Gas Forge Layout Opinions

[NoGoodWithUsernames]

I'm building my gas forge with what I could find and that ended up being part of an old water heater, slightly larger diameter than a propane tank forge, and I want to have some more experienced opinions regarding my layout before I cut holes and rigidize and cement everything in.

The tank is 16.5" ID x about 14" long (not including shallow dome on one end)

I have the end dome with 1 layer of wool, then two layers around the outside leaving me about 11" ID (not counting 1/2" of cement all the way around of course leaving me with 10")

I think layering a few extra pieces on the bottom would be beneficial to both reduce volume and get closer to a flat floor without having to pile up the cement on the bottom of the forge as much. Is this a good plan? If not what are better options?

Also I think having the burner offset aids in "swirl" and helps forge efficiency? Should it end up about flush with the inside of the forge or be recessed into the cement/wool lining a little bit?

Here is a photo to help visualize what I have/am planning.

[Mikey98118]

Your ideas about the ceramic fiber are pretty good, except you need a double layer at the ends of the forge; not the single layer you describe.

I hope you are planning on using refractory; NOT cement!

The position you show the burner in is wrong. Place it at two o'clock with the same amount of tangent, but slanting inward; not outward.

Yes, your idea about raising the floor is sound; especially in this larger cylinder diameter, which will also widen the floor more like a "D" shaped forge; a win-win outcome

If you run a little short on ceramic fiber insulation for the floor, Perlite from the garden department of your local hardware store, will work just fine as a supplemental layer of insulation between the fiber and the steel shell in the area of the floor.

[NoGoodWithUsernames]

Mikey,

Thank you for the feedback! I'd rather here "you did this part wrong" and be able to correct it than to waste time and materials!

I'll get some more wool on order to double up the ends, I did not calculate it into my order the first time so what you see in the picture is what I have except a few scraps. 

Yes refractory cement, NOT regular cement. Just called it cement because I was too lazy to type out refractory every time. My bad.

Burner position sounds good easy enough to move still since I haven't drilled anything.

Good to know about the floor and Perlite. 

 

Thanks again, and if anyone else has input or constructive criticism or even wants to poke fun at it feel free!

[Buzzkill]

47 minutes ago, NoGoodWithUsernames said:

Yes refractory cement, NOT regular cement. Just called it cement because I was too lazy to type out refractory every time.

No, not refractory cement.  Pretty much anything called "cement" or "mortar" is designed to stick pieces together, not to be a hard flame face subjected to constant high temperature flames that exist in a forge.  You want a castable refractory material.  The usual recommendation on here is a water setting insulating high alumina castable refractory such as Kast O Lite 30.  Refractory mortar or cement may work for a short time, but they will typically degrade much faster than the aforementioned material.

[Paul Kin]

Thatll be a nice size forge for big work! You might need a 1” burner though? If I understand your dimensions right, even if you filled it half way up for the floor so its a half circle, youd be at just about 400 cu/in no?

Anyway, Mikey and Buzzkill know so much more then me about these things its not even funny! So Id go with what they say over anything. This is just something I noticed and may or may not be correct!

[NoGoodWithUsernames]

Buzzkill, thank you for that clarification. I thought the Kast O Lite was a form of refractory cement.  I am indeed using KOL-30 ordered from Glenn.

Paul, once I add insulation to the ends and castable refractory to the inside it should end up at 10" diameter x 9" OAL give or take a little bit. So that's about 440"3, add in the floor and I get about 293"3. (figuring the floor to take up approximately 1/3rd of total cylinders volume) Does that sound like a more acceptable volume for a 3/4" burner?

[Buzzkill]

Then you are set as far as the right materials go.

Paul does have a valid point about the volume of your forge though.  I estimate you'll have a volume even larger than he indicates.  If that is the case you would need a single 1 inch diameter burner or two 3/4" burners to achieve forge welding temperatures.  A third layer of blanket and raising the floor up to the halfway point would bring you much closer to a chamber size where a single 3/4" burner might suffice.

With propane forges I had to shift my thinking from "better to have the size and not need it..." to "how small can I make the forge and still do what I want to do?"  Everything is more expensive the larger you go.  The initial materials cost is higher of course, but over time that is dwarfed by the additional fuel costs. 

If the cost of propane is not a big deal and you plan to forge larger/odd shaped objects  then the size you have is fine, but plan on adding a burner.  If you tend towards the more frugal end of things you may want to come up with a design that ends up with a chamber which is 350 cubic inches or less in volume.

[NoGoodWithUsernames]

Buzzkill, I apologize for not quite understanding. Would you mind typing out your calculations? I gave the over all dimensions of the cylinder I'm using, so if with 2 layers of wool and one 1/2" layer of castable I should be in the ballpark of a 10"Diameter x 9"or10" OAL cylinder I think, which is what I based my calculations on in my previous comment. 

It's totally possible that I'm off on that so if you don't mind sharing why your calculation is so much different than mine?

I am all for frugality, I can't imagine I'll be doing anything larger than the 8"x3" door in the back of it (will be the same size on the front), so given there should be a little bit of a lip to retain the fire I am okay getting as close to that as possible/need be. I already need to order more wool so doing a 3rd layer would not be a big deal.

[Buzzkill]

Sure.  You give 16.5 inches ID for the cylinder.  2 inches of blanket around the circumference will subtract 4 inches from the diameter, giving us 12.5 inches.  For the length you gave 14 inches, so 2 layers of wool at both ends will subtract 4 inches from the length.   If we assume that you'll put a quarter inch thick layer of refractory all around then we'll subtract another half inch from each of those dimensions.    Half the diameter is the radius. 

So based on the formula for volume of a cylinder we get 6x6x3.141x9.5=1074.222 cubic inches.  If you cut the cylinder in half by raising the floor to the halfway point you can divide that volume in half, so you get 537 cubic inches.  If you add the 3rd layer of blanket then the diameter will be close to your dimensions given above.

I think I did my math correctly, but if you spot a problem don't hesitate to bring it to my attention.  I've been wrong before and will be again.

[NoGoodWithUsernames]

Got it, I think our difference comes from me using the 11" as measured with the wool loose in there, which should probably be tightened up a bit to get closer to planned dimensions. I will for sure do a third layer of wool, maybe even on the ends to reduce that volume further. 

Thanks again for the advise to a rookie, it is appreciated.

[Mikey98118]

My interest in your forge isn't casual. The tank size you start from affords the chance to play with its interior shape; not just to fill in interior volume with added fiber for the usual ho-hum flattened cylinder, that most of us have made. I hope you will spend the time spent waiting for added construction materials reading about oval forges and "D" forges, rather than wasting this opportunity.

[NoGoodWithUsernames]

Mikey, I think I was inadvertently leaning towards a "D" Forge, or at least "D-ish"... I will read up on those, I found Andy's "D" Forge thread and will read through that. Are there any others that would make for some good reading?

After just a few minutes of reading up I'm kinda thinking a hybrid D/oval forge, make it oval with a flat floor. This would in theory smooth the transition to the floor a little bit better as well as reduce some volume by lowering the ceiling of the forge. 

[Mikey98118]

Glad to hear it. You will be in good company, because most "D" forges are modifications from what the builder first look at. We LOVE seeing innovative forges

[Frosty]

About using perlite to help make the floor. Make SURE it's as far from the fire as possible, between the Kaowool and the steel shell. I know Mike said against the shell but I just wanted to emphasize that. 

Frosty The Lucky.

[Paul Kin]

Sounds like you have it figured out! These guys know their stuff when it comes to forges, much more then me. Im still going to follow though cause it sounds like this will get interesting

[NoGoodWithUsernames]

Hey all, just wanted to check back in and let y'all know this is still moving along. It got put on hold again for a little while, but I have some extra ceramic wool on the way now. I'm hoping to have it wrapped up in a few weeks to start working on Christmas presents for the season.

[Mikey98118]

We never got around to discussing were you planed to mount your burner(s), but changes in inner shape and insulation thicknesses make that important.

[NoGoodWithUsernames]

Mikey, great question. I'll be shooting for 4 layers on the walls I think, for an 8" diameter with a flattened floor like so in this sketch. Per your recommendation above burner at 2:00 slanted slightly in look good? Though once refractory cement is in I guess that would drop it down to about 7" diameter. Still be plausible with a 9" end diameter and flat floor? 

[Frosty]

NO REFRACTORY CEMENT! Hard castable refractory. That's refractory. Period. No cements, mortars, etc. they will NOT hold up. 

I might lean the burner a bit more but it looks pretty good. You don't intend to have it that far in the forge though. Do you? 

Frosty The Lucky.

[NoGoodWithUsernames]

I apologize, I don't know why I can't get that terminology out of my head. 

*castable refractory*

*castable refractory*

*castable refractory* 

I don't think I've actually considered burner protrusion much, but I was planning on flush or slightly recessed. Though I do intend to have the burner bolt on so I can adjust that if needed. 

[Frosty]

Were you sitting in a corer when you typed that? Hmmmmm? Too many guys are buying refractory cements and mortars because they read it somewhere. We have to jump on that one when we see folks say it here. I get having a wrong: word, term, spelling stuck in my head like a catchy jingle. 

You want the end of your burner nozzle as far from the forge chamber as you can get it, JUST through the shell is usually plenty of penetration.  This allows you to shape the Kaowool refractory layer into a burner flare. 

I'm thinking 4" of blanket is a bit much but a 4" 1:12 or less taper would be SWEET. The burner's induction would be so strong you could really use a large jet and the flame velocity would be deliciously low. 

I can't bounce numbers off the top of my head but it'd be worth experimenting a little.

Frosty The Lucky.

[NoGoodWithUsernames]

Of course, I even put my dunce cap on!

 

Oh interesting, makes perfect sense though to use the refractory as a sort of Venturi. 
 

This sounds really interesting, and to make sure I’m on the same page as you, you’re saying taper the entire length of the forge so the back is narrower than the front opening correct? 

[Mikey98118]

Yes, that's what Frosty is saying; he's right. The other advantage is that your won't be overheating the burner's mixing tube;something that could happen with it buried in 4"" of super-heating insulation

BTW, the rest of your burner positioning is fine.

[Buzzkill]

14 hours ago, NoGoodWithUsernames said:

taper the entire length of the forge so the back is narrower than the front opening correct? 

It sounds like you're talking about tapering the entire forge chamber.  Am I correct?   If so I don't know how that would affect performance.   I believe that Frosty was referring to tapering the hole for the burner from the outer shell to the forge chamber - narrower where the burner enters the outer shell of the forge and tapered to be wider at the forge chamber. This basically creates a built in flare for your burner.

[NoGoodWithUsernames]

Alright, I think the layout is complete. Pre refractory is 10" dia (with a raised flat floor so 8" height) x 12" OAL (NO TAPER TO THE CHAMBER) factor in refractory and it's 9"x7"x11" which gives me 584 cubic inches. Which means I'll be building another 3/4" burner (or should I build a single 1" burner instead?)