Bob Puhakka on Bifilm theory

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

  1. M35-1

    M35-1 Copper


    Banned again I suspect
     
  2. Jason

    Jason Gold

    He's a weird duck that's for sure. He'll say something that shocks someone and they report on him. He then gets pissed and pulls his content. Cycle repeats 6months later. Why he doesn't use bitchute is beyond me?
     
  3. Tobho Mott

    Tobho Mott Gold Banner Member

    Is there a link to Prof. Campbell's response? All I got out of Bob P's reaction video on YouTube was that he really did not like the article... or the experiment... or pretty much anyone, especially if they had anything to do with that paper.

    Jeff
     
  4. M35-1

    M35-1 Copper


    Hi Jeff,

    I'll find a link and post for you.

    By the way Prof Campbell's latest book is out.
    The Mechanisms of Metallurgical Failure: On the Origin of Fracture
     
  5. HT1

    HT1 Gold Banner Member

    he is refering to purging the Mold, not inerting the heat.

    V/r HT1
     
    Jason likes this.
  6. HT1

    HT1 Gold Banner Member

    are you serious? :rolleyes: did you note the Name of this Forum, HOME FOUNDRY
     
    M35-1 likes this.
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    Maybe I should have named the forum,
    "Doing the best with what we have foundry"
     
    M35-1 likes this.
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I actually do have a tensile tester. We use it to test weld joints among other things. Sample prep isn't a trivial task and if not done properly nullifies the validity of any subsequent testing. It can be especially tricky in castings because properties can be far from uniform throughout the part. It would make no sense whatsoever for me to test my castings because the sample prep and testing, along with the need for a statistically significant sample quantity would be 10x more work than the making casting itself. If it's not a critically stressed part it's just an academic exercise. If it's a production setting then it's process control and matter of manufacturing economics and meeting specs.

    Really just a matter of what you think work means. If you think it means eliminating all opportunities for bifilms to form then nothing works like when BP Ohh-pooh-poohs Argon degassing because it has trace amounts of O2 thus contaminates the melt..........but industry pros have reams of repeatable data that says it does significantly improve to melt quality. The vast majority of ingot sources have already failed the test in how they are processed. Doesn't mean that the processes don't help. Quite the contrary. Just means one needs to keep a firm grasp of how theory can be reduced to practice.

    It's an impressive casting...........but a 3500kg duplex SS casting has little relevance to a home caster. Still, the cost of not having first pass yield and the value of non-destructive testing is easily understood in a casting of that value.

    What HT1 said. 99% of the castings here are not critically stressed and the other 1% either shouldn't be attempted or would be better made by a process other than casting.

    The problem with Puhakka are his rants, eccentricities, and attitude toward people in general otherwise detracts from his credibility as a professional foundry man. He would be a far better ambassador of the Campbell doctrine and more effective force for industry change if he would ditch all that. Many foundry men like Racers have little interest in sharing the recipe for success and retain it as competitive advantage. Some even put misinformation out there. Depends on whether you'd rather teach or practice.

    So M35-1, do we have the pleasure of speaking with a Dr. Campbell understudy or just practicing disciple?

    Best,
    Kelly
     
    Last edited: Aug 12, 2020
  9. M35-1

    M35-1 Copper

    Hi Jeff,

    For some reason in can't get the link to work so here's a screenshot.

    Cheers
     
  10. M35-1

    M35-1 Copper


    Hi Jeff,

    Try this for Campbell's response letter.


    https://www.qgdigitalpublishing.com/publication/?m=55001&i=665235&p=19
     
    Tobho Mott likes this.
  11. M35-1

    M35-1 Copper

    Yeah i know it is, just interested. A lot of people on here are spending £££ on technical books so it's pretty serious stuff. And you're trying to push foundry technologies further. The very fact you know who Prof Cambell is and have an appreciation for what a bifilm might be puts you streets ahead of many commercial foundry operations around the world.

    I think its excellent, hats off to you all.
     
  12. M35-1

    M35-1 Copper


    Just to clear up the argon purge...i meant of the mould not the melt. Sometimes the practice of flooding a mould with argon is used to try and reduce reoxi products. The problem is getting the oxygen % of the argon / air mix down far enough is nigh on impossible inside the mould. Best we got it down to was about 1% O2 right at the bottom of the mould. But still too high.

    Therefore the first port of call should be sorting out the gating ensuring 0.5m/s velocity in. Use an offset step basin to reduce air entrainment..etc etc.

    I only posted the big casting as an example of a naturally pressurised poured job. Purely for anyone interested and to show how you can get fantastic results when it all goes right. I understand now that it's not the right place to post such casting photos and I apologise for that.

    Practicing Disciple
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Understood. It takes tight boundaries and lot's of gas. My comment was in regard to a separate Puhakka rant deriding people for the use of Argon rotary degassing (aluminum).

    It's actually easier with smaller molds, and with shell or block investment, fairly easily achieved with modest amounts of gas.

    Don't get me wrong, I actually do subscribe to Campbell's teachings for the most part, but he does occasionally discount the value of practicality. A lot of the ten rules were common knowledge. Naturally pressurized gating systems and the relation of bifilms (theory) to flaw populations and mechanical properties are the meat of the doctrine IMO.

    No need for apology. Pros are welcome here and we have a number of you. I lift whatever I can from industry to the extent it's practical in the hobby setting. I was just suggesting it may be a bit of a one-way street if you were looking for input reciprocity on steel and tonnage castings.

    Amen.

    Best,
    Kelly
     
  14. Tobho Mott

    Tobho Mott Gold Banner Member

    Well put*. Most of us aren't making parts for the Alpha Centauri colony ship here.

    But I definitely wouldn't put it past one of us to try!

    Thanks for the link to the good Professor's response, M35-1. I got a kick put of the author's reply to it as well!

    IMO Olfoundryman-style Campbell-lite casting using offset pouring basins and naturally pressurized gating (with or without spin traps) is simple enough to implement for those who are interested. Not any more difficult to mold than splash wells and runner extensions.

    Jeff

    * - I would also add that being a hobbyist sometimes gives us the freedom to experiment with Mad Max level overkill basically risk free, just because we find it interesting... :D
     
  15. June 2020 Modern Casting study is badly in need of critiquing
     
  16. Billy Elmore

    Billy Elmore Silver

    Has anyone ever seen a simulation of his offset basin and how the sprue fills during this initial filling? If so can you share? I can share some failed attempts.LOL
     
  17. Billy Elmore

    Billy Elmore Silver

    Some good info sometimes...LOL
     
  18. HT1

    HT1 Gold Banner Member

    they fail far too often without a plug and a very very skilled person on the ladle,
    I dont use them, and just hit the center of the hole hard and fast, but im making plaques , not submarine parts

    V/r HT1
     
  19. Jason

    Jason Gold

  20. Billy Elmore

    Billy Elmore Silver

    In my simulations I cant get them full. They are much worse than pouring straight down the sprue. I can taper the sprue and keep it full from start to finish but the old spill over method will not fill the top fast enough and leaves a void everytime.
     

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