Fergus Ontario
July 28, - 2011

Econo Norse Furnace using DD1 analog

Team Members: Neil Peterson, Richard Schweitzer, David Cox (last minute assistance by Darrell Markewitz)

The Iron Smelting Team of the Dark Ages Re-creation Company was approached by Darrell (wearing yet another 'hat') about undertaking a demonstration at this year's Canadian National Blacksmith's Conference as part of that event's public outreach.

The intent of the demonstration was to illustrate a simple to construct furnace made of easily available materials, DARC's own Econo Norse system. This included using the 'DARC Dirt' ore analog (made of potter's oxide). The activity was also carried out over a single day. With full expectations of a successful smelt, part of the bloom produced would be incorporated into the work of one of the other featured demonstrators, Jesus Hernandez.

Related Links:



Smelt Report on the DARC site

Commentary - by Neil Peterson

This smelt was rather amusing. For 90% of the smelt things seemed to go along just fine. At two points we did get some "burbling" from the airflow and needed to tap. But things were so mellow Richard even had time to try (and fail) at making a bead with the tap slag. We had the chance to show many folks what was going on by offering tours of the view down the airpipe. What we didn't know was that the bloom had formed off to the side and the slag bowl had formed quite high.
Each time we tapped it re-sealed much more solid leaving us at a point where we needed to tap again but couldn't get it to tap. We tried from the sides, we tried pulling out the fines in the base but we couldn't get anything through the base of the slag bowl. We even tried running a rod down from the top to poke a hole straight down, but only managed to weld the rod onto the bloom, which led to some funny comments when we extracted.
This inability to execute a third tap meant we needed to finish early in order to not lose the airflow and have everything freeze. We dragooned a couple of blacksmiths to hammer for us, and grabbed Darrell who was ordered to pull the bloom as we freed things up. We then knocked down the smelter - even though there was still charcoal and ore in the stack. This is the reason for the "minus 4" in the ore total. 4 Kg of ore was in the stack but not yet down to the bloom when we opened.
The opening and extraction went well sending the bloom over for a good consolodation. Our efforts to keep a forge going in the smelter didn't go so well as the tuyure was nearly frozen off. We did keep things hot enough that we could keep the bloom very warm until another forge could be prepared (it was nice being at a blacksmith's conference!). When another forge was ready we walked the red-hot bloom over to it. At that forge they consolodated again, then cut it into quarters. One quarter was then further worked until it was ready to use in the blademaking workshop

1) Overall set up
As usual this setup roved its worth. It took less than an hour to set up, Less than an hour to pre-heat. Then a simple straight forward 5 hour smelt - until the hassle at the end. Without that problem we would have had no issues in finishing off the smelt as planned. Even with the problem it produced a very nice little bloom.
2) Reaction to problems
Again this smelt proved the need to react FAST when problems crop up. We did react fast enough to save the bloom. We also reacted fast enough to save the smelt - it is just that our efforts to fix the problem failed. By reacting fast we actually had time to try different methods to save it one of which might have worked. If we had delayed our reaction we would not have had that opportunity.
3) Planning for failure
A little fine tuning on the plinth design leaving more accessable openings would have allowed us more opportunities to move the base and perhaps succeed on a tap.

Furnace construction details
Note: There were no field drawings made.

Furnace Internal Diameter
25 cm
Stack Height (above tuyere)
45 cm
+ 20 cm collar
Tuyere Size
standard 2.5 cm dia ceramic tube
Tuyere Angle
22 degrees down
Tuyere Penetration
about 2 cm
Tuyere Height
20 cm
above base

The images below were taken by David Daciw (used with permission)

The Construction Phase:

Richard cutting firebrick to hold tuyere.

Setting the tuyere in place in the second row of brick.

Neil helping to wire individual rings of bricks together.
Fitting the metal collar in place.
View down the collar, showing first two rows of brick in place inside.
Sand and ash packing added to secure the first two rows, third row of standard construction brick being added.
Placing additional layer of bricks (on their sides) to extend stack height.
Setting the air system to the tuyere.
Dave gets ready to start the wood split pre-heat fire.
Charcoal Monkeys!
(Dr. Ron Ross in the jumpsuit.)

Pre-heat Phase

Striking a Manly Pose
Addition of air via standard blower
Adding first fill of rough charcoal.
Jiffy Pop Ritual
Side view of furnace with air system.

Main Smelt Sequence
Explaining the process to the audience.
Display samples
(with complimentary 'Smelter Corn')
Addition of first ore.
Note reduction fire at top.
Adding ore via 'standard scoop'
Adding charcoal via 'standard bucket'.
Checking tuyere view port.
Attempting to wide slag into a bead!
Attemping a slag tap to lower the level...
... and some guy sticks his nose in.

Extraction & Compaction Phase
Darrell trying to lower the whole slag bowl,
but the air flow is freezing off.
Fast decision to extract the bloom!
Pulling the sheet metal collar.
Lifting off the hot bricks to expose the interior.
Bloom mass, still in place within the slag bowl.
Trying to pull the bloom free of the slag bowl.
Initial compaction on a wood stump.
Dave Kritz (R) on the sledge.
Knocking off pieces of loose 'mother'.
Compacting down to a block shape
Size reduces as the lacy bloom is hammered down.

Final Results
Time Construction about 1 hour
Preheat about 1 hour
plus organization
  Main Smelt Sequence 5 hours
plus consolidation
  Total Elapsed Time about 7 1/2 hours
Fuels Preheat wood about 2 milk crates full
  Graded Charcoal about 50 kg
Ore Total Added 26 kg
  Lost in stack 4 kg
Total Bloom Weight : Approximately 5 kg
Yield : About 22 %

Smelt Data Sheet

(alternate available on the DARC report)

The construction of the furnace was a bit rough, partially due to the condition of the fire bricks (which had been used for a number of other furnaces). Although the furnace ran well initially, it was found on extraction that some of the brick pieces around the tuyere area had fallen into the furnace, dropping in excess sand / ash packing and diverting the air flow.
The end result of this was that the furnace suffered a major blockage and cooling event, just at the point where the bloom was starting to pack on its dense mass. A quick decision had to be made whether to attempt to continue, or simply exact what bloom was available. Roughly the last 4 kg of added ore was still in process within the stack at this point, so lost to bloom formation. (In retrospect, this might have proved a better *demonstration* than having the furnace run perfectly. The fast scramble emphasized how even experienced teams often have to solve problems quickly - and that every smelt is still an experiment.)

The resulting bloom had a clear solid nugget to one side (below the tuyere) with more lacy material to the inside edges. After the inital compaction, the bloom was further worked by Michael McCarthy at his demonstration area. Cut into rough 'quarters', the best quality section was later used by Jesus Hernadez in his 'bloom to blade' demonstration.

The opinion was that the iron produced by DARC was 'nice soft workable iron'.

Unless Noted : Text and photography © 2011, Darrell Markewitz