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- From johnmenc@optonline.net Fri Apr 29 05:37:50 2005
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From: "John Lorenzo" <johnmenc@optonline.net>
Subject: Abraham Darby: Casting Process for GII & GIII contemporaries
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The casting process probably used for the GEORGE II and GEORGE III
1/2d and 1/4d's was UNQUESTIONABLY a form of the Darby process. Here
is a good back and forth between Peter King and Edgar?. Read Edgar's
post first ... understanding the fine art of casting (i.e., the lead
percentage is SO important <BG>) it may help 2-3 of you in
collecting this UGLY TYPE.
Date: Thu, 28 Apr 2005 01:01:01 +0100
From: Peter King <peter@PETERKINGIRON.FREESERVE.CO.UK>
Subject: Re: Sand casting developed by Abraham Darby
I am not sure that we really know for certain. There were no patent
specifications at that period, so that the patent only describes the
process
in a few words. It almost certainly involved patterns (probably of
wood)
around which the sand mould was formed. Today this is such a normal
part of
casting that no one thinks twice about it.
The difficulty is that we do not really know how pots were cast
previously.
I think I have seen something to the effect that guns were cast like
pots.
Since there are descriptions of gunfounding, we can presumably
deduce how
pots were made. If so, a core was formed; then a grass rope was
wound
around it; and a smooth surface formed over that. On top of that a
loam
mould was created. The rope was removed leaving a void into which
the metal
was poured. After that the mould had to be broken to get the pot
out and a
new mould made from scratch for the next pot.
It is presumed that Darby's process of casting in 'green' sand meant
that he
could rapidly (and repeatedly) produce moulds. The best recent
article in
the subject is N. Cox, 'Imagination and innovation of an industrial
pioneer:
The first Abraham Darby' Ind. Arch. Rev. 12(2) (1990), 127-144. She
was
able to show that Darby's pots were thinner than those made by the
old
method. With less metal, they were inherently cheaper, quite apart
from any
saving in workmanship. Prior to Darby's arrival at Coalbrookdale
many blast
furnaces cast small quantities of pots each year. Within a few
years, this
ceased and Darby appears to have had the market to himself, that is
until
there began to be imitators after his patent expired.
I see your source is Samuel Smiles - I do not regard him as a source
to be
used, except where he is quoting documents which are not available
to us
today.
Peter King
-----Original Message-----
From: Arch-Metals Group [mailto:ARCH-METALS@JISCMAIL.AC.UK]On Behalf
Of No
Name
Sent: 25 April 2005 18:58
To: Peter King
Subject: Sand casting developed by Abraham Darby
I posted this to the Britarch list and was
advised to post here instead.
I read that Abraham Darby developed a system
of sand casting that allowed for mass production
of iron bowls.
Also that the sand casting basics were obtained from
Holland, and he imported Dutch experts, who along with
his brass casting experts from Bristol, developed this
process for him.
http://www.worldwideschool.org/library/books/hst/biography/Industrial
Biogra
phy/chap6.html
I am aware of basic sand casting, but could someone
give me a description on Darby's process?
Thanks,
Edgar
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