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

    Very Cool. I was able to select .25 speed on settings but still very rapid and turbulent fill. Would be great to see with a much smaller sprue but still are going to have to slow that stream down a ton with that much sprue height and/or move the part up the mold..

    I did some lost foam pours behind glass. It wasn't borosilicate/quartz, just regular tempered glass and it failed shortly after the pours but hung in there long enough to film.

    Best,
    Kelly
     
  2. Al Puddle

    Al Puddle Silver

    A very enlightening video. Oh, the popcorn just finished.
     
  3. ESC

    ESC Silver Banner Member

    It is really crummy after shooting with my phone from the computer screen, but full screen and inching through with time line there are some amazing bits of turbulence.
    I think my sprue is too large, and the gates are supposed to be large enough to slow the flow to 20" /min.
     
  4. Please publish some information. How big were the sprues?

    Interesting that the stream shot right up through the pattern and into the riser on the first one. And it looks like the sprue didn't fill until after you quit pouring.

    You're going to make me try to do a glass flask now.:eek:
     
  5. ESC

    ESC Silver Banner Member

    Standby, It's snowing and I have to go to the shop.:)
    The top of the sprue is .414" x .485".
    The bottom is .315" x .329".
    There is a slight taper on the runner , but the average is .300" x .276".
    From the top of the dam to the top of the runner is 5.5"
    The gate is 1" x .264"
     
    Last edited: Mar 12, 2019
    oldironfarmer likes this.
  6. ESC

    ESC Silver Banner Member

    Maybe the gate needed a square corner so it could fill vertically rather than shoot up a ramp.
    I see what you mean when I run it at .25 like Kelly did, and look at the slope in the basin at .12 when it goes over the dam.
    This is the cut of the part right where all the turbulence was. No visible bifilm or porosity.

    IMG_20190312_160656.jpg
     
    Last edited: Mar 12, 2019
    joe yard likes this.
  7. Thanks! Very interesting. I can't help myself, I've got to make a glass flask. I know I saw Kelly's way back but I don't remember a movie. That is really eye opening.

    I figured your sizes were way too big. Ha! Just what I'm using, basically. I edited to show areas above. In fact my sprue doesn't taper as much as yours.

    Really eye opening. It looked like your sprue didn't really fill until the system was about filled, and the pattern didn't fill. Is that true?

    I wonder how much smaller sprue before it cools too quickly to fill. One other way to slow it down is use a closed riser and rely on the permeability of the sand, or if your sand is not permeable just a fine wire for a vent.
     
  8. ESC

    ESC Silver Banner Member

    I set up Al's spreadsheet and I thought I looked pretty close, but I will have to compare the round to the rectangular dimensions.
    The both molds filled completely, but drained when the window failed:eek:.
    I think you are correct about the first sprue filling late. Maybe it needs to smaller and with less taper.
    The venting allows the expanding air to exhaust easily.
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I don't think it will positively affect the turbulent entry into the mold but a plugged sprue with a zero velocity start coupled with a few inches of head from a filled pouring basin may help get the sprue completely filled.

    Best,
    Kelly
     
  10. I didn't see the window fail. Is that in the video? It looked like the flange on the first mold didn't fill.

    I'm setting up a small flask to use the glass from a quartz light. I've got several of those, and they should have at least some heat resistance, but no matter, if I can get a shot of the velocities.

    The idea for a small vent is to build up air pressure and slow the flow coming up into the pattern. I've heard people talk about filling slowly, and metal splashing to the top of the mold wasn't my idea of filling slowly.

    I'll say it again. Your video was a real eye opener for me. Thanks again. I was envisioning a slowly rising pool of sedate aluminum rising into the pattern.
     
  11. I would think more head with a filled sprue will result in greater velocity into the mold. Which would negatively affect the turbulent entry into the mold.

    I guess maybe it would not if the full sprue has more resistance to flow than a partially filled one, but a full sprue has more mass pushing on the metal in the runner. You get a lot less flow through a partially filed pipeline than a full one. And it requires force to turn the corner and spurt the metal into the mold.
     
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Well, if you are a Bilfilm disciple you certainly cant accept a partially filled and turbulent sprue. The game is over before you start.

    K
     
  13. Absolutely, however turbulence in the mold cavity is generating bifilm as well, aspirating air into a sprue will generate the most oxygen contact, surely, but I'm still feeling like turbulence in the mold cavity is not good, especially with green sand molds where sand may be broken off by high speed jets of hot metal.

    Dribbling metal down a sprue is sure easy on the mold cavity, but not good for casting quality. Unless you have true bottom feed, or an inert purge in the mold, the first metal down the sprue will be quite turbulent anyway.

    It will be interesting to see how small size sprue will work, hopefully small enough it will slow the flow but still fill the mold.
     
  14. PatJ

    PatJ Silver

    I can see a lot of things in esc's video that I also see in the simulation in post #272, which is metal splashing up in the pour basin in a thin separate stream, splashing back up the sprue, metal hugging the right wall as it rises up into the mold cavity, and then rolling to the left in a big circle, making a big jumble of oxide films in the cavity, and a very high velocity shooting up and out the vent.

    Here are some screencaps of things at various times during the pour.
    This is the left side pour.

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  15. PatJ

    PatJ Silver

    And here is the right side.
    I see a sprue that never fills completely, and all sorts of air moving up and down the spure during the pour, plus all sorts of turbulence, etc.

    Image27.jpg


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    Image34.jpg
     
    joe yard likes this.
  16. I guess one of the things I'm seeing is the same metal flow could have gone through a LOT smaller sprue. Can you make the sprue small enough to control the metal flow rate without causing it to freeze before it gets to the runner?

    She always said a little one still works just fine.
     
  17. PatJ

    PatJ Silver

    Nice test.
    This is the sort of thing that allows perhaps a visual test of any calculations that may be done, and I trust this more than the calcs.

    .
     
  18. ESC

    ESC Silver Banner Member

    I go back to the cast iron attempt. That core plate almost poured out through a 3/16" diameter sprue bottom.
    Using the dimensions of the pattern I gave ironfarmer make a suggestion of the smallest size of the runner and I'll pour another one.
    No video though, I owe the Mrs. a new toaster oven and singed the fringe of my Tutu:D.
     
  19. Sorry about the toaster oven!

    Since you did so well with 0.08 in2 I'm going to try 0.04 in2, that's 0.2" square. Or even 3/16" round, .013 in2.
     
  20. ESC

    ESC Silver Banner Member

    In a quick look at spues in Campbell Casting Handbook a graph shows that too much taper or too little taper are both bad, and a 20% enlargement of the sprue entrance allows a quicker filling without increasing the velocity at the bottom.
    I will change the gate also. That was the most turbulence I saw, except maybe the conical sprue. Gate velocity should be less than 20 in/s.
     

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