One piece Vs sectional forge liner

[Simian]

Me again, Asking more questions (sorry)

I'm building a small forge - some where around 150 cu in (2.5 Litres). 

I'm struggling to line it with castable as the entrance is really small - I can barely get my hand in. Is there any major disadvantage to casting a large flat 1/2" thick floor (over 2" of Kaowool) for an upper shell to sit on? 

 

This would make it a D shaped forge, easily replaceable floor, and I'd be able to cast the upper easily. 

 

I'll draw an awful picture if that doesn't make sense

 

[Mikey98118]

There are semi insulating refractoroes, which will not become a burdensome thermal mass. High alumina kiln shelves are in this category. Even simpler is to buy some Perlite from a garden supply, and mix it into hard castable refractory. Add about one-third Perlite, by volume, to two-thirds castable refractory.

Well, why not use hard fireplace brick then? What is bad about hard firebrick is that it consists of clay. The amount of silica in clay--even fireclay--is way too high, because silica transmits heat seven times more readily than the other main ingredient; alumina.

[Frosty]

Another way to line a forge that small is to hammer and roll the refractory into an even sheet, 1/2" thick is a lot but not horrible. Then wrap the refractory sheet around a mandrel  allow it to dry and slip it inside the kaowool insulating outer liner.

I made my first multiple liner forge in a similar manner, I rammed the hard refractory between concrete form "sonotube" let it dry and fire cured it with charcoal briquettes. Then I wrapped it with Kaowool and compressed it with news paper and tape so it would slip into the forge shell.  Drilled the burner port with a couple old hole saws, one ground sharp to slice the Kaowool the other a masonry bit. Added a layer of hard refractory to the inside wall of the port and once the final bits that needed a refractory layer was all dried I fired it with the burner. The paper / tape holding the Kaowool compressed burned off pretty quickly and holds the hard liner solidly.

Those are two potential ways to skin this cat.

Frosty The Lucky.

 

[Buzzkill]

22 hours ago, Simian said:

Is there any major disadvantage to casting a large flat 1/2" thick floor (over 2" of Kaowool) for an upper shell to sit on? 

I have done this.  There are a couple things to consider.  The thicker you make the floor, the more it is a heat sink.  The result is more time required to heat up the forge and a longer cool down time.  A half inch isn't too bad, but it becomes much more noticeable if you go thicker.  Each forge/burner combination is different so it's hard to compare to what other people have done, but I'm still able to go from a cold forge to forge welding temperature in about 20 minutes with a cast floor as you describe and a "D" shape overall.  However, I'm using a ribbon burner and the volume of my forge is a little larger than yours.

The other issue I had was getting a good fit between the upper forge body and the floor.  It seems like it should be easy, but if you are trying to avoid having any gaps at all it is not so simple.  I ended up using strips of some extra kaowool, which I treated with rigidizer, as a gasket between the floor and the forge body.  That has worked well so far.

[Mikey98118]

2 hours ago, Buzzkill said:

I ended up using strips of some extra kaowool, which I treated with rigidizer, as a gasket between the floor and the forge body.  That has worked well so far.

Interesting; without rigidizer the strips would "take a set," and should work out pretty well as a gasket, but how does rigidizer affect their mechanical properties, when used the blanket is used this way?

[Simian]

Thanks guys - you've actually answered some other questions I had too

Mainly, I'm hearing 'find a way to make it one piece'.

buzzkill ;

[Mikey98118]

What you're hearing isn't what I'm saying; I doubt that it is what Frosty intends either. For me, every forge design has it inbuilt limitations, and construction "factors"; I am careful not to think of them as problems, so long as I like the design. "Problems" is a category used with forge designs I dislike. I could go even further and call them "points of interest"

[Simian]

Thanks Mikey, Message received!

I think I'm confusing too many factors - I'll break it down a bit and work through them one by one. 

I have the best High alumina castable I can find in the UK (recommended by other smiths). 

I've read a  lot on here to suggest that a 1/2" floor, and 1/4" layer of castable 'shell' is ample, and I'll use 2 layers of 1" Kaowool. I can make a steel case for it.

Is there any major downside to the image on the left, as opposed to the image on the right. (sorry for the awful drawing). Buzzkill has pointed out one - making the one on the left with no gapping.

I believe the image on the left will be much easier to build - that's all. 

 

Am I overthinking this? I have a habit of doing so!

[Frosty]

Sorry about that. A bunch of folks saying similar things can get confusing for sure. I only threw out a couple methods I've used to make a cylindrical forge and one of them is the last time I used either. I do NOT make nor recommend cylindrical forges. 

I'm a huge fan of D shaped forges though I am a bit miffed nobody recognized the superiority of VAULT forge for the shape. It seemed pretty obvious to me but OH NOOOOO!

Seriously I love the D for a chamber shape and have been recommending them for quite a while but not by that or any name. 

In fact I'd planned on building one like the drawing on the left but then NARB entered the picture and I never got around to it. There is a "version" on my sketch pad but it's significantly different and If I get around to making it I will by GOLLY INSIST everybody use the name I give it. 

There are tricks for making the two piece D forge to minimize leaks between the halves. Some easier than others. My first step is make the top half and make it with the flat edges on a uniform FLAT surface. Lay down parchment or butcher paper so it doesn't bond itself to the table. If it turns out uneven sand it FLAT on a concrete surface.

Make the table the same way, on a flat smooth surface. You will of course need to make allowances for the burner in advance but it won't effect the important places. Once they're set and cured the mating surfaces should match well enough to not leak much at all. A strip of refractory paper is all the gasket you'll need.

You can buy refractory paper at a pottery/ceramic/kiln etc. supply.

If I were to make one like your second pic I'd have to make a core that came free easily or just burn out. I'll leave that to others I'd make the two part one.

Of course you're overthinking things, it's what folk's who are breaking into a new craft, job, etc. do. We all do it if we have the imagination to be any good at the anvil that is.

You're good, bounce ideas off us it's why a lot of us are here.

Frosty The Lucky.

[Jimw3326]

I'd put a step on the floor for the one on the left. Cut the wool in half and double the floor thickness with the second layer inside the dome. That should take care of any leaks.

[Buzzkill]

20 hours ago, Mikey98118 said:

Interesting; without rigidizer the strips would "take a set," and should work out pretty well as a gasket, but how does rigidizer affect their mechanical properties, when used the blanket is used this way?

I delaminated the blanket so that the strips were less than half an inch thick.  I soaked them with rigidizer before putting them in place, partially to reduce the risk of airborne fibers.  I placed the forge body on the strips while they were still wet and fired up the forge.  While probably unnecessary, this essentially fused the floor and top shell pieces together.  I've had to take it apart once since then and the blanket gasket pulled apart in the middle.  So, ultimately I'd say the advantages of using rigidizer are a reduction in the likelihood of airborne fibers (although it's not a big risk due to the small amount directly exposed to flames) and probably a slightly better seal than the blanket alone. 

I should probably also mention that when I coated the interior of the forge chamber with a kiln wash the small amount of exposed blanket received a coating of kiln wash as well. 

20 hours ago, Simian said:

Mainly, I'm hearing 'find a way to make it one piece'.

Not at all.  I'm happy with the 2 piece constuction overall.  I was just letting you know a couple small issues to consider.  As far as I'm concerned it's the best design I've used so far.

16 hours ago, Jimw3326 said:

I'd put a step on the floor for the one on the left.

If done right this could work well.  It would certainly cut down on the amount of castable refractory needed for the floor.   I may give it a shot when I have to rebuild my forge the next time.

[Simian]

C'mon, do your worst. How badly have I messed this up?

Huge hole on side is for the ribbon burner, rear hole will get plugged unless needed... I just need to wrap it in Kaowool and steel.

 

For scale, the main former was a 2 litre soda bottle.

 

[Frosty]

Uh . . . It doesn't look very hot? Otherwise it looks pretty good at this stage. What refractory did you use?

Frosty The Lucky.

[Simian]

Cheeky! And impatient

It's a  1600C (2900F) 40% alumina castable recommended by some other smiths in the UK. Water setting, same as Kastolite. Close to 1/4" over most of it, 1/2" for the floor and around the openings.

Somewhere around 150 Cu in.

[Mikey98118]

On 7/17/2023 at 4:02 PM, Frosty said:

I'm a huge fan of D shaped forges though I am a bit miffed nobody recognized the superiority of VAULT forge for the shape. It seemed pretty obvious to me but OH NOOOOO!

Well, we could start calling the top part its "vault"; I like that term better than "top."

[Frosty]

150 cu/in is right in range for a 1/2" NA burner.

And we could build a groined vault forge with built in ribbon burner. 

Frosty The Lucky.

[Simian]

See the 1/2" Amal on the ribbon burner above, Mr. Frosty. 

once it's up and running I'll tune the 1/2" frosty burner on it, leaving the Amal free for other duties.

[Frosty]

I'd try both and pick the best one for the job. I'd have an Amal to check out if they weren't so expensive here. I'm always willing to adopt good ideas you know. 

Frosty The Lucky.

[Mikey98118]

What I don't see is an external supporting shell. Are you planning on adding external mechanical support with heavy layers of Perlite that is bonded together with water glass? That would also act as secondary insulation.

"water glass, also called sodium silicate or soluble glass, a compound containing sodium oxide (Na₂O) and silica (silicon dioxide, SiO₂) that forms a glassy solid with the very useful property of being soluble in water. Water glass is sold as solid lumps or powders or as a clear, syrupy liquid."

Copied from the Net

[Buzzkill]

23 hours ago, Simian said:

How badly have I messed this up?

Not at all as far as I can tell.  Looks quite good.

There is a very small design feature I did a bit differently and I can't tell you for sure if it really matters.   Around your front opening you have a thicker portion (I assume you did that for more durability at the opening) which effectively makes a lip going up into the insulation.  What I did on both ends was the same principle, but I put the lip inside the forge chamber.  My reasoning for this (again I can't say for sure is correct) is it would help keep the flame in the center of the forge chamber a little bit longer and therefore transfer more heat to the lining before exiting.  Of course I have most of the front and rear openings closed off/restricted while in use, but I'm hoping that the swirling gases try to "hug" the shape of the lining and will be slowed a little bit by having to go over the lip to get out of the forge.

Regardless, I think you're going to be happy with what you have when you get done with it.

[Simian]

gimme a shout if you want me to pick one up and send it on - I suspect it wouldn't end up much cheaper tbh (but I don't know how much they are for you in the US?)

 Whoa... Whut? There's me planning some Kaowool and a steel shell and you throw that into the mix? I now have MUCH reading to do on that...

Buzzkill  The thickness at the openings was indeed for strength, and I considered doing exactly what you described (the rear on mine is half closed anyway). due to the way I formed the... er... former, it would have been hard to achieve. Looking back, I wish I had tried harder on that. We'll see. Making another liner wouldn't be too hard if I think it's needed.

I also have a load of Colloidal silica and Zirconia silicate for a DIY IR coating. I'll hopefully get the insulation and shell done at the weekend, but for now, the liner is curing  

Thanks again for all the help/pointers guys.

[Frosty]

Thanks but I don't mess around with burners much anymore so doing comparisons to maybe learn a trick or two isn't really a thing fore me anymore.

Frosty The Lucky.