sold can /will go out of
calibration and it may not be found out for quite a while.We use both
Kerr and R&R and have also used a number of other investments.When
doing centrifugal casting, we use a 38/100 investment
ratio(recomended for strength) and we commonly use a 40/100 ratio for
vacuum casting which is presently our prefered method of casting.Hard
as it may be to believe, we commonly cast 1000 to 5,000 pcs /week and
have cast up to 115,000 pcs per week. Our typical loss factor in
casting is slighly less than 1 % overall ! These items range from
filigree items to heavy gold and silver pieces that weigh well over
an ounce per piece. During the course of years , we have also found
that sometimes a thin gate going into the pieces works better than
the common casting rules … provided that your temperatures are
correctly configured. I would also like to mention that the metals
and alloys we use have lot to do with our low reject rate. All our
alloys come from united precious metals co.Their # 930 white gold
alloy for 14k which is very white, ductile and casts easily using a
simple torch and vacuum table is to be highly recommended. regards to
all Daniel Grandi http://www.racecarjewelry.com


#7

Dear Dan,

I fully support your comments on investment detailing. Being very
consistant and particular are the only ways to minimize our common
battle of bad castings.

A couple of additional comments. I alway make sure the investment and
water are the same temperature. Your cycle times may be off with
different ingredient temperatures. Storage areas are not always heated
or cooled so a new barrel should be kept in the same room as the water
for a few days to stablize both temperatures.

The hardness of your water may also effect your powder / water
ratios.Here in Minneapolis we can only use the 40 / 100 ratio.
Otherwise the set time is screwed up. Also water from the cold water
tap should be the only water source. This should be used the next day
for temperature stablization also.

There may be a mfg date code put on the barrels now. This would help
deal with the shelf life and settling concern.

The dental investment packets would be great but I think the cost is
quite a bit more than the $65.00 / 100 lbs (or so) we spend now.

The casters I talk to that have the least amount of problems have two
things in common. First, they cast a LOT. Going through 100 lbs of
investment quite rapidly. The second is using a Vaughn or Busch vacuum
pump. The pump is a good key to consistently good castings. The pumps
sold on the commercial casting units are really the bare minimum of
suction.

Keep up the good work.
Regards,

TR the Teacher & Student