Gas Forge Improvements

[ShaunAnderssen]

I'm new to blacksmithing, and I bought this forge link removed from Amazon for cheap because of that. I have it setup on just a standard 15lb propane tank that you would use for grilling. For smaller projects, it has worked great, I can get my material heated up fairly quickly, and at a temperature I feel is good for working and moving metal. With smaller pieces, such as an old file, rebar, or an old punch, I am able to get it heated up to a nice bright orange when set around 10psi. I would estimate around 2,000-2,200 degrees. However, I discovered some old leaf spring steel in an old shop last week, and decided to try forging a broken back seax knife with it. I can't seem to get my forge to heat it up above 1,600 degrees. It heats to a bright red to cool orange color. I feel like this is too cold, and I may definitely be wrong in that assumption. Or I may be totally overlooking a quality of this steel, as I have never worked with it. Regardless, I am still curious as to how I can get my forge to heat metal more efficiently, and at higher temperatures. Here are some things I have tried. 

-Covering the back opening of the forge with a layer of insulation, and firebrick.

This heat the metal more evenly, as opposed to focusing all the heat directly below the burner, but didn't seem to bring the temperature of my leaf spring up very substantially. 

-Increasing the PSI.

I have toyed with raising the pressure, which heated my material faster, but caused my tank to start icing up and losing pressure. 

-Testing different amounts of airflow at the intake.

I have to admit I have no idea what affect this has on my forge, I have tried many different airflows, but haven't noticed a huge difference, other than the fire seems to "breathe" better with more airflow (fairly obvious). 

-Being patient.

I've tried my hardest to just give it time, but it seems to just reach a certain temperature and just plateau. 

-Adjusting the height of the burner in the forge. 

I have read about adjusting the height of the burner, but the design only allows me about a half inch of adjustment, so I am just looking for any suggestions as to better insulate, change my burner characteristics, or anything basic that I have overlooked in my unfamiliarity with blacksmithing as a whole. Thank you all for any responses. 

 

 

[Frosty]

Welcome aboard Shaun, glad to have you.

A larger piece of steel requires more fuel and or time to bring to a given temperature, just like a house. Bigger house bigger fuel bill. You need to turn up the PSI and get a larger propane tank, even 20lb. tanks are small and tend to freeze up with prolonged use. Say 4-5 hours of yellow heat on a 1 burner forge with a full 20 lb. tank tends to start slushing up and you lose psi. 

Do some reading in the Forges 101 section, regarding thermal baffles rather than doors on gas forges. I won't discuss those burners, I'm not generally impressed, they don't follow the basic ratios for a good propane burner is all I'll say. They can be MADE to work though.

Have you applied a hard refractory to the ceramic blanket liner? A kiln wash on top of the refractory is a performance booster too.

In general those aren't bad forges, lots of guys use them and get good service.  

Frosty The Lucky.

[Mikey98118]

You need to increase insulation, and re-emission in that forge. Not just by partially blocking the exhaust opening. Until you do that anything you do to increase internal temperature will mostly be lost through the forge walls, ceiling, and floor. At present, most of the heat your work receives is from hot exhaust gases. You need to change that to most of the heat transfer being from radiant energy.

[ShaunAnderssen]

On 10/21/2020 at 2:52 PM, Frosty said:

Welcome aboard Shaun, glad to have you.

Thanks for the response! I have done some reading on that thread, but I have to admit alot of it went over my head, you guys are very knowledgeable and I've never encountered or even thought of half of this stuff. I didn't have anything super for insulation to try yesterday, but I lined the inside with some old firebrick I found and it did make a big difference. My spring steel was heated much more evenly, and at a higher temperature, enough that I could effictively move it. But I still wasn't able to reach a nice yellow temp, even at 20 PSI. I think I know how I want to insulate it, I just need to order the materials. I know you said you didn't want to discuss the burner, but is there anything you can tell me on how to bring that closer to being a more effective burner? I'm under the assumption that you're looking for a nice sharp blue flame like a handheld propane torch, could I accomplish that with a smaller nozzle? Or shortening and/or lengthening the burner tube? I appreciate any input, and thank you for your time. 

On 10/21/2020 at 4:27 PM, Mikey98118 said:

You need to increase insulation, and re-emission in that forge. Not just by partially blocking the exhaust opening. Until you do that anything you do to increase internal temperature will mostly be lost through the forge walls, ceiling, and floor. At present, most of the heat your work receives is from hot exhaust gases. You need to change that to most of the heat transfer being from radiant energy.

Thank you. Your replies in Forges 101 have helped me realize that the burner is not what I'm supposed to be relying on to heat my work. 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. When I compare that to a color/temperature chart on line, this puts it around a bright orange at best. How are they achieving higher temperatures? Are they feeding it oxygen? I'm not understanding how it's getting hotter than the torch's output temperature. Again, alot of the technicals of insulation you guys discussed went over my head, I apologize if you have to repeat yourself. Appreciate any response and time you give me. 

[Frosty]

I don't have the site bookmarked so I held my thought instead of relying on my damaged memory. I mostly recall the burner having been planned and built by folks who don't really understand how they work. From the pic you posted it LOOKS like the mixing tube is way long which means the jet diameter is smaller than ideal to overcome the excessive friction, probably a 0.023 mig tip, set way too deep in the throat. A 3/4" pipe mixing tube burner, needs to be 6" long. The ratio is D x 8. .75" x 8 = 6".

Who says a propane forge can only reach 2,000f.? That'd be a typo or another person who doesn't really know what s/he's doing, claiming nobody's forge can get hotter than theirs to cover for HIS/ER's inability to make one up to snuff. 

There used to be a common myth that a naturally aspirated forge won't get hot enough to weld. The problem was almost entirely a matter of mis-tuning. They were getting hot enough but they were burning so lean the scale blocked / prevented welds. Properly tuned even a linear burner as seen on FIF can melt steel into a holiday sparkler.

Frosty The Lucky.

[ShaunAnderssen]

46 minutes ago, Frosty said:

I don't have the site bookmarked so I held my thought instead of relying on my damaged memory. I mostly recall the burner having been planned and built by folks who don't really understand how they work. From the pic you posted it LOOKS like the mixing tube is way long which means the jet diameter is smaller than ideal to overcome the excessive friction, probably a 0.023 mig tip, set way too deep in the throat. A 3/4" pipe mixing tube burner, needs to be 6" long. The ratio is D x 8. .75" x 8 = 6".

Who says a propane forge can only reach 2,000f.? That'd be a typo or another person who doesn't really know what s/he's doing, claiming nobody's forge can get hotter than theirs to cover for HIS/ER's inability to make one up to snuff. 

There used to be a common myth that a naturally aspirated forge won't get hot enough to weld. The problem was almost entirely a matter of mis-tuning. They were getting hot enough but they were burning so lean the scale blocked / prevented welds. Properly tuned even a linear burner as seen on FIF can melt steel into a holiday sparkler.

Frosty The Lucky.

Ahhh, I apologize. My generation is showing. I just trusted Google. That's why I'm glad this forum exists instead. Wow, if it only needs to be 6" then it is grossly overlength. I would've never thought of doing this before, but if I chopped that mixing tube down, and changed to a different diameter jet, something I'm sure could be calculated, I should be getting a more effective flame characteristic? 

[Mikey98118]

2 hours ago, 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 Dr 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 anwere help; they're the best I can do.

[Mikey98118]

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 qoute).

[Frosty]

Nothing to apologize for Shaun. If you'd gotten on my bad side you'd know when let my curmudgeonlyness loose on you.  

Those forges have been reviewed here a few times and they're not bad for the money and can be improved without too much trouble.

Frosty The Lucky.

[Irondragon Forge ClayWorks]

On 10/22/2020 at 1:05 PM, ShaunAnderssen said:

I just trusted Google

I trust Google for some things and I'm a lot older than you. My generation is WWII era.  A trick to use here is to add iforgeiron to your search term it will bring all the threads up, talk about information overload.