Hi all, The inclusions you mentioned are not caused by any of the
things you have mentioned.
I have seen castings with 'investment inclusions' . I noticed
a tiny pinhole on the surface of the casting and start to excavate
a bit with a needle or tiny ball burr and opened up a small crater
filled with investment. I have seen this caused by two things.
Improper sprueing ( the sprue wasn't totally connected leaving an
undercut that upon investing gets filled with a very thin fin of
investment) and from pierce out work (windows or azures) in the
model that taper to a very sharp point.
These inclusions, when you analyze what has been stated is actually
caused by a tiny airpocket inside the wax. when a wax with this type
of inclusion is invested, a tiny hole is caused when it is invested
under vacuum and due to the vaccuum, the investment finds it’s way
into the air cavity in the wax .This, then becomes aninvestment
inclusion in your casting. This is the only way that this happens…
Look at your wax with magnifiers and if you see any white spots near
the surface… these are tiny air inclusions that will be filled with
investment.
Hope this helps.
Daniel Grandi
Presently in Thailand and will probably be visiting with Dr hanuman
in Bangkok soon.
** Hanuman’s Response **
Looking forward for a dinner together on the banks of the JaoPraya river
Hi Dan, Kate, All,…Actually, you are both right. Investment can
break off and be carried in, AND, air pockets in the wax can be filled
with investment to be included in the casting. Both can be prevented
by 1) clean spruing practices, and 2) Inspecting for bubbles or
flaking in the wax and repairing. John, J.A.Henkel Co., Moldmaking
Casting Finishing
Hi Dan, I agree, an air bubble slightly below the surface can get
filled up with investment. I assure you that the other investment
inclusion scenarios in my post are also causes of this problem. When I
worked as Production Manager at the Franklin Mint (jewelry sales at
that time of 89 to 91 million dollars a year), one part of my job was
to resolve production problems with vendors . I toured 22 factories
in Hong Kong, Taiwan, and the US and worked with them to solve
production problems to ensure high quality and low reject rates. The
master model on one product had long triangular ‘windows’ pierced out
on the sides of the rings. In production, the acute points (now filled
with investment) were knocked off by the force of the molten metal,
causing investment inclusions (and the sharp end of the triangular
window was now truncated). We adjusted the model, filled in the
sharp pointed end of the window and used a graver on the surface of
the ring to cut in the point of the triangle. The problem was solved.
I also traced another vendors consistently high reject rates with
their improper spruing. On examining their master models and molds I
saw that the sprues were barely tacked on, and they didn’t bother
adjusting the molds taken from these models to make the flow of
wax/metal smooth. I was amazed they could even get a good injection.
When we adjusted the sprue area of all the molds (with a hot dental
pick or wax pen, we burned the molds to make a smooth transition from
the sprue to the model. Problem solved. I hope this helps. Kate Wolf
I must interject as to the comment Mr. Grandi made here. We all know
that Mr. Grandi is a very knowledgable person in the casting "game"
however, his comment in regard to "this is the only way this happens"
is incorrect.
These inclusions, when you analyze what has been stated is actually
caused by a tiny airpocket inside the wax. when a wax with this type
of inclusion is invested, a tiny hole is caused when it is invested
under vacuum and due to the vaccuum, the investment finds it’s way
into the air cavity in the wax .This, then becomes aninvestment
inclusion in your casting. This is the only way that this happens…
Look at your wax with magnifiers and if you see any white spots near
the surface… these are tiny air inclusions that will be filled with
investment.
If a small piece of investment breaks off in the pour, from whatever
cause, it can in fact lodge in the metal flow and can definately
create this issue. I want people to know that there are many causes of
this including what Mr. Grandi said, however the sprue, gates, air
bubbles in the waxes, proper investment mixing and cleanliness of
flasks can all contribute to this issue. I believe using great care in
all the processes, including checking the waxes for airbubbles, yet
not eliminating any of the other check points, will save headaches for
all down the road. I just want to make certain that everyone
understands to look at the entire process, not just limit their
thought process to one point and think that that is the problem or
the solution. Any questions, feel free to contact me at @Joe_Lovato. Joe Lovato Neutec/USA
Hi John, actually, when going back to the original statement From Kate
which mentioned a “pin hole on the surface of the casting leading to
a large amount of investment inside the pin hole when burred out”…
This is, as I said, An airpocket only. Investment can break off as we
all know , but I have never had this problem unless a wax wash was
used and it did not properly dry before investing. wax wash in a crack
in the wax will break off because it weakens the invesment.
Daniel Grandi
�Hola a todos! With all the respect that I also have for the
interesting and vast commentaries of Mr. Grandi I can not agree more
with Joe Lovato; The person from which I learned more about the theory
of casting was Mr. Cliff Wilson who had an enormouse experience on
Industrial (aeronautical) and jewelry investment casting. I heard him
thousands of times repeat the words “process control”. He insisted
again and again in cleaning through the whole process and controling
all the possible variables including air bubbles on waxes, proper
spueing, investment mixing time, water/powder ratios, avoiding old
investment residues, careful transportation of the flask, etc. All
this might cause investment inclusions of a geometrical form (not
round as gas bubbles).
Arq. David C. Duhne
Director Tecnico y Comercial
Diamantex S.A. de C.V.
Hi Kate, I don’t disagree with you …but what I must state is that
there is a method to analyzing what is causing a particular defect in
a casting… and your original statement which mentioned that you
found a tiny pin hole on the surface of the casting and when you dug
into this, you found investment.
Well, … this is caused by an air pocket in the wax 99.99% of the
time…
Investment that has broken off while pouring will look different when
analyzed… The other things that you mentioned in your email were
also correct.
What I am trying to do when I reply to any email is to explain the
reason why that Particular deffect happened so that whomever has
that particular problem will know what to look for. I believe I did
exactly that in relationship to that specific problem.
I could also explain how to analyze all the different causes of
defects in castings, But that was not my intent in that particular
email.
Hope this helps to clarify my previous statements. Daniel Grandi
Hi Joe Lovato, I would suggest that you read exactly what I said and
you will notice that my statement had to do with a “pinhole visible
in the cast product and after opening up this pin hole, there was
investment inside” This is without doubt , caused by an airpocket in
the wax. It is also a fact that other things may cause a similar effect
and all of that was mentioned in previous emails about the subject.
I personally have never seen investment break off in a casting unless
the wax had left over, undried wax wash or incorrectly mixed
investment. In rare cases, sprueing can have this effect and has to
do with correct flow patterns from the spue through the piece.
Other than that…what can be said is that there are extremely
complex parts that are cast that have sharp edges,thin sections,thick
sections ,holes,strange flow patterns all in the same piece … and
we don’t get breakage or inclusions… in these parts … done in
quantities of 1000 pcs at a time… The few times we have had a
problem were directly related to an accidental bad mix in investing
or the wax wash was not dry in every area of the piece.
We do inspect our waxes with a magnifier to eliminate air pockets in
the wax.
