JPH0139856B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a sprue in a continuous casting apparatus for metals having a relatively low melting point, such as aluminum.

BACKGROUND OF THE INVENTION There are various methods for continuous casting of low-melting point metals such as aluminum, but hot-top casting is currently the most popular method worldwide. Taking this hot-top casting as an example, the structure of the sprue and its vicinity in a continuous casting machine will be explained with reference to FIGS. 2 and 3. After entering the mold 23 (a part of which is cut out to become a runner 24), it is sent to the mold 25. The molten metal 22 that has entered the mold 25 is separated from the mold 25 by pressurized air jetted out through the pressurized air distribution groove 26 at the top of the mold 25 and lubricant oil jetted out through the lubricant distribution groove 27. It cools down while maintaining contact. Furthermore, cooling water 28 that also serves as cooling water for the mold 25 is injected to cool the ingot to below its melting point, thereby forming an ingot 29. In such a continuous casting apparatus, the sprue is required to have as good insulation as possible, to be impermeable to penetration of molten metal, and to have a high degree of durability so as to maintain a constant surface quality for a long period of time. In other words, if continuous casting is performed using a sprue using a material with poor insulation properties, no matter how durable it is, the temperature of the molten metal will drop significantly while passing through the sprue, and the solidification start line (first stage) of the molten metal entering the mold will drop significantly. 3
(located at position T in the figure) rises too much toward the sprue side, causing a so-called freeze-back phenomenon, making it impossible to perform continuous casting as described above smoothly, and resulting in poor quality of the cast product. Increasing the temperature of the molten metal to avoid this phenomenon increases thermal energy costs, requires more heat-resistant components of the casting equipment, and significantly accelerates oxide formation from the molten metal. There are many disadvantages such as deterioration of product quality.
Undesirable. In addition, the parts that come into contact with the molten metal and the parts below that come into contact with the pressurized air and lubricating oil (hereinafter referred to as the molten metal contact area to refer to these parts as a whole) are exposed to harsh usage conditions. Common insulation materials tend to crack. Once cracks occur, pressurized air and lubricating oil leak, and the action of these casting aids becomes unstable, resulting in a uniform change from molten metal to ingot as shown in Figure 3. In addition, it will not occur at the optimum position, resulting in significant deterioration of casting surface and other product quality.

Conventionally, tobermorite-based calcium silicate molded bodies reinforced with asbestos fibers have been used as sprues since they have relatively good suitability. However, products containing asbestos fibers have become less popular due to environmental hygiene reasons, and
Since it can only be used at temperatures below about 750°C, there has been a demand for a sprue that does not contain asbestos fibers and has better heat resistance. Japanese Patent Publication No. 57-49507 discloses a xonotrite calcium silicate molded body that was invented to meet such demands. This molded body is
It is characterized by the fact that it does not contain asbestos fibers and can be used at temperatures up to approximately 850°C under normal usage conditions, but this molded product also has durability when used as a sprue in a continuous casting machine such as the one mentioned above. As for sex, I was still not satisfied with it.

Problems to be Solved by the Invention The present invention solves the above-mentioned problems with conventional sprues for casting low-melting point metals, and provides a sprue that enables stable casting over a long period of time by having both high durability and heat insulation. This is what we are trying to provide.

Means for Solving the Problems The means adopted in the present invention to solve the above-mentioned problems is to form a small-walled molded product made of a high-density material that has good heat resistance and spall resistance and is difficult to wet with molten metal. The present invention employs a composite structure in which a heat-insulating molded product is attached to the back side of the molded product to form an equal contact portion and cover the back surface of the molded product.

Although the material of the molded material that makes up the contact area with the molten metal in the low melting point metal casting sprue according to the present invention has a high thermal conductivity, it has a dense structure with a density of approximately 1 g/cm ³ or more and is wetted by the molten metal. Silicon nitride is used because it is difficult to use and has good strength, heat resistance, and spalling resistance (resistance to cracking caused by heating). This molded product is desirably made into a shell shape with as small a wall thickness as possible (preferably about 0.5 to 10 mm in thickness) while still having the necessary strength.

Back side of contact area with molten metal, etc. (opposite side of molten metal contact surface)
A calcium silicate molded product with good heat insulation and heat resistance is used as the heat-insulating molded product to be attached to the
Among these, those with a density of 0.4 to 1.0 g/cm ³ (particularly preferably
0.6 to 0.85 g/cm ³ ) is suitable. A preferred example of the heat-insulating molded product is one in which calcium silicate consists essentially of zonolite and carbon fiber is used as a reinforcing material. The zonolite molded body reinforced with carbon fibers does not easily cause large cracks that can lead to complete destruction even when used alone to form a sprue, and exhibits excellent durability. Therefore, even when used in the sprue of the present invention, it has excellent durability. Show your gender.

The molded product that makes up the contact area with molten metal and the insulating molded product that is attached to the back side of the molded product do not stick to each other or fit closely together over the entire area, and can be deformed independently due to thermal expansion. It is desirable to keep it as such. Generally, it is difficult to construct the above two molded products from materials with the same coefficient of thermal expansion, so when the two are in close contact with each other, the thermal expansion of the contact parts such as molten metal exerts large stress on the heat insulating molded product. This is because cracks may occur. For this reason, it is preferable that only the radial contact portions of both molded parts are not brought into close contact with each other, and that a small gap is provided. In order to prevent the relative arrangement of the two molded products from becoming distorted due to the provision of a void, a compressible filler made of heat-resistant inorganic fiber cloth, paper, or felt is placed in the void. May exist.

Function In the sprue of the present invention, the molded product constituting the contact area with the molten metal is made of a high-density material with good heat resistance and spalling resistance, and is thin, so it can be heated to a high temperature by directly contacting the molten metal. On the other hand, even if it is placed under harsh operating conditions with parts being cooled by pressurized air or lubricating oil, or subjected to repeated heating and cooling, it will not easily cause damage such as cracks, chips, or abrasion. does not occur. Also, unlike porous calcium silicate molded bodies, it is difficult for lubricating oil to penetrate.
There is little change in physical properties or surface contamination due to the accumulation of carbides. Therefore, the initial properties of the molten metal contact surface are maintained over a long period of time. On the other hand, heat-insulating molded products share the heat-insulating part of the properties necessary for a sprue to prevent the temperature of the molten metal from dropping, and also act as structural reinforcement for the thin molded parts that make up the contact area with the molten metal. Become.

Embodiment FIG. 1 shows an example of a sprue according to the invention for the casting apparatus of FIGS. 2 and 3 above. This sprue consists of two annular blocks 1 and 2 stacked one above the other.
Each annular block is made of silicon nitride ceramics and is made of molten metal, etc.
and heat insulating materials 5 and 6 (xonotrite calcium silicate molded body reinforced with carbon fibers) combined to cover the back surface thereof.

The upper annular block 1 has a notch 7 extending from its inner circumference to its outer circumference, and this portion serves as a runner for introducing molten metal. The molten metal contact part component 4 in the lower annular block 2 is a 3 mm thick flange-like member, and its collar-like protrusion 8 is sealed to prevent pressurized air or lubricating oil from coming into direct contact with the heat insulating material 6. It extends to the outside of Packing 9.

The components of the contact part such as molten metal and the heat insulating material are in a fitted state without being bonded, but there is a gap of 1 to 3 mm between the two.
It is also possible to provide a gap and fill it with a compressible filler to prevent thermal expansion of the contact portion components 3 and 4 such as molten metal from exerting large stress on the heat insulating materials 5 and 6.

Note that the upper annular block 1 is the lower annular block 2.
It is not exposed to harsh conditions of use,
Furthermore, since the stability of the surface properties is not a problem, if the sprue is used under relatively mild conditions, such as when the temperature of the molten metal is not very high, it is recommended to have a structure in which the member 3 that contacts the molten metal etc. is omitted. You can also do it.

When this example product was subjected to repeated heating and cooling tests similar to those used in continuous casting of aluminum at a molten metal temperature of 700°C, after 200 cycles of testing,
There was no abnormality in the components of the contact area such as the molten metal, and only a few short hair cracks were generated in the heat insulating material radially from the inner peripheral surface side.

Effects of the Invention According to the present invention, which employs the above-described composite structure, many effects as described below can be achieved.

(b) Providing an excellent sprue that meets all of the characteristics required of a sprue, with the parts that come into contact with the molten metal being hard to get wet with the molten metal and having excellent durability, and the overall property being excellent in heat resistance and insulation. (For example, it is possible to easily provide a high-performance sprue that exhibits excellent durability even when used for casting highly reactive metals such as magnesium or metals with high specific gravity and high melting point such as copper.) be able to.).

(b) If the molten metal solidifies due to an accident during casting, with the sprue of the present invention, only the constituent members of the contact portion, such as the molten metal, can be replaced or reused, resulting in less damage. The same applies if either the molten metal or other contact portion constituent member or the heat insulating molded product is damaged due to other causes.

(d) Even if cracks occur in the components of the contact parts such as molten metal during casting, the cracks will not grow all at once to the outer periphery of the sprue, so there is no possibility of a major accident in which the molten metal flows out of the casting equipment. There is no risk of causing

(d) The sprue tip of a continuous casting device can be said to form a part of the mold, and its accuracy has a great effect on the quality of the casting surface. By being made of a material with excellent properties, there is less wear and tear over time, and there is less risk of damage when installing sprues and molds, ensuring high accuracy.

(e) A sprue made of a calcium silicate molded body is
When calcium silicate crystallization water or moisture due to moisture absorption comes into contact with the molten metal, it may vaporize and mix into the molten metal, causing bubbles in the casting. By not using it, there is no need to take measures to prevent such troubles.

Therefore, in continuous casting using the sprue of the present invention, stable casting for a longer period of time is possible at the same or lower molten metal temperature than when using a conventional sprue, and it is also possible to improve product quality and maintain maintenance. Simplification of work is achieved.

[Brief explanation of drawings]

Fig. 1: An example of a sprue according to the present invention is shown, with Fig. A being a plan view and Fig. B being a sectional view taken along line B-B in Fig. A. Figure 2,
Figure 3: An explanatory diagram of hot-top casting. 3, 4: Constituent member for contact portion with molten metal, etc. 5, 6: Heat insulating material.

Claims (1)

[Claims] 1. A part that contacts molten metal, etc. is formed by a molded product made of silicon nitride ceramics with a small wall thickness, and a calcium silicate heat-insulating molded product is attached to the back side of the molded product to cover the back surface. A sprue for casting low melting point metals. 2 Construct a contact area for molten metal, etc. with a small-walled molded product made of silicon nitride ceramics, and attach a heat-insulating calcium silicate molded product to cover the back side of the molded product to configure a contact area for molten metal, etc. A sprue for casting low-melting point metals, which is provided with a space sufficient to prevent the generation of stress due to the difference in thermal expansion between the molded products and the heat-insulating molded products. 3. The sprue according to claim 2, wherein the cavity is filled with a compressible filler. 4. The sprue according to claim 3, wherein the compressible filler is made of cloth, paper, or felt made of heat-resistant inorganic fibers.