[TheForge] Kaowool vs Soft Fire Brick

Thu Aug 18 21:26:12 EDT 2016

Thank you Frosty!  and everyone else!

I'll take pictures of the rebuild and let you know how it goes!!

Danr

On Thu, Aug 18, 2016 at 7:22 PM, jerry Frost <akfrosty at mtaonline.net> wrote:

> Daniel: First question is a NO, ceramic refractory blanket is a much better
> insulator than soft fire brick but it will dissolve in contact with hot
> borax like cotton candy and hot water, soft fire brick dissolves like a
> sugar cube. They're silica based so have little or no resistance to a
> caustic.
>
> I'm not a huge fan of cylindrical forges but they work well on several
> levels. Use 1" 8lb. ceramic refractory blanket for the outer liner or
> backer. Using two layers of 1" works better than one of 2" for a couple
> reasons. First no matter what you do a forge's liner is a wear item and
> it's
> MUCH easier to remove and replace one 1" layer than one 2" layer. 1"
> blanket
> rolls more smoothly so the interior surface of your chamber, (the Flame
> Face) will be smoother and cause less disruptive turbulence.
>
> I get 1" 8lb, Kaowool ceramic refractory blanket from a local HVAC supply
> and service company, "E.J. Bartell" by name. If you go to a service company
> they usually have drops going in the dumpster. They can NOT by law use
> scraps in someone's furnace, it must come off the roll. This means a little
> nice talk and schmoozing put me in Kaowool to last a life time. Just
> because
> I'm responsible for them selling mucho fire brick and now Kast-O-Lite
> refractory doesn't hurt. Our club is on their commercial acct. list. ;)
>
> Cut the blanket a little wider than will roll to size and compress it,
> it'll
> hold itself in position. Use a rigidizer on it, use a colloidal silica or
> sodium silicate rigidizer. Do NOT use one of the plastic rigidizers sold
> for
> sealing tile, stone, brick, etc. it will NOT survive in a forge. Wet the
> blanket then either spray or brush the rigidizer on and let it set up.
>
> A silica rigidizer does a number of beneficial things in the forge: First
> it
> encapsulates the ceramic fibers so they will not get loose and end up in
> your lungs. Breathing sharp particles is NOT good for you, even if it is
> pretty inert it's still a bad thing. There are ceramic blanket refractories
> that dissolve in water and don't constitute a breathing hazard but I'm not
> familiar with them.
>
> Another good thing about rigidizing blanket refractories, it makes them
> stronger they won't compress when you touch them. This will help the flame
> face survive mechanical abuse, if what it's laid on flexes it tends to
> break
> up.
>
> Okay that's the backer layer. Once rigidized you can use a sharp knife or a
> hole saw to cut your burner ports. More about aligning burners later.
>
> The Flame Face on any furnace takes the worst abuse and propane is one of
> the most chemically active fuels going. The three main things that wear out
> the flame face are: Thermal cycling, thermal erosion and mechanical
> erosion.
> Silica ceramics are not suitable for furnace liners in that they are
> susceptible to both high temp chemistry and caustics. Read the bag if you
> buy a castable refractory if that doesn't tell you enough pull the MSDS
> online. A MSDS won't tell you the formula but it will tell you what's in
> it.
>
> I line my propane forge with Kast-O-Lite 30. It's a high alumina ceramic,
> bubble refractory. High alumina doesn't care how much caustics you apply to
> it it's commonly used industrially in 3,000f+ ammmonia atmospheres
> furnaces,
> 2,600f borax is baby shampoo by comparison. The "bubble" part are little
> tiny vacuum filled(?) ceramic spheres seriously decreasing it's thermal
> conductivity. It's a MUCH better insulator than your typical castable
> refractory say Missou. I have ZERO bad to say about Missou, it's good stuff
> I just don't use it, I THINK the Kast-O-Lite is better.
>
> Like most water setting materials the less water you can get away with the
> stronger the set product will be. Still, if you're troweling it on it has
> to
> be wet enough to trowel, just do NOT get carried away with the water. Less
> is best! Follow the directions as closely as your application allows,
> especially setting and curing, it's a water set so it behaves very much
> like
> Portland Cement concrete, it wants to be kept damp or in a humid
> environment
> till it cures. Yeah it wants to be just barely wet enough to work and then
> wants to be kept wet while it cures. You guys who work concrete will know
> about this kind of stuff.
>
> What you're looking for is about  1/2" flame face, more is okay but much
> less and you need a different application technique called a "Kiln Wash."
>
> When I built my first double lined forge I used Sonotube (concrete form
> cylinders) to make the flame face. The outer tube had an inside Dia. the
> same as the OD of the hard liner I wanted. The inner tube had an OD the
> same
> Dia. as my target ID for the forge. I hot glued them to a board in position
> and rodded a castable refractory into the annulus. Once it was set I pealed
> the outer Sonotube and after a couple days dropped a couple lit charcoal
> briquettes inside to burn out the inside Sonotube. I let it cure for a long
> time with a light bulb in it I was working out of town so it was easy to
> let
> it be.
>
> I had my hard inner liner (flame face) and a pipe shell so I wrapped the
> hard liner with Kaowool and taped IIRC 3 layers of news paper around it to
> act like a ring compressor and slipped it into the shell. The first firing
> took care of the news paper nicely.
>
> Anywho that little digression is just an example of one way to make a
> double
> lined forge.
>
> Okay, lets assume you have your inner liner and backer in the forge shell.
> Did I forget the floor? Nope, don't use fire brick, it isn't resistant to
> hot fluxes and hard fire brick is a terribly good heat sink with an R value
> of less than 1. Soft fire brick is REALLY fragile even if you don't weld on
> it.
>
> Instead use high alumina kiln shelf. The stuff is strong, is very resistant
> to chemical erosion at temperature, has a low thermal conductivity # and is
> about the same heat sink as the hard liner/flame face.
>
> Kiln shelf is my recommendation for a forge floor, cut it with a carbide
> (veneer) or composition circle saw blade. Or you can score and snap it like
> glass or brick. Or if you're not confident about cutting it yourself have a
> ceramic supply store cut it for you.
>
> Okay, the last step, ITC-100 or equivalent, there are other products as
> effective and a LOT less expensive. Plistex and Metrikote come to my dented
> brain. Mix according to directions, wet the liner and brush or spray the
> kiln wash on, coat thoroughly and allow to dry according to the directions.
>
> I've been experimenting with adding Zirconium Silicate flour to castable
> refractory when making my flame face (inner liner) and not buying a kiln
> wash.
>
> Zirconium Silicate is THE magic ingredient in ITC-100 it's truly amazing
> stuff is the next hardest thing to diamond, has a vitrification temp around
> 4,500c and makes cool things like knives, hammers, etc.
>
> Anyway, that's the basic of a forge liner with good performance and about
> as
> long lasting as you're going to get without spending stupid HUGE $ on
> exotic
> refractories.
>
> Contact Wayne Coe for small quantities of forge building materials at a
> reasonable price. There are also detailed instructions for building forges
> and burners available on his site. We just do it a little differently his
> methods are sound.
>
> Wayne Coe
> www.WayneCoeArtistBlacksmith.com
> waynecoe at highland.net
>
> Now about Burners. Some of you are familiar with me and the T burner. It's
> a
> Naturally Aspirated (NA) propane burner that's easy to build and tune. Gun
> (blown) burners simply use a blower to supply combustion air rather than
> induce it with a propane jet.
>
> There is no real difference in performance between NA and Gun burners, how
> hot your forge gets is simply a matter of how much fuel:air in the proper
> ratio burns per second in the furnace chamber. PERIOD. Both types have
> advantages and disadvantages, just like everything, those arguments degrade
> into a blacksmith version of the Ford Chevy argument so use what you like,
> I
> don't have a dog in the fight.
>
> How you aim the flame in your forge does make a difference on a number of
> levels and there are a number of factors determining which you want or
> need.
> The important factors are what you're doing and chamber size. A common
> alignment is straight down at the center of the forge floor. My shop forge
> is aligned this way. It makes a hot spot directly under the burner and the
> chamber temp falls off with distance. I use the differential so certain
> areas of my work are more malleable. This allows me to work on one part
> without having the rest all floppy hot and need tweaking later.
>
> Guys who do a lot of welding, especially welding billets need a more even
> chamber temperature. In this case you want either a number of smaller
> burners or a burner aligned tangentially to one forge wall to induce a
> vortex. The spinning flame will even the chamber temperature significantly
> better than any perpendicular alignment.
>
> Cylindrical with a flat floor, or as I've started calling them "Vault"
> shaped, chambers are good for supporting a vortex UNLESS you align the
> burner to aim straight down at the floor. In that case the flame spreads
> and
> when it impacts the walls it's hitting a pocket and stalls. Sort of. If you
> align the burner so the flame impinges the top or one wall at a tangent the
> flame has no choice but to form a strong vortex in the chamber. Behind the
> burner port will be a low pressure zone so as the flame wraps around the
> chamber it impinges the same pocket that traps the perpendicular flame but
> now it's a low pressure zone so the flame turns up and goes on around.
>
> I need to find someone who can do cgi animations a picture is all you need
> to see all that talk.
>
> Anyway, aligning the burner to direct the temperature where you need it is
> important and easy to determine experimentally without building a permanent
> forge. Yes boys and girls I'm talking about the ever loving "brick pile"
> forge. This is one reason why I have a couple dozen fire bricks, hard and
> soft under a table. I can experiment with chamber shapes and burner
> placement without casting them in stone. They're not long term so I don't
> really care if they're efficient forges I'm just looking at temperature
> patterns, cold spots, etc.
>
> The other real benefit of a brick pile forge is doing demos. Most of the
> guys up here burn propane, decent smithing coal is a serious expense if you
> can get it at all. Anyway, I like to hope the occasional spectator at a
> demo
> will give it a try. However buying a forge is more expense than most folk
> are willing to invest just to try something out and visiting my shop isn't
> the same thing. $50 in fire brick, $15 in plumbing parts and another $50-60
> for a reg and hoses is within most folks test drive range.
>
> Long and rambly I know, any of you who read me on IFI know that already.
> I've been making T burners for some time now and since Mike Porter started
> posting on IFI we've been having some pretty in depth discussions of burner
> and forge design. Besides I LIKE playing with fire. ;)
>
> Frosty
>
>
> -----Original Message-----
> From: TheForge [mailto:theforge-bounces at mailman.qth.net] On Behalf Of
> Daniel
> Kretchmar
> Sent: Wednesday, August 17, 2016 3:59 PM
> To: Blacksmithing List Sponsored by ABANA
> Subject: [TheForge] Kaowool vs Soft Fire Brick
>
> I have questions for the hivemind:
>
> I wish to build a new forced air forge.  My current plan is (starting from
> the outside) 1. A shell from a 40 lb propane tank 2. A layer of fitted soft
> brick with high temp mortar or a layer of kaowool 3. satanite 4. Itc-100
>
> Questions: Will softbrick insulate as well as kaowool?  Will soft brick be
> more durable when using borax for flux or will it melt just as easily?
>
> Suggestions are appreciated.
>
> Danr
> www.,irontreeworks.com
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