Forges 101

[Rev. Mike]

On 5/10/2017 at 2:50 PM, Frosty said:

I just Googled "Red Devil 3000* F" and didn't dig deep enough to find the analysis so I don't know if it's silicate bonded or not. If it's a high silica refractory welding flux will erode it rather quickly. The closest Meeco product to the description is a refractory cement not a lining material. It's for cementing bricks and patching small flaws not a material designed to line furnaces. 

Frosty The Lucky I have a question for you or Mikey98118 has either of you tried ebay link removed. This Alumina-Reactive, ceramic & glass supplies it is 99.5 percent aluminum oxide to see if it is good for a Flame face ?

[D.Rotblatt]

On 3/23/2019 at 9:32 PM, u_p_country said:

I'll look into the Plistix and wait for more info from D.Rotblatt His methods are intriguing, especially his times to full heat!

OK.  I got the pint of colloidal silica (Nalco 1144) and ran some tests.  Upshot is that it works great!  You can read my tests below.  My recommendation is if you are using this colloidal silica/Zircon slurry for a shell to rigidize with a fused silica/H2O mix first rather then the Nalco.  

 The brand name is "Nalco 1144" and if you google "colloidal silica pint nalco 1144" you will find the supplier.  It cost me $11.98 and $5 for shipping. 8 oz is $7.99 and I imagine the same shipping.  There are many colloidal silica rigidizers out there from pottery supply houses, but only this one also mentioned that it was used for making a slurry for shell casting (which is the quality we need to make the shell for the forge liner), and came in small quantities.  It also says it can be used for rigidizing.  It looks different form my Adbond II and is a little thicker.  Note: any colloidal silica cannot freeze, therefor it cannot be shipped to areas that may it may freeze in route.  

Here's the details on my quick experiments:

TEST 1:

A: On a 6" piece of ceramic fiber I buttered it and then rigidized 3" with Nalco and the other 3" with a fused silica/water mixture (the powdered silica from amazon mixed with water).  Heated with torch to dry until I saw slight red glow.

B: Mixed two slurries.  Zircon/Nalco, and Zircon/Adbond.  Didn't measure, but tried to make each similar thickness, like latex paint.  The Nalco is thicker and makes a thicker mixture more naturally.  Buttered the ceramic fiber, painted a nice coat of Z/N on Nalco side, and Z/A on fused silica side. Dried with propane torch (about 2 minutes). The test piece was placed in the forge and heated to red hot.

C: the test piece was removed from the forge and allowed to cool (sped up by spraying it with a mist from spray bottle, no cracking = good thermal qualities, and no, I'm not a patient person about these things). A second layer of the two slurries was painted on and the drying/heat to red/cooling process was repeated.

D: A third layer of the slurry was added the same way.  Then the whole thing was left in the forge and turned up to welding heat for at least 15 minutes.  

E: OBSERVATIONS: Both sides looked about the same, the Z/N side was smoother.  As a rough test of hardness, I used the square end of a file to put increasing pressure on the middle each side until they broke.  The Z/A side tended to crack in the area under pressure and cracked easier. The Z/N side was much stronger, causing the blanket under it to compress until it cracked across the whole piece.   I broke several pieces off each side and measured for thickness.  The Z/A side was thinner, about .035" thick.  The Z/N side was about .050" thick.  Two hypothesis for the differences: The thicker side may have accounted for it's harder quality, or the fact that my Adbond II (which has a shelf life of about 1 year) is 12 years old.  

The Z/N side also shrunk on one end and on one side of this area the surface of the exposed blanket in about a 1/4-3/8" band below the shell layer was blackened (it seemed that that was the depth the Nalco had soaked in).  The shrinkage may have been due to it being pushed in and out of the forge repeatedly on that side, but it worried me having had the Adbond II cause shrinkage and melting of the blanket when used as a Rigidizer.  I was concerned that the Nalco was doing the same, or might do so at high heat over a period of time.

TEST 2:

So I decided to run another test only using the fused silica (which I know does not cause shrinkage or melting) for Rigidizer and the two zircon slurries for the surface coat.

The test was done exactly as Test 1, but I used fused silica/h20 mixture for both sides. There was no shrinkage of the ceramic blanket on either side.  

 

[u_p_country]

1 hour ago, D.Rotblatt said:

OK.  I got the pint of colloidal silica (Nalco 1144) and ran some tests.  Upshot is that it works great!

Dan, hope the camping was fun! Thanks for posting the pics from the borax works.

Thanks for running the tests and doing the write up. I'll be ordering some of the Nalco 1144 when things warm up here. Unfortunately that will be a month or so. I'm excited to have a new forge that heats up faster and still had some strength as well.  With my newly built burner it'll be like a whole new smithy!

Thanks again for the write up and be sure that I'll be posting my results here as well.

Adam

 

[D.Rotblatt]

You're welcome!  A little payback for all the information I've gotten on this site and the web in general!

Death Valley was a blast!  Ubehebe crater, salt creek and pup fish, Badwater, Darwin Falls....and best of all good bonding with my 16 y.o. son!  

Dan R

[D.Rotblatt]

This is the Colloidal Silica I bought:

18 hours ago, D.Rotblatt said:

The brand name is "Nalco 1144" and if you google "colloidal silica pint nalco 1144" you will find the supplier.

[Mikey98118]

Homemade Forges & Casting Furnaces

 

In recent years there has been growing interest in traditional metal trades, such as forging and casting. While the equipment, tools, and skills needed for each endeavor is quite similar, there has been strong resistance to combining these pursuits. Although short sighted, such tunnel vision is expected in hobbyists.

    Another natural tendency in hobbyists is to look for ways to profit from their avocations; and here the trouble starts. Whether you dream up a better widget, or just “go into art,” opportunists will be overjoyed to undercut your product. If what you produce doesn’t take much knowledge or effort, it also won’t take much to be copied.  

    The main difference between a casting furnace and a tunnel forge is that a furnace stands vertically, and most forges sit horizontally. Some people place their heating equipment in a cradle so that it can be moved back and forth between the two positions, and used for both jobs.

[Mikey98118]

It was while admiring a hinged and latched exhaust opening, that had been turned into a door, on a tunnel forge that the ideas occurred to me how nice it would be to use such a door on a box forge, so that that crucibles could easily be moved in and out, greatly enhancing its value.

[D.Rotblatt]

21 hours ago, Mikey98118 said:

a furnace stands vertically, and most forges sit horizontally

Good thoughts Mikey!  The other big difference is in the direction of the burner (more oblique angle) and that it is located near the bottom of the furnace.  Although I make forges with that oblique angle sometimes too to allow the gases to swirl.  Also I tend to make a forge with a flat bottom, not round.

That said, a two burner with a simple pivot (or different stand), round bottom and replaceable back would make a good double duty furnace/forge.  The hinge I put on the front door of the forge below allows it to be removed easily.  A simple pin in two holes, just lift it up.  Do that on the back and make a second "door" would allow you to replace the one with the small opening with one that is solid.  Since it's a two burner you would turn off the front/top burner and just use the rear/lower one.  One made out of a 20# propane bottle sized shell would accept up to a #10 crucible...that's 30 lbs of bronze or 10lbs of aluminum.  A lot of metal.  

As in all dual purpose tools, it isn't as fine tuned for forging as a single purpose forge, but it would certainly work fine.  Probably work the same as a single purpose furnace though.  For a shop with limited space, it'd be ideal!  Of course then you will need flasks, sand, rammers...sigh, there goes your space....

 

[Mikey98118]

Hidden costs

Propylene fuel costs about one-third more than propane if used from refillable cylinders; it also gets about one-third hotter, which means that the burner can be cut back a lot, for the same heat level in your forge, or a smaller burner can be used. Either way, the rate of internal atmosphere exchange within the forge interior can be slowed; this reduces fuel consumption per work heated drastically. Employing propylene calls for more expensive materials in the forge and in any flame retention nozzle, to withstand increased flame temperatures; thus cheaper building materials costs you once again.

 

You are quite right, Dan. There is no such thing as something for nothing

Getting heating equipment to due two different jobs well, takes extra work and minor sacrifices. A small forge/furnace would need two smaller burners in place of a central larger burner, but the burner angles would not be different than I recommend already (having started with casting furnaces).

The position of the forge/furnace would pivot, but the equipment wouldn't move. A simple box shaped carriage made of angle would allow the equipment to set on end, or on its side. The carriage would also support   exterior exhaust baffles made from round kiln shelves, trapped in a rotating steel frame, for both forge parts, and  for preheating and adding metal to crucibles. The rotation allows the baffle to pivot out of the way for placing and removing crucibles. A thumbscrew can lock the the baffle assembly in place for forge work. 

[Mikey98118]

On 4/2/2019 at 11:44 AM, D.Rotblatt said:

 Probably work the same as a single purpose furnace though.  For a shop with limited space, it'd be ideal!  Of course then you will need flasks, sand, rammers...sigh, there goes your space....

Yes, if you do very much casting, tools and space needed will expand, just as the further you get into blacksmithing of welding, or any other metalwork the  more space that will be needed. So, thinking about getting better service out of less equipment should be a foundational craft skill, just like drafting and budgeting

[Mikey98118]

Using Air/fuel torches as mini burners

Note: the self-igniting option on air/fuel torches doesn't usually work very long; its piezo eclectic crystal is durable, but the spark wire portion of the unit can fail in short order. What happens is that for a split second during ignition there is some blast force generated on the wire’s end; this gradually moves the wire enough to prevent the spark from jumping the gap between wire and the torch body (which provides its ground). You can push the wire back into position two or three times, and then it breaks off.

    There are a large variety of air/fuel torches, new and old, that can be remade into  equipment burners. Recently, I have been seeing MAP gas hand torches marketed online (AKA dual-use torches) that are rated to burn propylene as well as propane); some of them feature a stainless steel mixing tube, with makes them fit for use as equipment burners, with the addition of a doubling tube to prevent them being oxidized away.

    Some air/fuel torches now come with a short fuel hose, instead of just being mounted on a 16 oz. cylinder. Separating the torch from its fuel cylinder allows it to be easily positioned at any angle, while the cylinder, which must remain upright, can do so unhindered; but its value when mounted on a forge or casting furnace is that the fuel cylinder can then be kept a few feet away from the hot equipment.

    The latest versions of air/fuel torches also feature two needle valves. One valve is part of the cylinder fitting, while the other valve is mounted on the torch head. You may wonder why two valves? The answer is safety. With a separate valve at the fuel cylinder, the hose and torch can be exhausted of positive pressure after shutdown, while a second valve on the torch can then be closed, preventing ambient air from mingling with fuel gas in the hose.

    Without positive pressure, even a needle valve is unlikely to leak, while pure fuel in the gas hose is no more flammable than pure air is. We might think that simply detaching the assembly from the fuel cylinder will do the same job, but the reason that 1 lb. fuel cylinders are not supposed to be refilled is that, once opened, their valves are no longer reliable; they can leak.

    The whole point of discussing air/fuel torches is that they can be used, with some modification, as a practical substitute for 1/4" burners, which can be built, but would cost more than these torches, to do the same job; that job would be running two-brick and coffee-can forges; at less than $30 they are a bargain.

 

Note: there are fuel hoses of different lengths available, which have various fittings on their ends; some of them have female fittings on one end to connect with a fuel/air torch and a male fitting, with a needle valve included, on the other end to attach to a fuel cylinder; these allow you to use the torch of your choice to do the same jobs cylinder mount torches.

 

    “Flame tubes” are one of the various names manufacturers hang on the combination mixing tube and tip that their air/fuel torches use as flame retention nozzles. I have seen double, and even triple flame tubes on air/fuel torches; so long as their flame tubes are stainless steel, they should work okay inside miniature forges and casting furnaces, for a while. But, even when their flame tubes are made from stainless steel, things "are no slam dunk." My torch has a single stainless steel flame tube, which has an internal fin for helping to mix the fuel air mixture; that appears to also be stainless steel, but it might have been made of brass in a cheaper torch; this would have made it undesirable as an equipment burner.

    A double or triple flame tube isn't going to be easy to mount in a burner portal opening. More than one flame tube is going to be hard or even impossible to slip a doubling tube onto. My burner's flame tube wall is only about .030" thick. When mounted in a forge or casting furnace, the superheated portion even stainless steel tubing will oxidize away. Without a thick walled doubling tube, that torch wouldn't last very long. Also a doubling tube allows us to use thumbscrews in the burner portal’s tube to securely hold the torch in place. What it boils down to is that just because we can get away with a thing (for a while),  doesn't necessarily mean we should try to.

 

 

The STK-9 air/fuel torch: I choose this air/fuel torch, not because it will make the cheapest or hottest burner to build, but because it allows the easiest miniature burner to constructed, and is a reliable model. Aside from fitting a thicker doubling tube over its flame tube, all other parts are purchased with the torch, until you construct a forge or casting furnace and mount the torch in it.

    Building miniature burners from scratch are only fun for diehard enthusiasts. Furthermore, once you get down to a 1/4” homemade burner size, reasonably priced propane torches can more than match their output for less money that you would spend on building materials to construct a burner from scratch. So, for use as air/fuel hand torches, building such burners are largely a waste of time.

    Until recently, canister-mount air/fuel torches didn’t get mini forges and casting furnaces hot enough to be a practical choice; the problem was that their brass flame tubes had to remain outside the equipment’s burner portal, to keep from being melted; this led to excessive secondary air being inducted into the equipment by the flame,  interfering with proper heating.

    Stainless steel tubes have been appearing on some air/fuel torches in recent years, so that they would able to also burn propylene fuel safely (since the Canadian plant was switched over to it in 2008, all so called MAPP fuel has actually consisted of propylene since then).     

    A stainless steel tube also allows, “dual fuel” torches to heat miniature forges and casting furnaces (coffee-can size and smaller) efficiently, through mounting in a burner portal exactly like commercial and homemade propane burners; this also holds true for “two brick” miniature forges.

[Mikey98118]

A sensible box forge

So when might a steel shell amount to silliness on a forge? Let's talk  some about the why of box forges. Assuming that box forges started out as a way to accommodate straight refractory products like bricks, ceramic fiber board, and high alumina kiln shelves, Coming up with a box shape is no great stretch, right?

    And most of us don't want such expensive materials wrecked, so steel cladding comes quickly to mind. If you're running a busy steel shop that makes sense, but if that new forge is going to live in your studio, I would recommend just keeping gorilla types outside of locked doors; this will save wear and tear on a lot of other equipment too. Just post a sign saying "no brats allowed". Keep a whip and a chair handy; brats don't leave quietly.

Which brings us to what should sensibly follow in typical box forge construction:

(1) For most forge sizes: Morgan K26 bricks from Technical Ceramics for floor, walls, and ceiling.

(2) Refractory cement to glue the ceiling into one piece, the floor into one piece, and each wall into one piece (six parts in all), Cementing the bricks makes your forge more stable, but hampers its ability to change size, so run your forge  long enough to decide that its size and shape is where you want it most of the time, before cementing anything more than the ceiling bricks together.

(3) The thinnest high alumina kiln shelf you can find to cover the floor. Or a small sack of Kast-O-lite 30. A kiln shelf over the ceiling bricks is a smart bet too, but it can be an add-on.

(4)   four sections of angle, and four sections of all-thread, with matching nuts and flat washers to  allow the angle to keep the floor, ceiling and walls together.

(5) a floor flange, pipe nipple, six thumb screws to make a burner port to mount on the top side of the ceiling, and hold the burner. Most people find a floor flange makes a good anchor for a burner portal on brick.

(6) A good burner, with valves, regulator, hose, and fuel cylinder.

(7) Four extra bricks (minus whatever bricks you left out of one wall to leave an exhaust opening in the front of the forge) to make a baffle wall in front of the exhaust opening.

(8) Plistix or Kast-O-lite 30 to coat the wall and ceiling panels interior faces with.

(9) A large square pan, nearly full of Perlite from your nearest garden center to place to forge on.

Beyond these items there can be a long list if you like, but it will all be add-ons This list is all you need to construct a basically hot, efficient, and safe box forge.

[Mikey98118]

Forge size

It is a natural desire to go for the largest forge you envision yourself ever needing; and that is nearly always the wrong move. There is no such thing as a forge that is too small; if and when you outgrow a smaller forge, you will still find yourself using the small forge whenever possible, to save time and money. On the other hand, an oversize forge usually ends up collecting dust in a corner--to save time and money.

    Building costs of forge construction are directly proportional to size. What’s worse is that you will end up using second rate refractory materials, and burners, to save on construction costs in larger forges; this can end up tripling the expense of running your forge. The larger the forge interior the greater the heat loss through the walls, ceiling, and floor. The greater the heat loss the more fuel that most be consumed to keep the interior heated, which leads to increased heat lost through the exhaust opening.

    First class refractory and insulation choices are expensive; too expensive to be used in large forges. Propylene fuel costs about one-third more than propane if used from refillable cylinders; it also gets about one-third hotter, which means that the burner can be cut back a lot, for the same heat level in your forge, or a smaller burner can be used. Either way, the rate of internal atmosphere exchange within the forge can be slowed; this reduces fuel consumption per work heated drastically. Employing propylene calls for more expensive materials in the forge and in any flame retention nozzle, to withstand increased flame temperatures; thus cheaper building materials costs you once again.

    The hotter eqipment gets the faster it heats your work, reducing fuel use even more; not to mention time wasted. 

[Mikey98118]

First Forge for newbies

I am a great believer in "no one shoe fits all," and no single burner is the best for every purpose. However, I believe that ribbon burners do the best job for the least time invested by a typical beginner. What kind of forge you want is swayed by many factors. Someone into jewelry may find a coffee can forge rather large. A knife smith may never want more than a half-muffler forge. Someone into scroll work will prefer a clam-shell forge...and on, and on.

All this aside, most beginners long to "cut to the chase" and just come up with a good all around choice without earning an advance degree in forge design. For you people, I suggest making your first forge from a five gallon propane cylinder and running it from a ribbon burner. 

[jwmelvin]

46 minutes ago, Mikey98118 said:

For you people, I suggest making your first forge from a five gallon propane cylinder and running it from a ribbon burner. 

Do you mean a blown RB or a NA? I was under the impression that the NA ones are a bit fussy so have started with a NA linear-injector burner. I do have a hot tub blower (and a couple old vacuums) I might be able to use for a blown burner...

My first forge will be the five-gallon size you suggest. Any ideas on how to locate local suppliers for refractory materials? I’m in Northern Virginia and haven’t seen much from a couple web searches. There is a pottery supplier I need to call. I have a bunch of 2” Fiberfrax for a primary insulator. 

[HojPoj]

Jwmelvin, Clayworks in Alexandria should carry K26 bricks.  There should be plenty of places you could check for castable refractory (boiler services, etc.).  Also, look through the sites for the refractory manufacturers, they usually list distribution centers for their products. 

[Mikey98118]

9 hours ago, jwmelvin said:

Do you mean a blown RB or a NA? I was under the impression that the NA ones are a bit fussy so have started with a NA linear-injector burner. I do have a hot tub blower (and a couple old vacuums) I might be able to use for a blown burner... 

Either way.

[671jungle]

New forge build. Dropped the last one with the aluminum body and the kasto cracked. I didn’t bother sealing it up and the heat leak was too much for the aluminum. Which I knew/hope would happen. 

So, eager to build again (I think I’m more addicted to design than anything), I gathered more materials. I wanted the same D shape but even smaller.

I would like to use a 1/4” burner or burners. If more than one which I’m leaning to, how many? Is three too much? 

It will be insulated accordingly:

2” of rigidized wool everywhere coated with kasto.

[Mikey98118]

22 hours ago, 671jungle said:

So, eager to build again (I think I’m more addicted to design than anything), I gathered more materials. I wanted the same D shape but even smaller.

Good; I would like to see more people choosing to make "D" forges

[jwmelvin]

Any thoughts on best construction techniques to have the burner entry pointing towards the forge ceiling? I'm thinking of building up a refractory layer (kast-o-lite 30) on the blanket there and then using a topcoat of Plistix 900F or the like. This is my first forge, so I don't need it to last forever but I'd like to at least have a reasonable approach; but I would like the burner to enter from the bottom so the burner doesn't superheat after it shuts down.

[Mikey98118]

There has been at least one excellent example of this same forge design on the ribbon burner thread. You could do worse than to follow his.

[Another FrankenBurner]

We have a forge with bottom mounted burners.  It is built as you describe.  Two inches of rigidized ceramic blanket and 3/8 inch of kast o lite.    We used metrikote instead of plistix for the hot face but looking at the sheets on them both, I can't see much of a difference.  The burners are cooler at shutdown but also much cooler during running when compared to a top mounted refrigerant jug forge with the same burner.  We leave the chokes open after shutdown so the burners draw ambient air through them, keeping them cooler.  I like it so much I will probably never top mount another burner.

[jwmelvin]

Thank you Another Frankenburner, that’s helpful. 

[Mikey98118]

Kast-O-lite 30

Kast-O-lite 30 insulating castable refractory poured in a 1/2” thick layer gives a large measure of thermal protection, along with mechanical armoring, incase you are moving crucible tongs in and out of your equipment, and for general shop safety; it is use rated to 3000 F, is alumina based for flux tolerance, contains glass mini spheres for insulation, and is very resistant to thermal shock; it ways 90 lbs. per cubic foot (compared to 146 for regular refractory). Kast-O-lite 30 has been the favorite refractory for construction of home built forges and casting furnaces for over twenty years.

    This refractory hardens gradually enough that the edges of equipment surfaces can be scraped with a straight edge, so that those surfaces meet properly, allowing two part forges and furnaces to run with only minor flame leakage.

    Kast-O-lite's moderate insulating value is of great importance for protecting insulation from heat damage; when coupled with a re-emissive (heat reflective) finish layer, it will greatly lengthen the working life of insulation.  

Kast-O-lite 30 will stick too most materials. Use cooking spray, Crisco, or car wax on plastic or wood molds as a release agent. I have also used glass jars, and then shattered them with heat and water after the refractory was cured. Cardboard and wax candle molds both burn away conveniently.   

[Mikey98118]

Drain holes

 When you add a seal coat, it will be water based; as it dries, some of that water content will wick into the fiber insulation. Furthermore, any cracks, the burner opening, etc. will allow water vapor from the air to wick into fiber insulation, where a significant amount of it can collect over time . A drain hole on the bottom of the forge shell will allow steam and heated water a path to exit the forge, without building up and doing pressure damage. If is just a wise measure to protect your hot-face layer this way. A 5/32" drain hole is probably ideal, but 3/16" is good enough.

Moisture has twenty four-seven to to gather in your forge's insulation, but only minutes to be expelled once you fire the forge up; give it a little help.