JPS6216865A - Production of hollow casting - Google Patents

Abstract

PURPOSE:To easily produce an internally hollow casting by executing pressure casting while a solid material which gasifies at a prescribed temp. is held coated with a porous material then heating the casting to the temp. above the prescribed temp. CONSTITUTION:The porous body 1 consisting of an alumina short fiber molding, etc. the solid material 2 consisting of an epoxy resin, etc. having the desired hollow shape in the casting and a heat resistant metallic plate 3 are respectively prepd. and are disposed in a metallic mold 5. After the melt of an Al alloy 8 is poured into the mold, the high-pressure casting is executed by a pressing punch 6. The casting after solidification is taken out of the mold 5 and a vent passage 10 is worked. The casting is then subjected to a heat treatment at the prescribed temp. to gasify the solid material 2 and to form the cavity part having the same shape as the shape thereof. The casting is in succession machine by which a product piston is obtd. The casting having the cavity part of an optional shape in the inside is easily produced by the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a hollow casting having a cavity (hollow part) formed therein for purposes such as heat insulation, such as heat insulating screws 1 to 1 for deep-pil engines. This relates to a method of building A.

BACKGROUND OF THE INVENTION In recent years, in diesel engines, in order to raise the temperature of the combustion chamber of the engine to improve fuel efficiency and to prevent incomplete combustion at the initial stage of engine startup, it has been considered to make the top surface of the piston insulated.

As a right-handed means to insulate the top surface of the piston, a cavity is formed directly below the top surface of the piston, and the cavity is used to insulate the top surface. A method is known in which the material is made of a heat-resistant material. Specifically, a method is known 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. ing. However, with this method,
The top surface material and piston base material must be machined in advance, such as holes and screws, and bolting is also required, resulting in low productivity and high costs. There is also the problem that when the piston operates, the base material, especially the bolt hole part, creeps and deforms, causing the heat-resistant material on the top surface to deform.
The problem is that effective bonding strength between the base materials cannot be obtained.

Therefore, the top heat-resistant material can be firmly bonded to the base material,
Moreover, there is a strong desire to develop a method for manufacturing a piston with a heat-insulating cavity just below the top surface without causing high cost or a decrease in productivity. One such method is to apply the casting method, in which the top heat-resistant material is held together by the casting while casting the piston base material, and a cavity is left directly below the top heat-resistant material. Conceivable. In this case, the casting should be carried out smoothly,
Moreover, in order to prevent the occurrence of casting defects and to refine the structure of the piston base material, it is considered optimal to apply a pressure casting method such as a so-called high-pressure casting method as the casting method.

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. Another method has 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 As mentioned above, when high pressure casting is applied using a sand core, the molten metal is impregnated into the core due to the high pressure applied to the molten metal.
As a result, it becomes difficult to remove core sand from within the casting. 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 molten salt core is used, There is a problem that the core is prone to cracking.

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 generates gas at a heating humidity lower than the melting point of the casting base metal. A solid material to be oxidized is made in the shape of the cavity, and the solid material is placed in a mold while being covered with a porous material that is stable against the molten base metal, and the molten base metal is poured into the mold. A casting is created by casting the solid substance in hot water and pressure casting, and then the casting is heated at a temperature lower than the melting point of the base metal and higher than the gasification temperature of the solid substance to form the solid substance. This method is characterized by gasifying a substance and producing 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 disperses into the molten base metal, causing casting defects such as blowholes and cavities.
In addition, the cavity shape cannot be maintained against the pressure applied to the molten metal, making it impossible to obtain a cavity of the desired shape in the final product casting.

However, in the method of the present invention, since the solid material is covered with a porous material, the poured molten base metal does not immediately come into contact with the solid material. That is, a pressure is applied to the molten base metal to impregnate the porous body, and the molten base metal passes through the voids in the porous body and comes into contact with the solid substance for the first time. 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 a solid substance is so much that -L rises u'? J'', therefore, the solid material is prevented from becoming a scum due to combustion, sublimation, evaporation, or decomposition.If pressurized pressure is applied, the molten base material passes through the voids of the porous body and forms the solid material as described above. However, in pressure casting such as high-pressure casting, the contact between the molten base metal and the mold surface is very good due to the pressure, so the molten base metal rapidly melts. Therefore, even if gas is generated from the contact area due to contact between the base metal and the solid substance, it will not be dispersed into the base metal, thereby preventing casting defects from occurring in the casting. pressurize vi
As the molten base metal is rapidly cooled by the process, even if the molten base metal passes through the porous body and comes into contact with the solid material, there is a period during which the solid material is at or above its gasification temperature at the contact area. The period of time is only extremely short, and therefore the amount of gas generated at the contact portion is not so large, which also contributes to the prevention of casting defects.

Furthermore, as the molten base metal is rapidly cooled and solidified, the amount of base metal that communicates with the porous body and penetrates into the solid material is extremely small, so the shape of the part that should become a cavity can be changed quickly. will essentially be retained.

In this way, pressurize Vt? If the casting made by step i and step 1q is removed from the mold and heated at a temperature lower than the melting point of the base material and higher than the gasification temperature of the solid material, the solid material will be stubbed out by combustion, sublimation, evaporation, or decomposition. The solid substance will be oxidized and 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, it is usually good 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 is in contact with the mold surface during casting, Since that portion is exposed to the outside of the casting, and therefore the exposed portion serves as a gas vent passage, there is no need to form a gas vent passage again after casting.

In this manner, it is possible to form a casting having a cavity substantially corresponding to the color dimension of the solid material in the portion of the solid material placed during casting.

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, increasing durability. It plays a role in improving people.

Note that the process of finally gasifying and removing the solid substance by combustion, sublimation, evaporation, or decomposition can be performed simultaneously 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, which is solution treatment, quenching, and subsequent stabilization treatment, but this treatment can gasify and remove solid substances. 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 an insulating piston as shown in FIG. 1, a porous body as shown in FIGS. 2 to 4], a solid substance 2, and a heat-resistant metal plate 3 are prepared in advance, and Combine as shown in Figure 5.

The solid substance 2 may be a substance that maintains a solid state 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. Either an organic material or an 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. Inorganic materials include, for example, 5802.5n8r4, but are of course not limited to these. This solid substance 2 has a cavity 4 to be finally formed (see Fig. 1).
For example, it is formed into a disk shape so as to correspond to the shape of .

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. This porous body 1 desirably has a low thermal conductivity so as to prevent the humidity of the solid substance from increasing as much as possible during pouring of the base metal molten metal.
In this sense, it is preferable to use a ceramic porous body, such as a short fiber molded body of alumina or silicon nitride, and it is also possible to use a metallic porous body such as a stainless steel fiber molded body, but it is limited to these. Of course, it may not be possible. The porous body 1 is basically used to prevent the molten base metal from coming into direct contact with a solid substance when pouring the base metal, and from that point of view, the volume ratio is 5%.
The above is desirable; on the other hand, if the volume fraction is too high, it becomes difficult to form a composite with the base metal, so the volume fraction is preferably 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, and it is sufficient to cover the solid substance 2 so that the molten base 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. 1, one side of the solid material 2 is covered with the heat-resistant metal plate 3 and does not come into contact with the base metal, so the remaining surface except for that surface is covered with the porous material 1. a recess 1 into which the disc-shaped solid substance 2 is fitted so as to cover it;
It is sufficient to form A on one side.

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. In other words, 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 5LJS304, or JIS
5LIH heat-resistant steel, and even Fe such as Incoloy
Heat-resistant alloys (Fe-based superalloys, Ni-based heat-resistant alloys such as Inconel, Co-based heat-resistant alloys such as N1VCO (CO-based superalloys, JIS SCH cast steel, etc.) may be used. In the illustrated example, this heat-resistant metal plate 3 is formed by bending the periphery of a circular plate at approximately right angles to form four parts 3A, and further bending the tip 3C of the bent part 3B inward at right angles. It is made into a bent shape and is processed, for example, by hydroforming.

The solid material 2 and the porous body 1 are combined so as to be in contact with one side of the solid material 2 on the bottom surface of the recess 3A of the heat-resistant metal plate 3 having such a shape.

As described above, the porous body], solid substance 2, and 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 FIG. 6, 6 is a pressure punch, and 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 already mentioned, 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 metal molten metal 8 is pressurized using a pressure punch 6 or the like, the base metal melt 88 is impregnated into the porous body 1 by the pressurizing force, and that portion becomes the composite part 9.

At this time, the base material molten 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 the solid substance may be entirely gasified at the contact area, but as already mentioned, the molten base metal 8 is rapidly cooled and solidified by the applied pressure. As a result, the gas is prevented from dispersing into the casting base material, and the occurrence of casting defects is prevented. Here, the degree of pressurizing force is not particularly limited, but it can be used to prevent the occurrence of shrinkage cavities, etc., to make the casting structure finer, and to improve the contact state between the mold 5 and the base metal molten metal 8 for rapid cooling and solidification. In order to promote this and to sufficiently impregnate the molten base metal 8 into the porous body 1, it is desirable that the pressing force be about 300 kmcm or more. Further, as the pressure casting method, in addition to the high pressure casting method in which pressure is applied using a punch, a so-called Gui 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 became a composite part with the base material, and the casting for the insulating piston, in which the solid substance 2 and the heat-resistant metal plate 3 were surrounded by the base material 12 such as an aluminum alloy, was taken out from the mold 5. The state is shown in FIG.

Next, in the case of the adiabatic piston casting shown in FIG. temperature, evaporation temperature or decomposition temperature). If J is done in this way, the solid substance will be gasified and that part will become empty 1fil14. After this, appropriate machining is performed as necessary to form the gas vent passage 10 with, for example, a screw 11.
If it is filled with a similar material, an adiabatic piston as shown in FIG. 1 can be obtained.

When making automobile pistons from aluminum alloy castings, it is common to carry out T7 treatment after casting. There is no need for additional heating.

As shown in FIG. 1, the heat-insulating piston obtained as described above has a top surface formed of a heat-resistant metal plate 3, and
A heat insulating cavity 4 is formed directly below the heat insulating cavity 4, and the periphery and lower side of the heat insulating cavity 4 are reinforced with a metal-porous composite part 9.

Here, the bent parts 3B, 3 around the heat-resistant metal plate 3
In the portion 3D surrounded by C, the porous body 1 is
The base material molten metal 8 that has passed through the base metal enters, and therefore the heat-resistant metal plate 3 is firmly held in that part.

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.

Example [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 key density of 0.17 g/CC was used, and its dimensions were an outer diameter of 70.2 mm, a total thickness of 3 Q mm,
The diameter of the recess 1A was 6Qmm, and the depth of the recess 1A was 1Qmm. Epoxy resin is used as the solid substance 2, and its diameter is 5
Qmm, and the thickness was 1Qmm. Further, as the heat-resistant metal plate 3, a 4 mm thick stainless steel plate of 5US304 which had been hydroformed was used, and its outer diameter was 83 mm, the height was 15 mm, and the inner diameter of the opening end of the recess 3A was 7 Q mm.

These were combined as shown in FIG. 5, placed in a mold 5 as shown in FIG.
, 2% Cu - 1.0% Auxiliary - 2% Ni - 0.3% Fe) was poured into the molten metal 8, and then the pressure punch 6
High-pressure casting was performed by applying a pressure of g/ci.

The applied pressure was maintained until the molten aluminum alloy completely solidified. After solidification, the casting was taken out of the mold, a gas vent passage 10 with an inner diameter of 3 mm as shown in Fig. 7 was formed by machining, and then T7 heat treatment (solution treatment 490'CX 4 hours, aging treatment 220'CX 8 hours) was performed. When we examined the casting after this heat treatment, we found that the epoxy resin (solid substance 2
) was completely decomposed and vaporized, and it was confirmed that a cavity 4 substantially corresponding to the original shape and dimensions of the epoxy resin was formed inside the piston.

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.

Furthermore, instead of the epoxy resin as the solid substance 2, a piece of wood impregnated with polyester resin, a compression molded product of phenol resin and sawdust, and silicone rubber were used, and pistons were manufactured under the same conditions and in the same method as described above. A piston having a cavity substantially similar to the piston shown in FIG. I was able to Furthermore, when 5e02 and SnBr4 are used instead of 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. It was possible to manufacture a piston with

[Example 2] In manufacturing a heat insulating piston as shown in Fig. 8,
A stainless steel short fiber molded body having the shape and dimensions as shown in FIGS. 9(A) and (B) was used as the porous body 1, and an epoxy resin having the shape and dimensions as shown in FIG. 10 was used as the solid substance 2. Furthermore, as the heat insulating metal plate 3, FIG. 11(A), (
Using 5US304 stainless steel plates having dimensions and shapes as shown in B), these plates were assembled as shown in Fig. 12 and placed in a high-pressure casting mold 5 as shown in Fig. 13. A piston using JIS AC8A alloy as a base material was manufactured in the same manner as described above. The stainless steel short fiber molded body has a unit fiber shape of 44 μm x 55 μm x 3 mm.
A molded body having a bulk density of 2.36 g/CC was used. 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 was confirmed that it exhibits excellent durability due to the composite reinforced structure around the cavity. 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 startup to high-load operation. Improvements in fuel efficiency have also been achieved, making it clear that the piston is extremely superior as a piston for diesel engines.

[Example 3] Next, an example will be described in which a hollow casting other than a piston, that is, a casting as shown in FIG. 14 was manufactured.

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. The mold is placed in a high-pressure casting mold 5 as shown in FIG. 17 so that it is in contact with the bottom surface of the mold, and 550°C molten Zn metal 8 is poured into the mold, followed by high-pressure casting by applying a pressing force of 500 kgZcd. As shown in FIG. 18, a casting was produced in which the part of the alumina short fiber porous corpus luteum 1 became the composite part 9. Note that the first
In Fig. 8, 13 is a Zn base material. The obtained casting was heated and held at 400'C in the atmosphere for 3 hours.

As a result, the acrylic resin as the solid material 2 was completely decomposed and vaporized to obtain a casting (FIG. 14) in which the inside was hollow and the periphery of the hollow part 4 was compositely reinforced.

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 at the same time as forming the cavity. 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 the drawing]

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, 3 is a perspective view showing a 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;
Fig. 5 is a vertical cross-sectional view showing the assembled state of each member shown in Figs. 2 to 4, and Fig. 6 is a schematic diagram showing the situation during pouring of the molten base metal in the manufacturing process of the piston shown in Fig. 1. FIG. 7 is a vertical cross-sectional view showing the state of the piston shown in FIG. 1 in the manufacturing process before removing the post-casting material. 8th
The figures show other examples of heat insulating pistons as hollow castings produced by the method of the present invention.
(B) is a diagram showing a porous body used for manufacturing the piston of FIG. 8, (△) 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 screws 1 to 1 in Fig. 8, and Fig. 11 (A>
, (B) are views showing the heat-resistant metal plate used for manufacturing the piston shown in FIG. 8, (A) is a perspective view thereof, (B) is a longitudinal sectional view, and FIG. A vertical cross-sectional view showing the assembled state of each member shown in the figure, Figure 13 is the screw in Figure 8]
・It is a vertical cross-sectional view schematically showing the situation during pouring of molten base metal in the manufacturing process of . FIG. 14 is a longitudinal sectional view showing another example of a hollow casting manufactured by the method of the present invention, and FIG.
The figure shows the solid material (Fig. 14) used for manufacturing hollow castings.
16 is a vertical cross-sectional view of the solid material shown in FIG. 15 covered with a porous material (alumina short JA fiber molded product), and FIG. 17 is a vertical sectional view of the solid material shown in FIG. 14. Figure 18 is a vertical cross-sectional view schematically showing the situation during the pouring of molten base material during the manufacturing process of hollow castings. It is a vertical cross-sectional view showing the situation. 1... Porous body, 2... Solid substance, 4... Cavity part, 8... Molten base metal.

Claims (5)

[Claims] (1) When casting a hollow casting with a cavity inside 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 made in the shape of the cavity. Then, the solid substance is placed in a mold while being covered with a porous material that is stable against the molten base metal, and the molten base metal is poured into the mold and pressure cast to form the solid substance. A hollow material having a cavity inside is formed by creating a casting in which a substance is cast, 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. A method for producing a hollow casting, characterized by producing a casting. (2) The method for manufacturing 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 made of a substance whose melting point is higher than the temperature of the base metal molten metal during pouring. (4) The method for producing a hollow casting according to claim 1, wherein the hollow casting is a casting for a heat insulating member with a cavity as a heat insulating part. (5) The method for manufacturing a hollow casting according to claim 1, wherein the hollow casting is an insulating piston in which a cavity immediately below the top surface is a heat insulating part.