More Fire Bricks

Peter

I would be interested in a few bricks to make a brazing hearth with when they come into you. I am based in Oxfordshire, so not far away from you.

Cheers

Dave

Could I join the orderly queue please?

regards Mark Rand RTFM

Yes please Peter, I need enough for a brazing hearth about 3 foot by 18". I'm at boo ut clockwork dor freeserve dor co dor uk. The obvious needs changing.

Many thanks,

I wonder how good they would be in a hearth. Aren't these things really heavy lumps that absorb heat practically forever? If so you may need to wait an hour before things get hot enough...

When the farrier comes to shoe the nags his gas hearth is lined with very lightweight tiles (like space shuttle insulation material) to reflect heat back into the workpiece.

Julian.

Yes, although they don't conduct heat all that fast. But your gas bill will likely be high if you use them a lot in a hearth, as they will absorb heat for a long time.

Insulating firebricks for kiln use are usually 3 x 4 1/2 x 9 inches, and come in two weights, light and medium. They both cost £2.20 each at my local pottery supplier. The light ones are very light at 930 g (2 lb), the medium ones are about 3 1/2 lb. Both can be cut with a breadknife or similar, you could just about push a finger into the lightweight ones, a hacksaw blade is also good. The dust is probably bad for your lungs though.

I use a bit of 3/8 inch kiln shelf (again available from pottery suppliers, offcuts and broken shelves are cheap but full shelves are expensive) on top of lightweight insulating bricks for my hearth, the insulating bricks are a bit too frangible to use by themselves and the kiln shelf provides a durable and clean surface. Means the kiln shelf has to get hot, but that doesn't take long, five minutes or so, and it provides a bit of heat reserve. The kiln shelf is on half-thickness bricks on a thin metal tray, and it sits just above a wooden bench - which doesn't get hot, never mind scorched.

You could probably use the medium weight ones without kiln shelf as they are quite a bit stronger than the lightweight ones.

I would also be interested to make a brazing hearth.

Simo

-- simonm

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Ooops, I was wrong - firebrick for storage heaters is chosen to have a high thermal conductivity.

They are intended to prevent heat spreading out from the work area, you don't heat the bricks themselves!

Peter

-- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk

Its all relative though - storage heater bricks are still much better insulators than the average lump of metal...

Regards, Tony

I don't know many people who use them who don't pre-heat brazing hearths at least sometimes, usually if they have the time, and always if they are doing large jobs - but leaving that aside, if they are intended to prevent heat spreading then storage heater blocks are about the worst possible choice of ceramic material. They have high heat conductivity and heat capacity, and will absorb and spread heat like billy-o.

Another question might be the maximum temperature they can be used at, might not be high enough for a brazing hearth.

However, leaving theory aside, has anyone tried to actually use them for a brazing hearth? Tried a torch on them? Opinion?

It's been my experience, with propane burners torches, that you need every bit of heat reflected back that you can get. Big jobs, brazing and propane torches can be a bit marginal (or so I've found with the normal stuff from Machine Mart) I would think bricks from a SH would be counterproductive in that respect.

I'd love oxy/acet, but I just can't bring myself to pay BOC the huge annual rental charge for something that would get used about once/month. Sadly all the bottles are now scanned by the lorry driver so I think the normal avenues regarding 'illegal' bottles have been closed. I'm left with two empties now :-(

Julian.

Done a bit of googling. Seems most are now made largely of ferric oxide and have a higher thermal conductivity than stainless steel (25 W/mK vs 16 W/mK for 316), though only about a third that of iron (80 W/mK).

Some are made of 70% "iron granulate", which I believe is some kind of waste from foundries. I speculate that it's the solidified molten drops from a blast furnace, but don't quote me.

Many older ones were made of cast iron!

That's been my experience too.

My local supplier still does "X" size (ten litres, at 200 bar that's ~2,000 l of gas) cylinders for a week or weekend at reasonable prices with no delivery charge if you collect, and no hire charge, just a large deposit. I used to fill my own bottles from them and return them, and still might if I have a need for some unusual gas (note, this doesn't work at all for acetylene, and is especially dangerous for oxygen if you don't know what you are doing, but it's useful for inert gases for tig and the like in small but larger-than-disposable-cylinder quantities).

However a couple of years ago I bought a 4 lpm oxygen generator, £100-odd from Ebay, which runs my small oxy/propane torch just fine, and I use balloons, the ordinary party kind, which I first fill with oxygen and allow to deflate when I want to use a larger oxy/propane torch - I can fill many more ballons than I will likely need for a job as any extra oxy is almost free, only the price of the 'lekky. It has to be a low-pressure torch, and I doubt this setup could do cutting.

Mapp gas can also be helpful, and while oxy/propane or oxy/mapp doesn't match oxy/acetylene for performance it's still well good enough for most brazing and silver soldering, especially with propane/air preheating.

I keep the oxygen filled balloons in a closed wheelie bin for safety. I also use flame restrictors and doubled one-way valves (one meant for the job, one from aquarium suppliers, also a useful source for the t-joints for the balloons, but don't use aquarium valves, they leak) on the lines.

In that case I'd suggest something like lining a can with 12mm of cerablanket or kaowool with some water glass fixative. I've got a few m^2 from a failed burner experiment.

AJH

Just top reinforce what others have said, these are not the right thing for lining a brazing hearth, they are high density to absorb heat rather than reflect it and are not designed for high temperatures, they may well splinter dangerously when heated by a torch. The proper meaterials have exactly the opposite properties!. Greg

Since I've already had a pile of these (though I haven't yet built a stand to put them in), I thought I'd have a try.

I built a hearth out of six bricks (two on the floor, two at the back, one at each side) and put a 300mm bit of 40mm/5mm angle iron in the corner, making no particular effort to keep it off the bricks.

I have a small bottle-and-hose camping-gaz torch, which is probably slightly more powerful than a DIY jobbie but nowhere near a bullfinch propane torch. It got the end of the iron to a dull red in about 5 minutes. The surface of the brick incandesced under the flame. After cooling for 10 minutes the iron was still too hot to touch and heat could be felt on the top of the 'wall' for about an inch across the brick. The rear surface was almost unaffected.

I didn't have any other bricks available for comparison (that's why I scrounged these!) but it seemed workable to me. Nothing flaked off, exploded or caught fire, at least in this brief test.

Noting the comments, I shall probably add a couple of lightweight blocks for support and reflector pieces, but the storage heater bricks seem OK for the main bulk of the hearth.

-adrian

Did you try touching it with a brazing rod? I'm guessing that the dull red you got wasn't hot enough for it to flow. You may have been in luck with 'easy' silver solder.

The proof of the pudding really is to dangle the angle iron from some wire (or stick it out from a vice) and heat it again and see what you get. My guess would be that you would still get it to dull red, thus those storage heater bricks are not aiding you at all.

Julian.

Unfortunately I didn't have any to hand.

They're keeping the fire enclosed, which is what I wanted them for ! It remains to be seen whether they're sufficiently useful to help with the heating.

However, I'd have thought that retaining heat (and therfore keeping the work at an even temperature) also has some value.

-adrian

Sure, it depends really what you are up to. Normally I'm mucking about with steel, and to get it hot enough to forge or braze requires some doing. I guess if you just wanted to anneal aluminium then you would be fine.

Julian.