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Forges 101


Mikey98118

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10 minutes ago, EAlger said:

Mickey, regarding your entry " Using Silica Based Rigidizer",

I'm having a hard time visualizing inserting the "Rigidized" blanket into the forge shell? I'm guessing that by "permanent shape" that it would still be flexible enough to get it fitted inside the forge shell?

By Silica Based rigidizer, do you mean Fumed Silica, Sodium Silicate, ??

After I understand about Rigidizing, I would add Plistex 900 over the exposed areas, and burner port area, and add an Alumina Kiln Shelf.

Ed..

You don't want to use the rigidizer until after you have things in place. If you do it beforehand it will be rigid thus not necessarily flexible enough to get a proper fit in the forge shell.

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Michael.

You place the pliable blanket where desired, push it into shape, and spritz the rigidizer into it. Then, you heat cure it in that same position; presto change-o, a stiff monolithic structure is created; either all at once, or area by area, as you see fit.

By silica based rigidizer, I mean fumed silica in water; better known as colloidal silica.

Sodium silicate (AKA water glass) melts at 1900 F and is expensive and heavy. Colloidal silica is use rated to 2300 F and doesn't melt below 3000 F; it is dirt cheap, costs very little to ship, and once the water is steamed off the blanket it adds almost no additional weight, because it flows over ceramic fibers in a very thin layer, do to its capillary action (wetting).

Why than would anyone use water glass? It makes a better binder for lite weight aggregates, like Perlite--not ceramic fiber blanket.

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I've been meaning to ask Mike but it looks like you just answered my question. Colloidal and Fumed silica ARE the same thing? Does that mean I can stop trying to find Fumed silica and use the colloidal silica rigidizer I have?

Frosty The Lucky.

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Thanks Mickey for the information. I've been using  Colloidal silica for years and I didn't know it!  Colloidal silica  is also known as Cabosil which I've been using as an epoxy filler on my canoes. 

For a 2 layer blanket application, I assume that each layer, as applied, wants a spritz of Colloidal silica, curing as applied?

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frosty asked,

"Colloidal and Fumed silica ARE the same thing?" 

Dissolving fumed silica in water is the easiest way to end up with colloidal  silica; technially we cannot say that fumed and colloidal silica are the same thing, but add water, and one thing turns into the other:)

One of the main guys on here is already doing that.

EAlger,

Mix the proportions to suite yourself; I don't think it is easy to get them wrong.

Fumed silica is easily purchased through eBay; Colloidal silica based rigidizer is usually inexpensive to buy at a pottery supply store. It's paying for shipping it from an online source that I thinking foolish...this is why I brought the subject up a few months back; not because I hate pottery supply stores:)

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Colloidal" by definition is any substance that stays in solution with water.  Many minerals, which or heavier than water, can maintain their presence in it, by being  ground into small enough particles, which is where my interest in the subject started.

Caution: Letting the water freeze will turn this particular solution into worthless junk.

Seventeen years ago I used this phenomenon to separate smaller particles from larger ones by mixing a small amount of ITC-100 with some extra water in a clear glass container. It took only a couple of minutes for the cruder material to fall out of solution, and fall to the container bottom, leaving me with a colloidal mixture; more to the point, it was a refined mixture of the product, which thereafter worked MUCH better at 'reflecting' heat from forge walls, because the smaller the particles of its active ingredient the better it works when painted on a surface.

Silica based rigidizer works like magic on ceramic fiber insulation for two good reasons: First, the silica particles are very small, which means that the water it is in solution with will wet the surface of the fiber beautifully by capillary action; secondly, such small particles leaves a very thin of layer powder behind to melt on the fibers, and lock them in position everywhere the fibers cross each another; it is all those tiny little intersections that rigidize the fiber blanket (or board). But wait; didn't I say that the fibers don't start melting until they reach 3000 F? Yup; but them there ceramic fibers are made of alumina and silica; this difference is aided and abetted by the fact that the micro thin layer of silica powder that remains behind when the water dries out away are tiny, which makes them much easier to PARTIALLY melt. Use; they only begin to melt before they  become a permanent part of the fibers, and become just as hard to melt any further than the alumina/silica fibers they have just bonded too. In fact, the whole process is so similar to brazing of metal alloys that any description of how one thing is done will apply equally with the other.

Which brings us to the other rigidizer; alumina. You can find two kinds of alumina rigidizer:

(A ) Colloidal :D

(B) Cheap worthless junk :angry:

 

what is the difference? Review that big fat second paragraph above, until you get how the why of the what applies to colloidal alumina powder too.

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Unlike silica, those alumina particles won't begin to melt at much lower temperatures, so how can they bond to the ceramic fibers? In just the reverse of the first process; the silica content of the ceramic fibers bonds to then, and the "locking" action at every intersection happens just the same as with silica powders. The process is quite similar, but not quite the same. So, how does it work at all? Aluminum and silicon  LOVE each other; they have a great affinity, but if you want to know more, study brazing for a while (about six months should do it).

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Ahh Mikey, thank you so much for the tutorial :D. When I mixed Cabosil with my epoxy, I just added the filler until the epoxy felt thick enough.

As a rigidizer, I can see now that it'll take a little more experimentation.

Thanks,
Ed... 

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ALger writes:

"I've been using  Colloidal silica for years and I didn't know it!  Colloidal silica  is also known as Cabosil which I've been using as an epoxy filler on my canoes." Yes, Cabosil is fumed silica.  FS is also used as a thickener in shakes.
 

"For a 2 layer blanket application, I assume that each layer, as applied, wants a spritz of Colloidal silica, curing as applied?" This is the best way.

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 Moving beyond high alumina refractories

 

Zirconium dioxide ZrO2 (AKA zirconia) has three phases: Monoclinic at less than1170 °C , tetragonal between 1170 and 2370 °C  and cubic above 2370 °C. The transition between the first and second phase creates enough expansion to prevent it being used in hard refractory products, unless it is stabilized in the cubic form, or in its more useful partially stabilized tetragonal form.

A small percent of calcium, yttrium, or magnesium oxides can be used to partially stabilize zirconia; cerium oxide can also be used, but is too expensive for the purpose. Further high temperature manipulation can form fully stabilized zirconia, but adds further expense.

Zirconia has very low thermal conductivity, yet very high luminosity when incandescent temperatures are reached. These two facts combine to make it a preeminent heat barrier. Because of the high luminosity it can be used an effective method of heat transference on high temperature casting crucibles, when applied in very thin coatings (.004” or less), and yet thicker coatings can be used to “reflect” heat through re-emission, while providing insulation that only improves as heat levels rise. When it comes to various heat barrier coatings, very fine particles of zirconium is wanted, because the finer the particles the higher re-emission percentages go.

Government sponsored experiments in the nineteen sixties showed that phosphoric acid was able to hold stabilized zirconia onto heating surfaces despite phase change resizing; it was an important find—back then. But, stabilized zirconia is much cheaper than it was in the past, and so this more expensive product is the better choice for tough heat barriers, and nowadays for castable refractory.   Since the refractory makes a very large layer of super insulation, it contains very large particles of grog Fine particles of stabilized zirconia completes the job as a covering on such a refractory’s hot face. Zirconia based refractories, and alumina ceramics with stabilized zirconia included are famous for thermal shock resistance and resistance to erosion from incandescent liquid metals.

Note: Drying can produce up to 4% shrinkage in slip cast zirconia refractories, and firing at 1900 °C will produces up 15% further contraction; a factor to be considered when planning structures made of it.

Zirconia is available for use as loose grog, and is an effective insulation for very high environments; think of it as Perlite of steroids.

 

Zirconia also comes as stabilized ultra-high temperature porous insulating brick.

That should have read:

"Government sponsored experiments in the nineteen sixties showed that phosphoric acid was able to hold unstabilized zirconia onto heating surfaces despite phase change resizing;

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About kiln shelves

If you plan to include a high alumina kiln shelf to protect the forge floor, your burner should be positioned  at 10:45 or 1:15 o'clock, and aimed for the flame to impact one-third of the way in from the nearest edge of the shelf. This is done be using a small pipethat is trapped in the burner port's tube, so that it can rest on the shelf, while the port tube is welded, brazed, or mechanically connected to the forge shell with screwed on angle brackets.

The port tube holds the burner trapped in place by using two rings (not one ring) of three equally spaced thumb screws (not hex bolts), in a burner port two pipe size larger (not one size larger) than the burner tube. Taking care not to muff these particulars allows you to re-aim the burner as desired, help keep heat transfer from the forge wall down to a minimum.

Most people go by what looks best to the eye when making the decision about burner position and aim. You need to pay more attention to how much of  of the kiln shelf remains to help protect the forge walls, instead. It takes less angle to promote swirl of the flame path than people think.

What are so-called Mullite kiln shelves made of? Low content alumina refractory; why would anyone choose them over High (content) alumina shelves, or refractory?

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Most people consider a cast refractory floor, or high alumina kiln shelf to be needed to protect the ceramic fiber blanket forge wall from bumps and borax; both are very good reasons. But no more important than its duty as a shield from flame impingement directly on the blanket. So, if you're stuck someplace where a high alumina kiln shelf is all but out of reach, take advantage of the nature of high alumina redractories, like Kast-O-lite 30 to form an even better flame shield, by constructing a wood or plastic form to cast a better shape into, than a flat slab of a kiln shelf; think curved.

 

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Mikey, so I had planned to use Mizzou for my floor, but I could us Kast-o-lite 30.

So curved, top and bottom? Crescent moon shaped with pointed ends to meld into the wool? The floor could then be thicker in the middle? Or just flat sides and uniform thickness resting on the curve of the ridgedized  wool?

Ed...

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Your burner(s) well be positioned near the forge top, and aimed downward at the floor, so it should be a gently curved surface, similar to one-half of an oval, which has been flattened out somewhat in its center, with its edges curved up more.

Something like a modified "crescent moon shape" that has been flattened out somewhat, but with its ends stumpier. You don't want thin ends, which can too easily be broken. Remember, that the ceramic blanket becomes easily 
"spot" molded into shape, while it is wet with rigidizer, and then easily set into shape with the heat from a loose burner. Being careful to employ a resperator, you should even be able to sand the blanket afterward along the joint, so that the homemade kiln wash leaves the area smooth as a baby's bottom. Also,  a box knife can be used along the cast refractory's  edge, to allow the blanket to relax back even with the it, before rigidizer is applied.

Different diameters of plastic pipe sections, with strips of wood separating them, can be screwed together at the sections edges. If you use Kast-O-light 30, the mold can be unscrewed in twelve hours, with the inside surface of the mold left in place, while yo power sand the exposed edges of the casting, and sand it round, to make it easier to mold the blanket to curve around.

This are viable suggestions; mix and match among them as you please.

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Thanks Mikey for the ideas. I'm glad I didn't rush things along before asking questions.

It's gonna snow tonight and be just above freezing so my project will wait a couple of days. However, mean while I'll make a mold for the floor.
Thanks,

Ed..

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So, we have discussed how to fine tune the speed of combustion gases in the forge, to get the most heat from the least fuel use. But, there is another facet of that; which is to fine tune combustion and exhaust speeds within different areas of your forge.

To my mind, multi port burner blocks (ceramic ribbon burner nozzles) provide the most bang for the least effort; especially now that Frosty has given the lie to the false assumption that they can't be run from naturally aspirated burner body's. His discovery also paves the way for supercharging such burner bodies with much smaller fans than are needed to make relatively high pressure outputs on ribbon burners; which I strongly suspect will be needed to fine tune their flames. All this considered, why bother with more traditional burners?

Control; you can never get enough of that SUPER  VIRTUE.

which brings us straight back to "why bother with regular burners?"; they can be combined with burner ports, so that different sizes of burners can be changed out to fashion very different heated zones within a forge. It is obvious that two or three ports can use different size burners to provide very different heated zones in a forge, but perhaps less plain that mixed and matched burners can also be changed for as different burner sizes, AND DESIGNS, in a forge to control their output gases (nuetral, rich, and lean), to give even more control of the burn for the best use of fuel for various forge shapes and and sizes. At last you have an opportunity to use your first "not quite right" burners to full effect;)

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Ceramic chip forges

 The little bit of dependable information on gas based ceramic chip forges can be gained from brochures of  English ceramic chip brazing forges.  One or more burners must blow flame into something like a plenum chamber below an upper chamber that holds the chips; this creates severe problems, and limits their temperature ranges, because the lower chamber (plenum) must hold up the upper chamber, with its lode of chips, plus whatever part is being heated at high temperatures. Very hot standard burners cannot be used, since this last ended up with partially melted ceramic structures last time some one tried this (back in 2006). After helping encourage a willing victim into creating this mess, I decided that only a larger, and lower temperature flame, from a fan-blown burner could avoid a repeat of it.

That was then and this is now. If I tried to build such a forge today, I would attempt to cast ribbon burners into a support structure below and beside the chips instead of building a plenum chamber, as the best possible solution.

 

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