JP6956625B2 - Low pressure casting machine - Google Patents

Description

The present invention relates to a sprue bush and a low pressure casting machine including the sprue bush.

Aluminum and aluminum alloys are lightweight and have excellent workability, corrosion resistance, and functional properties, and are therefore widely used in parts such as cylinder heads of aircraft, railroad vehicles, and automobiles, and household products such as sashes. Aluminum can be molded by various methods, but among them, molding by a casting method is widely used.

A low-pressure casting machine is used to manufacture aluminum members by a casting method. The low-pressure casting machine generally includes a mold, a stalk provided in communication with a sprue bush provided at the entrance of the mold, and a crucible in which the molten metal is held. In the casting step, the molten metal in the crucible is pressurized, the molten metal stalk, then fed filled into the mold through the hot water inlet bushing is removed from the mold after solidification are cooled, supply the following melt Will be done. In the process of this series of operations, the sprue bush whose inside is exposed to the molten metal may be partially lost by the reaction with the molten aluminum, so-called melting damage may occur. When melting loss occurs, iron is dissolved in the aluminum member and becomes contamination, which may lead to a decrease in the strength of the aluminum member and a decrease in the manufacturing yield of the aluminum member. In addition, the sprue bush that has been melted is replaced with a new one, but after the sprue bush is replaced, the maintenance time until it stabilizes at the operating temperature condition is long, and the operation of the casting machine must be stopped during that time. It causes a decrease in productivity because it cannot be produced in a standard manner.

In order to deal with such a problem that the sprue bush becomes unusable in a short period of time, in Patent Document 1, a chamfered surface is formed on the inner peripheral portion exposed to the molten aluminum, and a lining layer made of a corrosion-resistant and wear-resistant alloy is provided. A sprue bush provided has been proposed. Patent Document 1 describes that 0.6 to 3.2% by weight of B, 0.5 to 8% by weight of Si, 5 to 37% by weight of Mo, and the balance Ni are used on a base material having a chamfered surface. A high-strength Ni-based alloy with corrosion resistance and abrasion resistance, which consists of unavoidable impurities and in which Ni-boride and Mo-boride are dispersed in the Ni-group bonding phase, is subjected to thermal spraying-remelting method, diffusion bonding method, and sintering bonding method. , Or the technique of forming by the brazing method is described.

Japanese Unexamined Patent Publication No. 2003-225794

However, even in the sprue bush that has been processed and treated as described in Patent Document 1, there is an interface between the base material and the lining layer that changes the physical characteristics, so that the molten aluminum is still used. The lining layer may be peeled off due to contact with. Further, since a dedicated facility for providing the lining layer is required, the manufacturing cost of the sprue bush increases, and the sprue bush itself becomes expensive. Therefore, the manufacturing cost of the aluminum member manufactured by using this increases.

According to the present invention that solves the above problems, a sprue bush having excellent erosion resistance and a long life, and a low-pressure casting machine provided with the sprue bush are provided.

According to the present invention
A low-pressure casting machine equipped with a sprue bush
The sprue bush, Ri Do from solvent loss of casting,
The erosion-resistant casting comprises a base metal layer and an oxide layer formed on the surface of the base metal layer.
The composition (% by weight) of the base metal layer is C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%, P <0.03%, S <0.02%, Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0. 50 to 0.70%, Nb <0.10%, Al <0.10%, the balance consisting of Fe and unavoidable impurity elements.
A part of the oxide layer extends like cilia at the grain boundaries of the base metal layer.
The base metal layer contains a carbon element and a base metal element, and contains
The oxide layer is a coating layer formed on the surface of the base metal layer, and the coating layer is made of a thermal oxide of the base metal element.
A low-pressure casting machine is provided in which a compound carbide which is a reaction product of the carbon element and the base metal element in the base metal layer is contained in the oxide layer on the base metal layer side. NS.

Further, according to the present invention.
A low-pressure casting machine equipped with a sprue bush
The sprue bush is made of a erosion resistant casting.
The composition (% by weight) of the erosion-resistant casting is C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%, P <0.03%. , S <0.02%, Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0 .50 to 0.70%, Nb <0.10%, Al <0.10%, the balance is a base metal layer composed of Fe and unavoidable impurity elements, and the oxidation formed on the surface of the base metal layer. It consists of a layer and
A part of the oxide layer extends to the grain boundaries of the base metal layer.
The oxide layer is a coating layer formed on the surface of the base metal layer, and the coating layer is provided by a low-pressure casting machine made of a thermal oxide of the base metal constituting the base metal layer. Will be done.

According to the present invention, there is provided a sprue bush having excellent erosion resistance, a long life, and an inexpensive sprue bush, and a low-pressure casting machine provided with the sprue bush.

It is a partial cross-sectional micrograph of a erosion resistant casting constituting the sprue bush of the present invention. (A) is a magnification of 100 times, (b) is a magnification of 200 times, and (c) is a magnification of 500 times. This is a temperature condition in a step of forming a erosion-resistant coating layer formed on the surface of a base metal of a erosion-resistant casting constituting the sprue bush of the present invention. A micrograph (magnification of 2000 times) of the ciliated oxide portion of the erosion-resistant oxide layer formed on the surface of the base metal layer of the erosion-resistant casting constituting the sprue bush of the present invention. be. It is a photograph of the sprue bush produced in the example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all drawings, similar components are designated by the same reference numerals, and description thereof will be omitted as appropriate.

The sprue bush of the present embodiment is made of a erosion resistant casting. The erosion-resistant casting includes a base metal layer and an oxide layer formed on the surface of the base metal layer, and a part of the oxide layer extends like a fibrous hair at the crystal grain boundary of the base metal layer. The base metal layer contains a carbon element and a base metal element, the oxide layer is a coating layer formed on the surface of the base metal layer, and the coating layer is the base metal element. The oxide layer on the base metal layer side contains a compound carbide (solid solution carbide) that is a reaction product of the carbon element and the base metal element in the base metal layer. It is characterized by.

The sprue bush of the present embodiment has extremely excellent erosion resistance because it is composed of a erosion-resistant casting having the above characteristics.

Further, when the aluminum member is cast by using the low-pressure casting machine provided with the sprue bush of the present embodiment, the present inventors accurately inject the molten metal into the mold without causing poor filling or formation of cavities. It has been found that this can reduce the occurrence of product defects in the resulting aluminum parts. The reason for this is not necessarily clear, but it is considered that the sprue bush of the present embodiment suppresses the behavior of the temperature drop of the molten aluminum. Normally, poor filling of the molten metal into the mold and formation of cavities are caused by the temperature of the hot aluminum molten metal coming out of the crucible dropping as it reaches the mold through the stalk and then the sprue bush. It is caused by an increase in viscosity. When the viscosity of the molten metal increases, it takes a long time for the molten metal to reach the entire mold, and a temperature difference occurs depending on the location of the molten metal in the mold. There is a difference in strength and composition between the region that solidifies slowly and the region that does not solidify, which is thought to lead to the formation of cavities. The erosion-resistant casting constituting the sprue bush of the present embodiment has a heat conduction property that does not cause such a temperature difference of the molten metal.

In one embodiment, it is preferable that the sprue bush has a cylindrical shape and an R chamfer is provided on the inner peripheral portion of the tip. The inner peripheral portion of the tip of the sprue bush is a portion that comes into contact with the molten aluminum. Since the inner peripheral portion of the tip is R-chamfered, the stress concentration applied to this portion by the molten aluminum is reduced, so that the damage to the inner peripheral portion of the tip is reduced.

FIG. 1 shows a cross-sectional micrograph of the erosion-resistant casting used for the sprue bush of the present embodiment. FIG. 1 (a) shows a partial cross-sectional micrograph of a erosion-resistant casting (magnification: 100 times), and FIG. 1 (b) is a partially enlarged photograph of the portion surrounded by a circle in FIG. 1 (a). One area 22 is enlarged and shown (magnification 200 times). FIG. 1 (c) is a partially enlarged photograph of the portion surrounded by a circle in FIG. 1 (b), and the first region 22 is further enlarged (magnification: 500 times).

As shown in the cross-sectional view (cross-sectional micrograph) of FIG. 1 (a), the erosion-resistant casting 1 used for the sprue bush of the present embodiment is formed on the base metal layer 10 and the surface of the base metal layer 10. The oxide layer 20 is provided. The oxide layer 20 is a thermal oxide obtained by directly oxidizing the base metal layer 10 by heating it without supplying a reaction gas. The base metal layer 10 includes a ferrite region 12 having a ferrite structure in the crystal structure on the surface layer side, and a pearlite region 14 having a pearlite structure in the crystal structure below (inside) the ferrite region 12.

The base metal layer 10 is composed of an alloy to which tungsten and cobalt are added, based on SKD61, which is a general alloy tool steel as a material for hot molds. The composition is as shown in Table 1.

According to the above composition, not only is it suitable for forming the oxide layer 20 having ciliated oxide 22a, which is responsible for erosion resistance, but also it has the original mechanical strength of SKD61. When the base metal is an alloy in which tungsten and cobalt are added to SKD61, the second region and the first region can be stably formed.

In the oxide layer 20, the ciliated oxide 22a, which is a part thereof, has grain boundaries (ferrite crystals) of the base metal layer 20 as shown in the partially enlarged cross-sectional views shown in FIGS. 1 (b) and 1 (c). It extends like cilia at grain boundaries 16). FIG. 3 is a cross-sectional micrograph (magnification of 1500 times) of the ciliated oxide 22a formed at another location. According to this, the ciliated oxide 22a appears at the ferrite grain boundaries 16 like a plant root. You can check how it is invading.

Since the ciliated oxide 22a extends to the ferrite crystal grain boundaries 16 in this way, the oxide layer 20 having excellent erosion resistance is firmly bonded to the base metal layer 10 and peeling is suppressed. Therefore, the erosion resistance is dramatically improved, and the deterioration of such characteristics is suppressed.

According to FIG. 1, the oxide layer 20 is composed of a first region 22, a second region 24, and a third region 26. The oxide layer 20 is conveniently divided into three regions due to the difference in composition, but all of these three regions are mainly oxides, and among these three regions, particularly the first region 22 and the second region. It can be said that there is no physical interface with 24 in the optical micrograph. Therefore, there is no separation between these regions, and in particular, the second region 24 does not separate from the first region 22. A qualitative analysis using an electron probe microanalyzer (EPMA) or the like can confirm the existence of an interface due to a difference in composition. In FIG. 1A, the interface is displayed for convenience based on the EPMA analysis result. The first region 22 has a ciliated oxide 22a, and the ciliated oxide 22a extends to the ferrite crystal grain boundaries 16 of the base metal 10 to exert an anchor effect. Therefore, the oxide layer 20 and the base metal layer 10 are bonded very strongly, and the erosion-resistant casting is excellent in erosion resistance.

The sprue bush of the present embodiment can be manufactured as follows.
First, the base metal having the above composition is cast and machined into the shape of the sprue bush, and then the oxide layer 20 is formed.

The steps of forming the oxide layer 20 are a first step of raising and holding the base metal to a predetermined temperature in a furnace in a normal atmosphere, and a second step of slowly cooling in the furnace while controlling the temperature lowering rate. It is composed of steps, and the conditions for raising the temperature, holding the temperature, and lowering the temperature are as shown in FIG. The heat treatment furnace used is a general annealing furnace and does not require special atmosphere control.

The temperature of the base metal is raised to 780 to 980 ° C. over 2 hours, and the temperature is maintained at the same temperature for a predetermined time. The temperature range maintained after the temperature rise is 780 to 980 ° C, but more preferably 900 ± 30 ° C. The holding time is adjusted according to the thickness of the base metal. For example, the holding time can be defined as 1 hour for a member having a thickness of 25 mm.

This temperature rise / retention corresponds to the first step of the present embodiment, and the oxide layer 20 is formed / grown on the surface layer portion of the base metal, a decarburized layer (ferrite trim) is formed, and the liberated carbon element is released. It is considered that the compound carbide (solid solution carbide) 28 is formed by reacting with the constituent elements of the base metal layer 10. Here, the oxide layer 20 is made of a thermal oxide produced by the above step of directly oxidizing by heating without supplying a reaction gas. The double carbide 28 is largely distributed in the first region 22 on the base metal layer 10 side, and a third region 26 in which almost no double carbide is present is formed on the second region 24. Therefore, the third region 26 is more excellent in erosion resistance.
Subsequently, the temperature of the base metal is lowered at a predetermined lowering rate, but the lowering rate is maintained in the range of 30 ± 10 ° C. per hour.

This temperature drop corresponds to the second step of the present invention, and the crystal structure of the surface layer side of the base metal layer 10 changes from pearlite to ferrite. Then, the oxide that continues to grow from the previous step extends like cilia at the ferrite grain boundaries 16. The ciliated oxide 22a, which is a part of the first region 22, bonds the oxide layer 20 and the base metal layer 10 very tightly.
Since the first region 22, which is the greatest feature of the present invention, is formed only when the temperature lowering rate is maintained within the above range, it is necessary to strictly control the temperature lowering.
Through such a step, an oxide layer 20 having excellent erosion resistance is formed on the surface of the base metal layer 10.

According to the above-mentioned manufacturing method, the above-mentioned series of steps can be performed in the same furnace, and it is not necessary to provide a dedicated heat treatment furnace capable of supplying various gases, so that the equipment cost can be reduced. Further, it is not necessary to continuously supply various gases during the heat treatment, and the running cost at the time of manufacturing can be reduced. Therefore, the target sprue bush can be manufactured at low cost.

The details of the formation mechanism of the second region 24 and the first region 22 in the production of the melt-resistant casting are unknown, but it is presumed to be as follows.

In the first step, an oxide layer is formed and grown on the surface layer of the base metal layer 10 and a decarburized layer (ferrite trim) is formed, and the liberated carbon element reacts with the constituent elements of the base metal to form a compound. A second region 24 containing the carbide 28 is formed. The double carbide 28 is largely distributed in the first region 22 on the base metal layer 10 side, and the third region 26 in which the double carbide does not exist is formed on the surface side of the second region 24.

In the second step, the crystal structure of the surface layer side of the base metal changes from pearlite to ferrite, and the oxide that continues to grow from the previous step extends to the ferrite crystal grain boundaries in a fibrous manner.

As described above, the sprue bush of the present embodiment can be manufactured by using a general annealing furnace and controlling the temperature rise temperature, the holding time, and the temperature lowering rate to produce a erosion resistant casting. Since the sprue bush of the present embodiment can be manufactured without supplying reaction gas in the heat treatment step, it does not require a dedicated heat treatment furnace capable of supplying various gases, and thus can be manufactured at low cost.

The sprue bush of the present embodiment can be used in a low pressure casting machine. The sprue bush of the present embodiment has excellent melt resistance and its heat conduction property controls a temperature drop of the molten aluminum, so that it can be suitably used for a low-pressure casting machine. The aluminum member manufactured by using such a low-pressure casting machine has high quality without cavities and filling defects, and has high product reliability.
Hereinafter, an example of the embodiment will be added.
1. 1. A sprue bush made of melt-resistant casting
The erosion-resistant casting comprises a base metal layer and an oxide layer formed on the surface of the base metal layer.
A part of the oxide layer extends like cilia at the grain boundaries of the base metal layer.
The base metal layer contains a carbon element and a base metal element, and contains
The oxide layer is a coating layer formed on the surface of the base metal layer, and the coating layer is made of a thermal oxide of the base metal element.
The oxide layer on the base metal layer side contains a compound carbide which is a reaction product of the carbon element and the base metal element in the base metal layer.
Gate bush.
2. The oxide layer contains a plurality of regions having different compositions from each other, and the amount of the double carbide is less in the region on the most surface side than in the region on the metal layer side of the base metal. The sprue bush described in.
3. 3. The composition (% by weight) of the base metal layer is C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%, P <0.03%, S <0.02%, Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0. 1. 50 to 0.70%, Nb <0.10%, Al <0.10%, the balance consisting of Fe and unavoidable impurity elements. Or 2. The sprue bush described in.
4. A sprue bush made of melt-resistant casting
The composition (% by weight) of the erosion-resistant casting is C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%, P <0.03%. , S <0.02%, Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0 .50 to 0.70%, Nb <0.10%, Al <0.10%, the balance is a base metal layer composed of Fe and unavoidable impurity elements, and the oxidation formed on the surface of the base metal layer. It consists of a layer and
A part of the oxide layer extends to the grain boundaries of the base metal layer.
The oxide layer is a coating layer formed on the surface of the base metal layer, and the coating layer is a sprue bush made of a thermal oxide of the base metal constituting the base metal layer.
5. 1. The sprue bush is cylindrical with an R chamfered surface on the inner circumference of the tip. To 4. The sprue bush described in any of.
6. 1. 1. To 5. A low-pressure casting machine provided with the sprue bush according to any one of.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

(Example 1)
The composition (wt%) is C 0.50, Si 0.45, Mn 0.70, P 0.02, S 0.01, Cr 5.50, Mo 0.65, Co 0.85, V 0. A sprue bush shown in FIG. 4 was prepared by casting and processing a base metal composed of 20, W 0.60, Nb 0.05, Al 0.05, and the balance Fe and an unavoidable impurity element.
This base metal is heated to 900 ° C. in an annealing furnace over 2 hours, held at that temperature for 1 hour, cooled to 200 ° C. at a temperature lowering rate of 30 ° C./hour, taken out of the furnace, and the sprue bush is removed. Made.

In this sprue bush, as shown in FIG. 1, an oxide layer 20 composed of a first region 22, a second region 24, and a third region 26 was formed on the surface of the base metal layer 10.

(Comparative Example 1)
A commercially available SKD61 (that is, a base metal having a composition in which tungsten and cobalt are not added in the composition of Example 1) is cast and processed to obtain a sprue bush having the same dimensions and shape as those produced in Example 1. Made.

(Durability evaluation)
The sprue bush of Example 1 and the sprue bush of Comparative Example 2 were attached to a low-pressure casting machine (LP-D series manufactured by Shinto Kogyo Co., Ltd.) to cast aluminum. The casting conditions were molten metal: AC4C, molten metal temperature: 720 ° C., and number of shots: 7 shots / hour.
The sprue bush of Example 1 reached the end of its life due to erosion after being used for 26 days.
The sprue bush of Comparative Example 1 reached the end of its life due to erosion after being used for 12 days.

(Quality evaluation of cast aluminum products)
The sprue bush of Example 1 and the sprue bush of Comparative Example 2 were attached to a low-pressure casting machine (LP-D series manufactured by Shinto Kogyo Co., Ltd.) to cast aluminum to produce an aluminum cast product. The casting conditions were molten metal: AC4C, molten metal temperature: 720 ° C. The appearance of the obtained cast aluminum product was visually observed, and the inside was observed with a fiberscope. A leak test was performed on the obtained cast aluminum product. The percentage of castings with cracks observed in appearance or inside or failing the leak test is shown below as the casting defect rate.
Casting defect rate of aluminum casting obtained by using the sprue bush of Example 1: 0.3%
Casting defect rate of aluminum casting obtained by using the sprue bush of Comparative Example 1: 0.2%

1 Melt-resistant casting 10 Base metal layer 12 Ferrite region 14 Pearlite region 16 Ferrite grain boundary 20 Oxide layer 22 1st region 22a Ciliated oxide 24 2nd region 26 3rd region 28 Double carbide

Claims (4)

A low-pressure casting machine equipped with a sprue bush
The sprue bush, Ri Do from solvent loss of casting,
The erosion-resistant casting comprises a base metal layer and an oxide layer formed on the surface of the base metal layer.
The composition (% by weight) of the base metal layer is C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%, P <0.03%, S <0.02%, Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0. 50 to 0.70%, Nb <0.10%, Al <0.10%, the balance consisting of Fe and unavoidable impurity elements.
A part of the oxide layer extends like cilia at the grain boundaries of the base metal layer.
The base metal layer contains a carbon element and a base metal element, and contains
The oxide layer is a coating layer formed on the surface of the base metal layer, and the coating layer is made of a thermal oxide of the base metal element.
The oxide layer on the base metal layer side contains a compound carbide which is a reaction product of the carbon element and the base metal element in the base metal layer.
Low pressure casting machine . The low-pressure casting according to claim 1, wherein the oxide layer contains a plurality of regions having different compositions from each other, and the amount of the double carbide is less in the region on the outermost surface side than in the region on the metal layer side of the base metal. Machine . A low-pressure casting machine equipped with a sprue bush
The sprue bush, Ri Do from solvent loss of casting,
The composition (% by weight) of the erosion-resistant casting is C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%, P <0.03%. , S <0.02%, Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0 .50 to 0.70%, Nb <0.10%, Al <0.10%, the balance is a base metal layer composed of Fe and unavoidable impurity elements, and the oxidation formed on the surface of the base metal layer. It consists of a layer and
A part of the oxide layer extends to the grain boundaries of the base metal layer.
The oxide layer is a coating layer formed on the surface of the base metal layer, and the coating layer is a low-pressure casting machine made of a thermal oxide of the base metal constituting the base metal layer. The low-pressure casting machine according to any one of claims 1 to 4, wherein the sprue bush has a cylindrical shape having an R chamfered surface on the inner peripheral portion of the tip.

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