My first pour went pretty well

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steamin10
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Re: My first pour went pretty well

Post by steamin10 »

OK, now pay attention, as this is how well memory serves, and why an information Library is key to continued success:

C W Ammen, wrote a book in my Library called 'The Metalcaster's Bible'. It was published by TAB books, of McGraw Hill. My copy is 1980.

Page 241; under Degassing: The removal of absorbed gasses from a metal bath by chemical or mechanical action. Deoxidizing Red Brass with phosphorus copper would be a chemical reaction. Removing gas from an aluminum bath by bubbling dry Nitrogen through it is a mechanical action as the Nitrogen does not react chemically with the aluminum or disolved gasses, but provides a mechanical vehicle, (bubbles), which the gasses attach themselves to and ride to the surface and out.

That is a verbatem statement.

:roll: Now , whether I added or crossed information, with something else I read is open to question. I consider it closed at this point, only to say that information diseminated here should be guiding and correct, with appropriate leads to information and cautions to be explored as necessary.

I will close by simply saying that metal casting has been done for literally thousands of years, since civilization came to need formed metals. It has progressed, and many facts can effect the success of the home foundry guy. Once you get beyond melting tooth paste tubes ( remember the tin/lead ones?) for toy soldiers or fish sinkers, you will require more information. Making Jewelry for Mom, or a Model Locomotive bring up the same qestions of use and technique. Happy casting... :mrgreen:

Harold: I hope this helps clear any questions, not that we are in conflict here.

There are several books that are written for casters. Mr Ammen has several, but it should be noted he writes from 35 yrs experience at the time, and while the US Navy manual for casting is helpfull it is rather sketchy, and depends an resources not readily available in a household. Art casting and similar books are focused on the small scale shop, and are worth exploring. At any rate, many books have a limited focus, and are less worthy of attention.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
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Harold_V
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Re: My first pour went pretty well

Post by Harold_V »

steamin10 wrote:Harold: I dont disagree, that hydrogen is a problem. But the question becomes why use Nitrogen?
Because it works, and eliminates the use of a hazardous substance, namely, chlorine. I do not claim to understand the chemistry involved, but I'll hazard a guess that nitrogen bonds with the hydrogen and is removed when the nitrogen escapes as a bubble. I've seen it in use, and that's the closest I can come to even a hint of an explanation.

There are other degassing processes, one of which uses hydrofluoric acid, along with other constituents. It would appear to me that the use of nitrogen borders on a miracle where safety is concerned.

If you have a few moments, do a little research on molten aluminum. You'll discover that the only gas that it dissolves is hydrogen, and the degree of solubility increases with temperature. While it's not the only source of inclusions in aluminum castings, it's one of them, and can be eliminated by proper degassing. Oxygen is not an issue with aluminum, aside from forming dross.

By the way, I mentioned that paint and oils are a source of hydrogen, but so, too, is water. Molten aluminum absorbs hydrogen from the atmosphere, a condition exacerbated by high humidity.

Harold
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Harold_V
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Re: My first pour went pretty well

Post by Harold_V »

steamin10 wrote: Removing gas from an aluminum bath by bubbling dry Nitrogen through it is a mechanical action as the Nitrogen does not react chemically with the aluminum or disolved gasses, but provides a mechanical vehicle, (bubbles), which the gasses attach themselves to and ride to the surface and out.
Hmmm! Ever wonder who thought to give it a try?

How fortunate we are to have those that have gone before us, to blaze the path, making our efforts more successful. I'm not convinced I'd have given the slightest consideration to the use of nitrogen, had I not read about it and seen it in use.

Harold
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gangel99
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Re: My first pour went pretty well

Post by gangel99 »

I've done a lot of Al casting using steel pipe crucibles - a bit larger than yours. Kiln wash (available from pottery supply houses) does a great job protecting the steel (and aluminum). Very cheap and little bit lasts forever. You brush it on and the furnace heat bakes it - needs a recoat every once in a while. I'm still on my original crucibles after 100 plus pours.

In the past few years I started using pool cleaner (dry chlorine crystals) to remover the porosity. I put about 1/2 tsp in aluminum foil, wrap it around a steel rod (piece of rebar), and push it to the bottom of the molten aluminum and give it a stir before I pour. For your size crucible I'd use about 1/4 tsp.

It definitely reduces the bubbles but as others have noted it does so by creating a poisonous gas (Hydrochloric acid I think). Although I pour outdoors I started wearing a respirator with the appropriate filter when I started using the chlorine. As an amateur foundry person, you can't be too safety minded. :)
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Re: My first pour went pretty well

Post by Harold_V »

The gas liberated is just hydrogen and chlorine, so far as I know, but it's very damaging to lung tissue, and can be lethal. You are wise to avoid contact. Considering hydrochloric acid is just the same gasses dissolved in water, I expect that's exactly what happens when you breath the gasses. You form HCl in your lungs.

Harold
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Re: My first pour went pretty well

Post by steamin10 »

Having worked in a plant that uses HCL to clean steel of oxides from as rolled sheet, I can tell you that the fumes released are very potent, as your body rejects Chorine as a poison. HCL acid is 32% in concentrated form in water, normally shipped at 28% specific. It is much like bleach, but with time will dissolve flesh. ( one of the chemicals that are harbored in your stomach). As a vapor, it quickly causes minor damage to the lung lining, as an irritant, and invokes chemical pneumonia. If you ever get a good dose of fume, you will know in just a few minutes, as your lungs fill with fluid to dilute the irritant. Bad part is, it tends to gas off slowly, having a huge affinity for water, so it continues to irritate. Normal treatment is high Ox concentrations to purge the Hydrogen Chloride, and help air exchange to promote comfort. Early on only 20 minutes of treatment will reverse the effects. Left for mere hours, damage can be permanent, destroying the olivi of the lungs. Smoking carries HCL as one of the imcomplete products of combustion and is responsible for some of the deteriorating effects over time.

I just step aside from the fumes. Not a big problem in the homeguys world, but worth mentioning.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.
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Re: My first pour went pretty well

Post by bluechipmachineshop »

I really hate when people start a topic, ask a bunch of questions and disappear. I haven't had alot of time to play with the furnace lately (with earthquakes and hurricanes), but thought I'd update a little. I did a burn with coal (unknown type) a few weeks ago with really dismal results. The coal works well in my buddy's forge, but wouldn't get the furnace hot enough to melt aluminum. The end result was a alot of smoke, stink, and a sooty crucible, and no ingots. I think the soot may have insulated the crucible to some extent, but I just never got any serious flame out of the coal. I had high hopes for it, but given how unpleasant it was to burn, I think I'm done with coal, and have started building my propane burner. Heres a couple of shots of the burn (couple of changes), and the smoke and soot.
I have ordered some refractory coating for the crucible and pig molds, and a high pressure regulator for the burner. So far nothing spectacular from the burner (similar design to the Budget Casting burner), which is the reason for the new regulator. The technology seems to be pretty basic, so I'm sure I can iron out the low heat output. I suspect my junkyard reg is the problem. Soon as I get the new regulator, I'll find out how smart I am.

Mick Finch
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SP&S700
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Re: My first pour went pretty well

Post by SP&S700 »

Dear Harold

Hope this is not seen as nit picking. This is one subject I would like to gain a whole lot more knowledge on. After reading the post I tried the link on the degassing, its been changed so I though I'd post it in case other had problems finding the new link.
http://budgetcastingsupply.com/Aluminum ... ts-601.php[/url] I'm not sure how this will come out so cut and paste if you have too.

Thanks for all your help folks

Clint
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Pipescs
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Re: My first pour went pretty well

Post by Pipescs »

Quote from the "United States Navy Foundry Manual" 1957 edition on degassing Aluminum

Aluminum should be degassed with dry nitrogen. Chlorine, either solid or gaseous, should not be used in Shipboard Foundries. A carbon or graphite pipe is connected to the tank of compressed gas with suitable rubber hoses. When the metal reaches 1,250 f, the gas should be turned on and the preheated tube inserted in the metal to the bottom of the crucible. The flow of the gas should be adjusted to produce a gentle roll on the surface of the metal. Fluxing times should be ten to fifteen minutes for a 100 pound melt. Difference in size will not greatly adjust fluxing times.

Of course I have purchased chlorine at Walmart for my use.
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steamin10
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Re: My first pour went pretty well

Post by steamin10 »

Ya, I saw that. I can only explain that shipboard, implies a room or shop of some confined dimension, unlike a garage with the door open, or driveway site, as most home casters would do. The small bit of Chlorine used in powder form is a very effective way of cleaning the metal bath and bringing dross together at the surface right before pouring. Because the fumes are dangerous, even metal vapors, like lead, zinc, and mercury, as contaminants that boil off, reasonable care should be taken about buildup of smoke and general ventilation.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.
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Re: My first pour went pretty well

Post by Pipescs »

It would seem that the ten minutes of blowing cool nitrogen into the aluminum would cool it a lot
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Re: My first pour went pretty well

Post by Harold_V »

Pipescs wrote:It would seem that the ten minutes of blowing cool nitrogen into the aluminum would cool it a lot
The sole experience I witnessed was with a rather large volume of aluminum, say 200 pounds. I'm trusting to memory here, as this was one hell of a long time ago---likely 25 years or more. I remember asking Marv about the process, and recall him telling me they'd slightly superheat the melt, then allow the nitrogen to percolate through the aluminum until it was down to pouring temperature. None of this was done without the use of a pyrometer, as you might imagine. With the large volume of metal, cooling wasn't rapid. Might not work as well with a small heat.

Avoiding the use of chlorine aboard ship was most likely mandatory to prevent lung damage and death. While it's relatively harmless in small quantities, it is very capable of killing when concentrated, and is extremely hazardous. It is for that reason it hasn't been more popular in the gold refining arena (the Miller chlorine process), as it is capable of yielding fine gold in short order, using the same basic technique that it is used for aluminum.

Harold
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