Minimizing Mass to Maximize Effeciency

[Glenn Randle]

I have offen thought it seems ineffecient to heat 1000+ lbs of furnace mass in order to melt a few hundred pounds of glass.

Of course a strong and durable container is required to contain molten glass, so it's obvious that the crucible must be up to the task. But besides durability is it necessary for the interior of our furnaces to be constructed from such dense materials? What are some ways we can reduce that mass without decreasing the furnace's lifespan or the glass' quality?

I realize the hard/hot face does reflect an amount of heat back towards the interior. But, how much high density material is actually required to accomplish that? I know folks have successfully used "all frax" furnaces, but I think that's a bit too "minimal" for me.

Has anyone tried using a thin, but strong, material like Zircar's Mold Mix 6 or perhaps the ceramic shell mold materials that's used for casting metal sculpture? Seems like something relatively thin (1/4"-1/2") reinforced with a bit of fiber in the mix would make a nice furnace interior. I have a couple of sample tiles Zircar sent years ago which are super strong, I recall a man standing in the center of a 2'x4' board of it suspended between two blocks. It was just available in sheet/board form, but the idea of using something like it has alway stuck in my head.

Has anyone here experimented with making a refractory mix, from the raw materials, which has these qualities? Maybe a slurry made with alumina and/or silica flour, shreaded frax, and some rigidizer. Seems like a worthwhile thing to test/reasearch, has anyone here done it yet? Also are there any high-temp reflective materials being used in furnaces these days?


peace,
Glenn


ps I took a break from the studio (& the boards) for a nice while, forgive me if I'm asking things which have been discussed already.

[Jordan Kube]

I think you'll run into the same durability problems as a fiber furnace. The interior of your furnace should be resistant to glass attack. I'm not saying don't do it.

[Eben Horton]

Glen, if your furnace ever crashes on you and you do not have a dense furnace liner, your furnace temp will drop like a stone...

[Glenn Randle]

I agree that it needs to be glass resistant. That's why I mentioned a material like Mold Mix 6, it's capable of producing reusable casting molds because glass doesn't even stick to it. It's so strong that for a 30-40 lb casting the mold only needs to be about 1/4" thick. I don't know what it's made of, but I think alumina is pretty glass resistant and relatively inexpensive. I think colliodal alumina, alumina frax, alumina flour (and however else it's available tabular, milled, granular, etc) would produce a hard and durable shell. I guess I'll read up on the "ceramic shell" metal casting info and see where that leads. I think the company to call is Remet (or something close to that). I got a bag of zircon flour from them a while back.

I was trying to make fake diamonds. (just kidding) :rolleyes:

[Glenn Randle]

Originally posted by Eben Horton
Glen, if your furnace ever crashes on you and you do not have a dense furnace liner, your furnace temp will drop like a stone...


Hey Eben!

How's it been? How old's the little one now?


The crashing is a "non-issue". I've found these indestructable crucibles from a guy named Pete. ;) The EC pots don't have a problem at all with crashing. During R&D with the waste oil burner I had my furnace crash very HARD multiple times, I mean I arrived in the A.M. to find the furnace @ 900f and the blower had been blowing cold air all night directly under the pot. I wouldn't be surprised to hear you could quench an EC pot in water from 2300 and still use it a couple more years.

Actually, I'm not sure that a well insulated furnace would drop too quickly. There's still a heck of a lot of mass between the crucible, it's supporting refractory, and also the glass itself.

When my furnace had crashed it was the Mono T-9 which cracked up. Oh well, that'll make it easier to dispose of!

Are you still burning gas?

[David Patchen]

Interesting question.

But one point you raised was particularly interesting: what's the reflective value of current inner furnace materials and is there a material that could just line the inside of a furnace that would be the most reflective of heat possible. It could then be insulated outside of that.

I think the issue of using super-thin materials is not that they're not strong enough, I think it's inefficiency from not being insulating. Dunno. Maybe Steve will weigh in--he's probably thought a ton about this kind of stuff...

[Glenn Randle]

David,
I don't know the physics of how heat is reflected, but I'd assume to some degree it's simular to light. Obviously there's another facet (or more) involved with reflecting heat, must have something to do with the material's density too. Anybody here have a friend at NASA?? I wonder what they coat the Shuttle's ceramic tiles with. They probably wouldn't share that information, but who knows the manufacturer of it probably brags about NASA using the stuff. Remember Tang?

Zircar probably sells it, their prices look like the Government's their main customer! :D

[Marcel Braun]

As has been discussed here before, you only have to heat that mass once so the longer you keep the furnace on the more efficiency you will see per melt with a heavy but well insulated furnace. You might actually be more efficient because it would take less intense bursts from the elements to melt in the charges...although in the end it still takes the same energy to heat the same material.

That said,if you were going up and down often to change pots for color melts or only working one week a month, a lightweight furnace would be likely to be more efficient. In making boro color they use very light, barely insulated furnaces to quickly melt 20 to 60 pounds of batch/cullet, pull it all out and return to room temp for the next charge.

I'm also curious to know more about possible lightweight refractory designs.

I don't think the shuttle tiles would help, it is my understanding that they are ultra high purity fiber coated with a special borosilicate glass engineered to be a strong IR Emitter. (something like cobalt or manganese in high saturation) They are only able to hold up for a short time before the heat soaks all the way through.

Just my speculatory .02

[Steve Adams]

I have wondered about the use of "ITC-100 ceramic coating" that is used in metal forges. It is a reflelctive coating that is painted on the interior surface and claimed to work well to increase the efficiency of a forge. Anybody heard of this or used it? Here is a link to it...

http://www.budgetcastingsupply.com/ITC.html

Steve

[Brent Hickenbotham]

Glenn I have often had a lot of similar thoughts recently, but until I can change the laws of thermodynamics, I will still be in constant R&D, its funny, I met Roger Parramore and we had a short conversation about refractory, and he told me to always remember that you start off behind and you'll never win. It doesn't hurt to dream though. My two cents is that you have to have a dense interior or you will have hot and cold spots to a bit more extremes. if there isn't an internal radiation from thermal mass then the heat loss is gonna find a way to quickly destruct that indestructable EC pot. just my opinion, I still have much to learn;)

[Henry Halem]

Eventually the alkali atmosphere will dissolve any and all fiber materials even if they are suspended in a mortar. Trust me, I found out the hard way. You are correct though that the greater the thermal mass the more energy required. There are lighter weight castables than Mizzou that work well as furnace liners such as Castolite 30. My feeling is that any liner under 2.5 inches is not structurally sound but I guess that also would depend on the size of your furnace. After that, one should backup with 7 -10 inches of fiber. Beyond that thickness and your creating a heat synch. The first 2 inch layer of fiber should be an 8 lb. HTZ and then one can switch to a standard 8 lb. 2300 deg. fiber. The use of Excelfrax as the last layer is recommended as 1" of Excelfrax is equal to 3.9 inches of fiber. The use of Excelfrax will also cut down on the thickness of the furnace insulation. The Excelfrax should be the last inch as it cannot handle high temperatures. Do not sandwich Excelfrax either. It should also be noted that most heat loss is through the crown. Excelfrax is expensive but worth the investment. the drawback to Excelfrax is that it cannot be molded around compound curves. It's best used flat.

[Steve Stadelman]

I wish there was a magic bullet, so far I design everything to be barely larger in diameter than the pot, slightly taller than the pot plus the elements, and round.

A cylender has about 25% less radiating area than the same size cube.

High zircon castable for glass contact areas.

[Glenn Randle]

Thanks all,

Much good info and things for me to think about. I'll let you know what I come up with.....might be a while.:) Keep posting whatever tips, thoughts, questions, links, & advice happen to come across your collective minds.

Thanks again,
Glenn

[Steve Stadelman]

Pete's furnace in Santa Fe has fiber end caps that have worked really well for several years now.

I tried this on a multipot furnace here in Oregon and it just didn't work. The customer uses numerous Spectrum cullet products (opaques................FLUORINE) and the ends got eaten right up. Less than four months and I ended up bricking up the ends with G-28s.

The saving grace is that the customer has had a $1500.00 monthly savings over running N.G. and still likes me because I fixed the problem with no Q's and no B.S.

I cannot say enough good things about fiber as an insulation.

I cannot say enough bad things about fiber as a hotface in a glass furnace.

[David Paterson]

You can download a free program that calculates heat loss through multiple layers of insulation and gives you estimated cold face temperatures:

http://www.pipeinsulation.org/


You will need to enter the insulation values in Btu·in/hr·ft2·°F of any materials you plan to use. I posted some insulation values for common materials here:

http://talk.craftweb.com/showthread.php?s=&threadid=2902


In one of the drop down menus you will need to configure the program for a vertical flat surface.

One insulation material that apparently out-performs all others as a back up material is Microporuos Insulation. One inch is supposed to be equivalent to several inches of fiber. I am planning a rebuild of my furnace and plan to add 2 inches to the outside.

There are several manufacturers/suppliers. So far the cheapest place to buy it appears to be Thermo Dyne:

http://www.thermodyne1.com/

I was quoted $9.75 a square foot for 1 inch microporous panel.

Another excellent board for backup in terms of heat loss is Skamol SUPER-1100 E. It appears to be almost twice as efficient as fiber.


If you play around with the heat loss program, it quickly becomes apparent that it should be possible to cut the heat loss through the walls in half or better by using the best insulation materials.

[Henry Halem]

Originally posted by David Paterson
One insulation material that apparently out-performs all others as a back up material is Microporous Insulation. One inch is supposed to be equivalent to several inches of fiber. I am planning a rebuild of my furnace and plan to add 2 inches to the outside. As per my posting above, 1 inch of Excelfax (Microporous) equals 3.9 inches of fiber. The Calcium Silicate board, Super 1100 E is, as David points out, an excellent backup insulation but will only work on flat wall construction.

[Ken Peterson]

marcel nailed it about 10 posts ago. Furnace weight doesn't matter when it comes to efficiency. Less weight just makes the temp crash when you open the door. I would highly discourage making a super light weight furnacce.

[Glenn Randle]

Has anyone tried the ITC-100 that Steve Adams linked to? I read the info about it and some of the other links that provided, but everything I found seemed to be posted by sellers of the product. It would be nice to hear from folks who have actually tried it in a glass furnace, glory, and/or annealer.

The material "sounds" good, but everything can sound good if you are only getting 1/2 the story. :rolleyes:

Mr Stadelman, I'd think the makers of ITC-100 would love to send a free sample to a prominent manufacturer of high quality electric glass furnaces for product evaluation. Have you considered trying the stuff? (not trying to tell you how to build furnaces, or run your business. Just seems like they'd naturally want you to try their product.)

[Steve Stadelman]

I don't think that I.T.C. has anything to offer a steady state application.

If it reflects heat the wat that they claim and you are in an application where you are starting cold and trying to heat up quickly (forge or kiln) that would be cool but our furnaces go up to temp and typically stay there for a year or more.

Even the best reflector will soon saturate and conduct heat to the next refractory layer and then you just have a thin coat of stuff to flake off into the pot.

[Mark Wilson]

large thermal mass furnaces are less efficient, if you change the temperature of the furnace, like ramping up/down to squeezing temperature. so if you close down your furnace weekly, like i do, you want the smallest thermal mass possible for the highest efficiency. but if you leave it at temperature and never squeeze, like for instance how dan mathur uses his furnace using FHC, the large thermal mass does not hurt. and as mentioned before, the large thermal mass helps to keep the temperature from crashing when charging. all in all, for maximum efficiency and minimum energy costs, you are better off with less thermal mass and having sufficient heating element capacity to power through temperature variations (maximum kinetic energy, minimum potential or stored energy).

as for coatings, ITC and other similar coatings that modify the surface emmisivity, do help to improve efficiency, but not that much. the key is does the reduced cost of energy use pay for the cost of applying the coating before you need to re-coat?

[Glenn Randle]

I can appreciate & understand that view. I was also thinking the elements might not like it reflecting heat back towards them, might cause them to over heat.

But, assuming it doesn't flake or bother the elements, and continues to reflect the IR back towards the interior/crucible I'd think it would save energy. And you know the saying "The more you buy, the more you save!" could actually be true. I mean all the energy which is absorbed by anything other than the glass is basically lost (through convection, I think that's what it's called).

In my mind I keep thinking of how light is reflected, because it's visible my mind can grasp it easier. And IR is light, only in the invisible spectrum. So I'm having a hard time "letting go" of the notion that a reflective surface would save energy.

Wonder how difficult the stuff is too remove it did become a flakey mess?

I've got an old glory hole, which could be a test unit. I know it's not the same in any respect to a furnace, besides it gets hot. But it could indicate whether the fuel savings is true and also the daily heat cycling would definitely give a good idea how well the stuff stays in place. My glory has both castable & blanket so it will test both materials. Might just have to give it a try.

[Eben Horton]

Ive said this before and someone reeemed me out for it but i am going to say it again- In the big picture saving 20, 50 or 100 bucks a month really doesnt make a difference to me- Having a shop that is comfortable to work in and having a shop I want to work in is more important- Id rather buy a couple new CD's to keep me more productive and crank out more work than to build a new furnace that might be a little more efficient. Further more, i would rather have more orders for my work and get more of my work out there than to spend the same amount of time it would take to get those orders than the time it takes to save $$

its an expense that is necessary for production.

ok... reem away :D

[Glenn Randle]

Eben,
You're 100% right about that....but we can't really sit around wasting time telling each other how to sell more glass, can we?

Btw, I want to get on the list to go and collect your past due $$$ in Philly. I've never been there. :mad: I hate crooks! :mad:


Oh I almost forgot, the point behind saving energy isn't about saving money.....it's about saving the planet. You know, the global warming thing. I'm an "environmentalist" glassblower.

What kind of CD's tend to make you work harder.....I could use a few of those!!

[Eben Horton]

Glen, salvage your waste heat to heat a grenhouse, heat your hot water heater, heat your hot tub, etc....thats doing your part to save the planet..

You should check out philly- its a cool town and i think i am going to get paid.. if not i'll go in by myself... im a big guy.

Music?? well i just got the sound track to Y tu mama tambien.. i like it.. right around 4:00 i will put on new music to keep me going.. i like any albums that have a quick tempo, are not anoying, and wont scare away my clients when they are in my gallery...

[Steve Adams]

here is another link to "ITC-100 ceramic coating" that shows an emergency furnace door repair using a piece of plywood coated with the stuff, must be something to it...

http://www.scarvapottery.com/opencontent/default.asp?itemid=111&section=PRODUCTS

Steve

[David Paterson]

Has anybody actually used this stuff?

[Glenn Randle]

Seems unusual that I can't find a link to the company who actually makes ITC 100. All I find are distributors making lots of very big claims about what it can do. Very difficult to imagine a plywood door at 2000f....

Also very strange that there's absolutely no mentioning it being useful in the "glass" industry, yet it's so useful in the other "high temp" industries.

I'll have to speak directly from the manufacturer's tech department before getting too excited about it. Wonder why they are so hard to locate. Anyone know their contact info?

[Todd Nelson]

I've used this stuff on kilns but haven't in a glass melting situation. It is really a reflective type product.
International Technical Ceramics, Inc.
58 San Juan Drive, PO Box 1726
Ponte Vedra, Florida
904-285-0200
I don't have any idea if they still answer their phone. Used to advertise in Ceramics Monthly but now I only see the product available thru vendors.

I liked it in my kiln as it seemed to make copper reduction reds pop easier.

[Kraig Richard]

Frax lined interiors. Ive had three. Frax has changed since early eighties, and results could be improved these days.

I like frax interiors OK. Be aware if you do go with frax that there is an incredible amount of shrinkage and it dosent take long for a heat worm to start tunneling through to lowergrade backup materials in your walls, so over lap or somehow design for and really take that great amount of movement into account. Prefiring the frax might help to get it to its final dimension. I never prefired frax for this reason. (I do prefire frax befor I mix it with sairset.)

Another thing with frax lined crucibles is sizing your burners and blowers. They can be smaller.

A third aspect to keep forward in your mind is running these things up for the first time. Especially with a high efficiancy exchanger, a frax furnace can go from 75F to 2950 f in a lot less time then you think, even idled down.

Never had crash issues using homemade "coil built" crucibles.

Frax is not everlast. However, its only the inside layer of it that really shits the bed. Decomposition is primarily a crusting of one eights to three eights of an inch thick, an "islandisation" of that crust, some partial flaking of the islands, all over a fairly long time.

Do floors (sand covered),walls or a door, dont frax an arch. I was a hot melter in a hurry and abusive. (I recieved therepy) A kinder gentler melter might get better behaviour from frax and use it for a roof.

[Steve Stadelman]

Kraig, what were you melting? I am really curious. My experience was aweful but industry uses frax liners in many high-fire applications all the time. Did you have a coating on your frax?

[Kraig Richard]

At that time I was mixing up a modified school formula. a high barium soda-lime with Arsnic+ Antimony. This batch empolyed the "shotgun strategy" of lot's of different ingrediants. (with Swanton Limestone a local product) using my own cullet around 10%. I melted (tried) lots of other colors too then. Stuff I'd never want to be around now that I got a kid. You cant keep wearing the same hazmat suit over and over.

The frax got "self" coated by the glass furnace vapors. Firm speculation here as there was tinge of cobalt, not just a clear/opaque of the frax layers. That was the only color I recall showing up. This furnace had two rear entry burners at floor level and (for comfy gathering) the exaust right down there inbetween them. An exaust up higher above the pot might tend to reduce furnace vapors on the wall . Not sure.

Hindsight construction for a frax situation ....One inch layer of not the very best frax, layed flat, oversized for shrinkage, as disposable liner. "Use once and discard" . Swap it out during a pot change if need be. This discarded frax still has uses.

Your currrent furnace configuration may be suitable for experimentation by using frax for the door to document degradation rates for yourself.

[Marcel Braun]

Hi all,

I've been the latest victim of the war on David....Thanks Pete, Steve, and Katie Moe for getting my account back online...

I've used the ITC products, the 100 and also the 200? ( a secondf coat for on top of the 100) and also the metal protection coating. The 100 and 200 are a little tricky to apply, if it doesn't stick it really REALLY flakes off. I liked the metal protection, it is rust colored and seems to help lowly mild steel resist attack. My GH doors' edges seem to be holding up quite well. It is no help where the heat saturates (like between the two sets of doors).

The 100/200 coating combo does seem to help reflectivity and especially helps bricks to act a little more like frax...quicker heat up and it seals the surface porosity. I think it works well to rigidize frax but frax really soaks it up and it is EXPENSIVE!!! It didn't do anything but flake on dense castable. It must be applied to a prefired surface with a siphon feed sandblast gun, and fired in between coats.


It might be worth it in a GH or a kiln but I definitely agree with Steve that it would be little use in a furnace for the reasons he mentioned. I'm not sure it would be any better than a straight up zircon wash. After using i decided I'd like to try a mortar slurry to rigidize the frax and a zircon wash for reflectivity. Haven't tried it yet....dont have data to really compare it to anything else effectively.

Bottom line from my experience: Frax GH-yes Brick GH- YES Kiln-maybe, Frax melter- maybe$$$$, conventional melter- No.

I like Kraigs idea of a disposable frax liner and would add that Ferize (of ITC) described this sort of design for a heat treating furnace he built....expanded metal shell, inconel wires through frax, tie off. Torch inside, apply ITC 100 add next layer when wet. Repeat till desired thickness, apply final coat 100 and 200. Replace inner layer as needed. He claimed a rough 6 foot tall 6 foot cylinder could reach 3000 in 20 minutes. I'd like to see his burner....OH yeah, that is a shitload of ITC $$$$$.

[Pete VanderLaan]

Originally posted by Glenn Randle
Hey Eben!




The crashing is a "non-issue". I've found these indestructable crucibles from a guy named Pete. ;) The EC pots don't have a problem at all with crashing. Are you still burning gas?
***************
I hate this belief that EC pots are indestructible. They aren't. They are simply better than most at not going down from thermal shock. There is no free lunch on this. They are better on thermal shock because of the coarse grain tabular alumina that is used in the formation of the pots. The flip side is that they will not withstand ultra high temperatures in melts as well as a fine grain clay La Clede will.

When you build a furnace, the mass allows the furnace to roll with the punches of the fresh batch thrown in the furnace and not subsequently plunging in temperature. That plunge is not good for the pot or the batch. The only way to overcome that huge swing is to apply enormous amounts of BTU's thru the burner or elements at the time of the charge. That will, in my opinion, likely cause the exterior of the pot to be heated beyond its design parameters while the furnace struggles to regain its equilibrium. The mass is your friend up to a certain point, particularly if well insulated.

In other words, I don't think its a good idea to try to cut mass.

[Glenn Randle]

[QUOTE]Originally posted by Pete VanderLaan
[B]***************
I hate this belief that EC pots are indestructible. They aren't. They are simply better than most at not going down from thermal shock.


Sorry Pete,
I thought I was saying good things about the durability of EC pots. My furnace has a lot of thermal mass, so obvously even when it "crashes" it does so much more gently than some other furnaces might. I was just supporting the "Bulletproof" claim you used to say. Obviously over the years some studios have abused their EC crucibles enough to find their thermal shock limits. The only thing that used to damage mine was "flame inpingement, and you had warned about that from the beginning.

I understand your view about the importance thermal mass plays in protecting the crucible.

[Pete VanderLaan]

I appreciate your support. I simply don't want people thinking the things can't be broken. I shot one with a 30.06 and it blew all to hell.

[Glenn Randle]

Pete,
That doesn't sound very "safe".;) I've had days like that too, uh come to think about it, "yesterday" was one of those days!! I wish I'd had a 30.06 and a spare crucible handy, it would have saved me a lot of cussing!!

It's all good. To have great days, you've got to have a few bad ones. No big deal.

:mad: /:angel:

[Pete VanderLaan]

I would also issue up a word of caution: There have been a lot of product names tossed around here for this application and my experience tells me to wait until someone else has tried them for about three years before you do. Henry did use some stuff that was raved about elsewhere and quite simply, It turned to shit.

These boxes are continuous duty relentless ,high alkaline environment furnaces. The atmosphere is testing you in its harshest way. Here's a thought worthy of remembering. I once talked to an AP Green engineer who simply said " The glass industry is the only one we really don't make products for." Now it just so happens that Kast-o-lite 30 and Mizzou are very servicable in the small studio environment IF they are cast at a minimum of three inch thicknesses ( Thank you Fritz). Beyond that, AP Green is not the company of choice to deal with. You are far better off with Pryor Giggy or certain products from Missouri refractories.

Lightweight furnaces should only be used by one person who really really is careful. They will never survice a door kicking staff. I would never build one for daily use , ever.

[Brent Hickenbotham]

Pete sounds like you got some extra time on your hands if your shooting crucibles just too see what happens.:D But I'm sure its in the name of science.;)

How's the winter up there?

[Pete VanderLaan]

I take it you refer to our extended mud season?