IMPROVEMENTS IN THE MANUFACTURE OF FILES
Year: 1881

page_text: "
LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, for an Invention of IMPROVEMENTS IN
THE MANUFACTURE OF FILES." A communication from abroad by Martin
Armstrong Howell, junior, of Chicago, in the County of Cook, State of
Illinois, United States of America, Gentleman.
COMPLETE SPECIFICATION filed by the said Alexander Melville Clark at
the Office of the Commissioners of Patents on the 21st December 1881.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of
Middlesex, Patent Agent. "IMPROVEMENTS IN THE MANUFACTURE OF FILES."
A communication from abroad by Martin Armstrong Howell, junior, of Chicago,
in the County of Cook, State of Illinois, United States of America, Gentleman.
The nature of this Invention relates to the employment or use of decarburised
cast iron blanks in the manufacture of files, in contradistinction to the use of
forged metal, as heretofore employed by the long practised and well known process,
and in the subsequent recarburisation of the same after the process of surfacing
and cutting of teeth is completed, in order that all the carbon essential to the
finished product shall be retained during the process of hardening, and not impaired
or reduced, as a result of the present well known process of reheating and forging
in the production of blanks. The Invention relates also to the use of cast metal,
whereby the granular texture of the metal in its natural state may be retained, that
during the process of recarburisation at the proper degree of heat the affinity of the
porous metal (for the carbon with which it is surrounded shall be the maximum, in
that the metal shall become (as it were) saturated in a limited space of time, as
compared to the more irregular and tedious operation of cementing forged or
laminated surfaces, as in the old and well known process of steel making.
Heretofore files have been made by forging the blanks from bars of steel after
several successive heatings and reheatings, whereby much of the combined carbon
at the surface is lost by oxidation, so that when subsequently annealed and cut the
essential property of hardness is impaired or reduced in a ratio of the degree of
LD

page_text: heat and the number of heats taken in the operation of forging the blanks. It, is
easily seen therefore that the present want of uniformity and regularity in the files
of the present day is largely due to this loss of carbon, which is the most essential
property to the hardening process.
To produce a file therefore which is not only more durable through its ability to
resist abrasion of the hard metals, but far cheaper by avoiding the unnecessary
expenditure of more expensive material, labor, and fuel, is a benefit to the public
through its superiority.
The process of manufacture is as follows:-I take a medium grade of white or
refined iron. I proceed in the ordinary way to cast from patterns in the sand or
in special flasks of refractory material. When the castings are removed they are
cleaned of the adhering sand; the blanks, now of hard brittle metal, are placed in
cast iron boxes interlaid with oxides or other materials having an affinity for
carbon placed in furnaces, where they are kept at a steady heat sufficient to enable
the oxide to take up the carbon in the form of carbonic oxide, leaving the surface of
the castings in a soft and decarburised condition, which renders them susceptible
to the cutting process, and renders the graphitic castings to a large extent free from
uncombined carbon, and in a condition suited to the subsequent process of recar-
burisation or saturation with combined carbon essential to the hardening process.
The softened blanks are then removed from the boxes after cooling, and surfaced
upon a grindstone, when they are cut by the well known processes, after which
they are placed in air tight boxes interlaid with carbonaceous, nitrogenous, or
azotised matter separately or mingled in a proportion to suit the taste of the
operator or the character of the work intended to produce, all of which is well
known and unnecessary to particularise. They are allowed to remain in this
cementing material exposed to a bright red heat for a time sufficient to saturate
the decarburised metal with carbon in the combined state, which when removed
and immersed in cold water imparts a hardness to the surface characteristic of the
diamond, when the temper can be "let down as required by the well known
methods of tempering.
"
It is well known that when refined or forged iron or steel is subjected to this
process of cementation in carbon, etc., and exposed to a necessarily protracted heat,
that the surface is apt to become blistered and injured as a marketable product, but
where the natural granular condition of the iron is retained unforged the affinity
for carbon is not only greater, but no danger from blistering is encountered.
It is well known that a superficial and irregular degree of hardness can be given
to iron when at a red heat by coating the saine with ferro-cyanide or prussiate of
potash, arsenious acid, etc., and immersing in cold water or water containing soda
and other ingredients, but all these processes are attended with uncertain results
and often fail entirely where a fixed character is desired in the product, therefore
they cannot be depended upon for regular work. I prefer therefore the use of the
process of cementation in carbon or other equivalents rich in carbonaceous, nitro-
genous, and azotised matter combined in proportions to suit the nature of the work,
as the prolonged contact of the files with such materials give a substantial character
to the product which is demanded by the consumers of files.
It will be readily observed that all of the usual processes of forging and hand
hammering are entirely dispensed with; that all waste of material or of fuel
necessary to the forging and reheating process is avoided in drawing the blanks to
their required shape preparatory to the cutting process; that the loss of carbon,
which by the usual processes employed renders the character of the work so very
irregular and objectionable, is wholly compensated for by the retention of every
atom desirable, and a cheaper and better article the result.
Having described the nature of the Invention with the process of manufacture,
what I claim and desire to secure by Letters Patent is,-
1st. In the manufacture of files, the process which combines the decarburisation
of cast iron blanks for the purpose of softening and cutting, with the subsequent
recarburisation for the purpose of hardening and tempering.

page_text: 2nd. In the manufacture of files, the combined process of surfacing, cutting,
recarburising, and hardening of decarburised cast iron blanks, substantially as and
for the purposes set forth.
In witness whereof, I, the said Alexander Melville Clark, have hereunto set
my hand and seal, this Twenty first day of December, A.D. 1881.
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