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Castings surface cracks


#1

Dear All,

Ned expert advise on the problem that I have been facing, my
castings once done have these surface cracks which appear immediately
or after filing the product and during the process of polishing.

The pieces crack at this point revealing a brittle metal look with
some black carbon like inclusions. this is prevalent in mainly plain
parts only.

Help Advise eagerly awaited.

Khushroo Kotwal from Mumbai where it has started to heat up
including the weather.


#2

Hello Mr. Kotwal,

What is the metal is it Karat Gold, or sterling silver? What alloy
are you using? What is the method of casting? Is it pressure over
vacuum casting or Vacuum casting or centrifugal casting? How many
times has the metal been recycled? Have tried using freshly alloyed
metal? What are the casting temperatures? From what you have written
I would say the metal needs to go to refining before it can be used.
The metal you are using is contaminated.

Warm Regards
Umesh
Mumbai


#3

Hi Khushroo,

I had a similar effect happen once and what I determined caused it
was I had over heated my silver and it seemed as if it had started
to break down. You might try not to over heat the silver. If it boils
it is too hot.

Good Luck,
Ken Moore


#4

Hard to say what’s going on without some more Khushroo,
but it sounds like either too much old metal, the metal is being
over-heated, the flask temp may be too high or it might be that you
are quenching it too soon after casting. Or maybe it is being caused
by a combination of some or all of the above.

If you can post a little more info, like what metals you are using,
whether this is a new thing or has been a problem for a while,
whether the cracks go all the way through the metal or are just at
the surface, or anything you may have changed recently, like a new
batch of investment or a new kiln or torch, we might be able to be a
little more helpful.

At any rate, I hope this helps!
Dave Phelps


#5

Hi, Try visiting this site: http://www.ganoksin.com/gnkurl/ep816q

Hoover and Strong refiners technical site.

be cool. luvbruce


#6

Hi there, I have had a similar problem before with small cracks that
appear upon polishing and brittle metal. In my case i believe the
cracks came from quenching the flask too soon after casting, and the
brittle metal was from incomplete burnout, contaminating the metal.
It can’t hurt to try waiting longer to quench and making sure the
burnout is completeand the investment is white when the burnout is
finished. For myself I had to add a vent in the door of my kiln to
get enough oxygen to completely burn the wax. Good luck.


#7

Dear All,

thanks for all the suggestions, things do seem to have improved with
the valuable inputs from all, and a personal thanks to Mr. Umesh who
since was available in our town came to the rescue.

Things have cooled down but the WEATHER has not.

Once again A Hearty Thanks to you all Orchidians.

“Warm” regards
Khushroo