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New forge liner issues


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I am more of a lurker than a poster but I have an issue with a gas forge that I have been slowly building over the winter. I used a 20lb propane bottle for the shell, cutting both ends off and using refractory bricks stacked at each end to allow for different sized openings to match the item being worked on. I lined the entire inside with a layer of 1" ceramic blanket (Kaewool), added a 1" refractory brick to the floor for durability, then placed a second layer of 1" blanket around the brick and the rest of the interior (see pic #2). I misted water onto the blanket then brushed on a coat of rigidizer. I let it sit overnight to dry then applied a second coat the next day. This coat was able to dry for almost two weeks before I brushed on a generous coating of ITC-100. The ITC coating was air dried with the help of ducted air from a fireplace. Once I completed the initial build of the burner and eventually got it tuned properly to my elevation (frustrating), I was able to run the burner for short periods of time in the forge, letting it cool between firings.

So far, so good... then today I fired it up to temp and began to heat some steel.


I had a good flame, good dragon's breath and all was looking good for the first 1/2 hour or so. Then I noticed that the blanket across from the burner was starting to deform, I kept an eye on it as I continued to heat and work the steel. Shortly after I noticed that the first 1" layer of blanket looked like it was disappearing from under the ITC-100 coating. I decided to shut it down at this point to have a better look.

Once cooled off, this is what I found:


Upon closer inspection, it appears that both layers of blanket were destroyed as the outer shell was exposed. The blanket had even started to droop above the area that burned through - possibly due to the heat getting in behind the blanket ???


Obviously I need to re-insulate the shell but why did this happen in the first place? Did I miss something in applying the blanket or coatings? Should I place another 1" brick across from the burner to prevent the direct flame from contacting the coated blanket?

Any knowledgable help would be appreciated.

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It looks like you bought too low a temp rated Kaowool, You really need the 2,600f 1" 8lb. blanket or higher rated. I run 2,600f 8lb Kaowool and my forge runs in the mid to high yellow heat in normal use. I can push the psi and melt the 3,000f firebrick floor but that's excessive for most anything the average person might want. The flux I use has made a spot about 2.5" diameter under the front burner melt at a lower temp so I have a puddle of goo after half a hour or so.


the point of all that being my Kaowool lid is loving life unless someone roughs it up poking work in the forge.


It looks like you built a Big T burner, what's the tube diameter?


Don't worry, we'll get your forge squared away.


Frosty The Lucky.

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Hi Frosty, thanks for your reply...


I have done some further investigating regarding the insulation, as it turns out the material I actually used was BGF Mat and only good to 1200F. I had this matting left over from a previous occupation in which I worked with both Kaowool and BGF... I thought my stock was Kaowool - apparently I was wrong :angry: !! I guess I will be buying some Kaowool. When I do re-insulate am I OK in having the burner directed into the blanket (3000F rated Kaowool) or would it be smarter to incorporate a 1" thick refractory brick at that point (similar to what I have for the floor)? The rigidizer and ITC-100 appear to have worked properly as there is a greenish glass like substance under the rock hard ITC-100 coating.


Regarding the burner, I built originally built a T-burner with a 1" tee and a 1" X 8" nipple that used a modified .035 MIG tip. I have used a burner of this spec and it worked beautifully, however I could not get it to stay running unless I added a bit of air with a blow gun. I tried different sized tips but none solved the issue. I started to think that maybe my elevation could be the part of the problem as I live 3000' higher than where I used that 1" burner.  I decided to try a 1-1/4" to 1" reducing tee in place of the 1" tee along with an .045 tip to flow more air volume and it seems to be working well. I was able to keep a stable neutral flame at only 3psi.


So, back to the drawing board insulating the shell. It will be another few weeks before I can get this done (work out of town) but I will let you know how it all turns out.


"Why do something once, when you can do it twice!" A Dumb A**   :P

Edited by Moderator54
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Well there you go. If the burner is directed at the fire brick floor rather than the Kaowool it won't damage it for a good long time. I have however had burners directed at washed Kaowool and it's stood up really well so I wouldn't do anything special.


A 8-9"x1" tube with a 1 1/4"x1" T with a 0.045" mig tip ought to bring a 700 cu/in forge to welding heat without problem. Elevation has a lot to do with tuning, it takes more energy for a jet to induce combustion air but more pressure means more gas and that means more air and that means. . . It can turn into a vicious cycle. Enlarging the intake ports is probably the best way to make the change.


You should only need to do a thing once if you use a smart donkey.



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Aw pshaw. I'm self taught for probably more than 30 years, then one day I discovered a blacksmithing book at a local book store and learned some stuff, then the internet went public and I really started climbing the learning curve. I tend to read everything and sponge everything I can from everybody I come in contact with.


We share what we learn and are paid back many fold. That and I like talking. Win win.


Oh, give your donkey a carrot, right fork, wrong fork, gotta take a fork or you ain't going anywhere new. Good donkey, have a carrot.


Frosty The Lucky.

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  • 3 months later...

I have been away from this site for far too long and realized that I never replied with an update on the forge. I relined the interior with properly rated Kaowool and ITC-100 plus incorporated another 1" thick refractory brick directly opposite of the burner. This set-up seems to be holding up well as it still looks really good after burning 20lbs of propane. The burner is dialled in nicely and the interior of the forge is holding it's heat as well as any forge I have seen or used. Thanks for your input Frosty!

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