Ted Ewert

I'm planning on putting 2" of wool around the inner tube. I want to get everything lined up and secure first before doing that as a final step. I checked the Kastolite test batch this morning and was able to easily remove all the acrylic tubes without any distortion in the cement. This was after 12 hours of setting in approximately 65 degrees. In light of this, I see no reason to use crayons or candles as a burn out medium, unless they are found convenient for their shape or economy. I am going to cast a new burner this weekend using acrylic rods (which are only about $5 for 6 feet). I have also found that after about 24 hours of setting I can shape a casting with the belt sander (Lots of dust though!). This is handy for squaring off the ends of the tube, or cleaning up any rough spots.

Anyway, I got more cement and cast the floor this evening. I also cut the hole in the side of the tank for the burner. I overestimated the amount of cement I would need for the floor so I made a test casting with various size acrylic rods stuck in with release agent on them. I want to see at what stage I can pull them out without affecting the shape of the hole (or sticking). Solid rods develop vacuum issues unless they have a vent hole. I also started rebuilding my burner

Darn right.

What mistakes am I making Frosty, and where does it say I am under any obligation to your agenda? This is an experimental forge design and I have made no claims to the contrary. I welcome any constructive criticism or suggestions, but in the end it's my project and I'll build it as I see fit.

Thinking and designing are what I like about projects. I like to try new things. Copying exactly what someone else has already built is no fun.

I've found that no stick BBQ grill spray works pretty good, which is what I used for the PVC pipe. Wax paper is also good in some places. The problem is cracking and splitting. If it holds together, a masonry bit in a hammer drill will make short work of it. Nevertheless, you also want straight holes that line up. That's almost impossible with a hammer drill. Casting is still the most accurate method. I've done a fair amount of casting, and I have a pretty good idea how I'll solve this one. I've got some more Kast-o-lite coming in tomorrow (the tube took about 18 lbs out of the 20 I had). Thanks for all the helpful suggestions! I've thought about this, and it is a concern. I really won't know until I fire it up for a good long test, but I'm hoping that the tubes are long enough, and the air velocity fast enough, to keep the flame from anywhere near the plenum. If the plenum starts smoking you got trouble.

The Kast o lite sets up pretty hard, although it may be possible to machine it within the first 24 hours of curing. The drilling would probably be dicey, but tapering might work. I'll cast a test piece and see how it goes. If I have to I can machine a bunch of tapered cones to mold around, but it's a lot of lathe work. If I can run the taper through some semi cured cement that would be optimal.

I'm not real happy about the way I built the burner. I think the basic design is fine, but the steel tubes are too long (and not exactly true) and stress the brick as they are inserted. I would just go ahead and cast it, which is physically stronger, but I found that it works so much better with a taper starting at the end of the tubes. The taper slows the gas down enough to keep the flame burning right at the brick, even at full air pressure. That taper would be a challenge to cast. I may try a hybrid: half cast, half brick. I can try a number of variations since the burner is removable.

I got the center cylinder cast. I built an acrylic "brick" to act as a form for the burner. The burner is going in at an angle to allow the flame to create a swirl in the chamber. Here it is all done and filled with cement: I allowed it to cure for 24 hours and pulled the forms off. Even though I cut a lengthwise slit in the inner PVC pipe, I still had to pound it out. Cement always shrinks towards the center and makes getting the center piece out a xxxxx. I put a couple of hose clamps around the ends of the cylinder as that part has a tendency to want to crack and break during form extraction. Edited for Language. Here's all the pieces afterwards. I built an acrylic ring to seal the bottom between the two forms. I also used lots of plumbers putty and Gorilla tape to seal the cracks where the "brick" went through the forms. The actual brick fits in the hole nice and snug. Once I fix the angle the burner is mounted at (probably horizontal) I'll cast a level platform for the work within the cylinder. Ted

I modified my ribbon burner by inserting a refractory brick over the tubes. Here's how it started out: I pounded a brick on to the tubes to get an impression, then I drilled the holes out about 2/3 the way into the brick. Since these tubes are 1/4" ID, I drilled the rest of the way through 1/4". There is a good 3 inches of brick between the end of the tubes and the final outlet. This provides lots of insulation so the tubes don't get hot and deteriorate. I also modified the input to accept a 2" pipe Here's the burner: I originally had straight holes coming out but that configuration wouldn't hold a flame. So I reamed out the holes to provide a widening taper, and also chamfered the end for a wider flare. This slowed the mix down enough to hold the flame close even with the blower wide open. This is full tilt... I have not tried this in the forge since my top opening isn't big enough. Nevertheless, I think this method can be developed as an alternative to casting. Further testing needs to be done, but it's promising. I achieved a good tight fit around the tubes, and I put the torch to every seam and found no leaks. The joint between the brick and the plenum could certainly be sealed easily enough if there were any doubt. Ted

I'm back to making this a forge again. I'm going to cast the chamber outside the forge, since I am integrating the burner into it. I have a couple of large PVC pipes I'll be using for the forms. The inner diameter will be around 5 1/2" with about an inch wall thickness. I'm putting a ribbon burner in it with a single line of holes. These will come in tangent to the radius of the chamber. I'm still trying to figure out a few details, but this may be a little different than your standard forge. I have plenty of wool and bricks to fill up the rest of the cylinder.

Thanks Tim, I appreciate all your input and pictures. I built my first oven the same way you did, with only angle iron, but I used clay bricks and it failed. I also prefer square for this type of oven and I'm going to take your advice and abandon the tank. I never had a good feeling about the tank as an oven anyway. I'm using 18 gauge for the element and we'll see how it goes. I've got about 10 ohms through the wire cold which should give me between 20-25 amps, somewhere around 4500 watts. That should warm things up pretty good. I'm making the top removable and will use thicker gauge wire as warranted. This PID doesn't need any precalibrating for ramp up. It automatically calculates the rate of heating and turns the element off if its heating too fast. I only have a paper copy of the manual, ebay link removed Ted

Here's an overview of today's work... I put a hinge on the front door. Not exactly a thing of beauty but it works good. I spent most of the day rewiring my control box for running 220 VAC into the element. I had to add a 40 amp mechanical relay (the black thing in back of the controller (PID)) and a switch to control it.The 220 goes through this relay and then through the SSR (solid state relay) which is controlled by the PID. The rest of the box runs off 110 which is a separate circuit. You can kind of see the SSR, which is the gray thing right below the mechanical relay. It has a heat sink below it, which I also added a fan today to keep it cool. Here's the front. The switch on the left is for powering up the box, and the one in the middle controls the 220 volt relay. It has a 110 VAC control coil which this switch activates. The red light indicates that the 220 volt circuit is active. This PID is specially programmed for heat treatment applications. You can ramp the heat up and down at whatever rate is indicated, and also soak the material for whatever duration you need. It's a little weird to program but not to bad. It works good once you get the hang of Chinese logic. Ted

These are refractory bricks (no clay) and make very good insulators. Probably made of the same stuff inswool uses. I also need a flat surface for the heating element to attach to, as well as support for that flat surface, and the bricks provide that. If I had the sheet metal I'd build a large box for this oven and put a solid layer of inswool around the bricks (which would be a better way of doing things). If the tank doesn't work I'll have to do that. I could always put a layer of wool around the tank too. We'll see.

I started out building a heat treating oven a few months ago. It was a total failure, other than a good learning experience. I'm going to try it again with new materials and knowledge as see if I can't make it work this time. I ordered a dozen insulating bricks a month or two ago. They arrived and most of them were broken, so I asked for replacements or a refund. the Vendor chose replacement and it's been nothing but me nagging him to ship them ever since. They finally arrived intact today, so I have lots of bricks. Square bricks in a round tube is not ideal, but I think it will fly. I need a good surface to mount the element on, and the bricks will serve well in that department. Here's what I got so far: The three bricks laying out are going to be the top. I bolted them together with some 1/4-20 SS threaded rod. I have some high temp gasket material which I may put between the bricks to seal the cracks. I'm just trying to figure out the layout at this point. I trimmed the lower bricks to fit the curve of the tank, and will do the same with the top. I will then fill in the gaps with wool insulation. The end of the tank I cutoff will become a hinged door filled with insulation. I also have to design a way to be able to replace the element should it fail. I talked to a guy who uses his oven a lot and has already gone through 3 elements. I may make the top so it slides out. I am also thinking of coating the inside with some Metricote for added heat retention. I'll update as I get things sorted out. Ted

Done! I'll start one when I get home and take a few pics.

If you have a stoichiometric mixture, it seems to me that the flame front speed is pretty much fixed. IMO, keeping the flame lit at the nozzle is key (more of a problem with blown burners). Once it leaves the nozzle unburned it mixes with the surrounding air and quickly becomes non stoichiometric. If I get a blue flame right off the nozzle, and no orange, I know I have a nice hot, clean burn.

Thanks Wayne, you're right. I decided to make it into a heat treatment oven instead. I have all the electronics and other parts ready to go. I wound the heating element last night and will start assembly this weekend.

I think a good burner is a lot like a rocket engine. The fuel has to get accelerated beyond the velocity of the flame front in order to keep the flame out of the burner, and inside the furnace. You can see in this picture that the gasses get compressed then expanded into the nozzle. The nozzle then shapes and directs the flame. We should be designing and building our burners with this general concept in mind. Our nozzles can be any sort of contained expansion area which shapes and directs the flame to our advantage. The nozzle should probably be cast into the chamber to increase durability and follow the natural contours of the chamber. The problem most people have with velocity is blowing the flame away from the nozzle. This condition can be mitigated through the use of turbulence inducing materials or shapes. Slowing down a portion of the flow in order to maintain the flame close to the nozzle insures a complete burn of the fuel before it escapes from the furnace. It also make the flame a lot hotter and more efficient. Ted

I have lots of insulation, so the width isn't an issue. I'll still make a fairly small chamber. It is a bit longer than I'd like. May have to get creative. May have to find something else.

I'm getting ready to dive into this build. The tank I have is 12" wide X 24" long with 18" of straight cylinder. I successfully evacuated all the air without serious incident. I'm going to take one of the ends off so I can get in and work without trying to stuff everything through a small hole. Anyone have a can of Weld-B-Gone I can borrow? I may just cut it front of the weld, won't make much difference. It's a nice solid tank. It was used to pressurize microwave transmission lines. We were tearing the site down and it was in the dumpster. It has nice feet too. Anyway, it's a start to a project I'm sure you all will be absolutely captivated with. All comments and advice are welcome.

That's what I meant Frosty. I just couldn't remember " high alumina water set refractory " at the time. I'm just getting ready to order some so thanks for the info.

The ribbon burner would be for the next forge I build. This one is just a test fixture. I'm going full refractory on the new one. I have an old air tank and lots of insulation. I still have to get some cement and a few odds and ends, but it's coming.

I'm leaning towards a ribbon burner in the next forge. It would be a single line of outlets tangent to the radius of the chamber. The diameter and number of the holes is the only thing I have some questions around. It could be cast it right off the pipe. Anyway, here are a few shots of the burner in question in the forge. The flame didn't turn out as bright as it looked to my eyes. I guess my camera sensor rolls off a little towards the UV spectrum. The threaded rod splits the flame a bit, which could be minimized with more careful fabrication. Here's a side view: Here's the simple setup I have. That blue handle is on a needle valve (not a common hose bib). All my valves are 1/2", which makes things simple as far as connecting the string together. Ted

I'll take a picture of it in the forge tonight for you. The orange flame is due to a slightly rich mixture. I'd have to rebuild the ribbon burner, as I used tubes which were too large in diameter. I would also want to cast it; the tubes are a pain to insulate. I got the idea for the last design from the Aerospike rocket engine. I watched a YouTube on it: This engine uses an inverted bell shaped nozzle to provide thrust over a wide range of atmospheric pressure. Although we aren't building rocket engines, a lot of the same principals apply.