Help with Bronze Investment Casting

Discussion in 'Lost wax casting' started by measuretwice, Oct 7, 2022.

  1. measuretwice

    measuretwice Copper

    Hi Everybody,

    I've been working on investment castings from 3D resin printed patterns. So many variables, I keep trying and learning and getting closer....but I need push. Here's a hand wheel for the reversing gear of a model engine. Its a little over an inch in diameter, the cross section of the outer torus is .110" in diameter.

    i've tried various resins, the last was with BlueCast Cr3A. Quite expensive (for me as a hobbyist), but with fails with other cheaper ones, I'm trying different things.

    I am using mystery metal. In this casting its a a slice of a never used bronze worm wheel. Maybe a tin copper alloy, there was no zinc telltale white smoke. I'm doing this indoors but do have a ventilation system running over top of the melter. Maybe I should get some silicon bronze grains, but I've spent so much so far, the credit card is about worn out.

    I'm using R&R Plastivest, 16 hour burn out, including 4 hours @ 750C (1382F) as suggested by the resin maker and the mold is at 525C (977F) for the pour. The bronze was at 1025C (1877F). Its vacuum cast; I turned on the vacuum just before pouring and shut it off after the metal wicks in. I don't touch it for 15 minutes then quench it.

    I've got runners going around the thing as shown. I thought that would be enough. I'm currently printing another version which has much heavier runners. Seems like lots of things get well cast without much in the way of runners, but I'm running out of ideas.

    First pic shows the both the problem and the amazing potential - the striations visible toward the bottom right are from the resin printer, perfectly replicated and they are about 700 dpi. Then on the right is the issue.

    So what do the experience guys say, what is causing this, what am I doing wrong? Thanks!

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    Last edited: Oct 7, 2022
  2. mytwhyt

    mytwhyt Silver

    If it were wax, my best guess would be air in the part. The damage would happen when vacuuming the part in the investment.. If you want to test that idea, invest and cast without vacuuming the part.. Use a de-bubbleize to help release the bubbles. Just the wheel part with all the spruing..
     
    Last edited: Oct 7, 2022
  3. measuretwice

    measuretwice Copper

    Interesting....I hadn't thought of that. The cured resin is brittle. I'll try it on the next casting, hopefully this weekend. Sorry for sneaking a resin pattern Q in, didn't know the most appropriate spot. Thanks for the suggestion.
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    Looks like a slag/dross inclusion to me. Looking at the top of the sprue and the oxides formed I would bet on your source metal being red brass and not silicon bronze.... get yourself a known alloy to start...
     
  5. mytwhyt

    mytwhyt Silver

    When I look at the wheel again I see white in several places.. That looks to me to be investment in the eroded places.. I don't know anything about printed parts.. Could it be air in the part and not evident and vacuum draws investment into the part.. Just under the surface. Could it be the direction its printed in.. Say again, I'm completely in the dark when it comes to printed parts.
     
  6. mytwhyt

    mytwhyt Silver

    If you have a bell jar, put the printed part in water, and draw a vacuum.. Watch to see if any bubbles come to the surface.. Should happen before the water boils..
     
  7. measuretwice

    measuretwice Copper

    The top of button did turn quite black when it cooled. Is that indicative of red brass? Any tricks to casting it, or is it just going to be trouble? I expected it to be a tin bronze coming from a worm, but you right, its mystery metal guess work.

    In dealing with slag, I used borax and tried to skim any dross....which is another thing I've struggled with: Skimming the molten metal in those deep small diameter graphite crucibles (the type used in an electric melter) is a challenge. The surface of the molten metal is small and deep in a hole. I made a sort of skimmer, small disk on end of rod (steel) but there is so little thermal mass in the small amount of molten metal, as soon as I touch the skimmer the metal just freezes on it. I might try a carbon rod, I have some gouging rods around I think. I'd love to hear any better ideas.
     
    Last edited: Oct 7, 2022
  8. measuretwice

    measuretwice Copper

    Will do, just have to get a cured print. I don't think its the printed part, the white in the second photo is just investment not yet cleaned off. It is a resin designed for investment casting, and a new box of investment intended for resin patterns. I've read everything I could on their use. I'm doubting there is any air, just based on how the print is formed and that I've not heard of it as an issue...but I'm not steeped in experience with this either.
     
    Last edited: Oct 7, 2022
  9. mytwhyt

    mytwhyt Silver

    I was thinking that the investment wouldn't be in the defect after casting.. How did the investment cling to the defect free areas,, I can't understand how it could be there after the fact.. But then there are so many things I don't understand..
     
  10. Jason

    Jason Gold

    Remember everything is backwards. If the investment flaked off inside the cavity, you would have boogers on your part. I'm okay with investment that flakes off, I can always grind back boogers... Or pick 'em! I think you had a metal issue, possibly crap in your metal or pouring not under a vacuum. Now if you DID have some crap flaky investment floating around in there, it could cause what you have when it settles inside the cavity. (improper burnout can cause this) With that said, you can wash out your hollowed out investment cavity with water after wax or whatever you burn out. Then the temp can be brought back up for pouring metal. Couple of tips with investment (I dont know what you are using, but this is pretty universal) Use COLD WATER and I really recommend distilled water unless you know your water isn't loaded with minerals and other crap. Be sure you mix per the instructions and always add investment to the water. Not the other way around. It's just like mixing plaster of paris.

    I'm guessing that thing is pretty small right? Say an inch or two across the widest part?? Are you pouring metal while pulling a vacuum on your flask?? David here pours some pretty big flasks while pulling a vacuum on his homemade rig.
     
  11. measuretwice

    measuretwice Copper

    I see what you mean, not sure either. Here's a close up. Seems to suggest the cavity was flawed before pouring? Or some may some investment logged there while cleaning? If its a mold problem, that is really frustrating as I'm using what are supposed to be quality products and diligently following the instructions

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    Last edited: Oct 8, 2022
  12. measuretwice

    measuretwice Copper

    Part is just over 1" diameter, cross section of the outer ring is .110"

    I'm using new R&R Plasticast. Bought it as its supposed to be for castable resins as I've been trying to eliminate sources of error (yeah I know, stop using mystery metal..I may have to). I mixed and use it to letter of their instructions, again trying to eliminate sources of error.

    https://www.ransom-randolph.com/_files/ugd/cc5f22_902ad781b4e74bf3b3d55bff34f7fe6c.pdf

    They say to have the water 72-73. I even bought a thermometer to make sure. Cold would be better? Burn out was to there instructions, except I used 4h for highest temp as per resin manufacturer. I didn't try distilled water, tap water is soft city water, probably lots of crap in it but its not hard like a well. I could try distilled.

    David mentioned the top of the sprue....here's a shot. The metal was clean to start with, new part and I scrubbed it before using it. I had the same type of button top on an earlier attempt using a different piece of bronze (that one had zinc, you could see it boiling and the whisp of white smoke. Point being, two different bronze alloys produce that crap on the button...is it dross? Does it mean I'm not fluxing/cleaning properly?


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    Last edited: Oct 8, 2022
  13. Mantrid

    Mantrid Silver

    You have some rough mounds next to some investment filled pits. I think what possibly happened is during wax burnout bits of investment broke off and deposited next to where they originated. Metal was then poured in, the metal filled the craters to create the mounds in the metal and trapped the broken off investment aginst the surface causing the pits where the bits of investment were sitting.
    Sorry if this has already been suggested as I didnt read all the posts
     
    Jason likes this.
  14. mytwhyt

    mytwhyt Silver

    The next step would be to ask R&R to offer up any suggestions as to the cause of your problem.. The cut casting seems to prove the metal and resin are working fine..
    Fredo
     
  15. Jason

    Jason Gold

    Make the part in wax and I bet your issue goes away. Burning out any whacky crap besides WAX is a crap shoot. You should see the burnout schedule we had to come up with for a printable resin in the B9C for jewelry work. R&R will be no help, been there, done that one. They haven't experimented enough to know or guarantee what works 100% of the time.
    This is still fairly new technology. I see the investment failed somewhere and ended up where you didn't want it.

    Play with the burnout schedule, make careful notes along the way with what works and what doesn't. You'll get there eventually.
    We were using conventional R&R ultravest investment and some yellowish resin. I can try to get the burnout schedule we were using if ya want.

    Another place to check is right here, search out b9c and see if I pop up somewhere. I might have just posted our adventure. Been quite a few years since then. Sorry.
     
  16. measuretwice

    measuretwice Copper

    I too have found R&R to be less than helpful. I'm using their Plasticast which is supposed to be better for resins. my 15 year old Ultravest seem to work as well.

    Jason if you could share the burn out that would be great! and the resin? I'm spending lots of money and wasting lots of time, a solid reference point of materials and process known to work would be amazing. I have a PID controller and have been following R&R's burnout guides, which seem to be supported by Bluecast's advice (I did search this site via google for b9c but couldn't find much)

    I'm also going to start writing the resin co's. It takes time and seems so rare to get an thoughtful response I've been avoiding it.

    That bluecast stuff used here, it is also hard to get prints that don't have distortion.....pisses me off as its like $300/litre and I stepped up thinking the cheaper resins might have been the issue.
     
  17. Jason

    Jason Gold

    Here's the rub.. The were using https://shop.b9c.com/b9r-4-yellow-casting-resin the yellow stuff and settled on plasticast for investment but also said they didn't see much difference from the regular stuff.. Here is their schedule.

    IMG_20221009_192009.jpg
     
  18. measuretwice

    measuretwice Copper

    Hi Jason,
    thanks for that. I will try some Boric acid, just ordered some. I can't find that resin in Canada and shipping by Fedex is brutal, might get some dropped shipped to Buffalo as I'm in Niagara weekly. David also gave some instruction on how to properly gate stuff so I will try again. Actually I have been trying again, but now the Bluecast resin isn't working, 4 failed prints in a row :(
     
  19. Jason

    Jason Gold

    Our guys started with blue, then red and ended up on the yellow. Some jewelry guys say the green works good too. What's the difference, I wouldn't have a clue.
     

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