JPH0236350B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a cavity (hollow part) for purposes such as heat insulation, such as a heat insulating piston for a diesel engine.
The present invention relates to a method of manufacturing a hollow casting having a hollow casting formed inside the hollow casting.

BACKGROUND OF THE INVENTION In recent years, in diesel engines, in order to increase the temperature of the combustion chamber to improve fuel efficiency and to prevent incomplete combustion in the early stages of engine startup, it has been considered to insulate the top surface of the piston.

An effective means for insulating the top surface of the piston is to form a cavity directly below the top surface of the piston and use that cavity to insulate the top surface. A method is known in which it is made of heat-resistant material. Specifically, there is a method in which the top surface is formed of a heat-resistant material made of a superalloy such as Inconel, a cavity is provided between the top heat-resistant material and the piston base material, and the two are bolted together. Are known. However, with this method, it is necessary to machine the top surface material and the piston base material in advance, such as drilling holes and threading, and also requires bolting, resulting in low productivity and high cost. There is also the problem that when the piston operates, the base metal, especially the bolt hole portion, undergoes creep deformation, making it impossible to obtain effective bonding strength between the top heat-resistant material and the base metal.

Therefore, it is possible to firmly bond the top heat-resistant material to the base material, and it is also possible to manufacture a piston with a heat-insulating cavity directly below the top surface without increasing costs or reducing productivity. Development of a method is strongly desired. One such method is the cast-in casting method, in which the top heat-resistant material is held together by the cast-ins during casting of the piston base material, and a cavity is left directly below the top heat-resistant material. Possible applications. In this case, it is best to apply a pressure casting method such as the so-called high-pressure casting method to ensure smooth casting, prevent casting defects in the piston base material, and refine the structure. Conceivable.

By the way, a common method for forming a cavity inside a casting is to cast a sand core such as a shell core, and then take out the core sand from inside the casting. A method has also been adopted in which a core made of a material that can be easily dissolved in a solvent, such as a salt core, is used for casting, and the core is eluted and removed after casting.

Problems to be Solved by the Invention When a high-pressure casting method is applied using a sand core as described above, the molten metal is impregnated into the core due to the high pressure applied to the molten metal, and as a result, the core sand is removed from the casting. It becomes difficult to remove. In addition, when a salt core is used, the same problem occurs when a compression molded salt core is impregnated with molten metal due to high-pressure casting, whereas when a salt core is melted and solidified, There is a problem that cracks easily occur in the child.

Therefore, conventionally, it has been extremely difficult to form a cavity of an arbitrary shape inside a casting by a pressure casting method such as a high-pressure casting method.

The present invention has been made against the background of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing a casting having an internal cavity, such as an insulating piston, without any trouble by pressure casting without causing the above-mentioned problems. The purpose is to

Means for Solving the Problems The method of the present invention, when casting a hollow casting having an internal cavity by pressure casting, maintains a solid state at room temperature and at a heating temperature lower than the melting point of the base metal of the casting. A solid substance to be gasified is prepared in advance in the shape of the cavity, and the solid substance is placed in a mold with a porous material that is stable against the molten base metal, and the molten base metal is placed in the mold. A casting in which the solid substance is cast is created by pouring molten metal into the metal and pressurizing it, and then heating the casting at a temperature lower than the melting point of the base metal and higher than the gasification temperature of the solid substance. The method is characterized in that the solid substance is removed by gasification to produce a hollow casting having a cavity inside.

Here, the solid substance that gasifies at a heating temperature lower than the melting point of the casting base metal means a solid substance that burns, sublimates, evaporates, or decomposes at that heating temperature. Further, as the porous body, a substance having a melting point higher than the molten metal temperature of the base metal at the time of pouring (therefore, the pouring temperature) is usually used.

Function: As described above, the method of the present invention uses a solid substance that remains solid at room temperature and gasifies at a heating temperature lower than the melting point of the casting base metal, and is shaped into the shape of the cavity to be finally formed. The solid material is shaped, and the solid material is placed in a mold with the base material covered with a stable porous material, and a molten base material such as an aluminum alloy is poured into the mold, followed by pressure casting.

If the solid material is not covered with a porous material and the high-temperature base metal is poured into it, the solid material will rapidly rise in temperature due to contact with the base metal and immediately burn, sublimate, evaporate, or It decomposes and gasifies, and the gas is dispersed into the molten base metal, causing casting defects such as blowholes and cavities.It also becomes impossible to maintain the cavity shape against the pressure applied to the molten metal, resulting in It becomes impossible to obtain a cavity with the shape of .
However, in the method of the present invention, since the solid material is covered with a porous material, the poured molten base material does not immediately come into contact with the solid material. That is, pressure is applied to the molten base metal to impregnate the porous body, and the molten base metal comes into contact with the solid substance only after passing through the voids within the porous body. In this way, the molten base metal does not come into direct contact with the solid substance during pouring, and the porous body interposed between the molten base metal and the solid substance is porous and therefore has high heat insulation properties. Sometimes the temperature of the solid material does not rise appreciably, thus preventing the solid material from becoming gasified by combustion, sublimation, evaporation or decomposition. If pressure is applied, the molten base metal may pass through the voids of the porous body and come into contact with the solid material as described above, but in pressure casting such as high-pressure casting, Since the contact between the molten metal and the mold surface is extremely good, the molten base metal is rapidly cooled and solidified. Therefore, even if gas is generated from the contact area due to the contact between the base metal and the solid substance, the molten metal will not be absorbed into the base metal. It will not be dispersed in the material and will prevent casting defects from occurring in the casting. In addition, as mentioned above, the molten base metal is rapidly cooled by pressure casting, so even if the molten base metal passes through the porous body and comes into contact with the solid material, the solid material will be gasified at the contact area. The period during which the temperature is higher than that is only an extremely short time, and therefore the amount of gas generated at the contact portion is not so large, which also contributes to preventing the occurrence of casting defects. Furthermore, as the molten base material is rapidly cooled and solidified, the amount of base material that communicates with the porous body and penetrates into the solid material is extremely small, so the shape of the part that will later become a cavity is substantially the same. It will be maintained as follows.

The casting obtained by pressure casting in this way,
After removing it from the mold, if it is heated at a temperature lower than the melting point of the base material and higher than the gasification temperature of the solid substance,
The solid substance is gasified by combustion, sublimation, evaporation, or decomposition and is dissipated to the outside through a predetermined gas vent passage, leaving the area where the solid substance was present as a cavity. Here, as the gas vent passage, normally it is sufficient to form a hole that communicates from the outside of the casting to the part of the solid material after casting, but if a part of the solid material comes into contact with the mold surface during casting, Since that portion is exposed to the outside of the casting and therefore serves as a gas vent passage, there is no need to form a gas vent passage again after casting.

In this manner, a casting can be obtained in which the portion of the solid material placed during casting has a cavity substantially corresponding to the shape and dimensions of the solid material.
Here, the porous material that covered the solid material becomes a layer that is composited with the base metal, and this layer has high strength due to the composite, so the area around the cavity is strengthened and the durability is increased. play a role in improving

Note that the process of finally gasifying and removing the solid substance by combustion, sublimation, evaporation, or decomposition can be performed concurrently with the heat treatment of the casting. That is, for example, in the case of an aluminum alloy piston casting, it is common to perform a so-called T7 treatment in which the piston is solution-treated, quenched, and then stabilized, but solid substances can be gasified and removed by this treatment. Therefore, in that case, there is no need to separately perform heating for gasification and removal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific configuration of the present invention will be described below, taking as an example a case where a heat insulating piston as shown in FIG. 1 is manufactured.

When manufacturing a heat insulating piston as shown in FIG. 1, a porous body 1 as shown in FIGS. 2 to 4,
A solid substance 2 and a heat-resistant metal plate 3 are prepared in advance, and these are combined as shown in FIG.

The solid substance 2 is a substance that remains solid at around room temperature and can be gasified by combustion, sublimation, evaporation, or decomposition when heated to a temperature lower than the melting point of the base metal to be cast, such as an aluminum alloy. Any organic material or inorganic material may be used. Examples of organic materials include resins such as epoxy resins and acrylic resins, wood or mixtures of wood and resins (e.g., wood chips impregnated with resin, or compression molded bodies of resin and sawdust), rubber materials (e.g. silicone rubber), and inorganic materials such as SeO ₂ ,
Examples include SnBr ₄ , but it goes without saying that the material is not limited to these. This solid substance 2 is formed into, for example, a disk shape so as to correspond to the shape of the cavity 4 (see FIG. 1) to be finally formed.

The porous body 1 is made of a material that is stable with respect to the base metal to be poured, such as a molten aluminum alloy, and preferably has a melting point higher than the pouring temperature. It is desirable that the porous body 1 has low thermal conductivity so that the temperature of the solid substance does not rise as much as possible during pouring of the molten base metal, and for that reason, it is preferable to use a ceramic porous body such as alumina or nitride. It is preferable to use short fiber molded bodies such as silicon, and in addition, metallic porous bodies such as stainless steel fiber molded bodies can also be used, but it is needless to say that the present invention is not limited to these. The purpose of the porous body 1 is to prevent the molten base metal from coming into direct contact with a solid substance during pouring of the base metal, and from this point of view, it is desirable that the volume ratio is 5% or more. If the ratio is too high, it will be difficult to form a composite with the base metal, so it is preferable that the volume ratio is 60% or less. Such a porous body 1 is created in advance in a shape so as to cover the solid substance 2.
However, it is not necessary to cover the entire outer surface of the solid substance 2;
In short, it is sufficient to cover the solid substance 2 so that the base metal molten metal does not come into direct contact with the solid substance 2 during pouring. In other words, when creating the heat-insulating piston shown in FIG.
A recess 1A into which the disk-shaped solid substance 2 is fitted may be formed on one side so that the porous body 1 covers the remaining surface except for that surface.

Although the heat-resistant metal plate 3 is not basically essential in the method of the present invention, it is necessary especially when a heat-insulating piston is targeted. That is, this heat-resistant metal plate 3 forms the top surface of the heat-insulating piston, and is made of a highly heat-resistant metal, such as stainless steel such as SUS304, JIS SUH heat-resistant steel, or Fe-based heat-resistant alloy such as Incoloy. (Fe-based superalloys), Ni-based heat-resistant alloys such as Inconel (Ni-based superalloys), Co-based heat-resistant alloys such as Nivco (Co-based superalloys),
Furthermore, JIS SCH cast steel or the like can be used. In the illustrated example, the heat-resistant metal plate 3 has a shape in which the periphery of a circular plate is bent approximately at right angles to form a recessed portion 3A, and the tip portion 3C of the bent portion 3B is further bent inward at a right angle. It is manufactured by, for example, hydroforming. Then, the solid material 2 and the porous body 1 are combined so that one surface of the solid material 2 is in contact with the bottom surface of the recess 3A of the heat-resistant metal plate 3 having such a shape.

As described above, the porous body 1, the solid substance 2, and the heat-resistant metal plate 3 are combined and placed at a predetermined position in a pressure casting mold, for example, a high pressure casting mold 5, as shown in FIG. That is, in the case of the illustrated heat-insulating piston, the heat-resistant metal plate 3 is arranged so as to be in contact with the bottom surface of the mold 5. In addition, in Fig. 6, 6 is a pressure punch,
7 is a knockout pin for taking out the casting.

Next, a casting base material molten metal 8 such as an aluminum alloy molten metal is poured into the mold 5. At this time, as described above, the base metal molten metal 8 does not come into direct contact with the solid substance 2, and therefore the solid substance 2 is not yet gasified by combustion, sublimation, evaporation, or decomposition.

Subsequently, when the base material molten metal 8 is pressurized using a pressure punch 6 or the like, the base material molten metal 8 is impregnated into the porous body 1 by the pressurizing force, and that portion becomes a composite portion 9. At this time, the molten base metal 8 that has passed through the voids inside the porous body 1 may come into contact with the solid substance 2 covered with the porous body 1, and some of the solid substance may be gasified at the contact area. As already mentioned, as a result of the molten base metal 8 being rapidly cooled and solidified by the applied pressure,
This gas is prevented from dispersing into the casting base material, and casting defects are prevented from occurring. Here, the degree of pressurizing force is not particularly limited, but it is necessary to prevent the occurrence of shrinkage cavities, etc., to refine the casting structure, and to
In order to improve the contact state between the base metal 8 and the base metal molten metal 8 to promote rapid cooling and solidification, and to sufficiently impregnate the base metal 8 into the porous body 1, the pressure should be approximately 300 kg/cm ² or more. is desirable. Further, as the pressure casting method, in addition to a high pressure casting method in which pressure is applied by a punch, a so-called die casting method can be applied, and depending on the shape of the casting, a centrifugal casting method can also be applied. Note that the applied pressure is maintained until the base metal molten metal 8 completely solidifies.

In this way, the porous body 1 forms a composite body 9 with the base material.
FIG. 7 shows a state in which a casting for an insulating piston, in which a solid substance 2 and a heat-resistant metal plate 3 are surrounded by a base material 12 such as an aluminum alloy, is taken out from a mold 5.

Next, in the case of the adiabatic piston casting shown in FIG. temperature, evaporation temperature or decomposition temperature). In this way, the solid substance will be gasified and that part will become a cavity 4
becomes. After this, if necessary, the piston is machined as required and the gas vent passage 10 is filled with, for example, a screw 11, thereby obtaining a heat insulating piston as shown in FIG.

Here, when making automobile pistons from aluminum alloy castings, it is common to perform T7 treatment after casting, but in that case, the solid substances can be gasified and removed by T7 treatment. There is no need to separately heat for gasification.

The adiabatic piston obtained as above is the first
As shown in the figure, the top surface is formed of a heat-resistant metal plate 3, and a heat-insulating cavity 4 is formed directly below it, and the surroundings and lower side of the heat-insulating cavity 4 are made of metal-porous material. This means that the composite part 9 of the body is strengthened.

Note that the base material molten metal 8 that has passed through the porous body 1 during pouring enters the portion 3D surrounded by the bent portions 3B and 3C around the heat-resistant metal plate 3, and
Therefore, the heat-resistant metal plate 3 is firmly held at that portion.

In the above example, an example of an adiabatic piston was explained, but it goes without saying that the method of the present invention can also be applied to other hollow castings.

Examples Example 1 In manufacturing a heat insulating piston as shown in FIG. 1, a porous body 1, a solid substance 2, and a heat-resistant metal plate 3 having shapes as shown in FIGS. 2 to 4 were prepared. As the porous body 1, an alumina short fiber molded body with a bulk density of 0.17 g/cc is used, and its dimensions are 70.2 mm.
mm, the total thickness was 30 mm, the diameter of the recess 1A was 60 mm, and the depth of the recess 1A was 10 mm. Epoxy resin was used as the solid substance 2, and its diameter was 60 mm and the thickness was 10 mm. In addition, as the heat-resistant metal plate 3, a 4 mm thick stainless steel plate of SUS304 formed by hydraulic pressure is used, and its outer diameter is 83 mm.
mm, height is 15mm, inner diameter of opening end of recess 3A is 70mm
And so.

These were combined as shown in Fig. 5, placed in a mold 5 as shown in Fig. 6, and aluminum alloy (JIS AC8A; Al-12%Si-1.2
% Cu - 1.0% Mg - 2% Ni - 0.3% Fe) was poured, and then a pressure of 500 kg/cm ² was applied using a pressure punch 6 to perform high-pressure casting. The applied pressure was maintained until the molten aluminum alloy completely solidified.
After solidification, the casting was taken out of the mold and a gas vent passage 10 with an inner diameter of 3 mm as shown in Fig. 7 was formed by machining, followed by T7 heat treatment (solution treatment at 490°C for 4 hours, aging treatment at 220°C for 8 hours). time) was applied. When we examined the casting after this heat treatment, we found that the epoxy resin (solid substance 2) inside had completely decomposed and vaporized, and a cavity 4 was formed inside the piston that substantially corresponded to the original shape and dimensions of the epoxy resin. It was confirmed that it was formed.

Thereafter, it was machined into a piston shape, and the gas vent passage 10 was filled with stainless steel screws 11 to finally obtain an adiabatic piston as shown in FIG.

Also, instead of epoxy resin as the solid substance 2,
A piston was manufactured using a piece of wood impregnated with polyester resin, a compression molded product of phenolic resin and sawdust, and silicone rubber under the same conditions and in the same method as described above, and the piston was substantially the same as the piston shown in Figure 1. It was possible to obtain a piston having a hollow portion. Furthermore, when SeO ₂ or SnBr ₄ is used instead of the epoxy resin as the solid substance 2, the former sublimes in the T7 treatment, and the latter evaporates in the T7 treatment, creating a cavity similar to the piston shown in Figure 1. We were able to manufacture a piston with

Example 2 In manufacturing a heat insulating piston as shown in FIG. 8, a short stainless steel fiber molded body having the shape and dimensions as shown in FIGS. 9A and B was used as the porous body 1,
In addition, an epoxy resin having the shape and dimensions as shown in FIG. 10 is used as the solid material 2, and a heat-resistant metal plate 3 is used.
As shown in Figure 11A and B,
Using SUS304 stainless steel plates, these
The components were combined as shown in the figure and placed in a high-pressure casting mold 5 as shown in FIG. 13, and a piston using JIS AC8A alloy as a base material was manufactured in the same manner as in Example 1. The stainless steel short fiber molded body used had a unit fiber shape of 44 μm x 55 μm x 3 mm and a molded body bulk density of 2.36 g/cc. In this case as well, as shown in FIG. 8, it was possible to obtain a heat insulating piston having a cavity 4 substantially corresponding to the original shape and dimensions of the epoxy resin.

Both of the heat-insulating pistons obtained in Example 1 and Example 2 have an extremely high degree of bonding between the top heat-resistant material (heat-resistant metal plate 3) and the base material, and have good heat insulation properties. It has been confirmed that the structure around the cavity has a composite reinforced structure, which provides excellent durability. In addition, when we conducted combustion characteristics tests, we found that the time and amount of incomplete combustion gas (smoke) was clearly reduced compared to conventional aluminum alloy pistons, from the time of startup to the time of high-load operation. Moreover, improved fuel efficiency was also achieved, making it clear that the piston is extremely excellent as a piston for diesel engines.

Example 3 Next, hollow castings other than the piston, that is, the 14th
An example in which a casting as shown in the figure was manufactured will be described.

A solid material 2 is obtained by molding acrylic resin into the shape and dimensions shown in FIG. 15, and this solid material 2 is covered with alumina short fibers as a porous body 1 as shown in FIG. is placed in the high-pressure casting mold 5 as shown in FIG.
High-pressure casting was performed by applying a pressing force of Kg/cm ² to produce a casting in which the alumina short fiber porous material 1 became a composite part 9 as shown in FIG. In addition, in FIG. 18, 13 is a Zn base material. The obtained casting was heated and held at 400° C. for 3 hours in the atmosphere. As a result, the acrylic resin as the solid substance 2 is completely decomposed and vaporized, and the inside is hollowed out, and the periphery of the hollow part 4 is compositely reinforced casting (No. 14).
Figure) was obtained.

Effects of the Invention As is clear from the above embodiments, according to the method of the present invention, it is possible to simply and easily produce a casting having a cavity of any shape inside, and also to form the cavity at the same time. The vicinity thereof can be strengthened as a composite part of the porous body and the base metal. Therefore, the method of the present invention is useful when applied to the manufacture of an insulated piston having a cavity immediately below the top surface.

[Brief explanation of drawings]

FIG. 1 is a cutaway perspective view showing a heat insulating piston as an example of a hollow casting manufactured by the method of the present invention, FIG. 2 is a cutaway perspective view showing a porous body used in manufacturing the piston of FIG. 1, FIG. 3 is a perspective view showing the solid material used in manufacturing the piston shown in FIG. 1, FIG. 4 is a cutaway perspective view showing a heat-resistant metal plate used in manufacturing the piston shown in FIG. 1, and FIG. Figures 2 to 4 are longitudinal cross-sectional views showing the assembled state of each member, and Figure 6 is a vertical cross-sectional view schematically showing the state of pouring the molten base metal in the manufacturing process of the piston shown in Figure 1. 7 are longitudinal cross-sectional views showing the state of the piston shown in FIG. 1 in the manufacturing process after casting and before removal of solid substances. FIG. 8 is a longitudinal sectional view showing another example of a heat insulating piston as a hollow casting manufactured by the method of the present invention, and FIGS. 9A and B show a porous body used in manufacturing the piston of FIG. 8. In the figures, A is a perspective view thereof, B is a longitudinal sectional view, FIG. 10 is a perspective view of the solid material (epoxy resin molded body) used for manufacturing the piston of FIG. 8, and FIGS. 11A and B are 8 is a diagram showing a heat-resistant metal plate used for manufacturing the piston of FIG. 8, A is a perspective view thereof, B is a vertical sectional view, and FIG. 12 is a combination of each member shown in FIGS. 9 to 11. FIG. 13 is a vertical cross-sectional view schematically showing the state of pouring molten base metal in the manufacturing process of the piston shown in FIG. 8. Fig. 14 is a longitudinal cross-sectional view showing another example of a hollow casting manufactured by the method of the present invention, and Fig. 15 is a perspective view of a solid material (acrylic resin molded body) used for manufacturing the hollow casting shown in Fig. 14. Figure 16 is a vertical cross-sectional view showing the state in which the solid material shown in Figure 15 is covered with a porous body (alumina short fiber compact), and Figure 17 is a molten base material in the process of manufacturing the hollow casting shown in Figure 14. FIG. 18 is a vertical cross-sectional view schematically showing the situation during pouring, and FIG. 18 is a vertical cross-sectional view showing the situation before solid material removal after casting in the manufacturing process of the hollow casting of FIG. 14. 1... Porous body, 2... Solid substance, 4... Cavity, 8... Molten base material.

Claims (1)

[Claims] 1. When casting a hollow casting having an internal cavity by pressure casting, a solid substance that remains solid at room temperature and gasifies at a heating temperature lower than the melting point of the casting base metal is used. The solid material is formed in the shape of the cavity in advance, and placed in a mold with the solid material covered with a porous material that is stable against the molten base metal, and the molten base metal is poured into the mold and heated. Creating a casting in which the solid substance is cast by pressure casting, and then heating the casting at a temperature lower than the melting point of the base metal and higher than the gasification temperature of the solid substance to gasify the solid substance. 1. A method for producing a hollow casting, comprising: removing the hollow casting by removing the hollow casting, and producing a hollow casting having a cavity inside. 2. The method for producing a hollow casting according to claim 1, wherein the gasification of the solid substance is combustion, sublimation, evaporation, or decomposition. 3. The method for producing a hollow casting according to claim 1, wherein the porous body is a substance having a melting point higher than the temperature of the base metal molten metal during pouring. 4. Claim 1, wherein the hollow casting is a casting for a heat insulating member in which the hollow part is a heat insulating part.
A method for producing a hollow casting as described in Section 1. 5. The method for manufacturing a hollow casting according to claim 1, wherein the hollow casting is an insulating piston in which a cavity directly below the top surface is a heat insulating part.