Need urgent help with lost foam casting

Discussion in 'Lost foam casting' started by Tika, Dec 29, 2022.

  1. Tika

    Tika Lead

    Hi All,

    I have been watching Kelly's videos for a while and mesmerized by the results he produced and tried to replicate them with little success.

    I would really really appreciate help casting with lost foam. I have made about 10 trials and ALL OF THEM FAILED!

    I have added some links to videos below of my trials.

    I can't narrow down the problem. Temperature, size or location of sprue, location or size of the gates. I really don't know. I am not coating the foam with anything, could that be it?

    In this video I tried the spru and gates from one side and the sprue and gates from both sides and top.

    Here I poured from the side and the roof caved in. There aren't many consistencies.

    Here I poured from the bottom

    Here is a video of one of the castings in progress

    Thanks for your help in advance.
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Tarek. your videos are all designated "private" and cannot be viewed. You need to go change the YouTube settings on those videos to "public".

  3. Tops

    Tops Silver Banner Member

    The coating (non-setting joint compound, Suspend-a-Slurry) is what keeps the unbound sand from collapsing into the space created by the melting-into-gas foam.
    Welcome to the forum and looking forward to seeing the videos
  4. Tika

    Tika Lead

    Thanks for the quick reply, I will try that and see the result.

    I will post the results when I do them.
  5. Tops

    Tops Silver Banner Member

    You are welcome. I am new to foam myself and appreciate the advice I have gotten here.
    If you could fix the permissions on the above videos , Kelly and everyone will be able to view them and offer more input.
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Unlikely the problem is just the absence of coating. -Can't help with what I can't see.

  7. Tika

    Tika Lead

    Thanks tops, I just fixed the permissions on the videos.

    Here is a picture of all the trials that I've done. The sand caving in was the problem in most cases, especially at the sprue or the top of the pattern. Most of the castings filled the lower section correctly.

    Most of the castings have been poured vertically.

  8. Tika

    Tika Lead

    Here is another video of some the sand caving in from the top again.

    I thought it was the pressure of the metal from the height of the pour so I decided to tilt the pattern 45 degrees.

    The second casting had one sprue and one riser at the top. I figured the gas was not escaping so I should add a riser to help it escape.

    I also vibrated the sand with a concrete vibrator.

    I'm puzzled by this video. He has no coating on the patten, just wrapped aluminum foil on the sprue and no cave in.

    Thanks for the help
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Hi Tarek,

    I've watched you videos and here are my comments and recommendations.
    • The primary issue is the top of your sprue and pouring cup are very close to the same height as the top of your casting, That means the last portion of your pour/fill has no "head" or metal pressure to fill the mold. If your pattern was burried deeper in the sand and you used a longer sprue, say >6", this alone would be tremendously helpful. Don't have your sprue protrude above the lower surface of your pouring cup. It only creates burining and turbulence in the cup. Place your cup around the sprue at the sand surface and then fill the mold to surround the cup. See illustration below.
    • Most mold collapse is usually caused by an interrupted pour, meaning the sprue becomes open and uncovered by molten metal during the pour. This is very bad. Your pouring cup is perhaps a little small for the size of your part. A larger cup would allow a larger "buffer" to ensure you can keep the cup full and sprue always covered with metal during the pour.
    • Attaching the sprue to the top of the pattern (top feed) will be best. Position the pattern so the open part of the "box" is slightly open toward the top of the mold. This will insure proper packing.
    • Forget about using "vents". They have no meaning in lost foam casting. The entire pattern surface where it contacts the mold is a vent, especially if you do not use any refractory coating.
    • Using a refractory coating will vastly improve the surface finish of the casting and probably the casting quality in general because it slows the rate at which gas can vent and allows the metal to displace the foam more tranquily. You remark in your video that the finish is very good. It will be 1o times better with a coating. In the US a common material is drywal jint compound. drywall is gypsum board. This is the material used to finish the joints. Plaster may also suffice. It should be thinned with water, applied thin, by brush or dipping and alowed to thoroughly dry. You'll be amazed by the result, especially if you sand you foam pattern with fine abrasive paper to improve the finish on the foam pattern.
    • Several of the pours looked like they had cold metal temperature. Pour hotter.
    If you have not already, you should read this thread:

    Confessions of a Lost Foam Caster, 5 Years on. | The Home Foundry

    Your part is not a difficult part for lost foam casting. Incorporate all of my suggestions and I think you will be pleasantly surprised.


    Pouring Cup Tarek.jpg
    Last edited: Dec 30, 2022
  10. Tika

    Tika Lead

    Thanks Kelly for the long suggestions I will follow them and read the full post.

    I will post updated videos soon.

    Thanks again,
  11. Tika

    Tika Lead

    Happy New Year all, hope you are having a great new year.

    Here is an update of the pour and the result. I lengthened the sprue, it is 8" and angled the box a bit and painted the pattern with drywall compound. I tried as much as possible make an uninterrupted pour but it was hard to see from the flame and finally heated the metal much hotter.

    The surface was amazing as can be seen in the video. I still got a partial collapse and I thin I know why, I explained in the video.

    Thanks for you support,

    Thanks a million,
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member


    In short, use a larger sprue, increase the contact area on the pattern, use a larger pouring cup, and position as shown.

    • Larger Sprue: Your casting is massive compared to your feed system. How much does it weigh? The pattern can take metal faster than the sprue can feed it. The sprue doesnt need to be round, in fact square or rectangular is better. I'm guessing 3cm x 3cm would would do it. Lighter weight EPS material will help.
    • Increase pattern contact area: Make this area at least as large in cross section as the sprue, or it will become the choke point.
    • Larger pouring cup: As a rule of thumb, I'd say 25% the volume of your casting. If you have a lot of smoke and cant see to keep it full a gentle breeze from a fan or an assistant manually fanning helps.
    • Pattern positioning: I think you are probably correct about the cause of collapse. You dont have adequate vibration. If you cant see the sand moving at the surface of the mold, it's not enough. As a check, your sand should settle 10% in height. Your mold media is probably not ideal, so that overhung area under your pattern doesn't get packed suffiiciently. The additional angle/on-corner positioning allows the sand to flow more easily into that area. I can see your mold media/sand looks very dusty. If the size of grains varies widely and there are a lot of fines, it will be harder to make the sand flow and pack under vibration. The sand must be very dry, or this will greatly inhibit flow under vibration. A large flask becomes very heavy when completely filled and it takes a large amount of vibratory energy to fluidize and pack the sand. If you vibrate as you fill while the falsk is not as heavy, it will help. If you are going to do a lot of lost foam casting, you'll want to make yourself a better packing/vibe system. I use this sand I buy at Home Depot (if you are US based). It is uniform, washed and dried, and inexpensive.
    Quikrete Fine.jpg

    I like your're going to be a good lost foam caster :)

    Tops likes this.
  13. Tops

    Tops Silver Banner Member

    The sand I am using for lost foam was originally billed as a paint additive (texture or no-slip) and was very clean, dry, and consistent around 60 mesh.

    I have been using an air chisel against a strip of plywood against the bucket with good results. The tool was handy, new in a box from 20 some years ago. I finally have something fun to use it for... :)
  14. Tika

    Tika Lead

    Thanks Kelly and Tops,

    So finally got a double success, temporarily....

    First, I cast one in lost foam with a generous coat of drywall compound with a long sprue and packed the sand well with a concrete vibrator and tilted the opening backwards. That turned out well. Thanks Kelly.

    The second trail was done with foam green sand with vents on the top, no coating just foam in green sand.

    Here are both videos, (I could not embed the videos because they are YouTube shorts) the links are below.

    So the second method is much faster in production which is foam in green sand but after some machining I started seeing some small holes. Here is a picture. What are these holes? I am suspecting it the steam escaping from the green sand going in the metal while it is still molten. The box is cast with the opening facing down so there is no place for the steam to escape except through the green sand. Is that the cause?

    I also coated the pattern with wax to smooth out the machining marks in the foam pattern before casting in green sand

    I don't know if these holes will appear in the traditional lost foam method. These holes are about 3mm below the surface.

    Tomorrow, I will cast and machine the same part in the traditional lost foam method and machine it to see if these holes persist.

    Or are the impurities in the a aluminum? I do use salt to degas.

    Thanks for the help,


    Last edited: Jan 2, 2023
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Congratulations on the success.

    I just make a few light strokes with fine (<220 grit) sand paper. You can generally improve the foam finsh all the way to 320 grit. What kind of wax? If it has higher melting temperature than the foam, using excessive amounts can cause some defects.

    Hmmm, ramming in green sand would never be faster than pouring in dry sand and vibrating, at least for me, and I would not want to risk damaging/distorting the foam pattern with ramming green sand. If you mean the coating process is slow, dip coating is much faster as opposed to brushing, but drying time is always required. Now, making a hard drafted pattern (unless the draft is objectionable), and running them in flasks on a molding machine in conventional green sand casting process would definitely be faster.

    I can't see the defects you describe very well in the pictures but I'd say likely porosity. How wet is the green sand? One of the advantages of lost foam is dry sand. Was the foam pattern also coated in this case?

    1. If by salt you mean a NaCl-KCl eutectic, it isn't really a degassing agent. It's a DIY drossing flux.
    2. What is your source of casting stock?
    3. What is the pour temperature of your metal?
    4. Is your furnace electric or fuel fired and is climate dry or humid where you are casting?
    What is the function of your aluminum box?

  16. Tika

    Tika Lead

    Hi Kelly,

    I'm using candle wax and heating it in warm/hot water so that it does not damage the foam for sure. I did notice more fire coming from the pour because of the burning wax.

    Yes exactly the drying time is longer for sure. I was hoping to make the pattern and cast it the same day. I use a make shift dry box to speed up drying.

    It looks like little dark holes in the casting. It shows up in the product as a defect since this is a mold. This is my only problem right now.

    The green sand that I use is not so wet, just normal moisture level. I agree, dry sand is a huge advantage it seems. I did not coat the foam with anything in the green sand.
    1. Not sure what the salt is, it is pink in color and especially for aluminum casting.

    2. The stock is Old car engines and alot of remelt from my previous trails.

    3. I don't measure it but I try to pour it hotter than normal, maybe I should get a thermocouple. How much of a difference does temperature make in lost foam casting?

    4. My furnace is a propane fired furnace.

    The box is the female part of a mold to be used in eps shape molding.

  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Salt is a generalization, like metal. If they are commercial degassing tabs, thats good but those are usually Chlorine or Fluorine based. Use in well ventilated area.

    Hydrogen porosity is the bane of aluminum casting. H2 is about the only gas that is appreciably soluble in molten aluminum. There are things that aggravate it. Dirty scrap, casting at higher than necessary temps, high humidity in the combustion air, and a rich instead of lean burner tune in a fuel fired furnace, the latter two tend to be the worst culprits of all, especially if you are degassing.

    In general, in all casting, you should cast at the lowest temp that yields success. Lost Foam typically requires +100F-150F higher temps than conventional open cavity sand casting. The solubility of H2 goes up with the metal temp so higher than necessary molten metal temps attract more H2. It comes out of solution as the metal cools and freezes and results in porosity. Buy/build a contact pyrometer so you know your metal temp.

    Make sure the burner tune is very lean for aluminum casting. Try to cast on low humidity days.

    Last edited: Jan 2, 2023
  18. Tika

    Tika Lead

    20230103_141536.jpg 20230103_141551.jpg
    Attached is a picture of the salt I use.
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Not familiar with that one. Could not find it on the web, but if it is formulated for degassing molten aluminum, it is 1 1/2 years beyond expiration date. Any of the solid chemical aluminum degassing materials I'm familiar with will rapidly degrade and cease to be effective if stored in open air, and even when stored in closed containers, especially in humid environments.

    I'd bet proper burner tune and reduced flow rate would produce a significant improvement especially if you are superheating your melt.

  20. Tika

    Tika Lead

    Noted, Thanks Kelly.

    Here is an update on the 3 types of castings that we did over the past couple of days

    Here is my furnace setup, any and all input is appreciated, Thanks

    Another semi successful lost foam casting today. I am getting some trapped air in the casting in the upper part, any suggestions?

    I learned a lot for degassing with Argon today and I am sure where the porosity is coming from. I turned the gas on at about 1L/min and saw a ripple effect on the surface of the aluminium which is exactly the same ripple effect that I saw on the open sand casting mold. It was the steam escaping from the green sand through the aluminium and creating a ripple effect. I saw the same effect when I poured some aluminium on a piece of dry plaster that was left outside for a while. Moisture is the enemy of aluminium casting, it creates small bubbles in the casting that look like porosity. Here is a video of the degassing.

    Thanks Everyone,

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