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Investment cracking


#1

Irecently posted a problem concerning my investment breaking away and
causing inclusions in my work. I have used one subscribers solution,
ie. putting boric acid in the investment to harden it, and have
solved the problem of investment breakaway. I now have introduced
another problem. My investment cracks during burnout and leaves fins
on my work. Sometimes this ruins my
castings. Any ideas out there?


#2

Sound like you a putting water in your investment and not letting it
dry long enough, also over heating will cause it to crack. Good luck
.
Bill D


#3

It sounds as if you are getting the lasks too hot,is your
thermocouple at the top or the bottom of your kiln ? Try dropping the
top burnout temp to 690degrees
Tim.


#4

I have had the investment breaking off and creating inclusions, very
frustrating. I felt that the investment I was using just was not
strong enough. I was using Satin Cast 20 and changed to Americast.
Have had very few problems since. Mixes up thinner and sets up
stronger. Reducing slightly the amount of water in the mixture might
result in slightly stronger molds. Good luck.

Bob Hord


#5

Some investing solutions: The best solution to your investing problem
is to get the product specification sheet and Usage sheet that
explains exactly the ratios of water/temperature/investment And drying
time related to your material.Follow them first. then experiment.

Boric acid is used for stone in place casting and will change the
setup time of your investment .If you use Boric and the original set
up time ,then you will have cracking problems.

Call your Investment Supplier … they may send you a new barrel free
if it’s not too old or they may give you better directions

Daniel Grandi Http://www.racecarjewelry.com


#6

One suggestion is to slow down your burnout time up to the 300 deg
point. What might be happening it that you are causing steam pops
which will dislodge the investment as you described. A slower rise
to the 300 mark will allow the moisture to leave without causing
stress on the investment.

Those fins you are talking about can be neat, not on the piece itself
but as a textured surface. A couple years ago, I was casting a small
pendant. For some reason the investment cracked at 90 deg to the
flask. When the piece came out, I had my pendant penetrating a gold
Pringles potato chip. I cut off the potato chip in as big a pieces
as possible to use for texture accents. The pendant turned out fine
also,

Don


#7

Hello,

Be sure that your investment had enough time to harden and follow the
specifications from the supplier.Normally, it takes about 1 1/2 hours
to set depending on the size of the mold.

Be careful and pay extra attention on the mold while you’re handling
it during pouring procedure.Investment is extremely brittle in an hot
condition and will crack easely if you handle it to rough.

Slower your ramp factor.Do not increase the temperature to fast since
this can cause all kinds of little fractures and unwanted
disformation of your wax pattern.

Some people like the idea of making their investment more liquid by
adding more water to the slurry(or less investment). Forget it
!!! The amount of investment you save is not worth the trouble.
Believe me, it’s not saving you anything at all !

Regards Pedro Palonso@t-online.de


#8

You may be heating your flask too quickly. Also, if the investment
hasn’t completely dried the steam created during burnout could crack
it too.

http://www.kerrcasting.com/Technical/suggeste.htm is a website with
suggested burnout temps and other investment/casting
They’ve been helpful in the past with suggestions when I’ve had
problems. You could also try
http://www.unitedpmr.com/alloy_technical_info.htm. They have also
provided me with good technicial support.

Hope this helps.


#9

What is the curing time after investing?. It generally helps to dip
the flask in water before vacuum dewaxing/burnout cycle if the sample
is very dry. This is generally caused by the dry conditions (as
opposed to moist).

Kayce Chidambaram Ph.D.
Principal R&D Chemical Engineer
The Bell Group
7500 Bluewater Road NW
Albuquerque NM 87121-1962
Tel: (505) 839-3523
Fax: (505) 839-3525


#10

Hello Hoods,

I have read the responses to your question on cracking investment.
Some of those suggestions are repeated here along with some of my
thoughts in a priority list.

  1. Check the gloss-off (G.O.) time of your investment. Don’t use it
    if the G.O. is over ten minutes.

  2. Make sure you have at least 1" of wall and head room in your
    flask.

  3. Mix the water/powder ratio within the manufacturers specs.

  4. Let harden for at least 1hr after G.O., before burnout.

  5. Roast at 300F for 2hr before proceeding. This will chase off the
    "free" water

  6. Slowly climb to 700F and hold there for at least 1hr. This will
    release “chemically bound” water before the crystobalite begins to
    expand.

  7. Do not exceed 1350F. Resist the temptation to open the kiln while
    at the top of the burnout cycle. Temperature shock can cause cracking
    also.

  8. Hold your casting temp at least 1hr when the temp is reached. Wait
    a little longer for larger flasks.

John, J.A.Henkel Co.,Inc, Moldmaking, Casting, Finishing