It is pity that there seem to be some big mistakes in their introductory
history of iron if Tony's abstract is anything to go by.
>
> This is a fascinating account of iron smelting in the villages of
> Pentyrch and Tongwynlais, about 6 miles north of Cardiff, in South
> Wales. The authors begin by outlining the history of iron smelting
> from Roman times at Trellech near Monmouth and at Caergwanaf near
> Llantrisant. They describe how, from Roman times to the 16th century,
> iron ore was smelted in primitive furnaces known as bloomeries. These
> furnaces relied on the wind to create a draught needed to provide the
> necessary oxygen.
As far as I know no British bloomery was wind powered - Some early
students of the subject speculated that some furnaces were wind-powered.
Gill Julef's work on the true wind-powered furnaces of Sri Lanka shows
that these putative wind-powered furnaces would not have worked in the
manner suggested. This needs a monsoon type climate to work reliably and
a furnace with a very large number of tuyere. The Laxton type furnace
may well be a natural draught furnace but that is not the same thing.
Most British bloomeries were mechanically blown (hand or foot blown and
later had water-powered for the hammer at least).
>Later the use of water power led to the blast furnace
>
It is quite possible to run a blast furnace without water-powered
blowing - it is almost certain that the European early blast furnaces
were not water powered as was the case for the chinese blast furnaces.
It was just by the time the technology reached Britian it had been
linked with water-powered blowing.
> and an example is shown in an illustration of a blast furnace from
> nearby Abercarn.
>
> The first blast furnace in Britain was established in the Weald of Kent
> and Sussex in 1496 and the two furnaces at Pentyrch and Tongwynlais in
> the 1560's were among the first blast furnaces in South Wales.
>
> It is said that the reason for siting a furnace at Pentyrch was because
> it was in a frost pocket. The reason for this was that the cold air was
> denser and contained more oxygen.
This is myth probably believed by the ironfounders themselves. Cold air
contains exactly the same proportion of oxygen as warm air. However, in
the winter the bellows worked more efficiently as a greater mass of air
was pumped through on each stroke due to its higher density, but that
is offset by the greater fuel consumption just needed to heat the air.
Hence the introduction of preheating the blast in the late 1820's. In
addition, the air pressure in winter is generally higher than in the
summer again this would mean a greater through-put of gas in the cold of
winter than the warm summer. (Again the modern blast furnace is
pressurised to maximum the mass of gas in it).
>Also all the ingredients were there.
> First charcoal was used, to be replaced by coal from the local mines.
> The iron also came from the coal mines in the form of ironstone. The
> final ingredients, limestone and water power were also in abundance.
> The local iron was high in phosphorous, which made it brittle.
> However, this problem was over come by mixing it half and half with iron
> ore from Lancashire. The iron produced was of adequate ductility to
> produce the thin plates required for the expanding tin plate industry.
>
> It has always been assumed that the Pentyrch ironworks were established
> where they were because of the proximity of the adjacent Lesser Garth
> Iron Mines, but the surprising thing is that this paper has confirmed
> that ore from this mine was not used until the 1820s.
--
Chris Salter,
Oxford Materials Characterisation Service,
Oxford University Begbroke Science Park,
Sandy Lane, Yarnton, Oxford, OX5 1PF
Tel 01865 283722, EPMA 283741, Mobile 07776031608
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