Mikey98118

Forges 101

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What I do know about vertical forges is how to put a mighty efficient one together; that, after all, is just the nuts and bolts of things. What I don't know is the why of them. Some pretty well known knife makers like this kind of forge, but I don't know why; possibly because of the effects of buoyancy? Tell me what you think of them; inquiring minds want to know:)

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Please give us a run down of how you make a vertical cylindrical forge Mike. I'll bet we have very different approaches and there has to be a better middle ground if we combine.

Frosty The Lucky.

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ouch! You just asked me for a how-to; that will take two or three days to type up, and will almost certainly need input and revision from the rest of you guys, since I'm clueless about the most important design element; the why for of them. Still, vertical forges is obviously of intense interest to some blacksmiths, so stay...

Leaving aside the buoyancy effect, with its tendency to speed up the flow of super-heated combustion gases through a vertical forge or casting furnace, thus cuasing increased heating in the equipment-- paid for with an increase in fuel fuel consumption--lets look at the changes in physical requirements, which mandate changes in the forge's construction:

(1) The heating stock cannot rest does not rest on a horizontal floor, let alone an external cross bar, but must rest on a floor which is the bottom of the forge; no system of clamps to hold the stock above the floor is practical.

(2) At lest the the edge of any top opening for introducing stock and passing exhaust gases through will need to be even tougher than the floor, to slow up damage (chipping and cracking) from the passage of parts in and out of it.

(3) The entire expanse of the hot-face also needs to be something pretty tough at heat, sence it will also get banged into by parts; although not as often of as hard as the exhaust opening and floor.

I would recommend a good high alumina refractory for the hot-face (abpit 1-1/2" thick, surrounded with ceramic fiber). The top opening should consist of a high alumina round iln shelf, which has been drilled out with a large hole saw, or made with a small cement bit and an carbide encrusted reciprical blade from Harbor Freight Tools; using expensive tools for occasional use is silly.

The floor should consist of a round high alumina kin shealf over a 1" thick layer of of the same refractory, over a 2" thick layer of ceramic fiber blanyet or board, which should be placed over a thick laryer of Perlite. If blanket is used, than the floor should deliberately be heavily compressed and restrained be temporary scewss therough the shell wall while the vertical hot-face is being formed and heat cured.

Ideally, the top kiln shelf should rest on the on the vertical wall, and inside of a steel shell. It should also feature six sheet metal screws placed so that about 1/8" of gap remains between them and the shelf's top suface: this prevents the shelf from moving enough when struck to cause damage, will providing more than sufficient space to safely allow the shelf to expand from heat.\

The burner opening must be placed near the forge floor, placed at a tangent, aimed slightly downward, with about  about 1-1/2" of clearance kept between its bottom edge and the floor. The utility of an adjustable air choke increases in a vertical forge, as it can help balance the exhaust flow, which is going to be much higher, to do buoyancy.

Wnat is the practical difference between a fan-blown  and a naturally aspirated burner if placed in a vertical forge? I predict that the NA burner will provide as much flame per second as a fan-flown version, but can provide a much hotter compact flame at the same time. Why can rather than will provide? Because it's up to its maker to produce a really hot burner flame; if he/she wants to build a second or third rate junk burner, its flame will be no hotter per cubic inch than a fan-blown flame; maybe not even as good.

Finale note for today: One of the features of vertical forges is a huge reduction in back pressure against the burner; that means that the thorny issue of how small to make the exhaust opening is correspondingly reduced.

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Hey mikey take your time... this is worth the wait. But its good info so far

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I guess I should've been more clear when I said we should compare vertical furnace notes. I thought we could start at the fundamentals.

The original reason for building a vertical cylindrical forge was to eliminate scaling and decarbing blade steel in a gas forge. This came about before folk discovered how to tune burners for neutral or carburizing flames. I'm in the run them a BIT rich camp but that's personal choice and situation driven. Don Fog popularized the vertical cylindrical forge probably 25-30 years ago he was making them before the internet went public and I got to meet him online.

Anyway, much of what you say above is true Mike and not that fundamentally different than any efficient gas forge. I have to differ with you on how you approach and handle boyance, (convection). Bernoulli observed and noted that hot "fluids" don't rise, cold "fluids" sink and displace the hot. I know that sounds pretty nit picky but it's there and represents energy in action.

In a vertical cylinder I get to use one of my favorite mechanisms the vortex. As you state orientating burners to induce a vortex is paramount in a cylinder or induced back pressure just kills efficiency. Orienting the burner so the vortex is descending prolongs contact of the flame and the subject being heated, most commonly a crucible. A cylindrical forge with top access is actually using waste heat from the furnace, the hottest zone is between the burner port and bottom of the chamber.

This brings to the fore another reason Don liked the vertical cylindrical forge, the top of the chamber was not only slower to heat material it heats VERY evenly as there is NO hot spot caused by flame impingement. Both advantages of a vertical cylinder are much harder to attain in a horizontal cylinder. Excess oxy is a matter of tuning and preventing outside air being drawn into the chamber. Even heat is tougher but hardly HARD to attain.

Personally I feel the vertical cylindrical forge has run it's course and is no longer desirable for general or blade forging. The one exception is heat treating long implements, swords for the most part.

Were I building a melter where I BELIEVE a vertical cylinder is desirable this is the general design I'd use. I'll use a moderate size suitable for 2 gas burners, I don't care which main type, NA or Gun we'll just assume they're built to do the job properly.

I place the outlets above the mean level of the melted material in the crucible oriented tangentially just lower than level forcing the vortex downwards in the cylinder like cutting a screw thread. The prime reason for downward & tangential orientation is to prolong contact of the flame and crucible and maximize heat transfer. 

The melter chamber has no exhaust port on top of the chamber.

As in most melters the crucible rests on a raised block. In my design the exhaust port is in the floor where the block is. Convection isn't a factor, exhaust is expelled by the force of the burners. The exhaust leaves the chamber and is then directed into the space between the flame face and the outer furnace wall where more of it's heat is transferred to the walls. This is known as a "Recuperative Wall". It's purpose is to prolong flame contact with the furnace and hence the crucible.

Only after the flame exhaust has reached the top of the annulus in the recuperative does convection remove the exhaust. The furnace has a short stack to induce convection if the flame force isn't great enough to exhaust waste gasses.

That in general is the cylindrical furnace design I believe most efficient. Applying it to a forge would be a challenge and not something I'd undertake unless generously compensated. ;)

Frosty The Lucky.

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You are certainly right in your claim that buoyancy places no part in a tube forge (convection is to general a term to suit me, as it is caused as much by fans as by natural displacement these days. I'm so used to buoyant flames in hand torches, and air/fuel burners out in the open air, that I mentally asigned it for vertical casting furnaces as well, despite all the evidence in front of my eyes for sixteen years:unsure:

I had wondered how much advantage was left in a vertical forge, since burners have come so far; doesn't seem like much. I  don't believe that a forge which has been made properly, so that it works as a radiant oven, well have any problem with hot spots, so long as it is running at yellow-white heat or better.  For very even heating within a cooler forge being used for tempering, there are ribbon burners. What than is the point of a vertical forge anymore?

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So the practical answer to how to get your forge worth and cast in it to has been put right under my nose still again; it was recently posted on page 7 of the Burners 101 thread; how obvious! Why didn't I see it before?

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"As in most melters the crucible rests on a raised block."

I think you must have meant to call it a pedestal, which is basically disc shaped?

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One benefit of the vertical format is your burner(s) wont suck exaust gasses... i assume since they should be below the exaust ports

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On 10/4/2016 at 4:17 AM, Mikey98118 said:

"As in most melters the crucible rests on a raised block."

I think you must have meant to call it a pedestal, which is basically disc shaped?

I'm not a caster so I don't know what if any shape they use or if it matters. IIRC the guys I know use half a fire brick. Oh the term came to me in a conversation, I think they call it a "plinth." Of course I could be way far off base and thinking of something else.

TFT: Naw, Don wasn't concerned with exhaust contaminating the intake air, he runs or ran gun burners below the forge. In the day when we were on the same email list the only reason he talked about for vertical forges was to control scaling in the forge.

Frosty The Lucky.

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My mistake, I thought you were wondering about the origin. I thought I'd stated my opinion of how pointless it is to go to the hassle of making a vertical forge already. The ONLY reason for them was to ensure complete consumption of oxy and prevent scale forming in the fire. Properly made and tuned burners makes verticals a waste of time and energy.

That's right, you disregarded the advice from all people who actually KNOW what they're talking about and using Plaster of Paris anywhere in a forge.

^_^

 

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Hey the only reason i went with the plaster is for the weight of it and heck i would of used gold if only it was cheaper........:ph34r:

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You want your forge HEAVIER? Are you not going to put a stand under it?

Look, I understand, you've gotten yourself emotionally invested in making a vertical forge work, I get it. I think most of us have talked ourselves into a corner and had to make mistakes other folk were warning us about, I know I sure have.

I shouldn't have replied about your burner comment. I'm having a hard time not being sarcastic. I don't want to discourage you from the craft I'd just really rather see you making something practical. Then again I've been wrong before.

I'll just watch quietly.

Frosty The Lucky.

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Emotionally invested? More like financially invested.

And yes i said heavier and i dont have a stand(yet) and want to get forging asap so im not gonna wait to make a stand.

And sorry but noone said a vertical forge was a mistake untill now .

Unless youre still hung up on the plaster... which noone has pointed out a reason not to use it how i have... under kitty litter under kastolite under insboard and under the major heat.

Ill just make my forge quietly then

 

 

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It isn't that a vertical forge is a mistake, but simply that the advantages of using one got passed by due to technical improvements by everything else over the last decade. If you make the forge with your eyes open, it will be okay to live with. Frosty has said many times that there is no such thing as a perfect first forge. I personally know that there ain't no such thing as a forge that anyone is perfectly happy with by the time it is completed, because we all get brain storms, just a little to late in the process; not even if it's our hundred and first one. Aside from proceeding with your eyes firmly shut, there is nothing worse that faces you than stalling; so go force and build the dragon brave knight ;)

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By emotionally invested I mean you got your mind set on this design. Before you started you asked about verticals and more than one person said a vertical forge is obsolete, why and more work that they're worth. If you were in a hurry to get forging . . . How long have you been working on this one now?

About me betting emotionally invested, it's a button of mine when someone asks a question then argues with the answers. Not using the answer isn't a problem, it's listing all the reasons why the answer is wrong that gets to me. It didn't before the accident and it's an issue I'm working on. No, it doesn't actually matter to nor bother me if you build things your way. That's what blacksmiths do we do things our way.

When I read my posts it's pretty obvious I was getting cross for no good reason. I'll back off this topic and not because of you doing what you wish, I'm the one with the issue and causing friction.

Frosty The Lucky.

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59 minutes ago, Mikey98118 said:

Valerian works for me; when ever I get cranky the wife asked if I've had my daily four pills of it...

It's a cross between TBI issues, broken neck headaches and low blood sugar.

Frosty The Lucky.

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21 hours ago, ThomasPowers said:

Still one up on me!

Which one?

Frosty The Lucky.

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Burner opening ports revisited:

Very few burner designs can achieve total combustion in their primary flame envelopes; therefore, most burners need some secondary air from  another source. The problem is that anything more than just enough secondary air cools the forge without producing anything you want added in your forge. Unfortunately, most forges acquire secondary air through completely open burner ports. Without some form of adjustable choke on the source, induction provided to it by the burner's flame, brings in far more secondary air than is needed. Yet, you really want your secondary air to enter the forge quite close to the burner flame(s) in order to completely consume it as early in the course of its passage as possible. Why? Because an efficient forge works PRIMARILY as a radiant oven, and only secondarily like a gas stove. 

I have noted that most burner port tubes only have run row of thumbscrews to hold the burner in place. Two rows; each of three equally spaced screws also allow the burner to shift its aim somewhat Think about that when you are deciding how much larger than the burner it should be. Since where on the the floor the flame impinges has everything to do with how well the flame circulates, dead-bang aiming is kind of important, yes?

Finally, the closer the burner tube is to the burner it surrounds the more heat it will transfer to the burner; why would you want that?

So, maybe you're thinking that moving the burner a quarter inch won't move the flame target area much. But we are considering aiming points, with will move the impact area a lot more distance by the time it reaches clear across the forge to the floor.

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Of course, fine tuning the burner's aim can't overcome placing the burner opening in the wrong place to begin with. The right burner port tangent on a tube forge is generally accepted as twenty degrees down from top dead center; not forty-five degrees as is seen all to often. It seems  that people are tempted to use the greater angle, because nobody ever told them that the burner tube doesn't face straight into the forge from whatever position it is set into the shell; It also is aimed at a tangent. So one error leads to the other.

You want to have your floor in place before welding, brazing. or trapping the burner port tube in position on the shell with hard refractory. Six thumbscrews also allow a spare bit of pipe to hold the port tube in exact position for permanently mounting it correctly in place.

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With the exception of ribbon burners, a forge with a built in burner portal has the capability to easily change out one burner for another, which makes oversized ports all the more handy.

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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..

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