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Thread: Lost Foam Cast Iron

  1. #11
    To heck with the pics of the furnace, any pics of the locomotive? Must have been a larger model, a Hudson or a Berkshire, perhaps? Very nice, probably would have been almost as easy to fabricate one from plate like a lot of other modelers do. Also, what scale? 1 1/2"?
    Vade Libram Harenae.

  2. #12
    Senior Member cactusdreams's Avatar
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    I'm switching over from my belt sander thread for the lost foam iron part on this. Finished up the foamies for the sander fence plus a couple extras from the foam scrap box.



    From the chart on pg 16 of this link http://cdn.intechopen.com/pdfs-wm/29758.pdf I decided to make recipe #2 based on the metals it works with and availability and price of ingredients. Had the bentonite from making green sand. Got the mullite here.
    http://www.ebay.com/itm/like/1519651...chn=ps&lpid=82 And the dextrin here http://www.pyrochemsource.com/search...ywords=dextrin



    Made a small test batch with 9.1 oz. mullite, .3 oz. bentonite and .4 oz. dextrin. Wasn't sure about the water amount so added a little at a time until it would roll off by itself and leave a smooth coating. Ended up being 4 oz. of water. I covered a small test piece and sealed the mix in an old dry wall mud tub and weighed it to see if I lost any moisture later. When I finished my foamies a couple weeks later and opened the tub there was a little mold growing on the sides. The dextrin I'm guessing. Scraped it off and the rest was fine. Hadn't even settled or separated.



    The technique I figured to apply it was to hold the piece over the bucket and mop the coating on with a soft brush. Then massage it with the brush to get good adhesion and fill the corners. The waxed areas resisted at first but stuck with a little extra massaging. Then a second heavy mopping so it would roll off smooth and even and some gentle shaking off the excess.



    It dries to a pretty hard shell. Feels lots sturdier than diluted dry wall mud. My test batch ended up being enough to do the job with about 1/4 cup left. Looking at the pictures on the PDF link theirs looks runnier than mine. I might have a slightly thicker shell as a result. The document stresses the importance of shell thickness related to porosity to let the foam gasses escape so we'll see how mine does. Will be a while before I can get an iron pour happening but don't see a problem with the extra dry time for the molds.

    Update: Was looking over the recipe and I may have erred. They seem to use a comma in place of a decimal point sometimes. I read the dextrin amount as 3-5% and it may have been .3-.5%. So possibly had 10x the dextrin. Hope it still works. At least the mold liked it.
    Last edited by cactusdreams; 02-11-2016 at 11:18 PM.
    People who say it cannot be done should not interrupt those who are doing it.

  3. #13
    Senior Member cactusdreams's Avatar
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    I put the coating to the test with iron. Here's the aftermath and setup.



    Looked OK. Ran out of metal just as the third one filled. Was prepared for 3 melts. While melting the next charge I had time to dump the firs three and glad I did. Total failure. Pic is the next day.



    Possibilities are my coating was too thick and didn't breath, had 10x the dextrose and didn't breath, needs vents and didn't breath, feed from bottom, all the above. Open to other thoughts. But the surface of the sprue shows the potential is there. So I didn't waste the other sander fence mold and still have 2 more foamies. And the session had a bright side but not really related to this thread. I was also prepared to sand cast 2 trivets I made from polymer clay. They came out pretty nice though there's got to be a better way to feed it. The draft wasn't great in a few spots but I can fix that on the patterns including the feet which were removable and added after ramming the drag so I didn't have to do any coping down. Needed an extra vent on the head of the octopus too. These two will clean up fine though.






    I also had a huge amount of what I thought was slag/dross I scooped out that was over 5 lbs. total. All the castings and sprues weigh about 14 lbs. and it all filled my #4 crucible twice. Am I fishing out stuff I should work back in? It made a bubbling, inflated dome in the crucible but the metal underneath was runny so I thought I should scoop it out. Seemed like a lot of material to be discarding. BTW, is this normal when adding charcoal? Thought it was all chunks and no dust. At least it showed me where the leaks in my lid gasket are.

    http://vid1379.photobucket.com/album...psxpsqughz.mp4

    So will give the coating some thought and another go sometime.
    Last edited by cactusdreams; 02-16-2016 at 01:40 AM.
    People who say it cannot be done should not interrupt those who are doing it.

  4. #14
    Quote Originally Posted by cactusdreams View Post
    I'm switching over from my belt sander thread for the lost foam iron part on this. Finished up the foamies for the sander fence plus a couple extras from the foam scrap box.

    Update: Was looking over the recipe and I may have erred. They seem to use a comma in place of a decimal point sometimes. I read the dextrin amount as 3-5% and it may have been .3-.5%. So possibly had 10x the dextrin. Hope it still works. At least the mold liked it.
    I'm coming in the middle, so you've probably answered this one. What's the goal of the coating?

    My daughter used Lost Foam at the last University of Kentucky Iron Pour, and apparently more extensively and with a lot more detail applied than even several of the grad students/instructors had seen before. She poured the sand directly over the styrofoam, with great success (and one incredible "failure", but that's another post).

    I know the bronze sculptors will coat a lost wax form in preparation for coating that with plaster, and that's your entire form. If you're burying the coated items in sand, I would skip the coating entirely, and just let the foam burn out on its own.

  5. #15
    Senior Member cactusdreams's Avatar
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    With lost foam AL, brass and bronze I found like others, a thinned drywall mud coating gave a much better surface finish. But I had blowouts with the higher weight and heat with brass and bronze. So I was curious what a more industrial coating might do, especially with iron. But as I mentioned, I think I messed up the recipe. Maybe someone can look at that document and see what they think of the willy-nilly use of decimal points and commas. Do you know the grit of the sand your daughter used or what kind of foam? I remember seeing a couple pics but more would be great!
    People who say it cannot be done should not interrupt those who are doing it.

  6. #16
    Quote Originally Posted by cactusdreams View Post
    With lost foam AL, brass and bronze I found like others, a thinned drywall mud coating gave a much better surface finish. But I had blowouts with the higher weight and heat with brass and bronze. So I was curious what a more industrial coating might do, especially with iron. But as I mentioned, I think I messed up the recipe. Maybe someone can look at that document and see what they think of the willy-nilly use of decimal points and commas. Do you know the grit of the sand your daughter used or what kind of foam? I remember seeing a couple pics but more would be great!

    The sand used was fairly low-grit, but came in industrial sizes (i.e. by the pallet bag) and I didn't ask exactly how fine it was. UK uses a resin-catalyst binary binder, so it glues down pretty tight, pretty quickly.

    As for the styrofoam, she based her piece on a commercial skull from Michaels, so it was standard "junk" consumer grade. We did use some available "blue" wall pieces cut into strips for sprews, etc., but all the main part was standard white styrofoam. She got the detail she wanted out of it by using wood carving tools to carve it one bead at a time.

    Personally, I'm looking to experiment with toilet ring wax as a "foam smoother". I suspect that it might work in the "smooth the rough edges" area for a few non-artistic items I'm looking to cast soon. I'll report in when I've had a chance to try it.

  7. #17
    Senior Member cactusdreams's Avatar
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    Lost foam iron coating v2 deja vu last weekend. I was able to rinse the old coating off the sander fence foamie I didn't pour last time with just running water. Was very careful on the proportions of dextrin this time and made it runnier. It went on smooth and after it dried a bit I poked holes in it with a pin. I made a second pattern from a white foam apple and banana modified and glued together to make a sand rammer. A bananarammer if you will. If you're humming Venus you're as old as me. I t-waxed the rammer as it had bad bead marks and the special coating would not stick to it at all. So I tried thinned drywall mud and it did stick with some coaxing. So 2 different foams and coatings this time. Mullite/bentonite/dextrin on pink foam and thinned mud on white foam.

    iron foamies.jpg

    And as before I molded a couple more trivets in green sand. Danged if I didn't get the exact same fails with the lost foam. Frustrating as I'm feeling good about melting iron now. As before, it choked right at the base of the sprue. Is this a venting issue? The pin holes didn't help so maybe bigger straw vents? Feed from the bottom? Try no coating but wonder what the finish will be like. You can see where the rammer started to fill and stopped but the heat burned out the rest of the foam down to that small piece from the bottom.

    iron foam fails v2.jpg

    Trivets came out nice again with one small spot that didn't fill on the octopus. Changed the gating to make them easier to clean up.

    trivets v2 castings.jpgtrivets v2.jpg

    Not sure if I'll keep after this because it really beats up my furnace. Amazing the black crud that builds up from iron. The trivets are coming out well though so might make some more patterns and cast a few at one session sometime. Curious to try the coating with brass or bronze. Here's how I get the Lodge black finish on the trivets after clean up and bead blasting.

    http://vid1379.photobucket.com/album...psd2tj7gke.mp4
    Last edited by cactusdreams; 03-12-2016 at 11:04 PM.
    People who say it cannot be done should not interrupt those who are doing it.

  8. #18
    I wonder if its just too cold, foam will drop the temperature some, and the glue joints especially. Can you eek out 50 more degrees? Other ideas are poke a hot wire in the foam before hand to make hollows sprues. Or try acetone to remove the foam if the shell is hard enough.
    Those trivets are coming out really well!

  9. #19
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    Bananaramma. Like!

  10. #20
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    Since this thread is iron casting lost foam, I hope you don't mind me posting into it, rather than making a new thread.

    The aim is to make the raw casting for a spindle housing. I want it to fill from below, and was wondering how to do this in green sand (Horn ingate probably), but lost foam looks like a much simpler solution. Run the ingate down the middle of the bore, then out into the casting, and three vents at the top.

    I whipped up a 5 minute hot wire cutter, after ripping the Ni-Chrone wire out of an old hairdryer.

    Since this is only going to be a raw part, which will machined all over, I just added 5mm to each dimension. When I hot-glued the foam together, there a a few defects in the join lines, where I am concerned that sand will get in. Rather than a ceramic dip to get a perfect reproduction of the foam surface, I will pit bits ot thin packing tape over those defects. I'm going to just bury the part in loose sand, so it should gas out just fine.

    First I need to get some bigger crucibles. I only have A5's currently, but sized the Calcium silicate furnace for A20 at a pinch. I am trying to get 2x A12's and an A20 from the supplier who sold me the A5's (Hohnen.de). Their A5's have held up really well.

    Mark
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    Last edited by rotarysmp; 03-20-2017 at 08:48 AM.

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