Improvements in Hardening Articles of Steel or other Metal, and in Apparatus therefor.
Year: 1892

page_text: COMPLETE SPECIFICATION.
Improvements in Hardening Articles of Steel or other Metal, and in
Apparatus therefor.
1, GEORGE GATTON MELHUISH HARDINGHAM, of 191, Fleet Street, in the
City of London, Civil Engineer and Chartered Patent Agent, do hereby declare
the nature of this invention (a communication to me from Hugo Wilisch, of
Homburg on the Rhine, in the Kingdom of Bavaria and German Empire, Manu-
facturer,) 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 hardening articles of steel or other metal, and to
apparatus for carrying out the process; its objects being to accomplish a thorough
and uniform hardening, to avoid warping or twisting, and to effect economy.
In the accompanying diagrams,
Fig. is a view partly in longitudinal section and partly in side elevation of
apparatus adapted for use in carrying out the present invention; Fig. 2 being a
corresponding view partly in horizontal section and partly in plan."
The ordinary process of hardening large articles of steel or other metal by
first heating them and thereupon cooling the same in a bath of water, oil or
sand is generally unsatisfactory, having the drawback that only a momentary
cooling of the surface is effected the article, owing to the heat retained in the
body thereof, not being cooled enough to produce a thorough hardening. With
water and oil especially, the vapours which are formed and do not escape check
the necessary abstraction of heat. This is also the case when the hardening is
attempted in quicksilver, which is very soon caused to boil by large heated articles,
and consequently is only suitable for hardening small and delicate steel goods.
Further, quicksilver cannot be employed for large articles ou account of its cost
and owing to the fact that the vapours it gives off are detrimental to health. The
other metals which have been proposed for hardening purposes, such as tin, lead
and zinc, are of no practical value, because each, when heated to its melting point,
yields a bath too hot for hardening.
By this invention, a thorough hardening of the articles is effected in a bath
consisting, not of pure metal, but of an alloy having a low melting point; the bath
being so constructed that in one part the alloy is melted to form the liquid
metallic bath, and in another part the additional heat absorbed by the bath on
large metallic articles being introduced is abstracted.
Plates, cylinders, discs and similar articles of steel or other metal are first of all
beated to an uniform temperature throughout, which is best effected in a metallic
bath wherein a clear red heat, such as is required for instance for steel, can be
produced quickly and economically. The red hot articles are then brought into
the hardening bath, which is composed of an alloy having a low melting point.
This alloy is preferably made of tin and lead.
If it be desired that the temperature of the bath should not fall for instance
below:358° Fahr., the following alloy is suitable :-
:
10 parts of tin, and

page_text: lead,
"
is suitable for a bath in which the melting point should not fall below a temperature
of from 203° Fahr. to 209° Fahr. Obviously any other metallic alloy can be
employed in the place of those given above provided that its melting point is the
one necessary for the particular operation. The point whereat the alloy melts is
important, because it has been established as essential that for certain technical
purposes the temperature employed should be identical with that at which the
alloy passes from the solid into the liquid condition, because at that temperature
a definite amount of fluidity is possessed by the bath, and this has an influence
on the hardening. Consequently, it is always advisable to select an alloy the
melting point whereof corresponds with the desired temperature, and not to use an
alloy the melting point of which is lower than the temperature of the bath.
In order to conveniently effect the melting of the alloy, and to keep the same in
a liquid condition, the tank containing the alloy is provided with a heating tube.
For the purpose of rapidly withdrawing heat imparted to the metallic bath by
large articles introduced for the purpose of being hardened, so that the hardening
operation may not be interfered with, the tank is provided with a second tube
through which a cooling liquid is allowed to flow.
It is hardly necessary to add that the heating and cooling tubes may be replaced
by any other suitable means for heating and cooling, so long as the nature of the
apparatus is not materially altered.
A is the tank for containing the bath of melted alloy. This tank is provided
with a bent heating tube B connected with the steam space of a boiler. If, for
instance, steam at 30 lbs. pressure, and consequently at 250° Fahr., fills the tube,
the alloy placed in the tank A melts; the temperature of the metallic bath being
about the same as that of the steam.
The articles to be hardened, after a preliminary heating, which is best effected
in a tank D containing a correspondingly hot liquid metal or alloy, are introduced
into the bath in the tank A, and retained therein until they have cooled down to its
temperature.
For the purpose of conveying heavy articles from one bath to another, a
travelling crane, to the chain of which the articles are connected, as indicated in
Fig. 1, may be conveniently employed.
The temperature of the hardening bath would, however, be raised by the metallic
articles immersed as they give off their heat, and, if the bath be not made of
unusual dimensions, it would, with continued working, reach too high a temperature
to enable the hardening operation to be any longer effected. The tank A is con-
sequently provided with a second pipe E, through which a cooling liquid is
permitted to flow when it is desired to quickly cool the bath. As soon as the
temperature of the bath in the tank A has sunk again to about 250° Fahr., that is,
to its normal temperature, the flow of cooling liquid is cut off by means of the
cock F. When the temperature of the bath is higher than 250° Fahr., the steam
contained in the pipe B exerts a pressure of more than 30 lbs., and this is indicated
by the weighted safety valve G, which allows steam to escape.
By regulating the flow of the cooling liquid, the particular temperature in the
bath necessary for the desired degree of hardening can be easily attained.
To automatically control the regulation of the temperature, the safety-valve G
and the cock F may be united by a lever band connecting rods in such a way that,
when the safety-valve G blows off, a corresponding movement of the cock I takes
place.
The advantages of the above-described process for hardening metallic articles in
a tempering bath consisting of an alloy having a low melting point, the temperature
of the bath being suitably regulated during the hardening process, are, first, that

page_text: the cooling is uniform, so that the articles acquire an uniform hardness, and are not
liable to warp or spring during the operation, and, secondly, that the hardening
takes place throughout the substance, whereas in the tempering processes hitherto
known, the hardening is mostly confined to the surface, and, owing to the want of
means for regulating the temperature of the liquid bath, each article is not
hardened so uniformly as desired.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I claim :-
1. In hardening articles of steel or other metals, the employment of a melted
alloy substantially as herein described.
2. For use in hardening articles of steel or other metal in a bath consisting of an
alloy having a low melting point, the improved apparatus substantially as herein
described, the same comprising a tank A for the reception of the alloy, which tank
is furnished with a heating device, such as B, whereby the said alloy is melted, and
with a cooler, such as C, for regulating the temperature of the bath.
Dated the 10th day of June 1892.
G. G. M. HARDINGHAM.