JPS61259870A - Filter medium for iron casting - Google Patents

Abstract

PURPOSE:To allow the quick passage of a molten metal through a filter medium for a ceramic iron casting having internally open cells without the failure of said medium by consisting the filter medium of specifically compounded silicon carbide, aluminum oxide and silicon oxide without contg. phosphate and adjusting the long diameter of the open cells to a specific length range. CONSTITUTION:The components of the filter medium for the iron casting which is the porous ceramic body having the three-dimensional network structure provided internally with the open cells are made of the compsn. which consists of >=70wt% silicon carbide, 2-20wt% aluminum oxide and 3-20wt% silicon oxide and does not contain substantially phosphate. The long diameter of the internal open cells is adjusted to a 1-8mm range. The filter medium formed under such conditions has high hot strength, low coefft. of thermal expansion, high heat conductivity, high room temp. strength and excellent thermal impact resistance, filters the molten metal with the minimized failure of the filter medium and filters quickly and surely the molten metal.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of the Invention The present invention relates to a filter material for iron castings that has excellent thermal shock resistance and hot strength and is capable of passing through molten iron castings well.

Compliance 4114 Conventionally, a ceramic porous body has a three-dimensional network lattice structure having an internal communication space, and the fluid flows while repeatedly colliding with the lattice when the fluid passes through the interior.
For example, it is known that ceramic foam obtained from synthetic resin foam and two-ohm ceramic noodles formed by randomly stacking or rolling noodle-shaped ceramics are suitably used as temporary materials for molten metal. (Special Publication No. 57-35047)

No. 35049), when using a ceramic porous body as a passing material for molten metal, when passing ordinary molten metal such as aluminum, tens to hundreds of tons of molten metal are passed through. - Increase the area of the molten metal passing surface of the overfill material (usually 900 to 3600 mm in diameter)
+ size of a) to increase the passing amount per unit time and to maintain a high removal rate of impurities in the molten metal, - lower the linear velocity of the molten metal passing inside the overfill material. There is. When installing the filter material in the filter chamber or tangish, F.

The structure for attaching the filtration material to the filter chamber or tangishish is designed to prevent molten metal from falling directly onto the filtration material, and as mentioned above, the surface area of the surface through which molten metal passes is increased to prevent heat from being applied to the filtration material. To reduce the impact,
- Preheating the filter chamber or tangish into which the filtration material is installed is carried out to near the melting temperature of the molten metal, thereby preventing damage to the filtration material.

However, when casting iron castings, tens of kilograms of molten metal are often poured into a sand mold in a short period of time, so it is not possible to preheat the overfill material or its vicinity. In addition, it is often difficult to secure enough space to avoid the impact of dropping the molten metal by passing it through the filtration material as a flow, so molten metal that has been heated above its melting point is dropped directly onto the filter material at room temperature. A method was adopted in which the process was completed in a short period of time, ranging from a few seconds to several tens of seconds. Therefore, the passing material made of a ceramic porous body through which the molten metal of iron castings passes through has the problem of being damaged by severe thermal shock and also being damaged by the mechanical impact of the molten metal.

The present invention was made in view of the above circumstances, and when filtering molten metal for iron castings, it is possible to prevent damage due to thermal shock and mechanical shock as described above, and to effectively filter molten metal for iron castings. The purpose of the present invention is to provide a filter material for iron castings that can be used for iron castings.

In order to achieve the above-mentioned object, the present invention provides a filter material for iron castings comprising a ceramic porous body having a three-dimensional mesh lattice structure having an internal communication space. contains at least 70% by weight of silicon carbide and 2 to 2% of aluminum oxide.
0% by weight and 3 to 20% by weight of silicon oxide, and has a composition substantially free of phosphate, and has a major axis of an internal communication space of 1 to 8+ am - for iron castings. It provides overfill materials.

According to the overfill material of the present invention, the ceramic porous body has the above-mentioned specific composition, and the pore diameter (internal communication space diameter) is suitable for use as a overfill material for iron casting, thereby increasing the four-hot strength. It has a high temperature, low coefficient of thermal expansion, high thermal conductivity, high strength at room temperature, and excellent thermal shock resistance, so it can filter molten iron castings by preventing damage to the filter material as much as possible. Along with gaining
Molten metal can be reliably converted to P in a short time.

The present invention will be explained in more detail below.

The filter material for iron castings of the present invention is composed of a ceramic porous body having a three-dimensional network lattice structure with internal communication spaces. Examples include ceramic foam obtained by adhering, drying, and sintering, and foam-shaped ceramic noodles formed by randomly stacking or rolling noodle-shaped ceramics. Ceramic foam having a regular dodecahedral cage-like lattice structure obtained from flexible polyurethane foam is preferably used.

Therefore, the present invention - the overmaterial has a composition of ceramic constituting such a ceramic porous body, which has silicon carbide as a main component,
The ceramic contains 70% or more (by weight, the same applies hereinafter) of the entire ceramic, and also contains 2 to 20% of aluminum oxide and 3 to 20% of silicon oxide. That is, by setting the amount of silicon carbide to 70% or more, the hot strength of the lattice of the ceramic porous body is increased, and it is possible to reliably withstand the gravitational force generated as a result of the molten metal head and flow resistance at high temperatures. , the thermal conductivity increases and the coefficient of thermal expansion decreases, resulting in a marked improvement in thermal shock resistance. In addition, in order to promote the sintering of silicon carbide, to promote the mullite formation of silicon oxide produced by oxidation of silicon carbide during firing, and to prevent an increase in the coefficient of thermal expansion, aluminum oxide has a content of 2 to 20% after firing. It is necessary that the substance be contained.

Furthermore, by containing 3 to 20% of silicon oxide, the material can maintain room temperature strength and reliably withstand mechanical impact when molten metal is dropped onto the filter material.

Therefore, according to the filter material of the present invention, even when molten iron casting metal is directly dropped onto the filter material at room temperature for filtration, damage caused by thermal shock and mechanical impact of the molten metal can be prevented. It can be prevented.

On the other hand, when the amount of silicon carbide is less than 70%, the hot strength of the lattice of the ceramic porous body is reduced, and the thermal shock resistance is also reduced. Furthermore, if the amount of aluminum oxide is less than 2%, the effect of promoting sintering of silicon carbide and the effect of converting silicon oxide into mullite during firing are poor. Silicon oxide is especially 2
Since it increases the coefficient of thermal expansion at around 00°C, it is not preferable in terms of thermal shock resistance, but if its content is less than 3%, the room temperature strength of the porous ceramic body decreases,
It cannot withstand mechanical shock when molten metal is dropped onto the filter material. Furthermore, if the content of aluminum oxide and silicon oxide exceeds 20% each, the heat resistance decreases, and the object of the present invention cannot be achieved in any of the above cases.

In addition, the more preferable range of each of the above components is that silicon carbide is 7
5-95%, aluminum oxide 2-10%, and silicon oxide 3-10%.

Furthermore, in the present invention, if phosphate is contained in the ceramic composition, it will react with aluminum oxide to produce aluminum phosphate, which significantly increases the coefficient of thermal expansion at around 200°C. The composition is substantially free of.

Furthermore, the ceramic porous body constituting the overfill material of the present invention has a coefficient of thermal expansion of 8 on average in the temperature range of 100 to 220°C.
,5X10-'/'C or less, more preferably 6.5x
It is preferable to set it to 10-''/''C or less, thereby further improving thermal shock resistance.

In the filter medium of the present invention, a ceramic porous body is formed to have the above-mentioned composition, and the major axis of the internal communication space of the ceramic porous body (the major axis of the pores formed by the lattice) is 1 to 8 mm. This allows the molten metal of iron castings to pass through in a short period of time.

On the other hand, if the major axis is smaller than 1 mm, the flow resistance of the molten metal will be large and it will take time to pour the molten metal, so the molten metal will harden before the pouring is completed, often resulting in defective products.
In addition, if it exceeds 8 m + m, the flow resistance of the molten metal is too low, making it difficult for the oxides in the molten metal to float to the top of the sprue at the right time, and the lattice surface area of the ceramic porous body becomes small, making it difficult to attach and remove oxides in the molten metal. In either case, the object of the present invention cannot be achieved. Note that a more preferable range of the pore diameter is 2 to 8 mm.

In addition, the ceramic porous body has a bulk density of 0.3 to 0.6 g/ryl in order to better pass the molten metal of iron castings.
It is preferable to form the Further, the shape of the filter medium can be appropriately selected, and can be formed into, for example, a cylindrical shape, a truncated pyramid shape, an inverted truncated pyramid shape, or the like.

Note that in the present invention, a commonly used method can be used as a method for manufacturing a porous ceramic body.

In addition, there are no restrictions on the manner in which the filtration material of the present invention can be used, and a normal filtration method may be adopted, but the molten metal is directly dropped onto the filtration material at room temperature and is filtered in a short period of several seconds to several tens of seconds. can be effectively adopted.

As explained above, the filter material for iron castings of the present invention has excellent hot strength and thermal shock resistance, and is resistant to damage even when molten metal falls directly onto it. This can be prevented and a good transition can be achieved in a short period of time.

Claims (1)

[Claims] 1. A filter material for iron castings consisting of a ceramic porous body having a three-dimensional network lattice structure with internal communication spaces, in which the ceramic porous body contains 70% by weight or more of silicon carbide, 2 to 20% by weight of aluminum oxide, and silicon oxide. What is claimed is: 1. A filter medium for iron castings, characterized in that the composition contains 3 to 20% by weight of phosphate and substantially no phosphate, and the major axis of the internal communication space is 1 to 8 mm.