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Mikey98118

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Burner positions are changing

Burners have improved over the years, and are continuing to do so. Refractory product improvements are expanding even faster than burner improvements. Both changes are shifting the ground rules for forge design. Top-down facing burners were the rule for good reason in the past, mainly because it played well with the limits of available materials. But while new materials, including K26 bricks, can simply be used to improve performance of standard forge designs; they are better when used to gain more distance between flame and work for complete combustion, and therefore a reduction in scale formation by pointing burners up and away from the work in tunnel, "D," and oval forges, or high on a side wall of box forges.

And the point of all this being? A neutral flame is not only hotter than even a slightly reducing flame, but it is much better for your health :)

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 A second look at K26 firebrick

"Circumstances alters cases" is become a watchword with me. Mainly what drives the thought is trying to make reasonable suggestions about construction materials in an ever changing marketplace. K26 firebrick is a good example of the problem; this is the best refractory brick to come along--EVER. But its price on eBay has more than doubled this year. Last year it made a great choice and value for making a brick forge; today, not so much on the valure end. It is still a smart choice if used sparingly with other materials. 1" thick brick can be use as an intermediate layer or a hot face, and backed up with ceramic fiber in box forges, with lower cost.

Probably the best bang for the buck is to use a K26 brick below a high alumina kiln shelf, or a cast refractory layer on the floor of a forge that has a top mounted burner.

Eventually, as the brick grows in market share, competition will lower its price again; in the meantime, it is better to use it frugally than not at all :P 

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Mike: I think we need to start specifying "Morgan Thermal Ceramics K 26" fire bricks. I haven't tracked it down yet, I just don't remember but I ran into the "K- xx" as a spec. based ranking system regarding fire brick and refractories. Red brick was IIRC K-12 and 3,000 f. hard fire brick was rated K-28 up to K-29. The old IFB (Insulating Fire Brick) that I used to use was rated at K-21 and those are the ones that started degrading after a couple firings. They have a max short term temp rating of 2,200 f. and are vulnerable to thermal cycling.

I'm afraid if guys call or walk into a supplier and ask for K-26 fire brick they'll get a product that meets the specifications on the K scale rather than the Morgan K-26 thermal tile product you and I love so much. There is significant difference between a max short term temp rating and a max daily working temp plus a safety margin and high thermal cycling tolerance. 

I'm not sure how we should address this IF what I read means what it looked like when I read it. If I'm not mistaken we're dealing with two visually identical products with the same name but significantly different performance specs. 

Frosty The Lucky.

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Perlite is so overlooked

It looks like K23 bricks are only good for secondary insulation; so guys might as well suit their pocketbooks about what brand they choose. For that matter, whether secondary insulation surrounding a full two inch thick layer of Morgan Thermal Ceramics K26 firebricks, or a third layer of insulation outside of of a two inch thick layer of ceramic fiber blanket, is where I would recommend Perlite from the nearest large hardware store's garden department. Perlite, whether trapped in position or glued into a monolithic layer is an ultra cheap highly insulating; and highly under rated choice for insulation (good to 1900 F).

I think that probably one of the reasons Perlite goes begging as an insulation for tertiary layers is that most people don't want to go through the bother of trapping loose Perlite, and think that sodium silicate is the only way to glue the Perlite chunks together. However, fumed silica is dirt cheap; it can be flowed through Perlite trapped in a shell as easily as water, and the overflow can be gathered in a pail under the forge shell and reused. Do I know this will work well? No; but I think it well, and intend to employ this method  to help build coffee-can and half-muffler forges this spring.

So long as temperatures next to the Perlite do not reach 1900 F, it will not degrade from thermal cycling at all, unlike 2300 insulating fire bricks do. Monolithic insulating forms made of Perlite and  sodium silicate (AKA water glass) have been used as outer insulation of glass working equipment for several decades, and hold up just fine. So why not cotinue with sodium silicate? I think it's getting a little pricey these days?

Thanks for the photo and note of warning, Curtis; this is very valuable information.

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I wrote myself a note as I typed my last message and remembered to call Distribution International this afternoon. Morgan or ITC, K-26 fire brick is $5.26 each for singletons not counting the club discount nor case lot price. That's still well less than 1/2 the price of the old IFBs that crumbled.

At what distance from the flame face do you think a person could use fiberglass insulation on a forge, Mike?

Frosty The Lucky.

 

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An update on the Zircon/Colloidal silica eggshell lining for my forge.  To recap: The shell is a small helium tank 9.5" in diameter with an added 6" in length, inside is 1" of ceramic fiber, rigidized with fused silica and water, then coated 3 or 4 times with a mix of Zircon and Colloidal Silica (as discussed on the page before this).  On the bottom is a soft firebrick (K26 I believe), the surface is also coated with zircon/colloidal mix.  I am considering cutting the brick 1/2" lower, and putting 3/8 " ceramic media from my tumbler on it so the bottom of the metal warms, and so I can brush it out and put in a kiln shelf if I want to use flux.  I've been playing with fluxes welds - I'll see if that works in the forge well.  This coating is basically what I've used this before with the following changes.  The wool was rigidized first with the fumed silica, and I applies more coats of the zircon bringing it to around 1/16" thick.  I must say, having rigidized the wool first with the fused silica made it much easier to apply even coats of zircon.  

Using a K type pyrometer; the forge gets up to forging heat (1600-1800F) in 3 minutes and starts to stabilize, and after about 5 minutes more is pretty stable in temperature.  I brought it up to 2350F and it seems happy as pie, that's probably hotter then I need to forge weld.  I had actually lined this forge first with 1/4-1/2" of mizzou refractory and fired it up, but it took so long to get to heat (it too over 20 minutes just to get to forging heat) that I ripped it out and relined it using my old eggshell technique.  Same burner, 1/10th the heating time.

Here's a pic of the forge:

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On ‎1‎/‎9‎/‎2019 at 12:36 AM, Frosty said:

At what distance from the flame face do you think a person could use fiberglass insulation on a forge, Mike?

My understanding is that fiberglass is only rated to 1200 F. I wouldn't even use it outside of the forge shell. Why bother?

D.Rotpatt,

Thanks for the update. Your forge is looking plenty hot enough these days :)

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About what I thought, I tend to think about the extreme sometimes. Insulation is only meaningful to a point and I can still touch the outside of my forge with a 2" Kaowool liner. I don't think better insulated would mean much on such a small furnace.

Frosty The Lucky.

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For me, the only point of insulation is to help the hot-face (the interior surfaces) of the forge to radiate in ever higher levels of incandescence. The better the insulation the higher that level of radiation can go; or the more fuel input can be cut back. So yes, added external insulation can help, but how much insulation we use before we are gilding the lily is another matter. Perhaps some different questions could give some perspective to insulation. Before trying to insulate outside of the forge shell, have we contained the induction of excess secondary air? Have we provided a good re-emissive coating on the hot-face surfaces to slow down heat loss into the insolating layers? Have we provided a baffle wall to reduce radiant heat loss along with exhaust gases? Have we upgraded the burner to transfer maximum heat into the forge from fuel use? Every one of those factors will do more for performance than tertiary insulation, so only after all of them have been addressed would exterior insulation make any sense.

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In my simplistic terms you want to keep as much heat inside the forge as possible. I paid for the fuel I want every BTU I can get for it. I'm a blacksmith and part Scot you know. B)

We're pretty much on the same page with maybe different terminology and views. I look at insulation as isolation between the fire and ambient. I know a difference without distinction. However changing terminology causes different ways of looking at things. Different view points is like having someone else look at it.

If you look at insulation as a way of reducing heat transfer, can't stop it of course, it invites the idea of, thicker is better. 

Now look insulation as isolation. Barriers don't necessarily stop transfer but may deflect or reflect whatever it's used for. 

Now, as you say making the flame face as incandescent as possible is the ultimate goal of a reverberatory furnace wall. Currently we're backing a hard inner liner, the flame face with refractory insulation to reduce heat transfer and allow the flame face to retain more heat to re-radiate. 

Now try thinking about everything after the inner liner as isolation instead. A vacuum thermos bottle is a perfect example, there is no, ZERO insulation, it's all isolation, Stainless inner liner, vacuum, stainless outer liner. All the stainless is polished to reflect IR and vacuum doesn't conduct . . . anything. Nothing's perfect of course so your thermos only keeps things hot or cold for a few hours. Now apply the idea of isolation to a furnace and give your mind's eye it's head.

Large recuperative furnaces have space between the inner liner and the next liner. Usually both hard thermal sinks but the furnace's exhaust is drawn into and circulated between the first and second furnace walls. The flame face isn't transferring heat at all, it's being heated from both sides.

The second liner has to be almost as robust as the flame face liner. The outer layers are the insulation to conserve the heat they can't redirect back into the furnace.

With me so far? Silly question I know Mike, you've looked at this stuff, maybe so long ago you haven't thought about it in decades. I may be talking to "you" but I'm describing this stuff for folks who haven't studied and thought on furnaces like we have. 

Recuperative wall construction is darned hard to use on something with 300-700 cu/in. Not impossible put a serious PITA. Making exhaust gasses flow through the space between is problematical especially if the door is open. I've been batting ideas around for a couple decades now and discarded most as silly hard to do or inefficient or . . .?

So, forget a recuperative wall, how about just dead air space? Radiation is the poorest method of heat transfer AND it can be reflected, especially if the environment can be cooled enough shiny things don't turn black and scaly. Monel, Inconel? <_<

What I've been thinking lately is a 1/2" castable bubble refractory inner liner, washed with an IR reradiating material. Then say 3/4" - 1" empty gap and now for the hard part, a shiny metal cladding on a second hard or maybe refractory wool liner. This configuration may require both walls in the space to be a hard refractory as temps may exceed Kaowool, etc. tolerances. 

Of course a person could use more than one dead air space to further isolate the insulation from the serious HEAT. 

Yeah, I know Ceramic blanket is largely dead air space "contained" by a material that's a really poor conductor but you can't reflect IR back through it. So there are the two main arguments, difficulty of construction aside, Better insulation vs. reflecting IR back into the inner liner. 

How I gauge adequate insulation in a forge is. Can I touch the shell after it's stopped warming? (terminal temperature?)

Anyway, that's what's been rattling around my head for a while now. Isolation vs. insulation and the potential implications.

Frosty The Lucky.

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Actually, I have thought about  recuperative forges since the Scandia laboratory's stainless steel recuperative forge came out; even bought a set of plans. The forge was worthwhile, even though it had to be completely rebuilt frequently. But not many smiths would do that more than once or twice. Double refractory walls have been used in glass day tanks for recuperation for decades, but as you pointed out, the smaller the equipment the trickier they get. However, with the refractory coatings we are stumbling across these days, added to the cast refractories now available, a recuperative forge is now practical. Unfortunately, most guys have to many good alternatives, which have also come along recently, to put in that much work :P

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The problem with the Sandia recuperative forge was overheating the fuel air mix in the burners it tended to burn back if you closed the damper very much. And rebuild frequency was a factor. I don't think any of the issues couldn't have been tweaked out but I don't think anymore development was done on it after ABANA published the plans. 

I tried a couple versions of fuel air preheat but ran into overheating problems, it's just not that hard to get it hot enough to pre-ignite in the burner. I considered it for the ribbon burner too but it's hard enough keeping the block cool enough to prevent burning back. 

I just keep coming back to the recuperative wall or a version or just letting all that beautiful heat leave the building. Man that just eats on the Scot in me.

Frosty The Lucky.

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I transferred this over as mentioned I should do. 

Here is my first attempt with mistakes upon mistakes but in the end, It works!

the post was this:

For several months I been using two propane torches to try my hand and forging small steel stock into flint strikers and other things. One torch is a bernzomatic BZ8250HT and the other is a modified Old bernzomatic all brass torch. Both are regular propane/mapp torches. I been reading for months about what forge to buy. Then decided since I don’t know if I really want one I’ll just make an easy mini can forge. I Used Koawool, Kast-O-Lite 3000 and Metrikote. Heat source will be my modded torch head. I do have a few atlas burners and regulator hoses from atlas. The 30k with 20psi regulator and the  dual 150k setup with 30psi regulator but I think I’ll save those for a nicer more thought out build. This was a fun build and works. I tried to angle the heat into a swirl and it does it well! It’s my first try so lots of mistakes and lots of things I’ll do different on my next bigger build. I’ll make the next one with a 5” diameter chamber that’s 12-15” long. There’s Many, Many mistakes on this build! But hey.... I tried  

 Heres some pictures. 

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22 hours ago, Frosty said:

I paid for the fuel I want every BTU I can get for it.

What he said.  I want it to be as affordable as possible.  Aside from carbon monoxide, wasted btu's are why a little green in the flame and/or the presence of blue dragons breath are things I try to eliminate, unless needing for a reducing environment or pushing the burners for welding.  Why waste fuel if you don't have to?

To my understanding, insulation thickness has a tipping point.  After a certain thickness it stops being useful all together and at that thickness we had passed the point of practical quite a bit before.  The extra cost of the insulation vs the length of time it would take to offset that cost by the extra cost of running the forge (ROI).  The higher the temperature differential, the thicker practical becomes.  As Frosty said, if the shell can be touched, I consider it good enough.  Striving for more makes the forge bigger and probably doesn't save much in fuel.  As Mikey stated, bigger differences in fuel use might be achieved with other upgrades which would be a better use of the funds.  For me, the biggest change in fuel consumption was noticed when I spent the money to build an idle circuit. 

I like the idea of a cheaper secondary insulation if the forge size doesn't matter and squeezing the btu's does matter.  It makes me want to put a thermocouple in the middle of the two inches of ceramic blanket to see how much heat is making it that far.  Maybe one inch of ceramic blanket could be used and a secondary insulation after that.

12 hours ago, AngryDaddyBird said:

Here is my first attempt with mistakes upon mistakes but in the end, It works!

That is a good looking micro forge.  Much hotter then all of the 2 brick forges I have seen.  Nice job.  

12 hours ago, AngryDaddyBird said:

I’ll make the next one with a 5” diameter chamber that’s 12-15” long.

That sounds like a refrigerant jug forge.  About 4 inch diameter at 12 inches.

 

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To begin with, congratulations on building such a hot forge. Great photos too. Please go into some detail on how you lined it. How long does it take to heat up, and what is the longest time you have run it for? That is the hottest micro forge I've ever seen running from a regular cylinder-mount burner :D

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As to your mistakes, there is an old saying; "If it's dumb and it works, then it ain't so dumb." At first I thought you had placed the burner port too close to the exhaust opening, but a second look makes me think that the exhaust blows out the large opening at the far end of the forge (its back), while work pieces are feed into the forge at it front. Normally the back end of a forge is sealed or only has a tiny opening, which would cause the exhaust gas to blow out the front opening past the work pieces. And--normally--that would overheat a brass burner head. What you have designed is not the most efficient forge, BUT IT SETS A NEW HIGH FOR PRACTICAL!!!

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4 hours ago, Mikey98118 said:

To begin with, congratulations on building such a hot forge. Great photos too. Please go into some detail on how you lined it. How long does it take to heat up, and what is the longest time you have run it for? That is the hottest micro forge I've ever seen running from a regular cylinder-mount burner :D

I’ll try to answer best I can and I appreciate allthe kind words.

I ran it yesterday 3 hours and the can didn’t get hit until the 1-1.5hour mark. My torch now gets about 2-3 hours on a 1lb tank but yesterday I backed it down and it’s still got about 1/4 tank left after a 3hoyr run. I find that after up to temperature I can back it off quite abit!  I think the heat out the end eventually reflects to the outer can or its overal so small it’s bound to get hot no matter what. I’m sure I could wrap koawool or even fiberglass around the outside and it be cool to touch. It takes 5 minutes to get up to good temperature and anything I place inside heats up fast!

I lined it first with Koawool and packed it against the wall tightly. Tried it and did ok just like that with a coat of Metrikote on the koawool. Then I decided I’d try putting the Kast-O-Lite 3000 on it and finished with the Metrikote. If I had to do it again I’d just do koawool andmetrikote or just Kast-O-Lite and Metrikote.

the burner/torch is 1.5” away brim the front opening  angles upwards and towards the back opening. I played around with jet/torch angle a bit before I was happy. The flame swirls the entire chamber length and heats to the very back of the forge. The bricks that are in back of the firge are 1/4” away. I tried blocking it but got better results with it open. Out the front is only A tiny bit of flame. I planed on using a regularforge burner but think this will be ok to play with. 

I already have the materials to make a second bigger version. I have 1/4” thick 6” square tubing 15” long. I’ll use it to make the next one. Also plan to make a nicer micro with 4” square tubing. I also have 20psi & 30psi regulator hoses, extensions and burners. So lots to play with once I decide what to make. I’m thinking I’d only need the 100k atlas burner and not the dual 150k for a 5” chamber 12-15” long but I’ll have to just test it and see. 

 

Heres some one things I just made in the pictures below. Mini log dogs and a snail striker. I heat treat only the face with a torch instead of the forge to keep the rest of the striker soft not brittle.

Thanks

Ryan

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It is always good to point out that what is needed to make a great little forge like this can be considered a minimum. While such upgrades as stainless steel burner heads, and special hoses to attached these burners to refillable propane cylinders can be added later on, if they are ever desired; some will want such upgrades, while others won't use a micro-forge enough to find them worthwhile.

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