Progress on the forge is going slow, mostly because it is very cold outside and I have not made much more fuel for it. So I figured now would be a good time to go over how the forge is/will be fueled.
Traditional forges were fueled with charcoal. Eventually coal was discovered and has been used ever since. My forge is being fueled with charcoal, because it is easy to make for free. I work at a hardware store with an indoor lumberyard. The lumber is shipped with many smaller pieces of wood used for stabilization. This wood is scrap, and is discarded as the lumber is taken off of the stacks. I occasionally collect this scrap wood and take it home. Once I have enough, I use it to make charcoal.
Simply put, charcoal is wood burned without access to oxygen. There are several way to do this. Traditionally, charcoal was made by making a large pile of wood, covering it with a light layer of dirt or sod, then lighting it. The covering restricted the flow of oxygen so that the pile burned very slowly, but very hot, with very little oxygen. This method was good for creating very large amounts of charcoal, but the quality was lacking, since some of the wood had to burn to ash in order to provide enough heat to turn the rest into charcoal.
A less efficient method of making charcoal is to place the wood in a container that has only enough venting for exhaust gases to escape, but not enough to allow oxygen to flow into the container. The container is then placed in a hot fire until the wood inside has been turned to charcoal. This method generally uses more wood to provide heat, but results in very clean charcoal. It is also better for smaller scale operations. This is the method I use. I have used empty aluminum cans (most of these are actually made of steel; aluminum would probably melt), paint cans, and a small metal garbage can. Paint cans can only be used a limited number of time, as they tend to corrode quickly. I have found aluminum cans to be generally too small for reasonable batches (I used juice cans). The garbage can works well, but it might be difficult to keep the lid on, as the can can build up some pressure. The garbage can I use has an unusually shaped handle that will keep the lid on when it is up.
The wood I am using is fir. Normally, charcoal is made from hardwoods, but I have read of issues with that type of charcoal. Others have found the hardwood charcoals produce more ash, often enough to clog and restrict airflow through the forge. The fir charcoal I am using does not produce significant amounts of ash. Fir charcoal is not as dense as hardwood charcoal. This means that I have to use a lot more charcoal to run the forge than if I was using hardwood charcoal. So, this is a trade; better forge operation, at the cost of having to make and use a lot more charcoal.
I may have come up with a solution for this problem. The compressed wood pellets used in pellet stoves are fir (the ones we sell where I work are, anyhow). These are far denser than normal fir and may even be as dense or more dense than hardwoods. In a few days, I am going to use a juice can to make charcoal out of some of these pellets. The can is full, so it will probably take a long time, since the amount of wood in the can is much greater than usual.
I do not know if ash will become an issue. Compressed wood charcoal will produce more ash when burned, but my use of normal fir charcoal has not produced even enough ash to build up a little bit (it seems that the ash is so light that it quickly floats out the forge as it is produced, but the volume is not large enough to see it leaving the forge). So, I do not know if the increased ash production will be significant.
In addition, the fuel pellets are smaller than the pieces of charcoal I normally use. This means higher burning surface area. This should cause the forge to burn much hotter. I may have to restrict the airflow into the forge to moderate the temperature. The compressed wood should last longer in the forge as well, since there is higher mass of wood. I may have issues keeping the pellets from falling down the hole in the bottom of the forge (which is used to force air into the forge), but if this fuel works well, I will design the new forge to work with it.
Once again, I will post more as I learn more, and as things progress.
Saturday, November 21, 2009
Thursday, October 15, 2009
Forge: Refractory Materials
So I think this is the final conclusion of my research on refractory materials. There are two major types of refractory. The first is standard firebrick that is commonly used in making things like clay ovens. This firebrick is generally quite dense and contains a lot of alumina (28% to 80%+). It conducts heat well, which works especially well for transferring heat to food which you are trying to cook.
The second major type of refractory is insulating firebrick. This also often contains a large amount of alumina, but is likely to contain more silica as well. Insulating firebrick is usually very light and contains a lot of air. The best example of this is the HRSI (High-temperature reusable surface insulation) tiles used on modern space shuttles. These tiles conduct heat so poorly that they can be held in hand, while white hot, without burning the skin (see the Wikipedia article Space Shuttle thermal protection system). These tiles contain only 10% silica and 90% air.
The type I am looking for is the insulating firebrick. First, it should be simple to mix good portions of alumina with the clay, to get a high alumina content, which should help prevent cracking. Since I do not have access to the silica fiber material used for HRSI tiles, my next best option is to add some perlite, specifically smaller pieces. Large pieces are likely to weaken the finished product too much, but if I mix in a moderate amount of perlite consisting solely of pieces between 2mm and 3mm, I should be able to add enough air to offer good insulating properties without weakening the fireclay significantly.
I think that the clay may actually have sufficient alumina to work fine if I were to add around 25% perlite to the clay (by volume). This time around, I would prefer to add some extra alumina anyhow, just to be safe, but I would guess that the 30% alumina is probably plenty for the forge. Once I have the forge working, I plan on trying different mixtures. I will make small balls or bricks (very small bricks) of the various different mixtures, then use the forge to heat them until they glow, then allow them to cool. I will repeat this procedure on each mixture, either until the pieces crack, or until I get tired of testing them and can conclude that the particular mixture is sound and unlikely to crack for some time.
My current bottle neck is producing alumina. I am still looking for a good source of scrap aluminum (since most "aluminum" cans produced currently are actually made of steel). Maybe I will have my parents save soda cans for me. For now, I am producing some alumina, but very slowly and in very small amounts.
The second major type of refractory is insulating firebrick. This also often contains a large amount of alumina, but is likely to contain more silica as well. Insulating firebrick is usually very light and contains a lot of air. The best example of this is the HRSI (High-temperature reusable surface insulation) tiles used on modern space shuttles. These tiles conduct heat so poorly that they can be held in hand, while white hot, without burning the skin (see the Wikipedia article Space Shuttle thermal protection system). These tiles contain only 10% silica and 90% air.
The type I am looking for is the insulating firebrick. First, it should be simple to mix good portions of alumina with the clay, to get a high alumina content, which should help prevent cracking. Since I do not have access to the silica fiber material used for HRSI tiles, my next best option is to add some perlite, specifically smaller pieces. Large pieces are likely to weaken the finished product too much, but if I mix in a moderate amount of perlite consisting solely of pieces between 2mm and 3mm, I should be able to add enough air to offer good insulating properties without weakening the fireclay significantly.
I think that the clay may actually have sufficient alumina to work fine if I were to add around 25% perlite to the clay (by volume). This time around, I would prefer to add some extra alumina anyhow, just to be safe, but I would guess that the 30% alumina is probably plenty for the forge. Once I have the forge working, I plan on trying different mixtures. I will make small balls or bricks (very small bricks) of the various different mixtures, then use the forge to heat them until they glow, then allow them to cool. I will repeat this procedure on each mixture, either until the pieces crack, or until I get tired of testing them and can conclude that the particular mixture is sound and unlikely to crack for some time.
My current bottle neck is producing alumina. I am still looking for a good source of scrap aluminum (since most "aluminum" cans produced currently are actually made of steel). Maybe I will have my parents save soda cans for me. For now, I am producing some alumina, but very slowly and in very small amounts.
Monday, October 12, 2009
Forge: Fireclay
Ok, so I have recently discovered that there is a terminology issue with my research. It goes like this: Many of the websites I have been finding have referred to refractory clay as "fire clay", but, as it turns out, the term is more often used to refer to clays that are fired to make pottery, etc. The site that I obtained my silica/alumina ratios was one that used the term to refer to pottery clays in general. So, normal pottery clays usually have between 24%-34% alumina and 50%-60% silica. The clay I bought was manufactured by Seattle Pottery Supply, so I emailed them and found that their Klamath Buff clay contains about 50% silica and 30% alumina.
To overcome this terminology issue, I began researching the contents of firebrick, since the term "firebrick" is used almost exclusively to mean refractory brick (although, in some cases it is called "insulating firebrick", while low temperature firebrick is just called "firebrick"). Refractory firebrick generally contains from 37% up to 90% alumina, with successively lower amounts of silica. The higher the alumina content, the higher the heat it can handle, but the softer it becomes. So, my current priority is to use electrolysis on aluminum cans to make alumina. I am planning on using 50%-70% alumina (this will be fun math, since the clay already contains 30% alumina).
A few days ago (around the time of my first Forge post), I took a 12v transformer I had laying around and a 5 gallon paint bucket. I attached the negative lead to a piece of stainless steel that I had used for this sort of thing in the past. The positive lead was attached to an aluminum can. Both were submersed in water (the copper leads were suspended a short distance above the water, to avoid contamination; copper will corrode in these conditions, if it is in contact with the water) and I turned the transformer on. For an electrolyte, I used baking soda (at 12v salt breaks down into chlorine gas and sodium; the sodium reacts with the water, contaminating it). The baking soda may be making the water more conductive than I want, so I will be looking into this when I have more time. Also, there is some evidence that the baking soda may be breaking down, so I will eventually have to do some more research on this.
Anyhow, after the first can had been mostly oxidized, I attached a Boyardee Ravioli can to the positive lead, assuming it to be made of aluminum. The water quickly turned a reddish brown. Evidently many modern "aluminum cans" are actually made of steel. I suspect large juice cans are also steel. So, next time I need iron oxide I know which cans to use (once the forge is finished I will be needing some of this for making thermite, which will yield iron and alumina when burned; I will probably write an article on this subject once I get there).
I will post again as things develop.
To overcome this terminology issue, I began researching the contents of firebrick, since the term "firebrick" is used almost exclusively to mean refractory brick (although, in some cases it is called "insulating firebrick", while low temperature firebrick is just called "firebrick"). Refractory firebrick generally contains from 37% up to 90% alumina, with successively lower amounts of silica. The higher the alumina content, the higher the heat it can handle, but the softer it becomes. So, my current priority is to use electrolysis on aluminum cans to make alumina. I am planning on using 50%-70% alumina (this will be fun math, since the clay already contains 30% alumina).
A few days ago (around the time of my first Forge post), I took a 12v transformer I had laying around and a 5 gallon paint bucket. I attached the negative lead to a piece of stainless steel that I had used for this sort of thing in the past. The positive lead was attached to an aluminum can. Both were submersed in water (the copper leads were suspended a short distance above the water, to avoid contamination; copper will corrode in these conditions, if it is in contact with the water) and I turned the transformer on. For an electrolyte, I used baking soda (at 12v salt breaks down into chlorine gas and sodium; the sodium reacts with the water, contaminating it). The baking soda may be making the water more conductive than I want, so I will be looking into this when I have more time. Also, there is some evidence that the baking soda may be breaking down, so I will eventually have to do some more research on this.
Anyhow, after the first can had been mostly oxidized, I attached a Boyardee Ravioli can to the positive lead, assuming it to be made of aluminum. The water quickly turned a reddish brown. Evidently many modern "aluminum cans" are actually made of steel. I suspect large juice cans are also steel. So, next time I need iron oxide I know which cans to use (once the forge is finished I will be needing some of this for making thermite, which will yield iron and alumina when burned; I will probably write an article on this subject once I get there).
I will post again as things develop.
Friday, October 9, 2009
Forge: Backstory
The forge project is nearing completion, but first I think I should update you on what has already happened.
The project started after I started making charcoal (I do not plan on writing about this here, but when my book is finished, I will provide a link to the information) was a coal forge. The forge was one of the things on my list of projects to include in the book, so I started researching materials that can withstand the heat produced. I quickly discovered that I needed to build the forge with a hole in the bottom, to pump air up through the charcoal. I already knew that clays and ceramics were probably my best bet for withstanding high temperatures, but I also knew that even clays can crack if heated quickly. So I begun my research into fire brick and fire clays, but at the same time I bought a 6in clay flower pot at a local hardware store.
The clay pot seemed like an ideal forge, because it already has a hole in the center of the bottom. The one thing I was worried about was cracking. To put air into the hole, I bought a copper pipe reducer and used my Dremel to cut the larger end into quarters, which I bent down and drilled holes in, so that I could screw it onto the bottom of the pot.
The drilling of the pot, with a masonry bit, worked fine, except that the holes did not quite come out straight. This did not seem like a problem until I was tightening the machine screws down and the stress created by the screws being in holes that were not quite straight caused the pot to crack across two of the holes. At this point, I knew the cracks would expand as the pot heated, but since I had nothing to loose (the pot was essentially already ruined), I decided to fire it up.
I had also bought a small fireplace bellows when I got the pot and the pipes (I also bought a few pipe fittings and a length of pipe, to direct the air into the fitting on the bottom of the pot). So I put some of my charcoal (made from fir) into the pot, used a lighter to get it smoldering, and piled in more, until the pot was full of charcoal. Next, I connected the bellows to the end of the pipe contraption (the end fit perfectly into a 1/2in coupler) and started pumping.
I quickly discovered that the small bellows was not sufficient for the task. Besides that, one of the tacks used to hold the leather on was too close to a moving part and stated wearing a hole in the leather. I returned the bellows to the store, since it was faulty, but I did not buy another one, because it did not provide sufficient air flow. As such, I am going to have to provide instructions on how to make a large bellows in my book, otherwise the forge will be useless. (I may post that project here, when I get around to doing it.)
My solution to the air flow problem (since I do not have time to make a large bellows) was to go to Salvation Army and buy a few used blow dryers. After disassembling one, in an effort to take out the heating coils, I ended up with a blower that operates at 12v (this was not intentional, but it turns out that the heating coils were an integral part of the 120v power supply leading to the 12v motor and the motor will not operate at 120v without the coils). The other blow dryer had a "cool" switch, so I modified it to be permanently on the "cool" setting (it still generates some heat, but only a little). I also bought a fitting to reduce the blow dryer down to the size of the 1/2in copper pipe that I am using for air (I also had to use a little duct tape).
Once the air flow issue was fixed, I piled in the charcoal again and fired up the blow dryer. Within about 3 seconds, every bit of the charcoal was burning and fire was shooting up about 1 foot out of the 6 inch clay pot. My brother, who was watching, backed up in surprise and awe. I just laughed, because that is about what I expected. The blow dryer worked very well, but I will still have to build a large bellows, because the blow dryer is limited by the length of the cord and the access to an electrical outlet.
So, once the forge was properly firing, the small cracks from assembly became very large and many other cracks started forming. Again, this is about what I expected. I only fired up that forge once more, at which time the cracks became large enough that it would probably fall apart with any further use.
I did some more research on refractory clay or cements and found that many hardware stores carry a sort of fireplace cement that is supposed to withstand high temperatures. So I went back to the local hardware store and discovered that they did carry a fireplace cement that is good up to 2100F. I bought another clay pot and was more careful about the drilling this time. As such, I managed to cause more damage than the last time, however it was not in the form of a crack running up the side of the pot, but rather, just a bit of the bottom broke out. I was able to repair this very well, with some of the fireplace cement.
Once the pipe fitting was installed, I lined the pot with about 1cm thick of the fireplace cement mixed with sand (about 1/3 to 1/2 sand). Once this set, I covered it with a thin layer of fireplace cement without sand. This one looked much more capable than the first, but the clay pot began to get hairline cracks the first time I used it. In addition to this, the fireplace cement (which was originally rough black) turned glossy white on the bottom and lower sides of the container. Since the cement is rated to 2100F, this tells me that the forge got hotter than that.
After a few more uses, the cracks became wider. So I used a hose clamp on the top rim of the pot to prevent the cracks from getting larger and I filled the cracks with more of the fireplace cement, in hopes that the heat will fuse the cracks closed. This is where I currently am on the clay pot forge. I have not fired it since patching the cracks, so I do not yet know if the patches will properly fuse and fix the forge.
Now I am working on making another forge, using fire clay (much higher temperature) and a paint can (1 gallon). There is only one pottery supply place near where I live, so I went there looking for fire clay. Turns out that they do not carry it (and were not even sure what it was), but they do carry high temperature clay. So I have decided to make my own fire clay. I bought a 50lb box of Klamath Buff clay. My research tells me that to make fire clay, I need to add to this 24%-34% alumina (aluminum oxide) and 50%-60% silica (silicon oxide). Obtaining these has been an issue, so I started doing research on how to make them.
Since it turned out that alumina is just aluminum oxide, I decided to use electrolysis to rapidly oxidize some aluminum cans (I have a 5 gallon paint bucket where this is occuring, as I type). The silica, as it turns out, is one of the most common compounds in the Earth's crust and can be easily obtained in the form of beach sand. Of course, it needs to be powdered, so I will probably end up bulding some sort of rock tumbler to tumble the sand in, until it turns to powder. The alumnia will be mixed with water when it is done (because the electrolysis takes place in water), so I will just boil it down until it is a sludge and then filter it and dry it.
Theroetcially, if I were to just powder aluminum and mix that with the clay, it would work for the alumnia, because it would quickly oxidize the first time the forge was fully fired, but I do not want to take any extra risks, so I am going to do this right.
In summary, I now have a temporary clay pot forge that is not likely to last more than 10 more firings, even with the repairs I did on it. I also have and am making the resources for another forge that will be made from homemade fire clay and contained within a 1 gallon paint can. I have managed to melt aluminum in the clay pot forge, using a 1 1/4in steel pipe cap for a crucible. Once the paint can forge is done, I will be drilling some holes in the crucible to make it easier to support over the forge and easier to pour.
Once I have a significant amount of alumina and silica, I will write again. For now, I am waiting.
The project started after I started making charcoal (I do not plan on writing about this here, but when my book is finished, I will provide a link to the information) was a coal forge. The forge was one of the things on my list of projects to include in the book, so I started researching materials that can withstand the heat produced. I quickly discovered that I needed to build the forge with a hole in the bottom, to pump air up through the charcoal. I already knew that clays and ceramics were probably my best bet for withstanding high temperatures, but I also knew that even clays can crack if heated quickly. So I begun my research into fire brick and fire clays, but at the same time I bought a 6in clay flower pot at a local hardware store.
The clay pot seemed like an ideal forge, because it already has a hole in the center of the bottom. The one thing I was worried about was cracking. To put air into the hole, I bought a copper pipe reducer and used my Dremel to cut the larger end into quarters, which I bent down and drilled holes in, so that I could screw it onto the bottom of the pot.
The drilling of the pot, with a masonry bit, worked fine, except that the holes did not quite come out straight. This did not seem like a problem until I was tightening the machine screws down and the stress created by the screws being in holes that were not quite straight caused the pot to crack across two of the holes. At this point, I knew the cracks would expand as the pot heated, but since I had nothing to loose (the pot was essentially already ruined), I decided to fire it up.
I had also bought a small fireplace bellows when I got the pot and the pipes (I also bought a few pipe fittings and a length of pipe, to direct the air into the fitting on the bottom of the pot). So I put some of my charcoal (made from fir) into the pot, used a lighter to get it smoldering, and piled in more, until the pot was full of charcoal. Next, I connected the bellows to the end of the pipe contraption (the end fit perfectly into a 1/2in coupler) and started pumping.
I quickly discovered that the small bellows was not sufficient for the task. Besides that, one of the tacks used to hold the leather on was too close to a moving part and stated wearing a hole in the leather. I returned the bellows to the store, since it was faulty, but I did not buy another one, because it did not provide sufficient air flow. As such, I am going to have to provide instructions on how to make a large bellows in my book, otherwise the forge will be useless. (I may post that project here, when I get around to doing it.)
My solution to the air flow problem (since I do not have time to make a large bellows) was to go to Salvation Army and buy a few used blow dryers. After disassembling one, in an effort to take out the heating coils, I ended up with a blower that operates at 12v (this was not intentional, but it turns out that the heating coils were an integral part of the 120v power supply leading to the 12v motor and the motor will not operate at 120v without the coils). The other blow dryer had a "cool" switch, so I modified it to be permanently on the "cool" setting (it still generates some heat, but only a little). I also bought a fitting to reduce the blow dryer down to the size of the 1/2in copper pipe that I am using for air (I also had to use a little duct tape).
Once the air flow issue was fixed, I piled in the charcoal again and fired up the blow dryer. Within about 3 seconds, every bit of the charcoal was burning and fire was shooting up about 1 foot out of the 6 inch clay pot. My brother, who was watching, backed up in surprise and awe. I just laughed, because that is about what I expected. The blow dryer worked very well, but I will still have to build a large bellows, because the blow dryer is limited by the length of the cord and the access to an electrical outlet.
So, once the forge was properly firing, the small cracks from assembly became very large and many other cracks started forming. Again, this is about what I expected. I only fired up that forge once more, at which time the cracks became large enough that it would probably fall apart with any further use.
I did some more research on refractory clay or cements and found that many hardware stores carry a sort of fireplace cement that is supposed to withstand high temperatures. So I went back to the local hardware store and discovered that they did carry a fireplace cement that is good up to 2100F. I bought another clay pot and was more careful about the drilling this time. As such, I managed to cause more damage than the last time, however it was not in the form of a crack running up the side of the pot, but rather, just a bit of the bottom broke out. I was able to repair this very well, with some of the fireplace cement.
Once the pipe fitting was installed, I lined the pot with about 1cm thick of the fireplace cement mixed with sand (about 1/3 to 1/2 sand). Once this set, I covered it with a thin layer of fireplace cement without sand. This one looked much more capable than the first, but the clay pot began to get hairline cracks the first time I used it. In addition to this, the fireplace cement (which was originally rough black) turned glossy white on the bottom and lower sides of the container. Since the cement is rated to 2100F, this tells me that the forge got hotter than that.
After a few more uses, the cracks became wider. So I used a hose clamp on the top rim of the pot to prevent the cracks from getting larger and I filled the cracks with more of the fireplace cement, in hopes that the heat will fuse the cracks closed. This is where I currently am on the clay pot forge. I have not fired it since patching the cracks, so I do not yet know if the patches will properly fuse and fix the forge.
Now I am working on making another forge, using fire clay (much higher temperature) and a paint can (1 gallon). There is only one pottery supply place near where I live, so I went there looking for fire clay. Turns out that they do not carry it (and were not even sure what it was), but they do carry high temperature clay. So I have decided to make my own fire clay. I bought a 50lb box of Klamath Buff clay. My research tells me that to make fire clay, I need to add to this 24%-34% alumina (aluminum oxide) and 50%-60% silica (silicon oxide). Obtaining these has been an issue, so I started doing research on how to make them.
Since it turned out that alumina is just aluminum oxide, I decided to use electrolysis to rapidly oxidize some aluminum cans (I have a 5 gallon paint bucket where this is occuring, as I type). The silica, as it turns out, is one of the most common compounds in the Earth's crust and can be easily obtained in the form of beach sand. Of course, it needs to be powdered, so I will probably end up bulding some sort of rock tumbler to tumble the sand in, until it turns to powder. The alumnia will be mixed with water when it is done (because the electrolysis takes place in water), so I will just boil it down until it is a sludge and then filter it and dry it.
Theroetcially, if I were to just powder aluminum and mix that with the clay, it would work for the alumnia, because it would quickly oxidize the first time the forge was fully fired, but I do not want to take any extra risks, so I am going to do this right.
In summary, I now have a temporary clay pot forge that is not likely to last more than 10 more firings, even with the repairs I did on it. I also have and am making the resources for another forge that will be made from homemade fire clay and contained within a 1 gallon paint can. I have managed to melt aluminum in the clay pot forge, using a 1 1/4in steel pipe cap for a crucible. Once the paint can forge is done, I will be drilling some holes in the crucible to make it easier to support over the forge and easier to pour.
Once I have a significant amount of alumina and silica, I will write again. For now, I am waiting.
Introduction
I am working on writing a book about post-apocalyptic technology. The main point of the book is to be a reference guide on how to make useful things if civilization fails. The first part of the book, which is more about survival techniques and social interaction, is nearly finished and now I am getting to the part about actually making things. While I am already well versed in making things like charcoal, I need some experience in making things like forges (think, iron forge/melting metals).
Currently I have been working on building a small forge from a clay pot and fireplace cement, but it turns out that my pot forge actually exceeds 2100F, which is the limit of the fireplace cement.
Anyhow, I have decided to start writing about my progress in various projects I have been working on. My current project is the mini-forge, however I have some other projects which are currently on hold, for various reasons. One of them is the creation of a very small pulsejet engine. Also, since my forge is already capable of melting aluminum, I will probably soon have some new projects related to casting aluminum, once the forge is finished and working properly.
Now, on to the forge!
Currently I have been working on building a small forge from a clay pot and fireplace cement, but it turns out that my pot forge actually exceeds 2100F, which is the limit of the fireplace cement.
Anyhow, I have decided to start writing about my progress in various projects I have been working on. My current project is the mini-forge, however I have some other projects which are currently on hold, for various reasons. One of them is the creation of a very small pulsejet engine. Also, since my forge is already capable of melting aluminum, I will probably soon have some new projects related to casting aluminum, once the forge is finished and working properly.
Now, on to the forge!
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