Bob Puhakka on Bifilm theory

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

  1. oldironfarmer

    oldironfarmer Silver Banner Member

    The riser filled at a rate I like, that is after the first jet from the gate. Was your runner full? I can't tell for certain but it looks like maybe it was.

    I think a blind riser without a straight shot through to the gate (baffle/weir/flow director) will give that effect. I'm sure liking the results I'm getting with a pre-gate blind riser but even so it's not doing anything for the bifilm results. I would think your riser was a better casting than your pattern.

    Have you calculated your runner velocity? Pretty easy with YouTube's hundredth's of a second count.
  2. ESC

    ESC Silver Banner Member

    Good one Pat. The MOV is really good quality, but the quickest way for me to get it to youtube was through my phone. I have since converted it to an Mp4, but it is still 200mb for 12 seconds.
    You also win the award for the first like ever received on my channel.
  3. PatJ

    PatJ Silver Banner Member

    Cool, is it a MAJOR award, like a new car or something, or just a minor award like a hardy handshake?

  4. oldironfarmer

    oldironfarmer Silver Banner Member

    I use my phone, but use Movie Maker to get it ready for YouTube and there is an option to process it for a cell phone that make it smaller and easier to upload, still takes a long time. My 41 second "Open End Test" is 21.6 mb. Movie Maker is a standard windows program if you open the video with it when it opens it will process it smaller automatically. I think it makes a .wmv file.
  5. Al Puddle

    Al Puddle Silver Banner Member

    Quick glance... it looks like Al2O3 density is 3.987 g/cc and 2.93 g/cc at 660C. Aluminum is 2.37 g/cc at 630C.
    Why am I expecting to find Al2O3 in the dross? What's floating at the top?
    I was wondering how long it takes for Al2O3 to float to the top of the crucible.
  6. oldironfarmer

    oldironfarmer Silver Banner Member

    OK, so I did a glass faced flask pour. Sprue o.22" by 0.21", 0.046 in2. Runner 0.22x0.21 as well. Blind riser, with a weir, gate 0.21"x0.42", .088 in2. Riser 1" half round.

    top of weir to top of runner 3.1", aluminum at 1,300F. Runner velocity 29 in/sec, gate velocity 9.8 in/sec. Only one test so far, I liked the results, small runner.

    It was a real blast.
    Tobho Mott likes this.
  7. oldironfarmer

    oldironfarmer Silver Banner Member

    Here's the slo mo, 1/8th speed.

    Al2O3, Jason and Tobho Mott like this.
  8. Petee716

    Petee716 Silver Banner Member

    Boy o boy. You can seek out the experts all you want. I have more regard for the half dozen guys doing the hands-on R&D right here than all the experts combined.
    Keep up the great work guys.
    Jason and oldironfarmer like this.
  9. ESC

    ESC Silver Banner Member

    Those shards are small, and really sharp. I ran my sand thru a riddle to get the big stuff, and threw away a layer on the floor. I think I got most out of my Petrobond.
    I liked the speed of the fill, and it looked like you had a good casting.
    Last edited: Mar 14, 2019
  10. oldironfarmer

    oldironfarmer Silver Banner Member

    Did your glass do the same thing? I'm wondering if there is a better glass or a way to treat this glass. I wonder if plain glass might do better. I had it inside because of high winds today so I've got glass all over. It was on a metal bucket half full of lost foam sand, I ran it through a screen but may throw it away. I work too much without gloves.

    I was really surprised by the speed of the metal with such a small sprue and runner. It is obvious the value of an entrance riser to slow the flow and give the pattern a moderate fill rate. I was really pleased with the slow pattern fill and no turbulence in the pattern. That has got to be the goal.

    My riser was not as tall as my pattern, and I think I'm seeing shrinkage at the top of the pattern so that is very quick unless the metal is draining due to the glass bowing. But I'm not seeing that. I knew that was wrong to have a shorter riser but I was running out of room. I should have cut the pattern off.

    Thanks, Petee! I'm learning a lot, and doing it helps retention.

    Note to self, don't stand in front of a glass flask. My phone was undamaged but I'm glad it was on a tripod and I was to the side.

    It is obvious I've been using sprues and runners which are way too large for the small castings I'm doing. This is the first pour where I've been able to keep the sprue full from almost the start. I need to weigh the metal poured and see how many ounces per second.
  11. dtsh

    dtsh Copper Banner Member

    I'm guessing the glass is just common float glass? If so, it has a fairly high thermal expansion, thus the breaking whenever it experiences wide swings of temperature. I would think a BK7 (think Pyrex) or possibly tempered glass might withstand it.
  12. oldironfarmer

    oldironfarmer Silver Banner Member

    It was the cover on a quartz lamp. I figured it was tempered and it mainly broke into small chunks like safety glass.

    Do you think a Pyrex baking dish would hold up? I think a little writing on the bottom would not obscure what I want to see very much. Mainly I'm interested in turbulence and metal front to calculate velocities.

    I've already learned more than I dreamed from this exercise. I really thought a 0.2" square (5 mm) would freeze up before it went six inches.

    But I really thought I could be successful in life too:eek:
  13. Jason

    Jason Silver Banner Member

    That was badass! I'm no glass expert.... (yet) but how about hitting it slowly with a weed burner and bring the temp up. Not that it's that important really.. I think we got what we needed to know watching that thing fill. Surprised the hell out of me!
  14. dtsh

    dtsh Copper Banner Member

    I think it'd have a better chance, but these temps are well beyond what I have any experience dealing with so I can only guess. What little I know in regard to the expansion of glass is mostly from grinding telescope mirrors; bk7/pyrex is reported to have very little expansion making it a preferred material.
  15. JCSalomon

    JCSalomon Copper

    Perry (swdweeb) has a new video out in the series, as he demonstrates the top-gate:
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The fill rate looks yet.

    If I'm interpreting what I'm seeing in the pouring basin correctly, it doesn't appear to be producing the Bifilm separation affect as shown in the Puhakka/other videos. To me, it looks like all the turbulence and foggy metal is in the bottom of the basin and the clean metal is running over the top of that into the sprue. You may need to check the proportions on the well (more volume in the basin side). That initial volume of metal looks to be quite excessive for the rest of the system to handle. One very easy thing to do that I think would help a lot is pouring from a smaller crucible, namely smaller diameter of the height needed to get the volume. That would reduce the initial volumetric flow of the pour. Another approach might be to weld a dam across the top of the existing crucible that restricts the opening size so you can achieve a pouring stream more proportional to the rest of your system.

  17. Petee716

    Petee716 Silver Banner Member

    I think it would be a stretch to make any solid observations about shrinkage and risers based on your test. Testing the runner and sprue size as well as the use of the weir to deaden the turbulance and collect crud looked like the real payoff to me. I'm sure a sharp eye could make a number of other useful observations as well but I think the temperature factors between a glass face vs a closed sand mold would make at least some difference in how the metal solidifies. This type of gating system might add some complication to the idea of directional solidification and riser placement.

  18. ESC

    ESC Silver Banner Member

    I should have given you a more specific warning. Sorry. I cropped the breakage in my video because it detracted from the visual impact of the interior turbulence. The slope the melt achieved before it went over the weir convinced me not to bother with the foil plug, but rather concentrate on sizing the system to control the velocity.
  19. oldironfarmer

    oldironfarmer Silver Banner Member

    I did use a propane torch, but there was a cold wind, and about 200 degrees was all I dared. With a crucible of hot metal I ddin't want to crack the glass prematurely. So I cut the temperature difference from 1,200F to maybe 1,000F. A help, but probably not a lot. Preheating along with making sure the glass can move will work together. I also had a large area of metal where the break seemed to start, so next time I think I'll hide the pouring basin in the sand and just leave the sprue against the glass.

    It surprised me too:eek:

    I read up a little on BK7, it is a borosilicate, which is what I have ordered. BK7 seems to have lower melting temperature than plain borosilicate, but I haven't really studied the subject of glass.

    Very interesting video. His runner is about 7mm square, if I understand him at 47 mm2 area. My runner in the test was about 5.5 mm square, or 30 mm2. So not a lot of difference.

    Then my gate coming out of my riser was almost twice as big as my runner. His gates totaled twice as much as his runner as well, given that his runner continued on to the spin thing at the end. I guess that is to keep the shock wave from a square end from coming back down the runner. Regardless, with an open top on the end most of the momentum would go right up. The nice thing about having premade runners is the spin gate at the end takes no effort.

    Thanks for posting that.

    Thanks, Kelly, I like that fill rate too. I can't go back to giant runners.

    In trying to make half a pouring basin I did get the well too small. With my largest basin I still had difficulty getting the top of the sprue to cover and stay covered. I really like Perry's basin and am going to copy that. Quick and easy. And his pour was very smooth. I was trying to dump quickly to get the sprue covered and stay covered. I can pour slowly and with some confidence I can cover the sprue that will happen. I had not thought about a smaller crucible and will give that some thought.

    The dam thing you mention is something I've been thinking about, specifically a dam with a round hole with a pouring spout on it. I think it would be appropriate to pour without skimming if I had something like a teapot spout. I've also been kicking around making a refractory ramp (maybe some cake icing) or even a closed tube to get the pouring level up and out of the flask and let the tube dump in at the bottom of the basin. Or do the same thing with a long teapot spout. If I'm always using the same size sprue, the a consistent size nozzle will work every time (not the same size as the sprue, but consistent, pour to pour). Crucible can be double sided, with a lip pour one side and a nozzle other side.

    Stuff to do!

    P.S. How did your glass break?

    I don't know much about directional solidification, but I have learned if the riser and it's connection to the pattern is not the hottest part then it won't work as well. Bobs off the end of a pattern have to get the coolest metal although if they're thicker they will retain heat longer, if the metal can get back into the part without a gat freezing.

    I guess I'm not done.
  20. oldironfarmer

    oldironfarmer Silver Banner Member

    Can you post the breakage?

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