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Températures, efficiency, arc vs OA y

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Températures, efficiency, arc vs OA y

Postby olek » Mon Nov 06, 2017 11:34 am

Hello

I was surprised to read that while my OA flame is 3150 degree celsius at its hottest, to get to 3000 celsius with arc I would need 200A, (for 23v)
and then only a part of that heat is actually used, more or less depending of the process.
(stick would use 20% of that heat only?)
That 3000 celsius is more than the double of steel fusion temperature.

We probably would experience much more holes and drips if the whole heat was applied, but I thought the heat was higher with arc (may be just confusing with plasma but is this is too different to be valid as a comparison?! In the end gas within the arc are they elevating the temperature above the one obtained by the watt computation?)

So flame welding should be more efficient? Or is the lack of gas protection a problem (is there any protection with OA in fact?)

Thanks
Last edited by olek on Mon Nov 06, 2017 12:14 pm, edited 1 time in total.
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Re: Températures, efficiency, arc vs OA y

Postby Farmwelding » Mon Nov 06, 2017 11:51 am

https://hypertextbook.com/facts/2003/EstherDorzin.shtml

That is a good overall chart on temperatures. The torch is typically less efficient.
I had a discussion with my welding instructor about welding chromoly tubing and how when he talks to old guys they say torch welding is the way to go. sure your torch has a lot o heat and melts the base metal, but compare the size of the flame to the size of say a tig welding arc that is significantly hotter and smaller. The heat input is way more with the torch because of how broad it is and the shear volume of heat.
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Re: Températures, efficiency, arc vs OA y

Postby olek » Mon Nov 06, 2017 12:24 pm

Farmwelding wrote:https://hypertextbook.com/facts/2003/EstherDorzin.shtml

That is a good overall chart on temperatures. The torch is typically less efficient.
I had a discussion with my welding instructor about welding chromoly tubing and how when he talks to old guys they say torch welding is the way to go. sure your torch has a lot o heat and melts the base metal, but compare the size of the flame to the size of say a tig welding arc that is significantly hotter and smaller. The heat input is way more with the torch because of how broad it is and the shear volume of heat.


Thank you, good document, with amazingly variable numbers ;)

I suppose a confusion occurs between the heat generated by the arc creation process at its basic (the 3000 celsius obtined from 4000W with 200 amps on 23V) and the temperature of ionized gases within the arc

Indeed I did not take in account the size of the dart vs the one of the arc.

To heat something, the torch will always be the tool of choice (as for cutting thick steel, if no high grade plasma cutter available
)

That said, very happy to work more closely with metal melting and TIG style welding, with the OA torch, that makes a new experience after and together with arc (MMA) prepping plates should be easier too, as working on fine steel . (very happy of that second hand equipment, for about 220 USD) Regards
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Re: Températures, efficiency, arc vs OA y

Postby PeteM » Mon Nov 06, 2017 3:25 pm

Don't forget about time.

Its a very important variable when calculating heat input.
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Re: Températures, efficiency, arc vs OA y

Postby olek » Mon Nov 06, 2017 3:56 pm

At first I was looking for the information on the temperature within the arc, and the French Wiki stated something about the same as the torch, with a computation based on the volts/amps watts result, it seem to be only the temperature of the electrodes at the begin of the arc, the arc itself have clearly a much higher temperature

Or this is just an enorme mistake,

here is that search https://www.google.fr/search?q=temperat ... e&ie=UTF-8
Ic comes from a wikibook and look just like a huge mistake
https://fr.wikibooks.org/wiki/Soudage/% ... 9lectrique



http://files.aws.org/wj/supplement/WJ_1976_08_s222.pdf

https://www.quora.com/What-is-the-tempe ... rc-welding

As seen on the sketch , depending of the position from the centre of the electrode, the temperature may vary from 3000c at the edge to 20000 c on a very small zone in the middle
the surfaces are in no mean comparable with the ones within the Oxy Acetylene flame
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Re: Températures, efficiency, arc vs OA y

Postby Arclight Ironworks » Fri Nov 10, 2017 7:27 am

@ olek - in TIG welding, the temperature in a plasma arc column varies from the tungsten (cathode) to the material (anode). The reported values in literature by arc physicists, institutions, and industry are all over the map, but 6,000 to 10,000 deg F is a generally accepted temperature range for the arc. This range reportable also holds true for Stick (SMAW) and MIG/MAG (GMAW) processes.

The concept of Heat Intensity is provided for context.

Irrespective of gas used, the heat intensity of "flames" [Diffuse Flame --> candle, campfire; Pre-Mixed Flame ---> Air/Fuel or OxyFuel; Jet Burner --> pre-mixed with higher pressure] vary from 10 W/cm^2 to 2,000 W/cm^2. Propane, Acetylene, Natural Gas, Propylene....none them best 2,000 W/cm^2. Here's the key. Only 10-20% of the heat from an OxyFuel flame actually crosses the "cold boundary layer" between the air and the workpiece. The remaining 80-90% heat is lost through convection/radiation with the surrounding air. The majority of the heat warms up the air and the welder and inefficiently delivers usable energy into the work piece.

An "arc", by contrast, is an electrically-enhanced flame that delivers 10,000 W/cm^2 from the fast-moving electrons which easily punch through the boundary layer. In an arc, about 80% of the heat comes from the the electrons and 20% from the 6,000 - 10,000 degF plasma column via conduction, convection, and radiation.

Notice from the chart that on the extreme end of the spectrum when heat intensities approach 10,000,000 W/cm^2, the material can no longer transfer heat away fast enough and electrons start to bore into the material. The energy begins to disintegrate the base material. And that's the magic of laser drilling.
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Re: Températures, efficiency, arc vs OA y

Postby olek » Mon Nov 13, 2017 2:34 am

Arclight Ironworks wrote:@ olek - in TIG welding, the temperature in a plasma arc column varies from the tungsten (cathode) to the material (anode). The reported values in literature by arc physicists, institutions, and industry are all over the map, but 6,000 to 10,000 deg F is a generally accepted temperature range for the arc. This range reportable also holds true for Stick (SMAW) and MIG/MAG (GMAW) processes.

The concept of Heat Intensity is provided for context.

Irrespective of gas used, the heat intensity of "flames" [Diffuse Flame --> candle, campfire; Pre-Mixed Flame ---> Air/Fuel or OxyFuel; Jet Burner --> pre-mixed with higher pressure] vary from 10 W/cm^2 to 2,000 W/cm^2. Propane, Acetylene, Natural Gas, Propylene....none them best 2,000 W/cm^2. Here's the key. Only 10-20% of the heat from an OxyFuel flame actually crosses the "cold boundary layer" between the air and the workpiece. The remaining 80-90% heat is lost through convection/radiation with the surrounding air. The majority of the heat warms up the air and the welder and inefficiently delivers usable energy into the work piece.

An "arc", by contrast, is an electrically-enhanced flame that delivers 10,000 W/cm^2 from the fast-moving electrons which easily punch through the boundary layer. In an arc, about 80% of the heat comes from the the electrons and 20% from the 6,000 - 10,000 degF plasma column via conduction, convection, and radiation.

Notice from the chart that on the extreme end of the spectrum when heat intensities approach 10,000,000 W/cm^2, the material can no longer transfer heat away fast enough and electrons start to bore into the material. The energy begins to disintegrate the base material. And that's the magic of laser drilling.



Thank you very much , your explanations made me understand how heat questions need to be treated

Best regards
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