Bob Puhakka on Bifilm theory

Discussion in 'Links to useful information' started by Gippeto, Feb 2, 2019.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Effective and seemingly tranquil....but not a Bifilm separating basin per say. -Still have some skepticism on whether all aspects of the teachings can be achieved in this respect for small short duration pours.

    You may never get to a smooth pour without a plug, and/or even a smaller sprue diameter. The sprue can always deplete the well before it can be non-turbulently filled and this will always produce a partially filled sprue for some (the early) portion of the pour.

    I struggle with pouring distance too because I can't always get the pouring cup/basin next to edge of my flask which means pouring from greater height. An extended pouring basin sitting on top on a loose sand lost foam mold will just produce run-outs at the bottom of the basin from the hydrostatic pressure in the basin, so thee basin must be buried. I've had similar thoughts about a trough. I don't think you want a tea pot spout because that's just another aspiration source and subject to all the same issues as sprue design. I think it was actually in a Marquardt paper post you made where he remarked he made extended pouring spouts for his crucible. I believe indicated he made them half round in cross section.

    Just remember, if you put multiple systems in series between your crucible and the sprue, it may become more difficult to keep them all in balance.

    A mere whimper and not nearly as dramatic as yours but it was just a 1/4" wide contact area. I did several of these in early lost foam experimenting.

    It was a couple years ago. Here's the post in a long thread over at AA.

  2. ESC

    ESC Silver Banner Member

    I'll try later, but it looked just like yours.
  3. ESC

    ESC Silver Banner Member

    That is one of the designs shown by Campbell, but more as a basin to streamline flow and improve metal yield. Every method of introducing the metal to the basin subjects it to acceleration and turbulence. So it seems any method to reduce it would beneficial.
    Oldfoundryman's sprue extensions help in hitting the sprue and he seems to position them at the edge of his flasks, but there is still the freefall of the melt.
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Sort of, but I don't think sdweeb's has a weir. Just a round basin transitioning (upward) to a round sprue. The pouring basin in my low mass furnace thread is based upon the Campbell "streamline", but I must say, that style pouring basin has been around for many years prior to Campbell, with possible exception to details of the weir.

    Agreed. A practical sized accessible pouring target, something that transitions the direction/momentum of the pour as tranquilly as possible, and sprue geometry that minimizes any separation in flow and/or aspiration at entry.

    Even if the Bilfilm separation properties claimed of the various pouring basin designs does occur at multiple thousand pound castings with multiple minute poring times, it's not a linear world and getting such to translate to our scale could require a difficult to achieve degree of precision. At least we don't have 10-15 ft sprue height to deal with.

  5. Tobho Mott

    Tobho Mott Silver Banner Member

    SWDweeb has shown and described his pouring basin quite clearly in just about every video he's made since he started getting pointers from Olfoundryman around a year or so ago - a 3cm deep round basin with a radiused-on-both-sides 1cm tall step between it and the sprue. I'm not 100% clear on what makes something a weir... Would that count?

  6. FishbonzWV

    FishbonzWV Copper Banner Member

    Yeah, that would be a weir. I tried Martins sprue well yesterday on two of my pours. The first I was concentrating on hitting the cup and when I looked at the sprue hole it wasn't full. The second one I paid attention to the sprue and the metal flowed smoothly.
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Maybe so. I've only watched a couple of his vids but in the one linked in post #315, at the 8 minute mark he spends about 15 seconds cutting it in and though you can see and recognize the result, it's hardly a standard of clarity that fits with the importance of offset pouring basin details (and there are many versions and variations) professed by the experts. That said, it appeared to be affective. A contradiction? I don't think so. I think it just shows those details aren't as important as other factors such as pour rate and technique.


  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    How bad do you want a transparent hi temp pane? Probably best for the money but still may not cut it for multiple uses. 10x10. 12x12 is 50% more. Quartz is better but very high priced.

  9. oldironfarmer

    oldironfarmer Silver Banner Member

    Thanks for that link, Kelly. I'm not sure how badly I want the visibility. That looks to handle aluminum temperatures, not too costly if the aluminum doesn't stick to it and make it one use anyway.

    I've got some borosilicate glass on the way, and have also thought about doing the same thing with lead. I need to look up the viscosity of hot lead but I think it's similar to aluminum. Density does not show up in the velocity calculations (neither does mass, of course). First chance I've had to say this "lead would be safer".

    As much fun as it was to break the glass, I really don't want to repeat that unless I really think I can learn something.
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I don't think Boro will cut it either.

    You might recall in the Puhakka video, it was commented that properties of water and molten aluminum were very similar. They must have been talking about kinematic viscosity because me thinks density still varies (~2.7:1), but if you are considering lead, this shouldn't be a concern. So there would be the same acceleration through the sprue but lower pressure at the bottom of the sprue due to the lower density of water....still, probably fairly representative results as far as aspiration and turbulence.

    Save the ooh and ahh factor with molten aluminum, it would be easy to do these simulations behind glass with water. You'd need to pull a plaster (or something) mold off the feed/mold system to be simulated. Much safer, easy to modify, and rerun tests. You could also glue together pieces of plexiglass and perform the tests without being 1/2 sectioned.

  11. ESC

    ESC Silver Banner Member

    I don't believe bifilm separation is the reason for the basin shape. There is still too much turbulence from the falling stream. With Pahakka's reverse delta, there is less volume in that particular basin and according to Campbell it is one Bob recommends. Or at least he did in 2011.
    Everything he espouses is based on clean metal, and then keeping it as free of oxides as possible until it solidifies.
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Actually ESC, I do believe they all claim the shape/geometry of the basin is an important factor in Bifilm seperation and the depth is even tailored to the alloy and oxides being separated. Now not saying I totally buy it hook line and sinker, but the story goes that you pour from below a critical height (below sessile drop), the vertical velocity is arrested in the bottom of the well, it fills and primes (maybe assisted by plug depending upon which guru you follow), then Bifilm skin on the pouring stream is stripped off where it impinges the surface, and what doesn't get stripped, buoyantly floats to the surface on the non sprue side of the well only thanks to conditions promoted by the weir, and the oxides collect and pile up on the well surface at such a rate they need to be skimmed off during long pours.....and we have sized the well height and sprue opening to conserve energy and have no entrainment/aspiration.

    Not my story....theirs, but Marquardt sums it up and credits everyone else in his acknowledgments. If you start reading at about page 20, that's the meat of the basin discussion. Highland - Marquardt.pdf

    Then there's his conclusion on the last page

    For the Naturally Pressurized Fill System to work as intended you must adopt the entire design. By incorporating bits and pieces, the improvements will be lost in the noise generated by the rest of your existing system. To be successful you need to be starting with a Foundry that has its process in control. As any poor sand, melting, and coating technologies can easily obliterate the positive results. Regardless of which ingate design you choose, by staying true to the principles and always filling from the bottom of your casting, and preventing the melt from being able to fall unrestrained generating. You can start to have greater confidence and predict the casting quality from your office instead of at shakeout or blasting.

    My point is just to consider the degree of precision required in each step and that whole chain of events occurring in the well, especially on our scale, to achieve such an out come, and then actually being able to measure the difference. Not saying there cant be improvements and gains but thinking defect/Bifilm free....?

    Don't think he can lay claim to originating that thought.

  13. ESC

    ESC Silver Banner Member

    Trying to figure this out. Still don't know where all the bifold junk went that I put into the crucible on one of my first experiments. If Al Puddle's densities are correct, the oxides are not lighter than the melt, and so do not rise. The description Bob gives of degassing attributes it to agitation, rather than bonding to hydrogen in the melt. I didn't do any of that, but my casting was much cleaner than my charge, puzzling.
    What is the significance of the pure zinc to test for an oxidizing flame at the exhaust to insure complete combustion of the fuel?
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I'm sure there's still some there. It's possible to improve a melt with remelt, depending upon your starting point and the furnace atmosphere conditions. If it was initially a superheated melt exposed to plenty of hydrogen, and poured that way, a remelt under more favorable conditions could improve it to the new equilibrium. Improved or better still may not mean good. ...and BTW, how did you determine it was better?

    I think all is comparing the elemental weights. Bilfilms are supposed to be structures with voids so they are less dense. The gurus say this makes Bifilms approximately the same density as aluminum. A grain of sand will sink in light metal but a core will float because it's porous.

    Yah, he's all over the road on that. He claims hydrogen diffusing into Argon is poppycock but in the next breath says the hydrogen diffuses into the Bifilm he likes Fick's law when it suits him but not when it doesn't. Also, Marquardt talks about Oxygen being present in the Bilfilm voids and it should not be there. The explanation is that it is trapped in the Bifilm. That's possible but free oxygen would still be diatomic O2 and at those temps, it would be quite energetic. In order for it to be trapped in a Biflm structure, the openings would have to be comparable to or less than the size of the O2 molecule or it would find its way out and by their own theory just become more Al2O3.

    Yes, color check for having achieved lean burn.

  15. ESC

    ESC Silver Banner Member

    He's calling it slightly oxidizing and coloring the zinc blue, rather than reducing. I adjust to absence of light and then fine tune to the loudest roar.
    I compared the samples visually. One was a sprue or riser from the wheel casting I posted the other is the half pillow block from my glass test.
  16. ESC

    ESC Silver Banner Member

    I've got some Desulco carbon increaser if you are interested in trying a sample of it to get softer iron. I've been using it to raise the total carbon, and it shows in the chill wedges.
  17. Tobho Mott

    Tobho Mott Silver Banner Member

    Ran across this this morning...


    joe yard likes this.
  18. PatJ

    PatJ Silver Banner Member

    Great video.
    Thanks for finding/posting that. :)
  19. Tobho Mott

    Tobho Mott Silver Banner Member

    The intersting part is that we didn't have diagrams of vortex gates or trident gates or spin traps here before, other than a few members' attempts, and the ones we knew of that were on YT before had been removed... Now we can compare our members' diy attempts to Campbell's own diagrams. And come up with our own gating based on them too if we want.

    I seem to remember in one of the disappeared videos, Campbell was saying in a talk he gave that the problematic filter in the vortex gate (which Puhakka was still working with/on at the time the talk was filmed) was only for steel casting. I guess that didn't work out... Anyone else remember that, or am I totally losing it?

  20. PatJ

    PatJ Silver Banner Member

    I have seen a bit of information about the trident gate, and its use to get rid of the residual air bubbles, and I suspected that things were going that way.
    The vortex gate would still be useful as a velocity reduction item.
    The spin trap I had also seen, and that seems like a good idea, although I don't think for a small casting there is much if any metal bouncing back from the end of a runner (just my guess).

    There are other things out there like tilting crucibles/molds that prevent having to pour the metal down a hole from above. Making contact between the pouring basin and the lip on the crucible is a similar example of eliminating the drop from the crucible to the pouring basin.

    Preventing aspiration of air down the sprue seems to be pretty much problem #1 as far as critical things.
    Everything after that is gravy as far as I am concerned.

    I was also aware that Bob had developed new technologies from what was in his videos, but he is wise enough not to share that online.
    I am not sure how Bob feels about John revealing some of his later techniques, but I feel like Bob will always stay one step ahead of the industry as far as innovation.
    Bob is a genius as far as casting stuff goes.
    His personality is sort of way out there in many respects (although much of what he says I tend to agree with; so I guess that puts we sort of way out there too), but there is no denying Bob's genius.
    I think the humble approach for Bob was not working to convince the casting world to take him and John seriously, so he uses the outrageously confrontational approach these days, with is sort of like Grant burning his way across the south (effective but won't win you any friends).

    Bob being an obsessive genius has the downside in that he obsesses about things that don't matter, or shouldn't matter to a person like him with his stature and money, and so it becomes a distracting (although highly entertaining) sideshow, and a sideshow that he cannot stop.
    Bob has taken down his videos, which is unfortunate since he has so much to offer the casting world, and especially us little minions.

    I also like much of Bob's philosophy of life, which summarized in a nutshell is "Stop being a little sheep and become a leader, not a follower".
    Bob came from the absolute nothing of a hardscrabble mining town and built a very significant casting company, which is no small feat. Building a successful one-man company is very difficult, much less an entire foundry that makes world-class castings.
    And I think the aluminum foundry is just a warm-up for Bob, and he has big plans ahead for steel and probably other types of castings, and no doubt he will be successful with those too.
    Last edited: Apr 18, 2019 at 11:03 AM

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