Pitting and Defects in Silver Casted Pieces (LOSING HOPE!)

[arkaysilversmiths]

For that style of ring, I would lower the flask temperature. I cast most of my sterling silver at 850°F flask temp. I can’t give you any insight into the metal temperature because I use an air/acetylene torch in a centrifugal casting machine to do my work. All I know is when the metal is fluid enough, I pull the trigger.

From first glance, you have debris in the flask, probably from the burnout. All surface negative defects, if not metal-related, are due to debris embedding itself in the walls of the investment. This could be due to ash from incomplete combustion of the resin (you didn’t describe your kiln equipment) or erosion of the investment either during combustion or when the metal is added.

Resin curing is tricky. It might looked cured on the outside, but the interior could still have some uncured resin. When the resin starts to combust, the liquid resin will release and potentially erode the investment. Gradual heating of the flask and model will allow heat to cure any uncured resin before it attempts to burn/melt within the cavity.

Another good experiment would be just to use a simple band ring without any flourishes, in order to perfect the technique. It always helps to remove extra variables from your process.

[RandyD94922]

Hi Aaron,
I agree with arkaysilversmiths your burnout is a little high which can breakdown the investment and cause the small pits you see. We don’t go above 1325f 720c. for 4x6" flasks. We’ve experimented with temps all the way up to 746c 1375f and our results were similar to yours. Make sure your items are fully cured. Make sure you don’t put your prints in water regardless of what anyone tells you. If you lower your temps and still get the same results I would focus on the curing of your prints. We use 12K Phrozen Mighty’s and 12K M5 Anycubics at the moment. I’ve enclosed some pics to help you understand what we do.
Regards,
Randy

[Brennan-AG]

Have you tried casting a wax item?

[wldlzrd1]

Hi,

well, in reply to you “expectation” comment… i do not print or cast, but i have had 3d models (signet style like yours) cast in sterling silver that have come out very clean, albeit with grow lines…noting rough like what you are getting,…so i would venture to say that your goals are realistic…

julie

[AaronM43026]

Hi Ron,

Funnily enough I have just been reading an article by Bob Romanoff on flask temperature in which he states “I generally recommend a flask temperature of 800°F (427°C) (Thicker designs) to 1000°F (538°C) (Thinner designs) be used. Sometimes a flask temperature of 1000°F (593°C) to 1200°F (649°C) is required for thin sterling castings due to the nature of the metal.” It definitely seems like that is something that is worth trying. Although, do you know the science behind why a higher flask temperature would be causing me issues?

I use a Prometheus PRO-7 programable kiln. I follow the recommended burnout cycle from SRS for their CadCast investment which is specifically designed for casting 3D printed models. It is designed to be a stronger investment which is rated for burning out up to 850c, but their recommend burnout is 750c which is what I follow. I’m not entirely sure what I could change in this part of the process? I feel a 13 hour burnout is sufficient enough to remove all the wax/resin from the casting and the Bluecast X One resin has been thoroughly tested by people on YouTube to leave no ash or residue after burnout.

I’m pretty certain it is not related to the curing of my 3D prints as I let them sit in ethanol for 20 minutes (10 minutes longer than recommended) to cure, and also used a UV curing machine for another 10 minutes just as extra precaution.

I think that’s a great idea to just cast band rings for now. I might try casting three band rings at once, one using my current resin, one using Siraya Tech Cast (my previous resin), and then just one made of standard wax.

Thank you for your help, I really appreciate it!

Aaron

[AaronM43026]

Hi Randy,

I actually used to use a burnout temperature of 730c with my pervious investment (SRS Silk), but since changing to SRS CadCast which is an investment specifically designed to cast 3D printed models, I have changed the burnout cycle. I decided to just follow their recommended burnout cycle which is a burnout of 750c, but it does state in the description on their website for that particular investment that it is rated up to a 850c burnout.

I always ensure my prints are completely cured and never come in contact with water. For the current resin I am using (Bluecast X One), I let them sit in ethanol for 20 minutes (10 minutes longer than recommended) to cure, and also used a UV curing machine for another 10 minutes just as extra precaution. I used to use Siraya Tech Cast (which seems like the resin you are using), in which I had to follow a slightly different curing process, but since changing resin, it hasn’t seemed to have made any change to the casting results I am getting, which leads me to believe that it is related to something else.

Thank you for your help, I really appreciate it.

Aaron

[AaronM43026]

Hi Brennan,

Before ordering new investment and silver, I did in fact try casting a wax ring on the same tree as some 3D printed models. Unfortunately I no longer have that ring to take pictures of, but from the naked eye it did seem like it came out very cleanly in comparison to the other models (granted it was just a band ring vs more complex models). Do you know what insight this gives me to improve my 3D printed castings?

Thanks for your help,

Aaron

[AaronM43026]

Hi Julie,

Well at least it is not a lost cause then aha. I guess I just have to keep making changed until I get it right. Fingers crossed.

Thanks for your help,

Aaron

[AaronM43026]

To anyone that has been helping me with my casting process and trying to determine the issues I’m facing, might I potentially have a problem with Shrinkage or gas porosity? I have been doing some research and it seems like those are the two most common causes of bad castings. If anyone has any insight into these two forms of porosity and whether that is what I am dealing with, your help would be greatly appreciated.

Thanks,
Aaron

[RandyD94922]

Hi Aaron,
I would check the temp of your burnout oven with some pyrometric cones to make sure it is accurate. I’ve seen the issue you’re having and I know it seems like your pounding sand but the last cast you showed was far better than the original pic. I had an oven that went crazy and though it showed 720c for top temp it actually was near 900c as the thermocoupler was bad. We have used phrozens wax resin and siraya techs blue wax and both cast fine. The issue for us was handling and storage not casting. If you check your oven and it’s correct then I would lower my metal temp a little and the flask temp as it looks to me like too much heat, I’m just not sure from which one or both.
Hope this helps,
Randy

[Brennan-AG]

I would include a wax model in all of your experiments if it’s possible. It tells you that the issue is related to the 3D print entirely and not the other parts of the process. It sounds like your 3D print isn’t burning off cleanly if the wax model is coming out clean.

[AaronM43026]

Hi,

So I just finished a new cast and let’s just say, it was terrible. The only variables I changed were the flask and metal temperature. I reduced the flask temperature from 580c to 450c and reduced the metal temperature from 960c to 950c. I did also flip the flask half an hour before casting to allow any trapped gasses to escape.

I am starting to think that the issues I’m facing are linked to the burnout of the resin and the fact it could possibly be leaving ash behind. My main assumption right now is that the temperature readout on my kiln could be inaccurate as @RandyD94922 suggested. The other minor assumption I have is curing the prints in bioethanol instead of standard ethanol is causing issues, although saying that, when I used to cast using Sirayatech Cast following their exact curing procedure, I was still experiencing similar issues on the castings.

From carrying out these recent castings, I have managed to disregard quite a few potential issues like the quality of the metal and investment, and also the cleanliness of the crucible. I also ensured that this recent casting was fully cured by washing in bioethanol for 20 minutes and UV curing for 15 minutes, but like I said, maybe bioethanol is a no go. I am also certain that the pitting is only occurring in 3D printed casts and not on wax casts which is another telltale that the pitting might be linked to the burnout of the resin.

A few observations I made about my recent cast is firstly, the areas which had the sprues entering the ring from the inside all had clear surface texture issues (as seen highlighted by the red circle). Does anyone possibly know why this rough surface texture would be occurring at all four areas the metal enters the cast? I also noticed that the worst of the pitting occurs along the top edge of the ring. I do find this odd as if the issue was linked to ash being left behind, how would ash settle on the ‘roof’ of the casting and not on the opposite edge at the bottom.

I didn’t spend much time cleaning up this particular ring as I didn’t see the point, but if anyone is able to determine anything from the information and images I’ve provided it would be greatly helpful. I think my next steps are to buy either a pyrometer or pyrometric cones to test the accuracy of the kiln, but if the kiln turns out to be accurate, then I am a bit lost on what to do next.

Thank you for everyone’s help. Hopefully I will get to the bottom of this eventually, fingers crossed.

Thanks,
Aaron

[jeffg-moderator]

Okay, I just went for a long bike ride and couldn’t get your post out of my head. I do my best thinking on my bike.

I’m am convinced that your problem isn’t partial burnout or inaccurate kiln temperature. I am positive that your investment is degrading with micro fractures and cracks. After thinking about this for an embarrassingly large amount of time today, I’ve come to the conclusion that it’s your sprues that are the source of your troubles. They are huge and are 3/D printed out of the same material as your model.

Now let me explain what I think the problem is. But before I do, let me say that I have fairly basic knowledge about 3/D printed model casting, but I do know a heck of a lot about traditional lost wax casting. In traditional lost wax jewelry casting, the sprue wax is designed to melt at a low temperature, so it is the first thing that melts out in a burn out. The logic is that because most things expand when they get hot, having the sprue wax melt out first, creates a space for the harder wax model to expand into as it begins to melt. Your problem is similar to what happens if you make a thick sprue and a thick model out of carving wax. You’ll often get similar kinds of imperfections.

I am convinced that because your huge 3/D printed sprues and your 3/D printed model are melting at the same temperature, everything is expanding at the same time with no place to escape to. The sprues are in essence creating a blockage which is causing all of these imperfections.

We know that you’ve switched to a specific 3/D printed model investment, (with extra strength) so that’s probably not the problem.

Here’s what I’d like you to do as an experiment. Take this same ring that you just cast and print another model with the same castable 3/D printed wax, but this time add the sprues manually with regular 8 ga sprue wax. Don’t over sprue. One or two sprues on the bottom edge of the ring (with the ring at a 45 degree angle) are sufficient.

Please use this burnout method.
Follow the manufacturers investment measurements and procedures exactly.

Let the mold sit untouched for a minimum of two hours after the investment sets up.

2 hours at 150C
2 hours at 370C
2 hours at 675 C
2 hours at 450C
(this is a little longer than what I usually do, but in this case it seems appropriate)

Others may disagree with things that I’ve said, but please give this a try. If I’m right, you can have a celebratory beverage in my honor. If I’m wrong, well, I did my best.

Jeff

[aggie.p]

I’ve only followed this a bit. Here is another thought. When doing larger statue casting, we had lead areas of the bottom of the casting. This allowed the metal to be drawn out the bottom before it started to pool. I hope that made sense. Think a finger pointing away. Next you might be right about the sprue going to the inside o the casting. It has a minimal (tiny) lip above it. It might be enough to cause a bit of turbulence where metals needs to go up a tiny bit at the same time going down. You can always saw the sprues o once it is cast. So why not let the sprue lead directly into the piece instead o being on the inside? Just my cents worth.

[wldlzrd1]

Hi,

a random thought…the band design is like two halves…one positive (thick background) and one negative (thin background)

the edge band on the negative side is thicker than the thin background

meaning that the metal flows thru the thick background, then on thru the thin background, and then into the thicker edge…and that thicker edge is affected by pitting…it is the last place the metal goes…after traveling thru a very thin area…perhaps progressive solidification issue…

current sprue placement has the metal flowing straight into a wall thus forcing the flow into a 90 degree angle, which then narrows and thins due to the sun and moon detail…and then into a thin area, followed by a thicker band area…

perhaps sprue the thicker side edge so that the metal flows straight thru…?

julie

[Yggdrasil]

As many has said, the conundrum continues and since we have no idea what the root cause is,
it is basically a guessing game.
How about doing a dry run with full burn out, then try to saw the investment in half
and inspect the inside thoroughly.
This can identify surface damages, but may not reveal incomplete ashing.

[AaronM43026]

Hi everyone,

I appreciate all of your feedback, it has been a great deal of help so far. Apologies for not replying to everyone sooner, I have been away for a few days.

I decided to go back to basics and cast a completely blank signet ring as well as a wax band ring for comparison. As before, I stuck to the same flask temperature of 450c and same metal temperature of 950c. The only aspects of this particular cast I decided to change were the water to investment ratio and the sprueing of the models. I changed the investment mix from 40:100 to 38:100 as I thought it would give the investment more structural rigidly and be less likely breakdown when pouring the silver. I also used wax sprues this time instead of printing them as part of the model.

@jeffg-moderator I decided not to follow your burnout cycle for this particular cast (will do for another cast) as I didn’t want to change too many parameters and not know what the root cause is. I also didn’t think the burnout temperature you recommend would be high enough to burn out the 3D printed models as resin requires a much higher temperature for this (please correct me if I am wrong). I think you were certainly right about my sprues being too big though. I don’t know why I never thought about this initially but it makes so much sense now. Having a lot of fast rushing metal entering the model creates a lot of turbulence and therefor will damage the investment. So for this particular cast I took your advice of using pure wax sprus attached to a wax trunk placed at 45 degrees. I know that 3D printing an entire wax tree in definitely feasible as I’ve seen quite a few people on YouTube do tutorials on it, but I think the issues I was facing on my previous cast were definitely a combination of my sprues being too large and other factors which I am yet to figure out.

As you can see from the images I’ve attached below, these two particular models came out far better than my previous cast (excuse the finish on the wax ring, I quickly made one from a block of wax and a soldering iron, so it’s not the smoothest aha). You can see that the wax ring has very very minute pitting, if none at all (I can’t really tell), and came out with an almost perfect finish. On the other hand, the 3D printed signet ring casted with quite a few areas of pitting, granted not as bad as the previous cast but still not to an acceptable standard. I did also notice on the signet ring that asides from the pitting, there does seem to be some sort of hairline crack on top (as highlighted by the red circle). If anyone knows what might have caused this, it would be greatly appreciated if you could give me some insight (perhaps my temperatures). Thankfully this particular casting has taught me a lot. The fact I wasn’t paying as much attention to the sprue size and placement as I should have been, but also the fact that the 3D printed model is the only one with major issues tells me a lot.

I feel like with each cast I do, I am getting closer to figuring out the root cause of my issues. Hopefully with this latest cast, it might give someone with more knowledge than myself an insight into what’s causing me these problems. I think I’ve covered everything I have wanted to say, but incase not, I will keep everyone updated.

Again, thank you for everyone’s help!

Aaron

[jeffg-moderator]

Shoot!

I’m not sure what the maximum temps are for the special 3/D printed investment are, but I know that the regular investment starts to deteriorate at 1400F/760C, so the maximum burnout temp is 1350F/732C. 1250F/675C is considered the “safe” zone maximum to not deteriorate your investment, which is why I suggested that max temp.

All of your jewelry that you’ve shown us is pretty thick. Do you ever make anything that is thinner? It would be interesting to see if less 3/D printed wax to burnout would have better results (even once). Casting thicker pieces is always more complicated.

Like you said, you’re inching towards success!

Jeff

[wldlzrd1]

Hi,

so…does the pitting (negative space) indicate that there is something left in the void after burnout (positive space)…?

julie

[AaronM43026]

Hi Jeff,

That makes sense, I see why you recommended that burnout temperature now. The investment that I am using made by SRS states on their website “Designed to burnout at 1560°F/ 850°C to help burn off resin residues and ashes” although I have been using a burnout temperature of 750c which is what they recommend on their downloadable PDF.

Unfortunately the type of jewellery I wish to manufacture is similar to all the pieces I have been casting recently (fairly thick), although like you said, maybe trying to cast something thinner might give me an insight into resolving the issues I am facing.

Thanks,
Aaron