Furnace castable questions

[Pete VanderLaan]

Oooh~ Trick Swedish question..

[Michael Ahlefeldt-Laurvig]

No science based, you guys not used to that after the last four years

[Pete VanderLaan]

Oh well, so much for humor. The mirror will fog if it is placed in a spot where the exhaust moisture from the casting will make the mirror fog. It isn't going to fog if it just sits inside the furnace. I suspect that Travis realizes that. One however, never knows.

There was some evidence recently with a member saying he preferred trial and error for most of his information. So, if you melt the mirror, that probably won't help with any conclusions either beyond a notion that if the mirror was to melt, one might presume that the furnace at that point was likely hotter than 100C.

But who knows? We have a newspaper which has a header saying something about "Inquiring minds.."

There's not a lot of evidence of the use of science lately, I'll admit.

[Travis Frink]

Originally Posted by Pete VanderLaan

Oh well, so much for humor. The mirror will fog if it is placed in a spot where the exhaust moisture from the casting will make the mirror fog. It isn't going to fog if it just sits inside the furnace. I suspect that Travis realizes that. One however, never knows.

There was some evidence recently with a member saying he preferred trial and error for most of his information. So, if you melt the mirror, that probably won't help with any conclusions either beyond a notion that if the mirror was to melt, one might presume that the furnace at that point was likely hotter than 100C.

But who knows? We have a newspaper which has a header saying something about "Inquiring minds.."

There's not a lot of evidence of the use of science lately, I'll admit.

I might have figured that out eventually through trial and error but thanks for clarifying that.

I was going on the assumption that the mirror trick would be used before turning on the main burner to really bring the temperature up- I.e. while still under 100c.

On reflection, it probably is a good idea to state things like that outright, though. A lot of people seem to be unable or unwilling to recognize science, common sense, or the bright red writing on every wall these days.

[Rich Samuel]

The James Coburn technique.

https://youtu.be/pFhD7dnqEbg?t=95

[Charles Friedman]

The mirror trick goes way back to potters. The idea was to hold up a mirror just outside of a peep hole or ajar door. During the first firing of the pottery (bisque firing) at start up, if you saw fog, do NOT turn up, if you did not see fog, then it was safe to turn up a bit more. Same thing with the first firing of any appliance. Steam is bad thing at this point. Patience is where it is at.

As for the vent, used as a dampener. that also is a pottery kiln trick.
It is called a "negative damper". It is usually found in the flue-way from heat source to the chimney. Just by opening a gap a bit with a brick or kiln-shelf it will reduce some of the hot air going thru without blocking it, like a positive style "guillotine damper" would do. The purpose of all this is, two things.
One is, to control the amount of air-intake from the heat source, to control the amount of reduction. The other is, to be able to tap off heat for other prepossess.
Added bonus is, a great spot to keep or cook a chicken or stew.

[Travis Frink]

Originally Posted by Charles Friedman

The mirror trick goes way back to potters. The idea was to hold up a mirror just outside of a peep hole or ajar door. During the first firing of the pottery (bisque firing) at start up, if you saw fog, do NOT turn up, if you did not see fog, then it was safe to turn up a bit more. Same thing with the first firing of any appliance. Steam is bad thing at this point. Patience is where it is at.

As for the vent, used as a dampener. that also is a pottery kiln trick.
It is called a "negative damper". It is usually found in the flue-way from heat source to the chimney. Just by opening a gap a bit with a brick or kiln-shelf it will reduce some of the hot air going thru without blocking it, like a positive style "guillotine damper" would do. The purpose of all this is, two things.
One is, to control the amount of air-intake from the heat source, to control the amount of reduction. The other is, to be able to tap off heat for other prepossess.
Added bonus is, a great spot to keep or cook a chicken or stew.

Thank you and sorry for this and sorry for the delayed response. I’ve been pretty busy putting roofs on some buildings I’ve put up and trying to get it done before the next rain, in addition to helping with my friend’s furnace build, and my doing own work full time-ish.

I did some online research on the negative damper but couldn’t really get a good image of it in my head from what little I found. Maybe I’m slow. Maybe I’m just tired. A friend who used it on his furnace that he also uses for reheats thinks it’s a good idea. It’s in a place that allows you to plug it up like it was never there if it’s not doing what you want it to. I just like to know how things work and this one eludes me now. Some things take time and some you just learn from experience I guess.

[Travis Frink]

So the build on this furnace is taking a while as I’m not able to help much help and the other parties involved start late, figure things out as they go, take coffee/beer breaks and finish early.

We are putting on high temp. fiber insulation now. It’s a weird shape so piecing everything in is taking SO LONG.

Layering (from inside) goes like this:
10cm 1650 castable
3-4cm “Fiber plast” putty mix of high temp fiber and rigidizer paste (spreads like thin cookie dough or a thick cake icing)
5cm 1300 fiber
5cm 1200 fiber
5cm 1100 fiber
Rigidizer

Front will be bricked up with tree different courses of brick from high density brick inside and lower temp, higher insulating bricks outside.

Can you post pics from an iPhone here? No luck so far.

I didn’t choose the insulation plan but would be interested to hear opinions on how others would do it differently/better.

[Charles Friedman]

Front will be bricked up with tree different courses of brick from high density brick inside and lower temp, higher insulating bricks outside.


If the "high density brick" is a hard brick, and if the "insulating brick" is a soft brick, then I think you might have it backwards.

[Pete VanderLaan]

having the hardbrick on the inside makes sense to me with the higher level insulation over it, then the lower value insulation on the outside. What I don't understand is Why is it getting bricked up?

Does it not just have a door or am I completely misunderstanding what you're doing here? Is this a kiln or a glass furnace. As a kiln it makes sense. Does it get bricked and unbricked each firing.?

I suspect that the negative damper is better thought of as a flue that has options as to where to direct the gasses. On my stacks, it's just one direction. I can put a brick over the top to restrict the exhaust flow and do that hand in hand with opening and closing the air gas mix.

[Travis Frink]

The sides and roof of the furnace structure are castable covered with fiber insulation. The bottom half of the front face is brick with a gathering port on Tom of that. The front bricks and port are removed to change the crucible and then replaced. Hard brick inside and insulating brick on the middle and outside layers.

The dampers on this furnace rout flue heat to the annealer for preheat with fine control with wire elements connected to a controller.

The “negative damper” (?) is at the bottom of the flue as exhaust exits the furnace and is not rerouting heat but pulls ambient air into and up the flue. This, in theory, reduces the volume of hot air being pulled up the flue and thus out of the furnace by replacing the hot air with ambient air. That’s my limited understanding based on what I was told. It might not be right. It is not related to the furnace build here and should probably be discussed in another thread (with pictures or diagrams for clarity) to avoid confusing it with other things here.


A picture or three really would make things easier to understand (I think) but I need a little more time to figure out how to compress photos small enough to upload here. Sorry I’m still half analog and right now I gotta go put a roof and walls on a shed I built for the kid’s new school bike (they usually ride bikes to Jr. high and high school here and that starts in April) and all my tools that are currently sitting in a leaky craft fair tent. I’ll figure out the photo thing tonight hopefully.

[Michael Ahlefeldt-Laurvig]

I had a bricked up door made of highest class dense bricks joined with a low bond mortar. It was simply too big to handle in a rational manner. Knocking it down and putting the pot in and then bricking it closed took no time at all. It was covered in 4 layers fiber as to not have the gathering port too far into the furnace, at the cost of lesser insulation. I would never have choosen soft bricks. On the other hand the whole furnace was insulated with a total of maybe 350mm-sides and top.
An electric furnace has more to gain on thick insulation than a combustion furnace- the hot gasses going out the flue is the main energy culprit

I dont care about thank yous, Its the discussion itself that is interesting in this place

[Pete VanderLaan]

Originally Posted by Michael Ahlefeldt-Laurvig

I dont care about thank yous, Its the discussion itself that is interesting in this place

*****
Quoting rex Harrison in my fair lady:

"By George, I think she's got it!!
She's really got it."

My furnace big pot only comes out with drill and blast, but the noise is not that bad. Sort of like a visit to the dentist.

[Michael Ahlefeldt-Laurvig]

That fluegas and electric combo is tricky- if you want 500C say, and youre drafting 490C flue gasses through the annealer, the controller thinks its too cold and will run the elements to compensate the chill effect. Its real easy to cheat yourself doing that

[Travis Frink]

Originally Posted by Michael Ahlefeldt-Laurvig

That fluegas and electric combo is tricky- if you want 500C say, and youre drafting 490C flue gasses through the annealer, the controller thinks its too cold and will run the elements to compensate the chill effect. Its real easy to cheat yourself doing that

This is an interesting and unexpected idea. I don’t think a comparison has been done with and without flue heat. I think the flow of air through the annealer does allow thicker/more complex work to be annealed in a shorter time. I have seen similar work annealed for 2-4 times as long in an electric annealer with no circulation/convection in very professional international studios producing high quality (and price) art work.

Originally (a long time ago) there were no electric elements in this particular annealer. Then glass stared breaking days/weeks/months/... after it was made. Now, complex work seems to be very stable and I see no signs of stress when I look at it through polarizing filters.

Using multiple layers of fiber is probably a better insulation than a couple layers of soft brick. It’s not my choice or decision now. I’m just trying to understand and learn so I can do as well or better when it IS my responsibility. However the outside surface of the soft brick is cool to the touch at working temperature. Does that mean anything?!

And thank you for your input. It means a lot to me to me able learn from so many people with so much experience. I doubt I have much to teach but I try to share what I know from here in hopes that it might be interesting or useful for someone. I know I enjoy seeing and learning all the different approaches to glass- and the people who make it happen.

[Travis Frink]

Trying to upload a couple photos I compressed

One is of the furnace in question from a previous pot change. One is from the current rebuild.

[Pete VanderLaan]

I'll leave the commentary on flue gas etc to others since I don't do it. I do however anneal and would make some observations about your assumptions.

Work that is put in the annealer too cold can take as much as 30 times longer to anneal than work put in at the proper temperature ( Frank Wooley senior melt engineer Corning Glass works) . The closer to the upper annealing range top makes relaxation of strain occur more rapidly. It is problematic in thinner work.

What you describe to me as taking days weeks months and all gradually breaking sounds for more like mismatch on linear expansion between colors than it does sound like annealing. Did any of that breakage occur when the work in question was being polished?

That is the first furnace I've seen to date which actually addressed the underside of the floor sufficiently. I think the heat loss through floors just goes unnoticed since it's difficult to access. I usually see two layers of brick where eight to ten would be better. The old furnace actually overdoes it.

[Charles Friedman]

Travis Nice work.

[Charles Friedman]

Travis Nice work.

[Travis Frink]

Originally Posted by Pete VanderLaan

I'll leave the commentary on flue gas etc to others since I don't do it. I do however anneal and would make some observations about your assumptions.

Work that is put in the annealer too cold can take as much as 30 times longer to anneal than work put in at the proper temperature ( Frank Wooley senior melt engineer Corning Glass works) . The closer to the upper annealing range top makes relaxation of strain occur more rapidly. It is problematic in thinner work.

What you describe to me as taking days weeks months and all gradually breaking sounds for more like mismatch on linear expansion between colors than it does sound like annealing. Did any of that breakage occur when the work in question was being polished?

That is the first furnace I've seen to date which actually addressed the underside of the floor sufficiently. I think the heat loss through floors just goes unnoticed since it's difficult to access. I usually see two layers of brick where eight to ten would be better. The old furnace actually overdoes it.

Point taken on assumptions and putting glass away cold.

Not all the work broke. Some is still sitting on a shelf 20-30years later. I notice a lot of opaque red, yellow and light green made with Kugler from the 1980s(?). I understand that there were/are LEC compatibility issues with that color range especially. It was before I met up with the owner but I was led to believe that a large portion of the breakage issue was resolved by more controlled cool down using elements versus flue heat only. It also seems like a lot of extra work going in to close the dampers 2-3 times after work is done- EVERY SINGLE DAY!!!

I recall reading here about the importance of a properly insulated furnace floor. This furnace has 4 courses of bricks with hard brick nearest the hot face covered with a layer of the fiber-rigidizer putty/paste that is so loved here. It works great but isn’t the most enjoyable stuff to work with. Probably isn’t good for you either as it isn’t available (for some reason I’m not privy to) anymore despite its popularity- maybe too dangerous to use or the shut down of nuclear power plants means they lost a large portion of their business? I’ve been too busy with other things to keep up with the grapevine on this one.

[Travis Frink]

Originally Posted by Charles Friedman

Travis Nice work.

Thanks Charles but I can’t take any credit for this design. I’m just the foreign laborer who make the flue forms, made sure the mud was well mixed and made sure the furnace forms didn’t blow out and dump 500kg of high temp castable on the floor.

I know of two other (older) generations of this type of furnace. The grandfather version is or was in the mezzanine level of an office/condominium building at the base of ‘Oranda-zaka’ (Holland Hill) in Nagasaki and made a lot of cobalt glass when I was last there.

Does the ‘negative damper’ actually have an opening to allow ambient air to be pulled into the flue? Or is it like the damper used insider the stove pipe of a wood stove?

I’ll see if I have a picture showing it on a different friend’s furnace.

[Michael Ahlefeldt-Laurvig]

Is it something like this:
https://www.unifrax.com/product/fibe...s-al-moldable/

[Travis Frink]

Originally Posted by Michael Ahlefeldt-Laurvig

Is it something like this:
https://www.unifrax.com/product/fibe...s-al-moldable/

That looks a lot like the stuff. Thank you. I’ve been wonder if there is a similar product and what it is called in on there countries.

The product we’ve been using up to now, “Fibercast” was very sticky, a little heavy, and high resistance to glass temperature and direct flame. The new product (can’t remember the name now) is much lighter, not as sticky, and we don’t know how it will perform. It was recommended by the best glass furnace maker in Japan as a replacement and sometimes you just have to trust....

[Michael Ahlefeldt-Laurvig]

Japaneese fibercast was sold here, Ive used it. Really good stuff, not for what you guys are doing but doing repairs right onto hot surfaces,- like around acrumbling gathering port for example. Smearing it on the dense bricks cold as an insulation layer is a total waste and real seriously stupid. 15 years ago it cost $15 a kilo and it came in 20 kilo buckets

[Charles Friedman]

Originally Posted by Travis Frink

Thanks Charles

Does the ‘negative damper’ actually have an opening to allow ambient air to be pulled into the flue? Or is it like the damper used insider the stove pipe of a wood stove?
I’ll see if I have a picture showing it on a different friend’s furnace.

Yes it has a opening. Look at new drawing.
No air in, but, some hot air out. It is not a very big opening.
The negative damper makes the chimney draw less air into the heating chamber to make a reducing atmosphere, without impleading the exit of hot gasses.

A wood stove pipe flue damper, is a positive damper style. It blocks the flow and can stall the rise in temp.