Is this bad casting from soft/degraded investment?

Jewelry Discussion
21

I agree with Andy C; this looks like shrinkage porosity to me. If the investment were degraded, there wouldn’t be any smooth areas. But this part has some, toward the bottom (as shown). If the tip of that cone on the top was the only place the metal could enter, then it looks like that tip froze first, sealing the metal off from the reservoir of molten metal it needed to draw from as it cooled. My guess is that if the size of that choke-point were increased, the surface would look better.

The way I’ve been curing my resin models prior to casting is by microwaving them for 5 minutes or so in a cup of water.

Andrew Werby
Juxtamorph.com

22

Hi Rick,

From reading all the posts, this is my somewhat thumb sucking opinion, for what it’s worth.

I don’t think that your investment is to blame because from my experience most general investments allow quite a wide margin of error before they fail badly.

To me your piece in the picture looks like there was either ash left in the plaster or the model material combined with the investment and subsequent burning out causes the mold surface to break away.

I say this because I have cast many organic pieces like insects and frogs and the like.

They generally produce ash after being burned out.

Sometimes the mucus skin combines with the investment and causes the surface to break away.

I normally blow the flask out with compressed air after burnout and before casting and this does help, but even so there still remains an ash residue that is picked up by the oncoming metal and it then deposited at the top of the organic model.

I mention this because the resultant cast has the exact same surface look as your cast does.

While this does not really affect he overall look of an organic piece, a smooth model like yours is obviously ruined.

I have read James Binnion’s paper and there he uses very complicated models that fit in perfectly with the printing genre.

So I ask this very respectfully.

Your model is very easy to make in metal.

To me it would seem much more simple to make a metal master, then use normal vulcanize/inject wax /sprue and cast method.

Unless of course, you are doing this as a resin casting learning process ( nothing wrong with that, for sure)

Anyway, my feeling is that ash is the root cause of your problem because only the top part of your model is bad, not the entire piece.

Disclaimer, I have never cast the resin you are using, so all of the above could be BS!

23

I think that Hans might have nailed it.

24

I’m sure that the grows have a descent surface on them. Seems like just
figuring out the casting would be easier. Mold making and injecting can be
a time consuming endeavor also, then you still have to cast and finish
them all. I would get some of the proper investment for the resin and try
it. I could send you enough for a couple flasks of you’d like to try it.
I’ve been casting grows recently with pretty great results. We are using
the same r&r mentioned above.
Like Hans said blow out your flasks. That wouldn’t have helped that one
pictured because there is investment missing from inside the cavity if
there are bumps on your casting . That is something else.

25

Could it be that the investment is reacting to the investment? Uncured resin somehow broken down by the liquid investment? Or perhaps a reaction at higher temps? But the placement of the defect seems to support Hans’ theory. The ash would collect at that point…

26

Yeah. Could be ash after looking at that pic again. Blowing it out could
help that. Hard to tell if it’s bumped off the original surface or pitted
into it

27

I have my doubt about ash Hans in all respect for your knowledge.
The reason why is that ash never form balls or bubbels and this is what
you see when you enlarge the picture …lots of bubbles.
Therefore, I like to outrule ash and believe in a moisture/water related
problem combined with temperature and raising it to rapidly.

I had this kind of problem when I was dealing with older batch of
investment which was not stored dry enough.
For this reason, I like to use silicagel and keep them together in a
plastic bucket together with the investment.
Never ever had to deal with this problem again.
Since I don’t cast thatmuch anymore (like to smith my pieces more then
casting them), I have a small quantity of realy old investment.
However, the castings made with this investment are still superb …
believe it or not.
Just saying …

28

Forgive me if someone else has already said this, I haven’t read all of the responses, I know some have already mentioned that you are vacuuming too long and the investment should be pancake batter consistency.
Also, while 2 hours is the minimum time to let the invested flask cure 24 hours is preferred, if not fully cured the investment could be breaking down or if it has gotten too dried out before the burn out.

Assuming that those things are correct, the resin may not be burning out fully or may have bubbles. Conversely, if you do too long or too high temp of a burn out for the type of investment, it can also break down, but you would usually see more flashing from this, and 8 hours is not that long. Your burn out temp should not be higher than about 1200 degrees F for the burn out.
Make sure your flask is at the correct melting temperature for the metal you are using and that the metal is not heated to the boiling point, especially argentium is pretty finicky.

Last, but not least, have you been waiting until the flask is completely cooled to remove the investment from the cast mold? Argentium must be completely cooled before submerging in water.

Unfortunately, many things can cause pits in a casting, you will want to try to make a few adjustments and see if the outcome changes to see what you have done wrong.
Here is a link to the Satin Cast instructions for the correct water ratio: http://www.kerrcasting.com/LiteratureRetrieve.aspx?ID=129094.

I hope this helps,
Holly

1 Like
29

I have to agree with Hans. This is a resin issue, not an investment issue. Resin and Satin Cast is problematic. Very few people have excellent results using satin cast.

I don’t have answers for you. There is a wealth of information on the 3DCadjewelry forum, because many have gone and are going through what you are.

I have a B9 Creator, Solus, and a Solidscape printer.
Solidscape wax prints cast beautifully. Resin…I’ve had identical pieces all treated the same way, and some came out perfect, and some like yours, in the same flask.
I stick with Solidscape because it’s dependable and consistent.

30

There are a couple of things to check to determine if a resin model is cured.

  1. It isn’t wet with resin - surface should be dry. If you wipe the print with a paper towel, it should not pick up any color from the resin.

  2. It shouldn’t smell like resin - if you haven’t smelled the uncured resin this might be tough, but if the surface is not fully cured, you will get the arcylic-y smell of the resin. It should smell ‘neutral’.

  3. If you have a piece that you can experiment on, cut into a section of it with your jewelers saw and look at the different in color as well as the waste from the cut. It should be dry and not stick of any significance to the blade.

Haunt the Form Labs forum to see how folks describe how their castable resin cures and that can give you some additional criteria to check.

A way to deal with uncured resin is to put a barrier coating on the print. I’ve seen different things thrown out including beeswax in touluene to spray fixitive to essentially rain-x. The key is to keep the wet investment from interacting with the surface layer of the resin model, leeching the uncured resin out and causing issues with the investment as it solidifies. This is highly dependent on the resin being used and its chemistry.

1 Like
31

Thank you everyone, so much for your help and advice.

I’m happy to report that I just cast a model made of Formlabs Castable Resin and I have zero porosity today.

I simply switched to R and R Plasticast, (the recommended investment for Formlabs Castable Resin).

I even used 100% recycled argentium and I still had no porosity. I used almost the same exact burnout schedule so I believe the investment change made the big difference.

As people have pointed out, there are tricks to casting resin with regular Satin Cast, like curing the flask for at least 4 hours, but the right investment made a huge difference for me.

I also heard from my friend that the Ultra Vest with fiber is so strong, that it does not expand and breakdown from curing resin in it either.

32

You were right, like many people,

Because switching to Plasticast investment worked perfectly, even with 100% recycled Argentium.

33

Dear Rick… I had the same problem with my castings here in India… I normally cast at least 50-80 flasks in a day … the size of the flask is 3.5 inches x 8 inches & 4 inches x 8 inches. Each flask contains about 60 pieces or more as per the design. I was using GOLD STAR GEM SET powder used for casting wax set stones. I had the same problem like you had on your Argentium.
At present I am using KERR SATIN CAST POWDER…
Fist of all this happens mainly because of following reasons:

  1. If your silica content in the powder crystallizes due to moisture absorption. the silica becomes hard & granular & this causes the rough surface problem. I suggest you sieve the powder with a fine mesh to try & find out the presence of Hard Silica Granules.
  2. If your powder is the one used for wax set stone then the boric acid content in the powder can cause the investment powder to become HARD & NON permeable which can cause this problem.
  3. Drying time after investment procedure not long…
  4. Too high Casting temperature for a metal like silver. (Metal temperature should be around 950-980 degree Celcius)
  5. Too high flask temperature for the metal … should be a round 600 Degrees Celcius.
  6. Check the mixing of investment powder. It should be for 8 minutes from the start up time, & should be under vacuum pressure.
  7. DO remember to keep the investment drum in a cool dry place…
    What is your burnout cycle temperature set for the furnace…
    IT should be like following…
    30 minutes 150 degrees celcius.
    60 minutes 250 degrees celcius.
    60 minutes 350 degrees celcius
    60 minutes 450 degrees celcius
    60 minutes 550 degrees celcius
    60 minutes 600 degrees celcius
    30 minutes 700 degrees celcius ( Use this stage of 700 degrees for without stone castings only )
    60 minutes 700 degrees celcius
    30 minutes 600 degrees celcius
    60 minutes 600 degrees celcius
    180 minutes 600 degrees celcius ( start casting at this stage as temperature will stabilize at 600)
    360 minutes 600 degrees celcius ( For holding till you have completed all flasks).

Quench the flask after 30-40 minutes in room temperature water.

If that is silver alloy I recommend that you use 950 - 980 degrees celcius for casting. Do not go higher above 1000 Degrees Celcius it is not required… You will get good results.

All the best … Do revert on results…
regards,
Prakash V Pai
INDIA

34

Wow, thank you Prakash!

Very kind of you to share your information on casting. You may be right that my investment absorbed a bit moisture as I live in a humid environment. I keep the powder in air conditioning but after a year, it probably does absorb moisture.

You are also right about finicky nature of silver alloys when casting. I didn’t know this until recently that silver is more of a pain to cast if not the right temperature compared to gold.

I’ll try your advice. I did get a perfect casting by switching my investment so you could be right about the investment problem in particular.

35

Some very good advice here. I live in the Tropics…Panama… very humid… in my shop I have the air conditioner running 24/7 as well as a dehumidifier that keeps the humidity down to about 35% which is great for my investment as well as all my tools… no rust problems and I have used 4 year old investments stored like this with great results.

36

Looks like your model was wet. This dilutes the investment on the surface of your casting. After mounting you can either wait or use an old hair drier to make sure your model is dry. We had this problem with old waxes that we cleaned before investing with green soap and hydrogen peroxide. This isn’t needed with the newer waxes.
Steve

37

I like Jo’s answer. She hit the nail on the head! What you are experiencing is investment erosion. The resin that you are using requires a different burnout cycle similar to what you would do with carving wax. The temperature is coming up too fast and the resin starts boiling before it can be eliminated. I’m sure James Binnion has specific recommendations as far as burnout cycle/temps.
The one other thing I would suggest is following EXACTLY the investment ratios and mixing/vacuuming precisely. The most common mistake that many bench jewelers make is thinking “I’ll just mix this investment to look like pancake batter”. Get a graduated beaker. If you do run into a problem when you get a new box of investment, the manufacturer has a tech. dept. that will walk you through any changes you need to make in your procedure.