Paul, at 4:19 one of the mistakes you made is that the band clamp only touches the corners. You need to put in spacers or bridges (I'm borrowing the term for the bridge on a violin that the string bends over) that force the band into a segmented arc along the sides of the square so they also apply compression to the bricks in the middle. The middle of every side of each brick along the perimeter should have a bridge, and the closer to the middle you get, the taller the bridge should be. This way, every brick gets some compression pushing it into the middle from the faces along the sides of the square, and not just the corners of the corner brick.
Yes! Cross-hobby knowledge sharing needs to happen. Often one group has solutions to problems the other group hasn't even considered. And although being into multiple maker disciplines can lead to a lot of need for space, it can also lead to efficient use of space: everything in my garage workshop has multiple purposes.
Absolutely! I started as a ceramic sculptor and potter. After school I learned glassblowing. I was also interested in blacksmithing and metal casting. Through all of these ventures I only needed one oven/kiln. It is probably 50 years old and still works like a charm. I have used kiln wash and I fix any new cracks accordingly.
I've seen over the last 10 or so years a lot of cross sharing between climbing, caving, highlining and even sailing and I think they've all benefited a lot from it and that'll be the same for this.
That's why a buncha hackers looked at your hobbies and said, 'yeah we can do that better' and we invented hackerspaces, putting one in every other city in the country.
The pain of knowing there was an easier way but you just didn't do it that way because it involved having to talk to a human being... I felt that. lmao.
I've never worked with fire bricks, nor have I done any particular masonry work, but seeing this my brain goes straight to using lap joints or tongue and grooves to allow for a more stable interface while accounting for thermal expansion
I came to the comment section to suggest tongue and groove and here it is. Wood workers who do furniture panels have to deal with seasonal expansion and shrinkage due to humidity, so they place panels floating in a frame with a groove all around.
Years (decades) ago in college we built a small kiln with a removable top. The top had a steel angle iron band around it and a slight pyramidal shape to combat shrinkage. Worked pretty good for holding together over a few years of usage despite being built by a couple clueless students. Instructor gave us a grudging "it'll do" on the job. Which from him was high praise.
I built boilers and furnaces. Firebricks are highly specialized and made for specific temperature ranges. They're bonded with a thin dipping mortar, and painted with the mortar when finished. Then there's a specific heating and curing schedule. For ceilings on fire boxes, wedge-shaped blocks are hung from I-beams, plywood is propped up beneath, and plastic refractory is packed in. Then the supports are burned out when starting the curing schedule. When fired, it looks like the bricks are coated with green glass. Memories, I did that 50 years ago.
You could use an adhesive specifically for kiln bricks to bond them together so it would move more as one. It would also help using ceramic wool on the outside surface for greater insulation. In our lime kilns we use ceramic wool, soft fire brick and then the harder fire brick on the inside for ware resistance. We also use a castable Fire brick but it’s very expensive. You should be able to find this material at an industrial concrete and brick supplier. Hope this helps
@@Boosted98gsx I’ll look into that for you and find the product name I’m using and let you know what temp it’s good for. We us it in our lime kiln and it seems to last there
thats a good idea for sure. this oven does have ceramic wool in the walls, though not all of them, for insulating. I keep thinking i need to add more where it's missing to boost efficiency a bit. It takes forever to heat more when it's above 2200
@@PaulsGarage Taking longer to raise the temperature is normal at high temps. The hotter it gets, the harder it is to get even hotter. This really starts becoming noticeable once you hit ~1800F, and then even moreso once you get up to 2200F-2300F as you mentioned. Especially since it looks like you're using electric elements instead of a burner (which will struggle at the higher temps). Electric elements will also burn out/wear faster the hotter the firing gets. My experience is almost entirely in pottery, but elements last considerably longer if they never go above Bisque-ing temperatures (around Cone 06 or ~1800F), compared to High Fire (Cone 10 or ~2345F).
Use baby powder and water to make paste, if its not scented its the same stuff in powder form. You could also pulverize a brick to get the same powder, but that's tedious and probably not quite as fine grainwise. Can be used to fix cracks too.
2 years ago I was watching you make the thing. Didn’t know you could get one cut to size like that. Depending on the price of course, that really could be a big benefit.
Suggestions to prevent issue in future. One simple way would be to swap the bricks around every so many hours of use, so the shrinkage ends up being even over time. Now unless you use special alloy steel, most steel and pure iron have similar melt temperatures, cast iron having a much lower tmelt. 99.999+% pure iron has a much higher melt temperature, but it is very hard to obtain in quantities enough for rods... nice thing about having a career in chemistry for 40 years, you learn a lot of interesting trivia... Now there are metals that would withstand much higher temperatures without softening, but they are quite pricey. Another note is that your holes need to be loose enough for expansion of the rods, or you will end up with cracked bricks, especially when they shrink onto the rods.
good points! the holes are mostly loose enough that i can push them in, but not tight enough that they fall out on their own. Since this was recorded i took the lid apart once and put it back together, and that seems to have loosened the holes enough that the rods can move a little
Actually you would want to use stainless steel rods and you can leave the holes fairly tight because insulator bricks are fairly soft and the little bit of expansion of the rods wouldn't effect it much as long as you mud all your joints
Wow, 2 years already... still got all the ingredients just sitting in my garage, unopened/unused... had wonderful plans 5+ years ago, but per usual, life happened. And so I chose to vicariously build with you, I'm very grateful you were willing to share along the way! Assuming life, well "actual life" doesn't stop happening anytime soon, I'll truly benefit from this shared knowledge, eventually, I'm sure, if I can just open the garage door... Again, thanks!
@PaulsGarage So very true, as we've both seen. Been quietly by your side, and I've witnessed you make similar sacrifices, all in love. Long-Short... I realize you're busy, so thanks for the reply, even if the conversation ends here. I genuinely hope all is well with you and yours!
Can’t believe I started watching you 5 years ago build this, it was what got me into this kind of stuff in the first place and melt my own metal, thanks!
When I first switched on my home made electric foundry all the joints wanted to open up and fall the thing apart. I switched it off and built a cage around it, a bit like your rods, but external. When (if) I build my next (bigger) foundry, I will keep this idea in mind. A very neat solution.
Potter here and this video was recommended. We've solved a lot of the problems you talk about in the first minute of the video! (Use fiber/castable refractory and your rebar solution is basically the Minnesota Flat Top kiln). I've always been interested in what else my kiln could be used for - although at ~10 Cu ft for the electric one and 30 Cu.ft for the gas one they're a bit big to fire up for small stuff. (Funnily enough the electric is a top loader (door is the lid - made of brick) while the gas kiln is a front loader (fiber door)).
The material you want is called Blakbond mortar made by BNZ materials. Also, not allowing for thermal expansion will spall the edges of the bricks, so looser band, plus strong mortar joints will work better. Many pottery kilns get destroyed because they are too tightly constructed. Gaps are your friend. Best of luck
Thanks for the info! I think the place I get the bricks from gets them from BNZ. I'll look into that mortar. In my experience the kilns I've used definitely get looser and looser over time!
Paul, your tighting band does not give direct pressure to the inside bricks. The band is giving pressure only at the corners. Shorten the corner bricks and shape them to get some overall octagonal design so the band can exert some pressure to the bricks in the middle. Or just add a wegde to the middle ones between bricks and band.
Want me to personally teach you how to use your 3D printer to learn sand casting? Click here: paulsmakeracademy.mykajabi.com/ Oven Build Playlist here!: ua-cam.com/play/PL-aAeRpJou31awkN9xQIeMpIHwiHwRqyt.html
you should use carbon rods to make pins to connect the individual bricks carbon will be unaffected by heat they are not as solid but they don't have to long just a 1 or 1,5 cm
wrong, the Roman buildings that still stand are due to survivor bias, not some magic. there were a lot more other Roman buildings that crumbled and even the ruins weren't found!
Now that you have the holes for reenforcing rods, cut some half-lap rabbets to interlock the bricks. It will make your lid a little smaller but it will be much stronger.
Bravo for making you own kiln/ furnace thing!!! Gaps can help you. Reduction kilns aren’t that tight. They get the reduction by burning more combustible material than there is oxygen ( extra gas,wood, or oil )There is always positive pressure in the kiln so small gaps don’t matter. A sagging lid isn’t so bad and it looks like yours was a far way from falling in. I’ve seen way worse that last for 20yrs in that condition. Kiln manufacturers use a type of kiln mortar and seal the inside of the lid and between each brick as well as using octagon shaped tops to keep compression more equal like you said. Bravo for you ingenuity and exploration!
Thanks! The bricks were definitely far from falling in for sure. The way i designed it the bricks could just be stacked on top without falling in, but the way the inner parts shrank I couldn't lift them off as one. The mortar is a good idea but I think I'll still avoid it for now just so I can change out bricks or use them for something else if I get a hard board lid or something
Is there a certain limit to how much those bricks could shrink? If there is, in theory one could fire them in a way to pre-shrink them and then they could be set from there. (Maybe that's not the case, but it would be interesting to find out.)
In my experience with the other furnaces, when the bricks are too hot for too long they begin to crumble, so there is no end to the process. This includes these 2800f rated bricks in kilns that I never pushed beyond 2300. 2300 for a loooooong time will still eventually destroy the bricks. I've heard no matter what you use, commercial iron/steel foundries consider the furnace liners to be expendable. You just can't beat the heat forever, at least not for any reasonable cost
The shrinking happens because the the quick heating and cooling of the system the only way to minimize it would be to slowly increase the temperature over the course of a few days and then don't shut it down until you have burnt the bricks up and need to replace them typically once or twice a year depending on how hot and hard you run it for instance running it at 1700 degrees everyday even when it is empty will burn up the bricks faster than if you ran it at 1000 degrees when it is full then bring it down to say 500 degrees when it is empty
@@personman8404 I've seen double thick walls with 2 inches of kwool between the brick and the steel wall get ash soot and slag make it all the way to the outer shell so yes it can happen will it happen on your first firing not unless it was installed wrong but it can and will happen but how well you build it has a direct relationship to how long it will last just like how you run it has an impact on how long it will last ie running it too hot for too long will deteriorate the bricks faster or constant heat changes causing shrinkage
i have built lids for my blacksmith forge and i used 3/8" Ceramic Hardboard coated in a ITC-100. ITC-100 is a coating that seals and protect the ceramic fibers, and it reflects/ re-emit the infrared heat as the heat up. they have held the heat for years, and have traveled from a dry climate to a humid one and are still very usable. my blacksmith forge uses 1" Ceramic Hardboard to insulate and the boards are extremely light weight.
I've worked in the steel Industry for years. My craft is in maintenance, not production. From what I gathered, keeping the furnace hot mitigates shrinkage of the refractory brick. The lentil entry to the reheat furnace fell in recently. They used metal to hold up the refractory, and the metal failed. The furnace had to be idled to ambient temperature for the reconstruction. Consequently, much of the other refractory had to be replaced.
I am casting my own bricks and molding a 1piece rocket stove using chicken wire for rebar. Recipe includes refractory cement, sand and mostly vermiculite and perlite.
Have you tried water glass? It’s a mix of desiccant silica gel beads and sodium hydroxide lye heated together in a stainless steel bowl to make the liquid. It can be stored in a #2 plastic bottle until use. Mix it with the perlite and sandblasting sand to coat inner surfaces of your oven or if you need to make any off shapes inside the oven (for instance it can be used to make a plinth to set stuff on). Might be useful.
I made my lids from fiber refractory board. It's more durable than wool, bit less than brick. However being a solid sheet, doesn't have this issue. You can coat the surfaces with kiln wash to hard face them to reduce damage, or repair erosion over time. Making a mount that prevents any sliding contact is a good idea, and usually allows for putting a bit of wool around the edges as a seal, which prevents wear and heat leakage. The mount also holds the hot door while you unload the crucible.
In between the bricks can be placed soft graphite gasket material. Exhaust system gaskets have a graphite ring, as an example. Graphite is one of those things you can't easily burn. It could save you on the electric bill and rate of cooling. I worked on one whose steel band was held closed with a turnbuckle on a spring. I might need a super-hot oven in the future, and any good-sounding ideas will be tried.
2:00 Funny you say that, because I was worried I was getting into too much at once. Forging, pottery, pyrolysis and distillation, composting. It all seems very exciting but it's just so much all at once. I appreciate all the videos you people make that I can watch during the work week and put into practice on my days off.
Absolutely agree on cross-hobby interactions. I do a lot of pyro stuff and frequently find myself gandering pottery and blacksmith resources because there's SO MUCH crossover. Shout out to all the ceramics guys keeping the cost of lithium and strontium compounds low. Love yall
totally agree! People making greensand for casting are spending time grinding kitty litter into bentonite powder... you can just buy 325 mesh bentonite straight from pottery suppliers for cheap! It always pays to talk to other people doing anything, even if you think it's unrelated.
@@PaulsGarage Kitty litter is easily the most underrated household... Thing in my opinion! Need to plug a rocket engine? Litter. Chemical spills ( within reason)? Litter Gotta keep that cross-craft communication goin'
This explains so much as a glassblower cause I've seen these built so differently depending on application in my field like most glass furnaces use the arches or the foundry style if the furnace is constantly hot vs annealing ovens which use less heat and less time hot are just cubes.
Another way to keep your lid bricks from shrinking would be to line the underside with kaowool. A piece of 2" thick should keep the bricks from getting hot enough to shrink.
I worked in an industrial foundry where the furnaces and heat treat kilns were larger than your living room. The furnace roofs are all made in arch shapes for this reason. A little shrinkage is taken up by the arch shape. Almost everything was high density fire brick arches supported by steel framework.
I worked for one of the klin manufactures around covid. They would cement the bricks together. I was actually citing the lids out when I worked there. You could also try cooking the bricks before using them. If you pre srink them it may help. I just don't know it it may damage them. They made some really big ones, like one that could fit a whole car and would open like a cup off a table.
@PaulsGarage I'm thinking about sending you some zinc ingots (pretty close to pure zinc, not alloys). At first I was dismissive of zinc but it doesn't take long to melt and it pours beautifully. At human temperatures, it is a lot like cast iron but shinier. Are you still at 1818 Milton Ave? Or did your address change when you moved? Cheers from Alaska
That would be great! Milton Ave is a post office, i have a P.O. Box there, it's still there so that works. Just let me know if/when you send it so i can check the box. I'm not very good about going there often
Steel rods - good start, if you shape them into an inverted arch inside the bricks and then post-tension them (steel stretches like a spring for when they are cold and larger) if the bricks can take that much stress. Post pensioning them from that inverted arch shape also pulls the outside bricks down, or the inside bricks up. And as pointed out mild steel may not be the best steel to use.
For my forge lid I go over all the joints with Kaowool reinforced refractory furnace cement. I use a furnace cement that comes in a Caulk tube just to make it extra easy.
wonder if you can get the clay for making those bricks you could make youre own and make them to size and shape , not loosing any material by cutting it you have pottery ovens so you should be able to bake them a few pieces at a time (excapt maibe a one piece lid and bottom )
Good idea! I think the bricks are made from alumina and some other stuff, with a filler that gets burned out to make them very porous (for light weight and insulation). I know for a fact the 2800 rated bricks are much heavier than the 2400 rated bricks, maybe less filler in the heavier ones? Not sure.
For industrial heat treatment furnace design (giant methane pizza oven style) all our furnaces had height-adjustable doors that were metal frames with bricks inside of the doors; I would venture using this as the primary access for a non conveyor style kiln/oven/furnace would work fine too and eliminate a lot of issues like what you are dealing with. On the flip side you have some degradation of efficiency at the joints for that style door, have to maintain positive pressure inside and may or may not need some kind of ventilation to pull fumes from the entrance (like I said, we used methane so some different considerations)
I used to work for a metals recycling company. We mostly had refractory brick for the furnaces. When we line the furnaces we intentionally add 1 few mm in between the brick with a bitumen pads so when we ramp up the temp to ~1000 C (~1900 F) the pads would burn off. Since we ran the furnaces at more or less temp constant 24/7 until the next relining we don't really have issues with the lining itself (except for the occasional worksmanship or material infiltration issue). We do have shrinkage cracking on the spouts we use to tap the furnaces and yes we usually use pottery clay to patch up/cover up those problems. We found that low moisture clays worked best for that application
There is something we use at cement plants called plastic refractory, we call it ram. It's like playdough that cures hard almost like castable. probably wouldn't have helped here but thought I'd put it out there.
Stainless steel anchors welded to the structure on the back side helps too - very common on large industrial furnaces and catalytic crackers (which have catalysts with the consistency of sand being blown round inside).
Ram can be used but you really need pneumatic tools to properly install it also because of expansion and contraction you really need to have some type of insulator board and or paper between the ram and the steel walls to account for it typically at least 1inch board or 1/4 or 1/8 inch paper for hotter furnaces 2 inch board is even better
Thanks for your entertaining presentation. I saw a few videos where they were making their own firebrick with a mixture of refractory cement, vermiculite and sand. With that you can cast a custom-shaped piece of any size. Perhaps include reinforcing iron within the piece?
That's an interesting idea! I'd be worried about the sand and vermiculite, i've heard those can vary a lot. I'm planning on getting some Kast-o-lite 30 and make some stuff, maybe cast a lid or some bricks, but that's a plan for when the budget is a bit "healthier" lol
They dont shrink per say kinda but more important is they expand when heated andcontract when cooling so if you make an adjustable clamp for your furnace you can tighten when you cool and loosen when you fire have to look at the specs on expansion rates for the brick you chose if your using an exposed flame you want the brick to be a hard brick or a superduty
Back in the 1970s, I worked at a lead smelter. We used a coke-fueled blast furnace. We used some kind of mud to seal the cracks between the fire bricks. Got it on pallets of 50lb bags. We'd throw a few shovels full in a 5 gallon bucket and mix it with water; no special ratio. It sealed the cracks well. It wasn't adhesive, so it came off pretty easily when we shut down the furnace. For a small oven like yours, you'd be able to use a chipping hammer that welders use to chip the flux/slag off of welds. There's gotta be somewhere you and your friends can chip in and buy some of what ever that was. I never knew what industrial supply we got it from.
I’m building a kiln this summer, as big as I can. I have as much clay as anyone could use in a lifetime. Tbh though, you can make your own fire bricks with plaster of Paris and sand, I don’t know the exact formula because I haven’t needed to make one yet. Fortunately for everyone interested, you can also add fiber glass to your mix to add some support in the mix. If you have ever seen the inside of a old coke oven, the walls and ceiling are basically glass.
Built a few kilns. Actually really surprised I only just stumbled on your channel since you do so much of the stuff I used to do. I like your idea about sharing experiences between disciplines. That's the way to learn new ways of doing crazy interesting stuff. Here goes with some of my experience with kilns. The biggest I've built was about 18 feet by 20ish feet. Basically big enough to park a 1 ton GMC Suburban inside with room to spare. Steel framed box suspended from a gantry. The gantry was on trolley rails. Took four guys to move it. It had two steel framed beds it could be dropped on so, basically... while one was firing the other was loaded and unloaded and serviced if it needed it. It needed it often. Structural mild steel really doesn't like glass firing temps and wool never seals up as well as I would have liked. The beds had 1/4" X 6" leveling blades bolted into the firebrick bed frame so that the top edge could be periodically lined up in a perfectly level plane a couple of inches above the fire brick surface. Then clay grog (basically non-scoop kitty litter) was poured in to fill the difference. That made it possible to use a screed to scrape the grog out perfectly flat and level. Economical to build and easy to maintain but not the most energy efficient beast. 200w 480v three phase power through mercury relay switches and a programmable controller. Ooph. Great fun to work around in the summer. Most were a lot smaller. 2' X 2' X 3' mostly. Great for almost anything. All of these used alumina foam firebrick on the inside and compressed ceramic fiber panels (basically space shuttle heat tiles) outside of that. There was a 2" L angle welded frame to buckle the firebrick together with threaded stainless rod to compress it together. Mild carbon steel threaded rod rots quickly and rotten threads make crappy fasteners. The ceramic fiber panels were fitted over that with a thin sheet of ceramic wool between to fill the space. Just adding that insulated it so well the outside was good and warm after a day long fire, but you could touch it without burning your hand. High fire nichrome coils were fitted into grooves in the firebrick walls and ceramic rod was run through the coils to prevent sag. Pieces of nichrome wire were used to fasten the ceramic rods to the walls (inside grooves) so that the coils were sitting about half in and half out of the wall surface. It's best to leave the coils as far into the kiln space as possible. The part in the groove tends to concentrate heat and when a coil burned out it would burn out facing the groove. The rods kept the coils from sagging so that wasn't a huge problem that they weren't stuffed into deeper grooves. Each of these had three coils for convenience but a couple of kilns I built like this used zoned heating so I could use a Terra cotta flower pot with a removable plug in the bottom drain hole, as a crucible for glass casting in the top of the kiln. A little high alloy steel rod and a ceramic cone set in the drain hole and after the glass had time to properly melt and fine (outgas) the rod could be pulled up gently by a cheap spring until the ceramic cone slipped out of the drain hole and let the glass melt flow into the mold. I even set up nichrome wire in random ladder-like arrays under the pot so that different colors of glass would drip down through it and become a bit better mixed but not fully blended together... Made awesome organic looking effects in the castings. Just measure the volume of the mold using sand... weigh the sand... put that weight of CoTE compatible glass into the flowerpot, plus 15%-25% for the glass that would cling to the pot and not pour into the mold... Ramp the kiln up so it didn't shock the mold and wait until the bubbles in the melt rose and mostly popped... pull the drain plug and start the cooling and annealing program. By using seperate controllers and zoned heating coils, the mold could be kept at a lower temperature than the crucible to keep the mold castable from breaking down while getting the glass melt hot enough to outgas and flow better. Hexagonal Boron Nitride makes a great high temp mold release for glass as well as a lot of metals and in case you want to put an actual top or side loading door on your kiln, this is what you want to use to lubricate any moving parts (hinges, pivots for a split top door, etc) It's a greasy white powder ceramic with the same molecular structure as graphite but much better heat stability. There... Probably as much as anyone is going to want to read from me for a minute. ✌️
Frankly, it was both bad engineering, and the bricks. When I make my kiln I'll be sure to "dome" the top. And do wedge-shaped bricks for the sides with compression bands that can be adjusted. And thank you for this info. You helped me a lot with these few words.
Refractory blanket works well for lids. It's light weight too, but it helps to be rigidized. An area the size of your kiln there would be quite affordable. The plus side is it's flexible, affordable and can be rapidly heated with no cracking issues. The down side is the dust is extremely irritating and potentially carcinogenic so it's a good idea to seal or rigidize, and it cools down very quickly compared to fire brick which can be an issue if you want to control the rate of cooling. I suspect you're probably well versed on the stuff. 304 stainless steel works very well for those kinds of temperatures. The issue with steel, like the threaded rod, is that heated iron will react with any CO2 generated by the firing and cause corrosion which can damage the bricks, an issue with both electric and gas pottery firing, and if the steel is galvanized the zinc fumes are toxic. 304 stainless has a ridiculously high melt point though at high temps it will oxidize but without the corrosion issues you get with iron. I come at it from a pottery perspective, now building my 2nd kiln, and could not agree more about sharing info between crafts as I've gleaned most of my deep in the weeds detailed info about gas, gas burners and construction materials from DIY forge builders.
Great video. Just wondering if you made the 4 outside bricks a half inch shorter, the band clamp would have much more force on the 4 middle bricks... wouldn't it?
Bud!!!!!... that was SOOOOO interesting!!... never cast a bloody thing in my life.. with heat i mean.. but your presentation was so good.. i stayed and watched it all. Good job on the presentation.. and very good skills there man!! Liked it a lot!
When I built pottery kilns many years ago we pinned them together with stainless steel rods. Snip them with big side cutters and instantly get a perfect bit. I never thought to ask "why stainless?" I only did it for a short while and it was just what they used.
You can bind various oxides, ceramics, carbon, ogneous rocks, etc with sodium silicate solution to make custom high temp components. Good for rocket nozzles, good for a foundry.
Bless Phil Rogers soul. Potter here, not an expert but just by observation, when potters build their kiln, especially wood fired kiln (Those big ones) we use at least 2 layers of bricks. Usually a primary layer of firebricks followed by a backing layer of clay bricks. We also use ceramic insulation cloth between the layers to further insulate the kiln. That being said though, I have not experienced a kiln repair as of yet and cant comment much on the shrinkage issue as our kilns usually "Settle" over time and its geometrical shape usually solves any problems with potential cave ins and such. Edit : Definitely forgot to mention that ball clay is used as mortar too.
The blast furnaces I have seen in foundries (for steel) had rounded tops, sort of like a coffin lid. IDK what was done to the bricks to fit them, but essentially it was a long, gentle arch. That would stop the cave ins, and work with your square furnace.
Worked in a foundry, did ladle repair, Cupelo operator, Cupelo starter, which was putting the bottom in and all that stuff in on the downshift poured iron random old machine used little hand box to make some tractor parts on the sly seen a few boom boom
If you go the direction of casting up a one piece lid in the future, use flat metal bar rather than round, works better on thin slabs. Theres a few videos that show you when to use flat bar and when to use the round rebar. I think that Grady guy from Practical Engineering has a video on it
@Paul's Garage I had a piece of copper pipe I found as a kid that had a fitting on one end and was long and curved at the end. It looked kinda like a smoking pipe. I would take dried grass and pack it into the fitting side that curved up, dip it in gasoline, let it drain out so it was just soaked in the grass, then light it with the fire pit and blow through the other end, sending 3ft flames out the other end. I miss those days, I will make a new pipe for it one of these days
Yeah, there's a lot to learn by trying to be more Interdisciplinary. I recently watching a video on a *bakery* that uses a woodfire oven. It operates like an kiln and in some ways even an old forge. Thinking about it, reflow soldering to make modern electronics basically uses a glorified toaster oven. {insert "It's All Connected, Man!" meme here}
exactly! when i started metal casting, people told me only forced air and probably not propane can be used to melt iron. Potters have been getting those temperatures for CENTURIES without forced air, just using wood! Clearly it's possible, you're just not asking the right people
If anyone wants to build a furnace fairly easily use ducting from the home store. It comes in sheets with a folded edge for fastening to the other edge. this is the ducting used in forced air furnace systems. You can combine any number of these to produce just about any diameter you want. 2-8"ducts and a 6" ducts = 22" diameter metal tube. Top and bottom are just sheet metal with the edges bent up and wired. Pipe can be bolted to the skin and used for raising the top and for legs. Just plop some castable stuff in those locations.
Consider longer threaded rods and tighten onto springs at one or both ends of each so the tension remains more or less constant with expansion and contraction. My 2c.
The insinuative firebricks you are using, notoriously shrink when heated. Whilst, glossy refractory bricks have microsilica (amorphous) added in addition to expansile minerals which maintain a balanced neutral linear change with heat. 0:22 this is a small sample of firebricks, 7th row down refers to the volume change. In the industry Andalusite brick is a good abrasive resistance when in contact with the flame but it will deform with temperature due to glassification of the aggregate (movement of crystalline silica), so they put in mortar gaps. Interlocking bricks are also used, which can be used without supporting structures. When not in contact with materials or flame turbulance, I would use kaowool which can expand and contract freely and be supported on the cold side.
Nice vid friend, I subscribed on the strength of it. I make my own alumina bricks by mixing Ball Clay, Calcined Alumina, China Clay (buy these dry from pottery supplies) and Sawdust, which burns out leaving your porous super duty fire brick. By chance did you happen to see NOBOX7's vid talking about high emissive coatings? Its a mixture of Potassium Silicate and Zirconia. You paint it on. It reflects heat back at your crucible full of metal instead of that heat leaking out through the sides and lid of the furnace. Increasing efficiency. More bang for your buck, as it were.
A buddy of mine who used to build heat-treating kilns would cut a channel in the sides of the bricks that would be deep enough [and wide enough] to accept half the width of a 1/4"x1" flat bar. That bar would slot through and be kept in place by the strap. Maybe this is something you could try, because the threaded rod will only hold the bricks along a single axis. It'll still gap out in the middle.
It will be interesting to see how long the steel holds up. I bet it'll go soft and the holes you made will just make the cracking problem much worse, since the steel is effectively conducting heat away from the center of the lid, creating a more extreme temperature differential in the thin brick between the rod and the inside of the kiln.
@@PaulsGarage Titanium may be more available than tungsten. If I am correct, titanium won’t take as much heat as the tungsten but will serve your purpose better than steel.
I used to be a professional potter. We had a gas fired kiln and fired in reduction. We used the entire natural gas service line that ran in the building for 4 burners and an additional 40K gallon propane tank run wide open on an additional two burners. We would fire to cone 11, which is hot for pottery. Total firing time was about 12 hours and then 12-18 to cool to ~350-500 degrees when you could start unloading and burning your gloves off. The roof of the kiln was built as a Roman arch. The floor and front door were on iron wheels on tracks so you could load and pull out the pots like a giant cart. The door was sealed with kaowool which is basically synthetic asbestos that hasn’t been banned yet. And if you pump in enough gas, any air leaks won’t matter. But kilns don’t last forever and it needed to be rebuilt every 5-7 years.
Have you thought of putting a spring at one end (or both ends) of the threaded rod to always be applying a compressive force on the bricks? Also doing the same at right angles to compress in both directions? Paul, Johannesburg
A) Use basalt rod. It will have a coefficient of expansion that is much closer to the fire bricks. B) Put a spring on the ends of your rod to maintain tension. C) cast a 1 piece top for your kiln. Recipes for thermal bricks are readily available.
I used high temperature mortar for mine. I'm not honestly sure if it expands or contracts at any different rate. So I don't know if there's going to be cracking issues. But I didn't have any. Granted, it's been years since I've been able to use a forge. But it was able to get hot enough to forge weld. Anyway, maybe something to try. Might not work for your application. But it worked pretty well for what I needed it to do.
@@PaulsGarage I didn't get that issue but I was also using kaowool or super wool? It's a ceramic wool made for high temperatures. It retains teeth really well and also doesn't have issues with expansion. But you do still need the brick around it. One thing that I've used was to make a dome out of the wool and coat the outside in high temperature mortar. Just as a structural foundation. And then let the hole in the top so I could kind of use a coal forge, almost like a directional blowtorch. This is all just experimentation I was having fun with. That might be worth looking into. Both of those you can get for not too much and in small quantities playlist before you invest heavily into.
I recently built my third electric furnace and have many of these issues too. I thought about sticking a metal rod through the lid, but worried about differential thermal expansion cracking the bricks. What i did was: - carve a groove on the exterior perimeter of the lid, and put a metal square frame there. The frame has some clearance to move around, but this clearance is much smaller than the grooves are deep, so thereś no space for the bricks to slip and fall, even with gaps between them. - the bottom of the lid has ceramic wool insulation. This helps a lot in keeping heat away from the bricks, so they don´t expand/shrink so much, and also seals the gap between furnace and lid, so it helps with efficiency. The wool insulation is glued to the bricks with sodium silicate, and i also put some steel staples made from fire. The top of the lid is barely warm to the touch when the furnace is melting aluminum, except in the air gaps between the bricks where it gets hotter.
that's a good idea too. I'm also worried about the expansion of the steel rod, but I think it will be ok. The rod won't increase in thickness enough to cause problems, but it could increase in length quite a bit, so it's just sitting in the groove. It's free on both ends to expand out of the bricks if it needs to, nothing is holding it in. Time will tell, though. I'll have to use it a bit.
@@PaulsGarage Might i add that maybe use basic round stock, not treaded rod as it looks like you used. With this there is more supporting surface area and no treads to eat into brick when there is thermal expansion in the rod.
adding any kind of insulation to the bottom of the lid may be enough to help reduce the issue and expand the life cycle of your lid.. I don't remember exactly what insulator we used in the forge shop I worked in but I do know we had massive steel doors with only the insulation just rawdogging the heat. They lasted a while as long as the insulation remained
I wonder if you could mix up a batch of " Star Lite" material. and put it on a thin steel sheet of steel even a piece of wood for a lighter lid. It will shrink and will need some patching at first but after it is burned in, it is pretty stable. It just won't work outside where it could possibly get wet. It is pretty amazing stuff. I have used it in place of Satinite many times for gas forges. Something to look into at least.
Is the shrinking a "Loosing main material" problem or a "Space decreasing between material" problem? If it's the second one then you could just fire some bricks during each project and eventually you'll have a good collection of static bricks.
Actually Roman concrete had a unique lime ingredient due to how it was made that gave it self healing properties. As cracks form over time water that gets in the cracks reacts with the lime and creates a calcium bond sealing the crack.
Idea for the lid. Cut the all thread so that it sticks out 2”-3” of the bricks. Put a washer against the bricks, a spring, capture the spring with another washer and nuts on each side.
Want to learn sand casting using your 3D printer? I can teach you!: paulsmakeracademy.mykajabi.com/joinus
Can I use them for pizza oven
Paul, at 4:19 one of the mistakes you made is that the band clamp only touches the corners. You need to put in spacers or bridges (I'm borrowing the term for the bridge on a violin that the string bends over) that force the band into a segmented arc along the sides of the square so they also apply compression to the bricks in the middle. The middle of every side of each brick along the perimeter should have a bridge, and the closer to the middle you get, the taller the bridge should be. This way, every brick gets some compression pushing it into the middle from the faces along the sides of the square, and not just the corners of the corner brick.
Make it round pizza points clamb together
Yes! Cross-hobby knowledge sharing needs to happen. Often one group has solutions to problems the other group hasn't even considered. And although being into multiple maker disciplines can lead to a lot of need for space, it can also lead to efficient use of space: everything in my garage workshop has multiple purposes.
I agree! And for space, there is never enough. It doesn't matter what you do, you could use more garage space
Absolutely! I started as a ceramic sculptor and potter. After school I learned glassblowing. I was also interested in blacksmithing and metal casting. Through all of these ventures I only needed one oven/kiln. It is probably 50 years old and still works like a charm. I have used kiln wash and I fix any new cracks accordingly.
There always a more efficient way to do things, it’s my goal to find them.
I've seen over the last 10 or so years a lot of cross sharing between climbing, caving, highlining and even sailing and I think they've all benefited a lot from it and that'll be the same for this.
That's why a buncha hackers looked at your hobbies and said, 'yeah we can do that better' and we invented hackerspaces, putting one in every other city in the country.
The pain of knowing there was an easier way but you just didn't do it that way because it involved having to talk to a human being... I felt that. lmao.
Story of my life haha
I feel attacked
I wonder if all is anti socials could deal only with each other how things would work…I bet the world would be very peaceful.
@@TrashTube-rt9jw💯
I've never worked with fire bricks, nor have I done any particular masonry work, but seeing this my brain goes straight to using lap joints or tongue and grooves to allow for a more stable interface while accounting for thermal expansion
I came to the comment section to suggest tongue and groove and here it is. Wood workers who do furniture panels have to deal with seasonal expansion and shrinkage due to humidity, so they place panels floating in a frame with a groove all around.
Years (decades) ago in college we built a small kiln with a removable top. The top had a steel angle iron band around it and a slight pyramidal shape to combat shrinkage. Worked pretty good for holding together over a few years of usage despite being built by a couple clueless students. Instructor gave us a grudging "it'll do" on the job. Which from him was high praise.
I built boilers and furnaces. Firebricks are highly specialized and made for specific temperature ranges. They're bonded with a thin dipping mortar, and painted with the mortar when finished. Then there's a specific heating and curing schedule. For ceilings on fire boxes, wedge-shaped blocks are hung from I-beams, plywood is propped up beneath, and plastic refractory is packed in. Then the supports are burned out when starting the curing schedule. When fired, it looks like the bricks are coated with green glass. Memories, I did that 50 years ago.
You could use an adhesive specifically for kiln bricks to bond them together so it would move more as one.
It would also help using ceramic wool on the outside surface for greater insulation. In our lime kilns we use ceramic wool, soft fire brick and then the harder fire brick on the inside for ware resistance.
We also use a castable
Fire brick but it’s very expensive. You should be able to find this material at an industrial concrete and brick supplier.
Hope this helps
That adhesive stuff doesn't last at 2500-3000F, you have to use a castable refractory cement.
@@Boosted98gsx
I’ll look into that for you and find the product name I’m using and let you know what temp it’s good for. We us it in our lime kiln and it seems to last there
thats a good idea for sure. this oven does have ceramic wool in the walls, though not all of them, for insulating. I keep thinking i need to add more where it's missing to boost efficiency a bit. It takes forever to heat more when it's above 2200
@@PaulsGarage Taking longer to raise the temperature is normal at high temps. The hotter it gets, the harder it is to get even hotter. This really starts becoming noticeable once you hit ~1800F, and then even moreso once you get up to 2200F-2300F as you mentioned. Especially since it looks like you're using electric elements instead of a burner (which will struggle at the higher temps). Electric elements will also burn out/wear faster the hotter the firing gets. My experience is almost entirely in pottery, but elements last considerably longer if they never go above Bisque-ing temperatures (around Cone 06 or ~1800F), compared to High Fire (Cone 10 or ~2345F).
Use baby powder and water to make paste, if its not scented its the same stuff in powder form. You could also pulverize a brick to get the same powder, but that's tedious and probably not quite as fine grainwise.
Can be used to fix cracks too.
2 years ago I was watching you make the thing. Didn’t know you could get one cut to size like that. Depending on the price of course, that really could be a big benefit.
Yeah you can get any custom shape you want. Not sure what the cost would be though
Suggestions to prevent issue in future. One simple way would be to swap the bricks around every so many hours of use, so the shrinkage ends up being even over time. Now unless you use special alloy steel, most steel and pure iron have similar melt temperatures, cast iron having a much lower tmelt. 99.999+% pure iron has a much higher melt temperature, but it is very hard to obtain in quantities enough for rods... nice thing about having a career in chemistry for 40 years, you learn a lot of interesting trivia... Now there are metals that would withstand much higher temperatures without softening, but they are quite pricey.
Another note is that your holes need to be loose enough for expansion of the rods, or you will end up with cracked bricks, especially when they shrink onto the rods.
good points! the holes are mostly loose enough that i can push them in, but not tight enough that they fall out on their own. Since this was recorded i took the lid apart once and put it back together, and that seems to have loosened the holes enough that the rods can move a little
he just needs to build it correctly..like a brick wall..repying on gravity. And his new lid is going to fall apart quickly
Actually you would want to use stainless steel rods and you can leave the holes fairly tight because insulator bricks are fairly soft and the little bit of expansion of the rods wouldn't effect it much as long as you mud all your joints
Wow, 2 years already... still got all the ingredients just sitting in my garage, unopened/unused... had wonderful plans 5+ years ago, but per usual, life happened. And so I chose to vicariously build with you, I'm very grateful you were willing to share along the way! Assuming life, well "actual life" doesn't stop happening anytime soon, I'll truly benefit from this shared knowledge, eventually, I'm sure, if I can just open the garage door... Again, thanks!
Yeah I know what you mean, sometimes life gets in the way a lot. But depending what kind of life, it might be worth it
@PaulsGarage So very true, as we've both seen. Been quietly by your side, and I've witnessed you make similar sacrifices, all in love. Long-Short... I realize you're busy, so thanks for the reply, even if the conversation ends here. I genuinely hope all is well with you and yours!
@@caleb1345 Same to you!
Can’t believe I started watching you 5 years ago build this, it was what got me into this kind of stuff in the first place and melt my own metal, thanks!
thanks for sticking around this long! and i'm always happy to push people into crazy hobbies 👍
Thanks for the entertaining education on fire bricks. I'm building a forge now, and didn't know the bricks shrink a little.
Glad I could help! And good luck with the forge!
When I first switched on my home made electric foundry all the joints wanted to open up and fall the thing apart. I switched it off and built a cage around it, a bit like your rods, but external. When (if) I build my next (bigger) foundry, I will keep this idea in mind. A very neat solution.
i think when foundry temperatures are concerned, everything is a temporary solution lol
@@PaulsGarage So true! My "temporary solution" has lasted for two years and still works. I keep telling myself the next one will be better.
Potter here and this video was recommended. We've solved a lot of the problems you talk about in the first minute of the video!
(Use fiber/castable refractory and your rebar solution is basically the Minnesota Flat Top kiln).
I've always been interested in what else my kiln could be used for - although at ~10 Cu ft for the electric one and 30 Cu.ft for the gas one they're a bit big to fire up for small stuff. (Funnily enough the electric is a top loader (door is the lid - made of brick) while the gas kiln is a front loader (fiber door)).
I don't know about fire bricks, but shrinkage has been a major problem in my life too.
Its not our fault, it's just cold here I promise
There are little blue pills for that, you know.
I love your style, easy sub. Informative with plenty of humor, just the right amount of editing splashiness
The material you want is called Blakbond mortar made by BNZ materials. Also, not allowing for thermal expansion will spall the edges of the bricks, so looser band, plus strong mortar joints will work better.
Many pottery kilns get destroyed because they are too tightly constructed. Gaps are your friend. Best of luck
Thanks for the info! I think the place I get the bricks from gets them from BNZ. I'll look into that mortar. In my experience the kilns I've used definitely get looser and looser over time!
Paul, your tighting band does not give direct pressure to the inside bricks. The band is giving pressure only at the corners. Shorten the corner bricks and shape them to get some overall octagonal design so the band can exert some pressure to the bricks in the middle. Or just add a wegde to the middle ones between bricks and band.
I'm so glad you brought cross-discipline knowledge. It's something that i think is sorely lacking in many professions
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Oven Build Playlist here!: ua-cam.com/play/PL-aAeRpJou31awkN9xQIeMpIHwiHwRqyt.html
You could also just flip the lid over with each use so it shrinks evenly on each side?
you should use carbon rods to make pins to connect the individual bricks
carbon will be unaffected by heat
they are not as solid but they don't have to long just a 1 or 1,5 cm
wrong, the Roman buildings that still stand are due to survivor bias, not some magic. there were a lot more other Roman buildings that crumbled and even the ruins weren't found!
Now that you have the holes for reenforcing rods, cut some half-lap rabbets to interlock the bricks. It will make your lid a little smaller but it will be much stronger.
Bravo for making you own kiln/ furnace thing!!!
Gaps can help you. Reduction kilns aren’t that tight. They get the reduction by burning more combustible material than there is oxygen ( extra gas,wood, or oil )There is always positive pressure in the kiln so small gaps don’t matter. A sagging lid isn’t so bad and it looks like yours was a far way from falling in. I’ve seen way worse that last for 20yrs in that condition.
Kiln manufacturers use a type of kiln mortar and seal the inside of the lid and between each brick as well as using octagon shaped tops to keep compression more equal like you said.
Bravo for you ingenuity and exploration!
Thanks! The bricks were definitely far from falling in for sure. The way i designed it the bricks could just be stacked on top without falling in, but the way the inner parts shrank I couldn't lift them off as one. The mortar is a good idea but I think I'll still avoid it for now just so I can change out bricks or use them for something else if I get a hard board lid or something
Is there a certain limit to how much those bricks could shrink? If there is, in theory one could fire them in a way to pre-shrink them and then they could be set from there. (Maybe that's not the case, but it would be interesting to find out.)
In my experience with the other furnaces, when the bricks are too hot for too long they begin to crumble, so there is no end to the process. This includes these 2800f rated bricks in kilns that I never pushed beyond 2300. 2300 for a loooooong time will still eventually destroy the bricks. I've heard no matter what you use, commercial iron/steel foundries consider the furnace liners to be expendable. You just can't beat the heat forever, at least not for any reasonable cost
The shrinking happens because the the quick heating and cooling of the system the only way to minimize it would be to slowly increase the temperature over the course of a few days and then don't shut it down until you have burnt the bricks up and need to replace them typically once or twice a year depending on how hot and hard you run it for instance running it at 1700 degrees everyday even when it is empty will burn up the bricks faster than if you ran it at 1000 degrees when it is full then bring it down to say 500 degrees when it is empty
@@jasondavis7567 Double walled kiln with simmering coals in the space between walls?
@@personman8404 I've seen double thick walls with 2 inches of kwool between the brick and the steel wall get ash soot and slag make it all the way to the outer shell so yes it can happen will it happen on your first firing not unless it was installed wrong but it can and will happen but how well you build it has a direct relationship to how long it will last just like how you run it has an impact on how long it will last ie running it too hot for too long will deteriorate the bricks faster or constant heat changes causing shrinkage
@@jasondavis7567 I was saying to use the coals as a preheater so you aren't temprature shocking the bricks, maybe increasing their lifespan. Thoughts?
You edit and display your nerdiness/personality well. Very fun to watch!
thanks!
i have built lids for my blacksmith forge and i used 3/8" Ceramic Hardboard coated in a ITC-100. ITC-100 is a coating that seals and protect the ceramic fibers, and it reflects/ re-emit the infrared heat as the heat up. they have held the heat for years, and have traveled from a dry climate to a humid one and are still very usable. my blacksmith forge uses 1" Ceramic Hardboard to insulate and the boards are extremely light weight.
Good info! I'm getting some itc-100 actually, i've only ever used satanite up until now
I've worked in the steel Industry for years. My craft is in maintenance, not production. From what I gathered, keeping the furnace hot mitigates shrinkage of the refractory brick.
The lentil entry to the reheat furnace fell in recently. They used metal to hold up the refractory, and the metal failed. The furnace had to be idled to ambient temperature for the reconstruction. Consequently, much of the other refractory had to be replaced.
I am casting my own bricks and molding a 1piece rocket stove using chicken wire for rebar. Recipe includes refractory cement, sand and mostly vermiculite and perlite.
Have you tried water glass? It’s a mix of desiccant silica gel beads and sodium hydroxide lye heated together in a stainless steel bowl to make the liquid. It can be stored in a #2 plastic bottle until use. Mix it with the perlite and sandblasting sand to coat inner surfaces of your oven or if you need to make any off shapes inside the oven (for instance it can be used to make a plinth to set stuff on). Might be useful.
I made my lids from fiber refractory board. It's more durable than wool, bit less than brick. However being a solid sheet, doesn't have this issue. You can coat the surfaces with kiln wash to hard face them to reduce damage, or repair erosion over time.
Making a mount that prevents any sliding contact is a good idea, and usually allows for putting a bit of wool around the edges as a seal, which prevents wear and heat leakage. The mount also holds the hot door while you unload the crucible.
In between the bricks can be placed soft graphite gasket material. Exhaust system gaskets have a graphite ring, as an example. Graphite is one of those things you can't easily burn. It could save you on the electric bill and rate of cooling. I worked on one whose steel band was held closed with a turnbuckle on a spring.
I might need a super-hot oven in the future, and any good-sounding ideas will be tried.
2:00
Funny you say that, because I was worried I was getting into too much at once. Forging, pottery, pyrolysis and distillation, composting. It all seems very exciting but it's just so much all at once. I appreciate all the videos you people make that I can watch during the work week and put into practice on my days off.
There is no such thing as too much, only too little space and time 🤣
Thanks for posting this and going over the subtle differences between two designs.
Glad it was helpful!
I dont do any foundry related stuff but i watched this whole video, love this guy
Thanks! i appreciate it!
Absolutely agree on cross-hobby interactions.
I do a lot of pyro stuff and frequently find myself gandering pottery and blacksmith resources because there's SO MUCH crossover. Shout out to all the ceramics guys keeping the cost of lithium and strontium compounds low. Love yall
totally agree! People making greensand for casting are spending time grinding kitty litter into bentonite powder... you can just buy 325 mesh bentonite straight from pottery suppliers for cheap! It always pays to talk to other people doing anything, even if you think it's unrelated.
@@PaulsGarage Kitty litter is easily the most underrated household... Thing in my opinion!
Need to plug a rocket engine? Litter.
Chemical spills ( within reason)? Litter
Gotta keep that cross-craft communication goin'
This explains so much as a glassblower cause I've seen these built so differently depending on application in my field like most glass furnaces use the arches or the foundry style if the furnace is constantly hot vs annealing ovens which use less heat and less time hot are just cubes.
So... Heat shrinks bricks unevenly. Got it. Thank you! I wouldn't have considered that. GREAT video!
Another way to keep your lid bricks from shrinking would be to line the underside with kaowool. A piece of 2" thick should keep the bricks from getting hot enough to shrink.
I worked in an industrial foundry where the furnaces and heat treat kilns were larger than your living room. The furnace roofs are all made in arch shapes for this reason. A little shrinkage is taken up by the arch shape. Almost everything was high density fire brick arches supported by steel framework.
Sounds like the way those large kilns are built. Always arched, steel supported. What did you make at that foundry? I'd love to hear about it
Have you tried swapping out the band clamp for an orchestra clamp?
Haha no I haven't! Sounds more my thing, I'm a violinist so I'd be more at home in an orchestra anyway
@@PaulsGarage Philharmonic Clampsichord it is!
I worked for one of the klin manufactures around covid. They would cement the bricks together. I was actually citing the lids out when I worked there. You could also try cooking the bricks before using them. If you pre srink them it may help. I just don't know it it may damage them.
They made some really big ones, like one that could fit a whole car and would open like a cup off a table.
Another great video!
Great comment about masonry arches.
Cheers from Alaska
thanks! masonry arches are pretty awesome
@PaulsGarage I'm thinking about sending you some zinc ingots (pretty close to pure zinc, not alloys). At first I was dismissive of zinc but it doesn't take long to melt and it pours beautifully.
At human temperatures, it is a lot like cast iron but shinier.
Are you still at 1818 Milton Ave? Or did your address change when you moved?
Cheers from Alaska
That would be great! Milton Ave is a post office, i have a P.O. Box there, it's still there so that works. Just let me know if/when you send it so i can check the box. I'm not very good about going there often
@@PaulsGarage The ingots are in the mail. They should show up in about a week or so.
Steel rods - good start, if you shape them into an inverted arch inside the bricks and then post-tension them (steel stretches like a spring for when they are cold and larger) if the bricks can take that much stress. Post pensioning them from that inverted arch shape also pulls the outside bricks down, or the inside bricks up. And as pointed out mild steel may not be the best steel to use.
That sounds pretty awesome but I'm not sure how I could drill the hole like that
@@PaulsGarage tig rod. buy a pack. W lasts in hot applications longer than mild steel. Dowel them bricks like tabletop boards =)
Thanks.
I worked with gas muffle furnaces years ago. Never had a problem like this.
For my forge lid I go over all the joints with Kaowool reinforced refractory furnace cement. I use a furnace cement that comes in a Caulk tube just to make it extra easy.
that sounds like a good idea
wonder if you can get the clay for making those bricks you could make youre own and make them to size and shape , not loosing any material by cutting it
you have pottery ovens so you should be able to bake them a few pieces at a time (excapt maibe a one piece lid and bottom )
Good idea! I think the bricks are made from alumina and some other stuff, with a filler that gets burned out to make them very porous (for light weight and insulation). I know for a fact the 2800 rated bricks are much heavier than the 2400 rated bricks, maybe less filler in the heavier ones? Not sure.
I have heard that filler includes sawdust.
(And yes, I want a small heat treating oven, for tools…. Need to get the $$$ somehow.)
A Catenary curve is the mathematical name for the curved archway. Your videos are always interesting and a good learning experienece.
For industrial heat treatment furnace design (giant methane pizza oven style) all our furnaces had height-adjustable doors that were metal frames with bricks inside of the doors; I would venture using this as the primary access for a non conveyor style kiln/oven/furnace would work fine too and eliminate a lot of issues like what you are dealing with. On the flip side you have some degradation of efficiency at the joints for that style door, have to maintain positive pressure inside and may or may not need some kind of ventilation to pull fumes from the entrance (like I said, we used methane so some different considerations)
I used to work for a metals recycling company. We mostly had refractory brick for the furnaces. When we line the furnaces we intentionally add 1 few mm in between the brick with a bitumen pads so when we ramp up the temp to ~1000 C (~1900 F) the pads would burn off. Since we ran the furnaces at more or less temp constant 24/7 until the next relining we don't really have issues with the lining itself (except for the occasional worksmanship or material infiltration issue).
We do have shrinkage cracking on the spouts we use to tap the furnaces and yes we usually use pottery clay to patch up/cover up those problems. We found that low moisture clays worked best for that application
There is something we use at cement plants called plastic refractory, we call it ram. It's like playdough that cures hard almost like castable. probably wouldn't have helped here but thought I'd put it out there.
I've never heard of that, I'll look into it!
Ramtite mouldable refractory, or plastic cement. Add a layer of ceramic wool and you'll never go back.
Stainless steel anchors welded to the structure on the back side helps too - very common on large industrial furnaces and catalytic crackers (which have catalysts with the consistency of sand being blown round inside).
Ram can be used but you really need pneumatic tools to properly install it also because of expansion and contraction you really need to have some type of insulator board and or paper between the ram and the steel walls to account for it typically at least 1inch board or 1/4 or 1/8 inch paper for hotter furnaces 2 inch board is even better
@@jasondavis7567 Look up 3M Nextel blanket… It’s a woven ceramic fibre cloth. (It’s also used for high temperature electrical insulation).
Thanks for your entertaining presentation. I saw a few videos where they were making their own firebrick with a mixture of refractory cement, vermiculite and sand. With that you can cast a custom-shaped piece of any size. Perhaps include reinforcing iron within the piece?
That's an interesting idea! I'd be worried about the sand and vermiculite, i've heard those can vary a lot. I'm planning on getting some Kast-o-lite 30 and make some stuff, maybe cast a lid or some bricks, but that's a plan for when the budget is a bit "healthier" lol
In the top 2 explanations of the month right here . I wondered how that worked.
They dont shrink per say kinda but more important is they expand when heated andcontract when cooling so if you make an adjustable clamp for your furnace you can tighten when you cool and loosen when you fire have to look at the specs on expansion rates for the brick you chose if your using an exposed flame you want the brick to be a hard brick or a superduty
Back in the 1970s, I worked at a lead smelter. We used a coke-fueled blast furnace. We used some kind of mud to seal the cracks between the fire bricks. Got it on pallets of 50lb bags. We'd throw a few shovels full in a 5 gallon bucket and mix it with water; no special ratio. It sealed the cracks well. It wasn't adhesive, so it came off pretty easily when we shut down the furnace. For a small oven like yours, you'd be able to use a chipping hammer that welders use to chip the flux/slag off of welds. There's gotta be somewhere you and your friends can chip in and buy some of what ever that was. I never knew what industrial supply we got it from.
In your older video about satanite I used that. Still holding up. I would suggest forming fire bricks to fit like a wood floor.
I’m building a kiln this summer, as big as I can.
I have as much clay as anyone could use in a lifetime.
Tbh though, you can make your own fire bricks with plaster of Paris and sand, I don’t know the exact formula because I haven’t needed to make one yet. Fortunately for everyone interested, you can also add fiber glass to your mix to add some support in the mix.
If you have ever seen the inside of a old coke oven, the walls and ceiling are basically glass.
I actually love aluminum borro silicate brick. I cast bronze hammer heads, (so far)...super easy to mill and cut.
they are really easy to cut, agreed. After a while the abrasiveness of the dust wrecks the saws, though. that's what home depot saws are for lol
Built a few kilns. Actually really surprised I only just stumbled on your channel since you do so much of the stuff I used to do.
I like your idea about sharing experiences between disciplines.
That's the way to learn new ways of doing crazy interesting stuff.
Here goes with some of my experience with kilns.
The biggest I've built was about 18 feet by 20ish feet. Basically big enough to park a 1 ton GMC Suburban inside with room to spare.
Steel framed box suspended from a gantry. The gantry was on trolley rails. Took four guys to move it. It had two steel framed beds it could be dropped on so, basically... while one was firing the other was loaded and unloaded and serviced if it needed it. It needed it often. Structural mild steel really doesn't like glass firing temps and wool never seals up as well as I would have liked.
The beds had 1/4" X 6" leveling blades bolted into the firebrick bed frame so that the top edge could be periodically lined up in a perfectly level plane a couple of inches above the fire brick surface. Then clay grog (basically non-scoop kitty litter) was poured in to fill the difference.
That made it possible to use a screed to scrape the grog out perfectly flat and level. Economical to build and easy to maintain but not the most energy efficient beast. 200w 480v three phase power through mercury relay switches and a programmable controller. Ooph. Great fun to work around in the summer.
Most were a lot smaller. 2' X 2' X 3' mostly. Great for almost anything.
All of these used alumina foam firebrick on the inside and compressed ceramic fiber panels (basically space shuttle heat tiles) outside of that. There was a 2" L angle welded frame to buckle the firebrick together with threaded stainless rod to compress it together.
Mild carbon steel threaded rod rots quickly and rotten threads make crappy fasteners.
The ceramic fiber panels were fitted over that with a thin sheet of ceramic wool between to fill the space. Just adding that insulated it so well the outside was good and warm after a day long fire, but you could touch it without burning your hand.
High fire nichrome coils were fitted into grooves in the firebrick walls and ceramic rod was run through the coils to prevent sag. Pieces of nichrome wire were used to fasten the ceramic rods to the walls (inside grooves) so that the coils were sitting about half in and half out of the wall surface.
It's best to leave the coils as far into the kiln space as possible. The part in the groove tends to concentrate heat and when a coil burned out it would burn out facing the groove. The rods kept the coils from sagging so that wasn't a huge problem that they weren't stuffed into deeper grooves.
Each of these had three coils for convenience but a couple of kilns I built like this used zoned heating so I could use a Terra cotta flower pot with a removable plug in the bottom drain hole, as a crucible for glass casting in the top of the kiln.
A little high alloy steel rod and a ceramic cone set in the drain hole and after the glass had time to properly melt and fine (outgas) the rod could be pulled up gently by a cheap spring until the ceramic cone slipped out of the drain hole and let the glass melt flow into the mold.
I even set up nichrome wire in random ladder-like arrays under the pot so that different colors of glass would drip down through it and become a bit better mixed but not fully blended together... Made awesome organic looking effects in the castings.
Just measure the volume of the mold using sand... weigh the sand... put that weight of CoTE compatible glass into the flowerpot, plus 15%-25% for the glass that would cling to the pot and not pour into the mold...
Ramp the kiln up so it didn't shock the mold and wait until the bubbles in the melt rose and mostly popped... pull the drain plug and start the cooling and annealing program.
By using seperate controllers and zoned heating coils, the mold could be kept at a lower temperature than the crucible to keep the mold castable from breaking down while getting the glass melt hot enough to outgas and flow better.
Hexagonal Boron Nitride makes a great high temp mold release for glass as well as a lot of metals and in case you want to put an actual top or side loading door on your kiln, this is what you want to use to lubricate any moving parts (hinges, pivots for a split top door, etc)
It's a greasy white powder ceramic with the same molecular structure as graphite but much better heat stability.
There...
Probably as much as anyone is going to want to read from me for a minute.
✌️
Loved the details, thats the type of information that fulfills my thirst for knowledge.
Frankly, it was both bad engineering, and the bricks.
When I make my kiln I'll be sure to "dome" the top.
And do wedge-shaped bricks for the sides with compression bands that can be adjusted.
And thank you for this info. You helped me a lot with these few words.
domed lids are ideal i think, wedge shape is good too. My foundry furnace lid isn't domed, just wedged, and there have been no problems
Would grinding the edges of the brick into a tongue and groove help the lid.
or would it even be possible I don't know how brittle those are.
It's probably possible, but yeah it would be pretty brittle. These bricks will break if have if you tip them over.
Refractory blanket works well for lids. It's light weight too, but it helps to be rigidized. An area the size of your kiln there would be quite affordable. The plus side is it's flexible, affordable and can be rapidly heated with no cracking issues. The down side is the dust is extremely irritating and potentially carcinogenic so it's a good idea to seal or rigidize, and it cools down very quickly compared to fire brick which can be an issue if you want to control the rate of cooling. I suspect you're probably well versed on the stuff.
304 stainless steel works very well for those kinds of temperatures. The issue with steel, like the threaded rod, is that heated iron will react with any CO2 generated by the firing and cause corrosion which can damage the bricks, an issue with both electric and gas pottery firing, and if the steel is galvanized the zinc fumes are toxic. 304 stainless has a ridiculously high melt point though at high temps it will oxidize but without the corrosion issues you get with iron.
I come at it from a pottery perspective, now building my 2nd kiln, and could not agree more about sharing info between crafts as I've gleaned most of my deep in the weeds detailed info about gas, gas burners and construction materials from DIY forge builders.
Great video.
Just wondering if you made the 4 outside bricks a half inch shorter, the band clamp would have much more force on the 4 middle bricks... wouldn't it?
Bud!!!!!... that was SOOOOO interesting!!... never cast a bloody thing in my life.. with heat i mean.. but your presentation was so good.. i stayed and watched it all. Good job on the presentation.. and very good skills there man!! Liked it a lot!
Thanks John I appreciate it! You cast stuff without heat? Like resin? How do you like that? I want to try that at some point
When I built pottery kilns many years ago we pinned them together with stainless steel rods. Snip them with big side cutters and instantly get a perfect bit. I never thought to ask "why stainless?" I only did it for a short while and it was just what they used.
that's interesting, thanks for the info!
You can bind various oxides, ceramics, carbon, ogneous rocks, etc with sodium silicate solution to make custom high temp components.
Good for rocket nozzles, good for a foundry.
Bless Phil Rogers soul.
Potter here, not an expert but just by observation, when potters build their kiln, especially wood fired kiln (Those big ones) we use at least 2 layers of bricks. Usually a primary layer of firebricks followed by a backing layer of clay bricks. We also use ceramic insulation cloth between the layers to further insulate the kiln.
That being said though, I have not experienced a kiln repair as of yet and cant comment much on the shrinkage issue as our kilns usually "Settle" over time and its geometrical shape usually solves any problems with potential cave ins and such.
Edit : Definitely forgot to mention that ball clay is used as mortar too.
I learned from TKOR and now im here just before i craft it
The blast furnaces I have seen in foundries (for steel) had rounded tops, sort of like a coffin lid. IDK what was done to the bricks to fit them, but essentially it was a long, gentle arch. That would stop the cave ins, and work with your square furnace.
2:14 Lol!
Edit: 3:56 even more lol!
I love the captions... Subscribed
Worked in a foundry, did ladle repair, Cupelo operator, Cupelo starter, which was putting the bottom in and all that stuff in on the downshift poured iron random old machine used little hand box to make some tractor parts on the sly seen a few boom boom
Ace used to sell the refractory cement, so, you can cast your own shape. They sold it in two gallon buckets or so.
If you go the direction of casting up a one piece lid in the future, use flat metal bar rather than round, works better on thin slabs.
Theres a few videos that show you when to use flat bar and when to use the round rebar. I think that Grady guy from Practical Engineering has a video on it
You could form and pour any one piece lid with castable firebrick mix. Add rebar for strength and extended a few beyond the edges to make handles.
who is this man and why is he so casually hilarious? is he my new ave?
I can't be the new AvE. I lack his Shakespearean grasp of creative foul language, for one!
Outstanding video! 👍🏻🎅👍🏻 Glad I clicked, liked and subscribed! 😂
I'm a pyro, if anyone needs me for something
This is the first video of yours that I have watched, and I'm dying at the words on screen
Welcome to the pyro party! I think everyone who does this stuff secretly just wants to burn and melt stuff for fun
@Paul's Garage I had a piece of copper pipe I found as a kid that had a fitting on one end and was long and curved at the end. It looked kinda like a smoking pipe. I would take dried grass and pack it into the fitting side that curved up, dip it in gasoline, let it drain out so it was just soaked in the grass, then light it with the fire pit and blow through the other end, sending 3ft flames out the other end. I miss those days, I will make a new pipe for it one of these days
Yeah, there's a lot to learn by trying to be more Interdisciplinary. I recently watching a video on a *bakery* that uses a woodfire oven. It operates like an kiln and in some ways even an old forge. Thinking about it, reflow soldering to make modern electronics basically uses a glorified toaster oven.
{insert "It's All Connected, Man!" meme here}
exactly! when i started metal casting, people told me only forced air and probably not propane can be used to melt iron. Potters have been getting those temperatures for CENTURIES without forced air, just using wood! Clearly it's possible, you're just not asking the right people
There's a reason many DIY reflow ovens are made out of toaster ovens.
If anyone wants to build a furnace fairly easily use ducting from the home store. It comes in sheets with a folded edge for fastening to the other edge. this is the ducting used in forced air furnace systems.
You can combine any number of these to produce just about any diameter you want.
2-8"ducts and a 6" ducts = 22" diameter metal tube.
Top and bottom are just sheet metal with the edges bent up and wired.
Pipe can be bolted to the skin and used for raising the top and for legs. Just plop some castable stuff in those locations.
Kaowool is a really nice insulation for that application just provide a support frame with handles
Kaowool is great. This oven has a bunch of it in the walls for insulation, you just can't see it because it's all covered
I’m 18 seconds in… it’s definitely my fault.
Odd. most people usually agree that its mine....
As long as someone takes the heat off of me, I'm happy 🤣
Consider longer threaded rods and tighten onto springs at one or both ends of each so the tension remains more or less constant with expansion and contraction. My 2c.
I use stainless steel welding rod like dowels in wood working. You can cut tounge and groove in the brick.
The insinuative firebricks you are using, notoriously shrink when heated.
Whilst, glossy refractory bricks have microsilica (amorphous) added in addition to expansile minerals which maintain a balanced neutral linear change with heat.
0:22 this is a small sample of firebricks, 7th row down refers to the volume change.
In the industry Andalusite brick is a good abrasive resistance when in contact with the flame but it will deform with temperature due to glassification of the aggregate (movement of crystalline silica), so they put in mortar gaps.
Interlocking bricks are also used, which can be used without supporting structures.
When not in contact with materials or flame turbulance, I would use kaowool which can expand and contract freely and be supported on the cold side.
good info, thanks!
I use ceramic wool with a steel shell :) Great video!
I was typing out you should form a circular dome lid just before you mentioned arch and wedge lids.
Nice vid friend, I subscribed on the strength of it. I make my own alumina bricks by mixing Ball Clay, Calcined Alumina, China Clay (buy these dry from pottery supplies) and Sawdust, which burns out leaving your porous super duty fire brick.
By chance did you happen to see NOBOX7's vid talking about high emissive coatings? Its a mixture of Potassium Silicate and Zirconia. You paint it on. It reflects heat back at your crucible full of metal instead of that heat leaking out through the sides and lid of the furnace. Increasing efficiency. More bang for your buck, as it were.
A buddy of mine who used to build heat-treating kilns would cut a channel in the sides of the bricks that would be deep enough [and wide enough] to accept half the width of a 1/4"x1" flat bar. That bar would slot through and be kept in place by the strap.
Maybe this is something you could try, because the threaded rod will only hold the bricks along a single axis. It'll still gap out in the middle.
It will be interesting to see how long the steel holds up. I bet it'll go soft and the holes you made will just make the cracking problem much worse, since the steel is effectively conducting heat away from the center of the lid, creating a more extreme temperature differential in the thin brick between the rod and the inside of the kiln.
we will definitely find out. If the bricks fail it will be an excellent opportunity to reengineer a whole new lid and not have this problem any more
@@PaulsGarage Titanium may be more available than tungsten. If I am correct, titanium won’t take as much heat as the tungsten but will serve your purpose better than steel.
@@katiedotson704 What are you taking about? I can walk into any harbor freight or welding supply store and walk out with dozens of tungsten rods.
@@Kineth1 6 inch long
@@GigsTaggart Well, yes, but that should be more than long enough to pin the brick edges together.
I wonder if you could do a tongue and groove construction on the edges of the bricks to keep them together in conjunction with the band clamp.
Then you'd have tongue and grove bricks that are shrinking and fit together poorly
I used to be a professional potter. We had a gas fired kiln and fired in reduction. We used the entire natural gas service line that ran in the building for 4 burners and an additional 40K gallon propane tank run wide open on an additional two burners. We would fire to cone 11, which is hot for pottery. Total firing time was about 12 hours and then 12-18 to cool to ~350-500 degrees when you could start unloading and burning your gloves off.
The roof of the kiln was built as a Roman arch. The floor and front door were on iron wheels on tracks so you could load and pull out the pots like a giant cart. The door was sealed with kaowool which is basically synthetic asbestos that hasn’t been banned yet. And if you pump in enough gas, any air leaks won’t matter.
But kilns don’t last forever and it needed to be rebuilt every 5-7 years.
Have you thought of putting a spring at one end (or both ends) of the threaded rod to always be applying a compressive force on the bricks? Also doing the same at right angles to compress in both directions? Paul, Johannesburg
A) Use basalt rod. It will have a coefficient of expansion that is much closer to the fire bricks.
B) Put a spring on the ends of your rod to maintain tension.
C) cast a 1 piece top for your kiln. Recipes for thermal bricks are readily available.
I used high temperature mortar for mine. I'm not honestly sure if it expands or contracts at any different rate. So I don't know if there's going to be cracking issues. But I didn't have any. Granted, it's been years since I've been able to use a forge. But it was able to get hot enough to forge weld.
Anyway, maybe something to try. Might not work for your application. But it worked pretty well for what I needed it to do.
High temp mortar looks like good stuff. It would have to expand with the bricks I would think it it would all break apart?
@@PaulsGarage I didn't get that issue but I was also using kaowool or super wool? It's a ceramic wool made for high temperatures. It retains teeth really well and also doesn't have issues with expansion. But you do still need the brick around it.
One thing that I've used was to make a dome out of the wool and coat the outside in high temperature mortar. Just as a structural foundation. And then let the hole in the top so I could kind of use a coal forge, almost like a directional blowtorch.
This is all just experimentation I was having fun with. That might be worth looking into. Both of those you can get for not too much and in small quantities playlist before you invest heavily into.
I recently built my third electric furnace and have many of these issues too. I thought about sticking a metal rod through the lid, but worried about differential thermal expansion cracking the bricks. What i did was:
- carve a groove on the exterior perimeter of the lid, and put a metal square frame there. The frame has some clearance to move around, but this clearance is much smaller than the grooves are deep, so thereś no space for the bricks to slip and fall, even with gaps between them.
- the bottom of the lid has ceramic wool insulation. This helps a lot in keeping heat away from the bricks, so they don´t expand/shrink so much, and also seals the gap between furnace and lid, so it helps with efficiency. The wool insulation is glued to the bricks with sodium silicate, and i also put some steel staples made from fire.
The top of the lid is barely warm to the touch when the furnace is melting aluminum, except in the air gaps between the bricks where it gets hotter.
that's a good idea too. I'm also worried about the expansion of the steel rod, but I think it will be ok. The rod won't increase in thickness enough to cause problems, but it could increase in length quite a bit, so it's just sitting in the groove. It's free on both ends to expand out of the bricks if it needs to, nothing is holding it in. Time will tell, though. I'll have to use it a bit.
@@PaulsGarage Might i add that maybe use basic round stock, not treaded rod as it looks like you used. With this there is more supporting surface area and no treads to eat into brick when there is thermal expansion in the rod.
IDEA: take the lid apart, and then put the shrunken sides of the bricks on the outside and the unshrunken bricks on the inside.
That what I did, yep
Try a castable refractory. You can make any shape and size you want. Mizzou castable is extra durable. Kastolite is lightweight
What about making interlocking mortise and tenon joints, on the 6 blocks
Paul, I like your style.
adding any kind of insulation to the bottom of the lid may be enough to help reduce the issue and expand the life cycle of your lid.. I don't remember exactly what insulator we used in the forge shop I worked in but I do know we had massive steel doors with only the insulation just rawdogging the heat. They lasted a while as long as the insulation remained
I wonder if you could mix up a batch of " Star Lite" material. and put it on a thin steel sheet of steel even a piece of wood for a lighter lid. It will shrink and will need some patching at first but after it is burned in, it is pretty stable. It just won't work outside where it could possibly get wet. It is pretty amazing stuff. I have used it in place of Satinite many times for gas forges. Something to look into at least.
Is the shrinking a "Loosing main material" problem or a "Space decreasing between material" problem? If it's the second one then you could just fire some bricks during each project and eventually you'll have a good collection of static bricks.
Actually Roman concrete had a unique lime ingredient due to how it was made that gave it self healing properties. As cracks form over time water that gets in the cracks reacts with the lime and creates a calcium bond sealing the crack.
Idea for the lid. Cut the all thread so that it sticks out 2”-3” of the bricks. Put a washer against the bricks, a spring, capture the spring with another washer and nuts on each side.