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I have been wanting to try a hearth furnace for several months now, but a leak in the master bathroom and the resulting repair work has had me occupied for a long time. Today I finally said I need eda mental health day and to do something fun. So hearth furnace run one. Did the (what seems to be becoming the ) standard 7 brick furnace with the blower from my first coal forge. Charged it with 5 - 200 gram charges of A36 that I had sitting around. Time between charges was about 5-6 minutes. Total recovery was about 800 grams.

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Furnace before first charge.

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Had two pieces come out. Here's the main one. Is about 770 grams.

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Spark test of beginning material.

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Spark test of furnace material. Same belt, same grinder speed, same pressure as the starting material picture. Any thoughts on carbon content? Also, as I was consolidating it after pulling out of the furnace, it seemed super solid. I was not able to move it much with a 4 pound hammer.

15_Spark test hearth steel_IMG_2242.jpg

Edited by Bill Schmalhofer
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Looks like you have made some ultra-high-carbon steel or white cast iron, one or the other.  You're on the right trail, but you may want to level out the tuyere a bit more to lower the end carbon content, if that puck has too much carbon to forge.  Cool stuff!

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Thanks for the reply Alan. I had a feeling I was a bit high in carbon. The tuyere was almost flat in when I was running. I dropped it by a brick height from where it was in the first picture after I got the fire going. I was thinking I may have to point it down a bit more to add some oxygen to lower the carbon.  

 

I also have a question for those that run hearth furnaces. Do you slag any of your fire bricks? This is what is left of the brick that the tuyere was stuck through. I don't remember seeing anyone else on the forum have this issue. The two bricks next to this one also had some damage but nothing like this. 

 

Lastly, my plan had been to heat the puck up to welding temperature in my forge and try to consolidate it and forge it flat. I'm assuming if the carbon is too high, if I go this route, it will just crumble when I pound on it?

 

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Edited by Bill Schmalhofer
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Round two of the hearth furnace and I decided to put Alan's frequent comment (you can use bottle caps, cans, lids, etc) to the test. Started with 1200 grams of material and final puck was 860 grams. The first run went very slowly for some reason. Had a total of 6 charges at 200 grams a charge and was averaging about 6-7 minutes between charges. At the end of the run, pulled a puck out of the furnace that was almost dead even with the tuyere. Was able to distinctly make out a few screws and a nail sticking out of it. Went to consolidated it and it crumbled into 5 chunks. The furnace was still glowing so I just fired it back up and ran the chunks through (nothing to loose right?). This time the charges went much faster. Was getting three minutes between charges this time. Pulled a single puck out that was well below the tuyere. Several small pieces broke off during consolidation, but I ended up with the 860 gram puck. This time it turned out to be bi-polar. Decent carbon on the top and what looks like wrought iron on the bottom. Between the two runs I have about 1600 grams of material. First nice day that I can get my forge out, I'm going to process them and see if I can combine the two. And I slagged another fire brick that had the tuyere going through it.

 

1200 grams of starting material.

1_Starting material_1_IMG_2267.jpg

 

Material after first run through the furnace. couple of screws and a nail clearly visible.

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Spark test of the top of the final puck.

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Spark test of the bottom.

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O1 as a comparison.

9_O1 Steel_IMG_2293.jpg

Edited by Bill Schmalhofer
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Toldja it would work. ;)

 

On any melt or bloomery smelt you're not going to have a homogenous carbon distribution.  That's why we hear so much about how many times the steel for katanas was "folded."  That's what you have to do to even out the carbon, assuming you want to even it out.  The other thing you can do is separate out the high-C stuff from the low, and use the high-C as blade material and the low C as wrought iron.  

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2 hours ago, Alan Longmire said:

Toldja it would work. ;)

Trust but verify...:D.

 

Don't think there is enough to be able to separate the two sides out. Going to try to fold and even it out and then combine with my first puck (if possible). It's interesting to note that when I did my first run, I was using fairly large solid pieces of starting material and the entire puck seems to be that super high carbon material. The second run was tiny pieces of bit and bobs and I got the very heterogeneous mixed puck. Have to keep track of this observation...

 

Also, the first puck is a solid chunk. The second one looks like a sponge on the edges - like something was being aerated through it as in sat in the charcoal. Any thoughts on this?

 

Thanks again for all your help.

 

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Looking good Bill. I still have a 3/4" square bar somewhere in my shop that I made from one of these little runs. I got a lot of slag bleed out from my bricks too, but nothing quite like you have. I got some good tips and feedback on that post back in April 2018.....holy  jamoly almost 3 years ago. Check it out.

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17 hours ago, Joshua States said:

Looking good Bill. I still have a 3/4" square bar somewhere in my shop that I made from one of these little runs. I got a lot of slag bleed out from my bricks too, but nothing quite like you have. I got some good tips and feedback on that post back in April 2018.....holy  jamoly almost 3 years ago. Check it out.

Thanks for the link to that thread Joshua. Good read. I feel very much like you did. What the H _ _ _ am I doing and am I doing it right. Alan's comments on Goldilocksing (not too much this and not too much that - JUST right...) the puck is what I was looking for. The first puck is pretty solid but unfortunately very high carbon. Worried it's just going to crumble on me. I'm just hoping to get enough to make a knife from. If successful there, I may be hooked on this. Drinking way too much beer to save up more bottle caps for the next run though :D.

 

Since I don't have a designated forge area, don't know when I'm going to get to consolidate this material down. Hoping for a nice, semi-warm day some weekend.

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If that first one proves to be too HC to forge, you can always run it through again with a slightly down-angled tuyere to decarb it.  When you make the steel, you can do whatever you want!

 

(This is how we hook you, you've been warned!:lol:)

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