A few comments to Peter's post-
> My friend Ronnie was criticised on occasion about his choice of
refractory,
> and his general set-up. His reply was on the lines of "you have to start
> somewhere". He of course, will be remembered for starting it all.
Most certainly! I want to make sure that everyone understands right now
that any disagreements we have with the conclusions of some other
experimenters are only that, and should never be construed as disrespect!
But I doubt that Mr. Tylecote would have maintained that he was infallible,
or even that he had more than touched the surface of the possibilities in a
process as complex, with as many variables, as bloomery smelting.
> In the absence of a water cooled, or any other, inserted tuyere slagging
>of
> the wall does produce problems - blocking of the tuyere hole and the need
>to
> repair the lining.
I agree that a tuyere protruding from the furnace wall reduces blocking
problems. We have also found that an increased blast, and higher furnace
temperatutes, tend to reduce tuyere blocking problems. I wonder if this
would be true when using a blowing hole as well? The slag, being at a higher
temperature, might be easier to clear, and not break away lining with it
when it is cleared.
Which sort of brings me around to our only significant disagreement with
Tylecote (et al)'s 1970 paper. They set an air rate of 300 l/min on the
basis of their fairly theoretical concept of the process, and never altered
it significantly, thus leaving out one of the hugest variables in the
process. They arrived at this blow rate according to their view of necessary
temperature (1200 C), and an acceptable level of of CO for reduction in the
stack, an never significantly varied it.
Tylecote's blow rate translates to .42 liters for each square centimeter of
furnace cross-section per minute. In our most successful experiments, our
air rates vary from 1.1 to 1.63 l/sq cm/min. Not only does this lead to
higher temperatures (and thus all reactions occuring more quickly), but the
isotherm of each temperature gradient is increasing in size. As the diameter
of each isotherm increases, of course its surface area is increasing
geometrically, and the chemical reactions (both reduction and carburization)
occuring at each temperature gradient increase likewise. And that means more
iron.
This increased air rate and temperature of course lead to vast changes
in other variables in the process as well.
>
> While I have said that it is not, in my view, archaeology that does not
>mean
> that there are not things to be learned from it. What is missing is the
> attempt to make the same slags (of which we have plenty) as the ancients.
>If
> the slags are different so is the process. Peter Crew's slags are very
like
> those collected from the archaeological site. This of course does not
prove
> that the process was the same.
Agreed. Would anyone be interested in looking at our slags?
>
> As for the occasional occurance of lime in ancient slags do we know how it
> got there? Some Northamptonshire ores were self-fluxing in the blast
> furnace.
Also agreed. The highest calcium levels we ever found in our slags came from
a smelt in which we added no lime. The damn stuff looked like blast furnace
slag. As many ores in this part of the world are deposited at the juncture
of limestone and sandstone beds, I guess that's to be expected.
Lee
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