forge glaze/cement?

[Shamus Blargostadt]

Back in the summer, a brother of a friend lent me his gas forge. It has two burners, rectangular shape about 2' long and both sides open up. The front side has a smaller access hole.  When I got it, the insides were lined with some white glazy stuff that kind of looks like glass when it heats up. It is black now and starting to deteriorate near the ends and in the middle where steel likes to sit. We  haven't been doing any forge welding in it... use coal for that.

any tips on how to build this back up or the proper care to maintain it? I'm not sure if I can buy some of this material and just patch up the deteriorated areas or if it needs to be cleaned out and redone completely. I want to take proper care of it though and the owner doesn't seem to know what to do. Been reading through topics in the forum but haven't come across anything that has given me a eureka moment to purchase something. 

 

[Mikey98118]

Jeff,

I can see that you're into taking responsibility for understanding and using "raw" materials, so yes, there are a number of choices that beat the heck out of ITC-100; not only costing less money, but giving better performance at the same time.  And since  a so called IR reflector (actually a high emissivity coating) will be of especial help in your situation, let's lay them out.

In the first place, ITC-100 claims "up to" 90% IR reflection. And, you guessed it; "up to" is actually a cover for the nasty truth that their formula can also mean "low as" 67% reflection; its all a matter of particle size. Being a naturally suspicious cynic, I tried separating the colloidal content from cruder particulates in their product by spooning some of it into a glass of water and presto; the crude stuff fell out of suspension and immediately sank to the bottom of the glass. So, I mixed in as much as I could, and painted the much thinner coating over an already ITC-100 coated surface. My forge went from bright orange to yellow-white incandescence with the same burner and regulator setting. Point proved.

When ITC products first came on the market, stabilized zirconia cost twice as much as the regular kind. Today, there are three different ways to stabilize zirconia, and the price has fallen to about one-third more than the regular stuff; this is an important factor to keep in mind.

So, if the colloidal stuff is so much more effective why have crude particulates in the content? MONEY; what is commonly called zirconia "flower" is nearly 100% colloidal, and will give you the full emissivity benefit; but it's not cheap. Why, did you know that a 500 gram bottle of this stuff will cost a full third of the price you are paying for ITC-100?!? But, wait, the ITC product has water content, and a SECRET ADHERENCE INGREDIENT!!! Obviously, you can't get along without their product...or can you?

Zirconia changes its crystalline structure at about 900 F, from square to hexagonal and then back to square again during cooling, so twice a heating cycle, it also changes particulate size, which is very hard indeed on every other ingredient in a rigid refractory coating; as in turning them to dust; and so manufacturers of high heat crucibles (and others who's products justify the added expense) employ stabilized zirconia.

A product that became popular while waiting for reasonable stabilized zirconia prices to happen is zirconium silicate; since this has silicate and zirconium mixed in a crystalline structure, it makes an end run around the problem, and is reasonably priced. You can buy zirconium silicate already mixed with a binding agents (Zircopax?) Both zirconia and silicate are very resistant to flame erosion, and chemical attack, and are generally tough ingredients for a hot-face coating. however zirconium silicate separates out into its two constituents over time at high heat, and it is only about 67% IR reflective.

So, if you want maximum protection for your hot-face layer, stabilized zirconia mixed with a good refractory binding agent (ex. calcium aluminate) is the optimal path.

[Mikey98118]

To continue, the concept of high-emissivity coatings rather than using the technical shorthand phrase "IR reflector":

Yes, there actually are substances that reflect infrared energy; the most notable being gold, followed by silver and aluminum. But the difference between cause and effect is important. Actual IR reflectors are only useful as ultra thin coatings on optical devices, such as light filters in welding helmets.

High-emissivity coatings can be used to more effectively transfer heat through a crucible wall (as a thin coating), or bounce deflect energy and also insulate surfaces against heat gain in thicker coatings; to illustrate the importance of the point, we will define thin zirconia coatings as one millimeter (just under .040") and thick coatings as three to five millimeters and up. And the higher the heat level the more effective high-emissive coatings become, while every other form of insulation loses efficiency as heat levels rise. And the thicker the coating the greater the insulation becomes. Induction "furnaces" for instance, use crucibles made of zirconia refractory, which is transparent to EMP waves, but is so efficient as a high heat insulator that with secondary insulating refractory between the coils and an inch or less of it beyound the coils, becomes the furnace as well as crucible.

[DSW]

If it's a commercially made forge, chances are you can get a lining kit for it from the manufacturer if it's deteriorated severely. Picts of the forge might help someone identify it if you don't know who made it.

[Mikey98118]

Sorry DSW,

Those two postings where meant for another thread. What you are describing is almost certain to be ITC-100

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[WayneCoeArtistBlacksmith]

If the base surface is still in good shape you could use Plistix or Metrikote IR reflective products.  Similar to ITC-100 but much cheaper.  I have used all three and can't tell any difference.  I have not done side by side tests though.  I do know that they all work.  If you paint the IR product on the inside of the forge you will get a white colored coating.

Let me know if I can help you.

[Shamus Blargostadt]

1 hour ago, WayneCoeArtistBlacksmith.c said:

If the base surface is still in good shape you could use Plistix or Metrikote IR reflective products.  Similar to ITC-100 but much cheaper.  I have used all three and can't tell any difference.  I have not done side by side tests though.  I do know that they all work.  If you paint the IR product on the inside of the forge you will get a white colored coating.

Let me know if I can help you.

Thanks Wayne. The stuff that is still there is in pretty good shape. Most of it is at least 1 1/2" thick. It just slopes down in the front such that pieces tend to fall out.  I can paint those products on top of what is already there, even not knowing what is in there?

 

[WayneCoeArtistBlacksmith]

Not knowing what you have I would think so.  It has no strength but will cover what is there and make the forge more efficient.  It might stick the pieces in place for a while.