Bob Puhakka on Bifilm theory

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

  1. Tobho Mott

    Tobho Mott Silver Banner Member

    They fixed it, refunded the extra $40 and change, awesome!

  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Agreed! I bought a lost foam publication too.

    AFS and Campbell.JPG

  3. Tobho Mott

    Tobho Mott Silver Banner Member

    Looks just like mine, it showed up today. :D

  4. I read most of this thread this week, and the concepts here are really interesting. One possibly naieve question: Would angling the sprue help at all? That way the metal doesn't fall straight down turbulently. Instead it would slide down a ramp, basically. Seems like a gentler flow that would help prevent agitation, and would be a little bit slower speed.
  5. JoeC

    JoeC Copper

    This is the idea behind tilt pouring, try to do just what you suggest, it can be made to work, but all the other considerations of air aspiration and avoiding splashing need to be considered

    download.jpg images (1).jpg images.jpg

  6. PatJ

    PatJ Silver Banner Member

    I briefly communicated with Bob Puhakka last year, and I mentioned tilt-pouring and a few other exotic ideas, and he basically said "quiet, we don't want this to get out".
    So I translated that to mean that Bob has moved beyond what was originally presented in John Campbell's book.
    There is a video online of John Campbell giving a casting presentation, and he mentions that Bob Puhakka has continued his casting research, and that he no longer uses the techniques that were groundbreaking just a few years ago.

    So it seems like casting techniques are evolving, and the industry may (or may not) finally catch on as far as using John Campbell and Bob Puhakka's techniques.
    I don't think that industry will ever catch up with Bob Puhakka though; Bob is moving the bar very quickly, and he does not have a huge corporate inertia working against him.
    The power of having control over your own firm is that you can instantly make decisions and go in any direction; there are no committees, no self-serving Dilbert bosses, etc.
    I can and do run circles around the big box companies; they can't begin to complete with me.

    I really miss Bob Puhakka's acerbic videos.
    He told it like it was, and the honesty was so refreshing in this day and age of extreme PC culture.

  7. Gippeto

    Gippeto Silver

    Just ordered it. Thanks. :)

  8. Al Puddle

    Al Puddle Silver Banner Member

    If the mold was purged with an inert gas such as N2 would that negate the worry about splashing inside the mold?
  9. It wouldn't create oxide films. Not sure if splashing has any other negative side effects. You'd have to make sure you purged it pretty thoroughly and poured very soon after, so oxygen doesn't seep in from the openings and the sand itself.
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    This was discussed in this post to this thread.

    David spotted what appeared to be purge gas being used by Puhakka in the video he posted. He is neither the originator nor only practitioner of inert gas mold purging. I don't believe any of the Puhakka videos are viewable any longer because he stripped his YouTube account of them.

  11. JoeC

    JoeC Copper

  12. Lol a helical sprue! I would love to see that. I'd keep that piece for some desktop art.
  13. PatJ

    PatJ Silver Banner Member

    Its not the atmosphere that is in contact with the molten metal that is important as far as splashing, but rather the velocity of the flowing metal.
    Inert gas could help to prevent oxide films (bifilms, folded oxide films).

    If your have a high velocity metal stream entering the mold, it will splash all over the place, and entrain air, sand, etc.
    There are mold-fill simulations on y-tube that show this.
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yes but no oxygen means no bifilm either by inert or vacuum atmosphere but that can be more difficult for large parts.

  15. PatJ

    PatJ Silver Banner Member

    You would need to be careful using inert gas on an industrial level (and perhaps in a tight shop with little or no ventilation), to avoid low oxygen situations.

  16. HT1

    HT1 Silver

    we actually did the Math on this in my first Foundry, which was quite small, but being on a ship water tight, it would take 5 entire full-sized bottles ( 330s) of CO2 (our concern) to make the atmosphere in the shop Deadly with the ventilation sealed off, not secured, sealed off. the possibility of this being possible in a proper foundry with the Air being exchanged 3 times per minute is very very very unlikely.

    V/r HT1

Share This Page