Forges 101

[Frosty]

Now if you'd stop trying to bury me under that big X in your hard.

Frosty The Lucky.

[Another FrankenBurner]

When I first showed up on IFI, I spent a couple of weeks reading Forges 101, Burners 101, the t burner thread, and the NARB thread.  Then I pestered Mikey and Frosty in private for a while.  They both took the time to answer all of my questions.  Since then, I have pestered several other people.  I am grateful to have a place with such great people.

[Chris C]

There's a plethora of knowledge from the folks on this forum.........all it takes for access is intelligent questioning.  I've not been turned down by anyone when asking for help.  No "smart-Alec's" here on the forum.

[ThomasPowers]

For folks wanting a thick wall shell for their gas forge; this one is available at the scrapyard in Polvadera New Mexico, 20 UScents a pound.

     

[Frazer]

That ought to cover it! Might be a little tough to mount your burner though.... ehh cross that bridge when you get there.

Might make a pretty good forge + improvised anvil combination!

[Marcus_Aurelius]

Nothing quite like a chunk of schedule 8000 pipe, there are a couple of those THINGS at my local steel supplier, but not nearly as monstrous. 

[ThomasPowers]

Naval Gun, only to be expected out here in the desert...Scrapyard owner would love for someone to buy it---seems he is having trouble cutting it into pieces that he can ship/sell on as scrap.

[teenylittlemetalguy]

On 8/10/2020 at 1:11 AM, Frosty said:

Now if you'd stop trying to bury me under that big X in your hard.

Lol! I had to read that 3 times... love you man!

[Frosty]

I didn't notice the auto correct typo till long after edit time was up. That was supposed to be YARD, not hard. 

Truth is you guys were getting a little carried away there, I mostly just pass things along, I've picked up from others. 

Love  you to Tristan.

Looks like I missed a good meeting, I sure hope the pandemic eases up soon, I miss the club.

Jerry

[Mikey98118]

The safe bet

I don't agree with the popular view that larger interior spaces demand larger burners. Like so many other accepted ideas, people don't listen to all the facts and exceptions!!! Cubic volume of heated interiors has to be balanced against insulation and re-emission  of the interior's surface.; against how well their burner and exhaust openings are managed, and most of all, how hot the burner is. Twenty years ago it was a safe bet that 350 cubic inches of forge required a 3/4" burner to reach welding heat. With the materials, designs, and burners available now that same burner size to volume  scheme can reach 2750 F. Do we want to weld on steel, or cast it?

I'm not saying to ignore sound advice. 3/4" to 350 cubes is still the safe bet; the smart bet. After doing your best, you overachievers  can always turn the burner down and still enjoy the benefits of all your hard work. What I'm saying is not to accept a rule of thumb as your limit

 

[Frosty]

I agree Mike, a rule of thumb gets you in the ball park, they're not THE RULE. 

What we see so often are guys who need the rules of thumb, heck we all do, breaking into something new. Beginners are always working undiscovered country, especially when following directions by guys on the internet who's only qualification is a camera and internet connection. 

My general advice is: When you build a forge that works using the rules of thumb and burner size to volume to name but one, you'll start figuring out some of the finer details and your experiments will take you up the curve.

Down the road a ways I'm expecting to see 1/2" Frankenburners heating 350 cu/in to melting temps. Of course nobody should think of a Frankenburner as something built by rules of thumb. 

Frosty The Lucky.

[pre6422hornet]

I currently am almost done building my first forge.  Interior dimensions after blanket/satanite/matrikote will be roughly 4.5 tall x 5 inches wide x 12 inches long.  Frosty gave me some advice that I took and installed (2) 1/2" T burners instead of one 3/4" (thanks again Frosty!).  I have not let the forge heat up fully yet as I just fired it briefly to set the wool after rigidizing.  Today I buttered on the satanite and now she is quietly sleeping in the shop for a day or two. 

But from what I saw and felt, at only 7 psi and only kaowool, it was pretty xxxx hot after only running two minutes.  Once I get her complete I will post up pics and how she runs. 

PS the reason for the taller/wider than normal forge is I make cleavers and wanted them to fit....

[Mikey98118]

Show us a cleaver too; we love that stuff

[G-son]

On 8/10/2020 at 4:36 PM, Frazer said:

That ought to cover it! Might be a little tough to mount your burner though.... ehh cross that bridge when you get there.

With the proper machinery you can make the hole through the wall the right shape to BE the burner. Just add something to hold the gas jet and it's done!

[Mikey98118]

Yes, but just because we can do a thing doesn't necessarily mean we should. The devil is in the details. Not so much details of construction, but in maintenance. Whatever you use for the burner's end is going to be degraded by the gas flame; will that be a small item to maintain, or a real pain...?

[Mikey98118]

On 9/7/2020 at 2:20 PM, Mikey98118 said:

3” disc with a 5/8” arbor hole

Duh! Not likely.

[Mikey98118]

Small burner sizes

Naturally aspirated burners have large turn-down ranges. So, it seems a wide selection of burner sizes isn’t needed. But heat management is about more than how well fuel burns. The reason burners, whenever possible, are aimed on a tangent, is to cause their combustion gasses to swirl around equipment interiors; creating a longer distance from burner flame to exhaust opening. A long exhaust path increases the amount of "hang time” for energy to be deposited on equipment interiors. That seems obvious doesn't it?

    What isn't so clear is that most of the increased heat isn't gained by hot gases blowing farther at a given velocity; it’s through a continuing drop in velocity over that additional distance. Hot combustion gases begin to slow as soon as they leave the flame envelope, but small flames decelerate faster than large flames.

    The smaller flames of two 1/2" burners will use the same amount of fuel as a single 3/4” size, but will drop velocity much faster in a five-gallon propane cylinder forge, greatly increasing efficiency; because they can burn faster/hotter without creating a tongue of fire out the exhaust port. What about people who want to build a two-gallon forge or furnace from a non-refillable helium or Freon cylinder? They will need two 3/8" burners to do the same trick. Someone who wants to forge hand tools or cast jewelry in a one-gallon paint-can or three Lb. coffee-can forge or furnace will want two 1/4" burners to run it proficiently; the 1/4" burner is ideal for a “one-brick” forge that so many people attempt to run from a store-bought propane torch.

[Mikey98118]

One Brick Forge with Torch

This forge was dreamed up by a member right here on IFI last year.

[ThomasPowers]

I used to use a one soft firebrick forge run off a cheap propane torch back in the 1990's when I lived in Ohio and some winters found it too cold to forge outside and so did small work in the basement using such a forge.  Quite handy and an easy way to start forging small stuff.  (I also forged fine silver and copper in it.)

[Mikey98118]

What makes them so worthwhile now, is the improvements in both bricks and air-fuel torches. You can now get torch heads with a thin stainless steel flame tube, which allows the tube to be run through a much smaller hole in the brick, so that excess secondary air doesn't ruin performance, and better grades of insulting brick that can withstand higher forge temperatures; a win win situation. For a final touch, SS tubing can be run over the last couple of inches of the flame tube, to keep it from rapidly being oxidized away

[Mikey98118]

• , so this affords the opportunity to add insulating layers inside, as you come across suitable materials; these can consist of Morgan K26 brick, hard ceramic fiber board, High alumina kiln shelf, and re-emitting coatings. Giving you a generous amount of materials to choose from, locally.

Gotta be this or that

Why should ceramic blanket be left off material lists for box forges? Because ceramic blanket's main plus is its ability to conform to curved surfaces; it has minuses to go along with that. Therefore, it should be ignored in box forge design. The whole point of box forges is that they can be constructed from brick, hard ceramic fiber board, high alumina kiln shelf, etc. Why would anyone put up with the disadvantages of box designs, and then add the disadvantages of fiber blanket?

[Mikey98118]

Place your problems aside

Most box forges waste all kinds of interior space for simple lack of foresight. Top-down facing burners need a lot of height to keep large flames from impinging on your work, creating scale, and burning  some carbon content out of steel.

Some clever smiths started mounting their burners high on a side wall, thus blowing the gas over their work pieces; this gives just as much space for flames to finish combustion before impingement as vertical-down facing, leaves plenty of width for large pieces like axe blades, armor, etc., but allows wasted space to be divided in half. An all around winning choice. 

[Mikey98118]

On 10/22/2020 at 10:45 AM, ShaunAnderssen said:

Another question I have is on say, Forged in Fire, they're able to heat their steel to a nice bright yellow hot enough for forge welding, I've even seen them get their metal TOO hot. But when I look up the temperature output for a propane forge, it's only listed around 2,000 degrees.

That's a good question. The answer involves one of my pet peeves.

There are a number of way that flame temperatures are measured. The ultimate possible temperature of any given fuel gas can be calculated mathematically, and such numbers, both for air-fuel flames and oxy-fuel flames are listed. Air-propane flames have an ultimate possible temperature of around 3600 F give or take 50 degrees (it's been about fourteen since I last looked this up). In practice you would need something as complex as a jet engine to reach this goal

There are optical comparitors (spelling?) that can measure flame temperature accurately, for a whole lot of bucks, and a steep learning curve.

Finally, we mere mortals are reduced to looking at sales literature, and comparing one claim with another; this rapidly leads to the conclusion that, while every last salesman on earth may possibly not be a compulsive  liar, most heads of advertising departments probably are. The second conclusion reached is that most of the 'facts' they use boils down to one talking head imitating another

When I first started looking up propane flame 'information' (AKA outright lies) on flame temperature, most 'experts' claimed 2200 F for air propane flames from their various torches. During the following two years those claims reached 2450 F; when some of them started claiming 2600 F I gave up.

So, what can we rely on as closer to the truth than sales BS? First, forge temperature cannot exceed flame temperature; it works the other way around. Two different guys on IFI claimed their forges had registered temperatures of 2750 F with my burners. Aside from flattery, what evidence is there to support this?

Air propane flames have a spike in No production between 2800 F and 3200 F. The smell is unmistakable. Not every Mikey burner can produce it, but I have tested more than one burner that did.

Before you think this is a brag fest, let it be known that Another Frankenburner, on this very group ,has come up with a burner design that blows mine right off the road

I have looked over the burners they advertise on the Forged in Fire, and have no reason to doubt their claims, or to think they aren't worth every penny they ask. Hope these answeres help; they're the best I can do.

Mikey98118

Posted just now

That should have read "NOx"

Nitrogen oxides are produced in combustion processes, partly from nitrogen compounds in the fuel, but mostly by direct combination of atmospheric oxygen and nitrogen in flames. Nitrogen oxides are produced naturally by lightning (Wikipedia quote).

[Mikey98118]

On 10/22/2020 at 12:21 PM, Mikey98118 said:

Another Frankenburner, on this very group ,has come up with a burner design that blows mine right off the road

And since we are looking for proof, what do I base this conclusion on? Well, a properly constructed Mikey burner's flame retention nozzle will reach bright orange heat out in the open air, when burning propane. The same burner will reach yellow heat on propylene. Propylene burns about six hundred degrees hotter than propane in an oxy-fuel torch. I think it is safe to estimate four hundred degrees hotter in an air-fuel burner. I consider this suficient proof to conclude his flame are above 3200 F. We should ask him if he gets an ozone smell from his burners. I'm betting he doesn't 

[Mikey98118]

In recent years there has been growing interest in traditional metal trades, such as forging and casting. While the equipment, tools, and skills needed for each endeavor are similar, there is strong resistance among beginners to combining these pursuits. Tunnel vision is only to be expected in a novice; going forward, 3D printing should make the utility of casting more obvious for art and tooling.

    Hobbyists commonly look for ways to profit from their avocation, which is where their troubles start. Whether you dream up a better widget, or just “go into art,” opportunists will be overjoyed to undercut your product shortly after you market anything worthwhile. If what you produce requires little knowledge or effort, it also won’t take much for it to be copied to death. “Keeping things simple” is okay, until that includes keeping things easy; don’t “curse the locusts” in that case.

   

    The main difference between a casting furnace and a tunnel forge is that the furnace stands vertically, and most forges sit horizontally. Some people mount their heating equipment in a cradle so that it can be moved back and forth between the two positions, employing it for both jobs. A hinged and latched door on a box forge, will allow crucibles to easily be moved in and out, greatly enhancing its utility. The synergism in combining these two crafts can be endless.

    The beginning of forge and furnace training is the study of burners. The end point of burner design is the equipment they heat. Whatever plan you favor, every choice made leads you toward your desired goal--or away from it. One half of heating equipment’s utility comes out of its design; the other half rests on how well you execute its construction. Muff ether one, and you create an inefficient mess. Every part of a forge or furnace has a purpose; find out what that that is, and you’ll design well.