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I Forge Iron

Drilling and cutting firebrick questions?

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Hello all, I am finally getting around to building my first forge.  I am using an old portable air tank for the outside shell and plan on use a combination of fire brick and refractory cement for the lining.  The brick is rated at 2700F and the cement for 2800F.  The brick is Rutland 9x4.5x1.25.  And the length of the forge will be 18 inches.  So I was planing on on having 3 of frostys T-burners.  KISS principle is being followed for this build.  I like the ribbon burn design but for now just want to get this up and running.  For a little background I was a welder in the Navy decades ago, like 3 and over the years have build a nice little machine and fab shop here on the farm, so any machining or welding is not a problem.  Also this will live its life outside in the weather and I live in Northern Illinois.  So the burners will be removable, and I will make a cover for the forge.  I will likely make a base for it I have move with the forks on the tractor.

My real question is what is the best way to drill or cut the fire brick/ best practices.  Or should I just use the castable cement refractory and form it around the burner tubes?

I am trying to keep costs down but if I have to buy a tool etc. that is fine.

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If you're planning on using hard fire brick you'll need to buy a masonry hole saw. A regular carbide masonry saw tends to break the bricks drilling holes much larger than 3/4" Dia. Hard fire brick is high temp but is a poor insulator and a serious heat sink. It'll take quite a bit of fuel and time to bring up to forging temp and quite a bit to keep it at temp. 

If you plan on using IFBs (Insulating Fire Brick) an old worn out hole saw works a treat. Morgan Ceramics K-26 IFBs withstand the rapid thermal cycling and high temps of a propane forge. Standard IFBs dont last long. IFB lined forges come to heat quickly and it's good insulation makes maintaining temp much  more economical.

The advantages of having a deep heat sink liner is how quickly it will heat steel which is a real advantage if you are cycling a lot of pieces quickly. Say you're making chisels, forging out blanks can be done in a few blows with practice so having a number in the forge heating constantly makes sense. Yes?

However if you're a hobbyist rather than a production shop a forge that comes to and holds temp economically makes more sense. I want to walk out to the shop, light the forge, cut some stock, pick out the ready tools and maybe sweep the floor or similar. My insulated forges come to working temp in a few minutes and welding temp in maybe 8-10 minutes. Rather than half an hour for a hard brick liner.

I wouldn't line a cylindrical forge with brick, it's more technically difficult and demanding, I favor a ceramic wool blanket outer liner and hard refractory inner liner AKA flame face. See Forges 101 thread for discussions of: shapes, materials, construction, etc. However I have a case of K-16 IFBs on hand. I  model forge ideas to determine: size, openings, burner layout, numbers, etc. and usefulness of a general idea. Brick pile forges are also excellent demonstration forges. Lots of folks would like to give blacksmithing a try but buying a commercial forge or welding up one with ceramic blanket and hard refractory liner is generally too intimidating just to give it a try. However buying a dozen IFBs and building a T burner is well within basic shop skills and tools.

One last bit on the economics of brick forges. The money you save buying 3,000f. hard  fire brick will be eaten up pretty quickly buying propane to get and keep it hot. K-26 IFBs and enough Plistex kiln wash is more expensive up front but will pay for itself in fuel economy and time pretty quickly. 

Frosty The Lucky.

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Frosty thanks for the reply!  The cost between the 2 types, is not that bad.  Saving money on fuel is good.  My use will be definitely as a hobby.  More use in the cooler months and less in the summer.  I hate summer, too f-ing hot.

I assume I can use a grinding wheel to shape the bricks as needed?

I really appreciate the insight in the material differences for the refractories.  I am lacking knowledge there.  Fabrication of the steel is easy for me, no worries there.  Just looking to add skills, enjoy making things and more toys!!!

One more question if I use the IFB in the lining, I was thinking I could use a couple of hard brick on the floor of the forge to protect the IFB and use hard bricks as the doors/gates on on the ends.

TIA, Ron.


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You're welcome, it's my pleasure.

If you use IFBs you can shape them with a hand saw and rasp. K-26 are more durable than the old type but not hard to shape. 

You can certainly use hard fire brick for the floor, I recommend split brick if you want to go that route. The upside to a hard fire brick floor is as a heat sink, it helps maintain a more steady temperature in the forge and will speed heating pieces. Some alloys have narrow forging temperature ranges, stainless steel and titanium come to mind. The forging range is sometimes maybe 100f. too hot and it turns to cottage cheese under the hammer and too cold it won't move, force it and it crumbles. In that case the project won't be out of the forge more than a few seconds before it cools too much to work, if it's thick enough you can get 30 seconds.

However for general work I recommend flattening the bottom for a flat floor and an overall Vault shaped forge. Mailbox and D shaped are a common terms, I just like vault. It's a preference thing and a simple web search will provide endless perfect examples of vaulted architecture. Sorry for the sidetrack 

Anyway, filling the bottom curve with Kaowool feathered at the edges to make a smooth transition and flat deck then after rigidizing and setting the rigidizer plaster the entire interior with a 3,000f. water setting high alumina hard refractory. Kastolite 30li is one of if not the current current favorite, it contains evacuated silica spheres to lighten it and improve it's insulating properties. It's concrete hard and tough at 3,000 f. 

What you end up with after applying the hard refractory is an inner liner AKA flame face that is reasonably proof against: propane flame contact, mechanical and chemical erosion. 

Read up about what Mikey has to say about thermal baffles rather than "doors" on forges. Hard brick will work but IFBs are better for the above reasons. Mike does a much better job of explaining than I usually do. I tend to be wordy and side track easily, it's a TBI thing.

Frosty The Lucky.

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