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hard firebrick for gas forge interior


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#1 anvillain

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Posted 11 February 2009 - 08:44 PM

I was wondering if anyone has tried using 1" x 4 1/2" x9" hard fire brick on the inner wall of a gas forge. I would be using the kaowool outside the firebrick and then outside the kaowool I would fabricate a steel jacket for durability. I've made one with kaowool inside and coated with ceramic, but it is too fragile in my opinion

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#2 Steve Sells

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Posted 11 February 2009 - 08:56 PM

use the fire brick, but why use the Koawool at all ?
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#3 ralphy

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Posted 11 February 2009 - 09:43 PM

I've never used Kaowool, but I've used fire brick with some luck. I also used lava rock inside to help the heat get around the piece, but watch out because it will pop alot at first. I've also got access to 1/2" 4x4 ceramic like they line kilnes with I'm gonna try this summer.

#4 anvillain

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Posted 11 February 2009 - 09:45 PM

I've read that it has more insulating value. And also I already have it and would like to keep the shell as cool as possible. Another concern of mine is the possible airborne particles from kaowool. It seems that the hard brick would be less likely to disintegrate into the air. Thanks for your reply

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#5 chyancarrek

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Posted 11 February 2009 - 09:54 PM

Here's a variable-volume gasser I built a few years ago and she's still going strong with the original Kao-Wool lining. The wool is up out of the way of any stock moving through the forge.

Hard brick base, and the wool lines the top. It's a good set up for the kind of work I do (formed vessels).

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#6 Steve Sells

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Posted 11 February 2009 - 10:05 PM

I guess I was not clear, I was attempting to point out that on the outside of the bricks the koawool won't help as much as on the inside. Either way the fibers will still have to be addressed with a coating.

Edited by steve sells, 12 February 2009 - 08:35 AM.

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#7 Jymm Hoffman

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Posted 11 February 2009 - 10:17 PM

anvillain,
You are on the right track, that is how I used to build my larger forges. The firebrick will absorb the heat while the ceramic fiber blanket reflects it. Having ceramic blanket underneath will help keep the heat from transferring out and help reflect the heat in the firebrick back up into the forge where you want it. That is one of the reasons why my systems work so well. However, I have switched to a ram refractory to cover the "wool" on the bottom. It does not break down as the fire brick will. Even if you do not do any forge welding, it will eventually break down, from thermo shock and scale from the metal. If you have a quantity of these thinner fire brick, you may just consider them sacrificial, I did in the beginning of my use of a gasser. However, replacing them will probably cause you to damage the blanket around them.

The other concern about containing the fibers is legitimate. However, the brick will be insufficient for that. You need to coat the blanket. Some like the expensive ITC. I use a 3,000 degree F mortar that comes premixed. I thin it down to coat the blanket and the entire system. It is much less expensive and will do the same, contain the fibers. I have had firebrick/blanket suppliers tell me that all ceramic material, fire brick, blanket, etc all become a carcinogen after reaching a certain temperature. Regardless of the fuel, so firebrick in a coal forge can be dangerous to handle as well. Wear a mask to keep the fibers out while working with this stuff. It is an irritant when new, carcinogen after firing.
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#8 anvillain

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Posted 11 February 2009 - 10:18 PM

Thank you for your input,everyone. I like that forge setup and it looks like it really gets hot. Approximately what gas pressure was being used in the picture. Are those bricks on the base insulating firebrick? The brick I have are very hard and heavy. I also was wondering, if they are the soft insulating brick do they produce much airborne dust?

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#9 chyancarrek

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Posted 12 February 2009 - 12:40 AM

Hey Anvillain,

The base brick is hard (rated at 3K) - the soft brick would not do well at all due to it's fragility and low thermal rating.

The forge typically runs around 7-8 psi but I usually have the valve at the burners closed about half way as I mostly forge 1/8" - 1/4" plate so I'm only looking for good even heat over a large surface area right around 1500 - 1800 degrees.

Jymm's right when he says that coating the wool is the best way to go both for thermal efficiency and safety. Sorry, I should have mentioned in my earlier post that the wool in mine is coated with a homemade mix similar to what Jymm mentioned above. That's been a major factor in how well it's held up.

#10 Frosty

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Posted 12 February 2009 - 03:54 AM

Double lining a forge is a good system though it's more hassle up front and if you ever have to rebuild it way more hassle. On the upside if you do it right it'll last a long long time compared to a plain ceramic blanket liner and be a lot more efficient than a straight hard liner.

What makes Jymm's liner so durable against flux is it's a phosphate bonded rammable. High phosphate or phosphate bonded refractories are not susceptible to caustics like molten borax, unlike silicate and alumina refractories.

Coating the blanket is important and depending where in the forge it is there are different products to use. If you're using Kaowool as the outer liner then you don't need a flame contact coating or a rigidizer. What you want is one of the stabilizer products as described on the refractory sites that carry ceramic blanket. ITC makes a stabilizer for blanket, it's just not ITC-100.

However, any forge liner will benefit from a coating of ITC-100 in the fire chamber, as it's a black body IR reflector. Meaning it reflects the infra red (heat) back into the forge chamber rather than letting it soak into the liner. ITC-100 is NOT a stabilizer for ceramic blanket, it will help keep fibers from breaking free but that is NOT it's purpose. Using it on an inner liner is a waste and expecting it to keep particles out of the air is misguided.

This is my variable volume forge. The floor is 3,000f split brick over a layer of 2,300f castable refractory. The side walls and lid are 2,300f soft insulating fire brick. All the fire contact surfaces are coated with ITC-100 and it comes to heat in about 5 mins. And I can touch the outside of any of the brick bare handed after hours of running time, provided it's not on an edge of course.

The burners are my design "T" burners in 3/4".

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#11 saintjohnbarleycorn

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Posted 12 February 2009 - 09:04 AM

my hoffman\


I use a 3,000 degree F mortar that comes premixed. ??
is this the product that u use. I am getting ready to put together a gasser and I am interested in saving some money and improving the design, The blanket is costly enough, but I don't mind getting the ITC if it improves efficiency. I am paying about $17 for a tank of propane . thanks

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#12 Shane Stegmeier

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Posted 12 February 2009 - 11:16 AM

In many industrial applications they use multiple types of refactory. Hard refactory for durability, (and sometimes as a heat sink to help smooth out forge temps when loaded with cold steel, the hard refactory will keep the forge hot enough to be efficient in combustion.) Softer reflective refactory to prevent heat transfer. Making sure the BTU's go into the forge chamber, and not bleed into the forge and the whole surrounding area just makes sense. Dragon's breath is one thing but having the whole forge radiating heat that you don't want to get close to is another.

The ramable materials is good stuff, I redid the bottom of my Mankel blown horseshoers forge with it and it does hold up exceptionally well.

Frosty sounds like he has an excellent design too.

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#13 anvillain

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Posted 12 February 2009 - 07:05 PM

A quick thank you again to all. I feel more educated for sure. and the pictures are very interesting. I'll probably not get back here until some time tomorrow. very good replies from all.

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#14 anvillain

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Posted 13 February 2009 - 12:02 AM

Hello Frosty,
Your "T-burners are interesting. What size orifice do they have? Do you use a choke of any kind, or do you control it with the gas pressure? Also is there two separate chambers there with a brick in the middle? Maybe you run one side hotter than the other?

I really enjoy looking at all the different configurations and ideas that each person arrives at.

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#15 anvillain

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Posted 13 February 2009 - 12:21 AM

Fionbarr:
Yes, what you describe is very well put, and kind of spells out what I need to accomplish better than my original post did.
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#16 Frosty

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Posted 13 February 2009 - 01:48 AM

Hello Frosty,
Your "T-burners are interesting. What size orifice do they have? Do you use a choke of any kind, or do you control it with the gas pressure? Also is there two separate chambers there with a brick in the middle? Maybe you run one side hotter than the other?

I really enjoy looking at all the different configurations and ideas that each person arrives at.

Anvillain


It's a variable volume forge. Basically a table with lid on a jack, I can lift the lid and move the firebrick sidewalls around to make as large or small or whatever shape chamber I need. I can and have run two separate chambers at once for two stations. If I wanted I could run four chambers but that'd get really crowded.

The burners are 3/4" tubes and use a 0.035" mig tip shortened to a bit under 1/2" long for proper sapcing from the throat. No chokes, they're tuned and controllable via psi.

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