Degassing aluminum

[todd goff]

I degas mine with argon; the lance is galvanized steel pipe with the end welded shut and a nipple on the other end. I have small holes drilled in the end for the gas to flow through. I stay away from flux powders as they were eating the silicon carbide pots. I believe in larger spurs as the larger a sprue the more metal that can feed the casting. Yes it is more clean up but nothing like a casting with a shrink; bigger is better in my opinion.

[ghornbostel]

Todd, I doubt you are gassing your melt in the furnace unless you are sturring the melt or taking a long time to melt your heat. I use a McEnglevan Speedy melt furnace that has about 850,000 btu output. A #40 crucible of aluminum takes about 15 minutes and you have to cut your heat once you get about half a crucible heel. I have used this same burner/blower unit to heat a #225 crucible in a larger furnace shell and it would melt that amount of aluminum in about 1 hour. If you are pouring your castings directly down a large sprue then this is probably where the gas is coming from. You probably are doing this because you have been having misruns (voids in the thin walls or your castings) and being able to pour metal into the mold quicker took care to the misrun but the turbulance that resulted from the increased flow has now given you a gas porisity problem. Larger is not better when we are talking about sprues. The ratio that works is 4:1 ingates 4 times the sprue. Aluminum likes a ingate that is wider than it is tall. Stay away from round shapes and too much fillet on the corners of your gating patterns. Make a overflow pouring basin to place on top of your sprue after the mold has been made. I use a pattern mounted on a board and ram sand in a 1/8" steel flask for the basin. The finished mold (if you can call it that ) is about 6 X 8 X 4 inches tall. You pour into the basin that fills and overflows into the sprue. You must pour fast enough to keep the sprue full at all times or it will asperate and gas the metal. If the casting misruns then you probably don't have enough flow and will have to change your gating. I agree that 1350 is about right for most castings however much is to be gained by lowering that temp to where it misruns and then raise it to where it doesn't. I used the 225 crucible to pour a large 5' X 7' marker. This casting was poured one-up and off one side of the pattern using 4:1 gating at 1450 degrees. It took about 1 minute to pour the casting and 8 hours for the casting to cool before the mold could be broken down without warpage. The flask was 10' X 8' and 6" over 6" using green sand for the mold. I really wish I had photos of this mold but in 2002 a tornado completely destroyed my foundry and no paper that was inside of the building survived. Each and every pattern is different. Use experience as a starting point and develop the casting from there.

Best of luck
Greg Hornbostel

[steamin10]

ghorn: Thanks for the contribution. According to the post number you are new here, welcome.

Just to comment on your post, it is reasonable to assert that the numbers and dimensions given are starting points, and there is nothing written in stone. But far from fly by night or seat of the pants judgements, there is a progression of do's for any given job, based on your knowledge of your particular equipment and routines. Reading for the meaning of your post, I sense your experieince for the feel of larger work than I do, in a home shop setting. The success or failure of any particular cast, is mostly in the hands of the craftsman of the art.

I hope you find time to contribute further in the future.

[todd goff]

That was some very good information ghorn. I have basically taught myself how to do foundry work through books and what not. My grandfather taught me some when he was alive (he worked in a foundry for a textile mill mainly doing iron). Casting is something I enjoy; it gives me an escape from the routine grind. Seems that I learn something every time that I do a pour.

[ghornbostel]

Dave, My experience in foundry work is in aluminum and brass/bronze. Green sand and permanent mold. The size range was 1lb to l80lbs over a period of 25 years and drawing off the knowledge of a employee that had been there 20 years prior to my ownership. Mainly a cast aluminum/bronze plaque foundry that turned into a tilt-cast permanent mold foundry. Over the years I found out that there are two methods that work in the foundry, those that you can and those that you cannot make money at using the process you have in house. If you want to change that process look to the area that is most successful at it and try to pick their brains clean of that process. If that fails or falls short then go to AFS. This organization is cut and dried. Yes the numbers vary some but not a whole lot and in the end I have found that all the different castings I've been involved with all fell within these gating, sprue and heat values. Now, there is another value called directional solitification. Without this you probably won't be able to make a casting that will pass a pressure test. Once you understand this concept all your castings, pressure tested or not, improve. The only way I've found to attain this is with gating systems with the above or near above numbers. AFS has a publication actually two.. Casting Aluminum and Casting Copper Alloy Metals. Not the actual titles but in the ball part. Like I say, its cut and dryed you just organize the numbers in a different way.

[ghornbostel]

Dave, Sorry I got distracted and hit send instead of save. Back to AFS, these two publications are quite expensive but the oversight into all the casting techniques of both aluminum and copper base is worth the price. Now, I believe the title of the blog is The Home Machinist and we all are making do with the junk we have . I have to admit that I've invented the wheel many times only to find that round still works the best but you never know until you try something else. I decided after about 20 years of this, that we as a foundry industry based on over 3000 years of practice, have some pretty basic rules. I follow the basics and bend the hell out of the rest . Todd, if you really enjoy it as a hobby go for it but be very careful!!!

Just an old man rambling on in the middle of nowhere

Greg Hornbostel

[Harold_V]

Just an old man rambling on in the middle of nowhere

Greg Hornbostel

Ramble on, Greg. This old dude is sucking up your comments.

One I enjoyed in particular is the comment that the wheel is already round, and is hard to improve. I moderate another forum, one that revolves around refining precious metals, and that's one of the hard things to convey to those that think they should alter what has worked for ever.

It's nice to have you on the board. Foundry work is one of the areas where we have little expertise on which to call. Please do keep your comments coming.

Harold

[steamin10]

Ghorn: I worked at Blaw Knox Mill Machine and Foundry, In the early 80's. We made the last M-60 tanks for Chrysler Tank, and poured the first turret bases for the M-1. The other side of the plant made rolling mills and mill rolls for the steel and sheet rolling industry. I was a craneman first, then Millwright, assembling huge machines. I got dusted, toasted and roasted in various ways, and finally was dubbed and Ace Craneman, where they used me as relief in the huge machine shop, where a bump from a 2-300 ton casting broke really expensive machining equipment. I got to study many aspects of iron and steel (armor) castings, and the making of cores and Furan bonded sands. Not to mention really large machine work. I started fooling with aluminum casting as part of my Model Train interests, and learned from there. I built one furnace and then bought a Speedy-melt, and two McEnglevans through school auctions. Indiana dumped machine work into Junior Colleges, mostly because of the rising risk in unruly schools.

My Personal experience in small founding is solid, but small. I do not have assay equipment, to determine alloy, but rely on best guess from published product charts, for probable alloys. I get skunked now and then, like a dead bronze bell. Leaded bronze must have been in the scrap, cause it was a dead 'DUNK' when hammered. It tarnished really fast, and thats a dead give away. Any lead in bronze or brass, lets it machine like butter, but at the cost of not being able to keep the part polished, and being unusable for a bell, of any shape, or size.

Anyway, beyond my ramblings here, I appreciate the company of some experience.

My Furni are taken down, as I have a space problem, among other things. But I want to cast a few parts out anyway. Mostly truck frames and dreadnaught car ends, and gon ends. In Bronze I have some Stationary Engine patterns, but nothing has drawings, so it is a slow process to bring them out..

[steamin10]

Todd: You are wasting very expensive gas with Argon. The reaction is the Oxide of Nitrogen from the high heat pulling disolved oxygen from the heat. The idea is to pull the gas out before the liquid solidifies on pouring. Just like Ice has to drop it gas before freezing. Argon is inert, Nitogen forms Oxides with disolved Oxagen at high temps giving NO2.

I think you are wasting your gas, and your time.

[todd goff]

I wonder which gas would work. I hear a tale of a 75/25 nitrogen argon that they say works good and I wonder if that's what I should use. I have been told that a 16 crucible should not need degassing. I am fixing to crank up some larger furnaces, putting a steel pot in one, putting the rats unit in place and getting a rotary degasser. Fact is that it is costing a decent little sum (at least to me) but it is used equipment and is a fraction of the cost. I am hoping to grow and take on larger jobs and feel that this will help out in the future. Man, I wish everyone on here was closer to me but I am down here and y'all are up there.

[steamin10]

Well, Nitrogen is the gas of choice for the chemistry for Aluminum, and I dont know of any positive effect that Argon will give you beyond welding shield gas.

Pretty much Flintstone for my operation. I think my largest vessel is a #30, and it remains unused. I have an overhead hoist and trolley system, but never got that heavy to go beyond a hand shank and pouring rail. The machanics are simple, it is the details, like wet aluminum, not preheated enough before adding that gets you, (splattered). Or spills on concrete. That kind of thing. Small things always bark at me, and I pay attention, because the bites are not fun. Anyway I am NOT a huge founder, but have done enough to know. I dont know your advanced equipment, so you are on your own there.

[ghornbostel]

Todd, there is a test you can do to determine if you have gassed your melt. Simply weld a bottom on a 2" I.D. tube about 8" long and pour aluminum into it and let it solidify. If it pipes down there is a pretty good chance there is no gas present or at least a small quanity. If it domes on the top you have problems for sure. If you have a machine shop to go along with your foundry that slug makes really good spacers and other objects out of downright scrap. Not everything needs to be machined from 6061 bar stock.

regards
Greg Hornbostel