More tuning woes

[Rich82]

First up, hi all I'm new here. I dabble in a bit of everything but mostly knife making. I'm currently at the stage where I need to heat treat a knife that I've made from s90v (1150-1175°c) and I've decided to try the salt pot method.

I've made the usual rookie mistake of building a propane forge and not really knowing what I was getting myself into and I can't seem to get above around 890°c - though it's time for a propane refill.

I have a burner that I bought to save a bit of time, frosty style and with a 1" flare iirc, 6" pipe but I'm not sure what size jet. I'm at 30ft above sea level.

The flame looks quite good to me, I'll get pictures next time I run it. I'm using a converted propane cylinder in the upright position with approx 11" tall by 7" internal chamber, 2.25" refractory cement lining and 4.5" exhaust. The burner is at the very bottom and arranged to create a swirl (like the devil forges). 

I get an orange flame out of the exhaust, not like unburned fuel to my mind - more like super hot fumes, of course I may be talking rubbish there though. I've had the regulator everywhere between 5psi and around 20psi - to get the very highest temperature, I need the pressure as high as it will go. The cylinder freezes in around 15mins at any pressure but it did start out around 1/2 full and we're 6-10°c outside at the moment.

 

Any thoughts about what I might have wrong? Just from gut feeling and working on similar projects, I'm tempted to blame the refractory cement  (looks a lot like mortar) but could do with you guys' more experienced opinion before I start throwing money at the problem.

 

Any help would be much appreciated 

Inside the lid, showing the refractory that I used (Still not quite dry at that point)

[ThomasPowers]

Did you use an insulating refractory? Or does that burner have to heat the entire mass up to raise the temperature?

[Rich82]

Actually, I didn't know there was such a thing so may well be that it's trying to heat the whole thing.... I do know it had a percentage of alumina and was rated to 1400°c for what it's worth?

[ThomasPowers]

Is it very heavy?

[Rich82]

It is yes, 60lbs at a guess

 

Is there anything that can be done with it or is it more a case of starting again?

[Frosty]

Welcome aboard Rich glad to have you. If you put your general location in the header you'll have a chance of hooking up with members living within visiting distance. Also many of your questions have a location dependent answer. 

Refractory CEMENT is formulated for cementing things together like bricks, it is NOT suitable as a flame face like the inside of your furnace.  Worse if you really used 2.25" of it without insulation it's a huge heat sink and will REQUIRE probably a couple hours just to warm up and one burner isn't gong to do it. 

You should've maybe done some research BEFORE you built? By research I don't mean watching Youtube videos, few are anything but BAD or outright dangerous how tos.

If that thing is actually cast solid then your best fix is to take it to the dump and start over with a proven design. A number can be found in the gas forge section here. Forges 101 is the most current discussions regarding forge designs, materials, builds and better still they are mercilessly vetted by people who have been making and using furnaces for decades. You'll know the good designs by who likes them.

I wish I had better advice than start over but I don't.

Frosty The Lucky.

[Mikey98118]

The orange exhaust flame could be bad, or not, depending on the why of it. Without a clue of what refractory you used, it could be from the calcining process (temporary), or from a heavily reducing flame, which needs burner changes, or from an undersized exhaust opening, which requires a different fix. Open up the lid after it heats to incandescence. and see if the orange flame changes--or not; that will at least provide a clue.

[Rich82]

I'm in the UK but, my guess is this refractory came by the pallet load from China....

I really don't know any more than already stated apart from it was sold as castable refractory.

So, I'm ok with starting from scratch and probably going the kaowool route - can anyone recommend a UK seller of ceramic fiber/wool blanket please? I could do with keeping costs down after my self-imposed-fail

[Buzzkill]

So, are you just trying to use this to heat a salt pot in preparation for quenching?   The configuration you've used is far more common for foundries than for forges.  If you only need to use this occasionally for hitting prescribed quenching temperatures you may not need to start over, but you will have a choice to make.  Based on my calculations of your chamber volume you do not have a big enough burner to hit your desired mark - assuming that's a 3/4 inch mixing tube.

To bring that volume up to the temperature you indicated you would need a burner with a 1 inch mixing tube and appropriate jet orifice - and that's for a properly constructed/insulated forge.  What you have will be a gas hog, but if you only need it occasionally for short periods of time that may not be a deal breaker for you. The T burner can be scaled up fairly easily for about 20 USD in parts.  That might be worth a try.  If you plan to use it frequently for forging then I would also recommend starting over.  The orange flame color is potentially no concern as Mikey indicated.  Right now it's near the bottom of the list of things you should focus on.

To keep your propane tank from freezing up you can place it in a shallow pan/tray of water.  You don't want it so deep that it floats the tank as it goes empty.  Just enough to be in good contact with the bottom of the tank will do. It does not need to be hot water. Pretty much anything a little warmer than freezing temperatures will work here.

[ThomasPowers]

Hard/heavy refractory is usually used for commercial systems where they will heat it up and run it for a long time and push a lot of material through it.  (Some places only cool down once a year for repair and replace!)  Such places are concerned a lot with durability and so are willing to take the fuel hit; though nowadays a lot of them are using insulating refractory around a hard inner shell to try to have their cake and eat it too.  For most of us hobby folk the gas costs are a bigger factory than the durability as rebuilding doesn't shut the factory down!

[Irondragon Forge ClayWorks]

1 hour ago, Rich82 said:

I'm in the UK

Welcome aboard...

We won't remember that once leaving this post, hence the suggestion to edit your profile to show it.

[Rich82]

Thanks again, I suspect what frosty said is the cause of the issue; just too much heat being soaked up. I ran it for around 45mins and couldn't get above 890°c (1634f) I've tried that twice with the same result

 

The orange flame, I'm not concerned about yet. My guess is either fumes from the salt being burned off or the same for something in the refractory but I'll obviously keep an eye on it from now on.

 

Initially, I've built it for heat treating knives but I figured it'll be useful for other jobs too, or perhaps more accurately the mk2 version may be. The upright configuration made most sense for getting knives in/out of the salt

[Rich82]

I've ordered some blanket and some water based ht adhesive to make sure it stays where I want it to.

The next problem is the only suitable cylinder I have is a stainless beer keg, it's a little on the big side but I'm not overly concerned about that (20"x15" very roughly) it's the shape that may be an issue - would it be a mistake to use what's left of that cement to make the inside closer to cylindrical? I.e. it's wider in the middle, could I fill some of the widest part before putting the "kaowool" in?

 

Internal volume is reduced significantly by the pot of salt which is around 5" x 9.5" and the blanket I bought is 2"

[Buzzkill]

Are you planning to build another vertical configuration with a cylinder salt pot?  If so you'll want the chamber to be as close to perfectly cylindrical as is reasonable to promote flame swirl around the salt pot.  Since the salt pot is the specific thing you need to heat up you should not deduct that from your calculations for internal volume.  You need to get all the air/gases *and* the salt pot to your specified temperature.

As I mentioned before, what you've shown us earlier is pretty much a foundry design.  The only real difference is that there would be a crucible inside for melting metal instead of a salt pot.  That type of setup does not lend itself well to being used as a forge.  Did you decide to go with propane over electric due to cost or was there some other reason?

[Rich82]

Mostly because I had a cylinder and regulator to hand, I've used coal and a hair drier up to now but from the little experience I have, hitting near white hot with that much air present doesn't often end well - for me (though I've only ever ended up in that position by mistake)

 

It seems I'll have a good amount of wool offcuts too so I should be able to create a cylinder shaped liner one way or another 

 

I think, without getting into wrapping  knives in foil instead of the salt idea, it'll need to stay upright but I'll try to keep an open mind for now

[ThomasPowers]

It is possible to make a system that can be set upright or laid down and used.

[Mikey98118]

You can even do that with your existing equipment, by placing it in, or mounting on it, a square carriage.

[Buzzkill]

Burner placement for the vertical foundry type of configuration is probably not ideal for the horizontal forge orientation though, so you'd probably want to have more than one option if you plan to use it in both orientations.   Also, for a propane forge you generally want a hole (pass-through) opposite of the front opening so you can work on longer stock.  Of course these issues can be handled in a way that will allow for both vertical and horizontal orientations, but it will best to give these aspects some consideration in the planning and building rather trying to "fix" it after the build is complete.

[Rich82]

I'll make do and mend if needs be, it's not something that'll get a lot of use really - more something that does get used occasionally and may get me out of a hole sometime. That being said, I'd still like to make a good job of it; if a job's worth doing and all....

For a vertical setup, should the burner be more or less level with the base (the bottom of the nozzle and the "floor" of the forge/foundry) or is 1/2" or 1" or whatever better? How about pointing upwards at a slight angle or perpendicular?