Second Forge Oval Shape

[Adam R]

I am in the planning stages of a new propane forge. My first build was a brick pile that I have used for a few months. All of the soft bricks are cracked, but it has provided some valuable experience. I have read many posts on forge design here as well as Wayne Coe, Zoeller and other sites. I have contacted a local refractory supply company regarding basic information, but wanted to make sure I am on the right track before I start ordering supplies.

To start, the brick pile has shown me that I need a bigger chamber for making scrolls etc. than the 4 1/2 square x 9 I have right now. I want to be able to start making some architectural pieces, as well as the normal blacksmith/woodworking tools that so many of us wanted to make which led us to this addiction. I don't want to make the over-sized mistake that has been mentioned so often. I have had the chance to use a disposable helium bottle forge with 1" of insulation. The interior size 7 1/2" ish diameter by about 12" gave me the capacity that I think I can live with.

Here are some general specs for forge lining that I have gleaned. Please let me know where I need to adjust:

Insulation- 2) 1" layers of 8lb. Durablanket. the local supplier has that brand in 2300 and 2600 degree. I have read the temp rating used is not as important as the coatings that will make it durable and reflective. The 2300 is significantly cheaper, but if the 2600 is going to pay for itself over the life of the liner that will be what I choose.

Rigidizer- Ludox Collidil Silica is available in as small a quantity as a pint. I have read that it should be applied between the insulation layers and "fired" to cure. I seem to recall someone mentioning they fired by placing the forge in an old oven. That isn't really an option since the only one I have is in my kitchen, and the warnings I have been reading about liner materials make me want to do all of the work outside away from the kiddos.

Forge floor- I mentioned the High Alumina kiln shelf that Frosty recommends to the salesman that I talked to, and he said it was very expensive, and that he recommended a #1 Split fire brick. I know that has been STRONGLY recommended against here, but he was talking to me while he waited for his lunch to arrive so I didn't push harder on that point. I was going to call for more definitive pricing, but thought someone here will probably have a recommended supplier. Or at least some pointers.

Kiln Wash-  Here is one of the places my understanding is incomplete. Some posts recommend going straight to a kiln wash, while others say to apply a castable refractory first. I would like to make the surfaces as efficient, durable, and long lasting as reasonable. I was told there was a Zirconium kiln wash (not sure of the brand) available that is $3.90 lb. for dry mix.  The salseman recommended 1/8" thickness as an reflective surface. There is probably a spec sheet available, but not on their website.

Forge body- You were no doubt thinking at some point, "Where is this kid going to put his forge lining?" This is where I am diverging slightly from some standard forges. I was able to purchase an old 20 lb propane cylinder from my local propane supplier for $1, which I suspect went to the vending machine. That being said I am not married to the thing so I could skip using it for this build entirely. One of the problems that I have seen in other posts is that the chamber of a 12" diameter by rounded 12" (the whole cylinder) lined as described above (8"x 12" roughly finish) is around 603 cubic inches. This is way over-sized for the projects that I am likely to build. Mikey mentioned in his Forges 101 thread that oval shapes are an improvement on the tube forge. I ran a calculation on a 6"x 8" oval shaped cylinder 10" long and got a volume of 377 cubic inches. If you throw in a kiln shelf, that is pretty close to the volume where it is possible to forge weld with a 3/4" Frosty-T burner that I already have made. My thought is that if I cut the ends off at 10" then cut an inch strip out of each side, I would have a more oval shape that would get the volume and forge chamber that I think I need at this time. If I cut some relief cuts in the outer edges I could flatten the top and bottom to make it more oval shaped still. I imagine there would be a point at which the ceramic insulation would not want to support itself. There would probably also be some diminishing heat reflection/circulation as the shape became too flat. After the shape is made and possibly lined, I would probably rivet the two halves back together by overlapping the one inch on both sides instead of removing them all together. The burner will be attached through the top about 45 degrees off of vertical. If you all don't think I am too crazy I am planning on just the one burner. Front and back closures will start as fire bricks until I learn what I really need for pass through and access.

This turned out to be a really long post. Thanks for reading this far. I figured it would be a good idea to mention as much info as possible in one place instead of a liner thread, and a forge shape thread.

[Latticino]

Sounds to me like you are on a good path (provided you mean two 1" layers of refractory blanket).  If you are concerned about longevity and cost tradeoffs I would certainly see if you can get the inner layer of blanket at 2600 degree rating and the outer layer at 2300 degree rating.  It really only depends on what the inner face will be exposed to.  The direct flame impact zone will be hottest (directly in front of the flame) and that could be up to 3000 deg, so I usually err on the side of caution and use the higher temp blanket for an inner layer.  I also like to use some form of castable refractory as an inner liner; after the rigidizer and before the IR reflective kiln wash.  I have used a number of different materials including MIzzou, high alumina refractory (like Greencast 97), and multiple layers of high temperature furnace cement.  The first two do add more thermal mass to your forge, which is a mixed blessing (longer to heat, but holds heat better when the door gets opened or masses of metal get put in - kind of like a heat battery).

I've never done two layers of blanket with rigidizer in between each layer.  Not saying it is a bad idea, but not completely sure why it is a good one.  As I understand it, the intent of the rigidizer is to capture the blanket fibers after they heat and become more friable as well as maintain the overall thickness of the blanket (from crushing) and the general shape of the forge chamber.  Not sure how an intermediate layer helps there, but guess it could contribute to structure if nothing else.

Hard brick splits are not the worst thing to use for a forge floor, provided that you put the same layer of insulation under them as you have in the forge walls.  It is when you use them as a floor without any backing that they draw the heat right out of your forge.  They won't have the same kind of resistance to flux damage that a high alumina kiln shelf does (check with a local potter, they may have broken shelves that are just the right size for you.  Shelves can be cut with wet diamond wheel tile saws), but they are very cheap and can be replaced as a consumable.  You can even give them a coating of Wayne's bubble alumina and they will last pretty well.  I've had pretty good success with a loose casting of Mizzou for a floor that is pretty resistant to flux damage as well.

Your forge shape as an oval sounds good to me.  If you have concerns about odd shape forging you might want to consider designing a side door that will open to allow shapes like that to be heated.  Good door design is tricky though and something I still struggle with.  Just remember to put something directly opposite the burner outlet that can take the extreme heat of the flame.

[bigb]

For some reason my first reply with a link in it will not post. Anyway I was considering an oval shape as well but at Frosty's suggestion I am planning a D shaped one. You can see my drawing in my post "Decisions". Can't provide a link since it doesn't allow the message to post for some reason.

I like that the D shape allows for a wide floor with a very low cubic inch area. By the way I am a real greenhorn, just putting this out there in hopes of further discussion/learning that could benefit both of us.

[Adam R]

Latticino- The different rating for the layer was something I hadn't considered. I like that idea. There are some Mizzou 3000 degree castable refractory materials. I will check on pricing and quantities available from my supplier.

I think the dual rigidizer application might help keep the shape of the layers thus saving the air pockets/insulation value. Any idea on how to fire/cure the rigidizer other than just air dry?

bigb- I somehow missed or forgot about your post. That is an interesting idea as well. It reduces my internal volume even more. That will take some more thought.

[Latticino]

Alan,

Honestly I've never fire cured my rigidizer, so can't comment on that.  Since I only used one layer, the air cure worked fine for making it solid enough to support the inner liner of refractory.  Then when I fired the refractory slowly I assumed that both layers got fired together.  I expect that you could fire the first layer of  rigidizer inside your shell with your burner.  The underlying blanket does not need to be babied as far as heating rate goes (one of the big advantages of blanket). 

[Mikey98118]

Lots of good stuff here, guys:

"Heat battery" was brilliant imagery: I will shamelessly use it at every opportunity. I agree with everything Latticino head to say; especially about putting something opposite the burner outlet to soak up the heat of the flame. For me, the wider floor area available in oval forges, and even more so in "D" shaped forges are just as important for the larger target they provide in the area of impingement, as they are for providing more area to accommodate larger parts.

As to having both an inner and separate middle layer of refractory; the middle layer would not work as a heat battery, becuase, being surrounded by insulation there would be no way for it to give back the heat built up within it to the working surfaces of the forge.

I am a fan of "D" shape forges, so it might seem odd that I spend my time discussing oval forges. A "D" has all the advantage over an oval forge as for how well its internal apace can be used; it is much easier to build, and can be built for a good deal less money on refractory materials, since it invites use of Perlite outside of the fiber insulation. I believe it also does a better job of circulating heat within the forge. Finally, a "D" shape is probably the best choice of forge for use with a ribbon burner, which needs a support table or cart anyway.

Underdog, save me!!! Poor old Doc Frankenburner has painted himself right into a corner!

Or maybe not. The one thing "D" forges tend to suck at is being portable. Oval forges excel  at portability, but if you want a "D" forge to last it better have a dedicated table to rest upon. If a person OWNS his shop, and has come to a point in life where moving from place to place is likely to be over, then choose a "D" forge; otherwise, stay with an oval. The fact is that most of the people I write for have still got a lot of moving to do, and that goes double for tradesmen with landlords.

What can a perfectionist do in such a quandary? One way to have your cake and eat it too would be to combine the virtues of both kind forges, by modifying the shape, so that  a "D" forge sits on a gently curved bottom instead of a flat surface. Even a gentle curve will add that extra rigidity to the whole structure, and encourage airflow past the bottom surface to help keep the forge shell from overheating in that area.

You can always trust Mikey to vote for the complicated solution

[Mikey98118]

"I think the dual rigidizer application might help keep the shape of the layers thus saving the air pockets/insulation value. Any idea on how to fire/cure the rigidizer other than just air dry?"

I lot of people just use rigidizer to stiffen part of the blanket. You want to soak the blanket completely through, to get its maximum benefit. One of the benefits is keeping the fiber where you place it.

u

Ceramic fiber products are so porous that water runs right through them, unlike solid refractory, which must be slowly dried out, and then heat cured to prevent damage from build up of steam pressure during drying and curing. So, ceramic fiber can be "cured as you go," which means that nothing prevents you from slowly rotating an outer layer of blanket on a curved surface, spritzing the rigidizer to each area that is laying flat under the weight of the liquid, using your burner (turned down low and constantly moving over the wet fiber), to stiffen  the blanket into permanent shape, and then moving on at your convenience. After creating a smooth stiff surface inside the structure, you proceed to install the inner layer the same way. One of the joys about completely soaking the blanket through, is that both layers will bond together. Any rigidizer that soaks into the outer layer will run right over its fibers surfaces by capillary action, the same as it did the first time, causing no build up to degrade the insulating value of the outer fiber layer.The whole process is mostly idiot proof.

I did say mostly idiot proof; if you dream off, you could burn yourself from the steam that will be created. If you turn a really high speed burner on at maximum and completely dream off, it is conceivable (but not likely) that you could even melt a pap of fiber. Finally, someone on drugs might be stupid enough to point the burner at himself...

What is there to keep Murphy from messing up your efforts? Firstly, the fiber is partly alumina, and partly silica; the alumina pretty much prevents it from melting, while the silica content bonds beautifully to the colloidal silica in the rigidizer. Secondly, the individual fibers in the blanket are very thin, which maximizes capillary action of a liquid across a surface. During heat curing, the colloidal silica that has wet every surface becomes a permanent vitreous outer layer on the fiber, which creates welded joints everywhere the fibers cross each other. This glass sheathing is permanent. More rigidizer applied over it simply adds another layer after heating.

[Adam R]

Great input to think about. My forge will reside in an old grill with 1/4"x1" steel straps to support it. Although with the lower height it may fit inside on the original grates. That should be enough support, and if the outside of the forge is getting hot enough to damage cast iron, my insulation needs improvement I would think.

You all have me thinking of a D shape now and flattening the lower half of my tank.

I got some prices on kiln shelf. 5/8"x12"x24" silicon carbide for $68 (no broken pieces in stock 3/4" in the same size $96). That does seem expensive, but I can cut it (can't I with a wet tile saw?) and make 3, 8" pieces which would make 3 different forge floors. They didn't have high alumina?? They also only sell castable refractory in 50lb bags $48 (no split open bags). If my shelf covers the floor would I need castable? If castable is that important, I can find it in smaller quantities online.

If I install the durablanket before I attached the two halves i could fire the digitizer as Mikey described with a plumbers torch I would imagine.

Thanks for the great info I have the day off tomorrow and might pull the trigger on some supplies. Any more thoughts are greatly appreciated.

[ThomasPowers]

Did you call around any ceramics shops and see if they had broken pieces they would be willing to sell cheap?  (Not the suppliers but the users.)

[MonkeyForge]

My ceramics supplier cuts tiles to size, they have leftovers for cheap. Might be the same for you. For me thinner is better, but I run a 90 cubic inch forge. Thinner also means replacing it more often, especially if you accidentally melt something

[Adam R]

I called around for kiln shelf, and wasn't able to find a good local source. I would check users as TP suggested in the future. I wanted to get the other supplies before they closed early. I placed an order, and met the salesman I had talked to. While we were chatting he mentioned that he some offcuts that were available. He cut me a piece of nitride bonded silicon carbide to the dimensions of my planned floor size. He gave it and a remnant of silicon carbide shelf for testing purposes. As it turns out he and his grandson are going to be working on a propane forge build in the near future. The small quantities of ceramic blanket were offcuts and thus free too. Maybe this part belongs in the "It followed me home" section. It never hurts to chat with your local supplier!

I picked up a bag (55 lb) of Missou castable plus (3000 degree). While I was there. He wanted me to make sure this was the right product before I opened it. As they would take it back unopened. Please advise on this as a durability layer. It seems similar to the recommendation from other posts. I am fine with using and keeping/sharing with other local folks especially since I have received so much for free on this build.

[Mikey98118]

Nitride bonded silicon carbide should make a serviceable choice for a forge floor, unlike the older plain silicon carbide kiln shelving, which I wouldn't even bother with. I still prefer high purity alumina kiln shelving, but you need to go with the available products in your area.  You will want to extend Frosty's kiln wash coating to include the forge floor since both silicon and carbon are poor insulators, compared to high alumina.

 

[Mikey98118]

And yes, a plumber's torch will work just fine.

[Adam R]

The (Advancer) Nitride bonded shelf is only about 5/16" thick, so I would think it wouldn't take too long to heat up. I am not very familiar with either product. Knowing how strongly people have advised against split hard fire brick, I figured almost anything would be an improvement. Getting something free especially when it is a product that is extremely expensive ($190 for 12"x24") tends to get a newbie excited. It is possible the sample I was given is a specialized product for what I don't know. Small forges are not the suppliers main business. The spec sheet said it was rated to 2600 degrees.

On the subject of high alumina kiln shelf, I found on Continental Clay's website they have a reasonably priced shelf rated to cone 11, and a premium alumina shelf rated to cone 13 for twice as much. I haven't seen any discussion of different grades. From the earlier comments I would imagine the lower grade with a kiln wash is recommended. If I have missed the answer somewhere, maybe it will help someone else that hasn't asked.

I will try to find the mix for Frosty's kiln wash, or pm him.

I read over the forge 101 section again and found the answer to the castable question. I know I read it before, but I wasn't looking for that question apparently.

[bigb]

Having almost finished my roof over my smithy and now that is is cooling off a bit I will soon be ready to start my build. I am going to refer back to this thread often and hope you post pictures of yours as you proceed.

[Frosty]

I've been following this and the other forge build posts and a thought came to me a while ago I just don't remember while I'm looking at one of these threads.

In a reverberatory forge the flame heats the liner and the liner radiates the IR heating the stock. Right? Now about a vault (D) shaped chamber. Being as IR is radiation isn't the D shape a lens focusing it in the center of the floor? Hmmm?

In Alaska sodium silicate is considered a hazmat and nobody wants to pay the freight to ship it in. The rigidizer available is colloidal silica with a percentage of propylene glycol and requires heat curing to harden. I'd LOVE to be able to buy a couple liters of sodium silicate but the smallest quantity I can get shipped is a gallon.

Frosty The Lucky.

[aessinus]

10 hours ago, Frosty said:

...... I'd LOVE to be able to buy a couple liters of sodium silicate but the smallest quantity I can get shipped is a gallon.

Frosty The Lucky.

Several places on amazon have quarts, but + shipping.  The rutland gallon is prime eligible, free shipping for the same money ($30)

[Frosty]

20 minutes ago, aessinus said:

Several places on amazon have quarts, but + shipping.  The rutland gallon is prime eligible, free shipping for the same money ($30)

Not to Alaska. Somebody may be willing to ship but the fines for getting caught are ruinous and paying the fees to do it legally . . .  I'm looking at $110/gl. plus shipping, EPA fees, insurance, etc. The heat curing colloidal silica rigidizer is working, it's just more hassle but a boy can afford it, what's another day.

Frosty The Lucky.

[Adam R]

I will be taking pictures as I go, and probably posting all at once. I have been reading a lot on safety precautions associated with the forge lining materials before I jump into those processes. I want to make sure I am taking the proper precautions. There is a lot of info on IF about this that should be heeded.

I wound up cutting the tank 2" off-center to give myself the option of making the inside a bit taller. After I cut the tank apart, my brother told me he found a disposable helium tank by the dumpster of the clubhouse room where they live. The straight section of the tank is almost exactly the same as the propane tank section I am using. The wall is thinner so would have been easier to cut. If modified/squished appropriately, you could make an oval forge with the helium tank that is almost as big as the D-shape I am starting. I made a pan out of some light sheet metal that will hold the insulation for the bottom. I have stalled out a bit on progress after the weekend with other obligations and safety research, but hope to get some pictures uploaded next week. Not sure if the D-shape will concentrate the heat in the middle. That may be an advantage if forge welding temps are acheivable. I still could make an oval out of the pieces I have, but D-shape is growing on me.

Anybody know what sort of drying times that should be observed before firing the forge for the castable refractory? I imagine it should be a couple days to dry, then turn the burner on very low for a few minutes to get the forge warm, turn off, seal with fire bricks to retain heat, repeat with increasing heat/time for a couple cycles. I haven's found much info here.

[Oberu]

I found this, hope it helps

http://hightemptools.com/faq.html

[Adam R]

Oberu- that link has some great info. Thanks!

[bigb]

10 hours ago, Adam R said:

 

I wound up cutting the tank 2" off-center to give myself the option of making the inside a bit taller. 

I was going to do the same thing, plus the return curve at the bottom may help to retain the liner materials.

[Frosty]

12 hours ago, Oberu said:

I found this, hope it helps

http://hightemptools.com/faq.html

Thank you, that's the most concise and understandable directions for using refractories and such I've seen and I looked.

Frosty The Lucky.

[TFT]

Good thing im thinking of buying my supplies there... having good instructions for their products

[Adam R]

So after some life has happened, here are some pictures of my progress. I've lined it with the ceramic insulation, rigidized, and installed a first coat of castable refractory. The bottom pan was a bit of a trapezoid, and now that I've added the castable, there are some gaps on the sides, and between the top and bottom. I'm thinking that I still want to leave the two pieces separate, after I cure them, for putting on the infrared wash. However, I also want to seal between the two pieces with castable. Not sure exactly the sequence here, any thoughts would be helpful. I'm thinking of possibly laying a layer of castable down on the bottom and putting a barrier of plastic in between, to get the surfaces to "mesh", then take it apart after a couple days of drying. 

To mix the castable, I poured the dry mix into a large ziploc bag, added the water, then sealed it to mix. I figured this would help to eliminate the dust, which is the biggest health concern associated with this product. It worked pretty good, and then was disposable afterwards. It wasn't spreading very well with a putty knife, so I wound up using my hands with gloves on, and tapping the material into the corners and into a layer. That was as close to vibrating it as I could come up with on short notice and for a thin layer. I covered the pieces, with the wet castable applied, in plastic, to let it slowly dry for a couple days. One of the thicker spots actually took over 24 hours to fully set. I haven't seen it described before, but the castable acted like sand mix concrete with some quarter-inch stones.

After I figure out about getting the fit up right between the two pieces, and apply the IR wash, I plan to use zip screws with some bridger strips to hold the two pieces together. The inside dimensions of the forge are about 3 3/4 inches high by 7 3/4 inches wide. Between the insulation and refractory, I have lost a little bit of my desired dimensions, but I can possibly add a little bit of height when I do the next layer of castable, to make the seal.