Pushing VA Air - Smelter Bellows Test

Air Volumes - Theoretical Viking Age Smelter Bellows
Tested May 26, 2012

Ken Cook on the Smelter Bellows - Vinland 3

Operator	strokes	velocity			volume	pressure
		km/hr			litre/minute	ounce/inch2	psi	inches H20	mm mercury
		low	high	average
Richard	76	38.5	41.5	40	327	1	0.06	1.7	3.2
	86	37	41	40	327	1.5	0.09	2.6	8.4
Mark	86	36	40	38	310	1.5	0.09	2.6	8.4
	90	47	52	47	384	3	0.19	5.2	16.8
Darrell	86	41	43	43	351	1.25	0.23	2.2	7.0
	86	39	42	41	335	1.5	0.09	2.6	8.4
Neil	86	43	45	44	359	1.75	0.11	3.0	9.8
	84	46	48	48	392	1.5	0.09	2.6	8.4
averages	85	41	44	43	348	1.6	0.12	2.8	8.8
area	27 dia	572 cm2
ideal volume	at 1.2	686
	at 1.5	858

This test done at the start of 'Icelandic 5', with full charcoal inside a 27 cm ID furance x 58 cm tall.
Individual operators worked a roughly 5 minute cycle on the bellows with measurements made over 30 seconds.
Figures in itallics were generated mathmatically. Richard & Darrell have past experience with this unit.

Icelandic 5 - Results

This is a short overview of the iron smelt at Wareham on Saturday May 26.
For details on the experimental objectives, see Hals / Icelandic 5 - Furnace Construction

Ore : 31.8 kg DD 1 Analog (48% Fe content)
Charcoal : 49 kg (graded fuel)
Time : 5 1/2 hour main sequence (plus 1 hour pre-heat)

At the beginning of the smelt sequence, showing the air system layout.

Our test furnace is dug into a bank rather than raised above the surface as at Hals. The V shaped slot is here lined with concrete blocks to retain the earth bank. The size of the slot was dermined by the space required to hold our Viking Age style iron smelting bellows.

Later in the smelt, tapping off excess slag

Needing to tap slag illustrates one potential problem with our suggested Hal's based layout. With the bellows in the slot, how do you get access to the front of the furnace for tapping? At the very least, the bellows would have to be connected to the tuyere via a short length of hose. This made of leather?

The hot bloom during initial consolidation with hand hammers, which also serves to knock off any remaining slag 'mother'.

Bloom : 13.8 kg
Yield : 42 %

Secondary compression, then cutting, under the hydraulic press.

The typical planno-convex shape of the bloom was roughly compressed to a flat disk using two compression cycles under the hydraulic press (heating between steps via the propane forge). This disk was then cut in two, the step seen above.

The roughly compressed pieces.

Hals / Icelandic Five - Furnace Construction

As I had detailed in Wednesday's post 'Return to Iceland', Saturday May 26 will mark our return to the Hals / Icelandic series, based on excavations and insights from Kevin Smith.
Our smelts # 38 , # 39 in Fall of 2008 had tested the general work dynamic around the Hals style construction, plus use of a bellows plate and blow hole system. (This method does not use a tuyere, and has been researched and tested by Michael Nissen of Denmark.)

Field drawings of Icelandic Three & Four

 Because of too much going on and too little time (brain power!) this will be a fast overview - primarily in images.


Icelandic Five will serve two purposes:
1) To re-acquaint the team to the Icelandic system
2) Reduce the furnace wall thickness to 3 cm.

I cleared out the remnants of the 2008 furnace and built a new furnace yesterday (Thursday).
At the end of the last smelt, a plastic pail had been placed down the interior of the furnace. A metal cover was placed over the top. Normally liquid water seeps through the earth bank every spring. 

Remains of the 2008 furnace. The upper portions consisted of smaller pieces of sintered clay held in place by soft raw clay (on the earth side). The lower portions had little heat effects visible, and were still soft clay.

Portions of the lower part of the original solid clay walls. Roots have grown into the clay over the last three summers, actually helping to re-enforce the portions of the walls that remained.

The hole remaining in the earth bank after all the previous wall material had been removed

The first layer of the furnace wall. The metal rule is 3 cm wide, and was used as a gauge to set the rough thickness of the walls. Note how the shape is determined by the hole in the earth bank.

Finished construction, with old sand/ash packing fill. This will both help dry and stabilize the soft clay. The two boards placed against the front surface hold the exposed wall in place

Today (Friday) later in the day, I will remove the packing material. Then a small tap arch will be cut in the front. For this smelt the standard ceramic clay tuyere will be used, mounted above the taping arch. Extraction will be from the top.

Finally, a small wood splint drying fire will be started. The ideal would have been to have constructed the furnace much earlier, and allowed it to air dry for several days.

For smelt day tomorrow, roughly 20 kg of DD1 (red oxide bog ore analog) is already on hand. A small amount of previously prepared (crushed and sized) charcoal is on hand. The remainder required will have to be worked up while the furnace is pre-heating.

Stay tuned!

Forging 'the custard'

Edited from my ongoing on  Don Fogg's Bladesmithing Forum

Darrel so when you say 'weld in all the edges'... do you mean basically turning it on it's side and hammering down all the little bits at welding heat?   I'm assuming this is easier with lower carbon steel and iron.  On my very high carbon stuff.. those little bits just fall off.  

Scott

I would most certainly *not* hold my working methods up as the ideal!

That being said, I'm just coming off a two month research / learning project called 'Bloom to Bar'. So for while there all I was doing in the shop was working up some of my big pile of blooms (!)
So, that being said, take a look at :
'A Typical Work Session' (on Bloom 2 Bar)

Jesus Hernandez also has a good visual tutorial over on his web site.


I have also seen on this forum some good advice given by Lee Sauder on this same topic.

Blooms have a structure that Lee describes as 'like a custard' - think of a lemon meringue, turned upside down.
The centre is a hard 'nut' of iron, often quite dense, with a spongy layer, often with a lot of air spaces and more slag included around the outside. As you might guess, a larger bloom might be cut apart, so more like a wedge of pie than the whole thing like you see on a small bloom.

(There is a variation in carbon content within a single bloom as well. Lets just leave that one. If anything, this carbon variation exaggerates the effects.)

Of course, the two different densities of metal move at different rates. That's one reason a press, squeezing in one direction does work more effectively than hand tools. The raw size of the mass also works against anyone attempting this process working alone. With excellent skill and co-ordination between a master hand and striker, of course the compaction process can be carried out by hand. (Watch Lee and Mike McCarthy work some time!)

So your first step is just pressing downwards at welding heat, collapsing the air spaces of the outside 'meringue' and forcing them on to the hard nut in the centre.
This does help on the edges however, which remain ragged. I have had some luck placing the then flat disk on its edge and pressing in / down. Its a tall thin shape, with soft edges, so the press tends to slide it sideways and I certainly find that process hard to control. Also the press works in a flat plane, and most often the bloom disk is round or oval.

Taken together, I had found it just as effective to hand hammer the edges in. I would place the disk flat on the anvil, then lean way over so I can fire blows almost dead horizontal from the far side of the anvil back towards the disk and my tong hand. This also allows you to both heat and forge on section of the bloom disk at a time.

Clear as mud?