Forges 101

[SLAG]

Frosty,

Thank you for the heads up.

WOW!  I thought that the symbols at the head of the 'reply text window'  were for decorative purposes only.  (sort of like tribal marks).

I was SO wrong.

Learning new things every day.

[Frosty]

They are decorative and my "know how to use em" list is pretty short: Italic, bold, underlined and strike through, mostly. Wow using them all in one line of text isn't particularly useful. Emojies . I've never used the link, brackets, quote marks, bullets or numbered lines etc. off the menu, they show up or I just type them in where I need them. Margins occasionally, text color and size for dramatic or comic highlighting. I should use the preview but I usually submit then edit. I try to keep my life uncomplicated. 

Frosty The Lucky.

[Glenn]

It is all about the readability of the forum.

We try to limit the use of text color and text size in the forum as it can be distracting to the reader. Bold is used to draw attention or provide emphasis when needed. Strike through is usually used to indicate a change of wording, or cancel that, use this 

 

[Mikey98118]

Practical box forges need...and don't need

Since most box forges are made from brick, how well they work depends on the choice of the brick. The only excuse for not choosing cheap, super light and insulating, thermal cycling resistant K26 brick is total ignorance.

The shape should be about one-quarter deeper and higher than it is wide for top mounted burners, to insure that the flame has enough distance to finish combustion before impinging on work pieces; the forge needs to be deeper to allow enough hang-time to allow sufficient transfer of energy from flame to forge walls; for the same reason a burner or burners should be mounted closer to the rear of the forge and away from the forge exhaust opening.

But, for side mounted burners, height to width dimensions should be reversed, so long as the burner is mounted near to the forge ceiling.

You have probably heard a lot about slanting burners so that the heated gases swirl properly, in order to increase hang-time and to avoid "cold spots". This advice is especially true with tunnel forges, where flame swirl is all but guaranteed. Ironically it doesn't work as well in box forges, where it is most needed. Fortunately, the hot gasses tend to swirl well enough in box forges just fine without slanting the burners. And yes, you might ( but probably wont) end up with appreciable cold spots. So what? Are you cramming your forge plumb full of parts? Are you so lightning fast at the anvil that some colder parts won't have enough time to completely heat? Not all problems are a big deal; lighten up already!

But what about enclosures? We can't just leave the forge wide open in the front, right? Right; but your brick opening is what I call an add-on; no one is going to forget it because exhaust heat from a wide open forge opening will remind them 

 

[Mikey98118]

Commercial forges belong on this forum too

I have never purchased a forge, but long before building my first one I looked for a forge online, and some of them looked pretty good at the time. As a long time builder I may be too picky these days. But there are loads of people trying to make the decision whether to build or buy, and even more people trying to decide what kind of forge they might want to construct. Their are way more commercial forges to choose from nowadays then there were back them; and some of them at bargain prices.

This forum is sadly lacking in ready information on commercial forges, which both groups need to see. I don't mean advertisements. I mean personal accounts from satisfied--and dissatisfied--owners. A dedicated thread for owners to speak about their forges would be best. If there isn't enough interest in doing that, let them speak their minds on this thread.

[Mikey98118]

Exhaust openings

As in so many other matters, NO exhaust size or shape is ever perfect. Therefore V-A-RI-A-B-L-E becomes the optimum; all other dimensions can be outright wrong, but never just right. This is one of the many reasons for controlling exhaust with an external baffle wall beyond a larger than otherwise needed shell opening; thus allowing the least heat loss through radiation, while maintaining perfect backpressure in the forge.

    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 get enough heat to stay in the equipment interior to do your work. Of course, the closer to the "right" opening size your equipment has the stronger the forge or furnace can be built. Just don't get suckered into confusing the right size for the perfect size. As long as burner output can by varied (turn-down range), there can't be any such thing as a perfect exhaust 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). If you want best performance at lower gas pressures, they can easily be provided by an exhaust opening that is a baffle wall. How to do this, unless you already have a r-e-l-i-a-b-l-e figure to start from? You need to make up something with an exhaust hole in it that can be varied in shape size; like hard firebrick, or with several round kiln shelves with a variety of openings to fit stock through.

    Even should you get the best possible performance from your burner with a given exhaust opening, you are likely to be fighting very poor fuel economy. Try separating exhaust losses from radiant heat losses by putting up a movable barrier of brick, or a changeable high alumina kiln shelf with a small center opening for your stock. Keep the bricks or shelf at a small distance from the opening, to allow exhaust gases to move up and out, just between the exhaust opening and the baffle wall, while bouncing radiation off of a re-emissive (heat reflective) coating, and back into your forge. You can move a hinged and latched door holding containing a baffle wall, which can be moved closer and farther away from the forge opening, depending on how forcefully you are running the burner, while keeping the stock opening 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 highly desirable trade off, but how exactly is this trick done? As the gas exits through the restricted area of the exhaust opening, its flow speeds up due to buoyancy, much as a river's water speeds up as it approaches the falls. But isn't any opening subject to buoyancy? Yes, but the less its restriction to flow the less flow speed is slowed down in the forge interior, and the less it is sped up at the exit.

    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; it also minimalizes infrared and visible light from impacting your eyes and skin. Both factors improve your health and comfort.

    Is there any improvement to be made over firebrick as a “baffle wall? Yes, but only after you use the forge enough to know what size and shape opening you normally favor: even then you may want to keep the brick on hand for occasional use with unusual parts.

    For the long haul, high alumina kiln shelves are seven times more insulating than hard fire brick; it is also tougher at forge 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 is okay, but building an elaborate system of moving kiln shelf parts to ape the ability of bricks to change their openings with, comes under the heading of "gilding the Lilly." The additional energy savings it provides probably isn't worth the effort.

[Daguy]

OK, so time for a couple of "Show your ignorance" questions for the more experienced Forge Tipplers and Tricksters.  I've built the shell (Turkey) and insulated it with Ceramic wool (Duck) of my Turducken forge and it's time to stuff in the refractory (Chicken).  How in the heck do I line it with a cement-like substance 360 degrees against gravity?

I thought maybe turn it on end (sitting on one of the openings) and just apply refractory from the bottom end up.  Would this work?  Or is it possible to coat the bottom 1/2 and let it dry, turn it over and do the other 1/2, and have a durable seal between them?

Those are the first two ideas I came up with.  Would either of them work? Or is there some other obvious technique I'm missing?

[Frosty]

I do it in sections, Kastolite bonds to itself wet or dry. Butter the edges of the dry sections with a little water for max bonding. Spritz water on everything with a spray bottle and you're golden.

Everybody's ignorant, how do you fix that little fact of life if you don't show it? Sure you can lurk or ghost and hope someone answers your questions but I hate relying on luck to solve problems, especially when there are easier ways like admitting you don't know. 

Frosty The Lucky.

[Buzzkill]

45 minutes ago, Frosty said:

Kastolite bonds to itself wet or dry.

Before it's heat cured. In my experience adding new Kastolite to cured Kastolite does not work well.   Maybe someone else figured out a way to make it work, but I did not.

[Frosty]

Did you brush it clean and butter it first? I haven't had problems the couple times I've added to a cured surface.  The company that makes it says you can trowel or gunnite apply Kastolite patches to a hot furnace. 

What did you do? I'm not a fan of having surprise problems lurking in the wings to ambush me or others. 

Frosty The Lucky.

[Buzzkill]

I was out of butter, so I used a vegetable oil based substitute

It's been a while, but my recollection is that I used a wire brush to rough up the surface and then compressed air to get rid of all the loose stuff.  After that I just applied the fresh Kastolite to the cured surface and tamped it down like I normally do when casting.  Perhaps getting the cured side damp first is the key ingredient I missed.  I only tried it once and in my mind I filed it in the "does not work" folder so I never tried it again.  Regardless, I had separation between the old and new layers fairly quickly.

[Mikey98118]

I also recommend rigidizing and curing the ceramic fiber before applying the refractory layer; can you skip doing this step? Yes, but why would you? I  believe in setting up a job as well as possible, to ensure good results.

[Daguy]

 

9 minutes ago, Mikey98118 said:

I also recommend rigidizing and curing the ceramic fiber before applying the refractory layer; can you skip doing this step? Yes, but why would you? I  believe in setting up a job as well as possible, to ensure good results.

I actually rigidized and cured both layers of Cerawool one at a time with Zeofree 80 as I laid them.  I was kinda surprised that a 5 minute cure with a small propane torch (1 lb canister type) not only cured it but turned the wool back to white.  the food coloring burnt right out.

[Daguy]

I don’t want to add any personal pages to this already long thread, but ya’all are invited to check out my first forge:

My First Build - completed 10-2018

A special shout-out of thanks to Frosty, Mikey, Wayne, and everyone for all the great advice.  Truly could NOT have done it without you.

 

THANKS

 

[Mikey98118]

Giberson Burner heads

Back in 1999 I ran across "A Glassblower's Companion" by Dudley F. Giberson Jr, the inventor of a multi-flame  refractory burner head  clear back in the seventies. If you you ribbon burner fans want to know the answers to what kind of hole configurations are practical on what kind of of burner, and on how small a piece of heating equipment, you can find it on his Joppa glass website in the small burner head section. You can also find lots of technical information there too. Giberson is into hot glass work, so just substitute "forge" in your mind for "small glory hole."

Gentle hint; he uses his heads on both fan-blown and naturally aspirated burners.

[Mikey98118]

 

Be practical first and efficient a long way second

The number one efficiency possible in a forge is provided by a small internal -volume. It takes a certain minimum burner size to heat any given volume of forge interior. If you place a 3/8" burner beside a 3/4" burner, the bottom line on efficient forge design becomes abundantly clear. Within reasonable limits, how hot a burner gets, how well the forge insulates, or how well its openings are designed become secondary issues, because their contributions to forge performance are inevitably reduced as the needed amount of fuel necessary to heat a given volume of interior is reduced along with its area.

Some burner designs are hotter and/or more efficient than others; that's a fact, which there is no getting around. But, after more than two decades designing them, I would estimate the energy output between the best burner and an acceptable (second rate) burner is no more than twenty percent. Think again of the two burners mentioned above; now just where do you expect to find the most savings; design or size?

Most of a forge's heat goes out it's exhaust openings, so thinking that forge insulation is provided to reduce lost fuel efficiency directly is insane; insulation allows the hot-face surface of the forge to glow with higher levels of incandescence; this provides more radiant heat to transfer into the work. Beyond the goal of high incandescence, all insulation can provide is a more comfortable forge exterior to be around.

Ditto for exhaust opening sizes and other refinements such as baffle walls.

An over large forge can provide a lot more heat and fumes to exhaust from your work environment, and higher fuel bills along with extended heat times to get the work ready for the anvil; it will not provide efficiency, no matter how well it is built. This is why small forges get used in hot weather by the very people who think they have outgrown them, but oversize forges gather dust in a corner...

[Mikey98118]

So now we come back to why it could possibly be worth the time, effort, and digging for information to build a first class forge; especially if you're a busy artist. I don't think it is worthwhile to save money, or work; it used to be, but there are bargains to be had on import forges these days. You can buy an ever increasing variety of worthwhile forges at reasonable prices; even low prices when you consider the time to construct a home built model. So, why not buy your forge? Well, what do you want to buy? There's the rub. You can work around everything necessary to building a good forge...except digging out the information about what makes a forge good

[Frosty]

2 hours ago, Mikey98118 said:

except digging out the information about what makes a forge good

B-e-c-a-u-s-e . . . . ?

What makes a forge good is subjective. Good for me isn't necessarily good for you.

Frosty The Lucky.

[Mikey98118]

And how did you decide what was good for you?

[ThomasPowers]

(He listens to the Northern Lights telling him so!)

[Irondragon Forge ClayWorks]

I listen to my wife.

[VainEnd84]

At Mikey’s request I am posting a build of my forge. This is iteration 1.5, I built the original a while ago and was not getting the type of performance was expecting and indeed hoping for. I will start with a supplies list and then get into some of the specifics as well as some photos and video of it running.

The body of the forge is an auxiliary compressor tank, 9.5" diameter and 16” long. I cut a roughly D shaped opening in either end, and left the flap attached to on of the ends, originally this was supposed to support the stock, but I found that is served much better as a place to have a firebrick to close off the back. I then decided to add an extendable front stock support. The body is tack welded to a section of sheet metal which sits on the forge stand. The body is lined with 2 layers of 2600F rated 1” ceramic blanket, which has been rigidized and coated with ~1\4” of castable refractory, that is similar in composition  to plistix. The floor of the forge has ~1\2” of a bubble alumina castable refractory, and the whole interior was then coated with a kiln wash, the kiln wash was supposed to add an additional hard facing layer as well as be resistant to flux, but it froze overnight after applying it and the layer crackled, so it has some small protective ability against physical damage it doesn’t do much else unfortunately.

The burners are two ½” T-burners built (finally) to Frosty's specific specifications. ¾” run with a ½” branch. And a .23 mig tip that has been trimmed down, the mig tips are mounted in a drilled and tapped flare fitting with some pipe dope in the threads to prevent leaks. The flare fittings are screwed in the top of the pipe T which has been drilled and tapped to the same thread pitch as the threads on the exterior of the flare fitting, I used a steel washer as a spacer between the flare fitting and the pipe T as the threads on the flare fitting don’t bottom out and when screwed into the T would wobble. The flare fittings are then connected to gas rated ¼ turn ball valves which are connected to a common supply point by some very ugly if functional plumbing. I have a 0-30psi adjustable regulator at my tank. The burners are mounted to the forge using some 1 ¾” pipe that have two conduit locking nuts (one inside the forge shell and one outside) to hold it in place. I formed a nozzle on the interior of the forge using a wooden form(turned by a friend of mine) to hold the castable in the correct shape.

While writing this the temperature here has dropped to -16C so when I fired it up for the purpose of taking some pictures and video, I wasn’t getting great performance as my tank started icing up pretty quickly.

This is a video of the forge running, the first half is at 8 or 10 psi, and the second half is at 1.5psi
https://youtu.be/j1j43lz2sEE

Next are some photos of it running at about 3-4 minutes intervals, as well as photos of the thermocouple showing the temperature reached. The last photo shows the forge running at 1.5psi and the temperature it holds with in a 5F range.

 

 

Overall, I am quite happy with this forge, it does have hot spots as it heats up but the even out fairly well as the forge runs. I couldn't get it up to its max temp, or atleast the max temp I've run it at due to the xxxx winter here. Here I have attached a photo of what it did to the jackhammer but that sat in the forge for about 15 min running at 12psi on a warm day.

[VainEnd84]

Another thing to note, is that the mixing tubes that are currently installed are overly long, I haven't had time to shorten them yet.

[Mikey98118]

Thanks for posting your forge; I especially like how hot it gets with the two 1/2" T"" burners.

[Frosty]

On 10/28/2018 at 4:20 PM, Mikey98118 said:

And how did you decide what was good for you?

It burns off 1/2" stock before I get bored waiting. I usually turn it down though, I don't drive with my foot to the floor either but it's good to know it's there if I need it.

Good one Thomas but the northern lights only get one vote just like the other voices.

Frosty The Lucky.