Forges 101

[VainEnd84]

Thanks Mikey, I'm quite proud of it. It is a little big for much of what I do so I am planning on making a smaller, or atleast a shorter forge, probably with a larger diameter inner chamber, and I'm thinking of using a pair of 3/8" mikey burners. But as it's so cold I'll be spending the next 4 or 5 months using coke to forge and working on the burners, I just need to assemble all the components! I feel like I'm probably going g to end up with like 5 or 6 forges for all of my wants and needs. I feel the start of a problem 

[Mikey98118]

I  like to encourage people to make ever smaller burners, but if you are planning on building a shorter forge a single 1/2" burner would probably constitute a better use of your time. Having salved my conscience...ket ne know if you need any help with the burners

[VainEnd84]

Well I am a bit of a glutton for punishment, and since I like tinkering g so much I'm probably going to build a 3/4" because it seems the most forgiving, then a 1/2", and then 3/8", because I can, and I want to, and I have 5 months of forging with coke, outside in the cold to look forward to . And that reminds me, I need to fix my blower .... this hobby sometime feels like a full time job! But atleast it's more fun 

[Mikey98118]

It is a good plan to start with larger burners, and use what you learn (especially about using diamond coated burrs to ease your work), before tackling the smaller models.

[b1llvance]

Hi everyone.  I've been lurking for a while now but think I'm going to give into the itch to finally build something. I've come up with a rough idea of what I'm planning, and spent a little time on Google Sketch-up trying to illustrate it.  Take it easy on my Sketch-up skill, today was my first time playing with it!

Anyway, I'm planning on a 3/4" NARB updraft configuration.  I'd like the forge chamber to be 6" diameter not accounting for an approximate 1 inch floor.  The inner castable would be 3/4" Kast-O-Lite 30, with 2x 1" layers of rigidized wool wrapped around the castable.  All of that would be wrapped in 20-22 gauge sheet metal.

Something like this:

Due to my Sketch-up skills, everything is polygonal, instead of nice and smooth, and I also couldn't get the burner holes to be actual holes so they show as cylinders instead. My plan is to cast the tube around a piece of 6" pvc pipe with something (cardboard or wood) where the burner would be to make the opening.  Then when I cast the burner, I'll use a piece of the pipe to make sure that right hand portion of the burner has the same profile at the rest of the tube. The plan is to have at least a 1/4" gap around the burner to fill with wool and allow for a little error. I'll wash the entire interior burner and all with a refractory wash and figure out doors later. 

I have a couple of questions....

First, what is wrong with this plan?  I've read a lot on here, but not all 34 pages. I've read the NARB thread, and multiple build threads and again a lot of the burners thread but not all of it.  What am I missing? I know I'm probably complicating the design more than it needs to be, but I have fun building this kind of stuff so I'm okay with that as long as it works. I like the idea of a up draft, just to keep as much heat off the burner face as possible, and I was trying to move it as far to one side to make the usable floor as wide as possible.

Second, do you think there is any benefit of canting the inner most burner holes a touch toward the edge?  My thought was to get the flame away from whatever metal is on the floor as much as possible and it should swirl around the tube in that configuration too.

Third,  Thoughts on the forge floor? I was planning on using Kast-O-Lite but I've also been reading about Bubble Alumina. In either case I think I would cast the floor separate from the tube in case I have to replace the floor for any reason. I would most likely put a thin 1/4" layer of rigidized wool between the bottom of the tube and the floor, more as a cushion to protect the tube than anything.

Finally I originally had planned on adding a couple of extra burner holes, I wasn't sure if the extended length of the burner holes in the outermost row would cause extra friction and cause back pressure.  I figured I'd add a couple of extra holes and then also cast a couple of plugs for them in the event that I didn't need them.  Do you think that would work, or would propane leak around the plugs and cause issues?

Thanks for everyone's help here.  This place is such a great resource and all the people here willing to share their experience are invaluable.

Bill

 

[ThomasPowers]

Why updraft? Seems like a way to have a lot of crud "drop" into an area that's hard to access to clean out. (When the forge is NOT running, and possibly some when it is running...)

You also lose floor space, a limited resource in a 6" diameter forge.

[Buzzkill]

First off, the updraft configuration.   I have done this and there are some good reasons or advantages to this style IF it is in a flat floor with a removable shell.  That allows you to put different size and shapes of shells on without having to worry about cutting and/or casting a burner mount in each one.  However, it does eat up some of your floor space. For pieces that aren't straight and flat you may find that they only fit in your forge with some of the stock blocking some of the flames from the burner.  For a cylinder with a NARB I'd suggest looking at this thread for a reasonable compromise:

https://www.iforgeiron.com/topic/60067-it’s-finally-burning-a-first-build-story-photo-heavy/

You'll probably be better off using something other than PVC for casting the tube.  Someone on here (Frosty maybe?) talked about rolling a section of linoleum into the right shape so that after your casting cures you can roll it inward to release it.  I've used cardboard sonotubes and just burned them out after the casting cured.

I've never used bubble alumina so I can't help you there.

I don't know about canting the burner holes either.  However, if one of your goals is to create a swirl (and that's a good thing) I don't think you want the flames of the different rows fighting each other.  For me at least, the forge gets up to temperature well with holes that just point straight out of the burner block.  It would be a potentially interesting area of experimentation, but it's certainly not necessary to have any angle to the "nozzlettes" coming out of the burner.

Yes, you can cast extra holes and plug some of them later if you find that you have too many.  When I was determining the correct number of holes needed for my NARB I cast way too many holes to begin with and had to plug off 6 or 7.  I just used small pieces of ceramic blanket for a temporary plug and then I recast the burner once I determined the right number of holes.  If you planned on a more permanent plug I'd suggest covering any blanket plugs with a little castable refractory to seal in the fibers.  Since a NARB has no blower to force the fuel/air mixture out the holes, the number and size of the holes have to provide the right amount of back pressure when the burner is in operation.   Too many holes and the burner will backfire (flame burns briefly inside the plenum) even at moderate pressure.  Too few holes and the flame may be blown out as you increase the pressure.  A little bit of flame lift off the face of the burner is normal when everything is cool, but the flame should not blow out completely.

[Mikey98118]

The whole point of ribbon burners are to produce short multiple flames, which slow much more rapidly than large single flames. As a result they simple don't need anywhere near the distance between burner flame and impingement area of single flame burners. In other words you are solving a non-problem with your choice of burner position.

[b1llvance]

Thank you all for the quick response. A couple of quick follow up questions. 

Buzzkill-Any specific reason you would want to be able to change out the shell?

Mikey- Thank you for the input. So if I rotated the burner to get it off of the forge floor is there any position that would have advantages over any other? 

Also regarding the PVC, I remember the mention of linoleum. I’m just not sure I’ll be able to get a scrap piece. Seems like everything around here is pretty thin vinyl nowadays. I was thinking of splitting the pvc in half and taking a small strip out of it. If I cut a strip to replace it, once the castable was dry I could pull the strip out, and the two (semi) half’s would have room to swing in. 

[Buzzkill]

7 minutes ago, b1llvance said:

Buzzkill-Any specific reason you would want to be able to change out the shell?

Sure.   For the sake of discussion if you were forging a number of items that required a greater distance from floor to ceiling to fit in the forge easily you may want to make that job easier on yourself.  You still have to pay attention to the overall volume of the forge chamber so you don't try to operate outside what the burner can handle, but you will most likely find that some pieces won't fit into your forge chamber the way you'd like.  I have 2 sheet metal screws on each side holding the outer shell in place on my forge.  So far I haven't made any other shells, but it will be quick and easy to change them out when I get around to making others.

[Mikey98118]

3 hours ago, b1llvance said:

is there any position that would have advantages over any other? 

Yes somewhere around 10 o'clock (or 2 o'clock), and prefereably aimed as much upward as inward.

Most people make the mistake of thinking that having the flame placed nearer the work will transfer more heat; that is only true in weak forges with a low level of incandescence. You want your forge to reach at least high-yellow incandescence; that will be above 2000 F; at that temperature more heat is transferred through radiation than from the hot forge gases. You want to forget about any other kind of heat transfer, and think of your forge as a form of incandescent oven, because in the practical sense, that is first and foremost what a good forge is.

[b1llvance]

Mike I’m a touch confused and I’m pretty sure it’s me and not your explanation.  I get the radiant oven concept, that’s been drilled into my head reading all of these threads. But I’m confused about the burner placement. If I mount it at either 10 or 2 isn’t it going to be pointed darn near the center? And if I mount it horizontally and point it from 10 to 2 it’s still not pointing “as much upward as inward” or maybe that’s the exact definition of horizontal?

[stevomiller]

I believe he’s saying to place the burner aiming on a tangent wher the point of intersection of line and arc is at 2 o’clock. This would make the flame still shoot up towards the ceiling, and it would follow the arc around the inner wall, vs just shooting it straight across the forge or aiming it downwards towards the floor. Mikey did I understand you correct?

[Mikey98118]

That's exactly "what he's saying" Steve. And I think you're saying it better

[Mikey98118]

A reason for everything

So, while we're on the subject of burner positioning;, on another thread a guy placed his burner high on the shell and facing across the interior space; not down toward the floor; this can be a superior position in a box forge. The trouble is that his forge shell is a five gallon propane cylinder; its a tunnel forge; that means that the flame is going to impact on the forge wall in just as short a distance as it would if the burner faced down toward the floor, so there is no distance gained, and it will impinge on a fairly thin castable forge wall at best, or on a very thin seal coat over ceramic fiber insulation at worst, instead of on a floor that has been prepared with an extra layer of insulation under a thicker cast area, or a removable high alumina kiln shelf; either of which makes a better area for the flame to impinge on than a forge wall.

Box forges usually have insulated brick walls, which added to the longer distance between flame tip and impact area allow a horizontal flame not to overheat the target area; not so in a tunnel forge.

What is the lesson here? Every design decision you make in a forge, should have good reason behind it; not "monkey see, monkey do."

[b1llvance]

So I just want to make sure I'm understanding all of this right.  If we are talking about a horizontal cylinder forge with a ribbon burner, and in my case I plan to make the face of the burner the same profile radius at the inner castable liner, why does burner placement matter if we are placing it at a tangent to the cylinder?  If we keep it off the floor to not give up that valuable real estate and don't point it directly at the floor, say the 8 o'clock position pointing down toward the floor.  Flame impingement on the wall will be exactly the same anywhere it is placed due to it being placed on a tangent. If anything I would think placing it at 4 or 8 o'clock facing up on the tangent would produce the most swirl before the flat floor had any impact on the swirl.

Please don't take this as criticism of your suggestions, I still think I may be confused about the tangent placement in the first place, I'm just trying to understand the why behind the how.

[Daguy]

5 hours ago, b1llvance said:

If anything I would think placing it at 4 or 8 o'clock facing up on the tangent would produce the most swirl before the flat floor had any impact on the swirl.

Because it's my build, and I started the thread, I really didn't want to be the one to draw attention to this, but did you follow the link to the thread Buzzkill suggested you read,

 https://www.iforgeiron.com/topic/60067-it’s-finally-burning-a-first-build-story-photo-heavy/  ?

If not, please do.  There are links toward the end of an only 2 page to youtube videos that may answer your questions better than paragraphs of responses, including some slo-mo that slow it down enough to see whats really happening inside the forge.

Daguy

[Mikey98118]

7 hours ago, b1llvance said:

Please don't take this as criticism of your suggestions, I still think I may be confused about the tangent placement in the first place, I'm just trying to understand the why behind the how.

You aren't confused about placing. You do seem to be confused about the extreme difference between single and multiple flame burners, though. The whole point of multiple flame burner heads (such as ribbon burners) is to get the hottest flame possible (which generally means a high speed flame or flames), while keeping as much hang time as possible (which usually means a slow flame). Multiple flame burner heads solve the conundrum by featuring many small flames, which start out fast, but naturally slow down far quicker than large single flames. They do such a dandy job of putting on the breaks that they can completely combust in a few inches.

Every advantage you gain in a forge tends to come at the expense of some other factor; therefore positioning the burner to attain far more distance from the work than is needed is a waste, and has already been pointed out will come at the cost of exposing your burner heads flame holes to falling debris, such as flux; why go there?

[Thursigar]

I've been reading this topic, burners 101, wayne's website, and Zoellers website trying to wrap my head around building a forge. I think I get the general concepts, but am unsure of the some of the details. My skills arent as good as b1llvance, but I did do a sketch of the design I have in my head for a 20 propane tank forge. 

Here are my questions: 

1. Is 1/4" castable refractory a good measure? I've seen everything from 1/8" to 2 inches. My understanding is the prupose of the refractory is to protect the ceramic blanket, add durability, have a good surface to apply IR reflective, and make it thin so its not too much of a heat sink. 

2. Welding isn't an option for me. So when I cut the top off the top off to be able to insulate, will a hinge bolted on work? Or will any holes in the frame cause issues? Same with bolting legs on? I considered just bolting down two iron angles and placing it between them. 

3. Once again since welding isnt an option, will 3/4' floor flanges secure a frosty T burner? 

4. Should I incluse the .5 kiln shelf into the equation for space-burner ratio? I assume no but my shelves wont be a snug fit either.

4. Notice any other flaws how I am picturing this design in my head? 

 

Thanks for all of your help. And Mikey, I LOVE the well-written tidbits!

 

[b1llvance]

Thank you all for the feedback.

Daguy- I had read your thread before and watched the slo-mo videos.  It's a great build, and thank you for sharing.  The biggest reason I was looking for a different burner placement was I didn't like the idea of the face of the burner heating so much and the heat creeping back into the plenum.  I know Frosty solved that problem by increasing pressure, and in all reality I most likely wouldn't be using the forge for long enough periods for it to be an issue,  I was just trying to build in a structural fix.

Mikey- Thanks for all of the replies and information. Originally I wasn't worried too much about flux debris, as I'm so new to this I didn't figure I'd be doing much forge welding, but I should probably assume at some point I'm going to want to give it a go. It took me a while to get the hang time/complete combustion/swirl right in my mind so I appreciate you sticking with me on it!

Thursigar- Your sketch looks great.  The labels are way better than the way I wrote it all out to explain it.  I'm sure the other guys will chime in here but I know I've read Mikey say he's never had issues with pop rivets and bolts whereas welds can sometimes be problematic.

[Thursigar]

I would edit my original post, but I am struggling to see if that is possible...I've obviously misnumbered my questions. 

6. Anywho, I know that the burner isnt suppose to go INTO the forge itself, but I guess I made an assumption about exactly where it ends. I know you can create a "flare"-like effect using the kastolite, but how far into the kaowool or kastolite should it be inserted since there is potentially 2 inches of material? Im thinking perhaps my plans were off and I should move it back to just past the first layer of kaowool (to protect the shell) so that it has a chance to flare out? 

7. I've read lots of items regarding burner angles, and how its suppose to hit a durable surface (which is why Im using a kiln shelf). I am currently aiming for the outer edge of the shelf as not to create a hotspot on it. But I've now read that other people LIKE the hot spot effect to better target areas of a peice of metal for bending etc. I think that makes more sense?

4 hours ago, b1llvance said:

Thursigar- Your sketch looks great.  The labels are way better than the way I wrote it all out to explain it.  I'm sure the other guys will chime in here but I know I've read Mikey say he's never had issues with pop rivets and bolts whereas welds can sometimes be problematic.

 

You are too kind. Thank you for Mikey's thoughts on bolts behind the kaowool. 

[Irondragon Forge ClayWorks]

Your diagram looks good to me. I would go with 1/2 inch of Kastolite. Of course as my wife says about my over building things, 2 nails are good so I use 4.

BTW the edit feature is only active for a half an hour.

[Mikey98118]

8 hours ago, b1llvance said:

Originally I wasn't worried too much about flux debris, as I'm so new to this I didn't figure I'd be doing much forge welding, but I should probably assume at some point I'm going to want to give it a go. It took me a while to get the hang time/complete combustion/swirl right in my mind so I appreciate you sticking with me on it!

Thursigar- Your sketch looks great.  The labels are way better than the way I wrote it all out to explain it.  I'm sure the other guys will chime in here but I know I've read Mikey say he's never had issues with pop rivets and bolts whereas welds can sometimes be problematic. 

I don't think any of us is saying it is likely to be a big problem; just that it is an easily avoided problem.

It is true that I have never had a moments problem from pop rivets in forges. Note that I use stainless steel pop rivets though; never aluminum. I also recommend self-threading screw screw for those who don't have a rived gun, or are worried about the strength of pop rivets. I spent over twenty years as a multi certified welder. So why don't I recommend welding a forge together? Because  few newbies understand how to weld forge parts in such a way as to allow them to withstand thermal cycling without distorting the forge shell. Why take that chance?

32 minutes ago, Irondragon Forge & Clay said:

Your diagram looks good to me. I would go with 1/2 inch of Kastolite. Of course as my wife says about my over building things, 2 nails are good so I use 4.

I would not go below 1/2" thick layer of Kast-O-lite either; I would never go that thin with any other cast refractory. Kast-O-lite is tough! Nevertheless, I would not trust even a 1/2" shell of castable refractory without thoroughly rgidizing the insulation that cradles it.

Four nails is good.

[Mikey98118]

Ceramic fiber insulation has good resistance against shear stress; that is to say, if you hold a two foot wide length of it between your hands and try to pull it apart, you will likely fail. Yet layers of the same fiber will de-laminate with near zero resistance.Ceramic fiber insulation is quite compressible until it is heated a few times; afterward it become very firm. In the words of Ron Reil "it takes a set." It also sheds it tendency to de-laminate at that point. Colloidal silica rigidizer takes that "set" a stretch further, causing that firmness to harden into a rigid solid; this results in a minor tendency for a large surface (such as a castable refractory shell) to move about when cradled in the firm "heat set" insulation, and to move not at all after the insulation is rigidized, locking the fiber in place. So, the three stages of this insulation would be "spongy" " firm" and "frangible solid".

In a different way thin sealant coating, such as Plistix, are greatly toughened when the fiber insulation becomes a solid, because "firm" provides much less protection from tears in these coatings than "solid" does; even a frangible solid.

[Mikey98118]

Frangible; capable of being broken.

So something that is easily broken could be described as highly frangible. Most grinding stones, although very hard, are also described as frangible; in fact that is needed to assist their function. Pottery is hard, but is also described as frangible, because it is easily broken by a blow or fall. More to the point the foam which fills a fiberglass surfboard is frangible, but supports the board's fiberglass skin, just as rigidized  ceramic fiber insulation supports the ceramic "skin" made by seal coats.