I am in the beginning stages of building my first foundry furnace. This is going to be a build using insulated fire brick only because I have seen a video that put this idea into my head before I came across this forum. So since I have the bricks, I will cut my teeth with this build. I foresee making a total of three furnaces in the distant future. This first one due to having the materials already. The next one will be of similar size with different materials to make a more durable and efficient furnace. The last one will be the one to do the large projects I have mentioned in my introduction thread. The second version will have to wait until the first one craps out. I look forward to your comments and suggestions. See you out there.
I have finally received the bricks and final parts for the control panel. The set up I am using for the control panel is very similar to the way I have my control panel for our 8' x 8' x 16' fiberglass curing oven. I don't have the stickers printed yet, but the green button is for the control panel power. It will turn everything on in the control panel, but not the output to the heater coils. The red button in the upper right corner is enabling the heater coil. This way I can adjust the temperature setting before actually enabling the coil, or if I want to turn off the furnace and monitor the temperature. The temperature controller is a fuzzy logic controller, and adjusts itself so I won't have to tune it, or that is the way it works on my fiberglass curing oven. Time will tell if it works as well with this casting oven. PID controllers of old needed to be fine tuned so that they wouldn't take for ever to get up to temp, or over shoot the temperature set point. The E-Stop button on the lower left, as an easy "slap it to shut it down" button in case things go very wrong. It is a lot easier to hit an E-stop button than getting a finger inside either of the other power buttons at the top of the control panel. In the lower right corner is an AC Digital Multi-function meter. It displays AC volts, current, active power, energy, and power factor. Most of that isn't necessary for the furnace operation, but could be interesting numbers down the road when I want to compare one furnace design to another. The key number is the current. On the right side of the control panel is a 32 amp breaker. I am expecting the coil current to be around 22 - 26 amps. A 32 amp breaker gives me some leeway but will trip if a coil shorts for what ever reason. I will be plugging this into a 208 volt socket that I use for multiple pieces of equipment, and I don't want to rely on the 60 amp breaker in the breaker panel to safeguard this furnace. This is the left side of the control panel, and here lives the heat sink for the solid state relay that will switch the heating coil on and off. I have not wired up the control panel yet. Just put the individual components into place. I will probably use the alarm output of the PID controller to trip the 32 amp breaker to prevent a thermal run away as the most common failure mode in SSR's is to short circuit. This means the PID could no longer control the temperature and might cause thermal runaway. Maybe set the alarm point to be at 2100 degrees to protect the coil and bricks. This will have to be experimented with once I have everything built. I can test it by disconnecting the coils and tricking the thermocouple input to see if the PID will trip the 32 amp breaker. This is the coil I made. I made it using 10 gauge Kanthal wire. The friend of mine I got it from called a Kanthal wire company before he made his first furnace, and the engineer he spoke to suggested to use a larger gauge wire for longevity. I got the wire from him so it is what I have. Due to the gauge, the length of the wire needs to be longer to increase the resistance to decrease the current. So to get the length of wire to fit in my build, I used a 5/8" mandrel to make the coil. This makes for a larger diameter coil than what I would have liked, but gets the coil resistance to 10 ohms which will put me at 21.5'ish amps (4.6'ish kw). I made it slightly longer to get to 10 ohms to test the performance of the furnace. If I am happy with it, I will leave it as is. If I want it to heat up a bit faster, I will shorten the coil to get a resistance of 8.5 ohms for 25'ish amps (5.3'ish kw). The friend of mine I got the wire from says the wire is rated for 28 amps. I plan to build the furnace so that it won't be a big wahalla to disassemble the main walls to adjust the coils as needed. I am interested in seeing what the current does through the coils as they heat up, as typically the resistance increases with temperature, which reduces current, which reduces temperature. If the effect doesn't slow the time considerably it takes to get to melt I will leave the coil length as is. Otherwise I will shorten it accordingly. Here are the bricks I received. The company I bought them from packed them pretty well, but did not pack them UPS proof. I am not sure if UPS proof is even a possibility. As I said earlier, I bought these bricks after watching the Vegoil Guys youtube videos on his electric furnace. Great videos, and I decided to make my first furnace based on these videos. Unfortunately, or fortunately depending on whether your glass is half empty or half full, I came across this forum after I had ordered these bricks. So I will build my first furnace using these, and once this furnace wears out, I will build the next version of it. The damaged bricks above are not a major problem for me as I will be cutting those corners off. The pile of bricks behind them though are damaged to the point of not being useful other than scrap filler parts. These are the bricks that UPS was very mean to. I know these bricks are very fragile, and based on how well the company packed them, tells me how rough of a trip they had to get to me. I chose to use K23 bricks (2300 degree) due to a couple of reasons. The thermal conductivity of the higher temp bricks are slightly higher. I was told I would not want to run the kanthal wire hotter than 2300 degrees anyways, so I figured that K23 bricks would insulate ever so slightly better than higher temp rated bricks. I have also read somewhere that higher temp bricks are a little bit tougher than lower temp rated bricks. After seeing what I got in the pictures above, and what I have read on this forum, I wish I would have gotten K26 bricks (2600 degrees F). What do they say? "Experience is earned based on past wrong decisions." The next step is to start cutting the bricks to shape and dry fitting it all together. I have other sticks in the fire, so this build is not going to be blazingly fast. In fact it might even be tortoise slow, but slow and steady will get me to the finish line at some point. I will post updates as they come. I look forward to hearing your comments and suggestions;-) Later, Roger
When K26 bricks do not insulate so good, you can also wrap the outside in Kaowool. How thick is the Kanthal ? The photo shows 1.5 mm (.06") alike as the diameter of the coil is 5/8".
Just curious about your voltage Roger. You current and resistance figures indicate just under 220VAC, so I was thinking maybe you had 3ph but only saw two poles on your circuit breaker. Most if not all US residential voltage is 120/240 these days not 110/220. Apparently you have but just confirming you've measured your voltage source? You'll be fine. As IFB density increases, so does refractory, but they also become less insulating, stronger, and harder to cut/work. If you were going to push the upper limits of the Kanthal, I'd probably recommend K26, just because the local temp in the coil shelf will typically be a couple hundred degrees greater than the furnace temperature. When the IFB is heated to near it's max service temp, it does become a little more brittle and weaker. I built my original furnace out of K23 and it was fine and probably would have had a long life had I not tried to disassemble it. Also, I used mortar to glue the bricks together and coat the surfaces for durability, and I wouldn't do that again unless absolutely necessary because the mortar and brick expand at different rates and over many cycles, this tends to fracture at the joints and cause surface coating to sluff and flake off. It's sort of the picking nits between K23 & K26 but one day, I would like to try a bronze melt in a Kanthal furnace......just haven't had the need. Best, Kelly
Just for clarity, the thermal conductivity of IFB are ceramic wool both in the neighborhood of .12W/mK. That varies a bit for higher temp vs lower temp wool and brick. If I could afford all the IFB I could use, I’d use IFB preferentially. Easy-to-cut, self-supporting, and an excellent insulator that does not lose loft (like ceramic wool) over time. Denis
Not sure of the clarification but as you know, 1" of ceramic wool (typically (6-8 lb/ft3) will provide far more insulation than 1" of K23 IFB (typically 37lb/ft3). More (dense) material will conduct more heat even though rate of conduction in the base material is approximately the same. But, perhaps to the point, most of the common refractories we use are primarily alumina-silicates with similar base properties so heat loss through a (furnace) structure increases as mass increases...... Best, Kelly
My Kanthal furnace is built from K23 bricks but I heat it up to 1200 C chamber temperature by the thermostat, which means that the coil temperature is at least 100C (180 F) hotter. I have done that many times to melt copper and the grooves in the walls do not show any weakening sign.
You'd have to be very gifted to visually detect a change in mechanical properties of alumina silicates but if you handled it and/or scraped with a finger nail it becomes more apparent. The most obvious example is handling ceramic wool that has been exposed to near it's thermal limits......it becomes brittle and much more delicate and friable. Best, Kelly
The Kanthal wire is 10 gauge and 0.1" diameter. The charts I have seen say it has a resistance of about 0.0808 ohms/ft which is fairly close to what this wire actually is based on what I measure over 100+ feet of wire. The outside diameter of the coil ends up being just shy of 0.875" due to spring back. That is a much larger diameter coil than what I originally wanted, but as my friend that I got the wire from says, it will add a lot of coil durability in the long run. We will see if my plan to make the coil shelves works well or not. We have 3 phase 208 here at the shop. The outlet I will be plugging into to run the furnace is one phase and measures 214 VAC. In this furnace, I don't have the real estate to run a 3 phase configuration, especially using 10 gauge wire. For the furnace I plan to build in the future for my larger projects mentioned in my introduction, I plan to use 3 phase power to drive the coils, which will make it similar in set up to my 8' x 8' x 16' fiberglass curing oven control panel wise. Heating elements will be different due to the temperature differences. sub 300*F for the curing oven compared to ~1800*F for the casting oven. Thanks for the advice about the use of mortar and the different expansion rates. In one of your other threads you mentioned that with the lift off set up, that your furnace walls didn't have to deal with needing to be wear resistant due to tongs never being used in the body of the oven. I will plan on eliminating the mortar where I can. Once again, the best decision I have made for venturing into casting was joining this forum. I have learned so much more since joining, that the time it will take me to get proficient and even start adding to the forum will be seriously shortened.
I said it would be a slow progressing project. Before moving forward I had to get a clients project completed and out of the shop before cutting the bricks. The method I used of soaking the bricks in water for a minute or so worked out really well. No dust at all. It did make a mess of my saw, but the clean up wasn't too bad. I guess localized clean up is better than a layer of dust on top of the layer of dust that is already every where;-) I have cut the bricks for the main body and have started using a router table to put the coil grooves in place. So far I am very happy with the results. I need a 1" Round Nose Router Bit now to complete the coil groove. At that point I will start constructing the base. Then I am visualizing the way I am going to solidify the body and base and how they are going to integrate with each other. Then I will need to think about how they will integrate with the lifting frame work. I am doing the things that I think will have to be done a certain way regardless of how the rest of it meshes together. I have some ideas as to how I want to implement things based on what I have read about on this forum, and I have some ideas of how I want to mix some ideas from different projects I have read about and videos I have seen. I am contemplating building a clamp kind of like a motorcycle muffler clamp. Something like a sheet metal cover that goes all the way around the main body and has clamping bolts that will pull the sheet metal snugly around the main body. That way I won't have to use mortar to hold it together. Wheels are slowly turning. Well, here are a few pictures to show the slow progress: Here are the two crucibles I got from a friend of mine. One is a home made steel crucible (left) and one is silicon carbide (right). You can see the main body in the background. It is made with K23 insulated fire brick. There are 8 bricks per layer, and 5 layers. I needed 5 layers so I could get 4 layers of Kanthal heating coil. Remember I am using 10 gauge wire so I need a good bit of length to get the resistance and power to a reasonable level. Each brick is cut at 22.5*. Here is a pic with the steel crucible inside the main body. The friend I got the crucibles from coats the inside of his steel crucibles with a layer of clay. He says he gets ~4 pours before needing to redo the clay coating, but the re-coating is quick and easy. The outside of the steel crucible seems to take more of a beating than the inside. And a pic with the ~A20 silicon carbide crucible. I can't say for sure it is an A20. Seems to be ever so slightly between an A16 from one source and an A20 from another source. I guess a mute point. Some people say tom-a-to, and some people say tom-ah-to. It is still a fruit. As long as it holds as much aluminum as I need, it will work. When it won't hold enough, this furnace has some room for a larger crucible. From one source, their A50 and A55 crucibles should fit in this furnace. That should take care of my near future casting projects. I will have plenty of time to learn with this one before needing a larger furnace for the fiberglass mold project. Due to not having much progress, maybe I can throw out there a couple of options I have to power this thing. I have also gotten a large variac from the same above mentioned friend. This friend of mine drives his furnaces with a variac just like this one. He likes it and works well for him. I like the idea of setting the temperature and it automatically controls the max temp. The first time I fire up the furnace, I think I am going to use the variac so that I can slowly heat up the internals due to soaking the bricks in water to prevent dust during cutting and wanting to slowly dry them out. Youtube vids suggest leaving them to dry for a week or two before firing them up, but the PID controller will whack full power to the coils, or nothing. I like the idea of gently increasing the temperature to dry the bricks and plan to use the variac to do this. I would like y'alls input on the following options to run the furnace under normal circumstances. I can either run it with the PID controller and the 214 VAC coming out of the wall, or I can run the power from the wall through the variac, and then through the PID controller. The real benefit with this option is that this variac allows me to get more voltage out than I put in, although at the expense of more current draw from the source. This is not a problem for me as the source has a 60 amp breaker. This would allow me to the input voltage to the coils really from 0 to about 250VAC. This gives me the possibility of pushing the coils with 25'ish amps for a total power of 6.25 kw if needed at the high end, and then can be turned back down to the 4.5 kw when I am not in a hurry for the melt to occur. This would be gentler on the coils and the bricks but would give the option of extra power when wanted. The variac is rated for 28 amps, and I believe the Kanthal wire is rated for 28 amps also. A good match. With the multi gauge readout mounted in the control panel, choosing the input voltage will be a simple step and I can easily monitor the coil current to prevent pushing them too hard. I just don't know if the extra complications are worth the squeeze. I definitely want the temperature controller so I don't have to worry too much about over heating the melt, but the variac might add some versatility. It will also make future coils easier to make as I won't need to calculate and make them so precise due to having control over the input voltage. What do you guys think? The ID Tag says Out V is 0 to 280 but that is with a 240VAC input. I am calculating that with 214VAC input, I could get 249+VAC out bringing furnace power to almost 6.25 kw. I am using a dollar bill to reference the size of the variac. The variac has a broken arm on the upper frame. One of my first projects might be to make a new one, exactly like it, but not so broken;-) Speaking of first projects, I have a pair of Bead Pro Tire bead breakers that I carry with me on my motorcycle adventures that I really like except for two things. One is they are cast steel so they are heavy, and two is the bead pry arms are a little bit short which means I have to take many bites around the tire to get the bead to break. I want to cast a set out of aluminum to be lighter, and with a longer prying arm in an attempt to pop the bead quicker. Maybe second aluminum casting project with slight modifications Before I make more progress on the furnace, it will be after Thanksgiving and once I have received the router rounding bit. Might be a week or so after Thanksgiving before I have more updates. I am looking forward to hearing your thoughts on using the variac or not. If I don't talk to y'all before, hope you guys have a great Thanksgiving . Later, Roger
There's no reason why you can't run the furnace off the variac, it's got the capacity at 7KVA rating. I don't know if it would have any advantage for melting aluminium after the bricks are dried out, but then I'm melting aluminium as fast as I can to minimize hydrogen pickup from the fuel burnt. You may be able to heat treat casting in the furnace with such a setup, I remember seeing video footage of Britten engine blocks being heat treated in such a way in a larger version of your furnace.
Thanks for the input. I do like the flexibility of having the variac incorporated, and very much like the idea of being able to use the furnace for other things than casting, ie., heat treating. I have gotten a lot of stuff from the above mentioned friend of mine, and some of that stuff is tenzaloy aluminum, which apparently tempers itself over time and is very strong. I won't cast everything I do with this stuff, as there are cheaper options. I can imagine that heat treating a part made from recycled engine heads would be worthwhile;-) Another technique I need to learn about. The day I stop learning is the day I want to be put into a wooden...maybe an aluminum box!! Later, Roger
How wet are the bricks? Are they so wet they'll be electrically conductive and create potential short? Could be an issue regardless of variac vs PiD/SSR. You might be surpised what a 200w light bulb would do tempwise inside a well insulated structure. Approached 300F for me. A small propane burner would also dry the interior side out but it may take much more effort to get the outer diameter dry. This was my structure. It was mortared together but is also got a layer of ceramic fiber and I made the sheet metal skin to package it up. The whole shebang slides in and out of the furnace shell on the lift. I did so, so I could also install a fuel fired version of refractory, which to date I have not done on this furnace but did do so on my larger furnace. On Variac vs PiD/SSR control, if you set the PiD at a low temperature first, say 200F it won't matter if it's full power on and off. Then just ramp up at whatever rate you're comfortable. No advantage to Variac in my opinion, especially in a melting furnace. You might be surprised how well the PiD will do at control. Best, Kelly
I don't think it is wet enough to cause conduction at the coils, but fuel coil heat to it while it might still be holding moisture was my big concern. Great suggestion to use the 200 W bulb. We will be out and about tomorrow. I will pick one up and put it to work. I am hoping the PID controller works similarly to my fiberglass curing oven set up. I usually see a temperature of +/- 1 degree, but that is at 255 to 275 degrees F setpoint. I don't expect to see such a tight tolerance at casting temperatures. I didn't want the delay in the thermocouple seeing the heat to cause moisture to turn into steam due to the full on coil. Not a concern for me now that I think it will be sufficiently dried after use of the bulb. Later, Roger
It has been awhile since I have done an update. That dang ole thing they call life gets in the way. Today I had an opportunity to work on the main body again. Descriptions following the pics: I ordered a 0.5" round nose router bit and cut the above profile with it. I first used a 0.5" square edged router bit to create the flats on the right side of the profile. This made using the round nose bit much easier as there was access to the round nose for the vacuum cleaner suction and allowed the bit to easily cut the groove. One in the upper brick and one in the lower brick to create a cavity that is about 1" in diameter to secure my about .9+ inch diameter coil. In one of my scrap bricks, I attempted to cut a groove using the round nose router bit without first cutting the flat edge, and found that the bit loaded up and progress was halted. Much easier if the dust has an escape path. Here are a couple of main body bricks with the coil in them. There is a little bit of extra space in the shelf area, but the opening does not allow the coil to escape, in theory anyways;-) Time will tell. And a frontal view of the coil in the shelf. I have not yet installed the coil into the main body yet. Each brick has a 22.5* ish cut on each side so I will have to form the coil a little bit at each brick joint. Also, my plan is to cut a groove between coil shelf layers, uncoil the coil at those locations, and continue the run around the inside at the next level. Wash, rinse, repeat. This way I only have two coil penetrations in the main body. The comes-a-inna and the comes-a-outta. This view is through the hole in the main body where the two bricks were removed to get the previous profile and coil in shelf pics. I never claimed to be a photographer, so expect bad pictures out of me. Every once in awhile, I will get lucky and get a decent photo taken. I hope they convey the progress, but I would rather put my energies into the project, and I don't want to overload my single cell brain;-) The pic on the left was before I got froggy. The picture on the right is the solution to a problem I thought I might have had otherwise. I decided to round the sharp corners on the exterior main body bricks as I wanted to build a sleeve that would hold all the main body bricks together. I envisioned a spring loaded skirt, and those sharp corners would make that difficult. Rounding the corners didn't make the wall thickness much thinner than other areas, and this will allow a skirt with springs holding it together to smoothly squeeze it all together without getting hung up on the corners. I made a quick and simple jig to use on our belt sander that allowed me to round each corner equally. The most difficult thing about that was cleaning up the mess. The spring loaded skirt idea came to me when I was reminiscing about when I worked offshore in the oil industry. The huge diesel engines used a clamp to hold the turbos onto the exhaust manifold, and there was a spring around the clamping bolt, which I ass-u-me was there to help the clamp deal with the temperature extremes causing expansion and contraction. My plan is to do something similar, but instead of maybe an inch wide with one spring loaded clamp bolt, I will make this 15'ish inches wide with multiple spring loaded clamping bolts. Rounding the sharp corners also got rid of the weakest part of the brick. It wouldn't take much force to break the sharp points so hopefully rounding the points simplifies the clamp design. Again time will tell. I will post more as the work progresses. The next step is to install the coils, and then to make the clamping system. One thing I learned today is that soaking the bricks in water (youtube suggestion) isn't necessary. It eliminated all the dust, but created bit of a sludgy mess while cutting. I took the router table outside and connected a shop vac to it. Between being outside and the shop vac, there was nearly zero dust, and the clean up was easier. I can't imagine the sludgy mess on the belt sander. I connected a dust collector to the belt sander and added some shrouds to help direct the dust towards the dust collector. The dust collector caught about 80% of the mess. The rest of the clean up was a broom and dust pan. I don't think I will soak the bricks in water anymore for future cuts. If I don't hear from y'all before the holidays, have a merry Christmas and a happy New Years!! Later, Roger
That looks very good Roger. You won't regret the retention features in your coil shelves or rounding the outside corners......both were very good decisions. Just make sure you get your coils pretty much stretched into their final shape before the first heat, they get more brittle after a few heat cycles. It's actually a good thing that they fit a little loose in the shelves because the coil will grow and shrink a lot through the temp cycle. If it's loose, the axial growth is absorbed by the coils. The radial growth is very small by comparison. Best, Kelly
