Degassing aluminum

[steamin10]

Yes , indeedy! It is real handy to make bar rounds, and discs of bronze and aluminum for stock to whittle on. While buying what you need is easy, price a foot of 4inch bronze, that I get to cast from swarf and leavings. Not only that , I can cast it with a preformed hole in it for an antique that needs it. Having the ability to cast things makes working old Babbitt stuff easy by comparison.

Todd, use the pointy end of a hand rammer to make a good beveled print in some sand and cast a test bar. It will freeze quickly. Put it in a vice and bend it with a wrench, or snap it with a hammer. Good cast aluminum will give a bit then snap, or fold into prezel shapes, depending on the alloy. If it snaps it will have large grain showing or not, and pourosity will be visible or not. The little test bar speaks mountains about what is going to happen, right before you pour. Once you 'get it' with your eyes, you will know without wasting your melt or mold, what you can do.

[todd goff]

I am planning on putting reduced atmoshperes in place. I actually have a dynarad tester and recently bought a rats 401. I am trying to get into casting on a larger scale and figure that when I get the rotary degasser in that having testing equipment and degassing equipment will be a selling point. In addition, I am working on a web site right now; what I am trying to do is make some castings off of the patterns that I have such as ash trays, nut crackers, coat hangers, mailbox decorations and plaques. When I get it done I will post the website to try to get everyone's opinion on it. I am hoping to get big enough where I will have the capabilities to pour at least 200 # aluminum castings. I know this will take some doing but I think it is possible. The trip to disney world did me good; in the words of walt disney; "trying to do the impossible is kind of fun sometimes." I hope to drum up some custom casting business; I love doing small volume but wouldn't be scared of jobs running up to 1 or 200 pieces. I have been finding that I am getting good results with aluminum stators out of torque converters and transmission housings but realize that if someone did spec out a certain grade that I would have to do that. I am not prepared to keep pallets full of ingots on hand and I guess that really if this were needed that I would have to set a minimum order to justify it. Am I on the right track right now with my ideas or has my train left the tracks (lol). No one is going to hurt my feelings with any criticism; I am just about past that; thanks again greg and steamin.

[steamin10]

Take a deep breath, and know this: You dont know a tenth of what you need to know.

You need to start small, and GROW a business and a standing. Dont worry about the money, just be a miser and make Nickles cry. People pay for ability and gimmics. Ability first. Making a reasonable profit is hard , and the best way to ruin a hobby that I know of.

I wish you luck, and bid you peace. Both are gonna be in short supply in your venture for a while.

[patternguy]

Todd, Big D and ghorn have it correct from my 27 years in the biz. I started a pattern shop 3 years ago, and one of my customers is an aluminum foundry. I was there today, and he told me he keeps the pot temp at 1440 degs. and degases with nitro. 1340 degs is a good pouring temp. He said to get started for you to use degas tablets. There is a place called Budget Casting Supply that has them. Ghorns other point about gating is also on the mark. There is no better way to make a sound casting than to have a good gating system. When I was an apprentice, I went to a two week AFS gating school. I have gated hundreds of patterns in my life, so I know how important it is. If you need help with gating, I can try to help,or we can get some info from my buddy at the foundry. Dave C.

[steamin10]

Ya, even a broken clock is right twice a day. I think those tabs are Chlorine, that is easy to get as pool tablets like HTH. I use them all the time. Break up a tablet to grainy powdered chunks, About a tablespoon of material, and wrap it in a square package about 3 inched across. Fold the corners over your infusor, a piece of stainless pot lid, on a broom stick about 30 inches long, and energetically plunge into your ready heat with coupla twisting motions to agitate the metal. Bend away from the fumes, the Chlorine is nasty for your body. Fumes will rise quickly, and withdraw your infusor immediatley after the swishes. Last quick skim and pour, with the temperature check. I have a Non-ferrous thermocouple that direct reads the pot. Mine says McEnglevan. It is important to have one, otherwise you wind up guessing at dull red heat for temps, not nearly as good. But I started without, that way, and had success, just got easier with the right items of equipment.

[ghornbostel]

Well guys, this discussion probably needs to go back to the original question, testing for gas. Everything discussed so far involves extra money to produce a casting (hypothetical I might add) that may or may not require attention because of a quality problem. Aluminum can be melted without gassing. It would be to your advantage to do this. I casted aluminum for about 30 years on a daily basis and really can't remember gassing a melt. You just really have to be doing something wrong to gas this metal at melt. A first and last sample that can be cut up to look for inclusions and gas is the cheapest way. You can at least reclaim the test which you can't do with an inoculant. Gas forms bubbles under the skin of the casting and oxide inclusions are the little black dots on a polished aluminum surface. To get either one of these you are not melting or gating your casting correctly. The oxide inclusions in your charge are there to begin with and must be floated to the top of the crucible where they can be removed or you have to put a filter into your gating system. All gas is gone on solitification. If inclusions are a problem with your customer then you will have to stop using scrap and buy specification ingot and be very careful about what you add back into your heat. Todd you need to get your feet wet i.e. melt some metal and pour it into some castings and cut them up looking for the defects that feel are present. Then you need to solve the problem, if it exists, like all of us have in the past, systematically. And then do it all over again. Thats why we call it foundry practice.
Regards
Greg Hornbostel

[steamin10]

ABSOLUTELY! Develop your system, and make it consistant. Reduce the number of variables you put in. Fix it if its broken, but if it works, stay withit. You will shorten the learning curve alot.

Two things that drove me nuts until I got smart, washing sand into the part, and cold shuts and misruns.

One is gating and pouring method.

The other nearly all temperature.

[jpfalt]

From what I recall, the issue isn't so much oxygen as hydrogen in the aluminum.

The hydrogen comes from oil, water or paint on the material going in, but also the combustion products of the gas flame used to heat the furnace. Once in, the hydrogen is difficult to get out. I know some people who put a lid on the crucible to keep out hydrogen from natural gas or propane fuel. I'm used to using the chlorine tablets which generate chlorine gas. The chlorine reacts strongly with the hydrogen to form hydrogen chloride, which is also a gas and which bubbles out of the melt.

An effective approach is to preheat the ingoing material to burn off the paint, oil and dry off water before it goes into the melt. Then use the chlorine tablet after melting. Some of the slag you skim will be aluminum chloride, but it's not enough to worry about. Not much extra effort, minimum expense and fairly reliable.

[todd goff]

I am assuming that the flux that I was using was chlorine. It was in a powdered form and was in a plastic bag. The bag had actually disintigrated and the powder went onto a particle board shelf. Well, long story short; it actually ate up the particle board; also, it was very corrosive to the crucibles which are so cheap (not really). I made a decision a while back to get away from this because of the extra expense and switched to the gas method which has proven to be about 90 percent better.

[Harold_V]

From what I recall, the issue isn't so much oxygen as hydrogen in the aluminum.

Thank you! I've been pondering that ever since oxygen was mentioned. It shouldn't be a problem, for hot aluminum is VERY reactive, so it quickly makes aluminum oxide, which would be skimmed as dross. Hydrogen is the culprit according to any reliable sources I have investigated.

Interestingly, my friend who runs a foundry in Utah casually mentioned oxygen was the problem when we were talking on the phone. Not being an authority on foundry practice, I said nothing, but it sure raised a red flag for me.

It should be noted that hydrogen is troublesome in other metals----the souce of hydrogen embrittlement in heat treated steels.

Harold

[Harold_V]

I am assuming that the flux that I was using was chlorine. It was in a powdered form and was in a plastic bag. The bag had actually disintigrated and the powder went onto a particle board shelf. Well, long story short; it actually ate up the particle board; also, it was very corrosive to the crucibles which are so cheap (not really). I made a decision a while back to get away from this because of the extra expense and switched to the gas method which has proven to be about 90 percent better.

Thanks for that comment, Todd. If using nitrogen eliminates corrosion, it's a damned good reason to make the switch.

Harold

[ghornbostel]

Harold, I guess the term oxides isn't a accurate term but is one that I have always used to identify the small black dots dispersed in a aluminum casting. I do know that they are caused by substances when subjected to heat tend to reduce to ash or hard particles that end up suspended in the metal bath. Adding back machine shop chips covered in oil and scrap automotive and other painted castings can really cause problems if this metal isn't inoculated or filtered. Even after all the precautions there can be a small amount of this substance adheared to the wall of the crucible and then cause problems when a later melt is sturred in the same crucible. I was also told that the cause of these dots was the result of not keeping the lip of the crucible close to the sprue and to be on the safe side to pour into a basin that overflows into a properly sized sprue. Just my experence and not a documented fact. It has also been my experience that this defect was also present when the humity was high as it often is in Nebraska. So is it absorbing it at melt or asperating down the sprue on pour? It was never a problem to my customers and as a consequence I was never driven to solve the problem short of making some observations and avoiding the obvious. If I needed a very clean casting I used a known crucible and melted commercial ingot. I don't think that this defect effected strength of the casting as during the development of a particular casting the customer subjected them to extensive and long term stress involving tensile, ductility, pressure and vibration. I guess this has become a very interesting subject for me again but someone else is going to have to do the foundry work.

Regards
Greg Hornbostel