Redbeard The Grey

heating large steel with open forge

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Hi folks,

I am looking for experienced input on large forging in an open coal forge. 

I have been heating and working with 3" square in an open coal forge which we open to be about 1.5" x 3" in cross section.

So far, my best bet has been to try to manage the fire under the steel and build in "heat lines" in order to fire a fresh cover of coal over the top in order to light it and keep something close to a surrounding heat.

Obviously, this isn't going to be nearly good enough by itself and it requires turning the piece repeatedly which breaks up my blanket and heat lines and I have to kersmudge some semblance of it back together for each turn until I get a relatively even heat throughout.  This problem of turning is exacerbated by the fact that I cannot heat into welding temp in the base of my fire or I will burn one surface while the other remains cold which means that the whole process takes a long time while I "rotisserie" the large piece.

Does anyone have any fire management experience with large pieces like this who can share some insights?




Edited by Mod34
Moved to Problem Solving

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Build a larger forge and definitely a larger fire to match the size of the work. 

Bruce Wilcock forges anchors using a coal fire. 


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If you are trying to weld pieces of very disparate sizes it might be best to use 2 forges and have a separate person watch each one.

With a big fire you will definitely need a bigger air source to be able to push the hot spot higher into the heap of coal.  Watching the old films of forging large items a lot of it seems to be done using jib cranes and chains so you can turn a piece without disrupting the fire as much. If you are having a lot of issues with the fire being disrupted you need to think about welding in an open fire rather than a closed one and so disruption doesn't make much of a difference.  Perhaps switching to just a coke fire.

It comes down to: if you want to do industrial sized work you have to have an industrial sized setup and crew!  If you do not you end up having problems...

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Surely you're not suggesting that you can't forge weld a ship anchor in a rivet forge!

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This is quite funny..  Yesterday I started the 2nd wrought iron hammer build and it is a welded construction..  so it is 2.25X2.25X4" long or I should say it will be.. 

Back when I running a masonry forge I could have heated up both 1.125X2.25X 4" sections in a heart beat both to welding temps in the same fire.. 

I just spent 1 hr trying to get the forge in the trailer to get hot enough to get these larger sections (which aren't that large) up to welding temps with both in the fire and it was a struggle.. I never did get them to weld as there simply wasn't enough heat to heat the center of the bar evenly.. 

I"ll swap out to a different coal next go around..  (it's been a few days since i started to reply and it's now fully welded with the use of a different coal)

But my point is that the masonry forge would come up to temp faster as it had more thermal mass even though it still used a cast iron firepot which is the same as in the trailer.. 

Ideally for doing larger sections like this another forge would offer the best or a larger fire pot or back blast with a large enough air source.. 

My old masonry forge was good enough to heat up a 200lbs anvil for corner redressing as well hardening..   The steel sheet metal forge in the trailer would be hard pressed to heat up anything this large.. 

The forge design also has to be looking towards insulation of the fire zone which traps the heat..   Larger air source with more volume/pressure.. A much larger firepot.. The Buffalo forge Railroad firepot was 14X17 at the top vs 11X14.. Was slightly deeper with larger piping and clinker breaker.. 

Using a closed fire with larger items is nearly an impossibility unless the object is round in circumference..  And unless it is a very deep firepot a hollow fire will burn up all the fuel before it comes to temp.. 

Most people don't have the fire management skills to work with a large fire as there is a lot of experimenting till it gets figured out..   

With larger forgings and a coal fire the bed needs to be pretty big to get the coal to coke..  With coke it can be smaller as there is no coking process needed.. 

For forge welding of 2 larger pieces as Thomas pointed out you really need two forges setup with 2 skilled operators.. 

The anchor video it is tenon and mortise construction to get it to hold together for welding..  In the old days a lot of the anchors were a lay up weld... 

A layup  is done with the larger object being brought up to welding temperature..  Then rods would be heated to welding temperature and tacked to the larger section quickly 1 bar after the next.. This quick action of adding the new welding temperature bars would keep the area at welding temperature and they could do complete build ups this way.. 

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A centaur forge sized firepot will handle somewhere near 8"-9" of steel no matter its size with no problem.

The dimensions are ~12"x14" at the top. The depth is ~ 4" deep.

So keep 4" of coke underneath and 2" or so on the top. don't let it get hollow, and with any good champion or canedy otto type blowers with 12" or14" fan and you should have no problem forge welding anything up to 4" square+ depending on your skillset.

Fire control is the same no matter the size of your work.

No green coal on the top, pull the coke into your fire to maintain your fire size and keep it from hollowing out. Then rake or pull coke from the top outside to keep at least 2" on top of your work. You should have no problem keeping the whole volume of your firepot full of coke with very little practice. 

Make sure you rotate your bars in the fire to get an even heat on your work. Rotate 180, back, then 90, then 180 etc.

As for air,, you will be adding a greater volume of air, but maintaining more or less the same velocity. Basically your fire should look the same as when you are heating up two pieces of half square, just bigger in size.

The beauty of a coal forge is that with practice, you can really control your fire size from a long skinny trough for knives to the whole fire pot cooking without burning your work or messing with cold spots for "big iron" like you are doing.

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Anvil, The outside dimensions are 12X14 but the working part or bowl is only 8.5"X10.5"  And yes it is plenty big enough for working materials up to a certain size.. 

The other big factor to the size of material is the coal or of course the coke used.. 

I bought two bags of coal to sample and they had so many fines in it that the air blast was limited just withing a few minutes and the fire would choke back.. 

The remedy was to input more air to blow the fines out of the way and out of the fire up the stack..  And yes the clinker breaker would let some fall through but as soon as you move the piece to rotate it the air blast would be right back down to nothing..  This coal works great on smaller pieces or again if the air is upped to keep the fines blown out of the fire.. 

On the other coal I have been using it's not much of a problem and heating a section of 2 or 3" sq isn't much of a problem in the forge that is in the trailer.. 

Again, the masonry forge with this same firepot was just that much better..  Of course it used a Buffalo Silent 200 14".. :) 

I recently  was looking at several different forge designed that used regenerative principals just like a cupola or iron smelter.. 

The Buffalo forge with smoke catcher and then again with the recent book you pointed out..   I've been looking at minimizing smoke and the intake system for coal smoke as it's heavy before it flames is said to offer greater btu potential..  As is a pre heating of the intake air..   Both designs I have interest in.. 

This first picture is of the new wrought iron hammer build.. It started life as 1.125 X 4.5.. Doubled and welded..  Then done again.. These 1.125X 2.250X 4.5"  were then stacked and welded into a 2.25X2.25X4.5" block for the starting size for the hammer.. 

On a larger fire the blower definitely has to be upsized if a person is running a smaller blower..  For this forge I use a Champion 400, but prefer a Buffalo silent 200 in the 14" variety  and also own a 16" variety for much larger forgings..   I used a silent 200 14" on the masonry forge in the old shop..  I also own a Cannedy-Otto and it works well..  

Really any of the main line blowers works well vs the newer variety.. 




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