Hefty Posted February 25, 2022 Share Posted February 25, 2022 Hi all, I've made a gas forge using two 3/4" frosty Ts into a party balloon helium tank (about the same size as a 9kg/20lb propane tank) with 2" of ceramic wool and a cast floor from a castable refractory called duracast. I've rigidised the ceramic wool, including spritzing the outer layer before installing the inner layer and then started with some shorter burns first and then built up the time. My intention was/is to apply several thin coats of satanite (I can't find Kast-o-lite in Australia) but I have used the forge for two 1 hour actual forging sessions so far and run into a problem. First session was great and it felt really good to use a working gas forge. But, I had to cut the second session short when the burners started sputtering unusually. I looked inside and discovered that the inner layer of wool has separated from the outer layer and sagged down from the top. I think the edges of the hole where the burner flame enters the forge may not have been accurate enough and the flame may have been impinging on them when I didn't realise. I know that this is harshest part of the forge environment, I guess I just didn't realise how quickly it would damage the wool. Is there any way to salvage this ceramic wool given that it sagged when hot and is fairly rigid again now that it is cold? I was hoping I might be able to gently push it back into place and use the satanite to reinforce it but I suspect it will crack or crumble if I try to push it. Cheers, Jono. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted February 25, 2022 Share Posted February 25, 2022 You have one-half of a solution. Push the wool back into place; rigidize the damaged area again, and fire it, with the forge turned upside down. Then start building up a healthy layer of the same castable refractory you made the floor with--at least 1/4" thick. You're simply asking too much from the Satanite. You can easily build a rigid inner shell in about 0ne-third of a cylindrical shape at a time. Revolve the forge, one it sets, and lay down the next third of a shell. Don't forget to whet the edge of the formed shell before laying the next third beside it. Whet both edges of the formed shell before laying the final third. Quote Link to comment Share on other sites More sharing options...
Hefty Posted February 25, 2022 Author Share Posted February 25, 2022 Ok, that sounds achievable. I get what you mean about doing a third at a time and I can visualise how this would work for the first and second "thirds" (or in this case probably the floor and the second "third") but even once cured, wouldn't the weight of the first two "thirds" cause them to fall out while I'm trying to shape the last layer? Any recommendations for how to support the previous sections while the last one cures? Also, how neat/accurate do I need to be for lining the flame entry holes into the forge interior? Obviously, I don't want them to interfere with the flame but should I cast around a small cylinder for each? Should I step the hole so the castable fits neat around the burner tube and then steps to a more "nozzle-like" diameter? Cheers? Jono. Quote Link to comment Share on other sites More sharing options...
pnut Posted February 25, 2022 Share Posted February 25, 2022 10 hours ago, Hefty said: should I cast around a small cylinder for each? Should I step the hole so the castable fits neat around the burner tube and then steps to a more "nozzle-like" diameter? A small inverted funnel would work to make a nice flared port for the burner. Pnut Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted February 25, 2022 Share Posted February 25, 2022 What pnut said ^^^ is how we did our burner port and it has worked out well for us. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted February 25, 2022 Share Posted February 25, 2022 Remember that you are to rigidize and fire the ceramic wool first. Secondly, that cylindrical shape has ends. Many people have used this method successfully. If you doubt that you have used enough rigidizer to stiffen it against the drag of gravity, then drill small holes all around the shell, and inject more (it isn't possible to use too much), and thoroughly fire the whole forge, to make the wool stiff. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted February 25, 2022 Share Posted February 25, 2022 Finally, nothing prevents you from laying down the end layers first, as a further help to ensure that all three portions stay in place. Only be sure that you give sufficient time for each portion to harden in place, before moving on. Also, don't forget to moisten the edges of existing portions of refractory, before laying down more. Be sure to drill at least one small weep hole in the bottom of the forge shell, even if you don't feel a need to drill many others. Quote Link to comment Share on other sites More sharing options...
Hefty Posted February 26, 2022 Author Share Posted February 26, 2022 16 hours ago, Mikey98118 said: it isn't possible to use too much Thank you for confirming that! I've trawled through a lot of the pages in forges 101 and other threads in the gas forges section and that's the first time I've found that stated so plainly! I actually suspect part of my problem was not having quite enough rigidiser for the amount of wool I used. The wool, rigidiser and castable were sold together as a kit intended for this size of propane tank or helium tank but the wool was one 2" thick layer. I had read your advice (Mikey), and others, to split it into two 1" layers to fit and shape it better and get more rigidiser into it but I think this may have stretched the provided rigidiser a bit too far. I'll stock up on rigidiser and more duracast and see what I can make happen! Pnut, I like the funnel idea. Did you literally use little plastic funnels, or just make a funnel shape out of something? Cheers, Jono. Quote Link to comment Share on other sites More sharing options...
pnut Posted February 26, 2022 Share Posted February 26, 2022 When we built the forge for my friend's shop we used two little plastic funnels from the dollar store. They worked great. We sprayed them with Pam before applying the castable refractory. Pnut Quote Link to comment Share on other sites More sharing options...
Hefty Posted March 2, 2022 Author Share Posted March 2, 2022 (edited) On 2/25/2022 at 3:32 PM, Mikey98118 said: Push the wool back into place; rigidize the damaged area again, and fire it, with the forge turned upside down. Mikey, would it help to lessen the cracking/crumbling of the wool if I sprayed/spritzed the rigidiser on before pushing it into shape and firing it? IE, will the liquid rigidiser soften the bonds from firing the fumed silica or does it become impervious to water once fired? Edited March 2, 2022 by Hefty re-phrased part of question Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 2, 2022 Share Posted March 2, 2022 Butter it (spritz with water) then the rigidizer, then push it into position and fire it. Once it's been fired the bonds made are NOT water soluble. Do NOT be shy with the rigidizer, there's hardly such a thing as too much. The first time I rigidized Kaowool I didn't have a spritzer bottle so I mixed up a largish batch in an old plastic dish pan and dipped it, let it drain back into the pan with an old paint roller tray thingy and stuck it in the forge. It made the ceramic blanket nicely stiff but might have had a slight effect on it's insulating properties. You can treat rigidizer wetted ceramic blanket like paper mache. The important thing to remember is to leave enough room to apply a hard refractory flame face. AND a good 3,000f high alumina kiln wash. NOT ITC-100 !! Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted March 2, 2022 Share Posted March 2, 2022 57 minutes ago, Frosty said: ou can treat rigidizer whetted ceramic blanket like paper mache. Nice simile. I like that. Quote Link to comment Share on other sites More sharing options...
Hefty Posted October 12, 2022 Author Share Posted October 12, 2022 Well, I finally found a local supplier of castable refractory so I could fix the issue. I went in to pick up the bag of castable and when I explained what I was doing he threw in a litre of rigidizer for free! I'll be going back there for sure! I got the castable in place in two sections (in addition to the floor that was already there) and used rigid PVC electrical conduit the same diameter as my burner tubes to make stepped flame nozzles in the wall of the forge. It's been so long since I came back to this post that I forgot the plastic funnel suggestion! In terms of casting and removing them, I just kept going back to the forge every half hour or so as the castable was setting up and just rotated the PVC so it the castable didn't stick to it. Once it was fully dry/set/cured (not sure what the right term is for this particular castable) they just slid straight out and I could put the burners straight back in and tighten the set screws on the mounts. But now I'm a little unsure of my tuning. It gets steel hot and I got the forge up to a bright orange, maybe a little into the yellow, after about 10-15 minutes at 30 psi, but my flames still sit quite a way off the nozzles in the forge and I think it may be a little oxidizing. I shined up some steel and put it in there soon after lighting and at 10PSI it came out again red hot but still shiny. Later I put steel in there at 20-30PSI when the forge was hot and my results were inconclusive to my limited experience. My combinations of photos are not very consistent but this is what I have: Here it is straight after lighting, at about 10PSI: In ambient lighting I couldn't perceive any dragon's breath out the front door. Here it is at about 20 or 30 PSI while still warming up: and here it is a few days later at 30 PSI: (I forgot to take one looking into the forge) The yellow of the interior or the forge and door in the photo was more of a bright orange to my eye at the time. The dragon's breath is about as it appeared to my eye. Any recommendations for tuning or is this looking ok? Cheers, Jono. Quote Link to comment Share on other sites More sharing options...
Frosty Posted October 12, 2022 Share Posted October 12, 2022 It looks pretty darned good from here, maybe MAYBE slightly rich but close to what I prefer if it is. Your shiny steel not scaling in the flame test says it's certainly not lean. The little bit of dragon's breath visible is another indicator it MIGHT be a LITTLE rich. How do you like it now, does it make steel hot enough to forge? Tried a forge weld yet? Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Hefty Posted October 12, 2022 Author Share Posted October 12, 2022 I'm loving it so far! I haven't used it much yet but I've been working on a railroad spike tomahawk and I'm taking much better heats than I was out of my JABOD because I'm usually too stingy with my charcoal. Haven't tried a forge weld yet. I'm keen to try but it's sooo loud at those higher pressures! I'm working my way up to it because I think my neighbour might get a bit sick of the noise. I'm also keen to try making some hammers now that I have the ability to heat a larger billet more easily. Thanks Frosty and Mikey and anyone else who helped with advice to get this one fixed and back up and running! Cheers, Jono. Quote Link to comment Share on other sites More sharing options...
Frosty Posted October 12, 2022 Share Posted October 12, 2022 I'd move making something for the neighbor higher on my priority list. Good PR is good for keeping the peace. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted October 12, 2022 Share Posted October 12, 2022 I don't think it really needs anything more than having the burners backed off somewhat. Maybe allow some air space between the exit opening and the door. Quote Link to comment Share on other sites More sharing options...
Hefty Posted October 12, 2022 Author Share Posted October 12, 2022 Can do. In the first photos I was using a soft firebrick which is easy to pull back from the opening. In the later photo I was using a door I made from the circular cutout of the ceramic wool, coated in castable. Unfortunately, I didn't make its base wide enough, so I have been having to lean it on the shell for stability. Not really safe for something getting to that temperature so I've decided I will bench it until I can make the base a bit sturdier and instead I'll put a thin layer of the castable over the brick. I also need to put a gusset under my front door shelf because it is made from the door cutout from the tank and is not holding up under the heat coming out of the door. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted October 13, 2022 Share Posted October 13, 2022 Most people use two hinges and a latch to secure the door. However it is wise to build the two hinges (which are simply constructed of two drilled pieces of flat bar hold together with a screw) so that the door is held about 1" away from the forge shell. The latch is also built to close with the door held away from the forge shell. Work pieces are slid back and forth in a small opening in the door; this allows exhaust to escape up through the gap between forge shell and door, while bouncing radiant energy back into the forge. A number of people have built their forges this way, and we have heard no complaints from them. Quote Link to comment Share on other sites More sharing options...
Frosty Posted October 15, 2022 Share Posted October 15, 2022 Warping is why I NEVER suggest steel for the porch. The farther from the opening you can keep steel forge parts the better. All the porches on my forges are hard firebrick supported by tubing, attached below the forge. The tubing acts as the forge stand and just so happens to be 2 1/2" from the forge to whatever it's standing on. Oh wait I cover the cart or metal table surface with concrete backer board so nothing HOT from the forge touches what it's not supposed to. My heat baffle bricks rest directly on the porch so the only part of the forge shell exposed to high temp is above the opening. That'll change if I build another forge. NARB hardly counts I built that as a test for the burners and didn't put enough thought into the forge itself. My bad. <sigh> Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Hefty Posted October 16, 2022 Author Share Posted October 16, 2022 Yep, lesson learned. I have some adjustable, sleeved supports under the front of the forge that I was able to use to support the porch for now but I will weld some RHS between them and put an old, broken piece of pizza stone on top instead. In the meantime, I did my first successful gas forge-forge weld on my rail spike tomahawk today to add a steel bit to the blade! (Well, at least I THINK it was successful!) You can see where I tacked it with my stick welder first. I ground the surfaces clean but didn't grind a scarf/taper around the edge. The back side: and the edges of the weld after grinding Again, the back side (*not the final blade shape, just grinding back to inspect the weld ) Does this look like an ok weld? Cheers, Jono. Quote Link to comment Share on other sites More sharing options...
Hefty Posted October 17, 2022 Author Share Posted October 17, 2022 Also, towards the end of the session, my burners started to sputter/backburn so I shut them down and checked the tank. It was icing up and getting low. I know this is common, but I want to make sure I'm understanding this correctly. Is it the low volume left that would have caused the sputtering? or, the icing up? Or are they one and the same in terms of symptom/cause? Quote Link to comment Share on other sites More sharing options...
Frosty Posted October 18, 2022 Share Posted October 18, 2022 Tank pressure is maintained by replacing the propane you draw off from the liquid propane in the tank. When you draw it fast enough the liquid boils to maintain tank psi. It doesn't do this because it's conscientious, it has to, tank pressure is the room temperature vapor pressure. Anyway when there isn't enough liquid in the tank to absorb enough heat through the tank walls to remain liquid it begins to turn to slush, the lower the temperature the lower the vapor pressure. All that said what you experienced is normal and to be expected. After it's happened a couple few times you'll recognize it when it happens and not get caught short. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted October 18, 2022 Share Posted October 18, 2022 Think of it this way: a full pot of water takes longer to get boiling than an almost empty pot. So a bigger tank or multiple tanks manifolded or your tank in a water bath to put heat into it will all help with freezing up. Quote Link to comment Share on other sites More sharing options...
Hefty Posted October 18, 2022 Author Share Posted October 18, 2022 Yep, both of those explanations make sense. Thanks to you both! Going back to the forge weld above: Is it normal to still have such a clear delineation between the two steels after grinding back, or does this suggest the weld has not taken properly? I know damascus shows delineation but that is more from the difference in brightness of the etched steels. I've only done two other successful forge welds and they were in a charcoal JABOD. Quote Link to comment Share on other sites More sharing options...
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