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#11
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How To Make a Smelter
On Jan 25, 9:36*pm, " wrote:
... Mine, I gotta sit it down. *So I have a Sitting Down Place. Concrete. *Dry. *... I cringed when I read this. Concrete isn't dry. There is always water retained in the matrix. Heated, it can flash into steam and explode small chips of concrete and whatever it was that was hot enough to explode it up into the air. It is best to use dry sand. If you can, heat it before each use to make sure it is dry. And between uses keep it covered as you never know when a cat is going to come by. |
#12
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How To Make a Smelter
"Fred the Red Shirt" wrote in message ... On Jan 25, 9:36 pm, " wrote: ... Mine, I gotta sit it down. So I have a Sitting Down Place. Concrete. Dry. ... I cringed when I read this. Concrete isn't dry. There is always water retained in the matrix. Heated, it can flash into steam and explode small chips of concrete and whatever it was that was hot enough to explode it up into the air. It is best to use dry sand. If you can, heat it before each use to make sure it is dry. And between uses keep it covered as you never know when a cat is going to come by. ----------------------------------------------------------------------------------------------------- You're right about concrete, but with the low melt temp of aluminum, 20 to 30 pounds of aluminum on a floor at least 2 or 3 years or so old is not a big deal. But concrete 3 to 6 months old, or higher temp metals can be real exciting. Sand, because it is loose and permeable, can contain 3 to 5% moisture with no problems at all. As much a 5% is often used for molding. |
#13
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How To Make a Smelter
Maxwell wrote:
"Fred the Red Shirt" wrote in message ... On Jan 25, 9:36 pm, " wrote: ... Mine, I gotta sit it down. So I have a Sitting Down Place. Concrete. Dry. ... I cringed when I read this. Concrete isn't dry. There is always water retained in the matrix. Heated, it can flash into steam and explode small chips of concrete and whatever it was that was hot enough to explode it up into the air. It is best to use dry sand. If you can, heat it before each use to make sure it is dry. And between uses keep it covered as you never know when a cat is going to come by. ----------------------------------------------------------------------------------------------------- You're right about concrete, but with the low melt temp of aluminum, 20 to 30 pounds of aluminum on a floor at least 2 or 3 years or so old is not a big deal. But concrete 3 to 6 months old, or higher temp metals can be real exciting. Sand, because it is loose and permeable, can contain 3 to 5% moisture with no problems at all. As much a 5% is often used for molding. Beg to disagree with you , but concrete which was cured properly ( kept covered or sprayed with water, so that the water can chemicaly combine with the materials in the cement ) has considerable moisture in it known as "water of hydration."--This bond can be broken with the application of heat.--I watched an asphalt storage building burn---the melted asphalt would run out on the floor and burn for a while, until POW! a large piece of the floor would explode flinging concrete & burning asphalt 10 or 20 ft away.---the floor was at least 20 years old or so..Poorly cured concrete still has some water bound up in it, maybe not as much--but it is not as strong as that which was properly cured. |
#14
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How To Make a Smelter
"Jerry Wass" wrote in message .. . You're right about concrete, but with the low melt temp of aluminum, 20 to 30 pounds of aluminum on a floor at least 2 or 3 years or so old is not a big deal. But concrete 3 to 6 months old, or higher temp metals can be real exciting. Sand, because it is loose and permeable, can contain 3 to 5% moisture with no problems at all. As much a 5% is often used for molding. Beg to disagree with you , but concrete which was cured properly ( kept covered or sprayed with water, so that the water can chemicaly combine with the materials in the cement ) has considerable moisture in it known as "water of hydration."--This bond can be broken with the application of heat.--I watched an asphalt storage building burn---the melted asphalt would run out on the floor and burn for a while, until POW! a large piece of the floor would explode flinging concrete & burning asphalt 10 or 20 ft away.---the floor was at least 20 years old or so..Poorly cured concrete still has some water bound up in it, maybe not as much--but it is not as strong as that which was properly cured. I think you misunderstood Jerry, I agreed he was right about the hazard of heat and concrete. My example was from personal experience. Spilling 200 to 300 cubic inches of 1400 degree aluminum, on a concrete floor more than a few years old, is not usually a really big deal. Uncontained, it will spread and quickly cool by 50% in a matter of seconds. In your example, obviously more than 1400 degrees, with an exposure time of many minutes, it can be a really big deal indeed. No matter how old the concrete. |
#15
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How To Make a Smelter
Maxwell wrote:
"Jerry Wass" wrote in message .. . You're right about concrete, but with the low melt temp of aluminum, 20 to 30 pounds of aluminum on a floor at least 2 or 3 years or so old is not a big deal. But concrete 3 to 6 months old, or higher temp metals can be real exciting. Sand, because it is loose and permeable, can contain 3 to 5% moisture with no problems at all. As much a 5% is often used for molding. Beg to disagree with you , but concrete which was cured properly ( kept covered or sprayed with water, so that the water can chemicaly combine with the materials in the cement ) has considerable moisture in it known as "water of hydration."--This bond can be broken with the application of heat.--I watched an asphalt storage building burn---the melted asphalt would run out on the floor and burn for a while, until POW! a large piece of the floor would explode flinging concrete & burning asphalt 10 or 20 ft away.---the floor was at least 20 years old or so..Poorly cured concrete still has some water bound up in it, maybe not as much--but it is not as strong as that which was properly cured. I think you misunderstood Jerry, I agreed he was right about the hazard of heat and concrete. My example was from personal experience. Spilling 200 to 300 cubic inches of 1400 degree aluminum, on a concrete floor more than a few years old, is not usually a really big deal. Uncontained, it will spread and quickly cool by 50% in a matter of seconds. In your example, obviously more than 1400 degrees, with an exposure time of many minutes, it can be a really big deal indeed. No matter how old the concrete. You sooo right---Ya Know, the reader usually puts more into the statement than the writer intended.. |
#16
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How To Make a Smelter
On Tue, 27 Jan 2009 16:47:51 -0500, "Morgans"
wrote: "Stealth Pilot" wrote hydrogen embrittlement was a big bogey man in home castings but it is easily understood and conquered. OK, I understand hydrogen embrittlement is a "bad thing" but my question is, where does it come from, start, or what do you do to prevent it from happening in the first place. I did like your hints for dealing with it, and can definitely relate on the hydrochloric acid in the nose bit. Also to be considered one of the "bad things." g I'm not an industrial chemist. this comes from watching what happens in my castings and reading some of the references mentioned. I first twigged to what may be happening when I grabbed some pistons that had been sitting outside and plopped them into the part filled crucible to get the volume up for a pour. they were damp. I thought a furnace at many hundreds of degrees would dry the stuff pretty well instantly. the casting turned out to be like aluminium foam. first time it had happened to me. the possible explanation is that the water didnt evaporate but dissolved into the molten aluminium. what points me to this is another oddity. you would think that copper with a melting point of 1500 degrees would be difficult to incorporate in aluminium which is only at 360 degrees or so but it isnt so. stir the mix with a copper tube or rod and the rod will absorb readily into the molten aluminium. I think that the same thing occurs with water believe it or not. the fluid appears to dissociate into its component parts in the molten aluminium. the oxygen causes lots of oxide froth on the top of the crucible. the hydrogen remains as a dissolved gas until the aluminium starts to solidify whereupon it comes out of suspension as bubbles. where does it come from? any source of moisture that gets to the molten metal. wet or damp oxide coated stuff that you are recycling has done it to me. personally I've never found it related to humidity in the air but Mr Ammen mentions it. the easiest way I've found of preventing it is to store the scrap inside and keep it clean and dry. melting clean dry stuff has always resulted in sound castings for me. It is a pity the hydrogen bubbles formed on cooling couldnt be controlled because the foam aluminium is quite light. you just cant control where the bubbles form and thus the structural integrity. Stealth Pilot |
#17
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How To Make a Smelter
Stealth Pilot wrote:
On Tue, 27 Jan 2009 16:47:51 -0500, "Morgans" wrote: "Stealth Pilot" wrote hydrogen embrittlement was a big bogey man in home castings but it is easily understood and conquered. OK, I understand hydrogen embrittlement is a "bad thing" but my question is, where does it come from, start, or what do you do to prevent it from happening in the first place. I'm not an industrial chemist. this comes from watching what happens in my castings and reading some of the references mentioned. What you are describing is not Hydrogen Embrittlement. Hydrogen Embrittlement is usually more of an issue for high carbon steels I believe, though it effects aluminum as well. You can find information on it under the heading of stress corrosion cracking and it is more of an environmental issue than casting, as it is a problem for forgings and weldments as well. It is the mechanism of failure I am pretty sure for the old VW cases, as magnesium alloys are very susceptable to SCC. Your description of the problem of the casting problem though is spot on, if misnamed. Here is a good link on this and other alumminum casting issues: http://www.keytometals.com/Article83.htm Charles |
#18
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How To Make a Smelter
"Charles Vincent" wrote in message ... Stealth Pilot wrote: On Tue, 27 Jan 2009 16:47:51 -0500, "Morgans" wrote: "Stealth Pilot" wrote hydrogen embrittlement was a big bogey man in home castings but it is easily understood and conquered. OK, I understand hydrogen embrittlement is a "bad thing" but my question is, where does it come from, start, or what do you do to prevent it from happening in the first place. I'm not an industrial chemist. this comes from watching what happens in my castings and reading some of the references mentioned. What you are describing is not Hydrogen Embrittlement. Hydrogen Embrittlement is usually more of an issue for high carbon steels I believe, though it effects aluminum as well. You can find information on it under the heading of stress corrosion cracking and it is more of an environmental issue than casting, as it is a problem for forgings and weldments as well. It is the mechanism of failure I am pretty sure for the old VW cases, as magnesium alloys are very susceptable to SCC. Your description of the problem of the casting problem though is spot on, if misnamed. Here is a good link on this and other alumminum casting issues: http://www.keytometals.com/Article83.htm Charles Actually it highlights his misunderstanding of the process. In an effort to look like he knows something about casting, he began searching the internet and found reams of confusing material discussing hydrogen embrittlement, and confused it with hydrogen absorption. Nice link, by the way, it at least begins to discuss the difficulties of pouring quality molten aluminum, especially in low volumes if you read between the lines. Saying you are going to pour a quality casting from melting old pistons, in a steel pot, with a propane yard burner - is much like saying you are going to grind you own crankshaft with a modified wood lathe and a hand grinder. |
#19
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How To Make a Smelter
Maxwell wrote:
Actually it highlights his misunderstanding of the process. In an effort to look like he knows something about casting, he began searching the internet and found reams of confusing material discussing hydrogen embrittlement, and confused it with hydrogen absorption. Nice link, by the way, it at least begins to discuss the difficulties of pouring quality molten aluminum, especially in low volumes if you read between the lines. Saying you are going to pour a quality casting from melting old pistons, in a steel pot, with a propane yard burner - is much like saying you are going to grind you own crankshaft with a modified wood lathe and a hand grinder. It highlights his misunderstanding of the nomenclature, nothing more. Not unusual when someone is self taught, especially via trial and error. I work in a highly technical field and am still plagued by pronunciations that I assigned to unfamiliar technical terms in my self study over thirty years ago. As far as getting quality castings out of a home shop, it takes the same two things in the home shop as in production. A quality repeatable process appropriate to the end results desired and essentially a statistical testing process. Both could be achieved in the home shop, but will require the casting not of just four heads, but more likely four hundred castings, with the majority hitting the scrap bin. I think Veedubers current tack is better alternative. Charles |
#20
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How To Make a Smelter
"Charles Vincent" wrote in message news Maxwell wrote: Actually it highlights his misunderstanding of the process. In an effort to look like he knows something about casting, he began searching the internet and found reams of confusing material discussing hydrogen embrittlement, and confused it with hydrogen absorption. Nice link, by the way, it at least begins to discuss the difficulties of pouring quality molten aluminum, especially in low volumes if you read between the lines. Saying you are going to pour a quality casting from melting old pistons, in a steel pot, with a propane yard burner - is much like saying you are going to grind you own crankshaft with a modified wood lathe and a hand grinder. It highlights his misunderstanding of the nomenclature, nothing more. Not unusual when someone is self taught, especially via trial and error. I work in a highly technical field and am still plagued by pronunciations that I assigned to unfamiliar technical terms in my self study over thirty years ago. Not really. The overwelming issue with hydrogen absorbtion in molten aluminum is gas porosity, not embrittlement. As far as getting quality castings out of a home shop, it takes the same two things in the home shop as in production. A quality repeatable process appropriate to the end results desired and essentially a statistical testing process. Both could be achieved in the home shop, but will require the casting not of just four heads, but more likely four hundred castings, with the majority hitting the scrap bin. I think Veedubers current tack is better alternative. Not true at all. |
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