PDA

View Full Version : ramping up gas furnace


Franklin Sankar
03-13-2012, 12:32 PM
In the good old days when you had gas furnaces mostly, how did you control the ramping up of a small gas furnace? Could you control it acurately like 60 def F per hr?
Is there a cheap gas flow device that you can send an electrical signal to and it will vary the oriface/gas flow?
Franklin

Pete VanderLaan
03-13-2012, 12:41 PM
It's actually very difficult with gas. I used to start furnaces up with little pilot venturis. The first issue was just staying below 212F . Quartz inversion was a little easier The upper end can be controlled with servo valves and butterflies. It's expensive. I never used servos.

Tom Fuhrman
03-13-2012, 12:59 PM
venturi burners were regulated with varying the pressure of the gas and how much air was added to it. Then a cheapo thermocouple/pyrometer could be inserted and you had a little bit of an idea where the internal furnace temps were. To start many would use a very small flame to bring it up slowly and then add to it gently. Once it started to glow you could do comparatives with color charts to see what temp your interior was. Most of the older ceramics books used to have a color temp chart in the back for reference.
In addition, back in the early years most were using invested pots, or day tanks so concern for breaking the pot was not as great.
I've seen some very sophisticated gas burners though that were installed about 20-25 years ago, but not sure if they are still in operation. I remember that Bowling Green State had a very advanced system that at the time cost them a lot of $. Not sure it is still in use or not. Their director at the time thought it was a waste of money but the powers to be at that time ruled and had some industrial guys do all the engineering and installation.
As I recall they had a complicated system at Greenfield Village in MI. as well. Haven't visited either in many years.

Kenny Pieper
03-13-2012, 04:51 PM
[QUOTE=
Is there a cheap gas flow device that you can send an electrical signal to and it will vary the oriface/gas flow?
Franklin[/QUOTE]


Here is one way to do it. Any machinist can do this for you. Just need to drill out the threads on the regulator and make a gear box for the motor. The motor can run on a controller.

Tom Clifton
03-13-2012, 06:44 PM
Might not want to mess with it, but you could use multiple burners. One that would have just enough capacity to hold the furnace at perhaps 1900 and another controlled by a PID (and thermocouple) driving a solenoid operated burner. It would cycle on and off to ramp up and down. It would presumably use the smaller burner as a pilot light. May not be "pretty" but it should work.

For burners you could use anything from a bunch of draft induced pipe burners to something with blown air...

Cecil McKenzie
03-13-2012, 07:27 PM
Franklin....Not knowing any better I used a set point controller and something called a Protectorelay to ramp up and operate my furnace. It had a Maxon burner with pilot and went on and off with the set point. I adjusted the burner with a co meter and then just left it at that setting and dialed in whatever temp I wanted. I would operate it with the pilot for the first night then gradually increase the set point. It had uv flame safety and a pressure switch to monitor the blower motor. Worked fairly well for 20 years. Are you contemplating a gas furnace ?

Michael Ahlefeldt-Laurvig
03-13-2012, 07:45 PM
[QUOTE=Tom Clifton;103961]Might not want to mess with it, but you could use multiple burners. One that would have just enough capacity to hold the furnace at perhaps 1900 and another controlled by a PID (and thermocouple) driving a solenoid operated burner. It would cycle on and off to ramp up and down. It would presumably use the smaller burner as a pilot light. May not be "pretty" but it should work.


Yes it works, Ive done it ramping up 300 kilo raw clay pots over 12 days- like 2.4 C an hour type thing- a small pilot and a weed burner.
But taking up a small furnace 60 F is easy just doing it manually with a weed burner- make a schedule on paper and just follow it. Its usually enough to check it every thirty minutes once you get a feel for how much to open your valve each time

Franklin Sankar
03-13-2012, 07:51 PM
Thanks for the replies. For a long time I was thinking about how they did it but I just could not figure it out. I wondered if you swapped out the Pots hot.Ie heat up a pot Outside and swap hot.
Elder Tom your memory is still valuable. Young Tom, I thought about using a on/off valve but that did not seem correct. Lighting a burner at 60 times a hour sounds explosive. Motorizing a metering valve sounds better. A stepper motor should do it if the burner does not go out. Then you have to sense if the gas flows or leaks when it should be off and shut down. Yes it gets complicated and expensive.
I am interested in gas because I want to experiment wit higher temps. You think I will kill my wires if I fire with gas after I reach 2100f?
Franklin
While I was typing some replies came in.

Tom Clifton
03-13-2012, 08:33 PM
Lighting a burner at 60 times a hour sounds explosive.

First off, safety is always top priority - some form of monitoring of the pilot is absolutely necessary. Regarding cycling on and off 60 times per hour - I have a home heating furnace in the basement that does that all winter long...

The only thing different is that it can use a tc to monitor the pilot while in a glass furnace an IR monitor would be needed. (and there is an air flow sensor in the flue to make sure the combustion chamber is purged before the gas comes on) As I would envision a substantial "pilot" running all the time the flue air isn't relevant in this particular situation, though forced combustion air (if used) and pilot flame most certainly are

Pete VanderLaan
03-14-2012, 07:05 AM
Hey Kenny, that's quite the rube goldberg device! I like it!

Michael Ahlefeldt-Laurvig
03-14-2012, 07:12 AM
Franklin- it doesn't cycle 60 times an hour because you adjust your “on-off” burner so low as to make it burn as long as possible while its on. You keep adjusting it higher as the furnace climbs. I had a mid sized soldering tip type burner as the pilot, with a naked (no sheath, for quick response) k-type tc and solenoid valve controlling the gas supply. And another solenoid switching the on-off burner as the set point climbs.
Its not like programming an electric furnace and going to the beach for three days and everything is ready to go when you come back, you have to keep a “watch” 24/7. But again for a small furnace with a fast ramp its not worth it- just do it manually.
Im not sure I understand you in your last post- you want to take your electric furnace higher on gas? 2100 F should be fairly good working temp…?

Franklin Sankar
03-14-2012, 07:50 AM
Thanks for the replies. I was thinking about pulsing the flame because I did not know how to adjust the size of the flame automatically. I did not think about doing it manually but that will work nicely if I dont go to the beach. Maybe I should move it to the beach. :):)
I want to go higher than the limit on wires for experimenting with bottle glass. The other thing is to use an assy pot/cup and ramp up a bit faster with gas. The faster rate will stress out wires but not with gas.
It will also cut down on time.
Franklin

Kenny Pieper
03-14-2012, 08:35 AM
Hey Kenny, that's quite the rube goldberg device! I like it!

I got the idea from Mark Peiser. He has a similar set up but uses a sprocket on the motor shaft, one on the regulator post and a chain to connect them. When melting color its great to have the control.

Pete VanderLaan
03-14-2012, 08:41 AM
It would figure to be Mark.

Allan Gott
03-14-2012, 10:40 PM
Could this setup be used to temporarliy, but intentionally, alter the atmosphere in an electric melter?

Pete VanderLaan
03-15-2012, 08:20 AM
I have never tried an electric gas combo but I have been warned off of it beyond immersion techniques. That is purely anecdotal.

Rosanna Gusler
03-15-2012, 09:56 AM
a potter friend says that putting an electric kiln into reduction is a major element killer. as i understand it, the reducing atmosphere strips the oxidised coating from the outside of the elements then when the kiln is fired in oxidation again the elements give up more metal to 'recoat' themselves . rosanna

Tom Clifton
03-15-2012, 10:09 AM
I want to go higher than the limit on wires for experimenting with bottle glass.

Fanklin - Do you use your bottle glass 'as-is' or do you prep it and add chemicals like of the methods mentioned in the paper at Clean Washington Center (http://talk.craftweb.com/showthread.php?t=6610&highlight=recycled+glass)?

Pete VanderLaan
03-15-2012, 10:16 AM
a potter friend says that putting an electric kiln into reduction is a major element killer. as i understand it, the reducing atmosphere strips the oxidised coating from the outside of the elements then when the kiln is fired in oxidation again the elements give up more metal to 'recoat' themselves . rosanna
********
That's an excellent explanation.

Franklin Sankar
03-15-2012, 11:29 AM
If the dual system could work I bet someone most likely would be doing now so, so much for that.
Adding stuff to the bottle glass seem to require some heavy heating at higher than normal(for me) temps. I have more or less given up on it because of the heat required but every so often I learn a bit more about using gas and my eyes light up but only to grow dim again. This time around I learned quite a lot. I need a little bit of molten runny glass for practicing encasment and Gas can do it quickly if the pot does not crack. Trying to heat it to a runny state in the GH is not as easy as diping in a small pot.
Franklin

Tom Clifton
03-15-2012, 12:58 PM
I need a little bit of molten runny glass for practicing encasment and Gas can do it quickly if the pot does not crack. Trying to heat it to a runny state in the GH is not as easy as diping in a small pot.

In addition to a reducing environment being hard on elements (next time you turn them on as previously noted) The higher heat is also going to be a bit tougher on your liner and backup insulation.

It might be easer on your primary furnace to build a "vertical" GH if you have the parts and materiels available. (That is a big 'if' - I understand your location and the associated challenges...)

Michael Ahlefeldt-Laurvig
03-15-2012, 01:47 PM
Franklin-
Its a long time ago that I blew soda glass but I think that if you melt bottles in a pot and get it hot then you cant actually gather it - its like gathering water. Just as you turn around to get out of the furnace with your teaspoon gather, it will drop 10 F and it freezes. Bottle glass is designed to "set" really fast in a machine mold. I think you discussed high lead glasses before- they are the complete opposite,- they are extremely "long"- they stay workable over a wide temp range- thats the whole idea.
One of the best questions Ive been asked from someone watching is - How long does it take to dry?

Pete VanderLaan
03-15-2012, 04:17 PM
My favorite is "Is this your hobby?"

Tom Fuhrman
03-15-2012, 05:03 PM
Mine is: "what did you do before you retired?"

Pete VanderLaan
03-15-2012, 06:20 PM
"Did your father blow glass?"

Cecil McKenzie
03-15-2012, 10:38 PM
Franklin You might try designing something like a muffle kiln. Where you heated past the critical points with electricity then had a muffle or passage way through the interior space of your furnace that you could heat with a small atmospheric burner.

Older muffle kilns I think were bottom fired with a tube or muffle going vertically through the area to be heated. Their purpose was for use where a reduction atmosphere was not wanted. The muffle would be made from a refractory that would withstand thermal shock and also absorb and radiate heat to the interior space.

Have you ever tried window glass ? Probably not since it would be more green that most bottle glass. You should maybe try to take a class at Penland or something like that.

Allan Gott
03-16-2012, 07:10 AM
If the dual system could work I bet someone most likely would be doing now so, so much for that.

Now now my boy let's not give up so easily.......you know me better than that........it's not like the elements are going to jump out of the kiln in protest when a flame is introduced.......time for a little cost/benefit analysis

Franklin Sankar
03-16-2012, 07:46 AM
I will sleep on it for a while.
Thanks
Franklin

Pete VanderLaan
03-16-2012, 08:02 AM
I do think you could have an arrangement something along the lines Cecil suggests with a pot standing on a stilt and heated from outside with elements. The pot lip would have to be sealed from the electrical portion with a piece of high temp board and then have a combustion chamber above glass line for gas entrainment. It would work since I have done similar things but muffling gas, not electricity. I did it in our really early cad /sel melts when I was worried about selenium loss through volatilization which I came to the conclusion was not an issue. so I threw the furnace out.

It would cost a good deal more to run since it has more space that has to be heated.