Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2000-12-15
2002-07-23
Lin, Kuang Y. (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S125000, C164S126000, C164S312000, C164S348000
Reexamination Certificate
active
06422294
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a casting apparatus and a casting method for cast-molding a cylinder head of an engine.
BACKGROUND ART
As is generally known, a cylinder head of an engine for an automobile engine or the like is provided with paths having complex shapes, such as air-supply and exhaust ports to a cylinder section, paths for engine cooling water (water jackets) and paths for engine oil (oil jackets), and also contains plug holes for ignition plugs corresponding to the number of cylinders and a number of bolt holes used at the time of assembling to a cylinder body; therefore, it has a complex shape as a whole which makes it difficult to apply machining processes such as cutting process, etc., and normally, its base material is therefore obtained as a cast product using an aluminum alloy, etc. as its material.
With respect to a casting method for cast-molding such a cylinder head, a so-called low-pressure casting method has been known in which molten metal inside a stoke is raised by pressing the surface of the molten metal inside a crucible by using compressed air, etc. so that the molten metal thus raised is supplied to a casting mold cavity to be cast (see, for example, Japanese Patent Laid-Open Publication No. 1-53755. In this low-pressure casting method, since the molten metal is pressurized by compressed air, etc., stable high-quality cast products can be obtained, and since virtually no or very little so-called feeder head is required in this method, it is possible to improve the yield of the material to a great degree; thus, this method has various advantages.
Here, in the case when gas such as air is contained in a casting mold cavity to which molten metal is injected to fill, such residual gas inside the cast product tends to cause cast defects such as “gross porosity”, etc. In order to prevent the occurrence of such cast defects, it has been well known that an effective method is to give directivity to the cooling process of the molten metal after the casting process so as to allow solidification to start at a portion as far as possible from the gate. By cooling and solidifying the molten metal under such directivity, the residual gas inside the casting mold cavity is gradually driven to the gate side, and finally comes to reside in the gate portion, and in this state, the solidification can be finished. Since the gate portion is cut and removed as a waste portion after completion of the casting process, the possibility of residual gas inside the cast product as it is can be reduced correspondingly, and it becomes possible to effectively reduce the generation of cast defects.
In particular, in the above-mentioned low-pressure casting method, the gate is often formed on the lower mold side of the upper and lower molds, and in this case, gas residing inside the cavity filled with the molten metal is generally allowed to rise to the upper mold side that is far from the gate; therefore, it is essential to carry out the cooling process of the molten metal with directivity in such a manner that cooling of the molten metal is allowed to gradually proceed from the upper mold side farthest from the gate.
Moreover, when the molten metal inside the casting mold cavity is cooled and solidified, the outer side of the casting mold cavity closer to the casting mold surface is generally more susceptible to cooling than the center side thereof due to natural heat radiation outward from the casting mold; therefore, gas tends to reside on the center side of the casting mold cavity. For this reason, with respect to portions on the center side and portions on the outer side of the casting mold cavity as well, it is preferably to carry out the cooling process of the molten metal with directivity in such a manner that cooling of the molten metal is allowed to gradually proceed from the portions on the center side.
In other words, generally in the casting process, in order to improve the productivity, etc., a cooling process is prepared so as to accelerate the solidification of the molten metal upon solidifying the molten metal after the casting process; and in this cooling process, it is essential not only to simply increase the solidifying rate, but also to carry out a cooling process with the above-mentioned directivity.
As described above, in addition to air-supply and exhaust ports, the cylinder head of an engine is provided with passage sections such as the water jackets serving as paths for engine cooling water and the oil jackets serving as paths for engine oil. Therefore, in the case when such a cylinder head is cast-molded, cores corresponding these passage sections are assembled in the casting mold and casting is carried out therein.
When these cores are assembled inside the casting mold, core prints are placed at the ends of each core, and the core is generally assembled in the casting mold through these core prints. Here, in the present specification, “core print” includes to any of those installed integrally with the core main body and those formed on a separate member and used in combination with the core main body.
Among the above-mentioned passage sections, the water jackets and oil jackets are normally placed at parallel upper and lower positions close to each other, after predetermined path cross-sectional areas have been provided respectively within a limited space in the cylinder head.
Therefore, when cores for these two types of jackets are assembled in the casting mold, it is essential to maintain the distance between the axes of the two cores as accurately as possible so as to keep the thickness between the two types of jackets properly.
However, since these two types of jackets are installed in a manner so as to extend virtually over the entire length of the cylinder head in the length direction, the cores have considerably elongated shapes. Therefore, in the case when these cores are respectively assembled in the casting mold independently, it is difficult to stably maintain the distance between the axes of the two types of cores at a fixed value. Moreover, this case results in an increase in the number of the core assembling processes, and also makes the assembling device for the cores more complex, which causes disadvantages in reducing the production costs.
In particular, an arrangement has been proposed in which at least one portion of a casting mold face corresponding to the side face of the cylinder head is formed by an inner side face of a movable side mold that is allowed to slide in a direction (lateral direction) orthogonal to the mold-closing direction of the upper and lower casting molds (for example, Japanese Patent Laid-Open Publication No. 1-53755). However, in the case when such an arrangement is adopted, after the lower-side water jacket core has been set in the lower mold, the upper-side oil jacket core has to be set in the above-mentioned movable side mold.
However, this case raises a problem in which, since a portion of the casting mold that supports the sliding operation of the side mold is subjected to abrasion due to repeated sliding movements, it is difficult to maintain the distance between the axes of the two cores at a fixed value in a stable manner.
Moreover, in order to assemble the lower-side water jacket core of the two types of cores in the lower mold core print stopping portions are formed in portions of the casting mold corresponding to core prints on the two ends of the water jacket core, and engaging sections that engage the core print stopping portions are formed in the respective core print sides; thus, positioning and securing operations are generally carried out by allowing the engaging sections to engage the corresponding core print stopping portions.
However, in such a conventional arrangement, since the respective engaging sections are set in their shape and dimension so as to engage the core print stopping portions in a manner so as not to move in any directions in order to prevent positional offsets of the core, the core is secured in a completely rigid manner by the core print portions on t
Matsubayashi Nobuyuki
Murata Akira
Nakano Akihiro
Nozaki Tomoyuki
Shouju Takayuki
Lin Kuang Y.
Mazda Motor Corporation
Nixon & Peabody LLP
Studebaker Donald R.
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