Ted Ewert

I've posted most of this material in one spot or another, but I thought a consolidated thread might be helpful. I like to use acrylic for forms in casting since cement won't readily stick to it. It's fairly cheap in small quantities, machines easily and is structurally rigid enough for this purpose. I use 3/16" sheet for the outer forms, although slightly thinner will work too. I buy scraps at my local Tap plastic shop for a dollar each, although I don't know if other locations have the same policy. For the holes I use solid round rod. I would not recommend tubing since it will shatter easily if you need to grab it with pliers (explained later). I also pour mine a little differently. This can be done in several different ways depending on your needs. I have been using a piece of 2" wide x 3/16" thick flat stock for my base. This gives me a good structure to clamp the forms around, and I don't want my burner to be the same size as my plenum. I then epoxy this steel base to the plenum to both attach and seal it. Some will wince at the mention of using epoxy, but in my case the plenum does not get hot and JB weld works just fine. If you have any reservations about heat, just cast it directly on to the plenum, which is the preferable method anyway. Whatever method of forming you use, holes in the pattern of your choosing must be drilled first. You then need to use some form of anchor to attach the casting to the plenum. I use several bolts which are threaded into the base. These, as I found out the hard way, will prevent your cement from seperating from the base. At this point I stick my rods into the holes. Acrylic rod is not dimensionally precise, so you'll get some tight fits and some loose fits. For the tight fits I put a little oil on the tip of the rod and lightly tap it into place. It just has to be in the hole enough to not move around when the cement is added, and you're going to have to pull it out, so don't pound it in too much. Also, don't worry about getting all the rods aligned perfectly. You can adjust them after the cement is poured in. You also want them to be an inch or so longer than the top of your form so you can have something to grab on to when you remove them. At this point you're ready to pour. I use an old baking pan with a sheet of wax paper in it to pour on. The wax paper makes for easy clean up since things get messy. I mix my cement a little on the wet side which makes this process a whole lot easier. I work the cement in with a thin piece of steel flat stock. The clear forms make it easy to see if you have any gaps in your cement. When you get it all filled in you can then adjust the rods to your satisfaction. Let it set for about 12 hours, then remove the rods. Leave the outer forms on for this step as it supports the still semi-soft cement. I grab the rods with a pair of pliers and give them a twist to loosen them first (this can take a little muscle on the tight ones). Once it's loose, keep twisting back and forth as you slowly and gently pull it straight out of the hole. Once you get it out of the steel base it usually slides out pretty easily. As you can see in the picture, I have used 4 tubes instead of solid rods. If you grab these with the pliers as they are they will shatter. I had to insert a steel rod in the middle of each one to prevent this before extracting them. That's why I recommend solid rods. I like to leave the forms on for at least 24 hours. At that point the cement is set up enough to resist crumbling along the edges. Once the forms are removed, you can sand the edges with some 100 grit sandpaper to smooth things out. I have also used the belt sander at this point to flatten the top and to take a little off here and there if it doesn't fit. If you use the belt sander, feed it in slowly and make sure the casting is well supported underneath. Like regular concrete or mortar, make sure you keep it damp for a few days while it cures. Questions and comments are welcome. Ted

I decided that this forge is a bit too long, so I decided to trim it by about 4". I figured all I would have to do is to cut the outer cylinder, the burn chamber, and then reassemble it. I was taking it apart this morning and got an unpleasant surprise when the inner casting fell apart I'm not exactly sure what caused this to happen, since it was pretty solid when I installed it. I may not have cured it properly, or it may have had internal stresses that caused it to fracture when high heat was applied. Had I just left it in there I doubt it would have been a problem since it was securely held in place by the insulation. Anyway, looks like I'll have to pour a new one. I don't think crazy glue will quite make it here. I noticed that one site was offering some stainless steel "needles" as reinforcement for high temp castables I may order some of these to use in the next casting.

I've just gone through the whole learning curve of propane forge building. If you want it hot and efficient, you have to use what these guys are telling you to use. The problem with using other materials is that they either don't insulate well, or disintegrate after moderate use (I know, I've tried). A small combustion area with a good burner, well insulated, with good materials, will give you a nice hot forge. When you're just starting out you only need to heat small pieces of metal. Plus, you only want to heat a small section. I'm cutting 4 inches off a forge I just built because it's too long. It heats up too much material. I think a small propane tank is a good size. I would also suggest setting your burner at a tangent to the radius of the inner chamber to create a swirl. A swirl gets the chamber really hot. I would also suggest a blown burner, but that might be more than you can afford right now. Mikey and Frosty burners seem to work quite well and should be fine.

I fired it up last night. Here was the test setup: The burner was sputtering initially, so I knew I didn't have a good mix of air and gas. I used it in the above configuration with the spinner and that smoothed things out. I figure that probably no one is going to bother to make a spinner like I have so I started thinking of different ways to mix the gas and air better. I tried a twisted plate: This worked better than nothing, but the flame was still uneven. So I next tried a mixing tube which sticks out into the flow of air. This worked even better than the spinner. the flame was smooth and I had to turn down both the air pressure and the gas to get the same flame I was getting before. I wrote more about the details in the "Burner 101" thread if you're interested. The burner itself works great. Ted

I set up a test today to see how the ribbon burner worked in my little forge. When I first fired it up I had a lot of sputtering in the flame. Even though I had the spinner on it, I had two 90s in the line and that messed things up evidently. I took out one of the 90s which helped a lot. I got to thinking about this mixing problem. There has to be an easier way. I tried a twisted piece of sheet metal to induce spin. This fits right inside a 2" pipe: It helped a little if I put it before the gas inlet. The flame still sputtered a bit though. The next thing I tried has probably been used before since it's fairly simple. I machined a piece of 5/8" round stock by drilling a hole almost all the way through it. Then I drilled a bunch of smaller holes as outlets: This fits snugly into the 1/2" nipple I have going into the 2" pipe. It sticks out into the airstream and distributes the gas much more evenly. I glued it into the nipple and assembled it into the valve train. This thing works great! I immediately had to turn down both the gas and the air to get the same flame I was getting before. The flame was nice and steady too. (I'm keeping my needle valve no matter what you say Mikey ) I had the blower wide open before this and had to turn it down to this point to get a good mix Here's the flame I can only conclude that this mixing tube has significantly increased the efficiency of the burner. I just picked a random drill bit and number of holes, so I'm sure some improvement can be made. I would highly recommend this to anyone who has a blown burner. Ted

I made a couple of additions to the forge. I added a little "head shield" below the burner. You can see how the swirling gas would hit the bottom of the burner. I also added little section on the roof of the front to try and contain some of the heat in the back Then I got the forge up to temperature and they both fell off. Didn't matter anyway since this forge gets #@!!%* HOT! All that work I did trying to figure out just the right taper didn't make a darn bit of difference. The forge is so hot that anything coming into it immediately ignites. You can't even see a flame. The only adjustment is how much flame you want coming out the front, if any. The whole inside was bright yellow. You don't want to get anywhere close to that slot either. The thing scares me a little. Heats up metal good and fast though.

Thanks Glen. I did manage to produce a recognizable object today. It's only a simple hook, but it's a start....

Kast-o-lite 50 refractory. Nevertheless, it sets up and cures just like concrete would. This is the forge I'm putting this burner in. I lined the inside with Kast o lite, cut the door off and filled in all the major defects. It's not ideal, but the fact that the chamber is small means it will get nice and hot. I still have to put up a ledge for the doors and an extension rest. I ordered all the plumbing for it today, so all I have to do is use the blower and tank from the other forge.

It is not interchangeable as it is a different size. I built this one for the other forge I have, which I'll post pictures of once I have it running.

I'm not saying it's better, just easier to make. Using investment casting is much more time consuming and labor intensive than simply drilling holes or using removable rods. Acrylic, as a nonstick framing material, is also easier than painting and screwing together wood. The end result is pretty much the same, although I also taper the holes once they are drilled (or formed). I use velocity as a means to increase pressure. I have a bunch of long 1/4" holes I have to push air through, and the more pressure I can generate the more air I can get through those holes. Nevertheless, this is still secondary to the mixing properties of a vortex. Another property of a vortex, which you may not be aware of, is that it allows more air to be blown through a given size pipe than a linear flow would. This is because a vortex creates coaxial laminations which have friction free boundary zones between them. This allows the inner laminations to slide past the outermost layer at whatever rate the pressure dictates. There is a patented device which uses this principal to pump highly viscous oil through long distances of pipe. If this all seems contrary to standard aerodynamics, it is. If you still need more convincing, study how a Hilsch- Rankine Vortex tube works. Cheers, Ted

Thanks for the kind words Mike, I appreciate it. This is the first forge that I built from the start with a general plan. Now I have to figure out how to beat hot metal into something recognizable.

Thank you for clearing that up. I was under the impression, from reading here and elsewhere, that having the flame directly on the work was to be avoided. Is there some difference of opinion on this subject?

You're right about forge design. I've started to think about the aerodynamics in my forge, as well as focusing the heat in one area. Swirling is fine for heating up the whole forge, but I'd like one spot that's really hot. I have some ideas...

I guess you're right. Most people want quick and easy. I don't know why I'm stuck on this combustion thing except that I find it strangely fascinating. Just got finished pouring a new ribbon burner with a slightly different nozzle configuration. I'll post pics and results in a day or so. If nothing else I'm getting good and building burners.

Mikey, you commented in another thread (Info Request DIY Ribbon Burner Forge Build): "I would be very careful that the burner head matches up with the volume of the forge. I'm not talking about whether or not the burner can adequately heat the forge. I'm talking about whether the forge is big enough to adequately combust the gas." I'm a little confused here by the concept of the forge chamber combusting the gas. It seems to me that if the burner is designed properly, and the mixture is correct, the gas should all be consumed at the burner. Given that there is a positive pressure differential between the forge chamber and the outside air, theoretically there is no external oxygen entering the chamber. Therefore, any dragons breath is the result of incomplete combustion at the exit port of the burner (I can see why this happens with crayon burners since they have no expansion chamber at the end of their ports). Do most people design their chambers to be able to handle the volume of this unburned fuel?

Like most folks do here, try and find a steel container to build your forge in. The type of steel doesn't matter as much as what you put in it. Mild steel is perfectly fine. Propane bottles are particularly popular.

Thanks Lou, glad you enjoyed it. If you have any questions let me know.

Finished it today. It heats metal quite well.

Had a busy day today in the shop.I finally got the forge insulated with 2" of K wool around the burn chamber. Once that was done I decided to set it up for a test run. It actually performed better than I expected it to. I was a little worried that the 1/4" holes might not be big enough, but that didn't turn out to be the case. Here's it running a little rich to show the swirl: You can also see that I goofed up the floor and had to relevel it. The new floor is still setting up so I only ran short tests. Here's a more normal burn: This burner runs quite smooth and adjusts well. Part of the reason for this is that I am spinning the air right after the blower. This not only mixes the gas better, but provides higher velocity at the input to the burner tubes. Here is a picture of my air / fuel setup: That black device right after the blower is the spinner. It spins the air CCW at a fairly high rate or speed. The unusual burner entrance takes advantage of the spin to increase the velocity of the gas as it enters into the tubes. Here's what the inside of the plenum looks like: Visualize the gas spinning CCW as it enters the plenum. The exterior layer of air has the highest velocity, so when it hits the tubes it translates into higher pressure. This is how I can increase the pressure of the gas at my tubes without getting a bigger blower. BTW, I cut all those metal tubes out and just made a long, skinny rectangular hole where they were. I tried this setup without the spinner and the flame was smaller and spluttered a lot. This type of spinner is also great on the input to an Internal combustion engine. I had this particular one on my old toyota Corolla and it increased the mileage considerably. For some reason, spinning air always burns better the a linear flow. Chears, Ted

Hi Wayne, I didn't put a baffle in for a couple of reasons. It's a short burner with a large input which takes up 1/3 of the total width. If it was a 1" input a baffle would help a lot. I'm also spinning the air as it enters the plenum. Centrifugal force alone will distribute the gas nicely. Mainly this is just a demo to illustrate the use of alternate materials and methods to achieve the same results. As Frosty said, "What Mike and I are hoping for here Ted is someone who'll take things other folk have done and come up with something better, easier, cheaper, etc." I think this qualifies as easier, maybe even cheaper too.

I wanted to build a ribbon burner without having to use any crayons or acrylic rods for the holes. What could be simpler than just drilling the holes out? I started with a 2-1/2" piece of square tubing, drilled an inlet port, welded on a 2" female fitting, welded a couple pieces of scrap sheet metal on the ends, and cut a big hole in the end opposite the fitting. Pretty standard start. I then cut some pieces of acrylic sheet and formed them into mold the same size as the manifold. This one was going to be 2-1/2" deep. I squared the pieces up and used 2 clamps to hold them together. I set these 4 pieces down on another piece of acrylic for the bottom, and filled the thing with cement. Then I set the manifold down on top of that, making sure the cement came up inside to catch the ledge. I don't use any glue for the form because it doesn't need any. A little water will seep out, but that doesn't hurt anything (I put a little extra in to begin with). The cement does not stick to the acrylic, even without release agent, so disassembly takes about 30 seconds. I leave the plastic protective sheet on the acrylic, then just peel it off for quick clean up. Forms can be very simple and easy if you use the right materials. 24 hours later...I uncrated it and got it set up in the drill press. I had to use two vises because of the fitting (maybe put the fitting on last next time), but I got it squared up. I used a 5/16" masonry bit for the drilling (same diameter as a crayon) and set the speed pretty slow. It took about an hour to drill all the holes. The bit will get gummed up with cement when it gets down a ways. I used a little wire brush to clean it off when it came up. The drilling went pretty smooth overall. The cement is still soft enough at this point to machine, yet hard enough to stay together. Once the drilling was done. I reamed out tapers for each hole. At this point you could also use a larger drill to create a step up in diameter for the gas to decelerate in. Perhaps a 3/8" or 7/16" bit drilled down 3/4" or so would do the same thing as a taper. I haven't tried it, but Mikey seems to like that method. May even work better, who knows. What I am trying to demonstrate here is that there are other ways to build and cast these burners, which may be easier for some guys. My total investment of time from start to finish was about 5 hours, not counting curing time. I just don't see using crayons and painted wood as the most efficient way of casting these things. Cheers, Ted

OK, I cut off that notch and reamed the holes again. Turned out much better. There was a little crumbling between a couple of holes but functionally it shouldn't make any difference.

I poured the burner for my forge this weekend. Grandkids were down for the day yesterday so shoptime was limited. I used 1/4" acrylic sheet for the form, and used acrylic rods for the holes. Since I buy scraps from Tap Plastic (a dollar for a 12 x 12 inch sheet), the form including the rods cost me about $7. I taped and clamped the form together, which worked well. I used some release agent on the rods, but frankly I don't think they needed it. They were a little snug in the steel base I used, but once they got out of that they slid right out. 17 perfect holes. The form pieces came right off too. I washed them off and they are ready to go again if I need them. Here's the setup (sorry about the focus): These are 1/4" rods. I chose 1/4" to be sure there was no chance of the flame burning back into the plenum. Crayons are 5/16". In hindsight that would have been fine. Here it is after the pour" I made a little raised area where the rods are to hook into the opening of the cylinder for support. That didn't turn out so great as I'll explain next. Here's right after I took the rods out: Everything is fine at this point. The problem arose as I began tapering the holes. I didn't allow enough space between the holes, so when the material got thin it started to crumble. The raised part is only 7/8" thick and the taper started infringing on the integrity of the outer wall. Consequently it turned out to look like this: Kind of a mess! I'm thinking of cutting that whole notch off in the bandsaw while it's still soft enough. Then maybe tapering every other hole and see how that works. If it doesn't work well I'll just cast another one. I don't know why anyone would want to use painted wood and crayons anymore. This method of casting is much easier. Ted

After 24 hours of curing, I tested the sample for machinability. I was able to easily ream out a taper in one of the 3/8" holes. The reamer blades will get clogged with cement but it's easily removed with a wire brush. Next came the sanding test. I sanded that rough surface you see above on my 6" stationary sander, and also beveled the edges a bit. I also did a test drilling with a regular steel bit in the drill press and it went through like butter. This material holds together pretty good at this stage of curing, but is still soft enough to machine. If you remove your form at this point you can hand sand any rough edges and clean up holes with a hand drill. You can also sand it down to size if you made it a bit larger. I suggest doing a test sample for yourself to get the feel of the material before machining a final piece. One other note... I removed the pieces of rod after 12 hours and it worked fine. However, the material was still pretty soft and I think 18 to 24 hours might be better for longer pieces to avoid any chance of deformation. Ted

I've been looking into the ingredients of Kast-O-Lite. It is basically a high temperature mortar type compound using a modified recipe of Portland cement, powdered quartz (SiO2), Aluminum oxide (Al2O3) and a fibrous substance to hold things together. Both Silica and Alumina have melting temperatures of over 3000 degrees F. What this means in terms of casting is that it is very similar to using concrete or mortar. Continued hydration after initial setting will increase the strength of the product, as well as having a similar curing duration. This may all be old news to you guys, but it lets me know what I can expect regarding casting parameters.