The Dollar Store: a source for cheap lost foam patterns

Discussion in 'Lost foam casting' started by Tobho Mott, Mar 13, 2020.

  1. Tobho Mott

    Tobho Mott Gold Banner Member

    https://www.sculpturesupply.com/det...ostone+(Southard)&cat=Plaster+&+Gypsum+Cement

    I'll see if I can dig out my bucket o'mud and try to bring some back to life for next time. Too late for this bunny creature... I was gonna sacrifice the other mutant bronze bunny to raise this demon, but he wouldn't fit in the crucible in one piece.

    Capture+_2020-04-10-22-08-29.png

    I'll go dig him up in a bit, fingers crossed. I interrupted the pour for a moment but I think it had filled up by then. It spat a few drops of bronze back out of the cup as you can see, which was unusual. No sign of float though.

    CO spiked up to 42ppm just after I lit the furnace for a minute, then back down and stayed around 7 for the duration of the melt. Back up to 26 when I opened up the furnace to skim, pull, pour.

    There was some goo in the skim from the new crucible too, I guess it does come from the bronze after all. Weird that it never happened before these last 2 melts.

    Jeff
     
  2. Tobho Mott

    Tobho Mott Gold Banner Member

    Looks like a winner! That glass is gonna be a pain though, maybe enough to drive me to coatings.

    20200410_225906.jpg

    Looks like the foam vapour blew a glass bubble on the inside of the back part. I can see the usual styrofoam geode type appearance (not floated) through the hole I popped in it.

    20200410_225926.jpg

    Jeff
     
    OMM, Al2O3 and Mark's castings like this.
  3. Petee716

    Petee716 Gold Banner Member

    That looks like it filled great Jeff. Given both of our experiences with greensand I'm surprised you didn't get more burn in. I'm anxious to see it cleaned up and mounted.

    Pete
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That-a-way Jeff. Now clean'er up.

    Best,
    Kelly
     
  5. Petee716

    Petee716 Gold Banner Member

    The one on the left looks like my oldest one only mine looks worse. I think that's a result of our old friend "too much air". I've retired my oldest recently which has been through alot throughout my experimenting with charcoal, anthracite coal, propane, and oil burners and all of the attendant punishment. The anthracite episodes and my lack of experience burning coal in general inflicted the worst damage because of too much air driven by impatience.
    Other than the mystery crud inside of yours, if it still rings it is probably still serviceable based on the exterior condition, but the base looks kinda toasted and if you're not comfortable with it then by all means pitch it.

    Pete
     
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  6. Tobho Mott

    Tobho Mott Gold Banner Member

    Kelly, go ahead and point out that you repeatedly told me so.

    Glass bead for sand and no coatings for bronze is just a bad combo. That glass between his horns is a real pain to chip away. And I have no idea how I'm gonna get the glass that melted into the cracks I carved in his horns and tusks and in the little corners everywhere. I won't use the glass for bronze again, and I might even start coating my foamies that're meant for bronze.

    Cleanup so far:

    20200411_111523.jpg

    20200411_111528.jpg

    20200411_111534.jpg

    20200411_111539.jpg

    20200411_111545.jpg

    Anyone know any black magic for removing glass from bronze? Can I use chemicals? Heat? Heat then cold? Just chipping away seems to be removing tinier and tinier particles of glass dust as time goes on, and I'm worried about scratching up the bronze if I push too much farther that way. Anything that was gonna come off in a chunk of any size is already off. Too bad I wasn't looking for a way to cast really strong pieces of black, burnt looking glass!

    By the way, there was another one of those air (foam vapour?) bubbles (like the one in the back side) between the bronze and the glass, with walls almost a centimeter thick, in the nook between his horns and ears. So weird, the casting froze in the desired shape with no mold material touching it there by all appearances. I had to hammer on it surprisingly hard using an old screwdriver as a chisel to punch a hole in that bubble that I could then gradually open up with a little more smashing and prying.

    Jeff
     
  7. Tobho Mott

    Tobho Mott Gold Banner Member

    Pete - thanks for the details about your own crucibles. Maybe the one I've retired could still keep going for a while, but even just for my own peace of mind I'm glad I won't be using it again. Every time I pulled that thing out of the furnace I worried it might crack open like an egg. And getting burned by molten bronze is no yolk. :D

    Jeff
     
  8. There is a perfect chemical for removing glass and sand from bronze: hydrofluoric acid :eek:. It's actually a weaker acid than hydrochloric acid but also highly poisonous...have you got access to a bead blaster?.
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Nah, not an I-told-you-so kind of guy. If you decide to coat in the future, quench the casting in a bucket of water and that will blow off a high percentage of the coating and a compressed air nozzle will make short work of what's left leaving a relatively, clean, bare, casting.

    Rats! Was really hoping Mark would have the chemical answer. Mechanical means it a bitch unless you know someone with a very hard abrasive like SiC or Al2O3 media, and even then, it will also cut the bronze surface a bit. What is typically used to etch ornamental cabinet glass? Will hydrochloric do it?

    Since glass is so brittle, something like a needle scaler would be good but with the small part and fine features......you'd need a miniature. I don't know what the melting temp of the glass is but I fear it would be too close to the bronze to use a torch......but if you heated it up very hot and quenched it, the thermal shock might fracture and separate the glass......you could try it on a horn and see if it works.

    Best,
    Kelly
     
  10. DavidF

    DavidF Administrator Staff Member Banner Member

    That horned bunny is.... well kinda scary...
    Like a dentist in a clown costume kinda scary.
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yah, horned demon bunnies on Easter and skull belt buckles.....Jeff definitely has a dark side LOL!!!

    Best,
    Kelly
     
  12. DavidF

    DavidF Administrator Staff Member Banner Member

    Wouldn't have him any other way :cool:
     
  13. Tobho Mott

    Tobho Mott Gold Banner Member

    A really pointy diamond dremel bit seems to take it off well, slowly but surely, but it's scratching up the bronze a bit too. I'll have to do some sanding. I would have had to do something to smooth it out a bit anyhow as the bronze didn't come out nice and smooth like the aluminum bunny did.

    Jeff
     
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That's probably due to the high density of bronze and mold pressures taking on the texture of mold media..........you know how to fix that :)

    Best,
    Kelly
     
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  15. About the strongest commonly available hydrofluoric acid is alloy wheel cleaner/aluminium brightener at around 10-15%..... It rumoured to be much less poisonous below 15% concentration but I've heard stories of people who washed their truck tray with the stuff having aching bones from getting it all over themselves with the hose. It may be worth a soak in undiluted aluminium cleaner to loosen up the bond so the particles can detach easily. You're not soaking it long enough to completely dissolve sand (silicates) particles. The link below is for a local product with 10% hydrofluoric and some sulphuric too. I'd try a runner as a test sample and see if it'll loosen up the sand/glass from the bronze.

    https://www.supercheapauto.com.au/p/septone-septone-ali-brite-aluminium-cleaner---1-litre/1747.html
     
  16. Tobho Mott

    Tobho Mott Gold Banner Member

    Thanks Mark, I'll look into local equivalents.

    Jeff
     
  17. DavidF

    DavidF Administrator Staff Member Banner Member

    I kinda liked the idea of heating it back up and quenching....
     
    Petee716 likes this.
  18. Tobho Mott

    Tobho Mott Gold Banner Member

    It does sound a bit more fun than dangerous chemicals... Good to have a few backup plans in any case. I already got almost all the glass off picking away at it with the dremel, which surely was less fun than using fire. Maybe I'll try that with the first bunny before I melt him again just to see if the glass pops out of bis ears.

    The paste wax didn't do much to smooth out the casting this time.

    20200412_003959.jpg

    Jeff
     
    OMM likes this.
  19. garyhlucas

    garyhlucas Silver

    Get the MSDS for hydrofluoric acid. It runs about 12 pages and explains how it can be absorbed through the skin and dissolve your bones so your arm can literally fall off! Nasty stuff.
     
  20. Tobho Mott

    Tobho Mott Gold Banner Member

    Yikes! I'm still going to see if I can find local equivalents, but maybe more just to know what to add to my do-not-drink list... In any case, I got all the glass off already. There's still lots left inside the back though, so if I'm feeling ambitious enough to not just leave it there, maybe I will try the heat and quench thing...

    There's a short video of the evil bunny pour and some blah blah blah about avoiding sand float and why coatings and real sand are the way to go, at least for bronze. But if you want an excuse to skip it, much of its 4 minutes is really just the pix from above in slideshow mode.



    Jeff
     

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