Improvements in a Compound for Carburizing Metals.
Year: 1892

page_text: Date of Application, 7th Apr., 1892-Accepted, 14th May, 1892
COMPLETE SPECIFICATION.
Improvements in a Compound for Carburizing Metals.
I, SAMUEL HENRY BROWN, of 141 Princeton Street, Boston, in the County of
Suffolk and State of Massachusetts, in the United States of America, Blacksmith,
do hereby declare the nature of this invention and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement :-
This invention relates to improvements in compounds for carburizing metals,
more especially low-grade iron or homogeneous steel or Bessemer steel.
The object of my invention is to so combine the ingredients composing the
compound that when confined in a retort heated to a proper temperature and
containing the metal to be treated they shall carburize such metal in a very short
space of time. Such a carburizing compound is particularly adapted to the treat-
ment of stock for spring shoe-shanks, where the introduction and confinement of such
stock within a retort for a few minutes is sufficient to give them the proper temper.
The degree or amount which the metal is to be carburized is determined somewhat
by the proportions of the ingredients. Thus for one hundred pounds of metal I
generally employ thirty-three pounds of the compound, or thereabout, and this
amount is to be varied according to the size of stock or mass of metal-the smaller
the pieces of metal the less the quantity of compound required.
This compound embodying my invention contains bone-carbon, tungstic acid,
calcined lime, soda-ash and sal-ammoniac. The proportions of the ingredients above
mentioned for one hundred pounds of the mixture are preferably as follows: eighty-
seven per cent. bone-carbon, eight per cent. calcined lime, four per cent. soda-ash,
one-half of one per cent. tungstic acid, and one-half of one per cent. sal-ammoniac.
My method of procedure is as follows: First place the above ingredients, with
the iron to be carburized, in the retort; secondly, close the lid of the retort
partially, allowing space for the free oxygen to escape as heat is applied to the
retort; lastly, upon elimination of the oxygen, which requires but a few minutes,
close the retort and hermetically seal it. There is then a vacuum, or nearly so.
The several ingredients act upon the metal in the following manner: The soda-
ash frees the oxygen from the metal and opens the pores or molecules of the same,
while the calcined lime eliminates the oxygen which is set free or which may be
contained in the retort. The bone-carbon then commences to throw off its carbon,
and by the aid of the ammoniacal gas generated from the sal-ammoniac a pure
cyanogen gas produced which permeates the metal. The pores of the latter being
open, as stated, and devoid of oxygen, the cyanogen gas enters, carrying with it the
free tungstic acid, thereby carburizing and hardening the metal. The tungstic acid
acts to give greater hardness to the metal. Cyanide of silver may be substituted
for the tungstic acid with equally good results.
It may be well to explain that in introducing the compound the carbon, the lime,
and the tungstic acid are allowed to heat first, being placed in the hottest part of
the retort, while the sal-ammoniac is kept in the front, near the door. Hence while
the sal-ammoniac is being decomposed into its several parts the ammonia-gas is set
free, and passing over the other specified ingredients helps to generate pure cyanogen
gas, which is the hardening agency.
When the metal is properly carburized, it is removed from the retort and plunged
into water or other suitable bath. In compounding the above formula I do not
desire to be limited to the exact proportions therein given, as they may be varied in
quantity, some increased and others diminished, in accordance with the quality or
form of the metal or the amount of carburization desired.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. A compound for carburizing metals, composed of bone-carbon, tungstic acid,
calcined lime, soda-ash, and sal-ammoniac in substantially the proportions specified.
2. A compound for carburizing metals, containing the following ingredients:
bone-carbon, calcined lime, soda-ash, and sal-ammoniac in substantially the pro-
portions hereinbefore set forth.
Dated this 28th day of March 1892.
SAMUEL HENRY BROWN.