Vitrification at the bottom of a forge

[Thr]

After over a decade of obsessing over most everything related to smithing, I finally managed to get myself a forge and anvil in recent months, and have been practicing with what scrap metal I can get. After a couple months of things going well, I've discovered this:

 

 

That large black spot at the bottom feels like glass, and seems to have somehow melted through the cement coating -- for reference, I'm using HT100 refractory cement. Can I patch this over with fresh cement, or do I have to replace the entire thing?

 

Thanks.

[Buzzkill]

I'm guessing you used some flux in the forge.  If so, what you're seeing is the result.  At high temperatures flux is quite caustic and can dissolve a lot of materials.  Even Kastolite 30 is somewhat susceptible to this.  Once it cools down, the partially dissolved material tends to end up as a dark/black glassy substance.

Forge lining and floors are consumable items.  They will have to be replaced periodically.  If it were me I'd keep using it for now.  I haven't tried to patch over the top of spots like that, but when reheated to forging temperatures the glassy black stuff will become sticky again and could potentially dissolve material cast over the top of it.

It's not that bad now, but I'd wait and recast the entire floor if it were me.   In the future you might want to cast or cut a removable floor piece to use when forge welding and then remove it for normal forging.  When it gets bad then  you just have to replace that piece instead of a major overhaul of the forge.

[LeeJustice]

I just noticed that shape is familiar.  Is that a Mr. Volcano or did you make it?  I have only just last weekend applied the first layer of Satanite in mine.  Second layer this weekend, maybe.  Possibly a final kiln wash would make it more flux resistant.

[Thr]

6 hours ago, Buzzkill said:

I'm guessing you used some flux in the forge. 

I tried using borax a couple of times to reduce forge scale, but if I'd known it'd have done this, I wouldn't have bothered. There's no way to remove it? I'm thinking of going in with a chisel to take it out, then patching it over with fresh cement. Alternatively, I might as well redo the whole thing, because I'm not certain I covered it with enough cement in the first place.

 

6 hours ago, LeeJustice said:

I just noticed that shape is familiar.  Is that a Mr. Volcano or did you make it?  I have only just last weekend applied the first layer of Satanite in mine.  Second layer this weekend, maybe.  Possibly a final kiln wash would make it more flux resistant.

 

It is a Mr. Volcano, albeit I used HT100 refractory cement instead of the regular satanite provided -- I've gone for some more expensive materials after doing some reading up. I live up in Canada, and it seems that most rigidizers and refractories will crack due to temperature changes in wintertime. And, what is a kiln wash?

Edited October 5, 2022 by Mod30
Trim quote.

[LeeJustice]

I thought that the layer over the wool looked quite thin, I hope you didn't just toss out the Satanite.  Plistix and Matrikote it seems are the more regularly recommended kiln wash.  They are more flux resistant and intended to be IR re-radiant into the forge.

Just because things cost more, does not necessarily mean they are better.  They may be for one application, but not for another.

[Thr]

14 minutes ago, LeeJustice said:

I thought that the layer over the wool looked quite thin, I hope you didn't just toss out the Satanite.  Plistix and Matrikote it seems are the more regularly recommended kiln wash.  They are more flux resistant and intended to be IR re-radiant into the forge.

Just because things cost more, does not necessarily mean they are better.  They may be for one application, but not for another.

I've still got the bags of satanite somewhere... I'm not happy about paying more since I'm stuck on a pretty serious budget, but I'm not certain if it's safe to have different refractories on top of one another

[Frosty]

I hope Pigsticker is reading this thread. Your brick is pretty typical of a split 3,000f hard firebrick that's been subjected to a well tuned propane burner. The flame in the sweet spot exceeds 3,000f if you're lucky. The glassy spot is the result of molten borax dissolving the silicate refractory in the brick and once it begins to dissolve the brick itself vitrifies and becomes less refractory so the degradation spreads. The outside edges crumbling is evidence of exceeding it's rated max temp.

Bummer about using ITC-100 instead of the proper refractory flame face, that is NOT what ITC-100 is for. It is literally a kiln wash it was formulated to prevent, ceramics, glazes, etc. from firing to kiln furniture. ITC 100 doesn't get hard it stays chalky so nothing sticks, the high % of zirconia is there for it's inertness so nothing CAN bond to it.

This means that applying Satanite or Kastolite to the refractory blanket just won't stay on, the ITC-100 will do it's designed job and prevent it. So, yes you need to replace the entire liner. 

Colloidal silica AKA Fumed silica is a common ingredient to thicken casting and laminating resins so check with a fiber glass supply or repair shop, eg. Boat repair. If they don't sell it themselves they well know who does and it's cheap. a pint can ran me $8 USD including shipping, then I discovered a local plastics supply / repair and they carry it on the shelf for nothing if I bring my own container. 

Once the new ceramic blanket is in place in your forge you need to wet it down with clean fresh water, this is known as "buttering" and is an important step. Don't skip it! If you put a few drops of food coloring in the spritzer bottle with the silica and water you'll be able to see how well it's covering. Don't be shy it's really hard to over do it but don't get silly. 

Once it's covered thoroughly with the rigidizer solution and relativey dry, damp is fine but sopping wet isn't good, not a deal killer but not good. Once it's reasonably dry heat cure it, a soldering torch works fine or you can fire the forge burner. It only needs to be heated to red and the burner will do it quickly so pay attention. 

Once it's cooled down apply the flame face refractory, Satanite if that's what you have. Butter the rigidized blanket first! It's important don't forget.

Follow the instructions for Satanite but apply multiple THIN layers rather than one or two thick ones! Thick layers shrink check as they set like an old dry mud puddle. This is a B A D thing. Thin coats shrink in thickness as they dry and don't check which is MUCH better. Follow the directions and let each layer dry thoroughly before applying the next one.

This gets tedious but your patience WILL be rewarded!

The last step is applying a kiln wash. ITC-100 if that's what you want to use goes on now. A thickish coat under the brick should keep it from sticking to the liner so maybe it's not a bad thing. I MUCH prefer Plistex as the kiln wash it has a working max temp better than 3,000f is high alumina so borax based flux won't effect it and it's a poor thermal conductor. This means the thermal energy from the flame can't pass through the kiln wash quickly and is retained and re radiated in the path of least resistance. BACK into the forge and your project where you want it. 

Plistex or Matrikote fire HARD like a ceramic coffee cup and resist mechanical abrasion at high temperature. 

I make my propane forge liners with Kastolite as the hard refractory inner liner (Flame face) and kiln washed with Plistex. I don't use a fire brick as the floor I just made the Kastolite a little thicker, about 1/2" in my latest 5 year old forge. When borax flux starts being a problem I use a piece of steel rod to scoop it out when it's molten. It never comes out completely but it's okay. 

How I apply the Kastolite is covered in the Forges 101 section of propane forge section, I've written out so often I'm starting to go a little nuts.

Frosty The Lucky.

[Buzzkill]

19 hours ago, Thr said:

There's no way to remove it?

The best way to try to remove it is at forging temperature.  As I said it will turn semi-liquid and sticky again.   At that point you can scrape most of the "bad" stuff out with some scrap stock bent to whatever shape helps the most.   You won't get all of it of course, but you can get most of it.   If you try to chisel/chip it out cold you'll most likely end up breaking the floor and you'll have to re-cast it anyway.

As I said, if it were me I'd keep using it for now.   I'd probably try to scrape some of that stuff out and/or cover it with a sacrificial piece of kiln shelf or castable refractory until it gets to the point where the whole thing needs refurbished.  Forging temperatures are brutal on a lot of materials and the thermal shock of heating or cooling rapidly tends to degrade or crack a lot of things we use in forges.  The interior will not stay pristine for long no matter how well you do on your construction.  Don't let perfect be the enemy of good enough here.

As a side note, one of the reasons I stopped using flux when forge welding is the mess it can make on the floor of a propane forge.  I'm almost exclusively forge welding stacks of uniform sized high carbon flat stock though, so it's not as much of a challenge to get good welds as it would be with mild steel or irregular shapes. I'm also fastidious with my prep work for the welds. 

[Thr]

Apologies for disappearing for a month, I came down with a bad case of a certain disease and am still recovering from it -- I've been unable to do much of anything as a result. Thanks so much for all your advice, I'll be going through more of it later when I'm feeling better.

 

Since I'll have to redo the lining, are there any recommended methods for removing the lining from a forge?

 

Thanks!

[JHCC]

Hammer and chisel. The occasional spritz of water to keep the dust down, and a shop vacuum cleaner to take it away.

[Frosty]

Get well quickly, we're pulling for you! 

A dust mask outdoors, hammer chisel judicious use of a pry bar, be careful you don't want to distort the shell if you can help it. If you have a shop vac and the wife allows it you can  have it running running with the hose in the forge. 

No easy way to remove the old liner but once they start breaking up it gets easier.

Frosty The Lucky.

[Thr]

I know I was extremely late to the party again, but I managed to take it off with little effort -- I guess I had to find out the hard way that HT100 isn't a proper refractory, but moreso just a coating.

 

I made another amateur mistake -- I didn't have a spare spray bottle around, so I simply dunked the wool blanket in a bucket of the mixed rigidizer I prepared. Only the edges got really soaked as a result; would I need to worry about completely coating the blanket with rigidizer, or can I get by without, as long as I'm careful with the refractory coating?