RichHallstrom Posted January 15, 2008 Share Posted January 15, 2008 anyone have any tips for minimizing forge scale and pock marks on your work? Quote Link to comment Share on other sites More sharing options...
Paragon Posted January 15, 2008 Share Posted January 15, 2008 Are you using coal or gas? Quote Link to comment Share on other sites More sharing options...
RichHallstrom Posted January 15, 2008 Author Share Posted January 15, 2008 i am using coal. Quote Link to comment Share on other sites More sharing options...
Archie Zietman Posted January 15, 2008 Share Posted January 15, 2008 Brush your piece w/ a wire brush before and after putting it in the forge, and always wipe off you anvil face before hammering. and don't stick your piece too low in the fire, too close to the tuyere. Quote Link to comment Share on other sites More sharing options...
RichHallstrom Posted January 15, 2008 Author Share Posted January 15, 2008 Leaving the steel higher in the fire reduces oxydation? Does the quality of the coal affect it as well? I have noticed that lower temps seem to reduce scale, but that leaves less hammer time per heat and can cause stress cracks on smaller parts. Quote Link to comment Share on other sites More sharing options...
Paragon Posted January 15, 2008 Share Posted January 15, 2008 If you have hot steel, all it is going to want to do is oxidize when out of the forge an in contact with the air hence the scale. The hotter the steel, the faster the reaction. It is just a natural reaction. Keep it brushed off and work fast. [more than you wanted to know or already know section] This is why welders use inert gas to cover the welding area to keep the weld area clean. OA torch welding has a protective area of CO2 from the burning of the oxygen and acetylene. Propane does not. This is why oxy-propane is not best suited for welding but can be done. The welds will not be as clean as with OA. If you were to take a white hot (to the point of melting) piece of steel and fire a jet of oxygen on to it, you would basically cut through it because of the fast oxidation reaction. Basic principal of oxy fuel torch cutting. It becomes self sustaining if you are good and can actually turn off the fuel cause it was only used to get the steel to the correct temperature for the reaction to happen. The reaction will heat the steel enough to keep it going. .. at least that is what I have read. Have yet to to any cutting with my torch. Quote Link to comment Share on other sites More sharing options...
MLMartin Posted January 15, 2008 Share Posted January 15, 2008 yes you can run a cut with only oxy after the cut is started, on 1/2" i have cut 4 or 5" but thats about it, vary hard to hold my hand that steady, if you jerk at all you loose the cut, good practice, also some times when im forging and i need to remove a little metal i grab my torch and just jet out OXY since my steel is already red hot Quote Link to comment Share on other sites More sharing options...
R Funk Posted January 15, 2008 Share Posted January 15, 2008 Yes those of you that discuss raising the piece in the fire will reduce oxidation are exactly on target. As the air enters the fire it contains about 20% oxygen and as the air moves up thru the fire more and more oxygen is consumed. Toward the top of the fire all or nearly all of the oxygen will be consumed and tied up as CO2 or CO. With no oxygen at the place you have it in the fire, the piece will not oxidize until you remove it from the fire. So with good fire management and placement of the steel oxidation in the fire can be controlled and minimized. In addition to placement of the steel, make certain you are not "over blowing" the fire. If too much air is provided the oxygen will not be consumed before it reaches the top of the fire. I have always wondered why it is very difficult to nearly impossible to weld with Ox/Propane. I know that Ox/Propane I have both Ox/Propane and Ox/ Accetylene The propane burns to CO2 & water just like accetylene... Has anyone seen a technical article on why it does not work? Quote Link to comment Share on other sites More sharing options...
Ice Czar Posted January 15, 2008 Share Posted January 15, 2008 The hotter the steel, the faster the reaction. protective area of CO2 as the air moves up thru the fire more and more oxygen is consumed. ^ Arrhenius equation (formula for the temperature dependence of the rate constant, and therefore rate, of a chemical reaction) in English the hotter it gets the faster it all goes to hellRedox (Reduction and Oxidation) in case you want a little more, within a hyperlinked context ;) Quote Link to comment Share on other sites More sharing options...
Tyler Murch Posted January 15, 2008 Share Posted January 15, 2008 putting water on the anvil face each heat helps to keep a cleaner surface by blowing off scale. I use this especially with welded tomahawks. The surface can be quite bad from the welding heats and the flux. forging on a wet anvil, paired with wire brushing before and after the anvil creates a clean surface in short order Quote Link to comment Share on other sites More sharing options...
robk Posted January 15, 2008 Share Posted January 15, 2008 My understanding of the issue with welding with propane is the rate of flame propagation. This is the measure of the velocity of the flame front through the gas. Acetylene burns at 5900* F with oxygen at a rate of 25 feet/sec. Propane burns at 5650* F with oxygen at a rate of 12 feet/sec. While the temperature of the combustion reaction for both gasses is similar (within a few hundred degrees) propane burns at approximately half the speed. Thus less heat is put into the metal being worked on. It should be noted that the gas velocity at the tip must not be less than the rate of flame propagation in order to avoid flashback. Quote Link to comment Share on other sites More sharing options...
RichHallstrom Posted January 15, 2008 Author Share Posted January 15, 2008 Yes those of you that discuss raising the piece in the fire will reduce oxidation are exactly on target. The next question is how high in the fire is high enough? I am about 3 inches up, which I thought was high enough. I also cannot forge weld. maybe too much airflow? Quote Link to comment Share on other sites More sharing options...
tzonoqua Posted January 15, 2008 Share Posted January 15, 2008 Hello, hope I don't offend by slight hijacking of this thread, but I too get excess scale, but its in my gas forge (Swan Mother). I phoned them up for advice and they sent me a new gas jet which I replaced, ( they also suggested I spend around Quote Link to comment Share on other sites More sharing options...
Paragon Posted January 15, 2008 Share Posted January 15, 2008 My understanding of the issue with welding with propane is the rate of flame propagation. This is the measure of the velocity of the flame front through the gas. Acetylene burns at 5900* F with oxygen at a rate of 25 feet/sec. Propane burns at 5650* F with oxygen at a rate of 12 feet/sec. While the temperature of the combustion reaction for both gasses is similar (within a few hundred degrees) propane burns at approximately half the speed. Thus less heat is put into the metal being worked on. It should be noted that the gas velocity at the tip must not be less than the rate of flame propagation in order to avoid flashback. Yeah.. that too. The hottest part of a propane flame is further away from the torch nozzle than with acetylene probably due to that.. iirc. Of course I have never messed with an oxypropane torch yet.Hello, hope I don't offend by slight hijacking of this thread, but I too get excess scale, but its in my gas forge (Swan Mother). I phoned them up for advice and they sent me a new gas jet which I replaced, ( they also suggested I spend around Quote Link to comment Share on other sites More sharing options...
easilyconfused Posted January 15, 2008 Share Posted January 15, 2008 The next question is how high in the fire is high enough? I am about 3 inches up, which I thought was high enough. I also cannot forge weld. maybe too much airflow? It depends on how much air you are using and the size of the fire. You are likely too low in the fire in this case and you are getting oxidation in the fire due to the air from the blower not being used up enough. Or, it's completely unrelated and you're just missing your forge welds and need to keep practicing and fiddling around with them. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted January 15, 2008 Share Posted January 15, 2008 One of the reason's I prefer a hand crank blower to an electric one is that it's easier to keep the fire in tune for less oxidation and I am a hobbiest I am not generally doing production work where the fast stock turnover in the fire would warrent using an electric blower. Tzonoqua; tuning the burner is the big answer but if you still have some problems afterwards I sometimes will line the bottom of my propane forge with coke or charcoal to provide an oxygen scavanging bed---usually do this only when heat treating knives where scale means a lot more work on a nearly completed blade Quote Link to comment Share on other sites More sharing options...
Paragon Posted January 15, 2008 Share Posted January 15, 2008 The flux should protect the steel form scaling, shouldn't it? Quote Link to comment Share on other sites More sharing options...
easilyconfused Posted January 15, 2008 Share Posted January 15, 2008 It should, but I seem to recall hearing that it can be overwhelmed if there is too much air. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted January 15, 2008 Share Posted January 15, 2008 If the flux starts to look "crunchy" instead of a clear liquid it's had too much O2 to deal with, clean (wirebrush vigoriously), reflux, and back in the forge. Quote Link to comment Share on other sites More sharing options...
habu68 Posted January 16, 2008 Share Posted January 16, 2008 On the gas forge, is the entry point of the flame directly toward the part? If so you may have the same problem as the coal forge because the oxygen as not been used up before striking the part. Try placing the part out of the direct path of the flame or direct the flame to the side of the forge. Also, reducing the door opening will give more back pressure to the forge giving the gases more time to burn in the chamber. ymmv (your mileage may vary ) Quote Link to comment Share on other sites More sharing options...
tzonoqua Posted January 16, 2008 Share Posted January 16, 2008 Thanks for info and suggestions, as far as I can tell, the flame from the (4) burners is a reducing flame, ie, yellow bits of flame at the ends, I would say a softer flame? (if that makes any sense, I am no expert obviously!) Thats what it looked like this morning when I was working, but I need to change the bottle when I go back out there, so I will see if that changes anything. Perhaps my problem is what Habu68 has suggested, I tend to but the metal under the burner, (impatience!) so I will try to put the metal out of the direct blast and see how that compares. I generally keep the doors shut as far as I can. Back door is always shut, unless I am doing a long piece that needs to go through. Front door, I keep open just enough to get the metal in and out. I get a little bit of 'dragons' breath coming out of the open door sometimes, if that means anything. Regards, Colleen Quote Link to comment Share on other sites More sharing options...
NeatGuy Posted January 16, 2008 Share Posted January 16, 2008 I like the water method as well ... especialy at demos when people are not paying attention.:rolleyes: Quote Link to comment Share on other sites More sharing options...
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