Dave is right. Exposure to either primary, or more commonly, secondary flames is no way to carbonize steel, because free carbon is the least of the combustionMessage 1 of 40 , Sep 2View SourceDave is right. Exposure to either primary, or more commonly, secondary flames is no way to carbonize steel, because free carbon is the least of the combustion by products it will be exposed to. Superheated free oxygen, carbon monoxide, and hydrogen molecules will also be quite heavy. Most operators try to keep even spent gases from total primary flame combustion as far from direct impingement on heated metals as is possible.
----- Original Message -----
Sent: Mon, 02 Sep 2013 12:19:39 -0000 (UTC)
Subject: [hobbicast] Re: Refractory blanket how-to for welding forges.
In a forge, when heating iron/steel, it is preferred to heat without direct contact with the flame. Someone building a knife forge usually angles the nozzle so that the flame hits the wall beyond the billet to reduce carbonization of the surface of the steel.
General purpose forges designed for larger items tend to have the nozzles facing directly downwards onto the iron/steel. In the forge that I purchased from NC Tools many years ago, the only two hot spots are the locations directly under the nozzles.
The goal in a forge is to have an area of neutral heat about the size of the area to be heated. By neutral heat I mean one that is balanced so that both oxygen and carbon have been consumed by the flame and neither oxygen or carbon is exposed to the iron/steel. Both oxygen and carbon are damaging to the surface of iron/steel. The exception is when iron/steel is deliberately *slowly* "soaked" in carbon in order to have the iron absorb carbon into its structure, but that is not done in a gas forge.
--- In firstname.lastname@example.org, Carl wrote:
> Dave:I don't know how metal is supposed to be heated in a forge. Is it heated by direct flame contact or from the temperature inside the forge? You talk about hot spots. ITC-100 will definitely cause less heat to be radiated into the insulation and out through through the shell of a forge. This will also lessen the heat-sink in the inner layer of castable. Maybe a certain amount of very hot refractory would even the temperature allowing the metal to be headed more evenly. I have read a few times where furnaces were coated with ITC-100 and the owners didn't like the results. Because the ITC-100 reduced the heat-sink the second melt took longer than without the ITC-100. You could still coat where the flame directly hits the refractory for protection. Possibly the ITC-100 could be placed on the outside of the castable next to the fiber blanket. Just a thought from somebody with no forge knowledge. Carl Â
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Recently someone on one of the casting groups commented that there was no such thing as a cement that can have all of the water baked out of it; I believe thisMessage 40 of 40 , Sep 15View Source
Recently someone on one of the casting groups commented that there was no such thing as a cement that can have all of the water baked out of it; I believe this was done in defense of the use of Portland cement in a homemade castable refractory. The official answer would be that the chemically locked portion of water in lime based cement cannot be baked out, but the chemically locked portion of water in refractory cements can be. I have always accepted this official version as the only reality...in the past. The limiting factors on "baking out all the water" are that the refractory must be taken to yellow heat in the first place, and that over time, water content can recollect in refractory if you're not careful to seal the refractory surfaces against water vapor in ambient air.
However, truth of any kind is seldom found effortlessly; including technical "truths". I suspect that a healthy debate, with both sides airing their views, might adjust what the majority of us accept as practical reality--to our mutual profit; this could be important for people wanting to make insulating refractories as secondary layers. Homemade refractory as an insulating secondary layer might be quite forgiving of official standards; standards useful for hot-face layers may constitute a waste of money in secondary refractory layers.
While casually dismissing the Portland cement idea, I have noted both resentment, and a strong hint of "I'll match your official facts with personal experience" in passing (heated) comments from the other side of this issue. Isn't it time they had a FAIR hearing; something open minded, maybe?