Flux buildup in forge

[Pancho07]

 I have no experience forge welding so this is probably common knowledge but not to me. Is there any buildup of flux in my forge that I need to worry about? I am using an old Redco propane forge if that makes any difference. Thanks in advance.

[Frosty]

Welcome aboard Pancho glad to have you.

What kind of refractory liner does your forge have? I don't know anything about Redco forges. Welding fluxes typically contain borax which is pretty caustic at welding temperatures and literally dissolves ceramics based on silicates that being fire brick, hard and soft and most ceramic blankets. Molten borax treats ceramic blankets like hot water treats cotton candy and isn't much nicer to fire brick.

There are simple and complicated solutions. A phosphate bonded ceramic refractory is proof against fluxes but has the same problem all hard refractories have it's a poor insulator and a great heat sink so it takes more fuel and time to get it hot and keep it hot. On the up side a strong heat sink refractory will heat the steel much faster so if you're going to have the fire running a long time and cycle a lot of pieces through hard refractories might be economical for you.

What is becoming more popular is using a kiln wash to protect the liner. Kiln washes are used extensively in ceramic kilns to protect the kilns, prevent glazes from welding to the liner and prevent chemical erosion. What borax does to silicates is chemical erosion. Another serious benefit of using a kiln wash on ceramic blanket refractories is encapsulating fibers which can pose a health hazard. See silicosis or mesotheleoma for the kind of health hazard breathing ceramic fibers pose.

Another benefit is the types of kiln wash that contains a high IR reflective material, usually zirconium silicate. Zirconium laughs at hot caustics and acids so we ain't putting anything in our forges that can touch the stuff.

There are other methods of dealing with welding fluxes that aren't so complex but not as effective. You can just lay a kiln shelf or stainless steel pan in the bottom of your forge to catch most of the spilled flux. Use split hard fire brick for the floor, kiln wash it and replace it when it's eroded.

Probably one of the simplest, cheapest and easiest ways to reduce flux erosion in your forge is don't use much. You do NOT need to douse your weld in flux, just a sprinkle is plenty if you've prepared the weld properly, get it hot enough and let it soak. Flux ain't glue it won't stick anything together, all it does is keep the oxygen off the steel so it doesn't contaminate it.

Frosty The Lucky.

[Pancho07]

It is brick lined, what kind I'm not sure. Dad got it in an auction years ago and even if they told him he probably wouldn't remember. I can say that theven bricks at the bottom of it look melted pretty bad. This won't matter a whole lot for this go round as we are getting new bricks in a few weeks. 

Thank you for the quick reply Frosty

[Alan Evans]

I remember someone (Jorgen Harl?) telling me he had some success with a layer of bentonite as a sacrificial "sponge" in the base of his furnace.

Bentonite is readily available as kitty litter in a pet supplies shop.

Alan

[Pancho07]

Now that you mention it I remember hearing something about bentonite and forges but I would not have made the connection with flux ingredients welds.

Thank you Mr. Evans

[ThomasPowers]

small stainless tray to hold the bentonite and protect the bricks, just bend up some sheet.   Makes it easier to clean out the sludge too.