Hello. Making some hard transition from lost in green sand to coated with dry sand.. With small parts all is ok. Thin part 5-6mm pour at 800 degree c, thicker one 750. On thick parts some problem with porosity - longer liquid time if compared to green sand. For covering i do use cheapest water based wall/ceiling paint and chalk 1/1 plus some water and detergent. And yes, i do use pouring basin..
Welcome Stanislavz. Our resident lost foam expert is Al2O3 (aka: Kelly), his thread: Confessions of a Lost Foam Caster, 5 Years on, has a lot of good tips in it, all of his threads in this forum are a must read for anyone starting out with lost foam
Hi Stan, I did receive your email but wasn't sure what you were asking. The short video shows a fairly large fold flaw. Can you post more details? Like: Gating and position of part in mold, wall thickness, casting weight, size of pouring cup. Best, Kelly
All three flanges are machinable. 6.4 mm dimension now was 5.5mm. All flanges were 12 mm thick for machinig too. Will try to make L gating connected to two bigger flanges, and gating cutted from eps. Now it was like this :
Stan, I wouldn't think those wall thicknesses would pose much of a problem. I still can't tell for sure where the fold flaw is in respect to the sprue, but I suspect, it was the last portion of the mold to fill with metal and it is where two metal fronts converged. I would try this orientation. One unknown to me is your coating formulation. I don't think chalk poses much of an advantage or disadvantage for aluminum. I am unsure of water based paint because most paints are formulated to be sealing layers and that is the opposite of what you want for a lost foam coating, which you would rather be permeable. Patterns that have low surface area to volume ratio (A/V), require a more permeable coating. For example, a cube or a sphere would have low A/V whereas a thin walled part higher A/V. Higher melt point alloys also require more permeable coatings. You need not be concerned about the chemically bound water in a gypsum/plaster based coatings. Many of the commercial lost foam refractory coatings are water based and when air dried, pose no problem and in any case have much less water present than green sand. You don't mention how thick you are applying the coating but I would recommend it be kept very thin, no more than required to change the color of the coated pattern to the coating color because thinner will mean more permeable. A gypsum or drywall based coating, dipped or brushed should perform fine for that part. I have cast many similar pieces. But, folds can be caused by both insufficient and excess permeability but for us hobby guys it's almost always insufficient permeability. In general: I try to gate into the most massive portions of the part, as long as it also facilitates good mold packing, avoiding undercuts. I've always found angled part orientations in the mold to be helpful in promoting more uniform advance of the molten metal front. Add some sprue height because more sprue pressure will generally aid venting of the evaporated pattern through the coated surfaces. Use a pouring cup, get the sprue covered quickly with molten metal, and keep it covered. Though this should not be needed, in very critical castings I sometime will add a "bob" at the very bottom of the part of similar A/V. It's just a small additional volume that will draw more metal through the mold. Sometimes during the initial pour and contact of molten metal with the foam, you get flame and burning (black smoke) and it produces some oxides and contaminates in the metal stream. These always seem to present themselves as fold flaws in the resulting casting in the last portion of the mold to fill. The bob promotes molten metal flow through the casting serves as a reservoir to attract and retain this initial stream of metal. Good luck and let us know how you do. Best, Kelly
Thank you for reply. I got this coating formula from this channel : at 29 minute. My coat is really thin, just covered color of foam. I do tried plaster -i am from eu. We do have different formulas. All that i tried - was slow curing and too thick if stick to foam. Add more water it just run off from foam. And char do not have chemically bounded water. My sand after pour is with some wet clumps. I am not protecting my invention. Got 6 nice pours except this one.
It may be fine. I just don't have any experience with those coating materials but the coating looks good. If on your other parts you're having good results I'd suggest trying the new part orientation before messing with your coating and...... Some small clumps are to be expected but if you have a lot of clumping and wet appearing sand after the pour, increase your pouring temp. Best, Kelly
Thanks. Yes, i wanted to make it at 850 c, but my ss crucible developed a leak again so it was a lets give it a try or no.. Got myself an 10 kg bronze capacity graphite/clay crucible yesterday. Will have to think of KISS lift and pour tong and we will go. Or convert to lift off furnace
So... it was not fail today Where are some imperfections, but only due to mold/waxing errors. Pored at 850 c, and new handle shows itself great
Some machining was done today - tools do stay sharp for much longer period compared to green sand lost foam.
Next casting sesion. Some cast was know to be on ok side, some "experimental". Big thanks for Kelly for inspirations. One extra thin was meant to be fail. Poured at one corner, part positioned at 45 degree. Next time will make it with triple sprue and part horizontal. And it will make mounting on lathe easier. Or double spruce will do the work ? Unsuported sand : Core was too "floaty" and go to the top of the casting. But it still remained it shape. it was meant to replace two parts and ~ 15 minutes of machining, but it was hard to coat and dry it from inside. And test without X ray. And some just good castings:
Lost foam cores still need to be anchored just like in conventional green sand casting. For intricate cavities like water jackets, make as many entry and exit holes to the water jacket as practical, preferably/at least at top and bottom to allow gravity aided flow of sand through the cored area. The openings do not have to be very large (say 10-12mm) and can be sealed with a threaded plug. Besides the sand flow allowing good sand packing, they also act as anchors like core prints in green sand casting. Unbound sand in lost foam casting isn't really unbound.........it's just loosely mechanical bound and the better vibration increases the state of binding. Here's a very simple example from years ago when I started experimenting with same. http://forums.thehomefoundry.org/in...ted-closed-loose-sand-coring-in-lost-foam.12/ Best, Kelly
Thank you, i have seen it already (As Yours other posts/threads) I thought of just ramming it with sand mixed with sodium silicate and runing co2 later.. I have two ports on sides, which could be used for support. But making parts separated looks faster in total and you could later just loctite it together. And all this is for this one Stirling engine: Redesigned already 100500 times. Some aspects was too hard to manufacture, other just plain wrong. This version is kind of balance betwenn fancy and beiing easy to make.. Here are some older posts: https://stirlingengineforum.com/viewtopic.php?f=1&t=5223 And here is a photo of mine firsts lost foam green sand casting in unsieved green sand (i have its laying for some years, covered in backyard.. ): And Kelly - you have to write a book - Lost foam casting for Dummies
Pouring cup close view Remake that fallen part, with two types of coating. Chalk with drywall sealer/primer (water and acrylic resin only) - do work as good as i need. I am limited now by my fantasy and foam quality.
I take it those were PoP or Hydrocal pouring cups, correct? Did you bake them before use? That first pour was dangerously close to a run out (where metal leaks at the prue and cup). I can tell by the small vapor stream escaping on the side which eventually ignites. You probably didn't have the height available in your bucket/flask but always a good idea to burry the cup near the top. Both of the pours in the video looked good, tranquil, very similar to my usual experience. The cups made a surprisingly big difference (improvement) for me. Best, Kelly
