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Forges 101


Mikey98118

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A few years back, I took a peek behind the curtain.  It was a brief but profound visit.  I think each person’s experiences are their own but I’d be glad to share privately if it might bring some comfort.  It brought me comfort when I needed it. 

That is for anyone interested but in private only.  That’s all I’ll say about it here.

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I don't recall being taken to the ER; testing, the helicopter ride to Rio Rancho, the surgery, etc. Several days later I "woke up" in the ICU and started the Gamma Ray Knife fights.  For someone who doesn't watch TV the hospital room doesn't provide  much entertainment.

BTT: some of my forge friends relined my gasser last week and I hope I can use it a little next week; perhaps a bottle opener....

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About to start building another forge, what do y’all think of this design? still deciding on what burners to use and the spacing of them along the length. I’ll probably also add slots near the bottom to slide in a kiln shelf. The less colorful image is it drawn to scale with each square equaling 1/2 inch

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Have we talked about this shape and proportion forge before?

If not, it's too tall for the width.

The burner orientation is a deal killer. Shooting directly into a corner like that will cause serious back pressure and inhibit burner performance. If it's a NA burner it could really inhibit performance.

I don't know of any experienced forge builders applying 1/2" of Kastolite, even on the floor, 3/8" is considered over kill.

1/4" of Plistex is just silly.

Frosty The Lucky.

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If you lower your forge, it improves the angle of impingement. If you also aim the burner so that the flame impinges on the floor, a little short of the corner, these two factors will solve the problem that Frosty is referring to.

You would be better off to use Kast-O-lite 30 on the wall and overhead areas. Then, use Plistix for the final smoothing, and heat reflecting layers.

In other words, I'm basically stating what Frosty is; just in other words :rolleyes:

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You're right, i am not experienced. And I thought 1/2 in was alot but i thought i saw it somewhere here that 1/2 in for the floor. My mistake. And I see i had the wrong idea of what Plistix is. I thought it was more kastolie than itc-100. What would be a good height? 

Thank you both for your help!

Edit - I just realized the wrong ideas i thought i saw from here i saw on facebook groups. Goes to show. Other than the height of the forge. 

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I have been known to use ½ inch of kast o lite.  I now prefer 3/8 inch.  Maybe you got the idea from me.

Recently, on page 125 of Burners 101, I posted a CAD drawing of someone else’s forge idea. I had ½ inch kast o lite in the drawing. Maybe that’s where you saw it.

Plistex is painted on in a few thin layers.

The benefit of the D shape forge is the increase in floor width to forge volume.  (Compared to a tunnel forge)  The shape that you posted is more like a box forge with a vaulted forge on top of it. Large forge volume without much benefit.

The larger your volume, the more expensive it is to run. Tall and narrow usually means extra unused forge volume and uneven heat patterns.

I personally prefer a flat bottom oval forge for the flow patterns and wide floor but several people like the D shaped forge. Usually that is either a half circle or maybe a little bit of side wall.

Burner orientation is also important. As Frosty stated, you don’t want to create back pressure.  Imagine aiming the burner so it runs along the wall or floor that spirals around the forge in as long a path as possible.

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5 hours ago, Another FrankenBurner said:

Plistex is painted on in a few thin layers.

Usually that is true. However, a few weeks back I ran across a YouTube video done by a guy that I suspect was discussing an aspect of his business, who was using this product, with far less water added, to be trawled into place in far thicker layers. I posted what a saw, and a link to the video, becuase Kast-)-O-Lite in small quantities had become one of the many products in short supply.

So, what you need to know about using Plistix in thicker layers is not if it is practical, but why you might want to do so...

When it comes to box forges only, there is a single exception to what we are describing as "just too tall". That is when the forge has a hinged and latched door in front, to pass casting crucibles through.

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Alright, I thought by doing that I could have the advantages of a D forge without losing the height on the side. I find myself to often have multiple pieces in the forge and sometimes they are taller so i was hoping to be able to use a D to encourage swirl while still having the height on the sides.  And I see what y’all mean by the burner angle, thank you for that info. Also Mikey, that is one of the reasons I made the forge this tall, I see a lot of casting projects in my future so I was hoping to make a forge i could also use for that but I see what y’all are talking about. It would be a waste of space to make the forge that big. I reckon I’ll just forego that and just make another forge for that if I need to.

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So, you have a good reason to go for tall. In that case, it becomes time to compromise.

 The simple way to accomplish that goal, is to temporarily place Morgan K26 bricks over the forge floor (to take up room), when it isn't needed. The down side of this method is that the higher you temporarily change floor height the further the point of flame impact moves away from near the corner; this isn't likely to be more than a minor point to completely sane people. Lest I should have my standing as an official geek doubted...I must protest, weakly:rolleyes:

Naturally, by merely including a second burner port, which can be capped when not being used, you could keep your forge closer to perfect. Whataya say? Want to take a dip in the deep end of "the people's pool"? We are always happy to drag victims down ther...I mean the ice water is just fine. You can trust me; really :D

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I was recommending 1/2" of Kastolite since before I discovered the stuff and didn't know just how strong it is. 

If you work on "tall" projects, I do now and then, laying them on their side almost never hurts anything that can't be tweaked back with tongs or a hammer tap.

Melters are EZ PZ, there's a lot of discussion about them in the casting section of Iforge.

Adjusting the height of the chamber like Mike suggests is a good solution if you wish to keep it that adaptable. Another burner and burner port cap is again a sample of the elegant solutions our master geek comes up with regularly.

Building a brick pile forge from K-26 IFBs allows you to experiment with size and shape at will until you find what works best for you. It's easy to protect K-26 IFB by painting them with Plistex individually and fire curing it before stacking. 

Frosty The Lucky.

 

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Brick Pile forges: An old idea is suddenly updated

Spring has sprung, which means most readers are busy closing in on forge ideas, rather than burner plans. Many of you have no strong vision for your first forge, so we commonly remind you that "brick pile forges" can be any shape or size desired, and can be changed in size and shape with very little effort. What we seldom point out is that everything you use to make it can be recycled into your final forge design. But the biggest change in these forges came with the introduction of Morgan K 27 insulting firebricks to the market. This brick is strong enough to be held in place with just some angle iron and threaded rod.

 

Morgan k27 insulating firebricks (use rated to 2700 F) are distributed through Thermal Ceramics in the U.S.A.; these bricks have many insulating air voids, but are much sturdier than the old 2300 F insulating bricks, which were standard up until recent years. You will want to seal their (flame facing) inner surfaces from erosion damage, with Plistix 900. These Morgan bricks will supply insulation that is equal to 2" thick ceramic wool blanket. You can use a cheap imported, or worn out, hole saw to drill a hole for your burner to set in. The brick is equally easy to saw to length with old worn-out steel tools.   

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Exhaust size and shape: Practical solutions

One thing backyard casters and blacksmiths both worry over is how large to make the exhaust openings on their equipment. Too small and you have high back pressure killing burner performance; too large and you can't retain enough heat to do your work. Of course, the closer to the "right" opening size your equipment is the stronger the forge or furnace can be built. Just don't confuse the right size for a “perfect” size. As long as burner output can by varied (turn-down range), there can't be any such thing as a perfect opening size. The right size is what is needed to accommodate the burner's highest output (the highest you are willing to take it to).

    Variable is the optimal opening size; all other dimensions can be outright wrong, but are seldom just right, with a burner flame that can be varied. This is one of the many reasons for controlling exhaust flow with an external baffle wall beyond a larger than needed ringed exhaust opening; thus, allowing the least heat loss through radiation, while maintaining optimal atmospheric pressure in the forge. Why include a ring around the exhaust opening? To divert hot exhaust gasses away from the shell, where it can superheat its metal.

    If you decide on a movable brick baffle wall in front of the forge, keep the bricks at a small distance from the exhaust opening, to allow hot gases to move up and out, between the opening and brick, while bouncing most radiated heat off of a re-emission (heat reflective) coating on the bricks, and back into your forge. Keep the stock entrance only as large as is needed to move parts through.

    This arrangement helps to slow the flow of expended gas in the forge interior, as it heads toward the exhaust opening; and then speeds the gas up through the opening; another desirable trade off. So, you are gaining hang time for the heated gas in the forge, and recuperative savings from bounce back of radiant energy; a win-win situation. A baffle wall also minimizes infrared and white light from impacting your eyes and skin, improving your health and comfort.

Doors: Maximum part clearance can be provided with a hinged and latched forge door (stainless-steel toggle laches are your best choice) that contains built-in changeable 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 opening. Best of all it allows closely contoured movable internal baffles to be used, which would not pass through a narrowed exhaust opening very well; this promotes the use of single burners for small pieces, saving money in any cylinder or box forge run by two or more burners.

The 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 in a pocket on the door. All these improvements don’t need to be seen to at once, so long as a hinged and latched door is included in the forge shell.

    While hinged and latched doors can work just as well on box shaped forges, people seem to prefer them to slide up and down. A movable kiln shelf that slides into slots at various heights above the floor would make a vertical door much more worthwhile.

    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 alternate 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 change 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 shelve door mounted baffle walls sparingly.

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

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Working with Kast-O-lite 30 refractory: There are several hard castable refractories used as flame faces in forges, and casting furnaces. So far, I think Kast-O-lite 30 serves best in both kinds of equipment.  You can carefully drill, grind, and scrape it, as this castable refractory is still setting up; it goes well enough, during the first hour, but far less easily after the refractory completely sets. During the week of air drying, the refractory continues to harden, very like concrete.” In fact, castable refractory is a form of concrete; what sets it apart is that the chemically locked water that remains after curing can be—CAREFULLY—steamed out of the finished form by firing. Concrete can’t be fired; it simply explodes when heated; this difference is due to what is used as the binder in concrete; its cement. Aside from firing, the more familiar you are with working with concrete the more you already know about working with castable refractory.

    The other differences are that refractory has no rocks used as filler material; instead, this refractory has ground up chunks of alumina rubble (aggregates), which help to stabilize the refractory against thermal shock. Insulating refractories, such as Kast-O-lite 30, also contains silica (or alumina) spheres, to create insulating voids (and are crack interrupters), along with calcium aluminate cement for a binder.

    It was Kast-O-lite 30’s resistance to thermal cracking that first made it popular among home casting enthusiasts over twenty years back. We were already using Perlite to make our own semi-insulating hard refractory, but the toughness of this product simply couldn’t be matched with other refractories.

    Mixing and drying instructions for refractory mixtures will be found on the 55-pound bag it originally comes in; but mixing and curing instructions are less likely to be included with smaller amounts purchased from resellers online. The most used refractory in home-built heating equipment is Kast-O-lite 30, because it is use-rated to 3000 degrees Fahrenheit, not inclined to thermal cracking, lighter weight then most refractory, and semi insulating. Kast-O-lite is what’s known as a gunning refractory, which means that it can be flung on walls of large industrial equipment through special nozzles, rather than only being cast in place; the qualities that makes it good for gunning also makes it useful for spreading in layers as thin as ¼” by hand troweling, onto the inside of curved surfaces.

    Layers of ceramic fiber insulation as thick as 2” (in two 1” layers) can be pushed into shape inside of steel containers, and stiffened with colloidal silica rigidizer. After firing, the stiffened insulation will adequately support up to a ½” layer of hard refractory, in up to a (bottom) third of a cylindrical wall while it dries. The next day the cylinder can be rotated, and a further third can be covered, and the final third can be covered on the third day. Remember to thoroughly wet down the older refractory area, where the freshly spread refractory will blend into it, to ensure complete adhesion between the new and old layers.

Kast-O-lite has up to one year expected shelf life, if stored in a dry container at moderate room temperatures (50-70F); it should be mixed with no more than 20 percent water, and mixed for three minutes, then poured within ten minutes, into stout water tight forms for best results. A small amount of vibration will improve the finished casting’s surfaces. Keep the casting covered with a damp towel during air curing, which takes between sixteen and twenty-four hours, and keep the casting above sixty degrees Fahrenheit while it is air drying, for a week.

    The first thirty minutes of set up time is the most important, as the mix is changing from thick liquid mixture into a solid. If you have cast horizontal mating surfaces for the upper and lower halves of a clam-shell forge, or vertical mating surfaces for the forge shell and door in a horizontal forge, you want to use the edge of a steel square, etc., to flatten the mating surfaces by scraping. If you did a good job of cutting and grinding forge shell edges for close tolerance, this is where it pays off; if not, well…aren’t you glad you read this section before you started pouring refractory?

    What if you did not? It isn’t too late to fix your mistake. Low places, which don’t meet up with mating surfaces can be filled in with refractory cement. Be sure the cement is rated for temperatures as high as your refractory. Thoroughly clean, and then wet the surfaces where you lay the cement. Place wax paper over the top of the cement, and then close the mating surfaces against it during drying and curing. The wax paper should come away from the surface of the dry cement easily; if not, just let it burn away during firing. High spots must be ground away. If you grind too far, just use the refractory cement to correct that mistake. Don’t try to do the whole job at one time. Correct your mistakes one at a time.

    How much firing? Once the chemically locked water is driven out, is firing finished? No; most people consider this to be good enough, but without frequent firing during wet weather, the refractory can still slowly regain some water content from ambient air; necessitating the same careful fire drying routine you used during the initial firing, to keep the accumulated water content from cracking the refractory from internal accumulation of steam pressure; unless you take firing to the next step, which is called calcining. Basically, you heat the fired refractory up to yellow incandescence all the way through the form. It will begin on the inside surfaces (flame faces) and slowly soak through the refractory until it reaches its exterior surfaces (cold faces).

    Technically, calcining is the process of removing, by very high temperature (but below melting point), any volatile particulates, and finishing the oxidization of anything that can be oxidized, in a substance. Many of the constituents of a refractory mixture are separately calcined long before being included in the blend. But the cast refractory article may also be “calcined” at the melting point of glass (because some lime is included in the mixture to lower the melting point of its silicon); this to improves strength and durability, while making the refractory far less porus. One example of calcining would be fine porcelain, which is fired at higher temperatures for extended periods versus a ceramic coffee mug, which is minimally fired at much lower temperatures. One of the binding agents in most refractories is silicon. Some of the other constituents in many refractories are materials that contain silicon (like clay, which is likely to contain up to 40% silicon). When a fired refractory product is kept at high temperatures for an extended period, the silicon content begins to liquefy, gluing the other ingredients together more thoroughly, and filling in any micro gaps between particles; effectively toughening and waterproofing the refractory.

    So, “calcining” is a word with a double meaning; its proper use is one thing, and the second use is closer to industrial slang. Despite all the good and honorable intentions of English teachers everywhere, industrial slang follows an extension of the ‘golden rule (“them what has the gold makes the rules.” In this case, “them what has the power makes the rules”). In other words, OEM sales departments choose what are proper industrial terms concerning their products. And as so many other lessons from the school of hard knocks, we can like it or lump it :rolleyes:        

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Water drain hole

Ceramic wool insulation (Blanket) is usually made rigid with colloidal silica, leaving water behind. Plistix 900 is mixed with water, and so is Kast-O-lite 30. So the inner surfaces of forge linings can need to have a considerable amount of water steamed off, during firing. You will want to drill a small hole (about 1/8") in the bottom of the forge shell, for that steam to exit through.

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On 3/28/2023 at 1:38 PM, Frosty said:

Building a brick pile forge from K-26 IFBs allows you to experiment with size and shape at will until you find what works best for you. It's easy to protect K-26 IFB by painting them with Plistix individually and fire curing it before stacking. 

Before Morgan came out with these bricks, the old insulating bricks (which were made be including a foaming agent in clay) were the standard 'solution' for the need of insulating firebricks; they were well beyond friable; I consider them as junk, and am surprised that they were used for so long.

The Morgan bricks, are filled with insulating voids, too. But instead of those voids being made by a foaming agent, they are created by high pressure steam; this leads a lot more strength in the firebrick. However, if you want that brick to last, those voids need to be sealed on any surface that is exposed to flame, to prevent damage from flame erosion.

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Both chemical and mechanical flame erosion occur simultaneously, but mechanical erosion is the dominant mechanism; they increase with forge temperature, and with the speed of combustion gases within the forge; one more reason to look fondly on multi-flame burner nozzles, and ribbon burner blocks :rolleyes:

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The whys of burner positioning

Flames backing up between the burner and the burner portal doesn’t happen all that often, but it happens often enough to be mentioned; this problem is usually encountered with  weak burner performance. If you position your burner (or burners) low on a side wall and facing upward, instead of high on a side wall and facing downward, it can’t happen at all.

Like everything else, forge design is an ongoing process. To when the game, you need to know what goes where, and WHY. The why of down-facing burners was to make their flame impinge on the forge floor, which was and still is the area best able to withstand it. However, with improved refractories, like Kast-O-lite 30, and improved insulation products, like Morgan K26 bricks, and ceramic board, flame impingement on far walls is no longer a problem. Furthermore, a series of two or three small burners, or a ribbon burner instead of a single large burner, helps to cancel the problem of yesterday's refractory materials even further.

It is still desirable to have the flames swirling around inside the forge. But the reason is fuel efficiency; not avoiding flame damage.

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Deciding on which commercial forge

Commercial forges is a subject most of us on IFI are careful about. Some of them come...only to go. Others change within a year or two, so that the good things we had to say about a particular brand, no longer apply to the "latest" product. If they are well received, they are nearly certain to have sharp price increases, best on nothing more than greed.

Many of the old 'tried and true' products have the opposite problem. After more than two decades of improved burner designs, these forges are heated by burners that are utterly out of date; a few of them, like Diamondback, were so well designed in the first place, that their pluses overcome this single minus; most don't. Equally rare are new commercial forges that have earned a good reputation, like Chile Forge. Some well established commercial forges were so poorly designed, I am amazed that they ever became popular to begin with!

But, describing their deficiencies to their purchasers is like kicking someone's dog. He may think it's a mangy hound, but others better not try to point that out.

So, we try to speak out as much as is helpful, but you need to discuss commercial forges with other buyers, to get all the dirt; then you must carefully consider each source. Think of the effort as a form of horse trading. If you don't look you're purchase over carefully, or bother to know what your doing, you're likely bring an overpriced nag :rolleyes:

 

"...likely bring an overpriced nag" should read "...likely bring home an overpriced nag."

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On 5/21/2022 at 1:35 PM, Frosty said:

I'd like to see a hex forge up and working as an active member's regular forge. I've seen them before sometimes HOT but I've never heard back. It'd be nice to know how they work as a long term tool.

The easy and obvious path to take with the new insulating firebricks, is the box shape, also known as a brick pile forge; this idea is so useful as to never become outdated. Never? Yes, because the manufacturers that come up with the best castable refractories, are very interested in using those same refractories in their latest brick products. Also, there is simply something elegant about such a forge being held in place with some steel angles and threaded rod.

That said, insulating refractory bricks are easily cut; including cut on angles to create domed or hex shapes. Modified hex shapes are able to be accommodated within "D" and oval forges. With an internal flame layer or cast refractory, such as Kast-O-lte 30, the brick becomes internally and externally supported. Thus, we have a happy congruence of circumstances and available products.

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