combustion temperature of Iron? 4

[metman]

following is the answer from the Answers website:
Answer:
According to my (not metman) welding book. The ignition temperature of steel is 1500 degrees Fahrenheit (816 degrees Celsius).

metman's handbook of Chemistry and Physics gives m.p 1535C = 1535F; b.p 3000C = 5432F

Is it possible for the ignition temperature of Iron to be less than the boiling point and less than the melting point?
If this is not true, then what is the ignition temperature of Iron? I understand that %Carbon will affect the m.p/b.p/ignition temp but I am not trying to split hairs.

This question arises from my fellow worker who is a certified welder and said that one can start cutting steel plate with an Oxy-Acetylene torch and then turn off the Acetylene. The Oxygen alone will continue to cut the steel if everything is set-up perfectly.

Is it Carbon in the steel (cannot be Hydrogen in the air at 55 parts/million)that provides fuel for this to occur or is the steel actually burning so that the steel is the fuel?

Design for RELIABILITY, manufacturability, and maintainability

 

[redpicker]

You have some errors in your C to F conversions, but I am not sure that matters.

I am not sure what you mean by the "ignition temperature".

Your welder friend is correct, however. When cutting steel with oxy-acetylene, once you start cutting, you don't need the acetylene. The oxidation of the iron is exothermic and produces enough heat to keep the reaction going.

By "keep the reaction going", I mean "melt the iron oxide so that the oxygen can react with the steel". The iron oxide will melt at a temperature below the melting point of the steel, so as you cut the steel, the molten iron oxide is blown off (by the force of the oxygen) and more iron is exposed, which oxidizes, releasing heat that is enough to both melt the iron oxide and heat the steel so that the process can continue.

rp

 

[metman]

Thank you redpicker
And yes this 1535C = 1535F was obviously a typo
1535C = 2795F

Design for RELIABILITY, manufacturability, and maintainability

 

[EdStainless]

Of course you can turn off the fuel. The burning of the Fe and C will generate plenty of heat.
Actually burning metals is balance between thermodynamics, kinetics, heat transfer, and product form.
According to the Air Force Steel will burn in pure oxygen below its melting point (pure Fe at 930C) and steel will even burn in air at 1230C.

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Plymouth Tube

 

[metengr]

metman;
There is plenty of good technical information on oxy-acetylene and oxy-fuel cutting of steel and effect of carbon content. I would suggest you look at ASM Handbook, Volume 6, Welding Brazing and Soldering. Under Oxyfuel gas cutting is a section on Principles of Operation. Read it and learn..................

Principles of Operation
Oxyfuel gas cutting begins by heating a small area on the surface of the metal to the ignition temperature of 760 to 870 °C (1400 to 1600 °F) with an oxyfuel gas flame. Upon reaching this temperature, the surface of the metal will appear bright red. A cutting oxygen stream is then directed at the preheated spot, causing rapid oxidation of the heated metal and generating large amounts of heat. This heat supports continued oxidation of the metal as the cut progresses. Combusted gas and the pressurized oxygen jet flush the molten oxide away, exposing fresh surfaces for cutting. The metal in the path of the oxygen jet burns. The cut progresses, making a narrow slot, or kerf, through the metal.
To start a cut at the edge of a plate, the edge of the preheat flame is placed just over the edge to heat the material. When the plate heats to red, the cutting oxygen is turned on, and the torch moves over the plate to start the cut.
During cutting, oxygen and fuel gas flow through separate lines to the cutting torch at pressures controlled by pressure regulators, adjusted by the operator. The cutting torch contains ducts, a mixing chamber, and valves to supply an oxyfuel..

By the way, carbon content will effect cutting rates using the above process. You can research this and find out why........,,

 

[arunmrao]

I attempted cutting a high carbon steel plate,by cutting off the acetylene supply ,once the cutting had begun. However,the trial was not successful. Where am I going wrong?

 

[EdStainless]

It is going to require a geometry that minimizes the heat dissipation. It may need to be fairly heavy material.
I saw a cutting torch used to salvage work, the fuel was diesel, they used some of it run an engine driven pump/compressor, and the rest in the torch, the cutting was done with compressed air. They were cutting 2" thick plate with it.

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Plymouth Tube

 

[arunmrao]

Ed, I agree it has to do with heat dissipation and the time at which you cut off the acetylene supply.

 

[metengr]

The higher carbon content will actually aid in reduction of the iron locally, which counters the oxidation of iron necessary for cutting.