Bifilm Pouring Basin

Discussion in 'Foundry tools and flasks' started by oldironfarmer, Mar 5, 2019.

  1. Trying to understand the Bifilm concepts I decided to try making a pouring basin. I've never been able to fill a sprue until the pour is finishing. I plan to use this first with lost foam, but if it works well may want to use it on sand casting too.

    Pattern for basin (7-1/2 in3, 3 seconds at 2.4 in3 per second)



    Sprue is about 0.19 in2. (7/16" square)

    I picked the first attempt too green but got a nice cutaway view


    The second attempt I pulled the pattern first and damaged the sand but have enough to pour through. Needs more operator skill or a fillet. Better add a fillet. It's spending the night in my CO2 chamber (I use vinegar and baking soda in a cup).


    Question: Can I heat cure sodium silicate sand?
  2. PatJ

    PatJ Silver

    I have not tried to cure sodium silicate with heat, but I seem to recall others doing that.
    Bob warned in one of his videos to have a smooth transition where the top of the sprue meets the basin, ie: no sharp edges or protruding edges/ledges.

    Your basin looks pretty good to me.
    I think I am going to make some basins out of sodium silicate bound sand too.
    I have used ss bound sand for riser jackets, and they will last long enough for the iron to solidify, but will crack before the cooling is complete (which is not a problem).

  3. DavidF

    DavidF Administrator Staff Member Banner Member

  4. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    I have hardened sodium silicate cores in my toaster oven. 15 minutes on the lowest setting was enough, or maybe more than enough.

    I built a small olfoundryman type pouring basin pattern a few months back that I haven't tried using yet, but I may scrap it and build one that is more like this, squarish rather than roundish.

  5. Melterskelter

    Melterskelter Gold Banner Member


    I would strongly suggest NOT exposing NaSilicate to CO2 overnight or for more than just 10 to 30 seconds. You will find that overexposure leads to a "punky" soft cure. You should just gas it for a short time. I read this and sort of disbelieved a when I read it as it did not seem to make sense. Then I tried putting sand / NaSi in a plastic bag with CO2 in it and letting it sit for a half hour or so. The resulting sand form was crumbly.

    I ended up springing for a small soft drink CO2 cylinder and regulator---found new on Craigslist. Now I just poke a few holes in the sand and use a 1/8" brass tube with a few side holes in it to spritz gas into a hole in the sand for a few seconds like a five or ten count. A single hole will cure sand for a couple inches radius. I cured some 24 by 12" mols with spritz's of CO2 and got good solid molds.

    I also heat cured NaSi and it works well for smallish items like you are showing. Just pop them in the oven at 250 degrees for an hour or two (as I recall). The time for heating probably depends on the size of the mold. I was curing 20 pounds of sand mold in the oven at the time. I am soon (today I hope) to be trying esther curing of Na Silicate just because it may be a convenient mix and forget method with the trade off being a little more cure time than CO2. Since I will just be making a few plugs for my pouring basin, time for sure is not as important as when I was making cores. It is more convenient for me to keep the CO2 cylinder out at my foundry and work with plugs and stuff here at my shop where I have some newly-acquired esther.

    Here is a very useful monograph on Na Silicate use that I have found containing information I have found to be reliable (there is also a fair bit of BS on the interweb):

    For making a pouring basin or plug, there should be no need to intentionally weaken the bond by mixing in sugar or other weakening agents. For making cores, weakening is important as the core, if unweakened, will be rock hard and difficult to remove.

  6. So you're saying I need a generous radius at the vertical transition?

    There is a little sand flashing between my basin pattern and sprue pattern which will get cleaned out.

    That looks like an all in one product, no sodium silicate needed? Looks like you use more but it's about the same price as I've had to pay for sodium silicate so I need to try that. My cores suffer from variable hardness.

    I'll try the toaster oven with my cutaway then on the "good" one. Thanks.
  7. Sounds like I'll be making a new one this morning. Thanks for the link.
  8. Melterskelter

    Melterskelter Gold Banner Member

  9. I think I'm getting good results with vinegar and baking soda, practically free. Maybe not in heavier sections, but my hammer head core (two in the pictures) cure in five minutes in the core box. CO2 really seeks cracks.

    You know you can refill that cylinder by removing the valve and dropping in dry ice. The air will come out first and you just watch the pressure as it warms up. I worked in a CO2 fire extinguisher shop one time and they had some heavy wall pipe with 1500# flanges they would fill with dry ice and let it melt under pressure to form the dense phase CO2, about 2,100 psi. If the cylinder is rated in pounds of CO2 you can add less than that in solid CO2 to refill.
  10. Melterskelter

    Melterskelter Gold Banner Member

    Hmmm, did not know that. Very good to know. Thank you! I suppose I can do a little math to figure out roughly how many ounces of dry ice to approximate the needed pressure and then keep an eye in the gauge as it warms an vent as needed. One fill seems to last a very long time for the way I use it. But, still, being a cheapskate, I would like to do the dry ice method.

  11. DavidF

    DavidF Administrator Staff Member Banner Member

    No, its a catalyst to be mixed with another component. Ive been using it with plain old SS just fine. I have also had trouble with my ss cores and variable hardness. Im guessing that it is partially caused by my ss being so old..
  12. OK, thanks. Do you still have variable hardness using the catalyst? I can't imagine sodium silicate going bad through age. I've thought about adding a little water to mine to thin it, though.
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    For the Esther catalysts I've used, you can affect the hardness with total amount of catalyzed SS % in the sand but not the amount of catalyst to mix with the SS, as long as you utilize the minimum recommended amount.

  14. DavidF

    DavidF Administrator Staff Member Banner Member

    The cores I made with the catalyst were especially hard... like throw against a brick wall and the brick fails first every time hard... Also the cores had a bit of an oily feel to them. I baked them in the oven for a bit and it went away.
    There is a shelf life to SS, just cant remember what it was.. Something like 5-7 years?? My ss is well over 11 years old, still works, but seems more temperamental then when it was fresh... When I made my own ss I could gas the cores and they came out nice, hard, and dry and did not require an additional bake before i used them. Im pretty sure that when i first bought my ss that it was pretty much the same way, but as it got older it need the extra bake to get good and dry. But this was many years ago so I may just be plain old nuts...o_O
  15. PatJ

    PatJ Silver

    No, I mean don't have sharp edges, overhangs, or underhangs at the sprue/basin transition point.
    Any sharp edge/protrusion will cause turbulence in the flow.

    Be very careful if you put dry ice into a closed container.
    One guy did that on another forum, and the pressure can very quickly exceed what can safely be used even with a high pressure cylinder, and you could have a very large bomb on your hands. Beware.
  16. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    Making dry ice bombs will get you locked up, in Utah. Just ask Grant Thompson... o_O

  17. Making dry ice bombs is different than recharging a CO2 container. But I get the point that if you intend for something to explode you are at fault. If you don't intend for it to explode but you are still determined to be in the wrong because it could have exploded we have a lot of felons running around who have not drained their air compressor tank and they will be charged with a felony because that bomb could explode.

    Do you have a link to that incident? I'd be interested in seeing what he had done. Certainly if the container is not capable of the required pressure it can be disastrous. It is very important to weigh the dry ice and know the pounds of CO2 that the container can hold at ambient temperature.
    Last edited: Mar 6, 2019
  18. My damaged pouring basin I had left in CO2 all night was OK today.


    The foam sprue (7/16") pushed in to the bottom of the weir.


    Buried it up to the penetration mark (eventually)


    Kelly asked for a video

    Not sure what happened, after it had fed for a while it burped and burned some. I did maintain liquid level throughout. Didn't burn anything like an open sprue burns.

    Pouring basin was split but no failure.


    I had put an ingot under it to level it, but when I saw that during pouring I thought I had a big leak.:eek:

    The result looked good, just a little leakage around the bound sand to loose sand joint.


    I cut the sprue and filed it smooth, then inked it and rubbed the ink off. The big cavity is about 0.037" in diameter.


    I think I'll etch that. I'll cut the large sprue section and have a look at it. There's not a lot of porosity, actually, but it is not clean either.
  19. After I finished I wanted to pour a burner manifold, and wanted to use a pouring basin on green sand. I thought about trying to scoop one out and realized I could just make one out of green sand. Why not?


    The flask was small for bound sand, but if this works out OK I'll make a bigger one for green sand.

    I lined up the sprue openings and set the basin on a light ring of green sand.


    Why not another video?

    It poured beautifully.


    But a shrink defect on the upper part. With the small feed system who could have expected that?


    Since it gets faced and tapped, it will still work. But I see no indication of sand erosion.


    Porosity is not spectacular, however. (It must be your eyes, it's clear to me)

  20. ESC

    ESC Silver Banner Member

    On a lot of the examples I have seen there are massive blind risers coming off the castings. The small gate was bound to freeze before the casting. Andy I didn't see any mention of temperature, but it looks very fluid, and the surface of the ingots is very nice.
    From my reading of the offset basin, that little stepped area in the sprue is not desireable. Better a straight drop into an aligned sprue and then a transition into runner with no expansion point at the bottom.
    The basins I made the other day were baked after gassing. That has given me the best results for durability.

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