Vacuum casting apparatus and vacuum casting method

Abstract

To provide a vacuum casting device including vacuum leakage prevention means that can freely adjust sealing and sliding properties according to each process of vacuum casting and molding, and to provide a vacuum casting and molding method.SOLUTION: A vacuum casting device includes: a plunger tip that slides back and forth in an injection sleeve; a plunger rod that is connected to an injection drive part operating the back and forth sliding of the plunger tip; and an adjustment ring that is arranged between the plunger tip and the plunger rod and can adjust a sliding gap with the injection sleeve. The vacuum casting device further includes a temperature control medium circulation part in which a medium circulation circuit is formed in which a temperature control medium circulates in a state where the plunger tip, the adjustment ring and the plunger rod are fastened together, and that has adjustment means of circulation pressure of the temperature control medium in the medium circulation circuit.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vacuum casting apparatus and a vacuum casting method for vacuum-sucking a mold cavity or an injection sleeve and injecting and filling molten metal supplied into the injection sleeve into the mold cavity.

Background Art

[0002] As a means for reducing casting defects such as oxidation of molten metal and void mixing due to entrainment of air, and reducing the amount of gas contained in cast products, vacuum casting is suitable, and the following steps are repeated. First, the casting mold is clamped to form a mold cavity (clamping step), and molten metal such as an aluminum alloy is supplied into the injection sleeve (molten metal supply step). Then, using a vacuum suction means provided in the casting mold or the injection sleeve, the inside of the mold cavity or the injection sleeve is vacuum-sucked (vacuum suction step). At the same time, the plunger tip is advanced to inject and fill the molten metal in the injection sleeve into the mold cavity (injection filling step), a pressure increasing step for adjusting the density of the molten metal in the mold cavity, and a cooling step for cooling the molten metal to the take-out temperature of the cast product. After that, the casting mold is opened (mold opening step), and the cast product is taken out from the mold cavity (unloading step). Subsequently, preparation steps such as cleaning the mold cavity and applying a mold release agent are performed, and the next shot is advanced.

[0003] The vacuum suction step is terminated at an arbitrary timing in the pressure increasing step or the cooling step. In this vacuum suction step, if the vacuum sealing means of the mold cavity and the injection sleeve is not appropriate, outside air flows into the mold cavity or the injection sleeve (referred to as vacuum leakage). In particular, when vacuum leakage occurs in the injection sleeve, the molten metal in the injection sleeve is disturbed by the flow of the inflowing outside air, and the molten metal may become grains and be sucked into the mold cavity (referred to as prior molten metal). The effect of vacuum casting is greatly reduced due to vacuum leakage, and the molten metal sucked in due to prior molten metal becomes a foreign substance and induces casting defects. Therefore, many means for preventing vacuum leakage of the injection sleeve have been proposed in vacuum casting.

[0004] Furthermore, if the injection sleeve is designed to enhance its vacuum leakage prevention effect (sealing ability), the plunger tip and the injection sleeve may come into strong contact during the injection filling process (galling). This galling can reduce the sliding properties between the plunger tip and the injection sleeve, potentially causing problems such as the plunger not moving smoothly forward. As a result, the filling flow of molten metal in the mold cavity becomes turbulent, leading to casting defects such as molten metal wrinkles and air entrapment. Therefore, a vacuum leakage prevention method that combines sealing ability and sliding properties is desirable.

[0005] For example, a plunger tip has been proposed that is equipped with a labyrinth seal having alternating annular convex and annular concave sections, as shown in Patent Document 1. According to this, the injection sleeve and the labyrinth seal are non-contact, thus providing both slipperiness and sealing properties. In addition, a plunger tip equipped with a seal ring and a sliding ring has been proposed, as shown in Patent Document 2. The seal ring is made of a material with a high coefficient of thermal expansion, and the sealing properties are enhanced by the thermal expansion of the seal ring, while the sliding ring is made of a highly lubricating material, thereby enhancing slipperiness. Although Patent Document 2 is intended to prevent molten metal leakage, it can also be used as a means of preventing vacuum leakage.

[0006] Furthermore, as shown in Patent Document 3, for example, it has been proposed to arrange two types of ring-shaped resin members made of different materials on top of each other on the outer surface of the plunger tip. According to this, even if the outer ring-shaped resin member expands due to heat, the inner ring-shaped resin member absorbs the thermal expansion, thereby achieving stable sealing and sliding properties. In addition, as shown in Patent Document 4, it has been proposed to adjust the gap between the plunger tip and the injection sleeve appropriately by adjusting the circulation state of the cooling water based on temperature measurement of the cooling water circulating inside the plunger tip. According to this, the thermal expansion of the plunger tip can be appropriately adjusted, preventing galling and leakage of molten metal, and achieving a balance between sealing and sliding properties. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2004-268051 [Patent Document 2] Japanese Patent Publication No. 2005-329431 [Patent Document 3] Japanese Patent Publication No. 2022-50742 [Patent Document 4] Japanese Patent Publication No. 2017-100184 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] For example, in vacuum casting using molten aluminum alloy heated to 650-700°C, the injection sleeve to which the molten metal is supplied is heated to approximately 400-500°C, and the plunger tip in contact with the molten metal is heated to approximately 500-600°C. As a result, components such as the injection sleeve and plunger tip undergo significant thermal expansion depending on the degree of heating. The amount of thermal expansion is greatest at the plunger tip, which is heated to a higher temperature. Furthermore, because the heating temperatures are not uniform, the amount of thermal expansion is also not uniform, and components such as the injection sleeve and plunger tip exhibit uneven thermal expansion, resulting in thermal deformation. For example, the injection sleeve may undergo significant curvature (known as banana deformation).

[0009] Due to this thermal expansion and deformation, it is thought that in Patent Document 1, the labyrinth seal and the injection sleeve come into strong contact, causing galling (loss of lubricity). This galling damages the labyrinth seal, resulting in a loss of sealing performance. Furthermore, in Patent Document 2, since a material with a high coefficient of thermal expansion is used for the seal ring, the thermal expansion and deformation of the plunger tip and the thermal expansion of the seal ring are added together, resulting in significant galling, severe damage to the seal ring, and a loss of sealing performance. In addition, the loss of sealing performance causes molten metal to leak, the sliding sleeve is melted and its lubricity is also lost. As a result, Patent Documents 1 and 2 cannot maintain stable sealing and lubricity.

[0010] In contrast, Patent Document 3 states that the inner ring-shaped resin member shrinks to absorb the thermal expansion of the outer ring-shaped resin member, thereby stably maintaining sealing and sliding properties. However, the repulsive force of the shrunk inner ring-shaped resin member increases in proportion to the amount of thermal expansion of the outer ring-shaped resin member, and is transmitted to the outer ring-shaped resin member, causing strong contact between the injection sleeve and the outer ring-shaped resin member and resulting in galling. Furthermore, the thermal expansion and thermal deformation of components such as the plunger tip and injection sleeve are added to the outer ring-shaped resin member, further intensifying the galling and significantly impairing the sealing and sliding properties of the outer ring-shaped resin member.

[0011] Furthermore, Patent Document 4 states that by appropriately cooling the plunger tip, thermal expansion of the plunger tip can be suppressed, thereby maintaining stable sealing and sliding properties. However, since no measures are taken regarding thermal expansion and thermal deformation of the injection sleeve, if large thermal deformation such as banana deformation occurs, it is difficult to reliably prevent galling between the plunger tip and the injection sleeve, and as a result, it cannot be denied that sealing and sliding properties will be impaired. Thus, even in Patent Documents 3 and 4, which take thermal expansion and thermal deformation into consideration, stable sealing and sliding properties cannot be maintained.

[0012] In the vacuum suction process, sealing performance is important, while in the injection filling and cooling processes, particularly in the injection filling and pressure boosting processes which are closely related to casting quality, lubricity is important for precise control of the forward movement of the plunger tip. In other words, in the vacuum suction and injection filling processes, a balance between sealing performance and lubricity is important. However, from the cooling process onward, the plunger tip only moves backward, so sealing performance is not required, and only lubricity is important. Thus, a means for preventing vacuum leakage between the injection sleeve and plunger tip that can suitably utilize sealing performance and lubricity according to each process of vacuum casting is desirable. Therefore, the present invention aims to provide a vacuum casting apparatus and a vacuum casting method equipped with a vacuum leakage prevention means that can freely adjust sealing performance and lubricity according to each process of vacuum casting. [Means for solving the problem]

[0013] The vacuum casting apparatus of the present invention is In a vacuum casting apparatus that vacuum-suctions a mold cavity or injection sleeve and injects molten metal supplied into the injection sleeve into the mold cavity, The injection sleeve comprises a plunger tip that slides in the front-rear direction within the injection sleeve, a plunger rod connected to an injection drive unit that operates the front-rear sliding of the plunger tip, and an adjustment ring positioned between the plunger tip and the plunger rod, which can adjust the sliding gap with the injection sleeve. The invention is characterized by comprising a temperature-controlled medium circulation unit having an adjustment means for raising or lowering the circulation pressure of the temperature-controlled medium, with the plunger tip, the adjustment ring, and the plunger rod being fastened together as a single unit, forming a medium circulation circuit through which the temperature-controlled medium circulates, and

[0014] In the vacuum casting apparatus of the present invention, The adjustment ring comprises a ring-shaped wheel that fits onto the plunger tip, a fixing ring that secures the wheel to the plunger tip, an elastic tip ring supported by the wheel and having a sealed space inside, and a medium inflow circuit that allows the temperature-controlled medium circulating in the medium circulation circuit to flow into the sealed space. Preferably, in response to an increase or decrease in the circulating pressure, the inflow pressure of the temperature-controlled medium flowing into the sealed space increases or decreases, causing the elastic tip ring to expand and contract, thereby adjusting the sliding gap.

[0015] Furthermore, in the vacuum casting apparatus of the present invention, Preferably, the elastic tip ring is made of an elastic material that has heat resistance.

[0016] The vacuum casting method of the present invention is In a vacuum casting molding method using the vacuum casting apparatus described in claim 1, The process comprises: a clamping step for forming the mold cavity; a molten metal supply step for supplying a predetermined amount of molten metal into the injection sleeve; a vacuum suction step for vacuum suction of the mold cavity or the injection sleeve; an injection filling step for moving the plunger tip forward to fill the mold cavity with molten metal from the injection sleeve; a pressure increasing step for adjusting the density of the molten metal in the mold cavity; a cooling step for cooling and maintaining the molten metal in the mold cavity under a predetermined pressure; and a preparation step for moving the plunger tip backward to prepare for the next shot of vacuum casting. The vacuum casting process is characterized by selecting, according to each step of the process, a sealing property formation step in which the inflow pressure of the temperature-controlled medium flowing from the medium circulation circuit into the sealed space via the medium inflow circuit is increased to expand the elastic tip ring, and a sliding property formation step in which the inflow pressure is decreased to contract the elastic tip ring.

[0017] In the vacuum casting method of the present invention, It is preferable that the inflow pressure increases and decreases in conjunction with an increase or decrease in the circulation pressure of the temperature control medium circulating in the medium circulation circuit.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a vacuum casting apparatus and a vacuum casting method equipped with a vacuum leak prevention means capable of freely adjusting the sealing property and the sliding property according to each step of vacuum casting molding.

Brief Description of the Drawings

[0019] [Figure 1] It is a conceptual diagram showing a vacuum casting apparatus according to an embodiment of the present invention. [Figure 2] It is a diagram showing a vacuum leak prevention means according to an embodiment of the present invention. [Figure 3] It is a diagram showing a vacuum casting method according to an embodiment of the present invention.

Modes for Carrying Out the Invention

[0020] Hereinafter, preferred embodiments for carrying out the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention according to each claim. Also, not all combinations of the features described in the embodiments are essential for the solution means of the invention according to each claim. Further, in the present embodiment, the scales and dimensions of each component may be exaggeratedly shown, or some components may be omitted.

[0021] (Vacuum Casting Apparatus) First, a vacuum casting apparatus according to an embodiment of the present invention will be described using Figure 1. The vacuum casting apparatus 100 shown in Figure 1 comprises a casting mold 10, an injection unit 20, a temperature-controlled medium circulation unit 30, and a vacuum suction unit 40. In Figure 1, the casting mold 10 and the injection unit 20 are arranged horizontally (a horizontal clamping horizontal casting vacuum casting apparatus), but the invention is not limited to this configuration. For example, the casting mold 10 may be arranged horizontally and the injection unit 20 may be arranged vertically (a horizontal clamping vertical casting vacuum casting apparatus), or the casting mold 10 and the injection unit 20 may be arranged vertically (a vertical clamping vertical casting vacuum casting apparatus). In any case, the components remain the same, and only the combination of the arrangement of the casting mold 10 and the injection unit 20 is changed, so the explanation will use the horizontal clamping horizontal casting vacuum casting apparatus.

[0022] The casting mold 10 comprises a fixed mold 11 and a movable mold 12 supported by a clamping mechanism (not shown). A mold cavity 13 is formed by clamping the fixed mold 11 and the movable mold 12 using the clamping mechanism. Molten metal such as aluminum alloy is injected and filled into this mold cavity 13 to obtain a casting. A release agent is applied to the mold cavity 13 before the molten metal is injected and filled to facilitate the removal of the casting from the mold cavity 13. In addition, to stabilize the temperature of the casting when it is removed, the casting mold 10 is adjusted to a predetermined temperature by a temperature control mechanism (not shown).

[0023] The injection unit 20 comprises a cylindrical injection sleeve 21, a pouring port 22 for supplying molten metal into the injection sleeve 21, a plunger tip 23 that slides in the front-rear direction within the injection sleeve 21, an adjustment ring 25, and a plunger rod 24. The tip of the injection sleeve 21 is connected to a gate 14 that communicates with the mold cavity 13. Here, with respect to the sliding operation of the plunger tip 23, the direction approaching the gate 14 is defined as forward F, the movement toward forward F is defined as forward movement, the direction away from the gate 14 is defined as rearward R, and the movement toward rearward R is defined as backward movement. The plunger tip 23, adjustment ring 25, and plunger rod 24 are connected in that order from forward F to rearward R and integrated, and the rearward R of the plunger rod 24 is connected to the injection drive unit 26. The injection control unit 27 operates the injection drive unit 26 to move the integrated plunger rod 24, adjustment ring 25, and plunger tip 23 forward, pressing the molten metal supplied into the injection sleeve 21 and injecting it into the mold cavity 13 via the gate 14.

[0024] The injection sleeve 21 and plunger tip 23 are provided with cooling means (not shown) including a channel through which a cooling medium such as cooling water flows, as needed. Furthermore, it is preferable to apply a lubricant to the sliding surfaces of the injection sleeve 21 and plunger tip 23 in order to prevent wear damage to the plunger tip 23, stabilize the sliding state, and suppress the adhesion of molten metal residue.

[0025] The temperature-controlled medium circulation unit 30 includes a medium temperature control unit 31 that adjusts the temperature and circulates the stored temperature-controlled medium, an inlet pipe 32 that flows the temperature-controlled medium from the medium temperature control unit 31 to the injection unit 20, an outlet pipe 33 that returns the temperature-controlled medium from the injection unit 20 to the medium temperature control unit 31, and a pipe joint 34 that connects the inlet pipe 32 and the outlet pipe 33 to circulate the temperature-controlled medium within the injection unit 20. A pressure adjustment valve 35 is located in the inlet pipe 32, and an on / off valve 36 is located in the outlet pipe 33. By operating these two valves (35, 36), the circulation pressure of the circulating temperature-controlled medium is adjusted to increase or decrease (referred to as a means for adjusting the circulation pressure). The on / off valve 36 is operated by a valve control unit 37. The temperature-controlled medium whose pressure has been adjusted by the pressure control valve 35 is returned to the medium temperature control unit 31 via an auxiliary pipe 38.

[0026] The vacuum suction unit 40 uses a mold suction unit 41 positioned in the casting mold 10 to directly vacuum-suction the inside of the mold cavity 13 via a suction groove 42. Alternatively, it uses an injection sleeve suction unit 45 connected to a suction hole 44 provided in the injection sleeve 21 to vacuum-suction the inside of the injection sleeve 21. Since the injection sleeve 21 and the mold cavity 13 are in communication via the gate 14, the inside of the mold cavity 13 is indirectly vacuum-suctioned. Furthermore, by vacuum-suctioning the mold cavity 13, the inside of the injection sleeve 21 is also indirectly vacuum-suctioned. The mold suction unit 41 or the injection sleeve suction unit 45 is operated by the suction control unit 43. Direct vacuum suction and indirect vacuum suction may be selected simultaneously, or either one may be selected. In vacuum casting, the operation of vacuum-suctioning the mold cavity 13, whether directly or indirectly, is called the vacuum suction process.

[0027] Vacuum casting is considered a suitable method for preventing oxidation of molten metal, reducing casting defects such as voids caused by air entrapment, and reducing the amount of gas contained in the casting. Therefore, high precision is required for vacuum suction within the mold cavity 13 and injection sleeve 21. To this end, vacuum leakage prevention measures, such as sealing members, are provided in the mold cavity 13 and injection sleeve 21 to maintain the effect of vacuum suction. Since the casting mold 10 does not move after the mold cavity 13 is formed, the vacuum leakage prevention measures in the mold cavity 13 can be made relatively robust. However, the injection sleeve 21 has an open rear radius, and the gaps in the vacuum leakage prevention measures change irregularly due to the sliding operation of the plunger tip 23 and the irregular thermal expansion and deformation of the injection sleeve 21 and plunger tip 23. It is considered a problem that outside air flows in through these changing gaps, significantly reducing the effect of vacuum suction.

[0028] Here, for example, if vacuum leak prevention measures are taken, such as setting a small gap in advance to account for irregular thermal expansion or deformation, the plunger tip 23 and the injection sleeve 21 may come into strong contact, causing galling. As a result, the vacuum leak prevention measures may be severely damaged, and the effectiveness of vacuum suction may not be sustained, which has become a new problem. Furthermore, since the state of molten metal filling and flow in the mold cavity 13 greatly affects the quality of the casting, the forward movement of the plunger tip 23 requires highly precise control. For this reason, good sliding properties between the plunger tip 23 and the injection sleeve 21 are required. In addition, the vacuum suction process requires reliable sealing to prevent vacuum leaks. On the other hand, the retraction movement of the plunger tip 23 after injection filling does not require sealing, and it is preferable to prioritize sliding properties. Thus, a vacuum leak prevention measure between the injection sleeve 21 and the plunger tip 23 that can suitably utilize sealing and sliding properties according to each process of vacuum casting is desirable. Therefore, a vacuum leak prevention means that can freely adjust sealing and sliding properties according to each step of the vacuum casting process will be explained in detail using Figure 2.

[0029] (Method to prevent vacuum leaks) Next, a vacuum leak prevention means according to an embodiment of the present invention will be described with reference to Figure 2. Figure 2 is an enlarged view of area D shown in Figure 1. From the front F to the rear R, the plunger tip 23, the adjustment ring 25, and the plunger rod 24 are integrally connected, forming a medium circulation circuit 232 through which the temperature-controlled medium circulates, and the tip of the medium circulation circuit 232 is connected to a circulation space 231 formed in the plunger tip 23. The temperature-controlled medium circulates through the medium circulation circuit 232 and the circulation space 231, thereby adjusting the plunger tip 23 to an appropriate temperature state. The vacuum leak prevention means is provided on the adjustment ring 25.

[0030] First, Figure 2(a) shows an embodiment of a vacuum leak prevention means prioritizing slipperiness. The adjustment ring 25 comprises a ring-shaped wheel 251 that fits onto the plunger tip 23, an elastic tip ring 252 supported by the wheel 251 and having a sealed space 253 inside, and a medium inflow circuit 255 that allows the temperature-controlled medium circulating in the medium circulation circuit 232 to flow into the sealed space 253. As shown in Figure 1, the temperature-controlled medium discharged from the medium temperature-controlled section 31 of the temperature-controlled medium circulation section 30 flows through the inlet pipe 32, flows into the medium circulation circuit 232 via the pipe joint 34, and flows toward the circulation space 231 (temperature-controlled medium flow 233). The temperature-controlled medium that arrives in the circulation space 231 flows in a swirling manner within the circulation space 231 (temperature-controlled medium flow 234) and returns to the medium circulation circuit 232. For this reason, as shown in Figure 2, it is preferable that the medium circulation circuit 232 has a double structure.

[0031] The temperature-controlled medium that returns from the circulation space 231 to the medium circulation circuit 232 flows through the medium circulation circuit 232 (temperature-controlled medium flow 235), and then, as shown in Figure 1, flows through the pipe joint 34 and the outlet pipe 33 to return to the medium temperature-controlled unit 31. In this way, the temperature-controlled medium circulates between the medium temperature-controlled unit 31 and the circulation space 231 (temperature-controlled medium flow 233-235). A portion of the temperature-controlled medium flow 235 passes through the medium inflow circuit 255 and flows into the sealed space 253.

[0032] At this time, the valve control unit 37, as shown in Figure 1, operates the on / off valve 36 to fully open it. By operating this circulation pressure adjustment means, the temperature-controlled medium circulates smoothly between the medium temperature control unit 31 and the circulation space 231, and the circulation pressure of the temperature-controlled medium flow 235 can be reduced. As a result, the inflow pressure of the temperature-controlled medium flow 235 that has passed through the medium inflow circuit 255 and flowed into the sealed space 253 also decreases, and the elastic tip ring 252 shrinks to its original size. The original size of the elastic tip ring 252 is set so that a gap is created between the injection sleeve 21 and the elastic tip ring 252. This gap allows the plunger tip 23 to slide smoothly, ensuring good lubricity. However, sealing performance cannot be expected in this state.

[0033] Next, Figure 2(b) shows a configuration of a vacuum leak prevention means prioritizing sealing performance. Note that explanations of parts that overlap with Figure 2(a) are omitted. With the temperature-controlled medium circulating between the medium temperature control unit 31 and the circulation space 231, the valve control unit 37, as shown in Figure 1, operates the on / off valve 36 to a fully closed state. This operation of the circulation pressure adjustment means causes the flow of the temperature-controlled medium 235 to stagnate and the circulation pressure to rise. As a result, the inflow pressure of the temperature-controlled medium that has passed through the medium inflow circuit 255 and flowed into the sealed space 253 increases, and the elastic tip ring 252 expands toward the injection sleeve 21. This expansion eliminates the gap between the elastic tip ring 252 and the injection sleeve 21, resulting in a strong seal. Note that in this state, sliding performance cannot be expected.

[0034] In this way, by operating the on / off valve 36, which is a means for adjusting the circulation pressure, the inflow pressure of the temperature-controlled medium flowing into the sealed space 253 increases or decreases in conjunction with the increase or decrease in the circulation pressure of the temperature-controlled medium flow 235, and the expansion and contraction of the elastic tip ring 252 can be precisely selected. By utilizing the expansion and contraction of this elastic tip ring 252, the sealing and sliding properties of the vacuum leak prevention means can be precisely controlled. Furthermore, by adjusting the balance of the increase or decrease in the inflow pressure of the temperature-controlled medium by operating the circulation pressure adjustment means and appropriately adjusting the amount of expansion of the elastic tip ring 252, it is possible to apply both the pressing force of the elastic tip ring 252 to the injection sleeve 21 (sealing properties) and the gap between the injection sleeve 21 and the elastic tip ring 252 (sliding properties). This makes it possible to provide a vacuum casting apparatus that realizes stable production of high-quality vacuum castings.

[0035] For example, by operating the on / off valve 36, which is a means for adjusting the circulation pressure, as shown in Figure 1, the valve opening can be adjusted within the range of a fully closed state and a fully open state to adjust the circulation pressure of the temperature-controlled medium flow 235 to any desired state. Alternatively, by operating the pressure adjustment valve 35, which is a means for adjusting the circulation pressure, a limit can be set on the circulation pressure of the temperature-controlled medium circulating between the medium temperature control unit 31 and the circulation space unit 231, thereby adjusting the circulation pressure of the temperature-controlled medium flow 235 to any desired state. Furthermore, the circulation pressure of the temperature-controlled medium flow 235 may be adjusted by operating both the on / off valve 36 and the pressure adjustment valve 35, which are two means for adjusting the circulation pressure. In addition, for example, the amount of temperature-controlled medium discharged from the medium temperature control unit 31 may also be used as a means for adjusting the circulation pressure of the temperature-controlled medium flow 235. It is preferable to appropriately select the expansion and contraction of the elastic tip ring 252 according to each step of the vacuum casting process.

[0036] Here, the elastic tip ring 252 is selected from an elastic material that expands and contracts (elastically deforms) in response to the rise and fall of the circulation pressure of the temperature-controlled medium flow 235 (the pressure at which the temperature-controlled medium flows into the sealed space 253). Furthermore, considering the temperature rise of the injection sleeve 21 and plunger tip 23 (heating by the molten metal and cooling by the temperature-controlled medium), it is preferable to use an elastic material with a heat resistance of 300°C or higher. For example, a silicone-based heat-resistant rubber material or a fluorine-based heat-resistant rubber material that satisfies both heat resistance and elastic deformation is used for the elastic tip ring 252. In addition, modifiers that can enhance heat resistance, such as glass fibers or carbon fibers, may be added to the silicone-based rubber material or fluorine-based rubber material to further increase the heat resistance. Alternatively, a new material called metallic rubber, which is said to exhibit rubber-like elastic behavior by applying a special treatment to the metal surface, may be used. Furthermore, it is preferable that the elastic tip ring 252 and the wheel 251 are shaped so that the temperature-controlled medium flowing into the sealed space 253 does not leak out.

[0037] Furthermore, for example, if the elastic tip ring 252 wears out and the effectiveness of the vacuum leak prevention mechanism diminishes, the wheel 251 and elastic tip ring 252 can be easily removed by disconnecting the plunger tip 23 and plunger rod 24 and releasing the fixing of the fixing ring 254. In this state, the elastic tip ring 252 can be removed from the wheel 251 and the elastic tip ring 252 can be replaced. After that, the elastic tip ring 252 and wheel 251 can be fitted onto the plunger tip 23 in the reverse order and fixed with the fixing ring 254, thereby restoring the vacuum leak prevention mechanism to a normal state. In this way, the effectiveness of the vacuum leak prevention mechanism can be maintained with simple operations.

[0038] (Vacuum casting method) Next, a vacuum casting method according to an embodiment of the present invention will be described with reference to Figure 3.

[0039] First, as shown in Figure 3(a), we will explain the preparation process for starting production casting after completing a test casting to stabilize the temperature of the casting mold 10 and injection sleeve 21, and to confirm the filling state of the molten metal in the mold cavity 13. The preparation process involves cleaning the mold cavity 13 and applying a release agent, cleaning the plunger tip 23 and injection sleeve 21 and applying a lubricant, and setting the plunger tip 23 to position A as shown in Figure 1. During the preparation process, the elastic tip ring 252 is contracted to ensure smooth sliding.

[0040] Next, a clamping mechanism (not shown) is operated to clamp the fixed mold 11 and the movable mold 12 together to form the mold cavity 13 and gate 14 (clamping step). A predetermined amount of molten metal is also supplied from the pouring port 22 into the injection sleeve 21 using a molten metal supply mechanism (not shown) (molten metal supply step). Subsequently, the injection control unit 27 operates the injection drive unit 26 to move the plunger tip 23 forward. When the plunger tip 23 reaches position B, the forward movement of the plunger tip 23 is slowed down, or preferably, the plunger tip 23 is stopped. Then, the valve control unit 37 closes the on / off valve 36, which is a means for adjusting the circulation pressure, to increase the inflow pressure of the temperature-controlled medium flowing into the sealed space 253, thereby expanding the elastic tip ring 252 and ensuring a seal (seal formation step). Following this sealing process, the suction control unit 43 operates the injection sleeve suction unit 45 or the mold suction unit 41 to create a vacuum inside the injection sleeve 21 or the mold cavity 13 (vacuum suction process).

[0041] Next, as shown in Figure 3(b), at any timing during the vacuum suction process, the injection control unit 27 operates the injection drive unit 26 to move the plunger tip 23 forward and perform casting. First, an injection filling process is performed in which the molten metal in the injection sleeve 21 is pressed and the mold cavity 13 is filled with molten metal. This is followed by a pressure increasing process to adjust the density of the molten metal in the mold cavity 13, and a cooling process to cool and hold the molten metal under a predetermined pressure. During this process, the forward movement of the plunger tip 23 continues. Finally, the plunger tip 23 reaches position C. The pressure increasing process also includes pressure adjustment (called the holding pressure process) in response to the solidification shrinkage of the molten metal due to cooling.

[0042] Furthermore, the injection filling process consists of a low-speed injection process that fills the injection sleeve 21 with molten metal, and a high-speed injection process that fills the mold cavity 13 with molten metal at high speed. The quality of the casting is largely determined by these low-speed and high-speed injection processes. Therefore, the plunger tip 23 and the injection sleeve 21 are required to have appropriate sliding properties so as not to hinder the forward movement of the plunger tip 23. In addition, since the injection filling process and the vacuum suction process proceed simultaneously, reliable sealing is also required. By appropriately adjusting the expansion amount of the elastic tip ring 252, a state that combines both sliding properties and sealing properties can be provided.

[0043] At any point between the pressurization process and the cooling process, the suction control unit 43 operates the injection sleeve suction unit 45 or the mold suction unit 41 to stop vacuum suction and end the vacuum suction process. After that, the movable mold 12 and the fixed mold 11 are opened (mold opening process), and the cooled and solidified casting is removed from the mold cavity 13 using a removal means (not shown) (removal process).

[0044] Furthermore, after the plunger tip 23 reaches position C, the valve control unit 37 opens the on / off valve 36, which is a means for adjusting the circulation pressure, in conjunction with the end of the vacuum suction process. This lowers the inflow pressure of the temperature-controlled medium flowing into the sealed space 253, causing the elastic tip ring 252 to contract and ensure slipperiness (slipperiness formation process). Following this slipperiness formation process, the injection control unit 27 operates the injection drive unit 26 to retract the plunger tip 23. This allows the plunger tip 23 to retract at high speed without contact between it and the injection sleeve 21 (without galling), thus shortening the vacuum casting cycle. When the plunger tip 23 reaches position A, the plunger tip 23 is stopped. If the unloading process has been completed at this point, the process returns to the preparation process shown in Figure 3(a). In this way, by freely selecting and using the sealing properties formation process and the sliding properties formation process according to each step of the vacuum casting process, and by adjusting the balance between sliding properties and sealing properties to an appropriate state, it is possible to provide a vacuum casting method that enables stable production of high-quality vacuum castings. Furthermore, by performing the sliding properties formation process at the appropriate timing, heat transfer from the high-temperature injection sleeve 21 is blocked, minimizing thermal damage to the elastic tip ring 252 and contributing to extending the lifespan of the elastic tip ring 252.

[0045] Although preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the embodiments described above. Various modifications or improvements can be made to the above embodiments. [Explanation of symbols]

[0046] 100 Vacuum casting apparatus 10 Casting molds 11 Fixed mold 12. Movable molds 13 Mold Cavity Gate 14 20 Injection part 21 Injection Sleeve 22 pouring spouts 23 Plunger Tip 231 Circulation space section 232 Media circulation circuit 233~235 Temperature control medium flow 24 Plunger Rods 25 Adjustment Ring 251 wheels 252 Elastic Tip Ring 253 Closed Space 254 Retaining ring 255 Media inflow circuit 26 Injection drive unit 27 Injection Control Unit 30 Temperature control medium circulation section 31 Medium temperature control section 32 Inlet piping 33 Outlet piping 34 Piping fittings 35 Pressure regulating valve 36. On / off valve 37 Valve control unit 38 Auxiliary piping 40 Vacuum suction section 41 Mold suction part 42 Suction groove 43 Suction Control Unit 44 Suction hole 45 Injection sleeve suction section F forward R rear D area A~C position

Claims

1. In a vacuum casting apparatus that vacuum-suctions a mold cavity or injection sleeve and injects molten metal supplied into the injection sleeve into the mold cavity, The injection sleeve comprises a plunger tip that slides in the front-rear direction within the injection sleeve, a plunger rod connected to an injection drive unit that operates the front-rear sliding of the plunger tip, and an adjustment ring positioned between the plunger tip and the plunger rod, which can adjust the sliding gap with the injection sleeve. With the plunger tip, adjustment ring, and plunger rod fastened together as a single unit, a media circulation circuit is formed through which the temperature-controlled medium circulates, and the temperature-controlled medium circulation unit has an adjustment means for raising or lowering the circulation pressure of the temperature-controlled medium within the media circulation circuit. The adjustment ring comprises a ring-shaped wheel that fits onto the plunger tip, a fixing ring that secures the wheel to the plunger tip, an elastic tip ring supported by the wheel and having a sealed space inside, and a medium inflow circuit that allows the temperature-controlled medium circulating in the medium circulation circuit to flow into the sealed space. A vacuum casting apparatus characterized in that, in response to an increase or decrease in the circulation pressure, the inflow pressure of the temperature-controlled medium flowing into the sealed space increases or decreases, causing the elastic tip ring to expand or contract and adjust the sliding gap.

2. The vacuum casting apparatus according to claim 1, wherein the elastic tip ring is made of a heat-resistant elastic material.

3. In a vacuum casting method using the vacuum casting apparatus described in claim 1 or 2, The process comprises: a clamping step for forming the mold cavity; a molten metal supply step for supplying a predetermined amount of molten metal into the injection sleeve; a vacuum suction step for vacuum suction of the mold cavity or the injection sleeve; an injection filling step for moving the plunger tip forward to fill the mold cavity with molten metal from the injection sleeve; a pressure increasing step for adjusting the density of the molten metal in the mold cavity; a cooling step for cooling and maintaining the molten metal in the mold cavity under a predetermined pressure; and a preparation step for moving the plunger tip backward to prepare for the next shot of vacuum casting. A vacuum casting method characterized by selecting, according to each step of the vacuum casting process, a sealing property formation step in which the inflow pressure is increased to expand the elastic tip ring, and a sliding property formation step in which the inflow pressure is decreased to contract the elastic tip ring.

4. The vacuum casting method according to claim 3, wherein the inflow pressure increases and decreases in conjunction with the increase or decrease of the circulation pressure.

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