Improvements in and relating to Method of and Means for Making Metallic Castings.
Year: 1899

page_text: Date of Application, 12th Dec., 1899-Accepted, 3rd Mar., 1900
COMPLETE SPECIFICATION.
Improvements in and relating to Method of and Means for Making
Metallic Castings.
I, WILLIAM DANIEL ALLEN, residing at the corner of Madison and Gates Streets,
in the City of Huntsville, County of Madison, State of Alabama, United States
of America, Dental Surgeon, do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
111
This invention contemplates an improved method of and means for making
metallic castings, the object of the invention being the attainment, in the finished
article, of perfection of conformation of the matrix of the mold, and freedom from
crystallization, fissures, pipes," blow holes," other flaws and defects which
if present render it liable to distortion and fracture and otherwise impair its
strength, durability and effectiveness.
My invention which is applicable to the making of all kinds of metallic castings
irrespective of their form, size and weight, and of the material of which they are
composed, consists, broadly, in heating throughout its entire body an open top mold
or the like, to a degree approximating that of the molten metal when run, main-
taining such degree of temperature during the pouring operation, and after pouring
withdrawing the applied heat from the mold or the like, commencing at the base
and continuing gradually towards the top, the heat being finally confined to the
exposed molten metal. My invention also consists in a means by which the method
may be carried into effect, which means in its broadest sense comprises a furnace
adapted to enclose the mold having around the wall of the mold chamber
a plurality of burners located
111 a number of planes, each plane
of burners having a separate valved fluid supply pipe, whereby the application of
heat to the mold is under full control, and the withdrawal of the heat therefrom
may be accomplished gradually beginning as above stated, at the base and ending
at the open top through which the metal of the casting is exposed.
This method differs from those universally practised in that by the withdrawal
of the heat in the manner stated, the casting is caused to cool from the bottom
gradually upward, whereas heretofore the cooling has been from the top down-
ward, notwithstanding the practice which is sometimes resorted to of applying
heat temporarily to the top of the casting to prevent chilling at that point.
This reversal in the direction of cooling the casting results in a product free from
the above enumerated defects, inasmuch as my improved method contemplates the
pouring of a surplus of metal into the mold, which surplus contributes to the
loss through shrinkage which the metal in cooling sustains; and the withdrawal
of the heat in the manner stated causes the casting to cool and set first at the
bottom and thence gradually towards the top, the molten metal through gravitation
compensating for the contraction, the result being an article perfect throughout
and conforming exactly to the matrix.
In the following detailed description my improved method and means of
accomplishment are set forth in connection with the manufacture of artificial

page_text: dentures, articles which are difficult of production in view of their peculiar shape
and the degree of thinness made necessary at certain portions in order to afford
comfort to the wearer. In the production of dentures and other like articles by
my improved method, I prefer to employ metals and metallic alloys which have
the property of contracting to a considerable degree in casting, and in this
respect there is presented a radical departure from the methods heretofore prac-
tised, more especially in connection with dental articles, all of which previous
modes, so far as I am aware, contemplating the use of metals and alloys in which
the degree of contraction in casting is the minimum. Metals and alloys which are
employed by reason of their comparative nonliability to contraction in casting are
well known to be weak under tensile strain, such weakness being largely due to
the greater or less absence of molecular cohesion; and to overcome this difficulty
has been the practice to augment the cross sectional dimension of the structure
to better resist the strain to which it is subjected. In addition to the great dis-
comfort arising from the use of a denture or the like of disproportionate thickness,
there are also present other disadvantages due to the failure to compensate for the
shrinkage which naturally results from the practise of previous methods even
though the metals or alloys are, comparatively speaking, non-contracting. The
shrinkage or contraction of a metal or alloy during cooling, though it may be
slight, results in a casting which is more or less non-comformable to the part to
which it is designed for application, and especially is this true in the case of a
full upper denture, where as is well known, the maximum contraction takes place
at the centre, or that part which receives the greatest strain both in cooling and in
the use of the finished article. It is obvious, therefore, that a denture or the like
made from a metal or alloy which is naturally weak in tensility, and which con-
tracts unequally even to a slight degree in cooling is in many ways undesirable;
and, on the other hand, that a method employing a metal or alloy which naturally
is of comparatively great tensile strength, and involving steps which result in
proper compensation for contraction, is of great value and constitutes a distinct
and advanced step in the art.
The details of the method and of the construction of means by which the method
may be carried into effect are hereinafter fully set forth, and in connection with this
detailed description, attention is directed to the accompanying drawing in which
is shown in longitudinal sectional view a casting apparatus embodying my
invention.
Referring to the said drawing by letter, A denotes a flask or mold containing an
investment B in which is formed the matrix. The opening a to the matrix is of
sufficient dimensions to enable a surplus of the metal to be poured, the metal
being exposed through said opening. The furnace D comprises a casting of
sufficient internal dimensions to accommodate the mold A. In the inner wall of
the casing, or what may be termed the mold chamber, are a plurality of burners e e
preferably arranged to project jets of flame in a downwardly inclined direction,
said burners being located in a number of planes as shown, and each plane of
burners being supplied with fluid through a separate pipe f, the pipes having each
a valve f by which the supply of fluid may be controlled.
In operation all of the burners in all of the planes are ignited, and the mold
being placed in the chamber of the furnace, is first subjected to a gentle heat to
thoroughly dry the investment after which, by manipulating the valves, the tem-
perature is raised sufficiently high to heat the mold to a degree approximating
that of the molten metal when run. With the mold in this highly heated con-
dition, the metal is poured, the uppermost plane of burners being preferably so
disposed as that the flame jets are caused to impinge against the stream whereby
chilling is avoided.
The matrix proper terminates some distance below the top
of the investment to enable what I have termed a surplus of metal to be poured
and it is this surplus which is exposed through the opening c to direct contact
with the flame jets of the top plane of burners, which jets, as before stated, are
directed downwardly. The jets of flame are caused to impinge preferably at

page_text: an angle against the entire outer surface of the mold before and during the
pouring of the metal, and thereafter the burners are successively extinguished,
commencing at the lowermost plane, whereby the heat is withdrawn first from the
base of the flask and thereafter gradually towards the top, and lastly, the
exposed molten metal is alone subjected to the direct action of the jets of the
uppermost burners. The effect of the withdrawal of the heat in the manner stated
is to preserve the fluidity of the metal át successive portions of the casting whereby
any contraction or shrinkage is at once compensated for by the molten metal
which, through gravitation, fills the spaces as they are formed, the surplus pro-
vided being sufficient to contribute to the making of a complete casting. The
remarks with reference to the manufacture of artificial dentures by my process are
equally applicable to the making of other articles, inasmuch as in all castings
there are present defects due to shrinkage or other cause, which impair their
strength, effectiveness and durability but which by my invention are entirely
avoided. My invention is also applicable to the making of castings from metals
or alloys which are, relatively speaking, non-contracting, by which is meant
materials in which shrinkage in cooling is the minimum. The maintenance of the
molten condition of the metal in the mold in addition to preventing the formation
of fissures, pipes, blow-holes and like defects, has the advantage of prolonging
the period of cooling, whereby there is secured a perfectly homogeneous structure
and one that is exactly conformable to the matrix.
While I have described and illustrated my invention as applicable to the making
of castings such as dentures, it is obvious that the method and means of accom-
plishment are applicable to the making of metallic castings generally, and I do
not therefore limit myself to the specific adaptation set forth. Also I do not limit
myself to the particular construction of means for carrying out my improved
method, as said means are susceptible of modification without departing from the
spirit of my invention.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
1. The herein described method of making metallic castings which consists in
subjecting an open top mold or like vessel into which the metal is poured to
the action of independent flames impinging on the mold at different heights,
pouring in the metal and successively extinguishing the flames commencing with
the lowermost, whereby the heat is withdrawn commencing at the base of the
mold and continuing gradually towards the top, the heat being finally confined
to the exposed molten metal.
2. The herein described method of making metallic castings which consists in
subjecting an open top mold or like vessel into which the metal is poured to a
degree of heat approximating that of the molten metal when run in by impinging
thereagainst independent flames at different heights, introducing into the heated
mold or like vessel molten metal in excess of the amount necessary to fill the
matrix, and successively extinguishing the flames, commencing with the lowermost,
whereby the heat is withdrawn commencing at the base of the mold and continuing
gradually towards the top, the heat being finally confined to the exposed molten
metal.
3. The herein described method of making metallic castings which consists in
subjecting an open top mold or like vessel to the action of independent flames
impinging on the mold at different heights to dry the investment, raising the
degree of heat approximately to that of the molten metal when run in, introducing
into the heated mold of like vessel molten nietal in excess of the amount necessary
to fill the matrix and successively extinguishing the flames, commencing with the
lowermost, whereby the heat is withdrawn commencing at the base of the mold
and continuing gradually towards the top, the heat being finally confined
to the exposed molten metal.

page_text: 4. In combination, a mold, flask, crucible or the like, and a furnace adapted to
enclose said mold, having around the wall of the mold chamber a plurality of
burners located in a number of planes, and a separate fluid valved supply pipe for
the burners in each plane.
Dated this 19th day of Dovom 1899
JENSON & SON,
77, Chancery Lane, London, W.C., Patent Agents.