I snagged a few more Styrofoam plates and while I was looking them over, noticed they were very inconsistent in their thickness. On some, one side was <.030" and the other ~.090". So I was selective in the ones I chose and matching thick sides with thin sides when I stacked two together and ended up back at ~.060” average at the perimeter. I built two new patterns identical to the larger of the previous two. Most of the work is in the gating so not much difference to cut two sets while I was at it. I employed a new gating strategy………take no prisoners. Ring gate and multiple contacts with very pattern high contact area to minimize the average metal travel distance. Here’s basic pattern and gate: Here’s the rest of the feed system... I try to make the gates and sprues to minimize the surface area to volume ratio (SA/V) which generally means a square or circular cross section. This minimizes heat loss through the feed system but minimizing the surface area also minimizes the rate at which vaporized foam can escape the walls for a given volume of feed system. This is one of the major contributors to the lost foam “pause” during a pour, because when the metal arrives at the pattern, there is usually a significant increase in the SA/V ratio and the metal advances faster. But, more complicated gating systems usually mean you have to expend more energy evaporating the feed system foam, and multiple contact points also require the metal to converge and knit together multiple times which increases the chance for folds and other flaws…….lots of tradeoffs. For an ornamental part, not much of a concern. They are dipped and drying……..rain this weekend but hopefully will have a window to cast. Best, Kelly
I dipped the two patterns and let them dry overnight. I tightened up the plumbing on my vacuum cart and was pulling 18”Hg. I poured at 1700F, ……..It surrendered peacefully. The plate, cup, and spoon are .060” wall. …and here are the three…... I have another pattern completed. I’ll pour it and assuming I get a similar result, I’ll degate one and keep the other with the gating intact. I also have a lot of footage and will put together a good process video. -More to come. Best, Kelly
That's awesome! well done!!. You could cast them separately and anodize them for use, although hot beverages would be a problem.
The entire portion of the flask containing the pattern/casting is exposed to vacuum. The flask has a screened floor (see link in post #1) that exposes the entire cross section of the bottom of flask to the vacuum source. The mold is filled to the top of the pattern's sprue A thin sheet of plastic film is placed across the flask, the pouring cup is positioned over the sprue, on top of the film sheet. The remaining 2-3" of the mold is filled with sand. The top 2-3"of sand above the film sheet is not exposed to vacuum but it holds the film sheet in place and seals it against the outer wall of the flask. The film is expendable. I use a small disposable grocery bag but virtually anything that is pliable will do. In addition to the hydrostatic sprue pressure (about 1 psig) the molten metal is pressurized to 1 atmosphere absolute and the mold is at about 1/2 ATM absolute. By investment casting standards, 1/2 ATM is not a lot of vacuum but that ~2:1 pressure ratio aids in filling the mold and driving evaporated gas through the refractory coating present on the foam pattern. I video documented the entire process. Will take me a week or so to finish up the project and edit the video. Best, Kelly
I cast the remaining pattern tonight. It came out like the previous and was successful. So I degated and finished one. The plate is 7” in diameter…….. .060” wall in sand via lost foam. So what to conclude from all of this? If I would have thickened up the wall to that of a typical cup and saucer, this would not have been a challenge. At .060” wall I think it is. 1700F is stupid hot and there aren’t many things I would ever consider pouring that hot in aluminum except maybe ornaments. I might have some success at lower temps with the improved gating approach but it’s not worth pursuing that to find out. Other than hotwiring thin sheets and planks, it would be difficult to machine foam patterns with .060” uniform walls. Even if you could do so, they would be very weak & flimsy thus difficult to coat and mold without distortion, but larger patterns could potentially contain some thin features. I’d say this makes >.125” wall look feasible in lost foam for modest spans and part sizes. I can’t think of too many machine parts where I’d want or need that thin of a wall so it’s mostly experimental novelty and process challenge. From that standpoint the casting is an interesting conversation piece…….but no practical use. I’ll work on the video. Best, Kelly
almost perfect! Give a brother a like. He deserves it! Always be a member first and administrator/moderator 2nd. You are forced to wear two hats.
Now what is he going to do next?? I cant wait to see.... I dont wear a hat....I just delete spam and verify new members before they can post. Pretty sure I'll have to delete a couple of them I approved earlier for being spammers but that's how it goes sometimes...even after checking their IP status. And I wont even talk about all the porn spam that gets sent through the contact button...
We all wear a hat. Don't think you don't! I do very similar work, vetting, IP background searching and spam overlay. You got your hands full no doubt. But you still can give a brother(Kelly) a thumbs up if you like his stuff and hard work.
I put together a series of three videos from this project. It breaks the footage down into more manageable duration for each and hopefully attracts a few new members to the forum and interest in lost foam casting. At the end, I’ve included links to the equipment builds and processes used in the project.....old hat to you guys but might be helpful to newbies. Thin Walled Lost Foam Casting - Part 1 Equipment and Pattern Prep Thin Walled Lost Foam Casting - Part 2 Pouring the Castings Thin Walled Lost Foam Casting - Part 3 Completing the Project Here are some related links for equipment builds and processes used in the above videos: Lost Foam Vibration/Vacuum Assisted Molding Rig Dip Coating Rig – The Big Dipper Vacuum Cart Dip Coating Lost Foam Lost Foam Pros and Cons Reusable Offset Pouring Basin Best, Kelly
I've said this before but I'm absolutely gobsmacked at what you've been able to do with lost foam. Great stuff!