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Cracked casting


#1

I just cast some small (1mm) layered looking (using a jury rigged
glue gun with homemade wax sticks) silver (925) rings. More than
I’ve ever tried.

Stacked 11 on my tree, using a 2 inch flask and vac cast. The room
was Very cold 42’ ? Oxy, acet, w/ rosebud. I also did my melt “in the
flask” I may know now to pour molten metal with vac on. But at the
time?? ANYWAY they all came out with small cracks at the edges. Very
disappointing. I know I’ll gain a lot by posting this so, THANK YOU
ALL, in advance


#2

Here are a view major topics you need to think of when you like to
cast.

The investment should be at room temperature aswell as the water
used for your investment. Investment needs to be stored in a DRY area.
This is very critical in order to performe nice castings.

What about the burn-out cycle and temperature? Did you start your
burnout cycle at the same day or did you wait to long causing your
investment to dry out? Was your burn-out cycle not to fast?

A rule of thumb is that you have to have a minimum free area between
your flask and the object of 1cm (approx 1/2").

Same rule is applicable for the space between each object on your
three.

Did you melt your metal in the flask? Why in heaven do you want to
do this, what is the reason for this? You will overheat your
investment by doing this! No wonder that your have problems! Metal
needs to be melted in a crucible not in a flask! All your metal has
to be at a certain temperature when casting and for thin items it has
to be hotter then for heavy items. Swith on your vacume caster BEFOR
pooring your metal in the flask. The vacume has to be build before
the pooring.

Never quench your cast befor you are 100% sure that all color is
gone in the button. Respect your cooling time preventing your casting
to crack. All the metal has to be solidified and be aware that small
objects are a subject to crack, easier then heavy ones.

By all means, I don’t know what level and/or skills you have talking
about casting but I advice you to buy/rent a book and study this
casting procedure.

What I don’t understand is that one can find so many instruction
(FOR FREE) on internet… in seconds!! Same instructions are
available from casters in this forum wit many years of experience and
tremendous knowledge about this matter. It’s all there and in your
language, you can even print it out and create your own casting book
(ask for permission If applicable). However, you’ll learn it the hard
way. Let me give you this link as a help and read it befor you dig
into trouble again. This is just A link I came up with and I do not
have any advantage or whatever from this company. Feel free to chose
any company as you like and check out the free video’s from
Ganoksin… it’s there to help you… go for it!

http://www.ganoksin.com/gnkurl/k

have fun and enjoy
Pedro


#3

I made the post about cracked castings… I think it may be mild
case of “oldshiemers” I FORGOT to ASK. WHY? Anyone ? I hope this
finds it’s way with my original post still up so I make sense. sorry
But Any help?


#4

Penumbra,

I once over heated and boiled my metal a I got a cracked casting. I
don’t know if that may have been your problem or not,

The best of luck,
Ken Moore
www.kenworx.com


#5

If the investment cracked, it’s likely because you used the pourcup
at the top of the mold as a crucible, melting your metal there
instead of in a melting dish. That subjects the delicate investment
mold to a lot more heat shock than a normal casting process would.
Next time, melt the metal separately, and pour it in when it’s
liquid.

Andrew Werby
www.computersculpture.com


#6

Hi Guys,

A lot of the following has already been mentioned on the list, a
summary is always good.

From Fred Sias’ book “Lost -Wax Casting: Old, New, and Inexpensive
Methods”

Cracks in castings can be possibly caused by :-

  • Too rapid cooling
  • Quenching too soon
  • Investment too hard (too little water)
  • Boric acid additive in investment when use with deoxidised alloys
  • Acid divestment of silicon alloys
  • Alloy contamination
  • Gate too small

Regards Charles A.