Help with Steel

[Stephen Downie]

Hi Ray,

Thanks very much! What are your thoughts on thermometers for a coffee can forge? Also is there a specific ratio of propane or MAPP to air that I should be shooting for?

[Ray Rogers]

When it comes to reading forge temperatures a thermocouple and a digital thermometer or pyrometer capable of reading at least 2000 F is what you'd need. For a coffee can forge you don't need one though, simply because you'll probably what to run it as hot as it will go. Anyway, it won't take much experimenting to know how hot to run it.

What ratio you'll be able to get will depend on exactly how you use the MAPP gas. Just straight by itself you probably can't adjust the gas/air ratio but with a burner (either venturi or forced air) it could be adjusted. Optimally, you want a gas rich atmosphere. You'll know you have this when the gases coming out the front of the forge are slightly yellow/orange. This is unburned gas igniting when it gets to the open air and it's proof that all the air inside the forge has been used. With no available oxygen inside the forge scaling will be reduced....

[Stephen Downie]

Hi Ray,

Thanks for taking the time to explain all this. I was under the impression that it was pretty important to hit the 1450 - 1500 degree range for hardening O-1. Can you tell the proper temp from the colour of the metal or just use a magnet?

[Ray Rogers]

It is important to hit that temperature range for hardening most simple carbon steels. The problem is, you have to build your forge very carefully and control your procedure very well before you could truly depend on a thermocouple to accurately tell you the temperature of a blade within that range. Color is subjective and affected by your surroundings so that's not very reliable either. Using a magnet and checking often and getting a lot of practice is probably the most reliable method.

With all that said, plenty of guys use the color or thermocouples or some other method and get good results. If all those blades could be checked in a lab we'd probably find that most of them were not at the optimal temperature when they were quenched yet they're still 'good' blades. It just means that full conversion was not achieved and that's not really a deal killer as long as a) most of the conversion took place and b) you test a few blades to destruction now and then so that you know how good they are or aren't and c) you keep doing that with the same steel until you can consistently produce good blades by whatever method you finally settle on.

Heat treating as most of us do it in a forge isn't science, it's a technological art ...

[pipecrafter]

Originally Posted by Ray Rogers

Pipecrafter's forge looks like a variation of my Mini Forge (http://www.rayrogers.com/mini_forge.htm) which, in turn, is a variation of the well known coffee can forge.

Yep, Ray - it's based on your design. I was going to go coffee can, but it wasn't going to be quite big enough for my purposes. Your design was the kick in the tail I needed to actually build the little sucker! I was going to go blown burner, but in the end I decided to keep it MAPP fired for simplicity.

But i caught the sickness bad. I was driving down the road and saw someone tossing out a party-store helium tank - and my scrounger instinct kicked in and I just *knew* it would make a nice forge with a blown burner. Then my wife found another one, which I stopped and grabbed. I figure I'll weld them end-to-end and make a nice long forge for longer knives or shorter swords. Then I'll definitely want it blown.

[Ray Rogers]

Yup, once you find out how easy it really is to build a forge it gets difficult to stop building them! Sounds like you may want two or even three burners on that long forge. If you decide to go with multiple burners you can run them all from one gas supply and one blower (if you have a strong blower). That's what I did on my big forge, although you wouldn't want to mount your burners at the rear like I did...

[Stephen Downie]

Alright, here's yet another a question: What are the advantages to a forced air burner or a venturi burner? I've been checking out both and they both seem to be pretty straightforward.

[pipecrafter]

Forced air burners are really, really easy to build. All you need is air, airtight pipe, and a gas supply that you can pipe in airtight. That's about it. A venturi burner needs to have the jet positioned just right, and the jet sized just right for the burner, and the burner end should be flared - ideally. Personally, after looking at designs and building a couple of both, I'm completely sold on forced air.

IMO, and experience, forced air is a lot easier to tune as well. You can tune a venturi burner, but I think a forced air burner is easier.

[pipecrafter]

Originally Posted by Ray Rogers

Yup, once you find out how easy it really is to build a forge it gets difficult to stop building them! Sounds like you may want two or even three burners on that long forge. If you decide to go with multiple burners you can run them all from one gas supply and one blower (if you have a strong blower). That's what I did on my big forge, although you wouldn't want to mount your burners at the rear like I did...

I was wondering how that was turning out. What's your experience like?

[Ray Rogers]

I agree that forced air burners are generally easier to build and tune and, without a doubt, they produce more heat than the average venturi burner (there are exceptions). That said, if you've seen my Dirt Simple Venturi you'd be amazed at how crappy a venturi can be built and still be capable of getting a forge to 1500 F which is enough for heat treating but not for welding. Yesterday, I took the Dirt Simple concept a smidge further. I stretched the pipe out to about 40", added another bell shape to the output end and then welded a 2" square section of square tubing over the bell and viola! I now have the weed burner from Hell! It's kind of heavy because the main tube is 3/4" steel pipe but it works super and it cost me nothing to build it except 30 minutes of my time,

As for my forge, I like it more every time I use it. There's no doubt it gets hot. I can tell because I have a 2500 F pyrometer and also because I have melted the 2300 F Inswool out of it twice already. I can't say there is any strong advantage o rear mounting the burners and there's definitely a disadvantage when you consider the difficulty in plumbing the burners. But, there's nothing wrong with how they work and there's nothing wrong with the concept of a single air source and a single gas source for multiple burners if you do it correctly....

[Stephen Downie]

Thanks for all the advice! My father has a 1ft by 3 ft stainless steel stove pipe that he's willing to give up. I've just ordered a blower and I'm looking around at Propane regulators.

[Ray Rogers]

1 foot by 3 foot is pretty big . Remember that the smaller the interior volume of the forge the easier it is to heat and hold a high temperature. In other words, a small interior with a moderately good burner might reach 2000 F where a large interior will need a better burner and more fuel to reach and maintain that temperature. Other factors come in to play, of course, but that's the basic idea. Also, while it's true that you can take a 1 foot pipe and shrink the interior with multiple layers of wool that method offers no real advantage over a single layer of wool in a smaller pipe. In fact, some argue that the single layer is more thermally efficient and there's no doubt that such a forge will reach it's maximum temperature faster than a heavily insulated forge. It looses that heat faster too once the heat is turned off but that usually isn't an issue .

BTW, when looking for the propane regulator try to find one that is adjustable, 0 -30 psi is pretty much what we all use but 3 - 30 psi will do if that's what you can get. Forced air burners are usually run from 3 psi to maybe 10 psi while venturi burners mostly stay at 10 to maybe 15 psi. A small propane tank can't deliver 30 psi for very long without freezing up and if you need that much pressure to reach the required temperature you need to build a new burner anyway...

[Stephen Downie]

Hi Ray,

Thanks for the advice on the regulator. I was considering the larger forge so I can play with some larger pieces and perhaps a sword or two at some point. I wouldn't mind having something that would be large enough and hot enough to experiment with Damascus and pattern welding too. With that in mind I'm thinking about getting an Ellis Forced Air burner. I've priced it out and including shipping it's maybe $5 less for me to run around to find all the bits and pieces I need and I won't have to do so much trouble-shooting for an untested system. Do you think a single burner will do the trick for a 3 ft forge? http://elliscustomknifeworks.hightem...dairburner.jpg

[pipecrafter]

Originally Posted by Ray Rogers

As for my forge, I like it more every time I use it. There's no doubt it gets hot. I can tell because I have a 2500 F pyrometer and also because I have melted the 2300 F Inswool out of it twice already. I can't say there is any strong advantage o rear mounting the burners and there's definitely a disadvantage when you consider the difficulty in plumbing the burners. But, there's nothing wrong with how they work and there's nothing wrong with the concept of a single air source and a single gas source for multiple burners if you do it correctly....

Would you still use Inswool, or would castable refractory like Kast-O-Lite work better? I was entertaining casting the entire interior of the new forge.

[Ray Rogers]

Stephen,

I'm sure the Ellis burner is about as good as any. Whether or not one burner is enough depends on what you expect it to do. If you were forging a sword and expect to word on only one section of the blade at a time (which is a common way of doing it) then it could be enough because one burner will give you a 'hot spot' in the forge. Just make sure the section of blade you want to work is in or near that spot. Of course. doing it that way means you don't need a forge 3 ft long, use a shorter forge and let the blade pass through.

One burner might raise the entire forge to temp (either for HT or welding) but it would take a long time. And, if you don't reduce that 12" diameter a lot it probably never will heat the whole thing. You might try one burner and see if it's satisfactory and then add a second one later if you need to. Frankly, I'm pretty sure you'll want two burners on a forge that size.

Pipecrafter,

Depends on what criteria you use to decide what 'works better'. A forge made with a single layer of Inswool will reach welding temp much faster than a castable forge. This works better if you do relatively short forging sessions, say two or three hours at a time, and is especially good if all you want to do is HT a blade. These forges are cheap and fast to build.

A castable forge takes much longer to build and the expense is considerable by comparison to wool. They will take much longer to reach welding temperature, often 30 minutes to one hour depending on the mass of castable involved. The good news is, once they get to temp they hold it very well so gas pressure can then be reduced thus saving fuel. These forges work better for long forging sessions, say a minimum of half a day. They are also useful for annealing steel as they cool down very slowly.

My forge has Inswool walls but a castable floor. There's 30 pounds of castable in the bottom of it. I built it this way as a compromise on the features mentioned above. I get the durability of a castable floor (flux melts Inswool) with the quicker heating of the wool. My forge is very heavy as it is and would be far heavier if it were all castable and I had to lift it onto it's 5 ft high stand by myself. It will reach forging temp in about 20 minutes in the hot spot but takes about 45 to raise the entire thing to 2000 F.

So, it's not so much a question of what 'works better' as it is a matter of building the forge that best suits your needs, budget, and the way you work...