Design question for helium tank forge

[JHCC]

I'm in the "batting ideas around in my head" stage of making my first gas forge, and there's one thing I'd appreciate some advice on. I have an empty disposable helium tank (left over from an office party) that I'm planning to make into a fairly basic D-shaped gasser (similar to Andy's "D" forge). The dimensions are about 12" in diameter by 14" long, so if the lining is about 2.5" thick (2" of rigidized kaowool, 0.5" of castable refractory, and IR coating) and I fill in the bottom up to the center line (maybe leaving space to add a piece of kiln shelf), I should get a semi-cylinder no bigger than 9" wide, 4.5" high, and 9" deep. This would give a working volume of about 285 cubic inches, well within the range of a standard 3/4" Frosty T-burner (mounted horizontally, roughly tangent to the top of the arch). So far, so good.

Now, I've seen tank forges that split horizontally and were hinged, and I've seen them with the ends cut off and hinged for doors. My question is this: could one do both? In other words, I'd split the tank horizontally and then cut the ends off the top half to make hinged doors front and back (with the usual openings for access and exhaust). Another option would be to only have a door in the front, but cut a permanent pass-through notch at the back.

It seems to me that having a full-length bottom half (with hard refractory along that entire length) would be more stable overall and would provide a larger surface for resting longer pieces. At the same time, hinged doors on the ends would give more flexibility for odd-shaped pieces. (I don't anticipate elevating the split top to increase the forge volume, but a separate top would presumably be easier to line.) I'm envisioning doors that would swing down vertically, so if the workpiece would fit in the forge but not through the door, I could put it in and then swing the doors down.

Any thoughts/suggestions/warnings-that-I'm-contemplating-disastrous-folly? Thanks in advance.

[WayneCoeArtistBlacksmith]

Look at the attachments on the Forge Supplies page at www.WayneCoeArtistBlacksmith.com.  The Build a Gas Forge attachment shows how I like to build a good, long lasting, efficient forge.  The instructions are for using a 20# Propane bottle.  You can also use a Freon tank or the Helium tank you have.

If you cut the D hole in each end the rounded over portion protects the ceramic blanket and the casting.  By splitting the tank along the line of the bottom of the D makes the casting so much easier.  I don't recommend cutting the ends off and trying to make moveable doors.  How would you keep the blanket and casting in place in the doors?  By having the tank split and put back together with hinges, if you have a need for a larger space you can remove one of the hinge pins and prop up the side with a fire brick.  I have had a number of times when I was making a scroll or other odd shaped project and did just that.  There is no limit to the size of project you can work then.  If you need further explanation send me an e-mail or give me a call.

Let me know if I can help you.

Wayne

[jmccustomknives]

Takes 2 sq ft of kay-o-wool, a little refractory for the floor. 

[JHCC]

1 hour ago, WayneCoeArtistBlacksmith.c said:

I don't recommend cutting the ends off and trying to make moveable doors.  How would you keep the blanket and casting in place in the doors? 

Yeah, that's the detail that was giving me pause. Reminded me of something my old advisor used to say in college: "You could do that. It won't work, but you could do that."

1 hour ago, WayneCoeArtistBlacksmith.c said:

Look at the attachments on the Forge Supplies page at www.WayneCoeArtistBlacksmith.com.  The Build a Gas Forge attachment shows how I like to build a good, long lasting, efficient forge.  The instructions are for using a 20# Propane bottle.  You can also use a Freon tank or the Helium tank you have.

Yes, I did read that. Very helpful information. 

A local potter has directed me to his refractory supplier, but if they don't have what I need or if it's too expensive, I will certainly be in touch about materials.

[WayneCoeArtistBlacksmith]

The problem with going to most pottery suppliers is that you need 15# and have to buy 55#, you need 1 foot of ceramic blanket and have to buy 25 foot.

Let me know if I can help you.

Wayne

[JHCC]

2 minutes ago, WayneCoeArtistBlacksmith.c said:

Let me know if I can help you.

Wayne

Wayne, what's your experience with the ceramic wool used by fireplace installers?

[Mikey98118]

It could be made to work just fine, but why bother. Just cut a 1" thick piece of high alumina kiln shelf (which gets a whole lot tougher at forge temperature) in place about 1" away from the forge shell, with a small opening near its bottom to put parts through, and paint the side facing the forge opening with a heat reflecting coating.

[JHCC]

2 minutes ago, Mikey98118 said:

It could be made to work just fine, but why bother. Just cut a 1" thick piece of high alumina kiln shelf (which gets a whole lot tougher at forge temperature) in place about 1" away from the forge shell, with a small opening near its bottom to put parts through, and paint the side facing the forge opening with a heat reflecting coating.

I'm sorry, Mikey, but I'm not getting what you're saying. When you say "It could be made to work just fine", which "It" are you referring to? Using the tank ends as doors?

[WayneCoeArtistBlacksmith]

JHCC, I know nothing of the insolation used in fireplaces, sorry.

[JHCC]

36 minutes ago, WayneCoeArtistBlacksmith.c said:

JHCC, I know nothing of the insolation used in fireplaces, sorry.

OK, thanks anyway, Wayne.

Another question: if I plan to use a piece of kiln shelf for the floor of the forge, would I still need to put a layer of refractory over the rigidized ceramic wool in the bottom half?

[ThomasPowers]

47 minutes ago, JHCC said:

.Another question: if I plan to use a piece of kiln shelf for the floor of the forge, would I still need to put a layer of refractory over the rigidized ceramic wool in the bottom half?

Let me rephrase this: "If I plan to use a piece of refractory for the floor of the forge, would I still need to put a layer of refractory over the rigidized ceramic wool in the bottom half?"

I would say it depends on the size and shape of your kiln shelf piece and the forge and how well they fit.  I often save the bits of kaowool from an old forge lining to stuff in nooks and crannies of a new forge lining to arrive at a smooth interior surface.

[JHCC]

1 hour ago, ThomasPowers said:

I would say it depends on the size and shape of your kiln shelf piece and the forge and how well they fit.  

Well, this is what I was thinking:

T = Tank

H = Hinges

K = Kaowool

R = Refractory 

S = Kiln Shelf

P = Burner Port

1 hour ago, ThomasPowers said:

Let me rephrase this: "If I plan to use a piece of refractory for the floor of the forge, would I still need to put a layer of refractory over the rigidized ceramic wool in the bottom half?"

That's a rhetorical question, isn't it?

[Mikey98118]

Your drawing shows the shelf extending clear from one side of the shell to the other; not a good move. Shorten the shelf, and allow the insulation to run between it and the shell. If you are hoping to support the shelf using the the shell's curve, use tabs or bolts running a short way under it from the shell in four places instead.

[JHCC]

13 hours ago, Mikey98118 said:

Your drawing shows the shelf extending clear from one side of the shell to the other; not a good move. Shorten the shelf, and allow the insulation to run between it and the shell. If you are hoping to support the shelf using the the shell's curve, use tabs or bolts running a short way under it from the shell in four places instead.

OK, good. Many thanks; precisely the kind of info I needed.

Another question about the bottom half:  if I have a flat shelf and 2 inches of kaowool  underneath, I will have a curved-bottom dead space about 3"-3.5" high at the very bottom of the forge. Should I fill that with kaowool, or could I use some other bulky (but perhaps less expensive) alternative?

[Mikey98118]

You could use Perlite in the "dead space", since it holds up under weight well, and is a good tertiary layer. Like fumed silica, it is very cheap, and it can be found in the garden section of most large hardware stores. It is also very lite. Just don't try to use it  directly under the kiln shelf; it needs the two-inch layer of ceramic fiber blanket between it and the shelf, to keep it from over heating, as it is only use rated for 1900 F.

 

[ThomasPowers]

I'd encourage the use of Perlite---they mine it in Socorro NM; I've got chunks of unprocessed rock and a friend has 3 dump truck loads that got rained on before they could get shipped...

[JHCC]

I guess that's why they don't mine it in Ohio: too much rain.

[WayneCoeArtistBlacksmith]

I prefer casting the floor about 1/2" thick.  Use scraps of the ceramic blanket to fill extra space.

[JHCC]

Just now, WayneCoeArtistBlacksmith.c said:

I prefer casting the floor.

To kiln shelf? Why so?

[WayneCoeArtistBlacksmith]

You should already have the castable, it will fit, if you use Kast-0-Lite it will add additional insolation and is cheaper.

[JHCC]

Does the Kast-O-Lite/IR coating combo have the same resistance to flux as kiln shelving?

[Mikey98118]

I don't often get to say something positive about Perlite; this is only because guys want to use it as a substitute for ceramic fiber (to save money), which doesn't work; instead of with ceramic fiber, which works better than endless layers of fiber; which also doesn't work. It's a question of taking time to become familiar with both materials.

Its the same sort of confusion that comes when deciding between fumed silica in water (colloidal silica), and sodium silica (water glass). It isn't just a mater of use temperatures. Ceramic fiber  has considerable springiness until it "takes a set,"  While Perlite can hold a lot of weight if it is spread out, like under a layer of refractory, or bricks, or can be poured in place, like sand, and then bonded into a monolithic shape using sodium silicate, or even treated like the aggregate in concrete, by adding it to refractory. But the best use of all is to mix layers of it with ceramic fiber to use the best physical characteristics possible.

Wayne likes insulating refractories over high alumina kiln shelves; If you cast it into a curved floor, it then is more desirable than kiln shelf in some forge designs, but with its positives comes a negative; it simply isn't as tough as the kin shelf. BUT, Supposing that you take advantage of its insulating superiority to place Perlite directly below below it, and use sodium silicate or more refractory to bond the Perlite into a monolithic? Now ya got something!

Where do I come up with such fanciful schemes? I don't; these things where pretty standard ploys for constructing homemade casting furnaces for years.  This is why, the king of picky-butts has never disagreed with Wayne's preferred construction methods; I've made a lot of casting furnaces just that way

He thinks that the greater toughening of a forge made his way, trumps the additional fuel efficiency of using strait ceramic fiber finished off with a layer of homemade kiln wash. I don't agree, but I don't disagree either; the favored methods are a close enough trade off to be a matter of personal preference.

[JHCC]

UPDATE: I haven't taken any action on this since our earlier discussion (mostly because of lack of funds for materials), but I've come to realize that going gas probably isn't going to be the best thing for me, at least at present. In a nutshell, the "Where do you put your Propane tank?" thread has more or less convinced me that figuring out the safety issues is more than I want to handle right now. So, I guess the helium tank is going to become an oil-quench tank rather than a forge.

Thanks for all your help.

[RobbieG]

On 1/3/2017 at 4:38 PM, JHCC said:

UPDATE: I haven't taken any action on this since our earlier discussion (mostly because of lack of funds for materials), but I've come to realize that going gas probably isn't going to be the best thing for me, at least at present. In a nutshell, the "Where do you put your Propane tank?" thread has more or less convinced me that figuring out the safety issues is more than I want to handle right now. So, I guess the helium tank is going to become an oil-quench tank rather than a forge.

Thanks for all your help.

Whilst safety is an obvious concern when using flammable gases, provided you use a common sense approach and avoid obvious risks, gas forges are as safe as any other piece of equipment outputting in excess of 1000 degrees celcius! One thing I have seen frosty recommend is to use copper hosing for all the connections within range of the forge - this is something I have not been able to do due to availability of parts locally but is something worth looking at. I wouldn't shelve the project just yet, gas forges are so convenient to use - especially if you have only short periods of time in which to forge.

For positioning of the propane tank, I keep mine just outside the garage roller door with the hose coming in under the semi open door (which also provides good air exchange). The forge is perpendicular to the hose so that the flames at exhaust cannot impact directly, and I have shut-off valves at tank end and forge end of the hose. Also have a CO monitor in the garage for safety.

[JHCC]

Of course, since my last post, a possibility has arisen of some extra cash coming in (from selling a concertina I haven't played in years), and now ideas are turning over in my head again....