Is my gating system adequate or completely overkill?

Discussion in 'Lost foam casting' started by Nick Lazenby, May 20, 2021.

  1. Nick Lazenby

    Nick Lazenby Copper Banner Member

    Hello,

    This piece has relatively thinner walls than I've done in the past so looking for some feedback on gating.

    Size: The squares are 3mm thick (+/- .25mm)
    Pouring Metal: Brass

    Also, I know there are some ugly joints here and there but I'll be cleaning those up in addition to narrowing the spruce and some shaping of the runners/main branching spruces. The base pictured will not be the final pedestal.

    gate 3.jpg

    gate 2.jpg

    gate 1.jpg
     
    Last edited: May 20, 2021
  2. Jason

    Jason Gold

    Modern art?
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I’ll take a closer look tonight on full screen but assuming the pink foam is the casting and white the feed system, it does look a bit overdone.

    What are the (approximate) overall dimensions and weight of the part with and without feed system?
    What are the cross sections L X W of those sprues and runners?

    Best,
    Kelly
     
  4. Jason

    Jason Gold

    Are you shoving that thing in a bucket of sand?
    Will you coat it with drywall mud or maybe ceramic shell??
     
  5. FishbonzWV

    FishbonzWV Silver Banner Member

    It would probably be helpful to see the piece without your gating.
    That way gating could be drawn in on the picture by others.
    It does look too complex.
     
  6. Jason

    Jason Gold

    "When in doubt, sprue the hell outta it!" ~ David
    20190605_182332.jpg
     
  7. rocco

    rocco Silver

    Not so sure that applies to lost foam, every bit of foam, pattern, sprues and runners all need to be evaporated and that takes heat, anything extra, robs heat from necessary bits.
     
  8. Jason

    Jason Gold

    Certainly not.;)
     
  9. Nick Lazenby

    Nick Lazenby Copper Banner Member

    The piece is around 16in tall and 12in at the widest point. I’m not sure the overall weight and I’m currently away from my studio and can’t get you any weight estimates. Unfortunately, I don’t have any pre-gating pictures.


    The spruces and gates are roughly less than an 1inx1in


    I’ll just be using regular silica sand with a thin coating of my drywall mud concoction.


    I also want everyone to keep in mind that I’m casting “art” and not something that needs to perform or function a certain way. So, my tolerance levels around defects is much larger than what most of you guys require. There have even been times where the cast “failed” yet the outcome was interesting enough to be a piece unto itself


    What are some general guidelines for determining those runner/spruce sizes? I felt like I needed to be feeding metal into each square section to ensure a full fill hence all those gates/runners feeding into the squares.


    You guys rock as always – I’ll post some pics when the patina is done
     
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Lost foam gating doesn't typically adhere to the conventional sand casting rules of thumb because the metal advances at the rate the foam evaporates not that dictated solely by gravity and feed system cross section and head pressure.

    When I gate, I think of completely feeding the part first, but also molding, pattern strength, and degating. The reason I asked size, if the whole part was 10" tall, a massive gating system isn't physically so massive, nor much metal to melt. If the part was 36" tall......different story. Also, getting a 2" square plate that is 1/8" thick to completely fill is much easier than one that is 8"+ square in that thickness.

    It's a difficult part to feed and I think you are well advised to use a generous runner that attaches to each thin, square section to insure each sees hot metal, otherwise the small contact points between each leaf would most surely result in an incomplete pour. If the size of the runner isn't objectionable from the standpoint of the amount of metal required, size of mold, and the work to degate, have at it. I'd suspect the branches from the main sprue could be as small as 1/2-5/8" square, with the main sprue in the 1 to 1 1/2" square.

    I would suggest you increase the contact area where each part is fed. Ideally I'd suggest something like picture below that either attaches to the entire top or side of each square section.

    Gating Example.jpg

    It provides a more massive runner to deliver hot metal but the necked down area will be easy to cut/degate. I've done a lot of lost foam casting, but thus far all aluminum.

    You will typically want to pour a couple hundred degrees hotter than most other forms of casting and the thin high surface area nature of the features would beg this even more. With brass, that may create some additional challenge because the zinc tends to boil off in the best of cases. Silicon bronze might be better in this respect. The other thing to consider is a utilizing a good pouring cup. Lost foam pours have a noticeable pause that lulls the caster only to then rapidly take metal and often cause and interrupted pour, exacerbated by obscured vision due to fire and smoke.

    I'm not sure how much lost foam casting you've done. You might have a look at these threads.

    https://forums.thehomefoundry.org/index.php?threads/saucer-cup-spoon-–-the-lost-foam-edition.1020/
    https://forums.thehomefoundry.org/i...ssions-of-a-lost-foam-caster-5-years-on.1650/

    Let us know how you do.

    Best,
    Kelly
     
    Nick Lazenby and Tobho Mott like this.
  11. Nick Lazenby

    Nick Lazenby Copper Banner Member

    This is great advice, everyone.

    The illustration really hits home because I always have that type of runner in mind but never actually follow through since I always think its going to make chasing difficult but if the part doesn't fill.. nothing to chase.

    My past pours involving Bronze (tin) always end up better and I wish I could cast everything that way but its quite cost prohibitive. I've found myself in quite the experimental phase so casting in Brass/Copper makes sense.

    I typically use Styrofoam cups, wrapped in foil to pretty good effect but know there might be better options out there.

    I've done enough lost foam casting to know that I still have a lot to learn about LFC ha. I've probably poured +40 pieces over the last 2 years and I'm just now getting to a point where I can confidently maintain consistent pouring speeds. Just need to work on actually implementing all the gating techniques I read about.

    I always get a little sense of pride when speaking with other artists and hearing them complain about foundry costs. Granted, many of them think everything done between mold making and chasing is "what the foundry does" but I'll save those rants for another time. Planning on cleaning everything up and casting during this upcoming 3 day weekend - Should have some nice pieces to post soon!
     
  12. Nick Lazenby

    Nick Lazenby Copper Banner Member

    I might have overdone it with the tape but I’m always paranoid sand is going to make its way into the joint or worst case come lose during vibration/packing. Never had any glaring issues with over taping but this piece might tip the scales ha.

    This piece is mostly experimental. Each square is a different size/thickness and I’m trying to get a better understanding as to my spec limitations. The squares also have varying degrees of finish so I can further test some patinas.

    Fresh
    01830D76-27FD-4A0A-A664-5DE313F333C2.jpeg

    Gated
    D8E33DA4-E99C-4B32-B4AD-42C651FA3ACA.jpeg

    Works pretty light tomorrow so hopefully I’ll have some time to vaporize this bad boy in some hot brass. Thanks for all the feedback!
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    There's a lot going on there. So the tape is just to seal up cracks and crevices? What's your thinking in wrapping with foil? You mention your coating potion. Do you brush or dip? Did you pour it yet?

    Best,
    Kelly
     
  14. Nick Lazenby

    Nick Lazenby Copper Banner Member

    There have been times where during vibration either the joint comes loose and/or sand makes its way in. Rather than taking the time to ensure my joints are tight, I've just been adding tape. Since using tape I've noticed a significant increase in outcomes. Granted, maybe this might just be a function of me getting better all-around.

    So early on I was running into situations where sand would collapse into my pouring cup and cause intrusions + blocking the overall flow. I know this is generally correlated with, among other things, how you are pouring while feeding the part. So I started thinking of different ways to mitigate improper pouring etc. After trying a few things out, I found that enclosing the pouring cup resulted in a MUCH better success rate.

    You'll notice the above piece has foil on not only the pouring cup but also two main spruces. I'm going to be honest, it's probably not necessary but I just wanted to see what would happen.

    I ended up deciding to forgo the coating since I wanted to cast the next day and was worried it might not dry in time. It ended up raining so I never ended up casting. Depending on the size/strength of the piece I usually dip coat all the patterns but for larger/cumbersome ones I just brush it on. I tried using a spray gun but that never worked out well ( mostly because I never took the time to adjust the numerous things that went wrong. one day)
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    If it is just to seal cracks, it's fast and easy and I see nothing wrong with it.
    In general, collapses generally occur from a disruption to metal flow. Since the sand is unbound, it causes mold displacement, especially near the surface of the mold where there is little sand pressure. The most usual cause is allowing the sprue to become uncovered during a pour. It can also be caused by pattern being evaporated more quickly than the feed system can manage or just inadequate mold packing. For the first couple years, I just placed a can/kush cup around the sprue, filled sand to the top of the outside of the can and poured. The sand would usually slightly displace around the sprue and form a shallow cone. So then I started making cones from foil tape to transition from the cup to the sprue. This seemed to reduce the amount of cup turbulence, smoke and flame. But a cylindrical pouring cup with transitional cone are shapes that tend to naturally aspirate air.

    So then I made the reusable offset pouring basins linked below, and the improvement was profound. What I've concluded is the sooner you can get head pressure sitting on top the pattern feed system the less likely you are to get fireworks and turbulence in the cup, and more likely to achieve a tranquil pour. The cup also provides a buffer volume of metal since the rate at which a lost foam casting takes metal from the cup changes (pause then gulp). This reduces the chances of uncovering the sprue and interrupting the pour. The offset cups with weirs also tend to naturally separate drosses from the pouring stream, and they continuously hold their shape throughout the pour in the region of the mold that has the least mold stability.

    It's possible the material used in the thread below would also work for Copper alloys, but an expendable version could be made/molded from sand bonded with sodium silicate.

    http://forums.thehomefoundry.org/index.php?threads/reuasbale-offset-pouring-basin.688/

    I don't think wrapping with foil does anything positive accept maybe seal cracks. It melts instantaneously and is probably a negative for good vibratory sand packing.

    Coating controls the rate of escape of evaporated foam and slows the metal propagation speed through the pattern/mold. It also vastly improves surface finish to that of the pattern. If you don't coat, you just need to insure you have a very generous feed system so the advancing metal can keep up with the rate of pattern evaporation.

    Best,
    Kelly
     
    Nick Lazenby likes this.
  16. Nick Lazenby

    Nick Lazenby Copper Banner Member

    Makes perfect sense. Do you pre-heat the basin prior to pouring? Also, right after typing I realized you probably don't pre-heat since its attached to the foam..?

    Side note: What type of sand are you using here? Maybe its just the lighting but at first glance it almost looks like brass chips and I'm going to assume that grain size is less of a factor when using a coating? I know super fine meshes should be avoided to allow for venting but the sand pictured below looks quite large? I purchase my sand from a local suppler (100lb bags) and its slightly "better" than HD/Lowes playground sand but I still end up sifting most of it and after looking at these pictures I'm wondering if that's not necessary?

    [​IMG]
     
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    No pre-heat. Besides being non-wetted by the molten metal, the stuff is super insulating and relatively low density so it robs very little heat from the melt.

    No metal in there intentionally unless it got swept up with the sand off the floor. I just use Quikrete fine sand sold in the construction materials section at the big box stores because it's convenient.

    Quikrete Fine.jpg

    It's about 50 mesh which would be very course for conventional sand casting but with pattern coating in lost foam it makes no difference. I've added some here and there for more capacity but have been using the same sand for 5 years and treat it with disregard......except, I try to keep it vey dry, and it passes through a coarse sifter on it's way back onto the sealed barrels so I don't have to smell it during storage.

    The Quikrete stuff is nearly white and turns tan/brown with use. Sometimes there is some residual polystyrene/sand clumps and just I just discard those. If you raise the temp of the sand to about 1800F it returns to looking like it did when it came out of the bag, but the energy to do that is more expensive than just replacing it, even at retail store prices of 6c/lb. Fresh sand does seem to flow a little better under vibration.

    Just about anything will work for LF as long it is dry and of sufficient refractory. If you are using beach sand, you just need to test for organics. Sometimes beach sand will contain a lot of fine shell and the Ca will react with iron and high melt temps. Other natural sand can have organics. The shape can matter too with regard to how easily and well it packs but I have no problem with the granular silica shape.

    Commercial foundries will often used rounded particle shape in Mullite or Zircon.

    Did you pour that yet?

    Best,
    Kelly
     

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