JPH09239513A - Die to be used for die casting of cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a formed body which is not cracked easily by using a composite die comprising a graphite die to form a cavity and a die to reinforce the graphite die as a die-casting die of cast iron to greatly reduce the thermal load of the die and suppress generation of the cementite structure in the die casting. SOLUTION: A die for die-cast injection molding basically comprises a graphite die 2 and a die 3. A cavity 4 is formed to the shape of a formed body inside the graphite die 2, and a runner 6 to be communicated with the cavity 4 is provided in a mating surface of the graphite die 2. The outer contour of the graphite die 2 is approximately of parallelepiped. The die 3 is made of the metal such as steel and copper, the graphite die 2 is inserted therein, a recess 7 to reinforce the graphite die 2 is provided, and a runner 9 to be communicated with the runner 6 formed in the mating surface 5 of the graphite die 2 is provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a mold used for die casting of cast iron.

[0002]

2. Description of the Related Art There are various types of die casting equipment such as horizontal type and vertical type, and the basic structure thereof is, for example, as in the vertical die casting equipment shown in the schematic view of FIG.
And a mold 12, and the injection device 11 includes an injection cylinder 13,
It comprises a plunger 14 and an injection sleeve 15, and the mold 12 is formed with a product cavity 16. Then, the die-casting uses the above-mentioned equipment, injects the normal molten metal 17 into the injection sleeve 15, sets the mold 12 in the injection sleeve 15 by advancing, and then drives the plunger 14 forward to drive the molten metal 17 into the cavity 16 It is injected into the inside and kept under pressure for a predetermined time, and then the mold 12 is retracted to take out the product and die casting is performed.

In the above die casting, when the molten metal 17 is an aluminum alloy, a magnesium alloy, or the like, which has a relatively low melting point, it has already been widely used by using a die 12 formed of die steel or heat resistant steel. In addition, a thixocasting method in which an alloy material (billet) is heated to a solid-liquid coexistence temperature range and die-cast is put into practical use. However, the die casting using cast iron as the molten metal 17 was developed in, for example, Japanese Patent Publication No. 52-447, Japanese Patent Publication No. 52-125422, Japanese Patent Publication No. 53-61520, and Japanese Patent Publication No. 53-95118. -Although it has been proposed, it has not been put into practical use due to the large heat load on the mold and the short life.

For this reason, in the production of cast iron castings, although a mold is used in part in gravity casting of cast iron, most of them are still sand mold castings, and the working environment is deteriorated due to the use of casting sand, and the waste is eliminated. Environmental problems such as sand disposal are very serious problems. Further, in gravity casting using the mold,
Although environmental problems such as foundry sand are solved, since it is cast by molten metal, the heat load of the mold is not as high as die casting that applies high pressure, but it is considered to be considerably large and it seems that there is a problem in mold life Be done.

On the other hand, there is a strong need for weight reduction in automobiles and the like, and there is a tendency for toughness and high strength in the casting industry as well. However, cast iron is mainly gravity-casted as described above, so the thickness is about 3 mm. This is the limit of thinning, and it is difficult to make thin castings with a thickness less than that unless it is a die casting method. But,
Die casting with molten cast iron has not been put to practical use as described above, and technically, thin-walled castings are subject to rapid cooling due to dies and cracks easily occur due to thermal stress.

On the other hand, recently, a rheocast method in which a cast iron slurry in a solid-liquid coexisting temperature range is directly injected into a die-casting sleeve, or a thixocast method in which a cast iron material (billet) is heated to a solid-liquid coexisting temperature range and die-casted (For example, Japanese Patent Laid-Open Nos. 5-43978 and 6-1.
No. 06321, JP-A-7-204820, etc.). Die casting methods such as the rheocast method and the thixocast method have attracted attention because they can reduce the heat load on the mold because they can be injected at a lower temperature than the molten metal.

[0007]

However, even when die casting such as the rheocast method or the thixocast method is performed, the injection temperature is lower than that of the cast iron molten metal, but it is a high temperature of 1100 ° C. or higher and a high pressure. Therefore, the heat load on the mold is still a serious problem. Further, in addition to the heat load of this mold, iron-cementite solidification is likely to occur because it is rapidly cooled in the mold, and a cementite structure with high hardness is generated, which easily causes cracking in the die cast product, and is particularly thin. Since castings are cooled rapidly because they are easily cooled, it is an important issue to prevent the cracks and improve the surface properties of the molded products.

Therefore, the present invention has been made to solve the above-mentioned problems, and the purpose thereof is to significantly reduce the heat load on the mold and to produce a cementite structure during die casting. The present invention provides a mold used for die casting of cast iron, which can suppress cast iron and produce cast iron products with less cracks.

[0009]

In order to achieve the above object, the mold used in the cast iron die casting according to the present invention is used in the cast iron die casting in which the cast iron is injected into the mold and held under pressure. The mold is composed of a graphite mold and a mold for backing up the graphite mold.

In the mold used for die casting of cast iron according to the present invention, a graphite mold may be provided in part.

The structure and operation of the present invention will be described in detail below. When a cast iron melt such as a molten metal or a slurry in the solid-liquid coexistence temperature range is injected into a mold as in the conventional case, the surface temperature immediately after that depends on the material of the mold and the casting method.
Reach over 400-500 ℃. Therefore, a temperature distribution is generated in the mold, and tensile or compressive stress acts due to thermal expansion, and if they exceed the strength of the mold, the mold is broken.
In addition, generally, repeated use causes a thermal cycle, which leads to the occurrence of cracks due to thermal fatigue. Normally, the strength of metals decreases with temperature, so
This is the reason why die casting of refractory metals is not realized.

The present invention uses a carbon material (graphite), which has a relatively small coefficient of thermal expansion and does not deteriorate in strength even at high temperature, on the inner surface of the mold, which is brought into high temperature by direct contact with the molten metal as described above. The temperature rise (heat load) of the mold can be suppressed and the life can be significantly improved. The rapid cooling of the cast iron melt injected into the cavity is mitigated, the generation of cementite structure in the die casting is suppressed, and the cast product with few cracks. Other than that, the graphite mold has good releasability because it is difficult to wet with cast iron molten metal, etc., and can be molded without using a mold release agent. The problem goes away. Further, since the mold is closely attached to the outside of the graphite mold, it is possible to back up the pressure applied to the graphite mold during die casting,
It is possible to stably manufacture the cast product with less cracks.

In order to obtain the above effect effectively, it is desirable that the thickness of the graphite mold is about 2 to 10 mm. If it is less than 2 mm, the heat load on the mold becomes large and the meaning of providing graphite becomes meaningless. , The graphite mold is easily damaged and requires careful handling. On the other hand, if the thickness exceeds 10 mm, the heat load on the mold is small, but it is difficult to control the temperature of the molten metal and the like, which affects the productivity of die casting.

On the other hand, in the die casting process by gravity casting, the contact state between the poured molten metal and the die becomes worse with solidification shrinkage, and the thermal resistance rapidly increases, which cannot be controlled. Although difficult, in the present invention, due to the high pressure during die casting and the action of the graphite mold, the thermal resistance of these is relatively small, and the material of graphite used as the mold, the shape (thickness, etc.) is set appropriately, and the heat flow Can be controlled, that is, the solidification and cooling rate of the molded article can be controlled. Although the heat flow locally differs depending on the shape of the molded product, the heat load on the mold can be made uniform by appropriately selecting the material and shape of graphite.

Further, one of the features of die casting is that a product having a thin portion can be molded. However, particularly in a material having low ductility such as cast iron, the thin portion has low strength, and cracks may occur due to thermal stress during cooling. Particularly at the boundary between the thin portion and the thick portion, a large thermal stress is likely to occur due to the difference in cooling rate. In the present invention, by appropriately designing the graphite mold of this portion as described above, the heat flow can be controlled, the thermal stress can be relaxed, and a sound molded product having no crack defects at the thin portion or the boundary portion can be obtained. To be

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view of a mold according to the present invention, wherein a is an overall perspective view of the mold according to the present invention,
b is a perspective view of a graphite mold according to the present invention.

The mold 1 according to the present invention is basically composed of a graphite mold 2 and a metal mold 3. Inside the graphite mold 2, a cavity 4 is formed in accordance with the shape of a cast iron product, and the graphite mold 2 is also formed. The mating surface 5 of the runner 6 communicating with the cavity 4
Is molded. Further, the outer shape of the graphite mold 2 is formed into a substantially rectangular parallelepiped.

On the other hand, the mold 3 is made of metal such as steel or copper, and is provided with a recess 7 for backing up by inserting the graphite mold 2 therein, and a mating surface 8 of the mold 3 is provided. A runner 9 communicating with a runner 6 formed on the mating surface 5 of the graphite mold 2 is provided.

[0019]

【Example】

[Embodiment 1] The vertical die casting equipment shown in FIG.
Set the mold 1 (the thickness of the graphite mold 2 at this time was 5 mm) and die cast it using the molten cast iron (3.09% C-2.01% Si), and the width 100 mm × height 150 mm shown in FIG.
× A plate-shaped product with a thickness of 6.3 mm was manufactured. Then, in this manufacturing process, the temperature inside the die during die casting was measured by a K thermocouple embedded at a position of 0.6 mm from the inner surface of the die 3. For comparison, a plate-shaped product having the same size was die-cast in the same manner by using only the mold (SKD61). FIG. 3 shows the temperature measurement result of the temperature inside the mold as it is injected into the mold. Further, FIG. 4 shows a temperature change upon repeated injection. FIG. 5 shows a cracked molded product obtained by a mold (comparative example).

As is clear from FIGS. 3 and 4, in the case of only the mold, the inner surface temperature exceeds 500 ° C., and it is expected that the mold material will deteriorate, crack, and be damaged by long-term use. To be done. Further, the molded product is highly likely to be cracked as shown in FIG. On the other hand, in the case of the mold 1 according to the present invention, the inner surface temperature of the mold 3 has been maintained at 300 ° C. or lower,
It was possible to use it for a long time by replacing the graphite mold 2, and no crack was observed in the molded product. In the present invention, by appropriately selecting the size, shape, and graphite material of the graphite mold 2 and cooling the mold 3, it is possible to further lower the mold temperature without affecting the cooling of the molded product. It is possible.

It should be noted that, in the above-mentioned embodiment, the example of the molten metal method using the cast iron molten metal having the highest temperature is explained, and it is sufficiently applicable to die casting by the rheocast method or thixocast method having a lower temperature than the molten metal method. Is.

[0022]

As described above, according to the mold used for die casting of cast iron according to the present invention, the heat load on the mold can be significantly reduced, and the cast iron molten metal is originally cast iron by the rheocast method or thixocast method. Die casting is possible. Further, graphite is inexpensive and easy to machine, and since graphite is provided in a place where a heat load of the die is applied to form a cavity, the life of the expensive die can be extended and the number of die types can be reduced. In addition, it is possible to suppress the generation of cementite structure during die casting and manufacture cast iron products with less cracks.

[Brief description of drawings]

FIG. 1 is an explanatory view of a mold according to the present invention, in which a is an overall perspective view of the mold according to the present invention, and b is a perspective view of a graphite mold according to the present invention.

FIG. 2 is an explanatory view of a plate-shaped product die-cast with a mold according to the present invention, in which a is a front view and b is a side view.

FIG. 3 is a graph showing the temperature of the inner surface of the mold when die casting is performed with the mold according to the present invention, in comparison with the mold (comparative example).

FIG. 4 is a graph showing the temperature of the inner surface of the mold when it is repeatedly die cast with the mold according to the present invention in comparison with the mold (comparative example).

FIG. 5 is an explanatory diagram showing a cracked state of a molded product obtained by a mold (comparative example).

FIG. 6 is a schematic view of vertical die casting equipment.

[Explanation of symbols]

1: Mold 2: Sand mold
3: Mold 4: Cavity 5, 8: Mating surface
6, 9: runner 7: hollow

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Morimoto Inventor Hiroyuki Morimoto 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Inside Kobe Research Institute of Kobe Steel, Ltd. (72) Yuichi Ando Takatsuka, Nishi-ku, Kobe-shi, Hyogo 1-5-5 stand, Kobe Steel, Ltd. Kobe Research Institute

Claims (2)

[Claims] 1. A mold used for die casting of cast iron, which comprises injecting cast iron into a mold and holding it under pressure, wherein the mold comprises a graphite mold and a mold for backing up this graphite mold. Mold used for die casting. 2. A mold used for die casting of cast iron according to claim 1, wherein a graphite mold is partially provided.