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Author Topic: How hot is the flame?  (Read 2959 times)
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Irene
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« on: January 09, 2015, 05:36:44 PM »

When ever I tell People about melting glass and making beads, I often get the question (most often from the guys) how hot the flame I'm using is, and I have to answer I don't know....  Anyone know how hot my Cricket torch is when using a normal, neutral flame?
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Fiona
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« Reply #1 on: January 10, 2015, 03:14:49 AM »

Just did a quick Google and someone on Lampwok etc asked the same question. The answer was as a ball park figure around 5000 degrees Fahrenheit.
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Pat from Canvey
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« Reply #2 on: January 10, 2015, 03:40:04 AM »

When I do a pot melt, I set the kiln to 930 deg C. This would suggest that a torch flame was at a similat or slightly higher temperature, not 5,000 F (2760 deg C )
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ajda
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« Reply #3 on: January 10, 2015, 03:47:34 AM »

The actual temperature of your flame is not a simple thing to calculate as there are so many variables... I think this is the thread Fiona's referring to - http://www.lampworketc.com/forums/showthread.php?t=160944 - (as Pat says, 5000F = 2760C)

Perhaps more relevant for those geeky guys would be the temperatures at which significant things happen to the glass while in flame or kiln:

Strain Point: temperature at and above which thermal stress can be introduced - hence need for annealing
Annealing Temperature: temperature at which, when uniformly heated in controlled conditions, thermal stresses can be removed
Softening Point: temperature at which glass begins to deform
Working Temperature: temperature that glassworkers need to attain in order to manipulate and control glass

And these are different for different types of glass - examples below of (approx) temperatures for the two main types of glass used in lampworking:

Soda-lime glass coe 104 (eg Effetre, CiM, etc)
Strain Point: 450C
Annealing Range: 490-520C
Softening Point: 570C
Working Temperature: 930C

Borosilicate glass
Strain Point: 510C
Annealing Temperature: 565C
Softening Point: 820C
Working Temperature: 1250C
« Last Edit: January 10, 2015, 03:50:19 AM by ajda » Logged

Shirley
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« Reply #4 on: January 10, 2015, 05:11:51 AM »

Great question and thanks for that info, Alan Cheesy . I often get asked about the temperatures when I'm at fairs, so now I can give a proper answer instead of 'er,um..'
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Val Cox Frit - Thai and Bali Silver 
Irene
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« Reply #5 on: January 10, 2015, 10:38:27 AM »

thanks everyone! Now I can give a better answer, I Guess I will say around 2000 C and that will be about right. The cricket torch can melt boro, I've never tried it but want to some day. I like the cricket for the heat, but I would like to find a torch With a bit more radiant heat, I think that would make stringer work a bit easier. I'm thinking of a cc Carlisle mini, it has a more bushy flame, and Works With a oxycon.
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ajda
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« Reply #6 on: January 10, 2015, 12:12:39 PM »

I can highly recommend the Mini CC - great torch with versatile flame - fine with a 5 lpm oxycon for soft glass and small boro, but more oxygen if you can get it is better for boro, not only for more oomph but because some colours behave badly unless worked in an oxygen rich flame. A larger oxycon or a pair of 5 lpm would give you a more scope. I upgraded to a Bethlehem Bravo when I started to get into boro properly - my partner still uses a Mini CC, but mine is lurking unused on the shelf now. I might be persuaded to part with it... one day... possibly... or maybe not...
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Irene
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« Reply #7 on: January 10, 2015, 02:06:28 PM »

well, Alan, I might be persuaded to buy it.... one day... possibly......
I will use soft glass for a long time yet.
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« Reply #8 on: January 14, 2015, 05:11:34 AM »

After also being asked this too many times I stored away this answer in my phone, and whip it out whenever questioned!

"glass melts at around 800 degrees C. The temp at the base of a Minor Burner is around 1800 degrees C.  That's roughly 1/3 the temp of the outer surface of the sun!"

Don't remember where I pinched it from, probably one of Sally Carver's posts on here!
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lampworklover
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« Reply #9 on: January 14, 2015, 06:57:12 AM »

thanks everyone! Now I can give a better answer, I Guess I will say around 2000 C and that will be about right.

erm, not 2000 C...... Shocked Shocked

I must admit I've always told people 'around 800 c'.
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oliver90owner
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« Reply #10 on: January 14, 2015, 10:50:10 AM »

I must admit I've always told people 'around 800 c'.

LWL,

Melting glass needs a lot hotter flame, to be able to transfer heat quickly enough from flame to glass.  2000 Celsius is a nice round figure - I would say a little less but never mind, that is close enough for propane/air.  Pure oxy-propane can reach 2800 Celsius, but is not hot enough to weld steels.  Those temperatures are the best achievable and don't last long.  They are called the adiabatic values (with no heat losses to the surroundings).

Remember the glass is losing a lot of radiated heat at its melting point!  The specific heat of the flame gases is not so great and much heat is radiated from the flame, followed by rapid dilution with air.  Even oxycons may have as much as 10% dilution gases going into the flame and that must also be raised from room temp to flame temperature.

Need well over 2500 Celsius flame temperature to melt steel, as in oxy-acetylene flame, where the carbon:hydrogen ratio of the fuel needs to be better for the energy density required. Oxy-acetylene (theoretical) is just over 3000 Celsius and steels melting around 1400-1500 Celsius gives an indication of how much 'extra' flame temperature is needed.  That is when kilns and furnaces are required to minimise heat lost to the surroundings.  

We melted Platinum and other precious metals in induction furnaces where the electrical heating energy was transmitted directly to the metal in the crucible and the crucible was heavily insulated. A couple thousand degrees and more in some of those.  Yes, and then we often carefully poured it into a large tank of swirling water! (not someting to do unless there is lots more water than metal - I have seen the results of molten metal spilt onto wet floors and it is not nice!).
« Last Edit: January 14, 2015, 10:52:48 AM by oliver90owner » Logged
Redhotsal
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« Reply #11 on: January 14, 2015, 03:42:20 PM »

Yeah - I tell people that it's about 1800C at the base, around 1200-1500 in the region where you melt the glass and about 500C at the top of the flame where the flame just about disappears, but of course it all depends on the gas mix, the burner and how much you've got it turned on! Smiley
Anyway - seems to be a satisfactory answer for most folks.
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lampworklover
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« Reply #12 on: January 14, 2015, 04:14:01 PM »


Soda-lime glass coe 104 (eg Effetre, CiM, etc)
Strain Point: 450C
Annealing Range: 490-520C
Softening Point: 570C
Working Temperature: 930C


.... I'm really confused now; if the above is correct, (and  most of my books would agree with these sorts of figures), there's a bit (HUGE) difference between these temps and 2000 C.

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ajda
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« Reply #13 on: January 14, 2015, 04:51:02 PM »

The thing is, as oliver90owner says, the flame itself needs to be at a much higher temperature than the target temperature of the glass in order to transfer enough heat energy into the glass to bring it up to working temperature and keep it there while you work it. Think of the element in an electric kettle as a comparison - it probably has to get to several hundred degrees in order to transfer enough energy into the water to get it up to its boiling point of just 100C.
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Irene
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« Reply #14 on: January 14, 2015, 05:55:23 PM »

Sounds right Sally, and the working temp is the most interesting temp, as you don't put the glass right at the base of the torch very often.

Quote
.... I'm really confused now; if the above is correct, (and  most of my books would agree with these sorts of figures), there's a bit (HUGE) difference between these temps and 2000 C.

I think you confuse the temp of the flame it self and the temp of the glass. I could theoretically have used a flame at 3000 C and that still would not change the thermal point at which the glass will melt.  Wink
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