natenaaron Posted January 30, 2016 Share Posted January 30, 2016 What is the difference between soft fire bricks and hard fire bricks? A welder friend of mine wondered over to my shop to see what I was up to. I was cussing my burner (another thread on that later) when he asked if I was planning to make knives. I told him maybe in the future but right now I am interested in making ornamental stuff. He informed me I would be very limited in what I could do with such a small forge. Apparently when he was first starting he worked as the ornamental welder in a production forge, The blacksmiths made the shapes and he welded them to the railings, the fire grates etc... He said the large forge was a big ole gas thing but there were small forges made from fire brick with bigger openings. He said they used hard fire brick not soft. From what he described it reminded me of Frosty's and others I've seen here, but those looked like soft fire bricks. So what is the difference? Does the soft stuff insulate better? Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted January 30, 2016 Share Posted January 30, 2016 The difference used to be that hard firebricks were made of high heat resistant cast refractory formulas, and soft firebrick (AKA insulating firebrick) was made by including a foaming agent in the a castable refractory formula. As with so many other things, today there are many different choices of both kinds on the market. It is not only refractory mixes that come in 3000, 2800, 2600, 2300, and 2000 F ratings with equally varying degrees of insulating ability; bricks are made in those same ratings. Furthermore, today hard firebrick comes in many specialty varieties. Quote Link to comment Share on other sites More sharing options...
Charlotte Posted January 30, 2016 Share Posted January 30, 2016 Soft brick is insulating fire brick. Hard brick is solid, heavy, and had the insulating ability of an open window. The use of hard brick is one, wearing surface, two, heat retention, three heat storage. Takes a lot of gas to heat hard brick but once it is hot it reradiates the heat and keeps a more even temperature. Hard brick is used in commercial furnaces/forges because they don't need to worry about the fuel cost just speed and convenience of a hot forge all the time. Hobby and Individual business men find a smaller well insulated gas forge more suited to their resources I personally find that solid fuel forges are more useful for ornamental items whitch often are three dimensional and don't fit in a normal gas forge.. Quote Link to comment Share on other sites More sharing options...
natenaaron Posted January 30, 2016 Author Share Posted January 30, 2016 So, out of curiosity what happens if the heat ratings are exceeded? I got my bricks from a guy in Flagstaff that makes fire bricks. He said they would work well in a forge but I saw no documentation. Quote Link to comment Share on other sites More sharing options...
Charlotte Posted January 30, 2016 Share Posted January 30, 2016 Short answer they melt or they fall apart or both. Quote Link to comment Share on other sites More sharing options...
Frosty Posted January 31, 2016 Share Posted January 31, 2016 12 hours ago, Charlotte said: Short answer they melt or they fall apart or both. Bingo. Hard brick usually melts Then falls apart, soft usually falls apart Then melts. If you can afford the gas, say have a large commercial shop and can leave the forge running all the time they'll last quite a while, no comparison really. Large power plants and BIG commercial forges only shut them down to replace the lining. If something causes the fire to go out they just let it go cold because they'll have to reline it. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted February 16, 2016 Share Posted February 16, 2016 If a guy was smart, he'd build a form and pour his own multi layered bricks, using Kast-O-lite 30 (1/2" thick), followed by Kast-O-lite 28 (3/4" thick), followed by Kast-O-lite 26 (3/4" thick), followed by Kast-O-lite 23 (2" thick); at this point you can use Perlite, calcium board, or ceramic fiber for any further insulation desired. The hot-face side of the bricks should be painted with your choice of high-emissive coating Quote Link to comment Share on other sites More sharing options...
Frosty Posted February 16, 2016 Share Posted February 16, 2016 You thinking those thoughts too Mike? I was playing around with Kaowool soaked in the phosphate bonded Green cast cement. I sifted the fines out of the refractory. Anyway, I mixed the Greencast cement as a thin slip that soaked into the Kaowool nicely and laid it in a form that had about 1/4" of straight Zircopax in the bottom. The excess Greencast slip soaked into the Zircopax. Being a water activated cement refractory it takes no heat to cure and the entire thickness of the Kaowool stiffened up considerably and it's still much lighter than soft insulating fire brick. I haven't run thorough tests on the "bricks" so I'll leave it at that. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted February 16, 2016 Share Posted February 16, 2016 Frosty, I look forward to hearing all about the outcome of your experiment; It's certainly a more economical method than buying all those sacks of refractory. I also like calcium board as the cold-face finishing material, but it must never be heated over its use rating (swells up and delaminates), and can never be exposed to flame. Quote Link to comment Share on other sites More sharing options...
Frosty Posted February 16, 2016 Share Posted February 16, 2016 Will do, I really need to make some test coupons and see how they do. It'll need to wait till we're clear of freezing temps, freeze thaw before it's fully cured messes up Greencast, even thin slip. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
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