The first successful?? casting is planned for this weekend. We'll see how that goes. The refractory cement has been applied for 48hrs. I need to cure it and my crucible first. I'm shooting for 1300F using 6xxx aluminum which is all I have on hand at the moment from extruded heat sinks. I found a very informative video concerning sprue, pouring and old guy theory I'm hoping to follow this weekend: TAG: Salt in molten aluminum, salt aluminum casting I see a lot of artices, blogs, videos, etc; people adding salt to molten aluminum. They claim it's a flux, cleans, makes it easier to pour. But I haven't found one "old guy" that mentions it. I can't imagine what if anything salt does therefore I plan to skip this step especially after seeing the above video. I found it fantastic to see the molten aluminum pour through an oxide sleeve which is exactly what I saw during my first ever pour two weeks ago (but didn't realize what was happening), tried to wiggle it off and dumped the oxide in my casting. This video was one of the better I've found for making green sand for this weekend since I haven't followed the advice given to me and ordered Petrobond yet. The part I plan to make is 5.5" diameter, 6oz aluminum. It looks like a brimmed hat with a 1/2" hole in the center (top). I really want to center gate it upside down so the brim is at the top, but the center hole is in the way and I don't know where to put the riser(s). With that said, I'll try to pass the melt through, sprue and runner one side, runner and riser opposite side. I think I can vent around the core pin. What do you think of using a screw thread for the core pin? I'm worried if I use a steel dowel, the aluminum will shrink and I'll never get it out. - Maybe it'll lock hard on the threads with the same problem. - Use a wood dowel which I'll have to replace every time? + If there's a hole there I can chase it with a drill.
Good luck with your casting session, it's been raining all week here. With your aluminium castings, it's possible to make a perfectly good serviceable casting with some hydrogen porosity and even sand inclusions. If the casting is "Fit for purpose" then other considerations are secondary. I'd heard that aluminium engine blocks by a major car manufacturer need dipping and impregnating in sealant but are otherwise perfectly fine. When I melt alloy wheels, I've skimmed the melt surface clean and been amazed at the crud brought to the surface by scraping the crucible walls below the melt. Don't be afraid to waste a bit of the melt to get all the crud out before pouring. For a half inch hole I'd be inclined to leave out a core and just drill it afterwards, one less point of failure during the casting process.
Thank you Mark. I plan a trip to the scrap yard in the morning to find some castings...... and I'll omit the hole for now. I'll have to research that some more because so far what I read didn't make sense. I did read a lot about hydrogen gas and aluminum though. I spent an embarrassing amount of time on a pine flask trying to get the frames flat. Wow. Devil Forge recommends 500F for 30mins which I did in the oven, then fire the crucible red in the furnace. I lit the furnace for the first time, tried to bring the temp up real slow at 0.02Mpa. The flame started blue/yellow. I tuned it to bright blue, which then faded to orange with soot no matter what I did so I cut the gas. As the propane in the lines used up the flame got hotter until it went out so I have an air problem. [Edit] If I light the forge, all is well initially, then I think the flame backs into the burner tube. When this happens I get a "bubbling" sound and the flame turns very dark blue, then eventually orange. If I lift the forge lid I get blue flames in a vortex surrounding the crucible out the top, but the flame is still orange from the burner with bubbling in the tube. The burner tube is completely open with no obstructions. Fast forward, I was missing a detail. Hopefully by admitting my ignorance it'll help someone else. Seems you're supposed to start the burner with the choke closed, which directs the flame into the furnace (because it has no where else to go) which produces a huge orange flame out the open furnace. Close the lid and slowly open the choke. The flame turns less orange out the lid exhaust, and advances the burn inside the furnace as you slowly open the choke until finally you have the sustained roar well contained inside. Devil Forge I guess assumed I knew how to set the flame, cause the instructions are quite vague on that bit. On a positive note, the mortar and crucible should both be ready for tomorrow. Duh. Any criticisms? If so I'll edit the instructions.
Looking forward to hearing how it goes. My propane burner seems to light and run fine with whatever air setting I concluded with the session before. I set a small bit of burning cardboard in the empty furnace, slowly open the propane until it lights and then add the charged crucible and close the lid. You may want to be a bit hotter than 1300 F to give yourself a little more time to scoop dross and pour the casting as it has considerable surface area.
when they say salt, they dont mean Table or rock salt, Back on AA YEARS back there was a long thread on using Rock salt and "salt Substitute" + pool shock ??? one of the other old member may remember it better, and share again first off FLUX is really overused with good clean metal you dont need it in non ferrous melting ;... Smelting is different and not interchangeable it requires LOTS of flux, because you are not starting with metal your starting with Ore entirely different process, go to this thread I discuss how i Degass Aluminum http://forums.thehomefoundry.org/index.php?threads/degassing-question.2179/#post-45060 yes Im that sawdust guy I dont really understand it, I used to use pool shock and occasionally git REALLY gassy aluminum ( Buy a new bag of pool shock every time, pool shock draw moisture , which will add gas to you metal rather then remove it ) when I switched to sawdust I have yet to have a gassy casitng does not seem to matter what type of sawdust as long as it is dry, I just clean out my tablesaw hopper, I suppose you could use hamster bedding if you have no other source for sawdust, just make sure it doesn't have a fragrence added here is another thread with alot of degassing info its on brass, but there is alot of crossover talk http://forums.thehomefoundry.org/index.php?threads/white-fluff.1443/ V/r Ht1
Interesting. I made ten lights with the same bad results until the procedure above where I had three perfect lights. I guess it's like driving my old car; Runs and drives fine long as you know it's quirks. I did see that discussion days ago. Thank you...... remember thinking the sawdust is a skin or barrier that prevents contact with air. I have plenty of saw dust. I also wondered how I could change my crucible to a bottom draw. Maybe I'll weld up a steel version. There was an ancient Chinese? cup that did this for drinking wine. I'm too lazy to look up, see what it was called. I'll look at the videos. Right now I'm taking a break from sifting new sand and cat litter all while grumbling because I didn't order Petrobond.
It's common to confuse fluxing with degassing aluminum. I don't think plunging salt flux into the melt does much of anything to remove hydrogen from the melt. Drossing fluxes just help the dross to stick together and be easily skimmed. They may also provide some benefit as an H2 barrier on the surface of the melt if left in place and removed just before the pour, but so does the dross itself. The one thing melting salt in your furnace will do is grow a layer of rust on your furnace steel and most ferrous objects nearby. I agree with HT1 that fluxing is way overdone and mostly unnecessary. I used it when I started but havent used it for years. Only exception may be if you are using very dirty uncleaned scrap that has lots of paint, oil, and trash present. Best solution to that is use decent melting stock. You mention 6xxx alloy. If it is clean, it will be ok to experiment with but it won't flow as well and will shrink more than casting alloys. Find yourself some cast scrap and chop it up so it will fit in your crucible. If it's even relatively clean you will have a shiney molten metal surface on your melt by doing nothing more than skimming before you pour. The homebrew flux mentioned is a ~50/50 Eutectic of Sodium Chloride (NaCl) and Potassium Chloride (KCl), which is table salt and sodium free salt subsitute. The mixture melts at a lower point than either of the two salts enabling it to be liquid at molten aluminum temps. As a first time caster, I think you have a lot of other more important things that will determine your degeree of success than fluxing your melt such as: Learning to optimally tune your burner for a lean flame. Rich burns can/will create very gassy aluminum. Use casting scrap instead of wrought or extruded alloys, definitely not beverage cans. Getting your green sand mixture tuned and prepped with the best proportion of binder and water. Buying Petrobond eliminates this first time variable. Pattern prep, gating, and molding. Rehearse and make sure you have a sound procedure for staging and handling the melt before and as you pour. Including measurement of molten metal temp is very helpful for repeatability. Gathering everything and getting started is the biggest step. The rest is refining and repeating the processes that work well for you. Best, Kelly
Progress report. I made 50# of green sand in 5# batches playing with the recipe to see what happened. The first mold fell apart so I went through the whole thing again, adding, taking away with no real confidence. Assuming I didn't pack it hard enough this time I used a rubber hammer with a spritz of water each time I rammed a level. Sand and SC red clay worked better than what I made today. I still had it sealed in a bucket with my very first pour out of the charcoal grill. The mold had setup rock hard like a brick as in, it won't break except with a hammer. At the moment I have the draft? side backing in the +90F sun today. We'll see. I called the only local place I could think of, no Petrobond. Now I'm really kicking myself for not ordering the junk. Maybe I'll learn some'ftin
Rejoice with me brothers, for I have created the world's worst green sand. Inside the can it forms perfectly. Once it sees air all the green little sands get useless and lazy. On a positive note though, I'm making more of this SC red clay because if you're patient it sets up strong for MAYBE a tomorrow pour. Think I'll call it RaYd, whaat, an blee-yoo sand.
Short story is I made a lot of sand. RWB sand packed and locked in hard and made a beautifully detailed mold in my opinion. 2nd to last attempt the core which is just a 2in tall bump on the parting line stayed in the part, so I rebuilt it and run a 3in deck screw in. Cut the sprue, runners, riser, but final assembly for the pour the flask flexed, dumped the sand out. I have a few improvements in mind for the flask. Right now it's 10 x 12in which is very heavy to lift rammed with sand. I think I'm going to make a 8 x 8in flask, put the sprue and riser in each corner. I have some more research to do...... I was so stinking close to pouring a part! I ordered 140 mesh Petrobond. I remember reading something about the super fine stuff not letting gasses escape else I would have ordered 190 mesh and had it Monday.
Sorry to hear it was so close...but glad to hear that you have a sense of humor and are still trying. What are you using for a parting compound and pattern prep? Are you using boards under the flask halves and complete assembly?
I used talc on the parting line and part. It seemed to work ok but my sand is a tad wet I think so some of the talc transferred with sand to the other side, but nothing that would stop production. I used sheet rock. It's flat, smooth, strong and easy to cut, plus it's a great doodle pad for working out ideas and keeping track of weights. Thank y'all for the help. I'll give it a go again soon.
You might augment your parting compound by using a very thin layer of dry sand as parting. I have found it to be remarkably effective. I also dust on some talc most of the time. But I think the sand alone is far superior to talc alone. I tend to brush it off of surfaces of the pattern as I don't want a lot of loose sand there. Denis
Thank you Denis. I tried the dry sand as you mentioned but it all run off my printed pattern and pooled at the bottom so I went back to the talc. I worked most the day on another attempt at my first pour but a minimal chance of rain turned into a pop up summer torrential downpour minutes after I shut off the furnace and got everything out of the weather. I did practice handing the crucible and planning the pour. I hope the mold stays intact covered up till I get another chance. Maybe a dumb question but..... So it's full sun, middle of the day and I could not see the flame in the furnace. It "Sounded" ok but I just couldn't diagnose the flame color at all. Is there a trick, or does it just come with experience? Oh, Petrobond is some amazing stuff for creating a mold. It's expensive, but wish I'd have heeded the advice and started with it instead of wasting time making my own sand.
Partial success. In my finite wisdom I built the mold up-side-down. My theory was I'd use the dome to vent gasses which I suppose would have worked given enough pour height, but it didn't. I had a little problem getting sand to stay inside the slots so I'm making a new pattern with 10deg of draft. I had a lot of trouble with the burner which I'm still sorting out. I was stuck at 900F for a while, then for some reason it "Flamed ON!", come up to 1500F melt over no time at all. I had so little dross I debated on even skimming it. The aluminum was too hot but I didn't see any degassing, but maybe I would have if the part had filled. Thank y'all for the help!
Too small of an ingate. Try making the ingate longer so you have more contact area to the casting. I would feed into two side. Wrap the gating around the casting and feed into each side. Also add a trap at the bottom of the sprue. Looks like loose sand nearly stopped up the runner/ingate.
Wow. Really, thank you. I see exactly what you mean. Loose sand did stop the ingate. I panicked and poured the rest of the melt down the riser which was pointless since the aluminum knit line stopped short of the riser. My gate was .5 x .15" which I thought would have been plenty. I'll look for a surface area vs. gate size "Rule of thumb"
Im not very experienced with aluminum gating but (head pressure) cope height, thickness of the casting and casting weight has everything to do with gating design. Depending on your level of tolerance for inclusions it is usually better to go too big with gating than to try and get it down to the exact thousandth of an inch. You will have to have all of your processes 100% accurate for such a finely tuned gating system but over sizing it will give you much more forgiveness if you sway out of your process range. It can also lead to slag inclusions and much harder gating removal but for beginners I would suggest going bigger for a higher rate of success.... so go big enough to know you will make it and clean your metal thoroughly before pouring.
With respect to using dry sand for parting, I do not use it for parting on the pattern itself as it does just fall off. But; after ramming up the drag, applying sand to the sand and pattern will help prevent the cope sand from bonding to the drag sand resulting in a clean separation of cope from drag. I usually brush sand off the pattern. Sure works well for my green sand molds. Denis
