Kast o lite 30, crack

[Wolgerrex]

What is the best way to repair/fix a crack in 1/2” kast o lite 30 over 2” of kaowool? 

[Frosty]

How large and where? How thick is the KOL? Is the kaowool rigidized? What caused it, do you know? Have a pic so we can get a look?  

I only have a couple SMALL cracks in the KOL I've laid and know what I did wrong. I rushed the cure on a thick section, NARB2 and fired it off too hot too soon.

Frosty The Lucky.

 

[Wolgerrex]

On the floor, from side to side, thin crack. 1/2” thick KOL, yes rigidized wool. Not sure why, I’m guessing cure process. I applied the KOL, bagged it with wet towels for about 40 hours. Then let it air dry over night. Did a low burn for about 5 minutes, let it cool over night. Ran it for about an hour an a half forging temp went fine. Next use about 45 minutes forging temp and noticed the crack. Never had this before with roughly same application process?? Kinda stumped on what to do? Thanks for any help 

[Frosty]

Hmmm. Sounds like you gave it plenty of cure time and a gentle firing. It looks to me like it was bent, maybe the forge shell warped a little as it heated up? Is there a matching crack in the ceiling? 

To patch it I'd maybe mix up some Plistex a LITTLE thick and press it in. Or same thing with KOL after sifting the aggregate out.  Mix it thick enough it isn't quite liquid lay some over the crack and roll your finger along it to press it into the crack. Butter the crack first say a folded wet paper towel and dab it with authority so water is forced into the crack. 

Frosty The Lucky.

[Binesman]

few layers of kiln wash fills that in without worry.

[Wolgerrex]

Yes I have Plistix, I usually wait to apply after I test out the forge. In case of fixes (burner port shape etc.)

When you say mix it THICK you mean less water than normal? 

No crack in ceiling, I fired it again and noticed the cause. The shell flexes at the openings, then shrinks back once cool. So no warping but it does expand when heated then contracts when cooled. I’ll weld some braces to help strengthen the shell sides. Stop the flexing and hopefully that will stop further cracking. I didn’t make the sides strong enough. 

[Irondragon Forge ClayWorks]

An overall picture of the forge may give more clues and advice.

[Frosty]

Yes, say almost tooth paste thick. 

If the shell is flexing it's warping, it doesn't have to be permanent deformation to be warping. I don't know if reinforcing the shell will work without at least seeing what the whole unit looks like as IDF&C says. 

If it's cracking do to warping there isn't much you can do about cracking. Laying a piece of kiln shelf on the floor will prevent bad effects to the Kaowool.

Frosty The Lucky.

[Mikey98118]

No amount of reinforcing can stop warping during heating cycles. You need to go in the opposite direction; allowing the steel parts some limited motion. This is why I never welded up any

forge parts, despite making my living for over four decades as a  certified welder. It isn't a question of what does it takes to properly weld up heating equipment; it's a question of WHY WOULD WE EVER GO THERE?!?1?

Please don't use welding in forge design; even when you succeed, it only encourages others to play with the bears! How can I make this any clearer??

[Wolgerrex]

Here are some pics, micro forge 180 cubic inches (to help with understanding sizing). 

The arrow shows where the expansion happens. The shell separates to just over 1/8” from the KOL. This only happens on the sides. 

Mikey, fellow welder (not as many years yet) forgive me I am not sure I understand you. Forges should not have any welded joints, frames, structure?

Is the flexing a good thing then?And should be left alone? Plistix and let it be? Or is this a crap forge shell I made to light. My other forges have been much larger and much thicker shells. Never had this problem. 

[Mikey98118]

I LOVED welding; that's why I did it for a living

Unfortunately, low cost portable short- arc (low line voltage) wire-feed welders have encouraged amateurs to try their hands at home style steel work; this is both good and bad. When amateurs weld together forges, without any understanding of where and in what directions plate will expand--THAT IS A BEAR TRAP.

Anyone who wonders how to properly design a forge with sheet-metal need only take a careful look-see at one of the commercial forges; alas, most don't. Lool up Diamondback forges; they are the easiest example to follow from a photograph. 

The red arrow in your photo does not indicate an area or direction of expansion that would cause the steel shell to warp.

Bottom line? You may never know the exact cause of those pesky cracks. Best direction from here is Plistex, for a whole raft of reasons.

[Latticino]

Another thing to consider is that many castables don't really like rapid thermal cycling.  Most of us use forges pretty hard and don't bother to heat or cool them slowly after the first firing cycle.  It is certainly important to plan for both expansion during firing and the potential for cracks to form as the material cools.  A crack in an arch can be squeezed back together by tightening the forge shell a bit.  Cracks in the floor. like you have, are best filled with a high alumina kiln wash (or bubble alumina) in my opinion (particularly if you will be using any flux in the forge).

Your crack looks like it is located almost directly below where your flame from the burner heats the material.  This area will be the hottest part of your forge in most cases.  Coincidence?

I'm typically not as concerned about welding the forge skin as I am keeping the heat away from that skin to avoid warping.  One of the key advantages to the blanket with internal castable liner construction is that you can "float" the inner liner in a enclosure of blanket.  The blanket will allow the castable to expand and contract in a way a hard frame never will.  That being said I've had some good long term success with welded metal door frames directly filled with castable, provided the metal frame is kept away from heat.

[Mikey98118]

I keep forgetting to mention that, in box forges, I prefer all hard refractory surfaces to be flat pieces trapped in place by their placement with the other pieces; and that refractory corners or bends be avoided. The most elegant engineering solution is the avoidance of problems, whenever possible