JPH07110404B2 - Antigravity casting method and apparatus using a thin shell mold supported by granules - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a high ability to withstand the stresses of mold removal and is used to counter-gravitate molten metal using a gas permeable thin investment shell mold that is supported in a granular support medium during the casting process. And a method and apparatus for casting.

[0002]

2. Description of the Related Art A method of casting a molten metal in a vacuum antigravity type using an air permeable (gas permeable) investment shell mold is disclosed in US Pat. No. 3,900,064, 4,34.
0,108, 4,532,976, 4,589,4
66 and 4,791,977.

To produce an air permeable refractory investment shell mold for use in such an antigravity casting method, first, a plurality of consumable (eg, meltable) prototypes of the article to be cast are prepared. The prototypes are then formed and then combined with the appropriate entry gate prototypes to form a prototype assembly (tree). (The prototype assembly is typically formed of a meltable wax.) The prototype assembly is then refractory slurry (refractory powder and a suitable binder solution that can be cured during the drying operation under ambient conditions. The mold assembly is coated with granular refractory material by coating (stucco) or sprinkling a relatively coarse refractory powder. Repeat this dipping and coating operation,
A multilayer refractory shell is formed having a thickness sufficient to withstand the stress exerted by subsequent prototype removal, firing and molten metal casting operations. In this way, the granular refractory material is exteriorly (invested) around the prototype assembly, and the exterior portion left after the prototype assembly is melted and removed is referred to as "investment shell mold" or "investment shell" or simply "shell mold". Or "shell".

More specifically, the prototype removal work has conventionally been carried out by heating in a steam autoclave. In that case, the above-mentioned exterior prototype assembly is put into a steam autoclave to be about 136.1 to about 178.1.
Heat to a temperature in the range of ° C (275-350 ° F) to melt and remove the prototype from the refractory shell. However, in the prior art, during the heating process in the steam autoclave, the refractory shell was damaged as a result of thermal expansion of the prototype (eg, wax) with respect to the refractory shell. Therefore, in the prior art, in an attempt to minimize damage such as cracking of the refractory shell during the steam autoclave heating process, the shell thickness is increased to increase the ability to withstand thermal stress as a result of thermal expansion. It was
However, unfortunately, increasing the wall thickness of the shell increases the consumption of refractory material to manufacture the shell mold and also increases the weight of the investment shell mold, resulting in a lower casting cost. Will rise sharply. Further, increasing the shell wall thickness also increases the time required for steam autoclave heating to remove the prototype assembly from the exterior prototype assembly to obtain the investment shell mold. Conventional investment shell molds typically used for antigravity casting of iron-based or other alloys according to the methods of the above-referenced patents have a wall thickness (mold wall thickness) of at least about 6.
It is manufactured to be 35 mm (about 1/4 inch).

The above US Pat. No. 4,791,977 discloses
It describes the stresses imposed on the refractory shell during vacuum antigravity casting of molten metal. That is, as described in the same patent, while an external vacuum is exerted around the shell mold during the casting process, the internal molten metal pressure is caused inside the shell by the molten metal filled therein. As a result, detrimental stresses are imposed on the shell. Such stress, coupled with the high temperature of the molten metal in the shell mold, causes displacement of the shell wall, penetration of the molten metal into the shell wall, leakage of molten metal from the shell, failure of the entire shell mold. May occur. These problems are especially likely when structural defects are present in the shell. The patent discloses a means of relieving such stresses imposed on the investment shell mold (ie a method of establishing a differential pressure between the internal mold filling passage and the vacuum chamber outside the shell mold).
However, the investment shell mold used in that patent still requires conventional wall thickness and strength to withstand stress during prototyping and molten metal casting operations.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art,
Its purpose is to improve the use of a refractory investment shell mold that is less likely to be damaged (for example, cracked) during operation such as prototype removal by a steam autoclave heating method, even though the wall thickness is significantly reduced. Anti-gravity casting method and apparatus.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is a method of casting molten metal in an antigravity manner, in which a consumable prototype of an article to be cast is heated. The prototype is sheathed with a multi-layer granular refractory mold material that is formed of a meltable material that expands when controlled to form a thin refractory shell having a thickness greater than 0 mm and not exceeding about 3.048 mm. And heating the sheathed prototype, for example in a steam autoclave, to remove the prototype from the thin refractory shell, thereby forming a mold cavity in the shell, the thin refractory shell having the desired After firing to impart mold strength, a refractory granular support medium is placed around the thin refractory material shell, and the mold cavity is placed below the lower molten metal insert located outside the granular support medium. To evacuate the mold cavity and to evacuate the mold cavity to compress the granular support medium around the shell to support the thin refractory shell against casting stress. The molten metal with the thin refractory shell still supported by the granular support medium and with the molten metal inlet communicating with the underlying molten metal source. Anti-gravity casting method which comprises upwardly anti-gravity suction into the evacuated mold cavity. Here, "evacuating" the mold cavity means decompressing and discharging the gas in the mold cavity.

The present invention is also an apparatus for casting molten metal in an anti-gravity type, comprising a refractory granular support medium disposed in a housing, and the granular support medium disposed therein. 0
a refractory investment shell having a mold cavity defined by a mold wall thicker than about 3.0 mm and not more than about 3.048 mm, and a particulate support medium for communicating between the mold cavity and a molten metal source thereunder. An externally located molten metal inlet, a vacuum source for evacuating the mold cavity, and around the shell to support the shell against casting stress while leaving the mold cavity evacuated. A movable wall or pressurizable air bag for exerting a pressure on the granular support medium to compress the granular support medium, and the mold to draw the molten metal upward into the evacuated mold cavity. The molten metal inlet is communicated with the molten metal source while the cavity is evacuated and the pressure is applied to the granular support medium. Providing anti-gravity casting apparatus consisting of a fit of the tube.

In the practice of the invention, thicker than 0 mm,
Contrary to previously recognized techniques, the use of thin wall refractory shell molds with wall thicknesses not exceeding about 3.048 mm is the result of the thin shell being more stressed by the expansion of the mold during the mold removal operation. It is based on the new knowledge that it has a high ability to withstand. That is, the present invention is based on the finding that the air permeability of a thin shell mold in which the wall pressure of the mold is reduced does not increase in direct proportion to the decrease in the wall pressure of the mold, but rather increases in an unexpectedly large ratio. It is based. For example, 0m
A thin shell mold having a wall thickness greater than m and not exceeding about 3.048 mm is more than twice the air permeability of a similar shell mold having a wall thickness twice that of the wall thickness, usually three times or more. It was found to have an air permeability of.

This increased permeability reduces the force exerted on the shell by increasing the amount of the outer surface portion of the initially melted prototype that penetrates into the shell wall during the prototype removal operation by the steam autoclave heating method. Was approved. In addition, the increased air permeability of the shell mold reduces the time required to remove the prototype by promoting steam penetration into the prototype surface during steam autoclave heating.

The use of a thin shell mold having a wall thickness of greater than 0 mm and not greater than about 3.048 mm in accordance with the teachings of the present invention also includes such a thin shell mold of the shell mold during evacuation of its mold cavity. It is based on the finding that by rigidly compressing the granular support medium around it it is possible to support it so that it can withstand the stresses acting on the shell mold during antigravity casting. For example, in one embodiment of the invention, a thin shell mold is supported in a loose (not tightly compressed, loosely held) granular support medium (eg, loose foundry sand) contained within a vacuum housing. The vacuum housing is evacuated and the pressure transmitting means is moved relative to the vacuum housing and the granular support medium to apply pressure to the granular support medium and compress the granular support medium around the shell mold. As such a pressure transmitting means, a movable wall of the vacuum housing for pressing the granular support medium can be used, the outer side surface of the movable wall is exposed to ambient pressure, and the inner side surface of the movable wall is moved. Exposing to a vacuum relative to the ambient pressure acting on the outer surface of the wall, thereby compressing the granular support medium around the shell mold to support the shell mold against casting stresses. You can Alternatively, the pressure transmitting means may comprise an air bladder disposed in contact with the granular support medium within a vacuum housing, the air bladder being pressurized when the mold cavity is evacuated. Can be compressed. Here, “relative vacuum” or “relative vacuum” means that in two spaces separated from each other by a surrounding wall, for example, the space inside the wall is relative to the pressure outside the wall (ambient). It means a state where the pressure is reduced. Therefore, there is a pressure difference between the two spaces.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the accompanying drawings, FIG. 1 shows a consumable prototype assembly 10 (since it is in the form of a tree, it is a "tree").
Also referred to as). A prototype assembly (hereinafter, also simply referred to as a “prototype”) 10 includes a cylindrical central rising passage forming portion 12 and a plurality of mold cavity forming portions 14.
And an introduction gate forming portion 16 connecting each mold cavity forming portion 14 to the central rising passage forming portion 12. The mold cavity forming portion 14 is shaped in the shape of the article or part to be cast and is spaced around the central upstanding passage forming portion 12 and along its length as shown. Has been done. Generally, each mold cavity forming portion 14 and its introduction gate forming portion 16 are formed.
Is injection molded and manually attached (eg, by wax welding or adhesive) to the riser channel forming portion 12. The rising passage forming portion 12 is formed by injection molding as a separate piece. Rising passage formation part 1
At the lower end of 2, a frustoconical refractory collar 18 is attached (for example by wax welding or adhesive) to the riser passage forming portion 12.

The prototype assembly 10 is preferably formed of a meltable solid (non-porous) material that expands when heated, as described below. Wax is a preferred material for the prototype assembly 10 because it is inexpensive and has predictable properties. Generally, the prototype wax melts in the temperature range of about 54.9 to about 66.1 ° C (about 130 to about 150 ° F). Importantly, the viscosity of the wax must be chosen to avoid cracking the shell mold 30 (FIG. 2) described below during the prototype removal operation (eg, 77.3 ° C.). The viscosity of the wax in should be less than 1300 centipoise). Urea resin can be used as a prototype material. Urea resin is about 113.7 to about 1
Melts in the temperature range of 30.5 ° C (about 235 to about 265 ° F).

In the practice of the invention, the prototype assembly 10
However, as long as it can be removed later by heating by a steam autoclave heating method or the like as described later, each part 12, 14, 16 of the prototype assembly 10 does not necessarily have to be formed of the same material.

Referring to FIG. 2, a thin air-permeable (gas permeable) multilayer fire-resistant shell mold (gas-permeable) is provided by coating the prototype assembly 10 with a multilayer fire-resistant material (mold forming material) 22 (investment). Below, "multilayer fireproof shell",
A “fireproof shell” or simply “shell” or “mold”) 30 is formed. This exterior (molding material) is a refractory material powder (eg, zircon, alumina, fused silica, etc.) in which the prototype assembly 10 is suspended in a binder solution, such as ethyl silicate or colloidal silica sol, and a small amount. It is performed by repeatedly immersing it in a refractory material slurry composed of an organic film forming agent, a wetting agent and a defoaming agent. After immersing the prototype assembly in the refractory slurry, each time,
Excess slurry is poured from the prototype assembly and the slurry coating coated on the prototype assembly is coated (stucco) or sprinkled with dry refractory particles. Suitable refractory materials for this stucco include granular zircon, fused silica, silica, and various aluminum silicates (mullite, fused alumina, etc.).

After each dipping and coating step, the slurry coating is cured using forced air drying or other means each time and either on the prototype assembly 10 or on the previously formed refractory layer. A refractory layer is formed on. The sequential steps of dipping, coating and drying are repeated until the multilayer refractory shell 30 having a desired wall thickness t is laminated around the mold cavity forming portion 14.

In accordance with the present invention, a shell forming process (ie, a shell forming process) is formed to form a multilayer refractory shell 30 having a maximum wall thickness t that does not exceed about 3.048 mm (about 0.12 in) around the mold cavity forming portion 14. , Dipping, coating and drying steps). As explained below, this wall thickness is
It has been found that the steam autoclave heating method exerts a surprising ability to absorb the stresses exerted on the shell during removal of the prototype. Generally, a multilayer refractory shell having a wall thickness not exceeding about 3.048 mm (about 0.12 in) is laminated with 4-5 layers of refractory material by repeating the dipping, coating and drying steps described above.

FIG. 3 shows the refractory shell 30 after the prototype has been removed by the steam autoclave heating method. More specifically, the refractory shell 30 includes a conventional steam autoclave 34 (e.g., a Leeds end blood hood).
It is inserted into a 286PT type steam autoclave sold by the company and heated. This heating removes the prototype assembly 10 leaving behind a thin wall refractory shell 30 having a mold cavity 36 connected to a central rise passage 37 via respective side entry gates 38. At this stage of the process, the upper and lower ends of the rising passage 37 are open.

During the steam autoclave heating operation shown in FIG. 3, the exterior prototype assembly 40 (multilayer refractory shell 30
The prototype assembly 10) (see FIG. 2), which has been packaged with, has a time sufficient to melt and remove the prototype assembly 10 from the refractory shell 30 from about 136.1 to about 178.1 ° C.
~ Steam at a temperature of about 350 ° F (steam pressure of about 5.
6 to about 7.7 kg / cm ² ). More specifically, in the initial stage of heating the steam autoclave,
The penetration of steam through the permeable refractory shell 30 forms a molten surface film on the prototype assembly 10. As explained below, the breathable refractory shell 30 has a surprising and unexpected ability to absorb most of this initial molten film, thereby
The expansion force of the prototype that would otherwise be exerted on the shell 30 can be reduced. Over time, the remainder of the prototype assembly 10 melts, most of it refractory shell 3
From 0 through the opening 18a of the collar 18.

As mentioned above, the wall thickness of refractory shell 30 is controlled in accordance with the present invention so that it does not exceed about 3.048 mm (about 0.12 in). The thickness of this shell is
Unexpectedly high air permeability for absorbing the initial molten thin film of the prototype assembly during steam autoclave heating (eg, adopted by the Investment Casting Society 104
It was found to exhibit a temperature of 6 ° C. (as measured by the well-known nitrogen permeability test). For example, about 990.1 °
C. (about 1800.degree. F.) with a wall thickness of about 3.
The refractory shell 30 having 048 mm (about 0.12 in) (4 layers of refractory material) has twice the wall thickness (ie, 6.096 mm wall thickness) as measured by the nitrogen permeability test above. It was found that the same shell composed of 8 layers of refractory material exhibits air permeability more than twice as much as the air permeability exhibited by the same shell. Specifically, a fire-resistant refractory shell 3 with a wall thickness of about 3.048 mm
The air permeability of 0 is only 316-4 while the air permeability of a similar shell having a thickness of 6.096 mm is only 80-120 ccN ₂ / min (nitrogen permeability 80-120 cc per minute).
It was 68 ccN ₂ / min (measured value).

The fired refractory shell 30 is formed in accordance with the present invention to exhibit at least about three times the air permeability of a similar shell having twice the wall thickness. As already mentioned, the thin fire-resistant shell 30 (thickness of about 3.048 mm
This unexpectedly high air permeability enhances the ability of the shell 30 to absorb the initially molten thin film formed in the prototype assembly 10 during steam autoclave heating, and the refractory shell 30
The stresses that would normally be applied to the shell as a result of the thermal expansion of the prototype assembly 10 relative to the shell can be reduced.
In the idea of the prior art, it is common sense to increase the thickness of the shell in order to withstand such stress when melting and removing the prototype assembly. It has been found that by reducing the wall thickness, it is possible to remarkably improve the response to the steam autoclave heating operation, and prevent the distortion and damage such as cracks of the shell. The better penetration of steam through the highly permeable shell 30 and the resulting faster heating of the prototype assembly 10 not only prevents distortion and damage to the shell, but it also allows the steam autoclave to heat the prototype assembly. The removal time is significantly reduced.

Further, as will become apparent from the examples set forth in Table I below, since a thin refractory shell 30 is used, the amount of refractory particulate material required to form refractory shell 30 is substantial. Be reduced to Therefore, the cost of cast products is also greatly reduced. For example, cost savings of 40-75% are achieved by saving on the amount of refractory used. In addition, the use of a thin shell mold allows the mold cavity forming portion 14 and the inlet gate 16 to be closely spaced to increase the number of castings that can be made in one mold. Therefore, the total output can be increased at low cost.

The shell is heated in a steam autoclave and then fired for 90 minutes at a temperature of about 1800 ° F (990.1 ° C).

In Table I, certain parts (eg, automobile rocker arms, window latches or cleats) were cast using a thick shell (ie, 6.35 mm thick shell), and the book. Comparative data on so-called load factors (i.e., the number of parts that can be cast per shell mold) compared to casting with the thin shell of the invention are posted. Thick shell (slurry dipping / coating process repeated 9 times), thin shell (slurry dipping / coating process 4-5)
Repeated times also using the same slurry and stucco material in a similar manner (eg, fused silica 1 with a 200 mesh size).
5.2% by weight and zircon having a particle size of 325 mesh 56.
9% by weight and colloidal silica sol (binder) 17.
It was immersed in an initial slurry containing 8% by weight and 10.1% by weight of water, and thereafter, Margrain® M-47.
15.1% by weight mullite, 25.2% by weight fused silica having a particle size of 200 mesh, 35.3% by weight zircon having a particle size of 600 mesh, and ethyl silicate (binder) 15.
After being dipped in a slurry containing 6% by weight and 8.8% by weight of isopropanol, zircon having a particle size of 100 mesh and Margrain M-having a particle size of 60 mesh were used each time.
47 mullite and 25 grain size Margrain M-
47 mullite). The shells were heated in a steam autoclave and then calcined in the manner described above.

Table I also shows the weight of the thick shell (ie wall thickness 6.35 mm) used to cast the above parts and the thin shell of the invention (ie wall thickness 2.54 mm). Weight comparisons are also made.

[Table 1] Table I Shell load factor and final refractory material weight Standard shell Thin shell Standard shell Thin shell load factor Load factor Exchange weight / parts Exchange weight / parts Parts Q'ty / shell Q'ty / shell rate% oz rate% oz Rocker 8ar × 13hi 12ar × 16hi 6.3 1.5 Arm 104 / Shell 192 / Shell 85 76 Window latch 12ar × 8hi 14ar × 10hi 6.7 1.5 96 / Shell 140 / Shell 46 63 Cleat 10ar × 24hi 12ar × 26hi 2.8 1.3 204 / Shell 312 / Shell 30 54 Note: In the above table, “quantity / shell” is per shell.
The number of parts to be molded, "weight / part" is per part
Weight (oz), “ar” is the mold key around the riseway.
The number of cavities, “hi”, is the mold key along the rising path.
It means the number of cavities.

As can be seen from Table I, the thin shell mold of the present invention significantly increases load factor and significantly reduces the amount of refractory material needed to form the shell. Moreover, these are achieved while maintaining the same or higher performance as compared with the conventional shell mold with respect to distortion and damage of the shell mold during heating by the steam autoclave.

According to one embodiment of the present invention, as shown in FIG. 4, the molten metal is subjected to a differential pressure (vacuum) antigravity type thin shell mold 30 (the shell mold is heated to a temperature of about 990.1 ° C. After firing in), cast in. In particular, the thin shell mold 30 is supported within a loose (not tightly compacted) refractory particulate support medium 60 contained within a vacuum housing. The vacuum housing 70 has a bottom support wall 72, an upstanding side wall 73, and a movable top end wall 74, defining a vacuum chamber 76 therein. Bottom support wall 72 and upright side wall 73
Is made of an impermeable material such as metal, and is movable top end wall 74.
Is made of a gas permeable (porous) plate 75. A vacuum plenum 77 that defines a vacuum chamber 78 is coupled to the air permeable plate 75 (outside). The vacuum chamber 78 is connected by a conduit 82 to a vacuum source, such as a vacuum pump 80. In order to allow the movement of the movable top end wall 74 relative to the upright side wall 73 while maintaining a vacuum seal between the movable top end wall 74 and the upright side wall 73, the upright side wall is provided at the periphery of the movable top end wall 74. A peripheral seal 84 is attached to the inner surface of 73 for sealing engagement.

In assembling the casting apparatus 100 shown in FIG. 4, when the shell mold 30 is installed in the housing 70, the frustoconical collar 18 is connected to the bottom support wall of the housing 70. The mold filling tube 90 is sealingly engaged. The mold fill tube 90 constitutes the lower molten metal inlet to each mold cavity through the rise passages 37 and respective inlet gates 38. In order to close the upper end of the rising passage 37, the fireproof cap 20 is provided on the top of the shell mold.
Cover. A loose, refractory granular support medium 60 (eg, loose silica sand having a particle size of about 60 mesh) is placed in a vacuum chamber 76.
It is introduced around the inner shell 30. This introduction is performed while shaking the housing 70 to assist the sedimentation of the support medium 60 out of the vacuum chamber 76. Then
The movable top end wall 74 has its peripheral seal 84 attached to the upright sidewall 73.
Into the open upper end of the housing 70 in a sealing engagement with
The inner surface of the air permeable plate 75 is directed toward the support medium 60 and brought into contact with the support medium (see FIG. 4).

After assembly, the casting apparatus 100 is positioned above a source 102 (eg, pool) of molten metal 104 to be cast. Usually, molten metal 104 is
Put it in. Then, by operating the vacuum pump 80, a vacuum is drawn through the air permeable plate 75 into the vacuum cup 77, and thus the vacuum chamber 76. The vacuum in the vacuum chamber 76 evacuates the mold cavity 36 through the air permeable thin shell 30. The degree of vacuum in chamber 76 is selected to be sufficient to draw molten metal 104 from pool 102 into mold cavity 36 when fill tube 90 is immersed in molten metal 104 as shown in FIG. To do.

When a vacuum is drawn on the vacuum chambers 76, 78, the top end wall 74 experiences atmospheric pressure (or ambient pressure) on its outer surface above its peripheral seal 84, while the inside of the plate 75 is exposed to the relative vacuum. Exposed to. This pressure difference between the inside and outside of the top end wall 74 causes the top end wall 74 to move downward along the side wall 73, whereby the plate 75 exerts sufficient pressure on the particulate support medium 60 to shell the particulate support medium 60. Compress around 30 to support the shell against casting stress. In this way, while the mold cavity 36 is being evacuated and sucking the molten metal from the pool 102, the mold cavity 36 is parallel to the plate 7 and the plate 7
5, the granular support medium 60 is applied to the shell 3
Compress around 0 to support the shell against casting stress. The amount of pressure exerted by the plate 75 to compress the particulate support medium 60 can be controlled by controlling the degree of vacuum established within the vacuum chamber 76.

As is apparent from FIG. 4, the molten metal 10
4 passes through the filling pipe 90, the rising passage 37, the side introduction gate 38, and is sucked into the mold cavity 36. Thereby, the molten metal 104 is cast in the mold cavity 36 in a vacuum antigravity manner.

When the relative vacuum is set in the vacuum chambers 76 and 78, the upper end of the rising passage 37 is located in the chamber 78.
Closest to the highest vacuum level inside. Further, the support medium 60 serves to reduce the vacuum level existing around the shell 30 near its bottom. As a result, the stress exerted on the lower portion of shell 30 by the combination of the head pressure of the internal molten metal in the mold and the outer vacuum around shell 30 is described in US Pat. No. 4,791,977.
It is reduced according to the principle described in No. This reduction in stress combined with the support of the shell 30 by the support medium 60 does not cause deleterious migration of the shell mold walls and causes molten metal penetration into the mold walls. Without high temperature molten metal (thickness 3.04
It enables antigravity casting into less than 8 mm).
Even if there are defects such as small holes in the shell 30, the support medium 60 around it helps prevent leakage of the molten metal 104 through the defect and, in any event, the leakage. Confine only around the shell 30,
Prevents damage to the casting equipment and allows the vacuum to be maintained until the casting in the shell mold solidifies.

Once the molten metal 104 has solidified in the mold cavity 36, the casting apparatus 100 is raised to withdraw the fill tube 90 from the molten metal pool. Then, a cast product take-out section (not shown) is provided for the top end wall 74 of the housing 70.
Removed, support medium 60 and metal filled (cast)
Remove the shell 30 from the vacuum chamber. After cooling, the support medium 60 can be circulated for reuse in casting with another shell 30. The metal-filled shell 30 is
After being removed from the vacuum chamber 76, it is cooled to ambient temperature. Since the shell 30 has a small wall thickness, it can be easily removed from the solidified casting. For example, cooling a metal filled shell 30 will often result in the shell
It peels off from the casting due to thermal stress received during cooling. Therefore, the time required to remove the thin shell 30 can be considerably shorter than the time required to remove the thick shell that has been conventionally used.

Referring to FIG. 5, there is shown a casting machine 100 'according to another embodiment of the present invention. In Figure 5,
Parts similar to those of FIG. 4 are indicated by the same reference numbers but with a dash. The casting apparatus 100 'of FIG.
The use of an annular vacuum cup 110 'provided around the housing 70' and a sealed bear at the open upper end of the housing 70 'to apply pressure to the particulate support medium 60' when the housing 70 'is evacuated. It differs from the casting apparatus 100 of FIG. 4 in that a flexible impermeable membrane 112 'is provided. However, the flexible impermeable membrane 11
2'is also similar to the casting device 100 of FIG. 4 in that it also constitutes the movable top end wall of the housing 70 '. The vacuum plenum 110 'has a housing 7
An annular vacuum chamber 114 'is defined around the 0'vacuum chamber 76' and communicated with the annular chamber through an annular permeable sidewall portion 116 'of the housing.

The vacuum chamber 114 '(conduit 118'
Once evacuated, the vacuum chamber 76 'and the mold cavity 36' of the shell 30 'are also evacuated. When a vacuum is applied to the vacuum chamber 114 ', the outer surface 112a' of the flexible impermeable membrane 112 'is exposed to atmospheric pressure (or ambient pressure) and its inner surface 112b' is exposed to relative vacuum. As a result, molten metal passes from the pool beneath it through the fill tube 90 'and the rise passage 37' and into the inlet gate 38 '.
While being pumped through the mold into the mold cavity 36 ', the membrane 112', as described above in connection with FIG.
A granular support medium 60 'is compressed around the thin shell 30' to support the shell against cast stress. Otherwise, the FIG. 5 embodiment functions as described with respect to the FIG. 4 embodiment, and provides similar advantages.

Referring to FIG. 6, there is shown a casting apparatus 100 "according to yet another embodiment of the present invention. In FIG. 6, parts similar to those of FIG. 4 have the same reference numbers. It is shown with two dashes. The embodiment of Figure 6 includes one or more annular inflatable members disposed in contact with a refractory particulate support medium 60 "within a housing 70". It differs from the embodiment of FIG. 4 in that it uses a bladder 120 ″ (only one shown). This air bag is
For exerting pressure on the particulate support medium 60 "when the mold cavity 36" is evacuated during the antigravity casting operation to compress the granular support medium 60 "around the thin shell 30". The housing 70 "includes a non-movable top end wall 74" consisting of an air permeable plate 75 "hermetically mounted on its top and a vacuum cup 77" coupled to the plate 75 ". Within the cup 77". The vacuum chamber 78 ″ is a plate 7
Above the 5 "air permeable portion 75a", the vacuum chamber 78 "is evacuated by a vacuum pump 80" via conduit 82 ".

After the top end wall 74 "is hermetically attached to the housing 70" and the vacuum chambers 76 ", 78" have been evacuated, the bladder 120 "is replaced by a suitable gas source 121" such as compressed air. Pressurization is performed through the supply pipe 122 ". The pressure (expansion) of the air bag 120" exerts pressure on the granular support medium 60 ", and in the same manner as described in connection with the previous embodiment, the granular support medium 60". Is compressed around a thin shell 30 ", thereby supporting the shell against casting stress. In other respects, the embodiment of FIG. 6 is similar to that of the embodiment of FIGS. Works the same as.

[0038]

As is apparent from the above description, according to the present invention, the number of cast products that can be cast per investment shell mold can be considerably increased.
It also reduces the stresses placed on the shell mold during casting by the internal molten metal pressure in the investment shell mold and the external vacuum conditions around the shell mold. During casting, the investment shell mold can be supported in a manner that prevents damage to the mold due to casting stress and prevents leakage of molten metal from the mold.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to the structures and modes of the embodiments illustrated herein, and deviates from the spirit and scope of the present invention. It should be understood that various embodiments are possible and that various changes and modifications can be made.

[Brief description of drawings]

FIG. 1 is a side view of a prototype assembly.

FIG. 2 is a cross-sectional view of the prototype assembly after being covered with a granular mold material.

FIG. 3 is a cross-sectional view of the thin shell mold after the prototype assembly has been removed by steam autoclave heating.

FIG. 4 is a cross-sectional view of an anti-gravity casting apparatus according to the present invention, in which the shell mold is held in a rigidized granular support medium in a vacuum housing, with external molten metal to the shell mold. The inlet is shown submerged in the molten metal pool below.

FIG. 5 is a cross-sectional view of an antigravity casting device according to another embodiment of the present invention.

FIG. 6 is a cross-sectional view of an anti-gravity casting device according to yet another embodiment of the present invention.

[Explanation of symbols]

 10: prototype assembly 12: rising passage forming part 14: mold cavity forming part 16: introduction gate forming part 22: refractory layer 30: air-permeable thin shell mold 36: mold cavity 37: rising passage 38: introduction gate 40: Exterior (investment) prototype assembly 60: Granular support medium 70: Vacuum housing 73: Upright side wall 74: Movable top end wall 75: Air-permeable plate 76: Vacuum chamber 77: Vacuum cup 78: Vacuum cup 80: Vacuum source (vacuum pump ) 90: Mold filling tube 100: Casting device

Claims (9)

[Claims] 1. A method of casting a molten metal in an antigravity manner, comprising: (a) forming a consumable prototype of an article to be cast with a meltable material that expands when heated; b) sheathing the prototype with a multilayered particulate refractory mold material controlled to form a thin wall refractory shell having a thickness greater than 0 mm and not exceeding about 3.048 mm , and (c) the sheathed prototype. To remove the prototype from the thin refractory shell, thereby forming a mold cavity within the shell, (d) disposing a refractory granular support medium around the thin refractory shell, the mold cavity is communicated with the lower molten metal inlet disposed external of the particulate support medium in its lower, to exhaust the (e) the mold cavity, while still exhaust the (f) the template cavity, the thin Use refractory shells against casting stress Pressure is applied to the granular support medium to compress the granular support medium around the shell to support and (g) the thin refractory shell remains supported on the granular support medium, and It said molten metal inlet to remain communicated with the molten metal source located thereunder, anti gravity casting method consisting in drawing up the molten metal in the counter-gravity upwardly into the exhaust by mold cavity. 2. The antigravity casting method according to claim 1, wherein the heating of the exterior mold in the step (c) is performed by a steam autoclave. 3. The steps (e) and (f) comprise supporting the thin wall refractory shell in a refractory granular support medium in a vacuum housing, evacuating the vacuum housing, and
The anti-gravity casting method according to claim 1, wherein the movable wall of the vacuum housing is moved with respect to the vacuum housing and the granular support medium to apply the pressure to the granular support medium. 4. The outer surface of the movable wall is exposed to ambient pressure, and the inner surface of the movable wall acts on the outer surface of the movable wall.
The antigravity casting method according to claim 3 , wherein the vacuum is exposed to a vacuum relative to an ambient pressure . 5. The steps (e) and (f) comprise supporting the thin wall refractory shell in a refractory granular support medium in a vacuum housing, evacuating the vacuum housing, and
2. The antigravity casting method according to claim 1, wherein the pouch is placed in contact with the granular support medium in the vacuum housing by compressing the granular support medium. 6. An apparatus for casting a molten metal in a counter-gravity, and Housing having (a) a vacuum chamber, and (b) disposed within the housing fire resistance particulate support medium, (c ) are arranged in the particulate support within the medium, from 0mm
Thick, a refractory investment shell having a mold cavity defined by the wall thickness of the mold wall by no more than about 3.048mm, (d) said particulate support medium the mold cavity and the molten metal source thereunder to communicate a molten metal inlet disposed external of the connection to the vacuum chamber in order to exhaust the mold cavity thereby to exhaust (e) said vacuum chamber
The vacuum source that is, a pressure such as to compress the particulate support media about the shell to support it against (f) while still exhaust the mold cavity, the shell casting stress The vacuum chamber was evacuated to add to the granular support medium.
When exposed to the differential pressure, the housing and the granular support medium are exposed.
Provided on the housing so as to move relative to the body
A movable wall that is, (g) said to siphon upwardly and the molten metal to the exhaust by mold cavity, said mold cavity while still discharging <br/> gas, and said granular said pressure A tube for communicating the molten metal inlet with the source of molten metal while still being added to a support medium. 7. The movable wall comprises a gas permeable end wall of the housing, the gas permeable end wall having an inner surface for contacting the particulate support medium and a vacuum cup located above the outer surface thereof. has, vacuum cups may be exhaust to the housing through the transparent temper end wall, the vacuum cup is subjected to ambient pressure on the outside surface, when said housing is exhaust, said end The anti-gravity casting device according to claim 6 , wherein a wall is moved with respect to the housing to press the granular support medium. 8. The anti-gravity casting device according to claim 6 , wherein the movable wall comprises an impermeable flexible end wall of the housing. 9. An apparatus for casting molten metal in an antigravity manner, comprising: (a) a housing having a vacuum chamber; (b) a loose refractory granular support medium disposed in the chamber. (C) It is arranged in the granular support medium, and from 0 mm
Thick, a refractory investment shell having a mold cavity defined by the wall thickness of the mold wall by no more than about 3.048mm, (d) said particulate support medium the mold cavity and the molten metal source thereunder to communicate a molten metal inlet disposed external of the connection to the vacuum chamber in order to exhaust the mold cavity thereby to exhaust (e) said vacuum chamber
A vacuum source, (f) while still exhaust the chamber, the particulate pressure such as to compress the particulate support media about the shell to support it against the shell casting stress To contact said particulate support medium for addition to the support medium
And disposed a pressurized free air sacs, (g) said molten metal to siphon upwardly into the exhaust by mold cavity, while still exhaust the chamber, and wherein said pressure granular A tube for communicating the molten metal inlet with the source of molten metal while still being added to a support medium.