Hi folks! I've been working on this for months now (admittedly with a few weeks' break while I made the muller), and it tipped over from fun and interesting to oh-goodness-when-will-it-be-done territory a while back. However, yesterday I had if not a 100% success then at least a very encouraging failure. Behold, for it is Sump! There'll be a video along at some point showing how I got to this point, but I wanted to share this before getting into all the editing. Also, this does have some defects. I'm really hoping that this one will turn out to be usuable (perhaps with a few pound notes given to the guy with the TIG welder if we find some horrors during machining) but if it turns out I need to pour another, I'd love any advice on how to deal with the following: There's what I assume to be a shrink defect in this corner by the flange: There's a boss there that makes the wall thicker in that section (~9mm rather than the 4mm that the rest of it is), plus the right-angled corner makes that bit even heavier. Also these little pits between the fins: I guess it's steam from the sand? Though I had expected the fins themselves to be the troublesome bits, not the valleys! I'd just re-mulled all my sand and added a little dextrin, and despite ramming it up quite firmly it didn't pack in tightly in places. I assume this is just ramming technique that I need to work on: Anyway, even with these problems I'm glad to find that the idea holds water... <drum sting> -- Olly
And incidentally, the complete pour with sprues was 4.5Kg of LM4, which is right on the ragged edge of my capacity - pretty much brim-full in a special new tapered crucible that's a skin-tight fit in the furnace. If the solution to any of the problems is more runners, then it'll have to go to a jobbing foundry!
17"X11" for the rest of normal people. That's a big chunk of sump. That's what I call them too despite being a yank. It's a nice looking piece, well done you! Now riddle me this. You pour a sump, fill it with water and it doesn't leach through the metal. Kelly pours some aluminum pipes for a ford and his leak. The poor guy had to jump through his ass to stop them from leaking! What gives?
I was told once that aluminium engine block castings would be vacuum impregnated with a special pore-sealing substance to keep the pressurised coolant in. Can't remember the name of the stuff now, and no doubt it would be hard to aquire in hobby quantities. Maybe sodium silicate could come to the rescue?
Kelly says it is sodium silicate. Hot motor oil is harder to contain than water, so a second test might be in order. Are the rib spots sand dropped onto the drag?
Huh, out of the blue my dad sends me a link... it's this stuff: http://www.surfacetechnology.co.uk/casting-impregnation-services/ultraseal-pc50466/ I imagine it would be impossible to apply after getting oil on it, so I might try to rig up some kind of crude pressure test to see if it needs a dip. The ribs are in the cope, so I don't think it's loose sand - if it was going to float, it would surely go up into the ribs? I thought it might be shrinkage at first, but there's no sign of it on the other side.
I shot peen my aluminum castings... so far no leakers... Also heard to put them outside and let them weather a bit to seal them up...
Glyptal?????? Last engine I built, I smoothed every oil passage and inside the block with a burr then painted and cooked on glyptal. That oil must have zinged back to the pan. https://www.eastwood.com/glyptal-red-enamel.html
I was using a Loctite Impregnating resin, (methacrylate) pulling vacuum and then immersing the part and re-pressurizing to drive the resin into the parts. It cures with low heat. You can read the whole thread but the meat of it starts here. http://forums.thehomefoundry.org/in...vacuum-casting-impregnation-rig.69/#post-4084 Prior to the modern impregnating resins Sodium Silicate was commonly used but they are often higher viscosity and more difficult to get good penetration. The active ingredient in radiator sealants is sodium silicate. I haven't tried shot peening as David mentions but if you can easily get at all surfaces that could be helpful too. My initial water neck castings were made from stock that had many remelts, sprue stock, and had to be gassy, but most of the castings were still water tight. I did have some leakers, some of which could be sealed with impregnation and some not. Here's is the first part of that project which was also my initial lost foam experience. http://forums.thehomefoundry.org/index.php?threads/tubular-lost-foam.11/ ...and here are the parts that were put in service. I've made quite a few of them now. http://forums.thehomefoundry.org/index.php?threads/automotive-water-neck.90/ My current approach is to cast with A356 virgin ingot. I'm still using the lost foam casting process. A member here helped me out with Sr and TiB (grain modifiers and refiners for aluminum alloys containing silicon) which are supposed to be very helpful for making hermetic castings. I have ten foam water neck patterns made up but haven't had a chance to run them with the new A356 with Sr & TiB yet. I can't say for sure but if your sump has some visible surface defects and shrinks, there's likely some porosity too. Over time when exposed to hot oil and crank case pressure it may "sweat" oil causing surface stains on the casting or worse. This can be worse at machined surfaces acting like a forever leaky gasket. It may also be fine as is. Keep us posted on how your project progresses. I've made a number of automotive castings and like to follow such projects. Will help out if I can. Best, Kelly
Thank you for the intel Kelly. It's going to be a while before my tame machinist has time to start the cutting on this thing, in the mean time I'm going to start making inquiries about finding someone who'll do methacrylate impregnation as a pound-notes job. If it's not super expensive it seems like cheap insurance. Obviously if there's an actual hole caused by shrinkage it won't help, but if there's just some general porisity all over then I don't want to end up chasing my tail forever getting it welded (since I don't have a TIG it'd be a very slow process going back and forth to someone who does). I've been pondering that (assumed) shrink defect between the thick boss and the flange, I guess it needs some kind of bob that's thicker than it to keep it fed? Maybe if I move my pouring location to that spot and put the riser right on top of it? Much more machining effort to remove the extra metal, but if it stops it being full of holes... I have some more automotive projects in the works (smaller than this one, thankfully!) so will no doubt be hitting you all up for some more advice.
If you have some welding touch-up to perform on your castings, do so before impregnating. It can contaminate the welds and make the repairs leaky. If you impregnate the castings, heat them to 150-200C to drive out residual water and let them return to room temp. Holding the castings at high vacuum for a few days will do the same. Mine were small enough to fit in my vacuum chamber which was amazingly well sealed and would hold high vacuum for days with out assistance from the pump. The casting should be machined before impregnation because any machining will likely be deeper than any impregnation. On this side of the pond, all of the commercial casting impregnators I contacted had $400-$500 minimum lot charges, so whether it was one piece or a thousand that was the cost. That didn't work very well for me making 5-10 piece batches. I bought 5 gallons of Methacrylate. Delivery cost was a killer as the activator carried a hefty hazardous material charge......think the landed cost was ~$400 US. I still have 95% of it and it has fairly long shelf life, especially if kept cool. If you pursue Methacrylate, Loctite offered heat curing and anaerobic curing versions. The latter cures on the shelf in the absence of oxygen but the unused portion needed to be continuously stirred/agitated to prevent curing.......so I opted for the version that cured at 90c for which boiling water does the trick. Best, Kelly
The sump is a really great effort. You're really putting a lot into this and you're getting great results. My first castings were a real mess! You may find this information helpful http://archive.hnsa.org/doc/foundry/index.htm#pg15 Pete
I agree with Pete, it's a great first pass at it Funkster. It looks like you have a pouring well and sprue in one corner of the part and a riser on the other with the part extending up into the cope. You may get some other helpful suggestions if you can further describe the other details of the metal feed system and flask dimensions. To me it does look like there may be some trapped mold gas causing the minor imperfections. If so slightly drier sand may help. Sometimes with parts like this some well placed vents combined with positioning the mold a slight incline to control the directional flow of metal/mold filling can be simple adjustments that prove very helpful. Best, Kelly
Thanks both. Considering this was my first full pour of my third ever casting, I was pretty chuffed when I found this buried in the sand. I will add some photos of the pattern and flasks later (not at my own computer right now) but you've got it pretty much nailed. The pouring well has a rectangular lump at the bottom that's about 50mm x 50mm x 70mm, and it extends 20mm into the drag. The riser is round, about 30mm in diameter, with no extension into the drag. Both are fed by sprues cut with 22mm plumbing pipe, and I put pouring cups on the top to give plenty of head. Everything else is in the cope, and there are no vents anywhere else - getting a good finish on the face with the fins on it (which is the highest unvented point in the cope) may be wishful thinking! This is also the least pretty part of the pattern as there's just so many edges to sand. I'm sure that in an ideal world there would be a runner feeding metal in at multiple points, and maybe multiple bobs & risers, but I don't have the furnace capacity for any more metal than this. I'm going to try to measure the thickness of the horizontal faces later, to see if they're thicker than designed as the calculations suggested I should have had metal left over which wasn't the case. A 1mm error over the whole thing would be a lot of extra metal!
Sometimes just poking a few holes through the cope with a wire the size of a coat hanger can provide adequate venting in otherwise difficult to vent locations with minimal disruption to the mold and casting surface. Best, Kelly
Yes I have seen that done and did consider it, but since this was the first clean-ish pull of that pattern I didn't dare poke at it! The cope weighs ~60Kg and I have to use my magical straight-and-level lifting device to have any chance, which works but the whole process is very slow. Moulding / pulling / flipping just the cope takes me over an hour. Do you poke holes through from the inside after pulling the pattern, or poke down to the pattern from the outside before pulling?
