Yes, it is very hot outside, but not quite as hot as it was here a few days ago. I avoid pouring in the direct sunlight just because it is so hot in the south in the summer. The good part is it is warm for much of the winter, with gives for a long pouring season. I was wondering how you were going to get the lifting tongs into the furnace, but the video cleared all that up. That is quite a furnace rig. The part looks very good. Great outcome for a first attempt. Nothing feels quite as good as a successful first-attempt casting.
Nicely done Kelly. Well thought out and executed. Regarding the leakers, looks like there wasn't enough sand pressure on the top row of ports to fully fill them. I've had success using dry sand as a core. Put clear packing tape over the ports, fill with sand, vibrate, tape over the other side. The mud keeps the tape from imprinting on the casting. But, if you're going to machine them, I guess it doesn't matter. It'll be interesting to see the dissection of the lines too.
Many thanks Bonz. As before and always, your input is much appreciated. I agree. The exact same features and orientation at the bottom of the mold suffered no leakers at all. But there is only a few inches of sand above the leakers. I was hoping the additional sand in the sprue extender might create some additional pressure, but with the flat flask lids, not so much. I’m going to think that one over along with the possibility of bound sand. I’m actually leaning a bit toward making a 10” tall flask extender. The reason being if 8” deeper in the mold the same features had no issues, why not add some mold height. I though I’d save myself some weight and sand but it’s $6-8 more sand. It’ll be another 75lbs of sand but I think I can just remove the extender and when I demold and from there it will be the same process as this go. I also wondered if I needed the sprue pressure at all and am considering just pouring from the top of the flask with a good cup….but think I need sand depth because even though height gives more sprue pressure, sand pressure isn’t just hydrostatic…..it’s also mechanical because of locking friction between the packed grains. I am going to machine them but…….I have another bite at the apple and want to improve. Agreed. I studied the casting a bit more. I confident those are knit lines because there are matching sets on both sides of the casting. The decomposed polystyrene and burnt mud highlight it but I do believe that part of it is surface phenomena but will cut it apart to see. It’s speculation on my part but I’d say the molten metal initially ran right down the center of the pattern and then there were several successive layers both left and right of the center filling out the mold. This was poured at 1570F. I do wonder about all the surface oxidation at the top of the casting. I used a low density (~.75lb/ft3) expanded polystyrene thinking I’d save some heat. Of course that’s the hottest part of the pour but if you subscribe to my speculation about the initial part of the pour running right down the center, why is it only the top 3” of the casting has a lot of surface deposits? I don’t know what the foaming agent is in EPS but the XPS sure seems to gas off cleanly. Might use XPS for gate in next pour but doubt it will make a difference. The metal at the cut I made in the gate looks very good. No visible porosity or sand inclusions. Since the sheet metal sprue doesn’t appear to be resuable, I have some thin 3003 sheet I may use on the next one and just leave it for the next melt. Just the muses of lost foam caster. Best, Kelly
Good job Kelly. I'm with Bonz as far as the top row leakers. A little more height as you mentioned, and based on the way you filled the flask in layers, just a bit more attention at those spots should fix it.
My first thought was kick up the temp 50 0r 100F. Second thought was a split gate, divide the edge into fifth's, gate into sections 2 and 4 with the gates as wide as the section. It should expel the gases quicker. Just a feeling
There is so much to digest here. Great work Kelly!! There do seem to be two schools of thought. Gas is expelled out ht esprue or gas is absorbed by the sand. In my little foam projects it seems a little of the gas is burned and expelled up the sprue but the majority seems to go through the mud and into the sand. My thought is that limiting the expelled and burned gas gives a better casting. The smaller the sprue the better the casting has been my experience. Good idea to use tape to prefill difficult cavities with sand.
I'm totally opposite, my presumption is all of the gas exits through the sprue. I oversize the gates and sprue allowing room for the styrene to exit and the metal to enter. The metal has to be hot enough for complete vaporization of the entire foam, which means quick entry and quick exit of the gas. I also try to orientate the part so the gas has a straight up path to the sprue. That's why I think a split gate will benefit Kelly's casting, the gas is traveling horizontal at the top. Edit: Possibly/probably melting the foam before the metal gets to vaporize it. Ever seen the gas form bubbles in your sprue? You would think that oxide folds would occur in the castings because of the bubbling effect but because it's styrene gas and not oxygen you don't get oxide layers. That's why I'm anxious to see the dissection. I don't think there will be oxide folds, just the rat tail on the surface. Of course that's just speculation on my part.
Im thinking along the same lines as Fishbonz, with the top of the flask bolted on like it is there is a limited exit point for the gases to escape and everything is channeled back up to that one sprue. Maybe it would be better to have the flask a little deeper and the top of it open?? Anyways thats still a pretty awesome first attempt.....
Why mess with success? Well, I need to make sure what I have is indeed success, examine those knit lines a little closer (if that’s what they are), and make sure they are well fused. Should know that after I cut it apart. Distributing the gate out across the top of the part and dreaming of the metal flowing uniformly from top to bottom is a nice thought but doesn’t appear to be what’s happening. The opening of the sprue is 2” x 1” so 2 square inches. The gate transitions from the sprue to a contact area with the part that is 14” x ½” or 7 square inches. Yup, will add flask height One thing that I do believe I have learned for a given temperature and sprue pressure there is a limit to the distance the molten metal can travel through foam as it loses heat to the mold and evaporating foam. This is why I lean toward a centrally located sprue on big parts…..it yields the smallest average travel distance. You can increase the feed pressure with sprue height or pull with vacuum and it speeds the metal propagation front and produces greater travel distances because the metal has less time to lose heat to the mold and higher feed pressure. Of course higher pour temps do the same but probably at the cost of metal quality at the very high pour temps. For my current set up, I have a feeling I could cut the contact area of the gate in half or maybe even reduce it to be comparable to the sprue area which would only be about 4” wide, and get a similar result, imagining that it would just run down the center of the pattern and then fan out on both sides filling the part from there. This would also vastly reduce the volume of foam that initially needs to be vaporized in the gate. Lost foam can be sort of counterintuitive compared to empty cavity casting, especially top pouring. I think you want a pressurized sprue and pouring system with slightly increasing pressure drop whereas in empty cavity aluminum casting generally the opposite is true. Bonz, somewhere along the line I am going to have to try taping off the potential blind leakers. This is also counterintuitive to me because I seem to have had the most success when I can flow vibrated sand through a cavity, even if the cavity only has a ¼” hole feeding it at the top, like back on this old post of mine. http://forums.thehomefoundry.org/in...ed-loose-sand-coring-in-lost-foam.12/#post-55 Seems to work for you Bonz so all the power to you on that. This is one area where we go different directions because I do everything possible to avoid gas flow through the sprue and feed system. I’m really just trying to emulate the commercial lost foam processes I’ve studied and the majority of the research work in the last 20 years has gone into permeable coatings and packing techniques (pattern foam too). Commercial operations all use vacuum on the flasks as well. However, none of the them use hollow metal sprues like I do. The commercial feed systems are just foam like the patterns. I’ve had mixed results with vacuum. I’ve had success filling thin intricate parts like my Halloween contest spider web. http://forums.thehomefoundry.org/in...halloween-casting-contest-2017.142/#post-1883 But I’ve also had problems with vacuum destabilizing sand causing it to be ingesed into the sprue and gate. In the future I think I may be able to avoid this with increased flask/sand depth. I’m very confident drywall mud is porous. I apply it very thin, just enough to change the color of the pink foam pattern to white. The thickness of the coating makes no difference on surface finish but it does on permeability. If you look at my pour video, the mold took metal for 19 seconds. Initially there is flame and turbulence. I had a very good view of the cup after the first couple seconds of the pour. There was no bubbling after the first few seconds and the flame and smoke was the decomposed foam burning off that had floated to the surface during the initial few seconds of the pour. When I pour with vacuum assist, there is only a brief flash and then it’s just solid feed to the cup and all the gas is being pulled off and through the mold. Here’s my working hypothesis….sorry fellas, have to go with something. Here are my thoughts on the next shot at this manifold lid......still evolving but below summarizes the current thinking. In addition I may add a little vacuum assist. Best, Kelly
The first pic is how I thought it would fill. Did you have any wax on that one? Waiting to see the results with round two.
Yes, but just 1/8"r around the base of the carb flanges where they intersect the lid. The detailed patterns have more bosses and fillet. We'll see how it goes. Best, Kelly
I did some dissecting of the first casting, cut it apart, and really couldn’t detect any metal anomalies at least as far as the naked eye goes. Polishing and magnification might have revealed more but as near as I could tell the markings were just surface phenomena. Shall we have a second go at this casting?............I think so. This is a fully filleted and detailed pattern. I pulled a silicone mold from the 3D printed script David made for me and made some wax embossments from the mold. So I made the changes suggested above for Round 2. The contact gate area was reduced to the sprue area, both at 2 square inches, and the gate was made from XPS foam instead of EPS. Here’s the prepped and fully detailed pattern, coated in drywall mud and mounted. 10” was added to the flask height Aluminum sheet metal sprue. I added a couple aluminum rivets to hold it together a few seconds longer A356.2 ingot stock. All else the same as first pour. Here’s the pour. -Pretty uneventful. It took metal for 24 seconds if I don’t count the last little bit I dribbled in. The first attempt was 19 seconds so the reduced gate area slowed things down a little bit. I could tell during the pour too because there was very little flame and smoke compared to the first pour and the aluminum laid down almost immediately in the sprue and then began very calmly taking aluminum…..which in my book is good! Here’s the demolding. Looks like success. And here’s a look at the result. Here’s the raw casting. It cast with a much cleaner surface than the first round. I suspect that is mostly due to the reduced foam volume in the gate. The virgin ingot may have contributed a bit as well but it drew metal from the sprue so calmly. I had a bit of leakage again in the carburetor bores but oddly enough, this time it was in the bank in the deepest part of the mold and the bank under the sprue were perfect. -I need to work on my vibration, frequency, and direction of excitation to get better packing. Here it is degated. The carb bores get machined anyway so minor leakers there won’t be a concern. I’ll look it over a little more closely, do some dimensional checks, and clean it up but it appears that it will be a perfectly serviceable part, and I still have two bullets (patterns) left! I’ll need to give some thought to what if any changes I may make for those. Best, Kelly
Looks great, Kelly! excellent job diagnosing the issues and making adjustments. Did you wire brush the first piece to see if the marks brush off? Do you have a vacuum setup to degas your silicone casting?
Thanks much OIF. I did not but they do brush off. I usually do so immediately after I water quench them because it comes off very easily then just with some quick hand brushing. If you let it set, it's a little more tenacious. I never intended to keep the first piece and those witness marks were at least some clues as to how the metal was flowing, so I didn't clean it up. They are present on this piece just a little more subtle. They pretty much follow what I expected with the adjustments. Here's the scoop as near as I can tell. I'll probably use light media blast and tumble this one to clean it up. Yes I do. I didn't use it on this small mold, just poured it with a very thin stream. I should have stopped and stuck a tooth pick in the center of the letters like the Bs, R, etc. to relieve the surface tension.....had a couple flaws. Best, Kelly
Outstanding work once again. This is making want to the get CNC router setup especially since I found 2" foam at home depot.
Saw your post on AA that you injured your hand/wrist. -Get well and best wishes for a speedy recovery. I have a couple other casting projects in progress too but I went back and reviewed my favorite commercial lost foam process video and will make some changes to my mold packing process on the next go. I will post up when ready. Best, Kelly
Thanks Mach. I want to build a CNC router too. The hardware is much less of a challenge for me than modeling or gcode. It would be the nuts for complex geometry and accuracy but the cycle times on my hand guided jigs are small fractions of what step-over programs would be. The 2" pink (Owens Corning Fomular 250) foam is slightly denser than the 1" (Foamular 150) but the both seem to work well. They're both scored so they break on stud centers which is somewhat a bummer but I cut around those flaws. Best, Kelly
