Patent Application
20160236274
The present invention relates to a casting apparatus for obtaining desired castings with a gas-permeable casting mold, and a method for producing a casting using it.
To produce castings by gravity pouring (hereinafter also called “pouring”), a gas-permeable casting mold composed of sand particles (so-called sand mold) is most generally used. With such a gas-permeable casting mold, a gas (generally air) remaining in a cavity of a particular shape is pushed out of the cavity by a metal melt (hereinafter also called “melt”), and the melt is formed into a casting having substantially the same shape as the cavity. The cavity of the casting mold generally includes a sprue, a runner, a feeder and a product-forming cavity, into which a melt is supplied in this order. In the conventional technologies, when a melt head in the sprue becomes high enough to fill a product-forming cavity, the pouring of the melt is finished.
A solidified melt forms a casting integrally extending from the sprue to the runner, the feeder and the product-forming cavity. The feeder is not an unnecessary portion for obtaining sound castings, while the sprue and the runner are merely paths for a melt to reach the product-forming cavity, which need not be filled with the melt. Thus, as long as a melt filling the sprue and the runner is solidified, drastic improvement in a pouring yield cannot be expected. In the case of castings integrally having unnecessary portions, considerable numbers of steps are needed to separate cast products from unnecessary portions, resulting in low production efficiency. Accordingly, the sprue and the runner pose large problems in increasing efficiency in gravity casting.
Recently, a revolutionary method for solving the above problems has been proposed by JP 2007-75862 A and JP 2010-269345 A. To fill a desired cavity portion, part of a cavity in a gas-permeable casting mold, this method pours a metal melt into the cavity by gravity in a volume smaller than that of an entire casting mold cavity and substantially equal to that of the desired cavity portion; supplies a compressed gas to the cavity through a sprue before the melt fills the desired cavity portion; and then solidifies the melt filling the desired cavity portion. By this method, it is expected to make it substantially unnecessary to fill a sprue and a runner with a melt, because pressure to be obtained by the melt head height is given by the compressed gas.
As a result of reviewing the method described in JP 2007-75862 A and JP 2010-269345 A, the inventors have found that necessary switching from a gravity-pouring step to a gas-blowing step is not well timed, resulting in stagnant melt supply to the product-forming cavity, and thus likely providing products with cold shut, pull down, and other defects. To avoid problems due to such stagnation of melt supply, a casting apparatus is required to conduct such switching as quickly as possible. However, any specific structures and operations therefor have not been proposed yet.
Accordingly, an object of the present invention is to provide a casting apparatus capable of quickly switching from a gravity-pouring step to a gas-blowing step, and a method for producing a casting using it.
As a result of intensive research in view of the above object, the inventors have found that the above problem can be solved by placing a gas- ejecting member at a position just above a tubular portion of a sprue at least at the end of pouring of the melt, and simply moving it downward after the pouring of the melt ends, thereby connecting the gas-ejecting member to the sprue. The present invention has been completed based on such finding.
Thus, the casting apparatus of the present invention for producing a casting by pouring a metal melt into a gas-permeable casting mold by gravity, comprises:
The gas-ejecting member is preferably placed by the above mechanism such that its gas-ejecting port is below the upper edge of the cup portion.
The gas-ejecting member is preferably placed by the above mechanism such that its gas-ejecting port comes into contact with the melt residing in the cup portion.
The gas-ejecting member is preferably a tapered nozzle capable of being inserted into the tubular portion.
The pouring means preferably enables a melt stream to move between a position just above or near the tubular portion and a position away from the tubular portion within a region of the cup portion.
The cup portion preferably extends in one direction from the tubular portion. Such a cup portion preferably has a racetrack shape, and preferably becomes gradually shallower as separating from the tubular portion.
The casting apparatus of the present invention preferably comprises a means for detecting a surface of the melt residing in the sprue and outputting the detected signal; and a gas-ejecting-member-position-controlling means for receiving the output signal from the melt-surface-detecting means, and driving the gas-ejecting-member-moving mechanism to move the gas-ejecting member according to the signal.
The method of the present invention for producing a casting comprises the steps of
In the method of the present invention, the gas-ejecting member is preferably placed such that its gas-ejecting port is below the upper edge of the cup portion.
In the method of the present invention, the gas-ejecting member is preferably placed such that its gas-ejecting port comes into contact with the melt residing in the cup portion.
The method of the present invention preferably comprises the steps of placing a stream of the melt, which is poured from a pouring means, at a position just above or near the tubular portion at an early stage of the pouring step, and moving the melt stream away therefrom within a region of the cup portion at an late stage of the pouring step.
The method of the present invention preferably comprises the step of controlling the position of the gas-ejecting member of the gas-blowing unit depending on a surface position of the melt residing in the sprue.
In conventional gravity-casting, melt supply would not stagnate unless a casting apparatus, etc. were malfunctioned, because a sufficient amount of a melt is poured into a product-forming cavity by gravity. On the other hand, in casting in which a gravity-pouring step is followed by a gas-blowing step, as proposed by JP 2007-75862 A and JP 2010-269345 A, the stagnation of melt supply, if any, should end in a short period of time while switching the steps, to avoid the deterioration of product quality.
In view of this, the casting apparatus of the present invention comprises a gas-blowing unit placed at a position just above a sprue and not interfering with a pouring means at least during gravity-pouring, such that the gas-blowing unit can be quickly connected to the sprue after pouring ends. Such a structure can shorten the stagnation of melt supply into the product-forming cavity. The present invention will be explained in detail below.
The casting apparatus of the present invention for producing a casting by pouring a metal melt into a gas-permeable casting mold by gravity, comprises:
As shown in
The gas-permeable casting mold for producing a casting by pouring the metal melt by gravity comprises a cavity including a sprue into which the metal melt is poured, a runner constituting a flow path of the metal melt supplied through the sprue, and a product-forming cavity to be filled with the melt sent through the runner. The cavity may include a feeder, if necessary.
The gas-permeable casting mold is generally formed by sand particles such as a green sand mold, a shell mold and a self-hardening mold, and may be formed by ceramic or metal particles. The gas-permeable casting mold could be formed by materials having substantially no gas permeability, such as gypsum, if gas-permeable materials were mixed, or partially gas-permeable materials were used to have sufficient gas permeability. Even a mold made of a material having no gas permeability at all, such as a metal die, can be used as a gas-permeable casting mold, when gas permeability is given by gas-flowing holes such as vents.
The sprue comprises a tubular portion constituting a flow path to the runner, and a cup portion having a larger diameter than that of the tubular portion to receive the metal melt poured from the pouring means. That is, the cup portion has a larger opening than that of the tubular portion. With such a cup portion having a larger opening, the sprue can receive the melt poured from the pouring means by gravity, even when the pouring means retreats from an operation range of the gas-blowing unit, thereby efficiently pouring the melt into the sprue by gravity until pouring ends. When a more melt than flowing down through the tubular portion is poured from the pouring means, the cup portion acts as a temporary storage of the melt, especially at an early stage of the pouring step, thereby preventing the melt from overflowing the casting mold.
The cup portion having a larger opening than the tubular portion has such a shape as a bowl-like, conical, pyramidal, truncated conical, or truncated pyramidal shape. With the cup portion having a large opening, the pouring means can retreat to a wide area. In the simplest apparatus permitting the pouring means to move in one direction as shown in
The cup portion may be generally formed by rotating a flat sprue cutter having a U-shaped edge. Such a sprue cutter can easily form a bowl-like or conical shape, which may be laterally stretched. For instance, by moving the sprue cutter for forming a cup-like recess laterally from the upper end of the tubular portion, as shown in
The pouring means may be a ladle, a pouring pipe, a pouring gutter, etc. For quick switching from a gravity-pouring step to a gas-blowing step, a gas-ejecting member described below should be able to be moved downward and connected to the sprue, immediately after pouring ends. To this end, the pouring means should not interfere with the gas-ejecting member to be connected to the tubular portion at least in the connecting step. That is, the pouring means should retreat from an operation range of the gas-ejecting member until pouring ends. The pouring means is more preferably located at a position away from an operation range of the gas-ejecting member before and during the pouring step.
The melt may be poured from the pouring means, for instance, by (a) pouring the melt to the tubular portion or its vicinity in the entire period of the pouring step; (b) pouring the melt to the tubular portion or its vicinity at an early stage of the pouring step, and then moving a stream of the melt away therefrom at a late stage of the pouring step; or (c) pouring the melt to a position away from the tubular portion in the cup portion having a larger opening, since an early stage of the pouring step. The pouring position of the melt can be controlled, for instance, by adjusting a tilt angle of the ladle used as the pouring means, or by using a pouring-means-moving unit described below.
Although the process (a) can most efficiently have the melt flow into the tubular portion, it may bring a melt stream into contact with the gas-ejecting member brought close to the tubular portion, thereby splashing the melt around, likely resulting in lower safety and shortage of the melt flowing into the tubular portion. Although the process (c) can place the gas-ejecting member close to the tubular portion at the early stage, it is less efficient in flowing the melt into the tubular portion than the processes (a) and (b). In addition, it inevitably brings all the melt into contact with an inner surface of the cup portion since an early stage of the pouring step, resulting in increase in damages of the cup portion due to the melt, inclusion of foreign matters, oxidation of the melt, etc. Accordingly, the process (b) is preferable because it has sufficient efficiency in flowing the melt into the tubular portion, without bringing the melt stream into contact with the gas-ejecting member brought close to the tubular portion.
As described above, the casting apparatus preferably comprises a pouring-means-moving unit, as a unit for moving the pouring means away from an operation range of the gas-ejecting member until pouring ends, and/or as a unit for placing the melt stream at a position just above or near the tubular portion at an early stage of the pouring step, and then appropriately moving it away therefrom within the cup portion at a late stage of the pouring step. This pouring-means-moving unit can move the pouring means away from an operation range of the gas-blowing unit until pouring ends, making it possible to quickly move the gas-ejecting member downward for connection to the tubular portion after pouring ends, thereby suppressing melt splashing due to the contact of the melt stream with the gas-ejecting member, damages of the cup portion due to the melt, inclusion of foreign matters, and oxidation of the melt.
A simple method of moving the pouring means in one direction (horizontal direction) from the tubular portion is preferable.
The gas-blowing unit comprises a gas flow generator and a gas-ejecting member having a portion to be connected to the sprue. The gas-ejecting member is placed at a position just above the tubular portion and not interfering with gravity pouring from the pouring means, by a gas-ejecting-member-moving mechanism described below; and then moved downward for connection to the tubular portion after the pouring ends. Subsequently, a gas is blown from the gas flow generator to push the melt into the product-forming cavity.
The gas flow generator may be a fan, a blower, etc. for supplying a gas flow, a compressor for generating a compressed gas flow, etc. The compressed gas is preferable because it can uniformly push the melt with larger pressure.
While the entire gas-blowing unit may be moved for connection to the sprue, only part of the gas-blowing unit, a gas-ejecting member, is preferably moved by the gas-ejecting-member-moving mechanism described below. This makes it possible to connect the gas-ejecting member to the sprue, to introduce the gas blown from the gas-blowing unit into the casting mold, and to efficiently fill the desired cavity with the poured melt, with lower energy in a shorter period of time than when the entire gas-blowing unit is moved.
The gas-ejecting member of the gas-blowing unit is preferably a nozzle. Fit into the sprue, the nozzle can be quickly connected to the sprue without gas leak. The nozzle preferably has a tapered side surface for easy fitting. When the sprue has a tapered side wall, the nozzle can be surely fit into the sprue.
Because the gas-ejecting member is exposed to a high-temperature melt, it is preferably made of refractory materials, graphite, alumina-graphite, silicon nitride, sialon, etc.
Though not restrictive, the gas used in the present invention may be air from the aspect of cost, or a non-oxidizing gas such as argon, nitrogen and carbon dioxide from the aspect of preventing the oxidation of the melt. Together with the gas, a cooling medium such as mist to accelerate cooling, or sold materials such as refractory particles as shown in JP 2010-269345 A to shut the runner off, may be supplied.
With the gas-ejecting-member-moving mechanism, the gas-ejecting member, which is at a position just above the tubular portion and not interfering with gravity pouring from the pouring means at least during the pouring step, is moved downward for connection to the tubular portion. The gas-ejecting member is connected to the sprue, for instance, by three steps of (i) placing the gas-ejecting member at a position just above the tubular portion of the sprue and not interfering with gravity pouring from the pouring means, (ii) bringing it close to the sprue, and (iii) connecting it to the tubular portion. A time required for each step (i) to (iii) should be shortened to quickly switch the gravity-pouring step to the gas-blowing step.
At least at the end of pouring, the gas-ejecting member should be placed at a position just above the tubular portion of the sprue and not interfering with gravity pouring from the pouring means, as shown in
“Placing the gas-ejecting member at a position just above the tubular portion 5b” means that the gas-blowing nozzle (gas-ejecting member) 1a is stopped at an arbitrary vertical position above the tubular portion 5b for a certain period of time or for a moment (not excluding direction change from a horizontal direction to a vertical direction, vertical direction change, etc.), or slightly moving to follow a melt surface, etc. Hereinafter, these variations may be simply called “placing.”
The gas-blowing nozzle 1a is placed at a position horizontally away from the tubular portion 5b of the sprue 5, before the pouring step begins, or at an early stage of the pouring step; moved to a position just above the tubular portion 5b and not interfering with gravity pouring of the metal melt during pouring [
On the other hand, as shown in
To shorten a time required for the step (ii) where the gas-ejecting member is brought close to the sprue, the gas-ejecting member is preferably placed such that its gas-ejecting port is below the upper edge of the cup portion. This makes the gas-ejecting member of the gas-blowing unit close to the tubular portion, thereby saving a time to connect the gas-blowing unit to the tubular portion. In this case, the gas-ejecting member of the gas-blowing unit may be moved downward to follow a lowering melt surface, as the melt pooled in the cup portion flows down into the tubular portion during the pouring step.
The gas-ejecting member at a position away from the tubular portion of the sprue may be first horizontally moved to a position just above the tubular portion of the sprue during the pouring step, and then moved downward to a position such that its gas-ejecting port is below the upper edge of the cup portion; or may be directly moved to a position at which its gas-ejecting port is below the upper edge of the cup portion.
The “during the pouring step” used herein means a time period from the beginning of pouring the melt from the pouring means to the cup portion of the sprue to the end of flowing the melt in the cup portion into the tubular portion. The term “the end of flowing the melt in the cup portion into the tubular portion” means a time at which the flowing of a sufficient melt to fill the product-forming cavity into the tubular portion is completed, though the melt may remain in the cup portion.
The gas-ejecting port of the gas-ejecting member preferably comes into contact with the melt in the cup portion, making the gas-ejecting member close to the tubular portion, thereby shortening a time required for the step (ii). In this case, the gas-ejecting port may enter the melt in the cup portion. To prevent the melt from intruding into the gas-ejecting member through the gas-ejecting port, the gas-blowing unit may blow a gas during the pouring step.
To place the gas-ejecting member close to the melt in the cup portion, the casting apparatus preferably comprises a means for detecting the melt surface in the sprue and outputting the detected signal; and a gas-ejecting-member-position-controlling means for receiving output signal from the melt-surface-detecting means, and driving a gas-ejecting-member-moving mechanism to move the gas-ejecting member according to the signal. With the melt-surface-detecting means and the gas-ejecting-member-position-controlling means, the gas-ejecting member can be automatically positioned to keep a proper distance between the gas-ejecting member and the melt, even if the melt in the cup portion has a varying surface, which is unavoidable in mass production that the melt is continuously poured by gravity into a plurality of gas-permeable casting molds.
The gas-ejecting-member-position-controlling means is, for instance, a robot comprising, as shown in
The casting apparatus of the present invention comprising the melt-surface-detecting means and the gas-ejecting-member-position-controlling means is preferable, though not restrictive, because it can conduct the following operations automatically.
One example is that when the detected melt surface at a position just above the tubular portion becomes below the opening of the tubular portion, the gas-ejecting member is automatically moved downward for connection to the tubular portion.
Another example is that the gas-ejecting port of the gas-ejecting member is controlled to closely follow a lowering surface of the melt in the sprue without contact, during the pouring step. This example is preferable because the gas-ejecting member is placed at a position just above and very close to the tubular portion while avoiding direct contact with the high-temperature melt, so that it can be connected to the sprue in an extremely short period of time after pouring ends.
As shown in
At an early stage of the pouring step, as shown in
Immediately after the melt M in the cup portion 5a fully flows into the tubular portion 5b, as shown in
After connecting the gas-blowing nozzle 1a to the tubular portion 5b, as shown in
In Embodiment 1, because the gas-blowing nozzle 1a is placed at a position just above the tubular portion 5b and not interfering with gravity pouring of the melt M, it can be simply moved downward for quick connection to the sprue 5.
A part of the ladle 2 is within the operation range 10 (surrounded by a two-dot chain line) at an early stage of the pouring step in Embodiment 2, while the ladle 2 is placed outside the operation range 10 (surrounded by a two-dot chain line) at an early stage of the pouring step in Embodiment 1.
When a part of the ladle 2 is within the operation range 10 (surrounded by a two-dot chain line) as shown in
In Embodiment 2, because the ladle 2 retreats from the operation range 10 (surrounded by a two-dot chain line) by adjusting tilt angle and/or horizontal movement until pouring ends, the gas-blowing unit 1 can be quickly connected to the sprue 5.
Embodiment 3 is the same as Embodiment 1, except that a tip end (gas-ejecting port) of the gas-blowing nozzle 1a is placed below the upper edge of the cup portion 5a, until pouring ends at a late stage of the pouring step.
With the ladle 2 placed outside the operation range 10 (surrounded by a two-dot chain line) at an early stage of the pouring step, as shown in
Immediately after gravity-pouring ends, that is, immediately after the melt M residing in the cup portion 5a fully flows into the tubular portion 5b, as shown in
Because the gas-blowing nozzle 1a is placed at such a position that its tip end (gas-ejecting port) is below the upper edge of the cup portion 5a at least at the end of gravity-pouring, the gas-blowing nozzle 1a is close to the tubular portion 5b, thereby saving a time taken to connect the gas-blowing nozzle 1a to the tubular portion 5b.
Embodiment 4 is the same as Embodiment 1, except that the gas-blowing nozzle 1a is placed such that its tip end (gas-ejecting port) comes into contact with the melt M in the cup portion 5a, until pouring ends at a late stage of the pouring step.
With the ladle 2 placed outside the operation range 10 (surrounded by a two-dot chain line) at an early stage of the pouring step, as shown in
Immediately after gravity-pouring ends, that is, immediately after the melt M in the cup portion 5a fully flows into the tubular portion 5b, the gas-blowing nozzle 1a is moved downward by the gas-ejecting-member-moving mechanism 11 to be fit into the tubular portion 5b, as shown in
Because the gas-blowing nozzle 1a is placed at such a position that its tip end (gas-ejecting port) comes into contact with the melt M in the cup portion 5a, until gravity-pouring ends, the gas-blowing nozzle 1a is close to the tubular portion 5b, thereby saving a time taken to connect the gas-blowing nozzle 1a to the tubular portion 5b. Furthermore, when the gas-blowing nozzle 1a is controlled to follow the lowering surface of the melt, the gas-blowing nozzle 1a can be more quickly connected to the tubular portion 5b.
Embodiment 5 is the same as Embodiment 1, except that the stream of the pouring melt M is cast to a position away from the tubular portion 5b within the cup portion 5a, and that the gas-blowing nozzle 1a is placed such that its tip end (gas-ejecting port) is below the upper edge of the cup portion 5a, or in contact with the melt M in the cup portion 5a, during the pouring step.
As shown in
During the pouring step, as shown in
As shown in
As shown in
Immediately after gravity-pouring ends, that is, immediately after the melt M in the cup portion 5a fully flows into the tubular portion 5b, the gas-blowing nozzle 1a is moved downward by the gas-ejecting-member-moving mechanism 11 to be fit into the tubular portion 5b, as shown in
Because the stream 2a of the melt M is cast to a position away from the tubular portion 5b until the ladle 2 stops pouring the melt M, the tip end of the gas-blowing nozzle 1a can be placed below the upper edge of the cup portion 5a even during the pouring step. Therefore, the gas-blowing nozzle 1a can be quickly brought into contact with the melt M in the cup portion 5a immediately after the ladle 2 stops pouring the melt M, thereby saving a time taken to connect the -blowing nozzle 1a to the tubular portion 5b, as explained in Embodiments 3 and 4.
Embodiment 6 is the same as Embodiment 5 except for changing a shape of the cup portion 5c. As shown in
The casting apparatus in Embodiment 6 is the same as in Embodiment 1, except for comprising a pouring-means-moving unit 12 capable of moving the ladle 2, or adjusting a position of the stream of the melt M, like in Embodiment 5.
During the pouring step, as shown in
Until the ladle 2 stops pouring the melt M, as shown in
Because the cup portion 5e extends in a direction A (shown by an arrow) from the tubular portion 5b as shown in
Immediately after pouring the melt M from the ladle 2 ends and while the melt M resides in the cup portion 5e without completely flowing into the tubular portion 5b, as shown in
Immediately after gravity-pouring ends, that is, immediately after the melt M in the cup portion 5e fully flows into the tubular portion 5b, the gas-blowing nozzle 1a is moved downward by the gas-ejecting-member-moving mechanism 11 to be fit into the tubular portion 5b, as shown in
Embodiment 7 is the same as Embodiment 1 except for changing a portion of a gas-blowing nozzle 1a connected to a sprue 5. In Embodiment 7, as shown in
According to the present invention, the gas-blowing unit can be quickly connected to the sprue to blow a gas into the cavity of the gas-permeable casting mold after pouring ends, thereby suppressing defects such as cold shut and pull down due to stagnation of melt supply.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-203824 | Sep 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/076229 | 9/30/2014 | WO | 00 |
