Reuasbale Offset Pouring Basin

Discussion in 'Lost foam casting' started by Al2O3, Mar 30, 2019.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    While I was building my low mass furnace I made this offset pouring basin from moldable ceramic fiber. I made a foam plug, troweled the moldable fiber onto it, and demolded after drying. I then fired it at 1800F.

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    I used it for the first time today. I wanted to use it on familiar casting so I experimented with one of my automotive water necks since I have poured a bunch of them.

    I made a sheet metal cradle for the pouring basin so I could grab it with plyers to extract and empty it while the metal was still molten. The opening in the well fits snugly on a 1” diameter foam sprue. This pattern has been dip coated so it is coated inside and out.

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    So the pattern was set in the sand, filled and vibrated so only ½” of the sprue was protruding.

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    Then the pouring basin was placed on the sprue and the remainder of the mold filled.

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    Here’s a video of the pour. I have to say, this was a bit of a wow moment for me. I have never seen such a tranquil lost foam pour. No flame, no smoke, no percolating in the pouring cup/basin….just a very slow tranquil fill.



    Compare that to all the flame and smoke in the pour I made immediately before using my usual foil sprue and 2 ½” Kush cup.



    Here’s what the mold looked like when I extracted the pouring basin.

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    The aluminum skin was easily removed from the pouring basin so it can be reused.

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    Here’s the resulting part. Some initial observations; the part is quite a bit cleaner than most of the other castings. The other very striking thing is the absence of all the scummy foamy dross that is always laying on top the surface of the pouring cup. It’s just clean metal and another benefit of the absence of turbulence, flame, and cup percolation.

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    So I think there are several things at work here. The offset basin seems to work very well at quickly covering the exposed sprue, quickly stablishing some initial head, and establishing stable hot gas layer that very calmly evaporates and consumes the foam sprue and eventually the foam pattern. In the past I have only coated the outside but with all surfaces coated, it really slows down the pour. Watching the video, I had the crucible over the pouring basin for 29 seconds. That was more than twice as long as the pours where the inside surfaces are not coated. Might further benefit vacuum assist.

    Best,
    Kelly
     
  2. Al Puddle

    Al Puddle Silver Banner Member

    Ohh Kelly, that's a nice pouring basin! You gotta spare one?
     
  3. oldironfarmer

    oldironfarmer Silver Banner Member

    That worked great. There was a little flame through the pour, but sure not much. Great job!

    My supplier didn't carry the material you used but I've ordered some from them. I really like the non-wetting feature.

    Not getting air down the sprue is an obvious advantage. And the 1" sprue is not too big when you can keep it flooded. Kind of surprising it would pour so slow but still be successful.

    I'm stuck on using a foam plug in sand casting now.
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Had to watch it a few times but there are a couple of small quick flashes, looks to correspond to when the basin fill level receded.

    It's strange stuff. Did you get the moldable or pumpable? It's a bit fragile but with care, very useful. It's easily patched and repaired. If you use my method of construction, put 3-5 degrees draft on your foam plug, and then use several coats of paste wax for release. I also used a little port to pop out the plug with compressed air. You can also twist in a long drywall screw and pull by on the head.

    I don't think the sprue size has much relevance (within reason) in this case because fill rate is paced completely by the permeability of the mud coating. The sprue isn't tapered but the flow velocity is some fraction of an in/sec. I bought some commercial lost foam coating and want to see how it compares regarding permeability. I also have some ideas on how to modify the permeability of mud coating. When ESC did his iron LF pour, he perforated the coating. I did that in a few selective places on Jack's back up sensor housings for the vacuum assist pour. They only vent after the metal reaches them but it probably does convey more differential pressure to the metal as the flow progresses.

    I'm also wondering how much of the flash and smoke in my previous pours is caused by the adhesive on the foil tape and the fact that foil is uncoated and as soon as it melts, can access a lot of oxygen through the sand. With the pouring basin and 100% pattern coating, it is much more controlled and the basin is an excellent insulator to boot.

    When you consider foam is 98% air, it's not much of a contaminate, especially if you have a feed system that diverts the initial flow from the casting. If it gives you the initial delay needed to get things started properly, it may be a very practical method for near zero velocity start down the sprue.

    Best,
    Kelly
     
  5. ESC

    ESC Silver Banner Member

    Good one Kelly. That was really calm pouring basin even with the dust devils circling your molds:). Did you do any pre heat of the basin? If not, that is neat stuff.
    Jack was pondering the fit to the car of the mirror bases and the suggestion was made to reverse sandpaper on the body to match them to the car. With the accuracy we are able to achieve with the LFC he should do that with the foams patterns. One or two swipes with foam compared to minutes at least with the finished casting.
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    No need to preheat. Probably couldn't do it with the foam pattern contact anyway but the stuff is such low density and such a great insulator, I could almost handle it (could pick it up for seconds but not hold it) with my bare hand immediately after it was extracted from molten aluminum. I can say with certainty it's a small fraction of the heat loss impact compared to the 2 1/2"diameter x 4" tall, .063 wall steel Kush cups.

    Agreed!

    Best,
    Kelly
     
  7. oldironfarmer

    oldironfarmer Silver Banner Member

    I'm a firm believer in a foam plug in sand. When it vaporizes I think it protects the metal front from oxygen.

    My foil cones are made from two layers of aluminum foil, no adhesive, and I think I get more smoke than you. I wear a respirator, I was getting too much nasty stuff to be able to pay attention to the pour.

    Your second pour from that cup will be better, all a matter of practice. I noticed you did fall behind a little. I like the cup being identical for each pour, that will help with the learning curve. I think if you'd been able to keep it flooded there would have been no smoke, or very little. I understand what you're saying with lost foam, size doesn't matter.:rolleyes: I'm still impressed that the metal front, moving more slowly, did not cool and cause problems.

    Did you notice all the oxides building up in your pouring basin? It looked to me like a lot. With pouring in basins I'm really noticing the solid oxide film surrounding the stream and covering the liquid. Aggravates me even more when I can't keep it full and take a big shot of oxides down the hole.

    Keep up the good progress!
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I can't say I did. In fact it looked like pretty shiny melt to me. But that last picture of the lump on top the sprue left over from me extracting the pouring basin is virtually devoid of the scum and dross typically present on top the pouring cup in lost foam pours. It's a radical improvement in that regard but I suspect it is in part due to the fully coated pattern and very slow fill rate.

    Best,
    Kelly
     
  9. oldironfarmer

    oldironfarmer Silver Banner Member

    Look at it closer around the 52 second mark. The fresh oxide film is very shiny. Don't know whether you noticed in one of my spout pours an oxide film is self supporting inside the crucible and then falls dramatically. I was really surprised to see that.



    It falls inside the crucible right at the 1:00 minute mark.
     
    joe yard likes this.
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Biggest problem was the pour was so long and slow, I couldn't maintain a continuous stream from the crucible and small slivers hanging off the spout kept freezing then dropping onto the pool in the basin and remelting. The affects of that I could see. This was aggravated by the windy conditions. If oxides on top the pouring basin were the measure of success, I'd have won that award long ago because every LF casting I've ever poured into a round Kush cup or otherwise has had all kinds of residual crap on the top 1/4" or more of whatever system I had feeding the sprue.

    In my mind, the absence of all that crap is the most compelling evidence that anything is different and indicative of vast improvement. I'd rather have pristine metal laying on the filled basin after the pour and never have introduced all the crud in the first place than have a bunch of oxides be there in the aftermath. What's causing the change? Well it's a sample size of one, but there may have been some other unintended factors.

    No doubt the pouring basin is a major contributing factor. Besides the metal flow arresting characteristics that have been thoroughly discussed, it limits the initial foam contact area to just the cross section of 1" diameter sprue and immediately develops several inches of head and comparatively tranquil metal above the sprue. Now the previous pours with the foil sprue and cylindrical cup also only had a 1" sprue, except it appears that turbulence caused by the lack of arrest and perhaps aspiration from the geometry of that system, and maybe volatilizing foil tape adhesive, continually allowed the initial liquid and gas layer of evaporated foam to be disrupted, escape, and reform, perhaps many times before things eventually stabilized. Simply that may be the source of the creation of all the typical crud.

    Pouring in the offset portion of the basin seems to be very helpful in avoiding this. As a side benefit, I was able to position the basin very close to the side of the flask which helped get the crucible spout much closer when pouring. I have another experiment cues up for today to see if I can eliminate those to very small flashes and get absolutely 100% of the vaporized foam to vent through the coated surfaces.

    The entire pattern, sprue, and basin were completely coated and isolating the melt from the mold media and air except at the surface of the pouring basin, at least to the extent the coating was permeable.....this made for a very slow and controlled pour and fill of the mold......this can't be a bad thing.

    Though the composition of the crud is no doubt well represented with oxides, the Bifilms in the Puhakka discussions were on the order of atoms thick and yes, larger when they supposedly unfurled. The collections in my previous pours are many orders of magnitude larger.

    Best,
    Kelly
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I used the offset pouring basin again today, this time with vacuum assist. Here’s a series of short videos. All ended well but the pour didn’t come off exactly as I was expecting after the previous pour. I’m a poor videographer. I really need to get some video editing software……seems like a lot of work.

    Lost Foam Aluminum Part 1- Pattern and Prep



    Lost Foam Aluminum Part 2 - Mold Prep



    Lost Foam Aluminum Part 3 - Staging for Pour



    Lost Foam Aluminum Part 4 - The Vacuum Flask



    Lost Foam Aluminum Part 5 - The Pour



    More videos in next post

    Best,
    Kelly
     
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    .....and the rest. I couldn't post more than five media/videos in a single post.

    Lost Foam Aluminum Part 6 – Demolding



    Lost Foam Aluminum Part 7 - Examining the Casting



    Lost Foam Aluminum Part 8 – The De-gated and Cleaned Up Casting



    Best,
    Kelly
     
  13. DavidF

    DavidF Administrator Staff Member Banner Member

    I saw that flash back and said "what the hell was that"..
    Commercial coating?? Do tell....:)
     
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Ya know, I think there's a chance that initial flash ejected some liquefied polystyrene and that's what flashed over in the crucible.

    Don't know much about it. Here's what's on the data sheet which is next to nothing. I got a little bit more out of them but not much.....will just have to try it.

    A proprietary blend of alumina and low density aluminum silicates, developed specifically for use on polystyrene patterns used in the lost foam process. This coating is most often used for the production of aluminum castings, but has been used with other metals successfully. The combination of binding and suspending agents, along with this unique mineral blend, allow the build-up of an appropriate layer of solids, while providing a nice combination of insulation and permeability. This coating will adhere well to the foam patterns and assists in preventing sand burn-in during the casting process.

    Best,
    Kelly
     
  15. oldironfarmer

    oldironfarmer Silver Banner Member

    Very interesting that the vacuum casting produced more smoke and flame. Everything else was identical, I guess except for the weather. It's almost like the vacuum assist somehow plugged the coating and lowered it's permeability. I know that does not make sense. At a point where the aluminum was sucked through the coating there would have not been any vapor, just liquid metal.

    Great thing about your pouring cup is it's insulated so the metal stays liquid, and if you should have some freeze in it the material will handle the temperature and you could bake the aluminum out.
     
  16. DavidF

    DavidF Administrator Staff Member Banner Member

    do you have or can get a SDS sheet on it??
     
  17. Al Puddle

    Al Puddle Silver Banner Member

    I'm curious whether the pouring basin has helped eliminate the weepage you've experienced with those water necks.
     
    Tobho Mott likes this.
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Not per say but here is what was listed on the data sheet.

    DPOLY600 Composition.jpg

    I don't think it plugged the coating, but hey, every time I think I might know what I'm doing I discover I don't. In addition to the hydrostatic sprue pressure/head, the vacuum may add as much a couple psig (depending upon the pressure drop across the coating) differential to the metal delivery system. It makes the metal advance and evaporate the foam at a greater rate. However, the differential pressure across the coating should also transport more gas. Here's the generally accepted transport mechanism.

    LF Transport Mech.jpg

    Higher pour temps will generally increase the length of the gas and liquid gap lengths for a given coating permeability. If the gaps get too big they can cause localized mold failure and become more insulating. Very high temp metals like iron require the highest permeability and refractory. I don't have a way to measure permeability by the GM method referred to above. Even if I did, the manufacturers say the coatings require experimentation to arrive at the optimum permeability. That usually means varying coating thickness. Parts that have high surface area/volume ratios will require less permeable coatings than those with low surface area/volume ratios.

    One thing to keep in mind, at any given time, it's only the portion of the mold surface exposed to gas and liquid that can actually vent anything. For low permeability coatings, if you poke a series of pin holes in the coating along the metal path, it will increase the venting for the brief period it is exposed to the gas and liquid gap (probably much more so the gas). Once covered with metal, it's done, but you can have a series of them along the part if you wish. The increased venting reduces the gas gap length and moves the metal closer to the foam which accelerates evaporation and the propagation speed of the melt. ESC did this with success on his LF iron pour.

    I may build a crude tester to compare the baseline permeability rates of coatings, but to get good data, you must be able to control coating thickness. I think drywall mud has sufficient refractory. Other than viscosity/thickness, I haven't come up with a good method to vary and control permeability. I need to be able to measure it. I do have a simple idea I'll put to the test in time but making the test apparatus and preparing samples will take some time.

    That was always hit and miss issue that affected yield. Most of them were fine, but pressure testing required a finish machined part so finding one that leaked at that point was a bit unrewarding. I will say this though, if you think your parts are hermetic, expose them to pressurized gas or a fluid with high surface tension like glycol and you may establish a new standard for such, particularly if they are thin walled castings.

    As an aside, there is one thing I haven't reconciled for myself with top gated lost foam castings. How does venting through the mold surface win over buoyancy? If you bottom gate this question seems as if it may be moot because buoyancy is always in the direction of consuming the foam pattern.

    Best,
    Kelly
     
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I made a couple more offset pouring basins. I made a larger one in the Marquardt quick prime style for my larger parts. The offset part of the basin is a 3” cube and the square priming sprue is 1 ½” at the top and tapered. I also made one more identical to the first so I can pour two molds with the same heat.

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    I mentioned I acquired some commercial lost foam coating. I dip coated two patterns with it. I mixed it with a paddle on my drill but must say that even after sitting a couple months it was still well suspended. Wow, that stuff was impressive in how it leveled and laid down on the pattern,.....just one quick dip and hang it.

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    I’ll pour one top feed as I have been and one bottom feed……never done that on this part.

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    Best,
    Kelly
     
  20. oldironfarmer

    oldironfarmer Silver Banner Member

    That commercial coating looks really nice. Care to share what it is and approximately how much money? Hopefully it will have a long shelf life.

    I like your new pouring basin. I guess it's not too hard to get a lost foam pour flooded, and I was surprised you had a little trouble keeping it flooded. Seems my only lost foam pour burped most of the way through as well.

    I sure like a square basin I've been cutting into the sand for sand casting. I just can't get away from putting a foam plug in, it stops the flow just long enough to establish some level. I've started making a square cavity around the sprue opening as well, with a wide weir you get a nice little tsunami rolling in. I'm getting ready for some more lost foam pours so I'll try a basin again but my moldable material is not in yet.

    Looking great! The bottom feed will be interesting.
     

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