edennis

Questions on Ribbon Burners

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I just have angle iron for the lower portion to hold the bricks.  Remember, heat rises.  It also appears that there is space between the bracket and the tank allowing heat to conduct up between the forge and the bracket.  You may be running to rich with to much dragon's breath.

Wayne

 

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There is no space between the two. It is completely welding around the opening. The heat is just transferring through. maybe I'll  try cutting the top part off and coming up with a new solution. 

Thanks,

Eric

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So, what do you guys think? Normal cracking  with expansion or an error in application on my part? Should I worry about it and try to patch it? If so, what's the best method? Or ignore it?

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@edennis I think Wayne is talking about the space between the internal insulation and the fire brick door, it does look like there is one which would cause a pocket to heat rapidly and cause the top bracket and shell to heat up that much

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Edennis, you did not cast the inside all in one shot, correct?  You troweled and hoped gravity wouldn't pull your refractory down but it did, so you had to go slow.   That line could be from the refractory curing at different rates since it appears to be where the flat meets the curve of the ceiling.  

  

 

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16 hours ago, edennis said:

So, what do you guys think? Normal cracking  with expansion or an error in application on my part? Should I worry about it and try to patch it? If so, what's the best method? Or ignore it?

 

I say ignore it.  Remember the castable refractory is there to protect the ceramic blanket, provide a little insulation and give your reflective coating a place to reside. For the most part you still have most of those features.  Go with it unless pieces start falling out of it.  I have no idea how you would repair the cracks, I think any attempt would just make a mess. 

 

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I was thinking  of maybe mixing some plistix and spreading into the cracks, but I think you are right. I am just going to ignore them for now. Thanks for response.

 

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So after about a month of use, the high alumina kiln shelf has split into 3 pieces and the molten borax seems to be eating into it. I was under the impression it would be more resistant to both of these issues. Any thoughts or insights? 

Thanks,

Eric

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Note that all "high alumina" kiln shelf is not created equal.  From my research the lower priced shelf cordierite/mullite will not either withstand the same temperatures or glass contact, as a true alumina shelf.  Paradoxically the thicker the shelf, the more prone it is to cracking from thermal shock.  I'm not sure how you shaped your shelf, but any significant surface irregularities or edge defects can turn into locations for crack initiation.  Even the best high alumina refractory is quite prone to thermal shock.  Used to take me days to warm up and cool down my glass furnace to avoid cracking the 1 1/2" thick high alumina crucibles. 

I've not used kiln shelves in my forge as yet (though I have certainly used them to support crucibles in a glass furnace).  If you plan on replacing the one you have I would recommend going for a 1/2" thick shelf, keeping it a consistent thickness, and carefully beveling the edges.  Other alternatives include just casting in a 1/2" thickness of Mizzou or a top coat of bubble alumina.

In any event, try not to have the shelf exposed to rapid temperature change (leading to thermal shock).  I use a side mounted burner, so that shortly after the burner gas gets turned off I can shut off the blower.  You can also close off your forge doors to allow everything to cool down more slowly.

Good luck and keep us posted.

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Thanks Latticino, it's good to have some first hand information. I looked through a lot of data sheets for Kiln shelf and had the same thoughts about the lower prices ones. I thought they were more resistant to thermal shock but am happy to get the straight poop without having to discover it myself. 

Beveling the edges is important is good working knowledge. Can I belt sand them? Will rounded work? Hey, I just got this new 2" x 72" belt grinder working so why not see what it'll do eh? B)

Frosty The Lucky.

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23 hours ago, Frosty said:

Can I belt sand them? Will rounded work? Hey, I just got this new 2" x 72" belt grinder working so why not see what it'll do eh? B)

You can belt sand (I used silicon carbide belts when I beveled mine, anything less "hard" will result in the shelf abrading the belt instead), but it helps to keep it cool while sanding.  I used a wet belt sander.  Just taking the corners off should be helpful, mostly you are trying to reduce the crack initiation points.  The manufacturer's do say that the mullite/codierite shelves are more thermal shock resistant (presumably than true high alumina, but they don't necessarily specify), but they are also less flux resistant.  Molten glass is a pretty aggressive solvent, which is why the big Corning Glass tanks are lined with a layer of platinum.  As I understand it alumina is a more cost conscious alternative.  Perhaps a good coating of kiln wash would do the trick.  Personally I think I'm going to go back to a thin layer of Mizzou cast in place (though then you don't have the alternative of easy removal when the forge floor gets loaded up with molten flux). 

The issue with thermal shock is pretty complex, and hard to generalize about.  The thickness aspect is pretty interesting, and mostly has to do with the interior of the shelf cooling at a different rate than the exterior skin when the forge gets turned off resulting in stress on the shelf surface.  Since the shelf is not a particularly good insulative material, it may not be as big a deal and the extra strength of a thicker shelf may offset that mechanism.  Just remember that typically the kilns these are made for warm up and cool down pretty slowly.

And now they have those new hollow core shelves as well.  I have no idea how those respond.

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I hadn't thought about it's hardness, vitrified it's gotta be what, sapphire hard?

I understand clearing chips, scratches, and such as crack initiation points. Just smoothing the edges do it? How about a diamond knife sharpener or do you need to break more of the edge?

Frosty The Lucky. 

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44 minutes ago, Frosty said:

I understand clearing chips, scratches, and such as crack initiation points. Just smoothing the edges do it? How about a diamond knife sharpener or do you need to break more of the edge?

It will certainly help.  I have done no specific empirical testing, but the theory holds and that is what I've done with my shelves and half crystallite bricks in the past (the latter are great for flux (glass) contact, but quite expensive.

I wouldn't kill a knife sharpener (though I did certainly use my wet diamond lap wheel on some brick as well and it worked).  I think the high alumina shelves are more in the glass range than sapphire, but have no real idea.  Either way silicon carbide belts will do it, and a spray bottle wielded by a friend can keep your belt wet enough (watch the spray around your motor though).

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I got to thinking about the sapphire statement later as probably way wrong. Just because they're both aluminum oxide, silica and trace elements doesn't make them even similar. BIG difference between vitrified and crystalized, world of difference.

I have an old diamond sharpening "steel" I hate as it removes way more metal from my blades than they need. Heck I only ever use an oil stone on the kitchen knives where a rough edge cuts better. My carry knives only ever need a quick brush on a ceramic stone or strop. Routine maintenance, it's how Dad taught me a knife should be. Heck, if something has a blade I sharpen it. I used to take a file to shovel and spade blades at work and got laughed at till people started bringing me their garden tools to be sharpened. If you ever use a sharp shovel or spade you'll never go back

Isn't that more back story than needed? The point being I have a diamond stone I was gifted with and never use. If I ever use kiln shelf I'm going to see how it works to soften the edges.

My experience working with glass is limited to slumping it into forged pieces, mostly the negative space in spread crosses. Even that limited experience showed me molten glass is super sticky stuff, draws out into hair thin fibers and sticks to everything it gets near to. I think the stuff is haunted. Everything within about 6' of the forge was Polterglassed.:o

What do you use for a release agent? 

Frosty The Lucky.

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1 hour ago, Frosty said:

What do you use for a release agent? 

Typically you don't use a release agent at all if the molten glass is being held inside the high alumina crucible.  The crucible gets a thin coating of glass that does not get gathered during the blowing operation (the dross glass on the bottom of the crucible was typically discarded or made into "fancies" like paperweights, glass canes and the like by glassworkers for private sale, it was usually too cordy from dissolved crucible material to be used in fine production).  Note that unlike metal casting crucibles, glass crucibles are rarely removed from the furnace, glass is gathered out of them with preheated rods or removed with a cold casting ladle (I used a 6" pipe cap welded onto a 6' long 1" pipe for a ladle).  The glass will temporarily stick to the preheated steel for blowing, then crack off once done if suddenly cooled due to differential thermal expansion of the glass and steel.  For casting, ideally the glass never adheres to the ladle at all, but it needs to be poured out pretty quickly.

For casting glass into molds, the typical release agent is a thin coating of carbon.  This can be applied using an acetylene torch (finally a good use for sootB)) or spray graphite powder.  I have also used block graphite molds, but it can be a challenge to use those effectively.  If they are too cold they suck the heat right out of the glass, putting chill marks and sometimes cracks on the surface.  If they are too hot the bonding agent in the block starts to burn out and they start to exhibit porosity and break down easily.

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Thanks, more info for the mental tool box. When I was playing with glass in the crosses I did some reading and more than once polished stainless was claimed to not stick to glass or vise versa. I had limited success reshaping and polishing an old serving spoon to use as a backer under the cross. I bent the handle around to hold the spread cross. 

I'd gone beyond slumping marbles to buying bright red frit and melting it. I was amazed at how penetrating molten glass is intuitively I never imagined capillarity would act so strongly on so viscus a fluid. I went so far as cutting a gasket from a refractory paper I bought at the local art glass place to try and keep the molten glass in the center of the cross. The stuff is like an escape artist with an evil sense of humor.

I picked up a color selection of torch work noodles as it's less sensitive to "proper" annealing, then bought the frit so it'd maybe fill the tight corners in the cross' negative space without having to become fully fluid. The guy sells a  "release" agent for molds but holy mackerel does he want a bunch for it and there wasn't a clue to what it is. Not graphite the stuff is off white.

Any ideas? I'd rather not have to grind the crosses smooth and flat the texture of the spread cross is a main part of their attractiveness. 

Frosty The Lucky.

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I have not encountered any of these problems. But I also never encountered cracking in high alumina kiln shelves after long storage. It occurs to me that I have simply been blessed in where I buy my materials; Seattle Pottery Supply.

On the other hand, zirconium silicate based refractory over Morgan's K26 insulating firebricks are what I plan to use for forge floors from now on, anyway. I looked for something superior to high alumina kiln shelves for the last eighteen years; I think this is it.

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On ‎8‎/‎11‎/‎2017 at 1:55 PM, Frosty said:

Any ideas? I'd rather not have to grind the crosses smooth and flat the texture of the spread cross is a main part of their attractiveness. 

Frosty The Lucky.

I'm really not a fan of casting normal soda-lime silica glass ("hard" glass) into steel at all.  Typically the different thermal expansion coefficients of the two materials interact to put the glass into fairly significant stress, which can result in cracking and spalling at unpredictable times.  Reportedly copper and brass are more compatible. 

On the other hand, there are a lot of different glass compositions out there.  Borosilicate glass ("soft"  or pyrex glass) is supposed to be less prone to thermal shock and there are a whole series of colored glass rods available that flame workers use that have different working and thermal ratios than I'm used to.  I would personally cast the centers in colored resin, but if you are insistent on using glass I would make up a polariscope and do some experimentation.  There is a whole field of engineering that is concerned with developing composite materials that marry either ceramics or glass to metal, I'd start looking there for formula suggestions.  You will likely have to try a number of different annealing sequences as well as material selections.  A cheap polariscope is great for checking on stress in the glass, but is does work best on clear glass.  Here is some info on how to DIY one: http://www.davebross.com/GlassTech/polariscope.html

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