JPH1085919A - Pressure casting method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the development of internal defect caused by solidified shrinkage of a casting and at the same time, to shorten the solidified time while improving the close contact property between the casting and a mold by giving direct mechanical pressure to molten metal in a feeder head or a sprue just after pouring the molten metal, at the time of casting the molten metal into an alloy metallic mold having comparatively low m.p. SOLUTION: A reverse gravity casting apparatus has a structure fitting a pressurizing device composed of a sleeve 12 at the tip part of a molten metal supplying tube 5 for pouring the molten metal 2 into a cavity 6 in the mold, a piston 11 for sliding the inner part thereof and a hydraulic cylinder 10 for driving the piston 11 and connecting with the sprue 6 in the mold 7. At the time of casting, after completing the pouring of molten metal into the mold 7 through the molten metal supplying tube 5 and the sleeve 12, the piston 11 is pushed in the range of pushing quantity corresponding to the vol. shrinkage quantity according to the solidification of the casting in at least the mold cavity 8 to the molten metal in the sprue 6 by driving plunger in the hydraulic cylinder 10 to give the pressure. Then, the pressurization is executed with the same method at the time of the metallic mold gravity casting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the field of casting technology, and more particularly to a casting method and apparatus for improving feeder capacity and shortening solidification time in die gravity casting and reverse gravity casting processes.

[0002]

2. Description of the Related Art The purpose of a riser is to cause a shrinkage caused by a difference in density between a liquid and a solid during solidification (referred to as solidification shrinkage) and a shrinkage caused by a temperature drop of a liquid phase (referred to as liquid phase shrinkage). The purpose of the present invention is to compensate for shrinkage and prevent shrinkage cavities and so-called microporosity (fine voids) generated in the liquid phase between dendrites inside or on the surface of the casting. The quality of the feeder design not only affects the presence or absence of the above defects, but also greatly affects the yield (the ratio of the product weight to the weight of the casting including the feeder) and the productivity of cutting the feeder section. Therefore, it is a particularly important part in the design of a casting plan, and every casting plant is constantly making efforts for improvement.

[0003] One of the objects of the present invention is related to a riser.
A conventional technique for improving the feeder effect, that is, the ability to replenish molten metal to compensate for volume shrinkage during solidification will be described. [Embedded Feeder System] As a technique first found in the literature, there is a method of applying a pressurized gas to a feeder embedded in a mold (hereinafter referred to as an embedded feeder system). It has been reported in Europe that it is effective in improving the yield and quality of large cast copper castings (for example, see Reference (1)).

FIG. 11 shows a basic form of the embedded feeder system.
A heat-insulating cup made of gypsum or the like having no air permeability is used for the feeder section. The operation is relatively simple, and after a short time after pouring, the valve is opened and a pressure of about 7 atm or less, which is normally obtained in a foundry, is applied to the feeder to maintain the solidification until the solidification is completed. According to the experience of applying Kononow (Reference (1)) to a wide range of relatively large cast steel castings (plate thickness of 50 mm or more, diameter of 100 mm or more) in Russia, the yield is improved by 20 to 30% compared to the case of ordinary feeder. It was stated. This is achieved by lowering the height of the riser and reducing the number of risers as compared to ordinary risers. It also states that material elongation and drawing have been greatly improved. Based on many years of operating experience, they have decided to adopt the shape of the embedded feeder, depending on the shape and weight of the casting,
It has established working standards for the timing and pressure of gas pressurization.

[0005] Berry and Watmough (Reference (2)) carried out pressure solidification with an argon gas by the method shown in FIG. 11 for an Al alloy sand casting having a large solidification temperature section (50 mm square cross section, 350 mm length). As a result, it was concluded that a pressure of about 1.4 atm was sufficiently effective and that various alloys were practical.

[0006] As described above, it has been demonstrated that microporosity can be reduced or eliminated by applying gas pressure to an embedded feeder. However, at present, there is no document that the method is widely used. The reason is that at that time, the physical concept of liquid phase flow between dendrites was not clearly established as a mechanism of molten metal replenishment at that time, and therefore, a mathematical method for describing this has not been developed. It seems that there was a fundamental reason that the riser effect could not be quantitatively evaluated. Therefore, the timing of applying pressure, the required pressure, and the like must rely on trial and error and experience, and there are cases where there is an effect and cases where there is no effect. In 3), a long sand casting having a relatively small cross section (3 to 5 inch square cross section,
As a result of conducting a pressure casting experiment of about 5 atm for a length of 10 to 24 inches), the effect of reducing microporosity was insignificant, and conversely stated a negative opinion on the feeder pressing effect of the present method).

[Counter-Pressure C
Asting Process] The casting process originates from the Bulgarian patent (4). FIG. 12 shows an outline of the device that is currently generally used. The mold (generally a mold) and the molten metal holding furnace are housed in a container having airtightness and are separated from each other. The operation procedure is as follows. After preparation of the mold, first, valves 1, 2, and 3 of pipes leading from the gas source to the molten metal holding chamber and the mold chamber are provided.
The opening gradually increasing the pressure in both chambers is set to a predetermined pressure P _1. At this time, the on-off valve attached to the mold is opened so that pressure is quickly applied to the mold cavity (the specific shape of the product is not shown). Then, molten metal by opening the open valve provided in the mold chamber at the same time holding furnace when the pressure and P ₂ of the mold chamber relief part of the gas to the outside air differential pressure △ P of the pressure P1 of the molten metal holding chamber (= P ₁ −P ₂ > 0) and introduced into the mold cavity through the hot water supply pipe. At this time, the open / close valve is closed. Then, the pressure in both chambers is maintained at P1 _and P2 until the molten metal solidifies. After the solidification is completed, the pressure in both chambers is released, and the casting is taken out.

This method is mainly applied to aluminum castings, and practically applies a pressure on the order of at most 10 atm. It states that a product having less internal microporosity can be obtained as compared with an atmospheric pressure cast product (for example, reference (5)).

Next, another object of the present invention, that is, reduction of the coagulation time, will be described. At present, most of aluminum automotive parts such as engine blocks and cylinder heads are cast by low-pressure casting (see Fig. 13). Pressurized gas is introduced into the holding furnace and the pressure difference from the atmospheric pressure in the mold cavity (1 atm or less) is applied. Is a kind of pouring machine). In the production of aluminum castings by low-pressure casting, there is a strong demand for suppressing the internal defects and shortening the casting cycle which directly affects productivity (the number of castings per day per low-casting machine). This is most effectively accomplished by reducing the solidification time, which accounts for the majority of the casting cycle, by changing the material of the mold (for example, changing from copper to a copper alloy), and the rate of heat removal in the water channels in the mold. In order to improve the cooling performance of the mold by improving the quality of the mold, a technique has been devised (for example, Reference (6)).

[0010]

As described above, it has been widely recognized that the riser (and plan) technology in casting is still incomplete and that castings have internal defects (microporosity, etc.). At present, the road is far from being cleared. The present invention seeks to eliminate internal defects that occur in gravity casting and low-pressure casting, which are used in the production of alloy castings having a relatively low melting point, such as aluminum automobile parts, among many casting processes. At the same time, productivity is increased by shortening the coagulation time.

[0011]

Therefore, in the present invention, the gravity casting of the mold and the counter gravity casting in which the molten metal is poured into the mold from below.
ng, one of the low-pressure casting methods described above), in these casting machines, a device for directly applying a mechanical pressure to molten metal in a feeder (or gate) after completion of a normal pouring operation in these processes. It is intended to solve the above-mentioned problem by adopting a configuration to be equipped. That is,
Finally, apply pressure to the riser or gate that solidifies,
At the same time as increasing the riser effect, the adhesion between the casting and the mold is increased,
This is intended to shorten the coagulation time.

[0012]

[Action]

[Regarding Feeder Effect] It has been proved by the above-mentioned literature that the internal porosity of a casting can be reduced or eliminated by applying pressure to the feeder. The amount of pressure required is essentially related to the liquid phase flow phenomenon between dendrites, and therefore depends largely on the type of alloy, shape and size of casting, type of mold, pouring temperature, etc. fluctuate.

The above phenomenon will be described using a theoretical formula. It is known that in a state where a dendrite crystal and a liquid phase coexist during coagulation, the flow phenomenon of a liquid phase between dendrites induced by solidification shrinkage and the like is described by Darcy's equation (see Reference (7)). That is, Vector V is the flow rate of the liquid phase, μ is the viscosity coefficient of the liquid phase, g _L is the volume fraction of the liquid phase, K is the transmittance, ΔP is the pressure gradient of the liquid phase, X
Is an object force vector such as gravity or centrifugal force. Solving equation (1) for ΔP When solidification progresses to some extent, X term on the right side (gravity only)
V term becomes dominant. That is, the pressure gradient is substantially determined by the flow velocity V. Therefore, the hydraulic pressure (P
_r ), the equation (2) is integrated along the path (three-dimensional) of the liquid phase flow from the riser to the product section, and the change in P along the path, that is, the pressure drop You can know. Then, when P reaches a critical condition given by the following equation, an internal porosity (void) is generated at that location (see p. 237 of Reference (7)). Here, P _gas is an equilibrium gas pressure in a porosity that balances with a solid solution gas (for example, hydrogen in an Al alloy) in a liquid phase, σ
_LG is the surface tension of the liquid-gas porosity interface, and r is the radius of curvature of the spherical porosity (see FIG. 14). For molten metal, σ _LG is on the order of 10 ³ (dyn / cm) (approximately 700 for Al), and if r is about 10 μm, −2σ _LG / r = −2 × 10 ⁶ (dyn / cm)
² ) と な り -2 (atm) and P _gas is on the order of several atmospheres at most, so the right side of equation (3) is small even if negative pressure is applied.

[0014] Therefore, it Shiteyare increased fluid pressure P _r of the in order not to cause porosity and held at a portion apart from a large case riser pressure drop in the pressure of the critical pressure. FIG. 18 is a diagram schematically illustrating the relationship between the liquid phase pressure drop and the porosity generation in the porosity generation critical condition equation (3). In the figure, porosity is generated in a region where the solid phase ratio is equal to or more than the critical solid phase ratio gs ^* . The reason for applying the external pressure to the liquid phase in the riser is to increase the P distribution.

The above discussion will be explained quantitatively using a one-dimensional Darcy flow. The following modeling is performed to simplify the physical insights (see FIG. 15): 1) There is no temperature gradient in the longitudinal direction (X) of the casting. The temperature is also constant within the cross section. 2) There is no heat flow from the end face (X = 0) of the casting. Also, the riser serves as a liquid phase replenishment source, but there is no heat flow to the casting. 3) The liquid phase density ρ _L and the solid phase density ρ _S are constant. 4) The solid phase does not move. Here is the list of required expressions:

From Darcy's equation From the continuous conditions for the liquid phase of the solid-liquid coexisting phase, The following equation for P is obtained by a simple operation of the equation. Here P _r is the pressure of the liquid phase in the feeder (X = L position). β is the coagulation contraction rate, Is defined.

The following equation was used for the transmittance K (Reference (8)). It is given by the following empirical formula. A and n are material constants.

[0018] h is the coefficient of heat transfer to the mold (assumed constant) and To is the mold temperature (assumed constant). The left side of the above equation represents the generation speed of latent heat due to solidification, and the right side represents the heat removal rate of the mold. For a cylindrical casting, the solidification rate is given by: Where D is the diameter of the casting. The temperature T in equation (11) is a function of time t, I have. It is well known (for example, see p. 34 of reference (7)). The above equations (4), (6) to (9), (11) and (12) are equations necessary for calculation.

From inspection of these equations it is clear that the second term on the right hand side of equation (6) is the hydraulic pressure drop term caused by the Darcy flow and is given by The porosity generation critical condition (Equation (3)) is easily reached (the reverse is porosity). Since the dendrite cell becomes finer (Equation (9)), the transmittance K (Equation (8)) becomes smaller.

[0020] The temperature T and the elapsed time t are obtained from the equations (12) and (11), and the K is obtained from the equations (9) and (8).
The P distribution was calculated from equation (6). The casting material is Al-3
wt% Cu, the dimensions were 50 mm in diameter and 500 mm in length. Table 1 shows the physical property values used for the calculation.

[0021]

[Table 1]

The heat transfer coefficient representing the cooling capacity of the mold is defined as h = 0.
In the case of a mold casting equivalent to 01 (cal / cm ² S ° C), the solidification time is 66 seconds and the dendrite arm spacing As shown in FIG. 16, the pressure drop is extremely large. The pressure drop is steep as solidification progresses showed that. Actually, such a large negative pressure is not generated, and the porosity is formed so as to satisfy the expression (3), and the hydraulic pressure is reduced. On the other hand, for comparison, h = 0.0
In the case of a sand mold set at 01 (cal / cm ² S ° C.), the solidification time is as long as 660 seconds, and the dendrite arm spacing is as large as 82.8 μm. Therefore, the pressure drop is much smaller than that of the mold as shown in FIG.

As described above, the required feeder pressure for suppressing the generation of internal porosity varies greatly from case to case, and therefore, as described in the above-mentioned reference (2), when the effect is obtained at several atmospheres. 100 if available
Porosity may remain even in atm. However, there is an effect of reducing the porosity corresponding to the pressing force. At present, gas pressure on the order of 10 atm is a tentative standard in the case of sand casting from various documents, but it is clear from the above calculations that there is no technical basis. The porosity of the casting surface is caused by the same pressure drop, but is omitted.
In this calculation, the temperature was treated as uniform, but directional solidification from the end of the casting to the feeder (or gate) is essential in order to effectively exert the pressure effect in the actual casting and obtain a sound casting. Needless to say,

[Features of Mechanical Feeder Pressurization] It is known that a small gap (air gap) is formed at the boundary between a casting and a mold at a relatively early stage of solidification due to shrinkage of the casting. This tendency is more pronounced when the mold is a mold having a large heat absorption capacity. When an air gap is formed in die casting, the heat flux (heat removal per unit area and unit time) to the die sharply decreases. As described above, feeder pressurization is for eliminating the air gap and increasing the heat flow.

The ideal plunger pushing amount corresponds to the sum of the liquid shrinkage due to the temperature drop of the molten metal in the cavity and the solidification shrinkage due to the density difference between the solid phase and the liquid phase. Thus, after the pouring is completed, the plunger pressurizing device may be much smaller than that of the die casting machine whose main purpose is pouring since it is sufficient to press the casting by the volume contraction of the casting.

During the solidification under pressure, if the solidification in the sleeve progresses and the solid phase ratio increases, the liquid phase in the solid-liquid coexisting phase is replenished to the casting side by the amount of the solidification shrinkage as the plunger moves, and Leave a low-concentration solid phase pomace (hereinafter called cake) (see FIG. 8). That is, in FIG. 8, the piston is at the point S (piston initial position) and the point E (100%
If a cake having a solid phase ratio of 100% is formed at a position close to S between the (density achieving positions), it is difficult to push the piston, and further liquid phase replenishment cannot be performed. Also, segregation with high solute concentration occurs in the casting. Therefore, it is important to take measures such as enhancing the heat insulating properties of the sleeve or applying an appropriate amount of heating to suppress the solidification in the sleeve during pressurization as much as possible.

When there is no solidification in the sleeve, it is considered that the force due to the pressure is mainly transmitted to the solidified layer on the casting surface via the liquid phase between the dendrites and pressed against the inner wall of the mold. FIG. 19 is a schematic diagram of the Darcy flow pattern used to explain this. FIGS. 19A and 19B show the case of die gravity casting, in which FIG. 19A shows a Darcy flow pattern in an alloy having a small solidification temperature section, and FIG. 19B shows an Darcy flow pattern in an alloy having a large solidification temperature section. FIG. 19C shows a case where pressure is applied in reverse gravity casting. Solidification The effect is smaller. Therefore, if X is neglected for convenience of consideration, the line of action when gas pressure is applied to the feeder coincides with the direction of the Darcy flow velocity vector V, and the gas pressure is transmitted along the line of action and the surface layer Is pressed against the inner wall of the mold. The line perpendicular to the line of action is the iso-pressure line (FIG. 19).
(D)). The above condition is satisfied while the Darcy flow exists, but when the Darcy flow does not exist, for example, when the liquid phase replenishment is sufficiently achieved by pressurization or the flow velocity V becomes zero, the above-mentioned acting force line loses its meaning and the transmission of force is performed. Is a general continuum mechanics problem. In any case, it is difficult to strictly evaluate the transmission of force by pressurization, but it can be seen that roughly, pressure is transmitted to the surface solidified layer via the liquid phase between dendrites. Therefore, the pressing force against the inner surface of the mold decreases as the distance from the feeder increases.

In the above-described differential pressure casting method using gas as a pressurizing medium, the inside of the cavity is maintained at the same pressure as the gate, so that the compressed gas exists between the casting and the mold and acts as a back pressure. No increase in adhesion can be expected and therefore no reduction in coagulation time. On the other hand, even if the adhesiveness of the sand mold having a small cooling capacity is increased by pressurizing the hot water, the effect of shortening the solidification time is small because the cooling capacity is originally small. As described above, the method of the present invention is effective only for a mold having a very large cooling capacity such as a mold. This is the reason why attention was paid to shortening the solidification time in gravity casting, and the scope of the present invention was limited to metallic molds.

[Experimental Example] Next, the pressurizing effect described above will be shown by experiments. The mold apparatus used for the experiment is shown in FIG.
Shown in Argon gas was used as a pressurizing medium. There is no inconvenience to use a gas body instead of the plunger as a means for examining the riser pressurizing effect. The mold is made of S45C steel, and the dimensions of the cavity are 50 mmφ × 30 mmφ × 41.
It was a 0 mm long tapered cylindrical shape. Dissolution is performed in an electric furnace in an argon gas atmosphere, and ethane hexachloride 0.3w
t% was embedded in the molten metal in the crucible and subjected to degassing treatment (degassing time was 20 minutes). Alumina coating is applied only to the inner surface of the feeder mold, and the mold is not preheated and is made of 70% Al-3wt% Cu alloy.
It poured at 0-730 degreeC. The pouring time was about 10 seconds. Immediately after pouring, the pouring cup was removed and the pouring opening was sealed with a bolt screw. A groove for mounting an O-ring is provided on the upper surface of the gate, so that confidentiality is maintained. Next, the valve 18 was opened and high-pressure argon gas was introduced to pressurize the surface of the molten metal in the riser. The pressurization start time was about 15 seconds after the pouring start time, and reached the predetermined pressure in about 3 to 5 seconds. The temperature change during solidification was measured with three thermocouples inserted from the side of the mold as shown. FIG. 21 shows the case of atmospheric casting, and FIG. 22 shows a measurement example (30 atm) in the case of pressure casting. Comparing both figures, the closer to the riser, the shorter the solidification time. After completion of solidification, position No. 1 is the position number. The temperature is reversed as compared to 2.

The solidification starting temperature of this alloy was 650 ° C., and the completion of the eutectic (eutectic temperature of 548 ° C.) was regarded as the completion of solidification.
In this experiment, the solidification time is relatively short compared to the pouring time (about 10 seconds) and the subsequent pressurization timing (about 15 seconds later), so that the molten metal flows through the mold cavity when calculating the local solidification time. The time required to rise and reach each temperature measurement position sequentially was determined, and these times were regarded as the start times. That is, the position No. 1, No. 2 and No. The measurement start time of No. 3 is calculated backward from the pouring time of 10 seconds to 6.6 and 2.7, respectively.
And 0.4 seconds later. FIG. 23 shows the measurement results of the local coagulation time obtained in this manner. As shown in FIG. 1, the time shortening effect is remarkably exhibited. Position No. farthest from the hot water Since No. 3 solidifies in a very short time after the pouring, it is not affected by pressurization. Position No. of the central part. 2 is still in a solid-liquid coexistence state 15 seconds after the start of pressurization (gs =
0.55) There is a slight effect of shortening the time due to pressurization.

Next, the length 410 mm was cut into an upper part (150 mm length) and a lower part (260) having a large pressurizing effect, and the weight and volume of each were measured to determine the density. As shown in FIG. Indicates that the density rises, and that the feeder effect is greater at the upper part. Each of the above measured values indicates the average density of the casting. Considering that the microporosity is deviated from the outside toward the center, the density difference at the center appears larger than the measured value.

The following can be said from the above experiments. 1) The effect of shortening the solidification time by pressurization increases as the temperature rises closer to the riser. 2) In order to shorten the solidification time, the pressurization timing should be set as early as possible as compared with the air gap formation time determined by the local solidification time of the casting. Since the actual mold is preheated to 200 ° C. to 400 ° C. and is coated, the local solidification time is considerably longer than in this experiment, and the timing of pressurization can be much earlier. 3) In reverse gravity casting in which the molten metal gradually rises from below and fills the mold cavity, since the full-scale solidification starts after the pouring, the timing of pressurization can be taken earlier, and therefore, the riser by pressurization The range of effect is further expanded. 4) Since the riser effect by pressurization is large, the volume of the riser (pool) can be reduced accordingly. This can further reduce the coagulation time. For example, the local It becomes 1/2.

[0033]

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLE 1 FIG. 1 shows a practical apparatus in which the principle of the present invention is applied to gravity casting of a mold. In FIG. 1A, the molten metal is poured from a pouring port 15 provided on a side surface of the sleeve 12. A gas vent hole 13 during pouring is further provided on the side surface of the sleeve between the pouring port 15 and the initial position of the piston 11. Reference numeral 10 denotes a hydraulic cylinder, which operates a plunger. 16 is a fixture for the hydraulic cylinder, 9 is a gas vent hole normally provided in the mold 7, 8
Is a mold cavity (specific casting shape is not shown).

The casting procedure is simple, and a predetermined pressure may be applied at a predetermined timing after pouring. Feeder shape and feeder volume suitable for individual castings (so-called feeder plan)
The predetermined pressure and timing may be determined by trial production. As described above, several methods are currently available, such as a double-pipe structure of a material having high heat insulation and heat insulation (ceramics, a composite material of metal and ceramics) and heat-resistant steel having excellent high-temperature strength. Other ideas such as arranging a heater on the outside and keeping the heat with a heat insulator are common sense and will not be described in detail. The pressure leakage from the gap between the inner surface of the sleeve and the piston, the problem of lubrication and the like have been solved by die casting, and it can be said that there is no problem.

FIG. 1B shows a case where a pouring spout is attached to a mold, and FIG. 1C shows a case where a pressurizing device is further attached to a plurality of feeders.

[Embodiment 2] FIG. 2 shows a practical apparatus in which the principle of the present invention is applied to a reverse gravity casting method. The hot water supply pipe 5 for introducing the molten metal from the holding furnace 1 to the casting mold 7 is bent as shown in the figure, and a ventilation hole 13 having a number of fine holes having air permeability is attached to the upper part of the runner.
A heater for preventing solidification is attached to the sleeve, and the temperature of the molten metal is kept constant. A more detailed cross-sectional view of the pressurization is shown in FIG. A case in which a high internal pressure is applied to the sleeve and a double-tube structure including a ceramic inner cylinder and a heat-resistant steel outer cylinder is shown in consideration of corrosion resistance to molten metal. In addition to this, there is a technology that sprays a metal-ceramic composite material with excellent corrosion resistance, heat insulation and abrasion resistance with the piston on the inner surface of a metal tube with excellent high-temperature strength to form an inner cylinder. Since these are put into practical use, it is also possible to employ them. In addition, it is common sense to take measures such as covering the outside of the sleeve with a heat insulating material to increase the heat insulating and heat retaining effect (not shown). Metals such as ceramics or cast iron are used as the substance having the fine air holes (these materials generally do not wet the molten metal).

Assuming that the radius of the hole of the fine vent is r, the liquid pressure of the molten metal is P, and the pressure of the gaseous material is Pg, whether or not the molten metal is inserted into the hole of the fine vent during pouring is determined by a differential pressure ΔP ( = PP
g) and 2σ / r (see FIG. 4). Here, σ is the surface tension of the molten metal. Assuming now that the differential pressure ΔP = 1 kgf / cm ² and σ = 1 gf / cm (standard value of the molten metal), the corresponding r is 20 μm.
m. That is, there is no insertion if a hole having a diameter of 40 μm or less is used. (In the case of aluminum low-pressure casting, r is 40 to 100 μm because a typical differential pressure during pouring is about 0.2 to 0.5 kgf / cm ^2. )

The operating procedure is as follows. Pouring is performed in the same manner as normal low pressure casting. The most common method is to introduce a pressurized gas into the holding furnace chamber 3 and introduce a cavity (8).
Pouring is performed by the pressure difference from the atmospheric pressure inside. Immediately after the pouring is completed, the plunger piston is driven and temporarily stopped at the position of the sleeve inlet 15 (the position shown in FIG. 3). At this time, pressure is applied to the molten metal in the cavity, and at the same time, the molten metal in the sleeve and the molten metal in the hot water supply pipe are separated. Next, when the pressure in the holding furnace is released (returned to the atmospheric pressure), the molten metal in the hot water supply pipe returns to the inside of the holding furnace. Alternatively, the atmosphere pressure in the holding furnace may be adjusted so that the hot water surface is held in the middle of the hot water supply pipe. Subsequently, the piston is pushed and solidified under pressure. The mold is separated and the casting is removed.

[Embodiment 3] FIGS. 5A and 5B show a practical device in which a plunger feeder pressurizing device is arranged laterally with respect to a gate in a reverse gravity casting method. The procedure is as follows. After pouring, the piston is pushed to the position shown in FIG. 5 (b), where it is temporarily stopped. At this time, the molten metal in the hot water supply pipe and the molten metal in the cavity are separated from each other, and a pressurization is started. The gas pressure in the holding furnace is returned to the atmospheric pressure. Subsequently, the piston is pushed and solidified under pressure. At this time,
When the rear surface of the piston passes through the sleeve inlet 15, the space 13 opened to the atmosphere communicates with the molten metal in the hot water supply pipe, and the molten metal returns to the holding furnace.

In this method, as in the second embodiment, it is possible to embed a heater in the sleeve to minimize solidification in the sleeve (for example, the solid phase ratio is 0.3). In addition to such a contrivance, a material having a large heat insulating property is used for the inner cylinder or a mold 7 is used.
It is relatively easy to delay solidification in the sleeve by taking measures such as providing a heat insulating space between the sleeve and the sleeve.

Alternatively, as shown in FIG. 6, a method is also possible in which an inner plunger is provided inside the main plunger, and after the main plunger cannot be pressurized, the inner plunger can be pushed in two steps. It is. However, as described above, coagulation in the sleeve causes various inconveniences, so it is better to minimize coagulation in the sleeve as much as possible.

FIG. 7 shows a specific example of a device in which a plunger feeder pressurizing device and a check valve 17 are combined in the reverse gravity casting method. After pouring, the check valve is closed, and then the mixture is pressurized and solidified by a plunger. After the solidification is completed, the piston is returned to the initial position behind the pouring, the pressure in the holding furnace is returned to the atmospheric pressure, the check valve is opened, and the molten metal in the hot water supply pipe is returned to the holding furnace. It is preferable to make a hole in the sleeve so that the inside of the sleeve communicates with the atmosphere when the piston is returned to the initial position. This makes the operation of returning the molten metal to the holding furnace easier.

The pressurizing device is as described in the third embodiment. The difference between this example and the third and second examples is that in the latter two examples, the molten metal touches the side of the piston when the piston passes through the sleeve inlet and is temporarily stopped, and is contaminated by the lubricant, but this example avoids this. There is a characteristic that.

In this embodiment, since the hot water supply pipe is always filled with the molten metal, care must be taken to prevent the temperature of the molten metal from dropping or solidifying.

FIG. 7B is an explanatory view of a mechanism for opening and closing the valve 17 by the movement of the valve stem 19 inserted into the flow path, and shows an example in which the valve stem is operated by an air cylinder having a built-in spring. Naturally, there are various opening / closing methods other than the air cylinder type, such as a hydraulic cylinder type, an electromagnetic opening / closing type, an electric motor and a gear type, and any of them may be used.

For the above check valve, valve seat, and valve stem, use is made of a material such as ceramics having excellent corrosion resistance and strength against molten metal. The contact method between the check valve 17 and the valve seat 18 can be various methods such as a tapered surface contact method in addition to the method shown in the above both figures.

[Specific Example 5] In the case of the current low-pressure casting method, one cycle of casting is a machine operation time such as shaping, pouring, and taking out a casting after solidification, solidification time, mold temperature adjustment time,
In addition, it consists of manual work such as repair of paint mold. Of these, the portion of the solidification time is generally the longest. Therefore, as described above, when the present invention is applied, the casting cycle can be significantly shortened by the effect of shortening the solidification time by the pressure solidification. Furthermore, the casting cycle can be further shortened by adopting a flow operation system using a plurality of dies for one casting machine. FIG. 25 shows a specific example of the flow operation method. The system consists of a main process unit consisting of a melt holding furnace, a pouring and pressurized solidification unit, and an auxiliary process unit that performs mold dispersion, removal of castings, cleaning of cavities, and coating. They are linked by moving tables. Then, the mold device is automatically moved between both processes by the feed mechanism, and a series of operations are performed to take out the product. The mold devices are in the auxiliary process device when one is in the main process device or in the standby position. The work procedure is as follows.

The mold A is set at the pouring position, injected into the mold cavity from the molten metal holding furnace by the method described above, and is pressed by the plunger as it is to solidify the casting in the cavity by pressure. The mold A is moved to the mold dispersion position, the mold dispersion is performed, and after the casting is taken out, the separated mold is cleaned and coated. When the coating is performed by an electrostatic coating method (which will be described later), the electrostatic coating is performed after removing and cleaning the powdery release material on the cavity surface. If there is a core, the core is set and matching is performed, and then the process moves to a standby state in preparation for the next pouring. In FIG. 25, a mold A is set at a pouring position, and a mold B is set at a series of working positions such as separation of a mold, cleaning, repair of a coating mold, insertion of a core, and mold matching. Show. In the case of this example, the time required for one cycle of casting is determined by the longer of the working time of the mold A and the working time of the mold B. In any case, a method of shortening the operation time of the mold B at the sub-process position is employed [for example, the mold separating operation is performed in a horizontal direction to facilitate the coating operation]. In addition, the mold device and the plunger pressurizing device should be designed so that they can be smoothly attached and detached. That is, an appropriate separation position is determined in the type of pressing from below in FIG. 3 or the type of pressing in the lateral direction in FIG. 5 [this is not difficult and will not be described in detail]. Also, the molds A and B do not necessarily have to be the same product.

[Comments] Finally, the gist of the present invention will be described, including those not mentioned above. (1) FIG. 9 shows an example in which a mold 7 and a holding furnace 1 as a molten metal supply source are arranged in a horizontal direction, and FIG. 10 shows an example of an apparatus in which a pouring electromagnetic pump 20 is incorporated. As an advantage of disposing the molds in a lateral direction as compared with the case where the molds are arranged directly above the holding furnace, it is pointed out that the mold can be cooled by water cooling and the molten metal can be easily managed. 9 and 10 show the case where the inlet of the hot water supply pipe is provided above the holding furnace, the relative positional relationship between the hot water supply pipe and the holding furnace is arbitrary, and the inlet may be located anywhere. The hot water supply pipe does not need to be a straight pipe. The operation method is essentially the same as that of the vertical type, and thus will not be described.

(2) The general configuration of the low-pressure casting apparatus is one mold and one product, and the number of hot water supply pipes is one. In addition, a plurality of dies are installed for one casting apparatus. There are multiple devices for casting a plurality of products. The hot water supply pipes are provided for the number of molds or are branched from one hot water supply pipe to the gate of each mold. In these cases, it is sufficient to attach several sets of molds for the former and one set of plunger pressurizing devices for the latter. The same applies to the case where the product size is large and one mold has a plurality of gates.

(3) At the time of pressurization, a force to separate the mold is generated on the inner surface of the mold due to the pressure received from the casting, so that a mold-squeezing force to oppose this force is required. [There are various mold-squeezing methods. These publicly known and used techniques may be used]. If the entire cavity is filled with molten metal at the time of pressurization, the force will increase and a large mold clamping force will be required, but in actuality the solidification has already started to some extent at the time of pressurization, so the separating force is much smaller. Become. Therefore, unlike the case where all the injection pressure acts on the inner surface of the mold as in die casting, the separating force is much smaller. The timing of pressurization is preferably earlier as described above, but may be determined on a case-by-case basis taking this point into consideration.

(4) The feeder pressure required to suppress the occurrence of porosity fluctuates over a wide range depending on the individual casting as described above. As for the upper limit, a value of 100 kgf / cm ² or 500 kgf / cm ² is expected, but it is considered that a considerably high pressure is possible in the plunger method of mechanically pushing. On the other hand, the pressing method includes a method of setting a pressure and a method of setting a pushing amount (stroke). Density 1
Needless to say, the latter is desirable to achieve 00%, but the pressing force may be excessive. Since the strength of the base sleeve becomes a problem, the pressure control method is used after taking measures such as increasing the strength of the sleeve.
It is important to point out again that it is important to perform directional solidification from the end of the casting to the riser in order to increase the pressure effect.

(5) It has been generally recognized that when the solidification rate is increased in an alloy casting and the dendrite arm spacing is made fine, mechanical properties such as tensile strength, elongation, and fatigue are improved (for example, see Reference (7)). ) P.3
41 to p. 344 describes aluminum alloys and other practical alloy castings in detail). It is common knowledge that the presence of internal porosity deteriorates mechanical properties in actual cast products, and there are many documents. Therefore, the porosity can be greatly reduced or eliminated by the casting method according to the present invention, and the mechanical properties of the actual product can be greatly improved by both effects of making the solidification structure fine, that is, reducing the dendrite arm spacing. it can.
This is important for increasing the strength and weight of automobile castings such as aluminum alloys.

(6) As described above, in the pressure casting according to the present invention, the degree of adhesion between the casting and the surface of the mold cavity is increased. Therefore, when removing the casting depending on the shape of the cavity, the coating layer on the surface of the cavity is scraped off. There are cases. Therefore, it is necessary to repair the mold every casting cycle, which is a factor of prolonging the casting cycle. In such a case, it is sufficient to perform electrostatic coating in which the application and removal of the coating mold can be performed in a relatively short time (for example, Shunzo Aoyama: Development of a new filling die casting method using a powder release agent, Japan The Foundry Society of Japan, Die Casting Research Committee, “Die Casting Defects and Countermeasures”, p.
(See December 996). In this method, a powdery release agent with chargeability is applied by sending it to the surface of the mold cavity charged to the opposite polarity and attaching it.The carrier of the powder release material is air etc. Is used. As a result, a highly uniform coating can be performed, and the mold is thermally protected by the heat insulating property of the release material and the air layer between the release materials. At the time of pressurization, the molten metal is inserted between the powders and comes into direct contact with the mold to increase the cooling capacity.

(7) The core is usually formed of a shell or a salt, but it is preferable to apply a mold to the surface of the core in order to prevent the molten metal from being inserted by pressure. In addition, since there is a possibility of collapse due to the pressure of the molten metal, a device such as using a solid core is used. In this case, one method is to use a salt core that is soluble in water.

(8) In FIG. 2 and FIG. 3, a filter (symbol 13) having fine ventilation holes is used. An open / close lid such as a container may be used. In short, what is necessary is just to have a function of closing the tank at the time of pouring and releasing it to the atmosphere or an inert gas atmosphere such as argon for preventing oxidation of the molten metal at the time of decompression in the holding furnace.

(9) In this specification, details of the mold are not particularly mentioned. For example, a method of reducing the pressure in the cavity in order to eliminate air in the cavity has been implemented. The method according to the invention is in no way limiting for these uses.

[0058]

The effect of the new casting method according to the present invention can be clearly understood by comparing with the conventional differential pressure casting method (FIG. 12). In the differential pressure casting method, since the entire casting apparatus having a large volume needs to be covered with a high-pressure gas atmosphere, the rigidity of the pressure vessel, high-pressure gas leakage, and the like become serious problems, and thus the pressure is practically limited. At present, about 10 atm is used, but it is impractical to increase the pressure to 100 atm or more, including safety issues. For example, in the case of a cylinder block of a standard V6 engine, if the cross-sectional area of the pressure vessel is 0.7 m ² , 10 kgf
/ Ton ² at 70 tons, 100 kgf / cm ² at 700
ton load is applied. On the other hand, in the method according to the present invention, it is only necessary to press the casting after the pouring is completed by an amount corresponding to the volume shrinkage of the casting. Can be small. For example, 100 kg for a 30 kg aluminum alloy casting
When applying kgf / cm ² , the cross-sectional area of the sleeve should be 100
Assuming cm ² , the load is at most 10 tons. The ideal indentation amount (density 100%) is 6% for shrinkage and 2.
If it is 5 g / cm ² , it is as small as 72 mm.

The idea of pressure solidification using a plunger in die casting of an alloy casting having a relatively low melting point, such as aluminum, is quite old, and several methods are currently being implemented. For example, there are well-known melt forging and squeeze casting. These are mainly intended to eliminate internal defects, and are characterized by locations where pressure is applied depending on the shape, size, etc. of the casting, or specific pressing mechanisms. On the other hand, the present invention is mainly directed to castings currently being manufactured in low pressure casting, and it is particularly important in low pressure casting that the gate portion, which is the final solidified portion, is regarded as a riser and the portion is locally pressurized. It is characterized by shortening the casting cycle, which has become an important issue, thereby greatly improving productivity and eliminating internal defects (microporosity). No prior art based on such a viewpoint is found.

The effects of the casting method in comparison with the conventional differential pressure casting method and low pressure casting method are summarized as follows. (1) Dramatic improvement in feeder capacity enables significant improvement in quality. This improves the yield. (There is substantially no feeder pressure in low pressure casting.) (2) As the adhesion between the molten metal and the mold is increased, the cooling rate is greatly increased, and the mechanical properties are improved due to the denser solidified structure. . Also, the dimensional accuracy of the casting is improved. (3) Improvement of productivity (number of castings per unit time) by shortening the casting cycle. (4) Higher safety than differential pressure casting. As described above, the superiority of the casting method according to the present invention which can obtain a much larger pressing force than that of the differential pressure casting method as well as the low pressure casting method is apparent, and its economic and technical effects are extremely large.

In the present specification, the description has focused on aluminum alloy castings. However, in the gravity casting of metal having a relatively low melting point, such as zinc and magnesium, the above (1) to (1) to
It is clear that the effect of (3) can be obtained. [Literature] (1) Kononow, D .; R. : "Compress
ed-air Riers ”, Iron & Ste
el, Vol. 30 (1957) No. 11, p. 4
89 (2) Berry, J.M. T. and Watmoog
h, T .; : "Factors affecting s
aroundness in alloys withlo
ng and short freezing ran
ge ", Modern Castings, Vol.
0 (1961), no. 1, p. 63 (3) Middleton, J.M. M. and Jacks
on, W. J. : "Compressed air f
feeder heads ", British Found
d. , Vol. 55 (1962), no. 11, p. 4
43 (4) A. T. Balevski and I.I. D. N
ikolov: Bulgarian patent no. 187 (196
1), Japanese Patent Publication No. 45-19585 (5) Catalog of Metal Technology Company:
Counter-Pressure Casting
Machines, (Bulgaria) (6) Tadao Takahashi, Ken Kanashi: "Current state and future problems of low pressure casting", Castings, Vol. 66 (1994), no. 1
2, p. 940 (7) Flemings, M .; C. : "Solidif
ication Processing ”, McGra
w-Hill, Inc. , (1974), p. 234 (8) Kubo, K .; and Pehlke, R .;
D. : "Mathematical modeling
of porosity formation in
solidification ”, Metallur
medical Transactions B, Vol.
16B (1985), p. 359

[Brief description of the drawings]

FIG. 1 is a schematic view of the present invention, wherein a pressure is applied to a surface of a molten metal in a feeder (or gate) by a plunger in gravity casting of a mold. (A) shows the case where the pouring cup is mounted on the side of the sleeve, (b) shows the case where the pouring cup is mounted on the mold, and (c) shows the case where the pressurizing device is mounted on a plurality of feeders.

FIG. 2 is a schematic view of the present invention, in which pressure is applied to a molten metal at a feeder (or dry mouth) portion by a plunger in reverse gravity casting, the molten metal holding furnace, a mold apparatus, a hot water supply pipe, and a vertical direction. Is shown in FIG.

FIG. 3 is a more detailed cross-sectional view around a plunger pressurizing section in FIG. 2;

FIG. 4 is an explanatory diagram in a case where a molten metal enters a fine hole having air permeability.

FIG. 5 is a schematic view of the present invention, in which pressure is applied to a molten metal at a feeder (or gate) portion by a plunger in reverse gravity casting, and the molten metal holding furnace, a mold, a hot water supply pipe and a horizontal arrangement are provided. A case is shown in which a plunger pressurizing device is used. (A) is a schematic view of the whole, and (b) is a more detailed sectional view around the plunger pressurizing portion.

FIG. 6 is a schematic view of a two-stage press-type press device using an inner plunger.

FIG. 7 is a schematic view of the present invention, in which pressure is applied to a molten metal at a feeder (or gate) in a reverse gravity casting by a plunger, and the molten metal holding furnace, a mold, a hot water supply pipe,
This shows a case where the apparatus is composed of a plunger pressurizing device and a check valve arranged in a horizontal direction. (A) is a schematic view of the whole, and (b) is a more detailed sectional view around the plunger pressurizing portion.

FIG. 8 is a schematic diagram for explaining a state of solidification around a pressure sleeve. Dendrites have been greatly expanded.

FIG. 9 is a schematic view when the molten metal holding furnace and the mold in the apparatus of FIG. 7 are arranged horizontally.

FIG. 10 is a schematic diagram in the case where an electromagnetic pump for pouring water is attached to the apparatus of FIG. 9;

FIG. 11 is a schematic view of a conventional embedded feeder gas pressure casting.

FIG. 12 shows a conventional Counter pressure.
It is the schematic of a casting (differential pressure casting) apparatus.

FIG. 13 is a schematic view of a conventional low-pressure casting machine.

FIG. 14 is a diagram showing microporosity generated in a liquid phase portion between dendrites. d represents the diameter of the dendrite cell.

FIG. 15: Flow of liquid phase between dendrite (Darcy flow)
1 is a one-dimensional solidification model used to calculate

16 is a diagram showing calculated values of a liquid phase pressure distribution between dendrites in the one-dimensional solidification model of FIG. Material is A
l-3wt% Cu alloy, cross section is 50mm in diameter, length 50
It has a cylindrical shape of 0 mm and the heat transfer coefficient table of the casting surface is 0.0
1 cal / cm ² S ° C. (equivalent to die casting).

FIG. 17 is a diagram showing calculated values of a liquid phase pressure distribution between dendrites in the one-dimensional solidification model of FIG. 15; Material is A
l-3wt% Cu alloy, cross section is 50mm in diameter, length 50
It has a cylindrical shape of 0 mm and the heat transfer coefficient table of the casting surface is 0.0
It was set to 01 cal / cm ² S ° C (equivalent to sand casting).

FIG. 18 is a schematic diagram for explaining a mechanism in which an internal defect occurs.

FIGS. 19A and 19B are schematic diagrams for explaining a mechanism in which a feeder pressing force is transmitted to the inner surface of a mold. FIG. 19A is a diagram illustrating an alloy having a large solidification temperature zone in mold gravity casting, and FIG. (C) shows a Darcy flow pattern in the case of an alloy having a small solidification temperature section in gravity casting and in the case of an alloy having a large solidification temperature section in reverse power casting.
(D) shows an acting force line and an iso-hydraulic line generated by the riser pressure.

FIG. 20 is a schematic view of a mold used in an experiment of the present invention.

21 is a diagram showing temperature measurement data of an Al-3 wt% Cu alloy casting obtained in the atmospheric casting experiment (without pressurization) of FIG. 20. No. 1, No. 2 and No. 3 are respectively 390 mm, 210 mm and 40 mm from the bottom of the casting
Shows the center measurement position at the position of.

FIG. 22 is a diagram showing temperature measurement data of an Al-3 wt% Cu alloy casting obtained in the 50 atm pressure casting experiment of FIG. No. 1 and No. Reference numeral 2 indicates the center measurement position at positions 390 mm and 210 mm from the bottom of the casting, respectively.

FIG. 23 is a diagram showing a local coagulation time obtained in the experiment of FIG. 20.

24 is a diagram showing the density of the casting obtained in the experiment of FIG. 20, where the upper part is an upper half (length 150 mm) obtained by cutting the casting except for the feeder into two in the length direction, and the lower part is the same as the lower part. Half (length 260 mm) and average indicate the density of the entire casting.

FIG. 25 is a schematic view of the present invention using a flow operation method, which includes a main process section including a molten metal holding furnace, a mold (die) device, a hot water supply pipe, a plunger pressurizing device, etc .; , A sub-process unit including a cleaning and coating device, and a moving table connecting the two process units.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Molten-metal holding furnace 2 Molten metal 3 Holding furnace chamber 4 Gas inlet to holding furnace chamber 5 Hot water supply pipe 6 Sluice (feeder) 7 Mold (die) 8 Mold cavity 9 Relief hole of gas in cavity 10 Hydraulic cylinder 11 Piston 12 Sleeve 13 Space having a fine vent or communicating with the atmosphere 14 Heater 15 Sleeve inlet 16 Hydraulic cylinder fixing bracket 17 Backflow prevention valve 18 Valve seat 19 Valve stem 20 Electromagnetic pump 21 Hydraulic cylinder 22 Post

Claims (11)

[Claims] In a casting process using a metal mold, a pressurizing device comprising a plunger and a sleeve is provided in a feeder or a sprue, and after pouring molten metal, the feeder or the sprue of the sprue is fed. A casting method comprising applying pressure to the molten metal by the plunger. 2. In a casting process using a metal mold, a pressurizing device comprising a plunger and a sleeve is provided at a feeder or a sprue, and after pouring molten metal, the feeder or the sprue of the sprue is fed. A casting method wherein the molten metal is pressed by the plunger within a range of a pressing amount corresponding to an amount of volume shrinkage accompanying solidification of the casting, and pressure is applied. 3. In a casting process using a metal mold, a pressurizing device consisting of a plunger and a sleeve is provided in a feeder or a sprue, and after pouring molten metal, the feeder or the sprue is heated. A casting method characterized in that the plunger is pressed into the molten metal by the plunger within a range of a pressing amount corresponding to at least a volume shrinkage accompanying solidification of the casting, and pressure is applied. 4. A mold in which a sprue directly connected to a mold cavity is disposed below the cavity, a supply source of molten metal such as a molten metal holding furnace, and a hot water supply pipe extending from the supply source to the sprue. In a reverse gravity casting process in which molten metal is poured upward through a through hole, a pressurizing device consisting of a sleeve, a piston sliding in the sleeve and a plunger for driving the piston is connected to the sprue and the piston A sleeve inlet provided between an initial position before pouring in the sleeve and a sprue connecting portion is connected to a hot water supply pipe, and after the pouring into the mold cavity through the hot water supply pipe and the sleeve, the plunger A casting apparatus wherein pressure is applied to molten metal in a gate and solidified under pressure. 5. The casting apparatus according to claim 4, wherein a gas such as air or argon is passed through a molten metal inlet at a position higher than or substantially equal to a molten metal inlet provided in said sleeve without flowing molten metal. Means for communicating with the atmosphere are provided, and after the pouring is completed, the plunger is actuated, the piston closes the sleeve inlet, the atmosphere pressure in the molten metal holding furnace is reduced, and the molten metal in the hot water supply pipe is returned to the holding furnace. A casting apparatus characterized by the above-mentioned. 6. The casting apparatus according to claim 4, wherein the pressurizing device is connected to the sprue portion in a lateral direction and the piston of the pressurizing device is located at a position behind the position where the piston blocks the passage of the molten metal. After the pouring is completed, the piston is actuated, the piston is temporarily stopped at the position where the piston closes the sleeve inlet, and then the atmospheric pressure in the molten metal holding furnace is reduced or the space is communicated with the gas atmosphere. Wherein the pressure of the atmosphere is increased, and then the piston is pushed in and at the same time the molten metal in the hot water supply pipe is returned to the holding furnace. 7. The casting apparatus according to claim 4, wherein a check valve which can be opened and closed from outside is provided in a hot water supply pipe between the feeder pressurizing sleeve and the molten metal holding furnace. 8. The casting apparatus according to claim 4, wherein
A casting apparatus, wherein a pressure difference is generated between an atmosphere pressure in a molten metal holding furnace as a supply source of molten metal and an atmosphere pressure in a mold cavity, and the differential pressure is applied to the mold cavity. 9. The casting apparatus according to claim 4, wherein
A device for applying an electromagnetic force (Lorentz force) generated by the interaction of a current and a magnetic field is provided to a hot water supply pipe between a molten metal supply source and a pressure sleeve inlet or a check valve, and the electromagnetic force is applied to a mold cavity by the electromagnetic force. A casting apparatus characterized in that a pouring is performed. 10. The casting apparatus according to claim 1, wherein said pressure sleeve is provided with a heat insulation device for preventing solidification of the molten metal. 11. The casting apparatus according to claim 4, wherein the hot water supply pipe is provided with a heating and keeping device for preventing solidification of the molten metal.