Patent Application
20160136726
The present invention relates to a method for producing desired castings by a gas-permeable casting mold, an casting apparatus, and a gas-blowing nozzle used in the casting apparatus.
To produce castings by gravity pouring, a casting mold composed of sand particles, which is a gas-permeable casting mold (a so-called sand mold), is most generally used. With such a gas-permeable casting mold, which may be simply called “mold,” a gas (generally air) remaining in a cavity of a particular shape is pushed out of the cavity by a metal melt (simply 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. 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 is solidified in a state of filling the sprue and the runner, 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.
A revolutionary method for solving the above problems is 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 in a volume smaller than that of an entire cavity in a gas-permeable casting mold (hereinafter referred to as “casting mold cavity”) and substantially equal to that of the desired cavity portion, into the cavity by gravity; supplies a gas (compressed gas) into 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 commonly disclosed in JP 2007-75862 A and JP 2010-269345 A, which may be called “pressure-casting 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 experiment to follow the pressure-casting method described in JP 2007-75862 A and JP 2010-269345 A, the inventors have found that in the method of JP 2007-75862 A for closing a sprue with a flange of a gas-supplying pipe to prevent the leak of a compressed gas supplied through the sprue, the positioning of the gas-supplying pipe in the sprue is difficult because the flange conceals the sprue, likely resulting in a slow gas-supplying timing and cold shut in products. In addition, because melt droplets scattered while pouring are likely attached to the sprue in contact with the flange, providing a gap between the flange and the sprue, a large amount of a gas may leak. It is thus desired to develop a means capable of supplying a gas quickly and surely after pouring a melt.
Accordingly, an object of the present invention is to provide a production method of castings, which can supply a gas quickly after pouring a melt without suffering gas leak, a casting apparatus, and a gas-blowing nozzle used in the casting apparatus.
As a result of intensive research in view of the above object, the inventor has found that with a gas-blowing nozzle having a structure of fitting it into a sprue, a gas can be supplied quickly and surely after pouring a melt. The present invention has been completed based on such finding.
Thus, the method of the present invention method for producing a casting by pouring a metal melt by gravity into a gas-permeable casting mold having a cavity comprising at least a sprue, a runner and a product-forming cavity, comprises the steps of
It is preferable that the gas-blowing nozzle has a side surface tapered in a gas-ejecting direction; that the sprue has a wall surface tapered in a melt flow direction; and that the tapered side surface of the gas-blowing nozzle is fit into the tapered wall surface of the sprue.
When the gas is ejected, the gas-blowing nozzle is preferably pushed in the gas-ejecting direction.
The casting apparatus of the present invention comprises
The fitting portion of the gas-blowing nozzle preferably has a side surface tapered in a gas-ejecting direction.
The gas-blowing nozzle preferably has a gas-ejecting bore having a diameter increasing in a gas-ejecting direction.
It is preferable that the sprue has an introducing hole portion constituting a path through which the metal melt flows downward, and a cup portion open on the gas-permeable casting mold, which is connected to the introducing hole portion and has a larger diameter than that of the introducing hole portion; and that the introducing hole portion has a fitting portion, into which the gas-blowing nozzle is fit.
The fitting portion constituting part of the sprue preferably has a wall surface tapered in a downward flowing direction of the metal melt.
The casting apparatus preferably has a mechanism of pushing the gas-blowing nozzle in the gas-ejecting direction.
The gas-blowing nozzle of the present invention has a side surface tapered in a gas-ejecting direction for supplying a gas into a cavity of a gas-permeable casting mold, which comprises at least a sprue, a runner and a product-forming cavity, through the sprue, such that a metal melt poured into the gas-permeable casting mold by gravity fills only a desired cavity portion including the product-forming cavity.
The method of the present invention for producing castings by pouring a metal melt by gravity into a gas-permeable casting mold having a cavity 5 comprising a sprue 12, a runner 7, a feeder 8 and a product-forming cavity 9, as shown in
After the sprue is exposed to a poured high-temperature melt, an inner wall surface of the sprue appears to be roughened and brittle. As a result of experiments, the inventors have found that the above fitting structure of the sprue, which was never considered before, is effective to solve the problems.
As described above, an important feature of the present invention is that a gas is supplied from a gas-blowing nozzle fit into a sprue constituting a melt flow path. Specifically, the gas-blowing nozzle is inserted into the sprue, and a gas is supplied with a tip end side surface of the gas-blowing nozzle in fixed contact with an inner wall surface of the sprue. The tip end side surface of the gas-blowing nozzle need not be closely attached to the inner wall surface of the sprue, but there may be clearance, as long as the supplied gas can keep enough pressure to charge the melt into the desired cavity portion and solidify it.
The gas-blowing nozzle of the present invention, which constitutes the casting apparatus of the present invention, need not have a member covering a sprue opening, such as a flange, and is easily positioned in the sprue having the fitting structure. Immediately after the completion of fitting, a gas can be supplied, resulting in a fast gas-supplying timing and improved casting tact, while preventing cold shut in products. It also makes it possible to avoid the influence of melt droplets scattered around the sprue.
Materials for the gas-blowing nozzle may be metals such as steel, aluminum alloys, copper alloys, etc., ceramics such as alumina, silicon carbide, etc., composite materials of metals and ceramics, graphite, etc. The gas-blowing nozzle is desirably detachable from the gas-supplying means.
The nozzle may be rotated slidably in the sprue for closer contact with the sprue to achieve higher sealing. Fitting need not be completely gas-tight, but there may be clearance, as long as the supplied gas has enough pressure to charge the melt into the desired cavity portion and solidify it.
The deeper fitting of the nozzle into the sprue provides a larger contact area of the side surface of the nozzle with the sprue, resulting in higher sealing, thereby advantageously preventing gas leak from the sprue. The deeper fitting of the nozzle into the sprue also makes a tip end of the nozzle closer to the product-forming cavity, advantageously decreasing the amount of a gas leaking through the gas-permeable casting mold.
On the other hand, the deep fitting is disadvantageous in taking time in setting the nozzle. Accordingly, a fitting mode is preferably selected depending on the mold and the melt.
It is preferable that the gas-blowing nozzle has a side surface tapered in a gas-ejecting direction, while the sprue has a wall surface tapered in a melt flow direction. It is more preferable that the wall surface of the sprue is substantially equally tapered along the side surface of the gas-blowing nozzle. The above shapes of the gas-blowing nozzle and the sprue make it easy to achieve the contact fitting of the tapered side surface of the gas-blowing nozzle to the tapered wall surface of the sprue. For example, a nozzle having a taper-free, straight side surface cannot be easily positioned at proper depth, in fitting into the sprue with clearance. On the other hand, the tapered side surface of the gas-blowing nozzle can be surely brought into fitting contact with the tapered wall surface of the sprue at a predetermined position. With this structure, the weight of the nozzle per se can be used as part of pressure for contact with the sprue, advantageous for sealing.
In the present invention, the supplied gas filling the sprue and the runner applies pressure to the gas-blowing nozzle to slacken its fitting. Though the weight of the nozzle per se and a friction force between the nozzle and the wall surface of the sprue may be enough to resist this pressure, the gas-blowing nozzle is preferably pushed in a gas-supplying direction during a gas-supplying period to ensure the fitting. As described above, with the side surface of the gas-blowing nozzle tapered complementarily with the wall surface of the sprue, the pushing of the gas-blowing nozzle in a gas-ejecting direction makes the contact of the gas-blowing nozzle with the sprue closer, resulting in improved sealing.
In the present invention, because the gas-ejecting bore of the gas-blowing nozzle has a smaller diameter than that of the sprue, the supplied gas impinges mostly a center portion of the melt in the introducing hole portion of the sprue. Particularly when the gas is supplied at a high speed, the melt is likely splashed from its top surface in an edge portion, so that the melt may not be pushed efficiently. With the gas-ejecting bore of the gas-blowing nozzle having a diameter increasing in a gas-ejecting direction, the gas preferably flows in the introducing hole portion at a uniform speed, avoiding the splashing of the melt, resulting in high efficiency of pushing the melt by the supplied gas.
The basic technology of the present invention will be explained below. The present invention utilizes the basic technology of producing castings by a gas-pressure-casting method, which is proposed by JP 2007-75862 A and JP 2010-269345 A, though not restricted to the disclosures of these references.
In a gas-permeable casting mold having a cavity comprising at least a sprue, into which a metal melt is poured, a runner constituting a flow path of the melt poured through the sprue, and a product-forming cavity to be filled with the melt supplied through the runner, the present invention is directed to a technology of charging a metal melt into only a desired cavity portion including the product-forming cavity. The cavity of the gas-permeable casting mold may have a feeder, if necessary. In this case, the desired cavity portion includes the product-forming cavity and the feeder.
The gas-permeable casting mold is generally a mold formed by sand particles for uniformly having some gas permeability, such as a green sand mold, a shell mold, a self-curing mold, though the mold may be formed by ceramic or metal particles in place of sand particles. The gas-permeable casting mold could be formed by materials having substantially no gas permeability, such as gypsum, etc., 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, etc.
In the present invention, the melt in a volume smaller than the volume of an entire casting mold cavity and substantially equal to the volume of the desired cavity portion including the product-forming cavity is poured by gravity. The volume of the poured melt is limited, because pouring the melt in such an amount as to completely fill the casting mold cavity does not contribute to improvement in a pouring yield. In a gravity casting method using a conventional gas-permeable casting mold, a melt generally fills an entire cavity including a product-forming cavity and solidifies to obtain sound products, resulting in a pouring yield of at most about 70%. Drastic improvement of the pouring yield has not been expected. On the contrary, using the basic technology of the present invention, the pouring yield of substantially 100% can be expected in principle.
In a cavity structure of filling a desired cavity portion simply by pouring a melt, a gas need not be supplied to fill the cavity. However, when a melt in a volume substantially equal to the volume of the desired cavity portion including the product-forming cavity (further, the feeder, if necessary) is poured as in the present invention, a gas should be supplied before the desired cavity portion is filled with the poured melt, thereby charging the melt into the desired cavity portion through the sprue and solidifying it.
The gas supplied to cause the melt to fill the desired cavity portion may be air from the aspect of cost, or a non-oxidizing gas such as argon, nitrogen, carbon dioxide, etc. from the aspect of preventing the oxidation of the melt. Though the gas may be supplied with a fan, a blower, etc., it is preferable to use a compressor, etc., because it can uniformly pressurize the melt.
Embodiment 1 of the present invention will be explained.
A mold 1 is a gas-permeable casting mold using green sand, which is placed on a bottom board 4 with an upper flask 2 and a lower flask 3 combined, as shown in
As shown in
As shown in
As shown in
A preferred mode of fitting a gas-blowing nozzle into a sprue, in which a tapered side surface of the gas-blowing nozzle comes into contact with a sprue wall surface tapered in a melt flow direction, will be explained referring to the drawings.
Because the gas-blowing nozzle 25 is not deeply inserted into the sprue 22 for fitting in Embodiment 2, its positioning is easier, resulting in a shortened period from the completion of pouring a melt by gravity to the start of supplying a gas. Because melt droplets generated when a melt is poured by gravity are less attached to the tapered wall surface 24, a close contact of the cup portion 22a of the gas-blowing nozzle 25 with the tapered wall surface 24 is not deteriorated. To have closer fitting and higher sealing, the gas-blowing nozzle 25 is preferably rotated slidably on the tapered wall surface 24 of the cup portion 22a. To achieve further closer contact, the gas-blowing nozzle 25 is preferably pushed in a gas-supplying direction (shown by the arrow A).
In Embodiment 3, fitting depth in the sprue 32 can be made constant more easily than when the nozzle having a taper-free side surface in
Because the tapered wall surface 34b of the fitting portion 33 of the sprue 32 in Embodiment 3 has a smaller angle than that of the tapered wall surface 24 in Embodiment 2 in a gas-supplying direction (shown by the arrow A), a center axis of the gas-blowing nozzle 35 is easily aligned with a center axis of the sprue 32, so that positioning is more precise in Embodiment 3 than in Embodiment 2.
This embodiment is the same as Embodiment 3 in a sprue of a gas-permeable casting mold, a side surface of a gas-blowing nozzle, and the fitting of the gas-blowing nozzle into the sprue of the gas-permeable casting mold, except that the gas-blowing nozzle is changed to have a gas-ejecting bore having an increased diameter in a gas-supplying direction as shown in
As shown in
0.7×D1≦D2≦1.0×D1,
0.3×D2≦D3≦0.5×D2, and
2.5×D1≦L1≦4.0×D1.
This embodiment is the same as Embodiment 3 in a sprue of a gas-permeable casting mold, a side surface of a gas-blowing nozzle, and the fitting of a gas-blowing nozzle into a sprue of a gas-permeable casting mold, except that the gas-blowing nozzle is changed to have a gas-ejecting bore having an increasing diameter in a gas-supplying direction as shown in
As shown in
0.9×D1≦D2≦1.0×D1,
0.5×D2≦D3≦0.8×D2, and
1.1×D1≦L2≦1.2×D1.
The present invention provides a method for producing castings by the pressure-casting method, which can supply a gas quickly after pouring a melt, while preventing leak during gas supply, without using a complicated apparatus. Accordingly, it provides an improved casting tact, with reduced defects such as cold shut.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-129326 | Jun 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/066248 | 6/19/2014 | WO | 00 |
