Forges 101

[Mikey98118]

Having mentioned two commercial forges on the high end of the market, it should be mentioned that there is one product on the low end worth mentioning: Mr. Volcano forges are still good value for the money.

[The Jeff]

I've been thinking about buying a Mr. Volcano forge, but I wasn't sure if it was worth it.

[Mikey98118]

The way I think of dollar value--yes, or no--is not just by function of the finish product alone, but when it comes to forges in the low end of the market, by the value of their parts.

As a commercial product, either the forge is fuel efficient, hot enough, and well constructed, or else not; none of these aspects is a given. One previously popular product line, at the high end of the market, was already starting to be jeered at twenty years ago, when I started paying attention to such things. You might wonder how it got popular in the first place; relentless andverstising. Only buys could now voice there dissatisfaction on the Net. Another main line brand was a fuel hog, and and didn't wear well, since since its shell was inclined to warp out of shape at production temperatures!

The low end of the market are forges that have only been around for a few months or years; some of these may be worthwhile for the value of the parts, if you don't like them; but only to people who are willing to rebuild and/or change the original forge, should they not work out, as is.

This winter I deliberately purchased a small oval forge, just for its parts; I haven't even started it up, and probably will not; but will junk its single top-dead-center mounted burner, and install two burner portals for 3/8" Mikey burners low in the side of its shell. All the rest of the forge parts well be recycled into the new forge.

I was tempted to use a Mr. Volcano forge for this purpose, despite its not having an oval shell, but could not bring myself to trash a product I approve of, in this way.

[Mikey98118]

This is not to say that Mr. Volcano is a perfect forge; what it is, is functional, and worth the money. For perfect satisfaction, a little additional money should be added to replace the finish coating, which comes with this forge, with Plistix 900. Anyone thinking about purchasing a Mr. Volcano, should read through its thread here on IFI, for a lot of helpful information, including just how very hot it gets.

[The Jeff]

If I did purchase a Mr. Volcano I had planned on adding plistix.

Would the plistix be applied over the refractory or am I misunderstanding the info?

[Frosty]

Plistex is an excellent flame face kiln wash. I don't know if it will protect Satanite well enough to make it long lasting (for a propane forge) but it WILL help a lot. Forge liners are wear items, they WILL burn or wear out, some last longer than others though.

Frosty The Lucky.

[Mikey98118]

What is castable refractory?

To make concrete, a mixture of Portland cement and water is mixed with aggregates (sand and gravel, or crushed stone.

Castable refractory consists of very similar ingredients, in similar amounts to concrete:

Concrete has a binder made of Portland cement and water; about 15% cement, mixed with 10 to 15% water.

Castable refractory has similar binders made of different cements, which unlike Portland cement can be slowly heated up, after air curing, to drive off the final portion of chemically locked water. This cannot be accomplished, using Portland cement as binder; so concrete will explode when heated. The silica content of clay also helps to further bind the mixture during firing; this is helped along with the addition of a minor mount of lime, to help the silica

 

Concrete consists of up to 65% aggregates; these are sand and crushed stone, or pebbles.

 

Better castable refractories are made up with about the same proportion of aggregates, but they consist of high alumina powder (instead of sand), and crushed pieces of high alumina kiln furniture, etc. (instead of crushed stone). High alumina (or silica) spheres are included in semi-insulating refractory.

Lessor castable refractories are mostly made up clay binders,  with about the same proportion of aggregates, but they consist of refractory brick powder (instead of sand), and crushed pieces of refractory brick (instead of crushed stone). Silica spheres are included in semi-insulating refractory.

High alumina products may fully or partially consist of man-made substances, or even be completely consist of superior clay powders. The difference between this and a lessor clay is a much higher proportion of alumina to silica.

[Mikey98118]

21 hours ago, Mikey98118 said:

Concrete has a binder made of Portland cement and water; about 15% cement, mixed with 10 to 15% water.

As with concrete, it is desirable to use no more water than you can get by with. Extra water weakens the finish product. As with concrete, a little vibration will improve the finish product.

[Mikey98118]

On 4/17/2023 at 2:05 PM, Mikey98118 said:

to help the silica

This should read "...to help the silica to melt."
 

[Mikey98118]

Castable refractory has similar binders made of different cements; (ex. aluminum phosphate; calcium aluminate; or even colloidal alumina), which unlike Portland cement, can be slowly heated up after air curing, to drive off its final portion of chemically locked water. This cannot be accomplished, using Portland cement as binder; so concrete will always explode when heated enough to create steam in its permanent water content.

    The silica content of clay also helps to further bind the mixture during firing; this is helped along with the addition of a minor mount of lime, to help the silica content to melt, further binding aggregates together. Silica content can be replaced with pseudo-boehmite, which does not turn into glass during firing, but instead sinters aggregates together, resulting in higher heat ratings in the refractory.

    Concrete consists of up to 65% aggregates; these are sand and crushed stone, or pebbles.

    Better quality castable refractories are made up with about the same proportion of aggregates, but they consist of high alumina powder (instead of sand), and crushed pieces of high alumina kiln furniture, high alumina brick, etc. (instead of crushed stone). High alumina (or silica) spheres are included in high-alumina semi-insulating refractory.

    Lessor castable refractories mostly consist of clay binders, with about the same proportion of aggregates, but they consist of clay based refractory brick powder (instead of sand), and crushed pieces of clay based refractory brick (instead of crushed stone). Silica spheres are included in cheaper semi-insulating refractory, but can be replaced with Perlite if those spheres are not readily available.

    High alumina products may fully or partially consist of man-made substances, or even completely consist of superior quality clay powders. The difference between this and lessor clay based refractories, is a much higher proportion of alumina to silica in the clay, and minimal traces of impurities, like salt minerals, sulfur, or iron present in the clay. 

Homemade insulating refractory: Homemade refractory isn’t a smart choice, for anyone who can find the kind of refractory desired in their local market; otherwise shipping charges can be more than the cost of the product. The greater the amount of refractory, the higher the shipping fees will go. Usually, this lack of local refractory is a only of the insulating variety. So, below are some solutions for this problem:

    

My buddy, Dan Brewer, used regular castable refractory for his casting furnace, mixed half and half with Perlite from the garden department of a large hardware store. His burner is a very hot tube burner design, and though he was only casting aluminum at the time, he always ran his burner turned up very high. In fact, he oxidized two #316 stainless steel flame retention nozzles away in six months! Yet, Dan’s furnace lining is still in excellent shape.

    Here is another guy’s description of how he, and one other, make different homemade refractories. It should be noted that what is sold as “furnace cement” is changing; some of it is, but some is actually castable refractory, sold at higher prices than is found in 50-pound refractory bags.

    John A. Wasser posted a recipe that calls for one part by volume of furnace cement (use rated at 3000 °F) to four parts by volume of Perlite. He states that “if you use much less than four volumes of Perlite for each volume of Furnace Cement all the passages between Perlite beads will be sealed, and it will take a long time for the cement to set (it needs contact with air). If you use much more than five volumes of Perlite for each volume of Furnace Cement the resulting material will be quite weak. You will also want to have some refractory [such as Plistix 900] to use as a sealing coat on your lining. The Furnace Cement has about the consistency of roofing tar and is very sticky. It is MUCH easier to work with if you add about 2 cups of water per gallon of cement. This makes it more like a thin plaster.” His comments give me every reason to conclude that Wasser is using actual furnace cement—not castable refractory.

    You have probably noted that this advice flies in the face of the half and half formula my buddy used, but he was using Kast-O-lite 30 refractory. Back in those days our casting groups allowed an entire week for the cast refractory to set up, warmed by a forty-watt incandescent light, or votive candles; and this was followed by a very slow increase in firing temperatures, until no out-gassing of steam could be observed.

     Also, I would only follow his advice about how to make a finish coat (flame face), if your “cement” states somewhere on the package that it is in fact castable refractory. If what you use really is only furnace cement, I advise using Plistix 900 as the flame face; it can be bought in small amounts from various knife-maker suppliers.

Four different from-scratch recipes for insulating refractory are available at:

Please note that refractory cement is NOT made with Portland cement; this is a common myth.

Commercial castable refractories use alumina spheres, or silica spheres, rather than Perlite, to create insulating voids; one or the other can usually be found where concrete is sold to contractors; not to the public at large.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            

 

 

 

 

[Mikey98118]

Please note that refractory is NOT made with Portland cement; this is a common myth; if followed, it will lead to the slow disintegration of your homemade ‘refractory’ during heating cycles.

 

Refractory products from fine porcelain to firebricks have been made primarily from fireclay for centuries. The best fireclay is flint based. To be known as fireclay, the product must withstand temperatures of at least 2,759 °F (1,515 °C). The best fireclays are good to 3,227 °F (1,775 °C). Today, high alumina refractories are more likely to consist of synthetic materials, but many still contain the best fireclay as a constituent.

    The next constituent in refractory is grog (i.e., aggregates); which consists of crushed brick or other previously fired filler content; this helps to strengthen the finish product, and stabilize it from over expansion and shrinkage during firing (either of which promotes cracking). Fireclay is only one of several products that can be used as binders. The less the clay content the greater the need for other binders (ex. aluminum phosphate or calcium aluminate), especially in really high temperature rated high-alumina refractories, such as are found in kiln furniture and casting crucibles.

[Mikey98118]

Doors: Maximum part clearance can be provided with a hinged and latched forge door (stainless-steel toggle latches are your best choice); it should contain built-in interchangeable baffle plates (high alumina kiln shelves are perfect for this). A door makes building the refractory structures inside of equipment much easier, and permits larger parts to be heated than would pass through a narrowed exhaust opening. Best of all, it allows closely contoured movable internal baffles to be employed, which would not pass through a narrowed exhaust opening; this promotes the use of single burners for small pieces, saving money in any tunnel, oval, or “D” forge, that is run by two or more burners; on these forge shapes,the forge door is a big step up from an exterior brick baffle wall; it should include a parts entrance that can be varied in size; for instance, with several round (or hexagonal) kiln shelves with different openings cut into them (for passing stock through); these can be exchanged, and held within a pocket structure on the door. These improvements don’t all need to be seen to at once, so long as a hinged and latched door is included in the forge shell.

     High alumina kiln shelves are seven times more insulating than hard fire brick; they are very tough at incandescent temperatures, which is an important consideration for something you will end up shoving parts back and forth through. Using exchangeable kiln shelves, with different part openings drilled and cut into them is fine, but building an elaborate system of moving kiln shelf parts to ape the ability of bricks to infinitely vary their openings comes under the heading of "gilding the Lilly." The additional energy savings it provides probably isn't worth the effort. Make up new openings in door mounted shelves sparingly.

    Diamond coated and carbide coated rotary burrs (and diamond or carbide coated hole saws) are the preferred way to drill holes in kiln shelves. Friction cutoff blades and diamond coated blades are the best ways to cut straight lines between those holes.

    A hinged and latched door, can also work on a box forge. Yet, movable bricks, trapped in an angle iron frame will work out better than the hinged door. Further, the angle frame works best, by sliding up and down, counter balanced by a weighted wire, running through pulleys.

    You want to coat the hot-face side of either kind of door with one of the re-emission coatings. You can use a formula of 95% zirconia silicate (zircon) and 5% Veegum (or 5% bentonite as an alternate); this mixture makes a tough heat reflection coating for wear surfaces. The ingredients should be available in ceramic supply stores. Zirconium silicate can also be mixed with fumed silica to make a tuff and heat reflective coating on hard refractories (but not on ceramic fiber products). There are other choices, Like Plistix 900F, but none of them are easily purchased in other countries, since zirconium silicate and bentonite clay should be readily available in pottery supply stores, all over the globe.

    All these advantages can also be applied in casting furnace mode, if a round kiln shelf is placed in a hoop, which can be swung into position above the furnace and swung out of the way during crucible removal. A mall center hole in the shelf allows observation and metal to be added to the melt; it also provides a rest for preheating metal to make sure it is thoroughly dry before placement in the crucible. But the hot exhaust gasses will heat re-emission coatings into incandescence, causing energy to be radiated back into the furnace.

[Mikey98118]

Note: fumed silica in water is also known as colloidal silica. Silica (silicon oxide) is the main ingredient in window glass. However, glass has a much lower melting temperature than silica, because lime and potash are mixed into it, for the express purpose of lowering melting temperatures (the lime), and promoting the process of melting (the potash). Fumed silica melts initially, because the powder’s particles are so small that it has a tremendous amount of surface area, to promote the melting process. After the initial firing, this silica becomes glass like, and remelting it would take far higher temperatures. This is why fumed silica easily melts (once) on the surface of ceramic fibers, to make rigidizer on fiber insulation. And why it works as one of the binders in high alumina refractories.

[Mikey98118]

We are overdue to have someone show us their new brick forge. I'm ready to see another two-brick forge being run by a commercial propane forge-head.

Or maybe a brick pile forge held in place with threaded rod and angle iron.

Some people wait for the sound of lawnmowers as a sign of spring; for me it means fresh new forges being shown off

[Frosty]

I'm waiting to see buds on Early Birch to begin to entertain thoughts of spring. I've shown the club bolt together brick pile forge enough times. Let's do see other folks versions, New is GOOD!

Frosty The Lucky.

[Mikey98118]

New is good. Practical, sensible, and efficient brick forges are very new indeed. Perhaps a hexagonal shape, which is widened into something similar to an oval shape?

[Kenny O]

On 4/14/2023 at 11:13 PM, Mikey98118 said:

This is not to say that Mr. Volcano is a perfect forge; 

I could not locate this thread,Would you be so kind as to post a link, and where can one find Plastix 900 for sale?

Edited May 8, 2023 by Mod30
Trim quote.

[Mikey98118]

Alas, it wasn't a permanent thread, and it just recently got put into the previous pages section (where you can still find it). Obviously, it would not be politically expedient  for IFI to turn evaluations of a commercial product into a permanent thread..."or the rest will be wanting one too"

[Mikey98118]

On the other hand, there is a trove of videos from satisfied customers, easily available on the web; I think you will find them to contain the very information you're seeking.

[Frosty]

Kenny: I the Iforge store carries Plistex, the link is at the top of the page under gas forge supplies I think. They were out for a while but I'm sure Glenn has restocked.

Frosty The Lucky.

[Irondragon Forge ClayWorks]

3 hours ago, Kenny O said:

could not locate this thread

If you do a search using your favorite search engine like this,

  Mr Volcano site:iforgeiron.com    It will bring up about 71 results for your viewing.

I can't control the wind, all I can do is adjust my sails. ~ Semper Paratus

 

[ThomasPowers]

Funny the mountain just west of Socorro NM has a Perlite mine in it.  A friend picked up 3 TRAINCAR loads of perlite when there was a batch damaged by a rainstorm...

 

[Mikey98118]

Blue sky and white puffy clouds; I never get tired of looking at that, Thomas. You can almost smell the clean air

 

Flame positioning: Burner designs have improved in recent years, and are continuing to develop. Refractory product improvements are advancing apace with burners. Both changes are shifting the ground rules of forge design. Top-down facing burners were the practical choice in times past, for good reason; mainly, it integrated well with the limits of reasonably priced refractory wall materials, by permitting flames to impinge on forge floors, which needed to be made of tougher materials anyway.

    But, while new materials (including Morgan’s K26 bricks), can be used to improve performance of standard forge designs, they are even better, when combined with greater distance between flame tips and heating parts, to ensure complete combustion before impingement occurs. Therefore, a reduction in scale formation will be gained by pointing burners up and away from the parts in tunnel, "D," and oval forges; or high up on a side wall of box forges. Clam-shell forges use an opening in the movable brick wall, between their top shell (where the exhaust hole is located), and their bottom shell.

    Ribbon burners (and other multiple flame nozzle designs) have little or no problem completing combustion before their flame paths impinge on work pieces, or forge walls. Single flame burners should be aimed to provide maximum distance, before impingement occurs. Two or three smaller burners provide far more distance for combustion to complete, than a single larger burner. Smaller burners are also easier to find room for, when facing upward from low in the forge shell.

    A neutral flame is not only hotter than a reducing flame, but it is much better for your health; employing lightly reducing flames in a gas forge has long been standard practice, in order to decrease scale on heating parts. Increasing the distance. between flame tips and parts is the cleaner choice.

[Mikey98118]

So far as I can trace things back, Jay Hayes built the first oval forge, and the first clam-shell forge; he was the first to sell an oval forge, and is probably still they only one to sell clam-shell forges. If I remember correctly, Jay is an actual heating engineer and one of the earliest of the “movers and shakers” in gas forges. His oval forges have been around for decades. I consistently consulted him while righting the section on propane hoses in my book. I believe he would have become famous, if he had leaned into keeping up a modern website. There probably wouldn’t have been a niche in the marketplace for Chile Forge to fill.

[Mikey98118]

What happened back then, to bring oval forges to the front of the line, and to send clam-shell forges into obscurity?

After all, clam-shell forges could do more tricks than the oval design...

First, Chili Forge chose to sell oval forges; they did such a good job of building their product, that their forge moved to the top of the market. Next, several new imported forges, at the low end of the market went with oval forges for their product line. This established oval forges as the "latest thing."

So, the clam-shell forge went from being the top subject of discussion, to a how-hum also ran. Looking back, it was the right result, for (typically) all the wrong reasons