JPS6242701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a casting method and a core assembly used in the casting method.

It is known to place cores of different shapes in a mold in order to make cavities, for example as cooling jackets or gas ports, for making castings such as engine cylinder heads. Conventionally, this method requires making and assembling several cores. Creating this core assembly required a relatively large number of cores and a large amount of labor.

Additionally, general purpose core assemblies require core-to-core coupling and subassemblies. Such core assemblies are subject to damage during handling, and whenever the cores are joined together, molten metal often flows between the cores to form flash. If these flashes protrude into the water (cooling) jacket, they must be removed as they tend to interfere with proper operation of the engine and restrict circulation.

Also, in mass production castings, it is not uncommon for cores to be bonded in such a way that a relatively large amount of the bond remains in hidden, hard-to-reach areas of the core assembly. This excess binder acts like a single core leaving defects, holes, or voids in the casting surface that cause the casting to be scrapped.

A further disadvantage of conventional cores is that they require a large base or locating core to hold the water jacket core and port core in place during assembly of the core and subsequent dispensing of hot water. be.

Also, a problem associated with general purpose cylinder head core assemblies is that port walls must be designed with relatively thick sections in order to properly assemble the port core. A cylinder head port wall that is thicker than necessary is disadvantageous for effective operation and for cooling the cylinder head.

In some types of core assemblies, some of the problems mentioned above are solved by U.S. Pat.
Some mitigation can be achieved by reducing the number of cores, as described in US Pat. No. 2,858,587. These patents show core arrangements for cylinder head molds in which multiple core assemblies are connected to a relatively small number of cores. Each final core is fairly complex to make and requires a lot of time and money. In addition, the core assembly requires that the water (cooling) jacket core and port core be placed on green sand in the lower mold of the mold to maintain their proper spatial relationship. This requires making recesses, protrusions, etc. in the green sand of the mold sufficiently precise to bring it into position. Additionally, water jacket cores and port cores cannot be assembled accurately without a mold base. This type of assembly is useful only if the core assemblies can be interlocked, unlike many types in which the intermediate core can only be positioned within the core assembly until the other outer core is in place. The core assembly has no commercial application.

Accordingly, there has been a need for a commercially applicable method that eliminates core bonding and its associated disadvantages and provides a core array that uses fewer cores.

It is therefore an object of the present invention to provide a new casting method and tool which reduces or eliminates the above-mentioned problems.

A second object of the invention is to provide a novel core assembly and method for making the same.

A third objective is to minimize flash and surface defects during casting operations.

A fourth purpose is to eliminate the need for a positioning core for positioning the core.

A fifth purpose is to improve the cooling characteristics of cast cylinder heads.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

FIG. 1 shows a general-purpose core arrangement used in the casting of cylinder heads for six-cylinder internal combustion engines. A base or positioning core 2 is used to assemble the core assembly thereon. The core assembly is set within mold section 4. The first core 6 is then inserted into the base core with the plurality of positioning portions 8 (only one shown in FIG. 1) of the core firmly embedded within the base core. The base core 2 firmly supports the first core 6 to keep it in the correct position. The second core 10 is attached with one end 10A to the first core 6 in a suitable and positioning portion thereof (only one is shown in FIG. 1) by embedding it in the base core. The other end 10B of this second core 10 is located on the surfaces 14 and 16 of the base core 2.

Next, glue (binder) is applied to the surface 18 of the first core 6.
Paint on. A third core 20 is placed over the first core such that the glued surface 18 contacts the surface of the first core. When the glue hardens, the first
And the third cores 6 and 20 will be firmly coupled. After this, one or more core 2
4 will be placed around the cores 6, 10, 20. The completed core assembly becomes the lower mold as usual, and the mold top (upper mold) is placed on top of the lower mold. The predetermined molten metal is then poured into the mold and occupies the spaces between the various cores to form the suitably shaped bore and jacket walls of the engine head. For example, the first and third cores 6
and 20 serve as cooling jacket passages, while the second core 10 serves as a gas port.

As previously mentioned, using glue to adhere the first and third cores can create flash and/or surface imperfections that degrade or destroy the cast part. Others, core 6,1
0 and 20, if the base is not solid, there is a risk that a proper finish or special relationships within the casting may not be maintained. This is particularly noticeable in the case of the first core 6 and the third core 20, which include a portion 20A located above the second core 10 and are further supported by a portion 8 located on one side of the second core 10. It is.

One proposed core assembly 50 according to the present invention to overcome these and other problems is shown in FIGS. 2 and 5. The core assembly 50 has a first or inner core 52 (FIGS. 2 and 3) similar to the older core 10 and has a base 52A, which will be described below.
Inner core 52 includes a port extension 52B projecting downwardly and laterally from the base and coplanar portions 52C at opposite ends of the base and port extension 52B. This inner core is manufactured in any suitable manner. For example, the inner core may be made from silica sand or a binder such as a phenolic or modified phenolic resin using conventional techniques.

Next, there is a layer 54 of destructible cellular plastic material, the inner core 52 (FIG. 4).
is formed around the port extension 52B. The cellular plastic material may be any low melting material such as a thermoplastic resin-like material or other cellular plastic material that vaporizes in large quantities without residue. Materials that have been found to be suitable include polystyrene and resinous polymeric derivatives of methacrylic acid.

Various cellular plastic materials suitable for use in casting processes are described in U.S. Pat. No. 3,374,827 and U.S. Pat.
It is clear in No. 3496989. For example, U.S. Pat.
No. 3,374,827 discusses the use of polystyrene and polyurethane as spacers inserted between cemented cores. U.S. Pat. No. 3,496,989 discloses the use of polystyrene and polyurethane as a mold for abutting and positioning a plurality of cores, and also as a mold for a casting technique for embedded cores. It's clear.

The term "destructible" as applied to the cellular plastic layer 54 refers to a material that is rapidly destroyed by molten metal, allowing the molten material to occupy the space originally occupied by the destructible material. It is for. This action is opposite to that of a "core", which may be called because of its non-destructive nature and resistance to the action of molten metal 50 to create voids during casting.

Destructible layer 54 may be cast in position around first core 52 by placing first core 52 in a molding machine. The partially pre-expanded polystyrene grains are used in casting and are expanded sufficiently around the first core 52 by a steam expansion method or other suitable method so that the interior surface 56 of the polystyrene grains forms the outer surface 58 of the first core.
forming a destructible layer that closely contacts and conforms to the surface of the material. Destructible layer outer surface 60
is shaped according to the desired shape of the cylinder head.

Since the plastic layer 54 completely surrounds a portion of the first core 52, due to the irregular topography of the surface of the first core 52, it always rests on it and cannot move in any direction.

The first core and plastic layer 54 form a core subassembly 55 that can be handled as a unit. If desired, this subassembly can be dried, for example in a high frequency oven, to remove residual moisture from the steam expansion stage. The assembly may also be immersed in a surface protection coating solution to provide a better casting finish for the final metal casting.

Thereafter, the second or outer core 62 - which is
A cooling jacket core, in this embodiment, is formed around a portion of sub-assembly 55 and is shaped to contact and fit therein (FIGS. 2 and 5). This is its subassembly 5
5 into the second core box and core blowing (core
blower) and blow around it appropriate core ingredients such as silica sand and binder. external core 62
is thus blown into position relative to a portion of the plastic layer 54 and surrounds or surrounds the latter. One inner surface 64 of outer core 62
closely contacts and conforms to the configuration of the outer surface 66 of the plastic layer 54. The outer surface 68 of the outer core 62 is configured according to the final desired shape of the cooling jacket passageway. Each section of the cooling jacket passageway is formed by casting an outer core around a solid vertical column 69 extending over a destructible plastic layer forming the valve guide boss of the cylinder head. The outer core 62 also has an overall supporting portion 6
Also includes 2A.

Due to the irregular shape of the sub-assembly 55,
The outer core 62 remains there permanently. That is, the exterior 62 cannot move in any direction.

The inner core 52, along with the plastic layer 54 cast in place and the outer core 62 cast in place, form the final core assembly 50 which may be replaced with the expedient cores 6, 10 and 20. This assembly 50 does not require a base or positioning core 2 and can be inserted directly into a cavity already created in the green sand of the lower mold of the mold. This results from the fact that core positioning portions 52C, 62A of cores 52 and 62 are part of a combination and serve to support core assembly 50 as a whole rather than as individual cores as before. In this way, the core
Assembly 50 includes spaced portions in two directions and is more stable within the mold than the individual cores of the prior art. Therefore, even without a basal core, adequate support is provided by the green sand of the mold. Eliminating the need for a basal core saves time and materials required for its handling and manufacture. The end 52A of the inner core 52 is formed using green sand to support one side of the core assembly 50 without the shoulders 14 and 16 of the base core.

The arrangement and configuration of the lower mold core assembly 50 is greatly simplified since it is treated as one solid body and does not require any fastening. A core, such as conventional 24, can then be placed around the core assembly 50.

The cope part of the mold is placed on top of the lower mold part. Molten iron is then poured into the mold to form the cylinder head. Cellular plastic layer 54 destructible as molten iron enters the mold
is gasified and replaced by molten metal. The plastic layer vapor may escape from the mold through suitable vents.

The metal forms the ports and jacket walls of the cylinder according to the configuration of the outer surfaces 58 of the inner and outer cores 52 and 62.

Since the present invention eliminates the need for a glued core, the cost of such methods is eliminated. Also, the formation of flash, pitting, and other defects associated with glue application are avoided.

Furthermore, it has been found that the present invention allows advantageous redesign of cylinder heads. In other words, the core
The wall portion 72 of the assembly (FIG. 2) is based on an optimal jacket passage design, rather than depending on the combined gap requirements for other cores, such as core 10 in the prior art (see FIG. 1). It can be shaped by The new position of wall section 72 made possible by the invention is shown in dotted lines in FIG. 1 for comparison. The port walls in this area can be made thinner and more uniform than before,
As a result, less metal is required in casting and heat dissipation is improved.

Although the present invention has been described above with reference to a combination of two cores and an intermediate region of cellular plastic material, it will be appreciated by those skilled in the art that core assemblies may include three or more cores. , each having a stack of cores with a layer of cellular plastic material in between. So, for example, if you want
Another layer of cellular plastic material is formed near the surface of core 62, and another core can be molded around the surface of this layer. These various combinations may include any number of cores and layers of plastic material as deemed appropriate.

It will also be appreciated that the invention is applicable to manufacturing by any type of metal casting process. Although the above has been described with respect to casting cylinder heads and appears to be particularly useful in this area, the present invention may be used in other types of casting manufacturing using any metal.

The invention is further illustrated on the basis of the following examples which are considered illustrative.

EXAMPLE The first core 52 is comprised of silica sand and a phenolic and/or modified phenolic resin binder mixture in a mold or core box. This first core 52 is placed in a mold or core box which is later filled with partially expanded polystyrene grains. Steam is poured into the mold, expanding the pellet and forming a breakable layer 54 in intimate contact with the first core 52.
The core subassembly, consisting of a first core and a destructible plastic layer, is dried in a high frequency oven until residual moisture from the steam expansion stage is vaporized. The core subassembly is then immersed in a surface protective coating to complete the casting finish.

This core subassembly is then placed into another mold or core box filled with triethylamine or dimethylethylamine catalyst activated silica sand and a phenolic isocyanate binder, and the second core 62 is inserted into the core. • Formed in close contact around the destructible layer of the subassembly.

The resulting core subassembly is placed in the lower mold assembly containing foundry sand, and other conventional core assembly parts are placed near the core subassembly to form a cylinder head for a six-cylinder engine. Form a mold assembly suitable for molding. The upper mold part of the mold assembly is joined to the lower mold part in conventional manner. Casting is performed using this mold assembly using conventional techniques. The interior of the resulting casting has a smooth surface, no pitting or fins, and is suitable for use as a cylinder head.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional core assembly arrangement forming the cylinder head of an internal combustion engine having six cylinders of the overhead valve type. FIG. 2 is a cross-sectional view similar to that of FIG. 1, but showing a core assembly for forming a cylinder head in accordance with the present invention.
FIGS. 3-5 are perspective views showing various stages of the development of a core assembly according to the present invention. 52...first core; 54...destructible plastic layer; 55...subassembly; 62...second core.

Claims (1)

[Claims] 1. A casting method consisting of the following steps: (a) Step of making a core assembly: This step is carried out as follows. creating a first core; creating a destructible layer of cellular plastic material around at least a portion of the first core having an inner surface closely conforming to the shape of the core; forming a core subassembly comprising a first core; an inner surface closely conforming to the configuration of the subassembly about at least a portion of the subassembly in overlapping relationship with the plastic layer; to form the core assembly. (b) forming a mold cavity in a pair of upper and lower molds; (c) placing said integrally molded core assembly into one of said upper mold or lower mold; (d) said above; (e) pouring molten metal into the mold cavity to complete the casting while destroying the plastic layer. 2. To create the destructible plastic layer, the first core is placed in a core box, and thermoplastic particles are provided around the first core to form the first core.
2. A method as claimed in claim 1, characterized in that it is carried out by expanding around a core. 3. Claim 2, wherein the thermoplastic particles are supplied with pre-expanded particles.
The method described in section. 4. A method for manufacturing a core assembly comprising the following steps: (a) making a first core; (b) setting the first core in a first mold and forming a core assembly around at least a portion of the core; (b) setting the first core in a first mold; (c) molding a layer of destructible cellular plastic having an inner surface that closely follows the outer shape of said core; (c) molding a second layer of said first core integrally molded with said plastic layer; completing the core assembly by placing in a mold and molding around at least a portion of the layer a second core having an inner surface that closely follows the contour of the layer; 5. In the step of molding the plastic layer, the first core is placed in a mold, thermoplastic resin particles are supplied around the core, and the particles are expanded around the first core to form the plastic layer. Claim 4: Shaped
The core assembly manufacturing method described in Section. 6. The method of manufacturing a core assembly according to claim 5, wherein the thermoplastic resin particles are pre-expanded polystyrene particles. 7. A core assembly for use in a casting operation, comprising: a first core; and an inner surface molded around at least a portion of the first core and closely following the outer shape of the first core. a layer of destructible cellular plastic material; molded around at least a portion of an integrally molded first core so as to overlap with the plastic layer, closely conforming to the contour of the plastic layer; The second one has an inner surface that follows
a core assembly having a core; 8. The core assembly of claim 7, wherein said plastic layer comprises a thermoplastic material. 9. The core assembly of claim 8, wherein the thermoplastic material is polystyrene. 10. A core assembly for casting a cylinder head for an internal combustion engine; for a port having a base and a plurality of port-forming extensions, each generally parallel, extending generally laterally and downwardly from the base. a porting core in which the base portion and the porting extension terminate below an essentially common planar locating member; a spaced layer of destructible cellular plastic molded around and having an inner surface closely following the surface of the port core and forming a valve guide boss for the internal combustion engine; a plastic layer comprising a plurality of vertical columns; a cooling jacket core formed around a substantial portion of the plastic layer having the vertical columns, terminating below with a locating portion; A core assembly comprising: a core for a cooling jacket having an inner surface closely conforming to and conforming to the outer shape; 11. The core assembly of claim 10, wherein said destructible plastic layer comprises a thermoplastic material. 12. The core assembly of claim 11, wherein the thermoplastic material is polystyrene.