U.S. patent number RE31,488 [Application Number 06/155,194] was granted by the patent office on 1984-01-10 for casting methods with composite molded core assembly.
This patent grant is currently assigned to Deere & Company. Invention is credited to David V. Trumbauer.
United States Patent |
RE31,488 |
Trumbauer |
January 10, 1984 |
Casting methods with composite molded core assembly
Abstract
A core assembly is formed by fabricating a first core, molding a
destructible plastic layer around the first core, and molding a
second core around the plastic layer. The plastic layer is
interlocked .[.wth.]. .Iadd.with .Iaddend.an irregular outer
surface of the first core, and the second core is interlocked with
an irregular outer surface of the plastic layer. The core assembly
can be used for casting engine cylinder heads to eliminate the need
for gluing cores together and the accompanying formation of fins
within fluid conducting passages.
Inventors: |
Trumbauer; David V. (Bremer,
IA) |
Assignee: |
Deere & Company (Moline,
IL)
|
Family
ID: |
26852086 |
Appl.
No.: |
06/155,194 |
Filed: |
June 2, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
733958 |
Oct 19, 1976 |
04093018 |
Jun 6, 1978 |
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Current U.S.
Class: |
164/32; 164/246;
164/34; 164/369 |
Current CPC
Class: |
B22C
7/023 (20130101); B22C 9/103 (20130101); B22C
9/046 (20130101); F02F 1/24 (20130101) |
Current International
Class: |
B22C
7/00 (20060101); B22C 7/02 (20060101); B22C
9/04 (20060101); B22C 9/10 (20060101); F02F
1/24 (20060101); B22C 009/04 () |
Field of
Search: |
;164/34,137,246,361
;264/221,317,DIG.44 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spruill; R. L.
Assistant Examiner: Lin; K. Y.
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Claims
I claim:
1. A method of casting metal castings comprising the steps of:
forming a composite core assembly by:
fabricating a first core having an irregular outer surface
portion;
molding a destructible layer of cellular plastic material around
said irregular outer surface portion of said first core, such that
an inner surface of said layer intimately contacts and conforms to
the configuration of said irregular outer surface portion of said
first core to interlock said first core and said plastic layer
together, and such that the outer surface of said plastic layer
includes an irregular surface portion; and
molding a second core in encompassing relation around said
irregular outer surface portion of said plastic layer, such that an
inner surface of said second core intimately contacts and conforms
to the configuration of the irregular outer surface portion of said
plastic layer to interlock said second core and said plastic layer
together, and such that the outer surface of said second core is of
nonconforming shape relative to the outer surface of said plastic
layer;
forming a mold cavity within a pair of mold halves; inserting said
core assembly as an integral unit within one of said mold
halves;
securing said mold halves together; and
introducing molten metal into said cavity to destroy said plastic
layer and form said casting.
2. A method according to claim 1 wherein said step of molding a
destructible layer comprises inserting said first core into a
corebox, applying thermoplastic resinous pellets around said first
core and expanding said pellets around said first core.
3. A method according to claim 2 wherein said step of applying
resinous pellets comprises applying pre-expanded polystyrene
pellets.
4. A method of forming a core assembly comprising the steps of:
fabricating a first core having an irregular outer surface
portion;
inserting said first core in to a first mold and molding a
destructible layer of cellular plastic material in encompassing
relation around said irregular outer surface portion of said first
core such that an inner surface of said plastic layer intimately
contacts and conforms to the configuration of said irregular outer
surface portion of said first core to interlock said first core and
said plastic layer together, and such that the outer surface of
said plastic layer includes an irregular surface portion; and
inserting as a unit said first core and said molded plastic layer
into a second corebox having a cavity which defines a surface of
nonconforming shape relative to the outer surface of said plastic
layer, and molding a second core in encompassing relation around
said irregular outer surface portion of said plastic layer such
that an inner surface of said second core intimately contacts and
conforms to the configuration of the irregular outer surface
portion of said plastic layer to interlock said second core and
said plastic layer together.
5. A method according to claim 4 wherein said step of molding a
destructible layer comprises inserting said first core into a
corebox, applying thermoplastic resinous pellets around said first
core and expanding said pellets around said first core.
6. A method according to claim 5 wherein said step of applying
resinous pellets comprises applying pre-expanded polystyrene
pellets.
7. A coring assembly for use in casting a cylinder head for an
internal combustion engine, comprising:
a port core having a base and port-defining extensions projecting
generally laterally and downwardly from said base in generally
parallel relationship;
said port-defining extensions having irregular outer surface
portions;
said base and port-defining extensions terminating downwardly in
essentially coplanar positioning members;
a molded-in-place destructible layer of cellular plastic material
disposed in encompassing relation around a substantial portion of
said port-defining extensions of said port core; said plastic layer
including a plurality of spaced upstanding posts for forming
cast-in-place valve guide bosses of the engine and forming an
irregular outer surface portion of said plastic layer;
said plastic layer including an inner surface which intimately
contacts and conforms to the irregular outer surface portion of
said port core to interlock said port core and said plastic layer
together;
a molded-in-place cooling jacket core disposed in encompassing
relation around a substantial portion of said plastic layer
including said upstanding posts;
said cooling jacket core terminating downwardly in a positioning
portion and including an inner surface which intimately contacts
and conforms to the irregular outer surface portion of said plastic
layer to interlock said cooling jacket core and said plastic layer
together, the outer surface of said cooling jacket core being of
nonconforming shape relative to the outer surface of said plastic
layer.
8. A core assembly according to claim 7 wherein said destructible
layer comprises a thermoplastic resinous material.
9. A core assembly according to claim 8 wherein said thermoplastic
resinous material is polystyrene. .Iadd.10. A method of casting
metal castings comprising the steps of:
fabricating a composite core assembly by
molding a destructible layer of cellular plastic material such that
a surface of said plastic layer includes an irregular surface
portion; and
forming a core in encompassing relation around said irregular
surface portion of said plastic layer by blowing a mixture of sand
and binder around said surface portion, such that a surface of said
core intimately contacts and conforms to the configuration of the
irregular surface portion of said plastic layer to interlock said
core and said plastic layer together;
forming a mold cavity within a pair of mold sections;
inserting said core assembly as an integral unit within one of said
mold sections;
securing said mold sections together; and
introducing molten metal into said cavity to destroy said plastic
layer and
form said casting..Iaddend..Iadd. 11. A method according to claim
10, wherein said step of molding a plastic layer comprises
fabricating an initial core having an irregular surface portion,
inserting said initial core into a corebox, applying thermoplastic
resinous pellets around said initial core, and expanding said
pellets around said initial core such that a surface of said
plastic layer intimately contacts and conforms to said irregular
surface portion of said initial core..Iaddend..Iadd. 12. A method
according to claim 11, wherein said step of applying resinous
pellets comprises applying pre-expanded polystyrene pellets.
.Iaddend. .Iadd. 13. A core assembly for use in metal casting
operations, comprising:
a first core having an irregular outer surface,
a mold-in-place, destructible layer of plastic cellular material
disposed around at least a portion of said outer surface of said
first core, with an inner surface of said plastic layer intimately
contacting and conforming to the irregular configuration of said
first core to interlock said first core and plastic layer such that
removal of said plastic layer from said first core in any direction
is prevented;
said first core and said plastic layer forming a composite core
subassembly; and
a formed-in-place second core encompassing a portion but not all of
said subassembly in overlying relation to said plastic layer and in
non-engagement with said first core;
an inner surface of said second core intimately contacting and
conforming to an irregular surface portion of said plastic layer to
interlock said second core and said plastic layer..Iaddend. .Iadd.
14. A core assembly according to claim 13, wherein said second core
comprises sand and binder. .Iaddend..Iadd. 15. A core assembly
according to claim 13, wherein said plastic layer comprises a
thermoplastic resinous layer..Iaddend..Iadd. 16. A core assembly
according to claim 15, wherein said resinous material is
polystyrene.
Description
BACKGROUND AND OBJECTS OF THE INVENTION
The present invention relates to foundry, tooling, processes and
methods and more particularly to a core assembly for use in casting
operations.
It is known to form castings such as engine cylinder heads by
various foundry techniques in which cores of different shapes are
placed within a mold to form voids, such as water jacket passages
and gas ports for example. In the past, this has required the
forming, handling and assembling of numerous cores. A comparatively
large number of cores and considerable assembly labor is used in
the fabrication of assemblies of this type.
Moreover, conventional core arrangements may require subassembly
and pasting or gluing of one or more of the cores together. Such
core assemblies are subject to some breakage due to handling, and
whenever cores are glued together there are numerous instances in
which molten metal flows between the cores and forms fins. When
these fins protrude into water jacket passages, they must be
removed as they would tend to restrict circulation and interfere
with the proper operation of the engine.
Also, in commercial foundries, it is not uncommon for gluing to be
performed in such a manner that relatively large amounts of glue
remain in hidden or inaccessible areas of the assembled cores. This
excess glue acts much as a core would, leaving a void and causing
surface imperfections or holes which can necessitate scrapping of
the cast piece.
Further disadvantages of conventional core arrangement may include
the need for using a large base or positioning core to hold the
water jacket cores and port cores in place during core assembly and
during pouring.
Another problem associated with conventional cylinder head coring
assemblies lies in the need to design the port walls with
relatively thick sections in order to allow for proper assembly of
the port cores. These thicker than necessary sections have an
adverse effect on efficient operation and cooling of the cylinder
head.
In certain types of core arrangements, some of the above described
problems might be alleviated to a degree by reducing the number of
cores in a manner described in U.S. Pat. Nos. 2,820,267 and
2,858,587, issued to Leach on Jan. 21, 1958 and Nov. 4, 1958,
respectively. These patents disclose core arrangements for a
cylinder head casting in which a number of core-assemblies are
combined into a fewer number of cores. The resulting cores are each
considerably more complex to form, requiring greater expenditures
of time and expense. In addition, the core assemblies disclosed in
these patents require the water jacket cores and port cores to be
positioned on the green sand in a drag half of a mold in order to
maintain their proper spatial relationship. This, in turn, requires
the formation of recesses, ridges and projections in the green sand
of the mold of sufficient precision to provide the required
alignment. Further, the water jacket and port cores cannot be
assembled accurately in the absence of the drag half of the mold.
This type of assembly is useful only when the core subassemblies
can be combined and is commercially inapplicable to many types of
core assemblies in which intermediate cores can only be located
within the core assembly before certain other outer cores are
positioned in place.
The search has thus continued for a commercially acceptable method
of providing a core arrangement which eliminates gluing of cores
and its resulting disadvantages and which provides for fewer core
components.
It is, therefore, an object of the present invention to provide
novel methods and tooling for minimizing or eliminating problems of
the sort dicussed above.
It is another object of the invention to provide a novel core
assembly and novel methods for fabrication thereof.
It is another object of the present invention to minimize the
formation of fins and surface imperfections in casting
operations.
It is another object of the invention to eliminate the need for a
positioning core in casting operations.
It is a further object of the invention to improve the cooling
characteristics of cast cylinder heads.
THE DRAWING
In describing the invention, reference will be made to a preferred
embodiment shown in the appended drawing in which:
FIG. 1 is a cross-sectional view of a conventional core arrangement
for forming a cylinder head of an in-line, six-cylinder internal
combustion engine of the overhead valve type;
FIG. 2 is a cross-sectional view, similar to that of FIG. 1,
depicting a core assembly according to the present invention for
use in forming such a cylinder head; and
FIGS. 3-5 are perspective views depicting various stages in the
fabrication of the core assembly according to the present
invention.
DETAILED DESCRIPTION
FIG. 1 illustrates a conventional core arrangement employed in a
foundry process for casting a cylinder head of an in-line,
six-cylinder internal combustion engine. A base or positioning core
2 is used in which the core assembly is built up. Later the
complete assembly will be set into mold section 4. A first core 6
is then inserted into the base core by embedding plurality of core
locator portions 8 (only one locator portion 8 being shown in FIG.
1) of the first core 6 firmly within the base core. The base core 2
provides rigid support to retain the first core 6 in a correct
position. A second core 10 is then installed by inserting one end
10A thereof through the first core 6 and embedding such end within
the base core by means of core locator portions 12 (only one
locator portion 12 being shown in FIG. 1). Another end 10B of the
second core 10 rests upon surfaces 14 and 16 of the base core
2.
Glue is then applied to a surface 18 of core 6. The third core 20
is placed upon the first core 6 so that the glue-containing surface
18 contacts a surface 22 of the first core 6. When the glue
hardens, the first and third cores 6 and 20 are firmly joined
together. Thereafter, one or more additional cores 24 are installed
around the cores 6, 10, 20. The completed core assembly is set into
the drag mold and a cope mold section is installed onto the drag
mold section in the usual fashion. When the molten metal is
subsequently poured into the mold, the metal occupies the space
between the various cores to form suitably configured port walls
and jacket walls of the engine head. For instance, the first and
third cores 6 and 20 form cooling jacket passages, while the second
core 10 forms gas ports.
As noted previously, the use of glue to bond the first and third
core sections can produce fins and/or surface imperfections which
can diminish or ruin the quality of the cast piece. Also, the cores
6, 10, 20 require a firm base in order to retain their proper
posture and spacial relationship within the mold. This is
especially evident of first and third cores 6 and 20 which include
portions 20A disposed above the second core 10 and yet which are
supported by the locating portions 8 situated to one side of the
second core 10.
A preferred form of core assembly 50 according to the present
invention for dealing with these and other problems is depicted in
FIGS. 2 and 5. This core assembly 50 effectively replaces the
conventional cores 6, 10 and 20. The core assembly 50 comprises a
first, or inner, core 52 (FIGS. 2 and 3) which is configured
somewhat like the conventional core 10, with the addition of a base
portion 52A for reasons to be explained. The inner core 52 includes
port extensions 52B projecting downwardly and laterally from the
base portion, and generally coplanar positioning portions 52C at
the ends of the base portion and port extensions 52B. Fabrication
of the inner core is carried out in any suitable manner. For
instance, the inner core can be molded of silica sand and binder
such as phenolic base and/or modified phenolic base resin, by
conventional techniques.
Subsequently, a layer 54 of destructible cellular plastic material
is formed around a portion, i.e., the port extension 52B of the
inner core 52 (FIG. 4). The destructible cellular plastic material
can comprise any suitable low temperature fusible substance, such
as a thermoplastic resinous material or any other cellular plastic
material which gasifies substantially without residue. Among the
materials which have been found satisfactory are polystyrene and
resinous polymerized derivatives of methacrylic acid.
Various types of cellular plastic materials suitable for use in
casting operations may be found in U.S. Pat. No. 3,374,827, issued
to Schebler on Mar. 26, 1968, and U.S. Pat. No. 3,496,989, issued
to Paoli on Feb. 24, 1970. For example, to Schebler patent
discusses the use of polystyrene and polyurethane as a spacer to be
inserted between cemented cores. The Paoli patent discloses the use
of polystyrene and polyurethane as a chaplet to abut and position
cores in place, and also as a pattern for full mold techniques with
a core embedded therein.
The expression "destructible" as applied to the cellular plastic
layer 54 is intended to designate materials which are quickly
destroyed by the molten metal, thereby enabling the molten material
to occupy the space originally occupied by the destructible
material. This behavior is contrary to that of a "core" material
which might be termed non-destructible in the sense that it is able
to resist the effects of the molten metal 50 as to produce a void
in the casting.
The destructible layer 54 can be molded in place around the first
core 52 by placing the first core 52 into a molding machine.
Partially pre-expanded polystyrene pellets can be applied to the
mold and fully expanded, via a steam expansion step, or other
suitable and accepted method around the first core 52 so as to form
a destructible layer whose inner surface 56 intimately contacts and
conforms to the configuration of the outer surface 58 of the first
core. The outer surface 60 of the molded destructible layer is
configured in accordance with the desired shape of the cylinder
head.
The plastic layer 54 completely surrounds or encompasses a portion
of the first core 52 and, due to the irregular surface
configuration of the first core 52, is permanently mounted thereon,
i.e., it cannot be removed in any direction.
The first core 52 and the destructible layer 54 form a composite
core subassembly 55 which can be handled as a one-piece unit. If
required, the composite subassembly can be dried, for example, in a
microwave oven to remove any residual water from the steam
expansion step. Also, the composite subassembly may be dipped into
a solution of protective surface coating to provide a better
casting finish for the ultimate metal casting.
Thereafter, a second or outer core 62, which constitutes a cooling
jacket core in the preferred embodiment, is formed around a portion
of the composite subassembly 55 so as to intimately contact and
conform to the configuration thereof (FIGS. 2 and 5). This can be
accomplished by placing the subassembly 55 into a second corebox
and core blower and blowing a suitable core composition, such as
silica sand and binder, therearound. The outer core 62 is thus
blown in place in overlying relation to a portion of the
destructible layer 54 to encompass or surround the latter. An inner
surface 64 of the outer core 62 intimately contacts and conforms to
the configuration of the outer surface 66 of the destructible layer
54. The outer surface 68 of the outer core 62 is configured in
accordance with the desired ultimate shape of the cooling jacket
passage. Portions of the cooling jacket passages are formed by
molding the outer core around solid upright post portions 69 of the
destructible layer forming the valve guide bosses of the cylinder
head. The outer core 62 also includes integral positioning parts
62A.
Due to the irregular configuration of the subassembly 55, the outer
core 62 is permanently secured thereto. That is, the outer core 62
cannot be removed in any direction.
The inner core 52, together with the molded-in-place plastic layer
54 and the molded-in-place outer core 62 form a final core assembly
50 which can be substituted for the conventional cores 6, 10 and
20. This assembly 50 can be inserted directly into a pre-formed
cavity in the green sand 70 of the drag half of the mold without
the need for a positioning core 2. This results in part from the
fact that core locating portions 52C, 62A of the cores 52, 62 are
part of a composite assembly and now function to support the core
assembly 50 as a whole, rather than only individual cores as was
previously the case. The core assembly 50 thus includes positioning
portions that are spaced in two directions and is more stable
within the mold than are the individual cores of the conventional
technique. Therefore, adequate support can be provided by the green
sand of the mold in the absence of a base core. By eliminating the
need for base cores, the time and materials required for their
fabrication and handling are saved. The end 52A of the inner core
52 is formed so as to engage the green sand 50 to provide support
for one side of the core assembly 50 in the absence of the
shoulders 14, 16 of the base core.
Alignment and installation of the core assembly 50 in the drag
portion is greatly simplified since it can be inserted in one piece
and no gluing is required. Subsequently, conventional cores such as
24 can be installed around the core assembly 50.
A cope portion of the mold is then positioned over the drag
portion, whereafter a molten iron charge is poured into the mold
cavity to form the cylinder head. The destructible expanded
cellular plastic layer 54 is gasified and replaced by the molten
metal as it enters the mold. The vapors of the plastic layer can be
allowed to escape from the mold through suitable vent holes.
The metal forms port and jacket walls of the cylinder head in
accordance with the configuration of the outer surface 58 of the
inner and outer cores 52, 62.
Since the present invention eliminates the need for gluing cores,
the expense involved in such procedure is obviated. Also, the
creation of fins, pitting and other imperfections associated with
gluing is avoided.
Moreover, it has been found that the present invention enables the
cylinder head to be advantageously redesigned. This is, a wall
portion 72 of the core assembly (FIG. 2) can be configured in
accordance with optimum jacket passage design, rather than in
accordance with the need for assembly clearance for another core,
such as core 10 in the conventional technique (see FIG. 1). The new
location of the wall portion 72 made possible by the present
invention is depicted in broken lines in FIG. 1 for purposes of
comparison. It will be realized that the port wall in this region
is rendered thinner and more uniform than before, resulting in the
use of less metal in the casting and better heat dissipation.
Although the present invention has been described above with
reference to a composite assembly of two cores and an intermediate
layer of expanded cellular plastic material, it will be understood
by those skilled in the art that the coring assembly may include
three or more cores, each core being formed onto and spaced from
the next inner core by a layer of cellular plastic material. Thus,
for example, another layer of cellular plastic material, if
desired, could be formed around the surface of core 62 and another
core molded around that plastic surface. The composite assembly may
thus contain any number of layers of cores and plastic as deemed
feasible.
It will also be understood that the present invention is applicable
for the production of any kind of metal casting. While it has been
described above with reference to the casting of a cylinder head,
and appears to be especially useful in this area, due to the
intricity of the core assemblies needed for the casting, the
present invention may be utilized for the production of other types
of castings using any metal.
The invention is additionally illustrated in connection with the
following Example which is to be considered as illustrative of the
present invention. It should be understood, however, that the
invention is not limited to the specific detail of the Example.
EXAMPLE
A first core 52 is formed in a mold or corebox from silica sand and
a phenolic base and/or modified phenolic base resin binder
compound. The first core 52 is then placed into a mold or corebox
which is thereafter filled with partially expanded polystyrene
pellets. Steam is applied to this mold to fully expand the pellets
to form a destructible layer 54 therearound in intimate contact
with the first core 52. The composite core subassembly defined by
the first core and the destructible plastic layer is dried in a
microwave oven until residual water from the stem expansion step is
evaporated. Then the subassembly is dipped into a protective
surface coating to perfect the casting finish.
The subassembly is thereafter placed into another mold or corebox
which is filled with silica sand and phenolicisocyanate binder
activated by a triethylamine or dimethylethylamine catalysis to
form a second core 62 around the destructible layer of the
subassembly in intimate contact therewith.
The resulting .[.sub assembly .]. .Iadd.assembly .Iaddend.is then
placed in the drag portion of a mold assembly containing foundry
sand and other conventional core assembly components are placed
about the .[.sub assembly .]. .Iadd.assembly .Iaddend.to form a
composite mold assembly suitable for forming a casting of a
cylinder head for a six cylinder engine. The cope portion of the
mold assembly is combined with the drag portion in a conventional
manner. A casting is made using this composite mold assembly using
conventional techniques. The interior of resulting casting is
smooth-surfaced, free of pits and fins and is suitable for use as a
cylinder head.
* * * * *