U.S. patent number 3,654,987 [Application Number 04/871,096] was granted by the patent office on 1972-04-11 for gasifiable casting care.
This patent grant is currently assigned to Full Mold Process, Inc.. Invention is credited to Erich Krzyzanowski, Johnannes Schade, Adalbert Wittmoser.
United States Patent |
3,654,987 |
Wittmoser , et al. |
April 11, 1972 |
GASIFIABLE CASTING CARE
Abstract
A casting pattern disposed in a molded material and having the
configuration of the article to be cast. A core member is located
within the outer body member and has the configuration of a cavity
to be formed and the casting. The outer body member and the core
member are each composed of a material gasifiable substantially
without residue upon being subjected to the elevated temperature of
a molten casting charge. A first layer of refractory gas permeable
material covers the outer body member and remains solid at the
elevated temperature of the molten casting charge. A second layer
of refractory material covers the entire outer surface of the core
member which is exposed to the body member for preventing contact
between the casting charge and the core member and being operative
to retard the transmission of heat from the molten casting charge
to the core member to prevent the gasification of core member until
a portion of the metal adjacent the second layer has
solidified.
Inventors: |
Wittmoser; Adalbert
(Lampertheim, DT), Schade; Johnannes
(Petit-Lancy-Geneve, CH), Krzyzanowski; Erich
(Ludwigshafen/Rhein, DT) |
Assignee: |
Full Mold Process, Inc.
(Lathrup Village, MI)
|
Family
ID: |
27087622 |
Appl.
No.: |
04/871,096 |
Filed: |
August 8, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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615866 |
Nov 1, 1966 |
3498360 |
|
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298678 |
Jul 30, 1963 |
3314116 |
|
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270085 |
Apr 2, 1963 |
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Current U.S.
Class: |
164/369;
164/246 |
Current CPC
Class: |
B22C
7/023 (20130101); B22D 7/10 (20130101) |
Current International
Class: |
B22C
7/02 (20060101); B22C 7/00 (20060101); B22D
7/10 (20060101); B22D 7/00 (20060101); B22c
009/10 (); B22c 007/02 () |
Field of
Search: |
;164/34,35,41,43,47,138,246,235,369,24,30 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Annear; R. Spencer
Parent Case Text
This application is a division of our copending application Serial
No. 615,866, filed Nov. 1, 1966, now U.S. Pat. No. 3,498,360, which
is a division of application Ser. No. 298,678, filed July 30, 1963,
now U.S. Pat. No. 3,314,116, which is a continuation in part of
application Ser. No. 270,085, filed Apr. 2, 1963, now abandoned.
Claims
What is claimed as new and desired to be secured by Letters Patent
is:
1. A core member for use in forming a cavity in a metal casting,
comprising a body consisting of an expanded plastic material which
is gasifiable on subjection to a molten casting charge and having
substantially the configuration of the cavity in the article to be
cast, and a layer of refractory material covering the entire
exposed outer surface of said body for preventing contact between
said casting charge and said body and which remains solid and gas
permeable at the elevated temperature of a molten casting
charge.
2. A core member for use in forming a cavity in a metal casting,
comprising a body consisting essentially of a gasifiable member
having substantially the configuration of the cavity in an article
to be cast and adapted to be gasified at the elevated temperature
of the molten casting charge and a layer of heat resistant material
covering the entire outer surface of said body which is exposed to
molten metal for preventing contact between said casting charge and
said body, said layer being gas permeable and retarding the
transfer of heat from a molten casting charge to said gasifiable
member until the melt adjacent said core has solidified.
3. The core member set forth in claim 2 wherein said body consists
of an expanded plastic material which is gasifiable substantially
without residue when subjected to the molten casting charge and
said heat resistant material is substantially incombustible at said
temperature.
Description
The present invention relates to a casting arrangement, and more
particularly, the present invention is concerned with improvements
relating to gasifiable patterns.
According to conventional casting procedures a pattern having the
shape of the casting to be made and consisting of wood-metal, wax,
synthetic resin etc. is embedded in an appropriate molding material
or molding sand respectively, in the mold. After packing the
molding material to form a mold body, the pattern is removed and
the melt is poured into the cavity which remains in the molding
material. For this procedure lost patterns can be applied that
means patterns which are destroyed after embedding, for example
when employing a wax pattern which is melted out.
It is another object of the present invention to improve the
usefulness of gasifiable casting patterns.
It is a further object of the present invention to provide improved
gasifiable casting patterns which can be produced and used in a
simple and economical manner.
It is a further object of the present invention to provide casting
arrangements including improved feeder head patterns.
Other objects and advantages of the present invention will become
apparent from a further reading of the description of the appended
claims.
The present invention includes a method of casting, comprising the
steps of embedding in a mold body a form which is gasifiable
substantially without residue on subjection to a molten casting
charge and which is shaped for exact reproduction as a casting and
the surface of which is covered with a layer consisting of a solid
material which remains solid and is gas permeable at the
temperature of the molten casting charge, providing in the mold
body and in the layer a passage for a molten casting charge to the
embedded form, and pouring into the passage a molten casting charge
for gasifying and replacing the embedded form in the mold body.
According to the present invention, the outer surface of the
pattern is provided with a shell-like, substantially incombustible
coat or layer which will not be affected by the temperature of the
penetrating melt and which preferably will be highly permeable to
gas or becoming permeable to gas during the pouring process. It is
also within the scope of the present invention, to incorporate in
the cellular plastic casting pattern solid or gaseous materials
which will act on, or react with, the molten casting charge, for
instance in the case of a molten metal casting charge, a material
which will cause a metallurgical treatment of the casting
metal.
The present invention thus overcomes the difficulties experienced
up to now in connection with gasifiable casting patterns and will
result in the production of cast bodies or castings of the desired
surface structure, even when embedded in a loose molding material
such as dry quartz sand which need not contain any binder. Even
metal shot or similar materials may be used as the molding
material. Furthermore, according to the present invention, not only
an improvement of the surface of the casting is achieved but also
of its inner structure which may be influenced by the incorporation
of suitable materials in the gasifiable cellular plastic casting
pattern.
The shell-like, substantially incombustible coat or layer on the
outer face of the cellular plastic pattern will also advantageously
act as a barrier preventing the escape of alloying and similar
materials which may have been incorporated in the cellular
gasifiable plastic casting pattern. In other words, when upon
contact with the molten casting charge the expanded or foam
cellular plastic pattern is burned out or decomposed and in any
event gasified and the thus formed gases pass outwardly through the
porous incombustible layer surrounding the cellular plastic pattern
and separating the same from the molding material, the surrounding
incombustible layer may be such as to prevent passage therethrough
of alloying or other materials which had been distributed
throughout the gasifiable plastic pattern. The porous layer thus
may be traversed by the gases formed, for instance, by pyrolysis of
the cellular plastic but will retain and prevent passage
therethrough of the particles of the alloying or the like material
in the mold, which particles of alloying or the like material will
thus be incorporated in, or react with, the casting charge.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. The
invention itself, however, both as to its construction and its
method of operation, together with additional objects and
advantages thereof, will be best understood from the following
description of specific embodiments when read in connection with
the accompanying drawings, in which:
FIG. 1 is a perspective view of a gasifiable casting pattern
according to the present invention;
FIG. 2 is a cross sectional view taken along lines II--II of FIG.
1;
FIG. 3 is an elevational view partially in cross section of a
casting pattern for a radiator, according to the present
invention;
FIG. 4 is a cross sectional view taken along lines IV--IV of FIG.
3;
FIG. 5 is an elevational cross sectional view of a casting mold
incorporating the casting pattern of FIGS. 1 and 2.
FIGS. 6-10 will serve primarily to illustrate embodiments of the
present invention which encompass a gasifiable feeder head;
FIG. 10 is a fragmentary, elevational, cross sectional view of yet
another embodiment of the present invention.
The casting pattern 1 which is illustrated in FIGS. 1, 2 and 5 may
serve as an example for producing a casting in accordance with the
present invention without requiring a core, while at the same time
providing the casting with hardened surface portions in the area of
the wheel body. Furthermore, as illustrated in FIG. 5, the casting
will be produced in accordance with the present invention so as to
be substantially free of cavities and pipings.
The upwardly extending portions 2, as shown in FIG. 1, serve for
reliable attachment of the risers and feeding conduits shown in
FIG. 5.
As illustrated in FIG. 2, the gasifiable foamed plastic pattern 1
carries a porous layer or coat 3 which covers the entire outer
surface of plastic pattern 1. Incorporated and substantially evenly
distributed throughout foam cellular plastic pattern 1 may be
alloying materials or other materials which will act on the molten
casting charge when the same is introduced into the mold so as to
gasify and replace the plastic pattern. Interposed between the
layer 3 of solid material, which remains solid at the temperature
of the molten casting charge and which preferably will be gas
permeable at such temperature, and the gasifiable member 1 may be a
layer 4 of a material adapted to act on and to influence the
surface portion of the casting during formation of the same, for
instance to increase the hardness of the surface portion.
FIGS. 3 and 4 illustrate one of the relatively rare cases when by
proceeding in accordance with the present invention it is
nevertheless desirable to use a core.
As illustrated, the outermost layer 31 as shown in FIGS. 3 and 4,
consists of a solid material which will remain solid at casting
temperatures and layer 31 contacts the outer surface of the
gasifiable cellular plastic pattern 32. The core consists of a
cellular plastic body 33 and a layer 34 interposed between cellular
plastic core 33 and cellular plastic pattern 32. Layer 34 consists
of a material of low heat conductivity so that upon introduction of
the molten casting charge and replacement of gasifiable plastic
pattern 32 by the casting charge, heat penetration toward the
gasifiable cellular plastic core portions 33 will be considerably
retarded, namely for a sufficient length of time so that
gasification of plastic core bodies 33 will take place only after
the portion of the casting charge adjacent to layer 34 has been
solidified and has become shape-retaining and self-supporting. Such
cores containing a gasifiable body are particularly suitable for
castings which include relatively thin walls and which are formed
with one or more inner cavities access to which is relatively
difficult.
FIG. 5 illustrates the casting pattern of FIGS. 1 and 2
incorporated in a molding arrangement which includes a shell 51,
mold body 52, open feeder funnel 53 and feeder 54 with riser 55.
Feeding funnel 53, feeder 54 and riser 55 consist, initially
similarly to pattern 1, of gasifiable cellular plastic material and
feeding funnel 53 and feeder 54 are surrounded by a layer of heat
insulating material 56. The foamed cellular gasifiable plastic
pattern again may have incorporated therein suitable alloying or
treating materials for acting on or reacting with the casting
charge. Heat insulating layers 56 may consist of the porous gas
permeable solid material which remains solid at casting
temperatures as described further above. The spherical blind riser
57 which is also surrounded by heat insulating layer 56 is formed
with a small cutout at its upper portion which will serve for
maintaining the elevated temperature of the melt for somewhat
longer period of time. The constriction underneath spherical riser
57 will facilitate breaking off the material which has solidified
in riser 57.
It will be understood by those skilled in the art that many
variations of these auxiliary devices are possible and are within
the scope of the present invention. Feeder and riser arrangements
which are surrounded by heating means, usually providing heat by an
alumino-thermic or the like process, or by insulating materials
have been known for a long time. However, up to now these elements
had to consist of pressure resistant, hard, ceramic hollow bodies
which had a relatively limited heating or insulating effect and
were quite expensive, while, according to the present invention,
these members will consist of a form of gasifiable cellular plastic
material which is covered with a layer of suitable insulating
material or the like.
Thus, in accordance with the present invention, by preforming
feeders, risers and the like of gasifiable cellular plastic
materials, which may be joined to the casting pattern of the same
type of materials, it is possible to utilize layers of insulating
materials which are highly insulating and relatively inexpensive
although affording less pressure resistance, such as layers of
mineral wool, and the like.
The materials which may be used for forming the solid gas permeable
layer 3 and which also may be used for forming the heat insulating
layer 56, are conventional materials which are, per se, known in
the art. Heat resistant materials which are porous or which will
become highly permeable to gas when exposed to the temperature of
the molten casting charge are highly suitable for the first
purpose. These materials include diatomaceous earth or kieselguhr,
asbestos, synthetic mineral fibers such as mineral wool, fire clay,
clay, pumice, bentonite, perlite, vermiculite and the like, to
which quartz sand or a similar material may be added if desired. As
binding agents for these mineral materials may be used
thermo-setting or preferably cold setting substances such as
plaster of Paris, cement, starch or synthetic resins, the latter
being preferred. In a most simple manner, the layer is formed by
preparing a suspension of the mineral material and binding agent in
water, to which suspension a suitable wetting agent and/or film
forming agent may be added and which is then applied to the
cellular plastic pattern, for instance, by hand, spray gun,
immersion or other methods. The coating or layer will require only
a short period of air drying, but it need not be subjected to a
special drying process and may be allowed to stand in wet
condition. The thickness of the coating preferably will not exceed
6 mm. and more preferably will be between 2 and 5 mm. The outside
of the layer or coating may remain in rough and uneven condition.
It is a further advantage of the above-described coating that it is
possible to incorporate therein without difficulty materials which,
when coming in contact with the casting charge, will affect the
surface properties of the casting. Moreover, it is possible to form
a layer of a material which will favorably affect the properties of
the casting between the cellular pattern and the heat-resistant
coating. Such layer, for instance, may be applied to the surface of
the cellular plastic pattern prior to forming the heat resistant
layer thereon.
In the production of castings which are required to have
particularly hard, wear-resistant surface portions, such as rollers
and cam shafts, such treating layer or coating may consist of
graphite, tellurium or ferrosilicon, in other cases, particularly
when producing light metal castings, a treating layer of silicon or
sulfur frequently will be found advantageous for improvement of the
surface quality of the casting.
The specific material of which the heat resistant gas permeable
layer is to be formed will depend on the type of casting which is
to be produced, such as whether an aluminum casting is to be
produced at about 700.degree. C. or a steel casting at about
1,500.degree.C.
For instance, in case of a casting to be formed of a metal having a
high melting point, the heat resistant porous layer may be formed
of a mixture of about 85 percent by weight of unblown perlite,
about 5 percent of water glass (aqueous solution containing 30
percent by weight of sodium silicate) as binder and about 10
percent by weight of ground graphite.
Water which may contain a wetting agent and a film-forming agent is
added in an amount sufficient to form a stiff paste which may be
easily applied to the cellular casting pattern by hand and which
dries quickly and adheres well to the surface of the cellular
plastic pattern. When it is desired to apply the layer by dipping
or spraying, then a greater quantity of water is added so as to
achieve the desired consistency which is best suitable for the
respective manner of applying the paste.
The perlite in the above-described mixture may be replaced by
similar proportions of mineral wool, kieselguhr, ground pumice and
the like.
The water glass binder may be replaced by a starch solution or a
suitable solution or dispersion of synthetic resin.
The graphite may be suitably replaced by ferro-silicon or
silicon.
The materials which may be incorporated in the heat resistant layer
or which may be interposed between the heat resistant layer and the
surface of the cellular plastic pattern, may either be mixed into
the mass of which the heat resistant layer is formed, or may be
applied as an intermediate coating, for instance dispersed in
alcohol or water containing a wetting agent and/or film forming
agent.
As has been described above, it is possible according to the
present invention to introduce into the casting charge while the
same is filling the space originally occupied by the cellular
plastic pattern, at least one additional material which will serve
to influence metallurgically the material of the cast workpiece.
This is done by employing the cellular plastic material as the
carrier for introducing such material.
The material which is intended to have a metallurgic effect on the
melt or casting charge, or to alloy with the same, may be
distributed as evenly as possible in the plastic material prior to
blowing of the same, so that as a result of the expansion of the
plastic material, an even distribution of the added materials will
be accomplished in the cellular gasifiable plastic pattern.
The gasifiable expanded plastic material which contains the evenly
distributed additional material may also be used to form the
pouring system of the mold. Thus, for example, to influence the
graphite formation in cast-iorn alloys, materials such as
ferrosilicon or nodular graphite-forming elements such as magnesium
and corium may be added. Powdery substances may also be added to
the expanded plastic for either preventing or promoting the
solidification of cast-iron alloys in the form of white cast iron,
for example magnesium and silicon (preventives) or sulfur and
tellurium (promoters).
Furthermore, alloying constituents, such as vanadium, molybdenum
and the like may be introduced into the melt in accordance with the
present invention.
Such alloying materials, or other materials which serve to
influence the quality of the casting formed of the molten casting
charge, are usually added in such quantities that, with reference
to the weight of the casting, the alloying metals are present in an
amount of up to 1 percent, silicon in an amount of up to 0.8
percent and magnesium in an amount of up to 0.1 percent. In order
to incorporate such proportions of added material in the casting,
when employing the gasifiable expanded plastic pattern as carrier,
the expanded plastic may contain up to 500 percent of its weight of
alloying metal or silicon, or up to about 50 percent of its weight
of magnesium, based on the weight of the expanded plastic.
In order to achieve a uniform distribution of such added alloying
or other material in the expanded plastic, the additional material
may be incorporated in the preexpanded granulate or in the monomers
of the plastic. In the latter case, the added material may be
distributed homogeneously, prior to the polymerization, in one or
more of the monomers prior to their admixture, or in the monomer
mixture. The added material should be introduced in finely
sub-divided form. This last procedure is particularly advantageous
because it will result in a very even distribution of the added
material, for instance an alloying constituent, in the expanded
plastic.
If, in customary manner, the expansion of the plastic polymer will
be carried out with the help of a suitable expanding agent under
the influence of the super-heated steam, then certain difficulties
are encountered when the added material, for example magnesium in
powder form, is attacked by water. If, on the other hand, the added
material is introduced into the monomeric resin, then the material
which is sensitive to steam will be distributed very homogeneously
in plastic expanded with the use of steam and apparently remains
protected against attack by water due to the plastic material
surrounding each of the particles of magnesium or the like.
Referring now to the heat barrier or layer of low thermal
conductivity, such as layer 34 of FIGS. 3 and 4, very good results
are obtained in the case of aluminum castings with layers formed of
one part by weight of a polyvinylpropionate resin dispersion
containing about 50 percent by weight of resin and 50 percent by
weight of water, two parts by weight of lithopone, two parts by
weight of white cement and three parts by weight of water with the
addition of a small amount of a wetting agent.
The thickness of the thus formed dry layer of low thermal
conductivity preferably will be about 2 - 3 mm. and its weight
about 300 grams per square meter. However, these quantitative date
should not be considered as limiting the invention since
innumerable variations may be made for specific purposes. For
instance, a metal powder or metal flakes and the like may be
incorporated in the layer, depending on the casting temperature.
The heat insulating layer 56 which primarily covers the cellular
plastic material which is located in place of the riser and feeder
conduits, preferably will consist of a material of the type which
is suitable for forming layers 3 or 31, and very good results are
achieved with respect to forming such porous layer by using
therefor mineral wool and a smoothening and binding agent such as
bentonite. However, layers 56 preferably will be considerably
thicker than layers such as layers 3 and 31.
The casting method of the present invention is not limited to any
specific casting charge or material. It is possible to cast
according to the present invention substantially all casting metals
such as bronze, light metals, iron, steel, heavy metals, as well as
glass and silicate melts (quartz), molten Al.sub.2 O.sub.3, SiC and
the like. Is is of course required that the melt will be
sufficiently fluid within a temperature range which will be
sufficiently above the decomposition or gasification temperature of
the foam plastic pattern, and the last condition generally is met
by a temperature of about 400.degree.C. Furthermore, it is of
course desirable that there should be as little reaction as
possible between the molten charge and the porous heat resistant
layer or the layer of low heat conductivity which covers the
plastic pattern.
The plastic pattern according to the present invention, with the
porous layer thereon, is also suitable for forming castings in a
mold body consisting of loose sand without binder, for instance of
free flowing quartz sand.
The incorporation of reactants such as alloying elements in the
cellular plastic pattern has the great advantage that, for
instance, starting with a casting charge of regular pig iron, a
cast body of alloyed metal can be produced. The loss of the usually
valuable reactants or alloying materials is insignificant and can
be further reduced by using the porous heat resistant layer
interposed between the cellular plastic pattern and the mold body.
When it is desired to influence the hardness or other qualities of
only the surface portion of the casting, then such reactants are
preferably applied as a thin layer or incorporated in a thin layer
on the surface of the cellular plastic pattern, as has been
described further above.
It is also possible according to the present invention to have the
closed cells of the cellular plastic pattern filled with a gaseous
substance which will affect the quality of the casting. Thus, the
cells may be filled with a gas which does not support combustion,
e.g. nitrogen, carbon dioxide, halogenated hydrocarbons such as
CF.sub.2 -CCl.sub.2 CF.sub.2 .dbd. CClF and similar materials which
are known by the trade name "Freonc." Thereby it will be achieved
on the one hand that combustion of the cellular plastic is
prevented and consequently the amount of gas which has to be
removed upon gasification of the plastic is reduced and, on the
other hand, it is possible in this manner to carry out the pouring
of the casting charge in a protective gas atmosphere. It is also
possible, according to the present invention, to incorporate
gaseous halogens such as chlorine in the expanded plastic, i.e. in
the cells thereof which halogens, particularly chlorine, will react
advantageously with certain light metal melts, such as a casting
charge of aluminum. Particularly the type of heat resistant layers
or coatings which become porous only when subjected to heat, will
permit the storing of the cellular plastic patterns covered with
such heat resistant layer for a considerable length of time,
without loss of the gas incorporated in the plastic pattern.
In general, cores are not required in connection with patterns made
of gasifiable expanded plastic material. If, however, in
exceptional cases such cores are required due to poor accessibility
of interior recesses of the plastic pattern, then the cores may be
incorporated when foaming the expanded plastic patterns or they may
be inserted thereafter. For this purpose it is possible to use not
only cores made of conventional material, i.e. bonded sand and the
like, but also cores which consist of gasifiable expanded plastic,
provided that the gasifiable expanded plastic core is surrounded by
a solid layer of low thermal conductivity, a so-called heat barrier
layer, which will retard the transmission of heat from the melt to
the expanded plastic core until after the melt layer adjacent the
core, i.e. outwardly and adjacent of the solid layer of low heat
conductivity, has solidified. Due to the high temperature of the
casting charge, the core will then be gasified and a recess will
remain in the casting, the latter being covered adjacent to such
recess by the barrier layer which can be easily blown off or
otherwise removed.
Such barrier layer may consist of gypsum, clay, magnesium, calcium
oxide or similar materials with hydraulic or organic binders such
as polyvinyl acetate resin, starch and the like, or including metal
powders or metal flakes, and the heat barrier layer may be applied
to the expanding plastic core in the same manner as the heat
resistant porous coating is applied to the expanded plastic
pattern. Usually a thickness of the barrier layer of a few
millimeters will be sufficient for retarding heat transmission
therethrough to such an extent that the core will be gasified only
after the portion of the charge adjacent to the barrier layer has
solidified.
It is possible to make not only the casting pattern of gasifiable
expanded plastic, but also the pattern for ingate, ventilation and
connecting conduits and/or feeder heads (so-called blind risers),
and to adhesively adhere the expanded plastic pattern to the
expanded plastic material of such conduits or feeders, either
during the foaming process or thereafter. The term "feeder" is to
be understood to denote additional storage space for the melt in
the mold, i.e. additional space which can be filled with molten
charge. Such an additional space is frequently desirable in order
to prevent hole or piping formation in metals which have a great
tendency to shrink.
Hitherto parts of the molding system being particularly susceptible
to shrink hole formation were provided with heating means or heat
insulating means by introducing suitable materials into the mold
cavity after having removed a conventional pattern. Thermite
mixtures were used as heating means and hard burned ceramical
materials which were brittle, rather expensive and of relatively
limited effect served as insulating material. The coating provided
according to the invention represents a considerable progress in
this respect, as it can be applied without difficulty near or at
all critical points of the pattern in any desired thickness in
order to secure the insulating effect required in every particular
case. The thickness of the coating may amount to 20 mm. or more. If
required, the insulating effect can be increased by conventional
heating means. The insulating portions of the coating may consist
substantially of the above mentioned mineral fiber materials, i.e.
asbestos or synthetic mineral fibers. Coatings of this kind have by
far better insulating effects than the hollow ceramic bodies
conventionally used for this purpose. In spite of the relatively
loose structure of such fibrous materials no difficulties arise
when embedding the pattern, as all forces or stresses occurring
thereby are absorbed by the expanded plastic pattern. The
gasifiable patterns are not only suited for molding metals but also
for molding other melts, as for example glass and silicate melts
and the like provided that their casting temperature is
sufficiently higher than the decomposition temperature of the
expanded plastic material.
As an example only without, however, limiting the invention the
solid content of the intermediate coatings 4 only comprise in
percent of weight: 75 - 95 pulverized silica, 5-8 ground graphite,
1-5 water glass, up to 3 bentonite, and Al.sub.2 O.sub.3 at the
balance.
It will be understood that each of the elements described above, or
two or more together, may also find a useful application in other
types of molding arrangements differing from the types described
above.
While the invention has been illustrated and described as embodied
in an ingot mold arrangement, it is not intended to be limited to
the details shown, since various modifications and structural
changes may be made without departing in any way from the spirit of
the present invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can by applying current
knowledge readily adapt it for various applications without
omitting features that, from the standpoint of prior art, fairly
constitute essential characteristics of the generic or specific
aspects of this invention and, therefore, such adaptations should
and are intended to be comprehended within the meaning and range of
equivalence of the following claims.
* * * * *