Small soft brick propane forge build

[NicZa]

Hello everybody!

I'd like to start of with a brief introduction since it's my first post; I've been lurking for a while and I really appreciate all the effort you guys put in to be able to have such a great and informative forum. I'm a male in my thirties located and from Finland. I've been interested in blacksmithing since my childhood and I finally bought my first forge a couple of years ago, It's an old 2-burner firebrick gas forge that I picked up for about 200€ (included in the deal was a brand new torch that I'm now planning of using in my build). So I'm quite new to the craft and haven't been able to forge as much as I would have liked, but now I'm trying my best to change that. Now on to the build and my questions!

 

My reasoning of building a smaller forge, and my requirements of it are as follows:

• I want an more economical forge for smaller projects
• I want a more easily movable forge
• My current forge is insulated with hard firebricks and I cant find an option to tune the airflow
• I want the forge to be able to reach forge-welding temperatures (my current one cant)
• I have an extra burner laying around
• Designing and making stuff yourself is extremely satisfying and fun!

 

Current design and where I'm currently at:

The soft fire bricks I'm using are IFB-30 from Vitcas. I'm planning on coating the chamber with adhesive sealer and ziconium zilicate coating (also from Vitcas) in hopes of making the bricks more durable and more flame resistant.

The chamber diameter is 120mm and the depth is 230mm. I am going to reinforce the structure (once it's finalized) using a steel plate, angle iron and threaded bars.

The burner I have is yet unidentified and I currently don't have any pictures of it, but it's a blue venturi-style burner and if I remember correctly the seller told me he ordered it from the US. The placement and shape of the burner chamber is drawn in the picture above. My intentions of the shape is to allow room for angle and depth adjustments in hopes of creating a vortex and to protect the nozzle from getting too hot.

In the bottom of the forge is a slot for a piece of hard fire brick (half thickness) for a more durable and exchangeable floor. I'm thinking of cutting slots around the edges on the hard fire brick to make it harder for flux to run down the sides (no clue if this is necessary or if it would even help).

As for the back I'm thinking of just using two soft firebricks to keep it simple and modular (if the forge works well I might build another one to be able to combine them if or when I need a longer chamber). And for the front "doors" I'm thinking of using hard fire brick (half thickness) on rails made of angle iron. 

 

Now to my questions:

• Do I have major flaws in my design, or do you find anything you would improve/do differently?
• Is the coating for the chamber proper or good enough, or is there better options/solutions available?
• Will the isolation choice/thickness be enough or should I for example split bricks to half thickness to add to the roof and sides?
• Could/should I add a plate of hard fire brick covering both of the bottom soft bricks to increase durability, or would the hard fire brick suck up too much heat or allow the heat to leak out trough the exposed sides?    
• Will the front "doors" insulate enough, or I'm better off using soft fire brick? 

 

Thank you for taking the time to read trough my ideas and thoughts!

All comments, questions and inputs are welcomed!

 

[swedefiddle]

Good Morning,

You will find that the soft bricks will break up on you, expansion and contraction.  Build a container,

Neil

[NicZa]

Thank you for the suggestion Neil.

It will definitely break up on me, I'm just trying to get it to last as long as possible. And a container would be the best option with longevity in mind.

 

My reasoning in choosing soft bricks is that currently I'm not certain of what size or shaped forge will suit my needs best. Or what suits me and what I like.

Soft bricks allow me to more easily make changes as I figure things out. Once I have more experience with different shapes and burners, I will definitely end up building a container forge!

// NJ 

[Mikey98118]

"Soft firebricks" is a relative term nowadays; yours are rated at 3000 F. With the coating you plan to add, they should last very well.

Such description as you gave regarding your mystery burner, narrows it down to probably being a Hybrid burner, which were built in the U.S.A. and all featured blue choke plates; this is a good design, although the company is out of business now.
 

[NicZa]

Not a mystery burner anymore! I looked up hybrid burners and the burner is indeed one of theirs, thanks Mikey!

// NJ

[timgunn1962]

It's worth noting that the gas threads on the Hybrid Burner (T-Rex?) are almost certain to be NPT with a 60-degree threadform, not the European standard "G" pipe threads with a 55-degree Whitworth threadform to the BSP standard. Some sizes share the same thread pitch in NPT and BSP are close enough to screw together, but it's best to get the correct threaded adapters to avoid leaks and/or thread damage.

The flare is mainly helpful when the burner is not in a forge. In a forge, it's not usually needed IME and using straight pipe eliminates an installation headache. If you have the end of the straight pipe back in the brick, you effectively get a stepped flame retention cup for free and dramatically reduce the amount of heat damage to the end of the burner. I can't remember whether the flare is easily removable on the T-Rex. I think the Hybrid Burners use mig tips for gas jets.

It might seem counter-intuitive, but a smaller gas jet will often get you a higher flame temperature, though it's not always the case. There's a good chance that whoever imported the T-Rex was thinking "bigger jet = more heat" and chose the biggest jet, maybe too big. 

[Mikey98118]

you're welcome, NicZa.

Tim,

You made good points, but he needs to consider all sides of the of the picture, when it comes to running that burner without its flame retention nozzle. Yes nozzles are not required if a burner is mounted in a forge, but losing it changes flame shape. Properly tuned Hybrid burners have long sharp flames; they will become shorter and bushier without the nozzle, which can be good or bad, depending.

    There is no such thing as a free lunch with burner design. Sans nozzle, the wear and tear, which the nozzle is meant to take (as a replaceable part), will simply get transferred to the brick wall.

[NicZa]

If I remember correctly the burner is smaller than the T-Rex, I think its one of their middle range in size.

Thanks for the tips Tim, especially about the threads! 

Mikey made some good points about the nozzle as well! I think it's probably best to use the nozzle at least in the beginning. I'd like to think the burner is designed with a nozzle for a good reason, whatever it might be. But I'm not against experimenting without the nozzle once I'm more accustomed with my new forge!

// NJ

[Latticino]

You may find that with such a small forge volume you have a bit too much burner for the forge size.  I'm not sure what the turndown ratio is on the hybrid burners, or how potential swapping of the nozzle or flare will affect same.  I typically go with Tim's recommendation to provide a step in the refractory to protect the burner outlet and configure the forge liner to double as a nozzle.  It does look like you are planning something like that.  I would expect that a short, bushy flame might be better suited for that size forge.  Note that in any case, the nozzle/flare should not be exposed inside the forge chamber.

I am not familiar with either the bricks you have specced or the coating you plan on using.  However, every soft-brick forge I have used or come in contact with has had issues with the brick getting very friable after heating and cooling regularly, and the remainder is quite brittle.  Hopefully yours will fare better, but I do recommend if you aren't going to include an enclosure, that you consider some kind of steel angle frame that can exert adjustable pressure on the bricks to hold them in place.

[Mikey98118]

You are correct to aim the burner to create swirl. However, you need to place it at the top, both to reduce stress on the brick wall, and to aim the the flame so that it can impinge on a hard half-brick, or high alumina kiln shelf (better) floor.

[NicZa]

I'm going to my shop today to get the burner so I can try to figure out the model.

I am indeed planning on having the forge liner double as a nozzle, and to make a frame from angle iron and plate once the size and shape of the forge is finalized.

I want to try avoiding placing the burner on the top of the forge. My reasoning for this is that heat rises, putting unnecessary stress on the burner. And due to the configuration of the choke, placing the burner horizontally would allow operating the choke with one hand.

The stress of the flame on the soft-brick is a valid concern, even with the coating. I try to think of a better solution for this. On the other hand, the top-right brick is rather easy to replace once it gives in.

 

 I really appreciate all of your tips, thoughts and comments!

// NJ

[NicZa]

So here is a picture of the burner, the previous owner have unfortunately lost the nozzle.

The outer diameter of the burner tube is 1" and the length is 12" excluding the nozzle, jet tube and its compression fitting.

I have a hard time finding good information of the hybrid burners, but as far as I understand this burner is larger than the T-Rex? 

Does anyone here know what sized burning chamber would be ideal for this burner?

// NJ

[Mikey98118]

Size comparison of parts in the photo isn't a good way to judge burner size. All of the Hybrid burners were built with mild steel schedule #40 pipe. Below is a list of pipe sizes used for minxing tubes. Compare your burner's mixing tube with it, to see what size burner you have. A 3/4" propane burner is considered large enough to properly heat 350 cubic inches of forge interior. For every pipe size large, double the number of cubic inches. For every pipe size smaller halve the number of inches.

However, it is good to remember that these burners have tremendous turn-down ranges. If your burner is too large, just reduce gas pressre until you are satisfied with the result

(A) 1/8” pipe is 0.405” O.D. x 0.270” I.D.     

(B) 1/4” pipe is 0.540” O.D. x 0.364” I.D.     

(C) 3/8” pipe is 0.675” O.D. x 0.493” I.D.      

(D) 1/2” pipe is 0.840” O.D. x 0.622” I.D.     1

(E) 3/4” pipe is 1.050” O.D. x 0.824” I.D.     

(F) 1” pipe is 1.315” O.D. x 1.049” I.D.          

(G) 1-1/4” pipe is 1.66” O.D. x 1.38” I.D.      

 

[timgunn1962]

1" OD on the pipe suggests 3/4" Nominal Bore, so it's a 3/4" burner. The rule-of-thumb for a 3/4" burner is 350 cu in. 

It should run the forge no problem, though it'll use more gas than a 1/2" burner. You (probably) won't just be able to just turn it down because there's a limit where the flame-speed through the gas:air mixture matches the mixture speed through the burner tube. If the flame-front moves faster through the mixture towards the Venturi section than the mixture is moving through the burner tube towards the forge chamber, the flame will run back down the burner tube. Not A Good Thing. 

Since you've been relieved of the need to worry about the nozzle, you can use it as a straight-pipe burner and arrange to provide either a flare or a flame-retention cup as part of the refractory structure.

Personally, I'd locate the burner 15 or 20 degrees anticlockwise from the location shown in the first pic. This should put the burner port in the side brick. I'd cut the hole to just clear the OD of the burner tube and fit the tube so that it's maybe 1/2" back from the chamber at its closest approach (the bottom).  Flame impingement will be onto the top IFB. If it turns out that this causes a problem, you can lift the top IFB, effectively increase the chamber radius and build it back to the chamber ID with hard refractory. I'd want to see what happens with the IFB first.

With the Venturi inlet well below the top of the forge opening, the convective flow after shutting down will tend to keep the heat-sensitive parts of the burner cool. 

I'd recommend you work with the parts you have, get it running, use it, understand your process, then, and only then, work out what you feel is worth changing.

[NicZa]

Thank you guys!!

Now I think I got everything I need to get to the first test-fire of the forge! 

I just need to find the time to get there 

// NJ

[NicZa]

I might as well post some updates along the way: 

I made the channel for the burner today and coated the bricks.

I'm not too happy about my placement of the burner since it's between 3 different bricks. Then again, in worst case, it's just going to be one of many mistakes to learn from! 

// NJ

[Frosty]

How'd you cut the channel? I use an old worn hole saw for soft fire brick, they work for hard fire brick but it tends to burn the teeth off rather than dull them.

I'm sure you've told us already but my brain is dented and I don't recall. What are you coating it with?

Frosty The Lucky.

[NicZa]

Hi Frosty, I got away with using an old rasp/file since the location is between bricks, worked wonders.

I used a large whole saw to shape the burning chamber though, I'm going to keep my eyes out for a smaller one for future builds!

I used a ziconium zilicate coating from Vitcas, they claim it has a maximum service temperature of 1750°C / 3180°F. 

// NJ

[Frosty]

Files work a treat. I like the sound of the refractory you're using. 

Frosty The Lucky.

[NicZa]

Got a lot done today! There's a bunch of tweaks and additions left to do but it's getting really close to a test fire!!

// NJ

[Goods]

That looks pretty slick. Can’t wait to see how it performs.

Keep it fun,

David

[Frosty]

Let it warm up slowly when you light it, the thin sections of the walls could fail with rapid thermal expansion. 

I'm looking forward to seeing how it works.

Frosty The Lucky.

[NicZa]

First test fire today!

It looks really promising, it's already way better then my old double burner forge!

 

First vid ~30 seconds after light up: https://www.youtube.com/shorts/l_1i8hNGbqg

Second vid once it got up to temp: https://www.youtube.com/shorts/olVBYh5x3N0

// NJ

 

 

[Frosty]

Nic, how about a couple still pics, I do not want to download your entire channel just to get a look at your forge.

Frosty The Lucky.

[NicZa]

Here you go:

// NJ