JP2002159810A - Filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter having capacity for removing phosphorus and sulfur of a casting without using special equipment in addition to the conventional removing capacity of floating enclosures to obtain the casting of high quality. SOLUTION: The filter has ceramics containing a calcium compound and carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter suitable for removing inclusions generated in a metal melting step and for removing nonmetallic inclusions such as phosphorus and sulfur contained in molten metal.

[0002]

2. Description of the Related Art In the production of castings, a step of removing inclusions floating in molten metal is indispensable for removing defects in castings. Conventionally, the removal of inclusions has been improved by improving the mold based on experience such as providing a weir. However, with this method, it is difficult to remove inclusions that have not completely floated. Therefore, in recent years, a method of removing massive inclusions in a molten metal by a filter using ceramics which is stable at a high temperature has been proposed and already put into practical use. For example, Japanese Patent Publication No. 58-5004
No. 34 discloses a filter having continuous holes of a three-dimensional network structure made of a refractory aggregate such as alumina. Ceramics used for the filter are made of silicon carbide (SiC), mullite (3Al ₂ O ₃ .2SiO ₂ ), cordierite (2MgO.2Al ₂ O _3. Refractory aggregates such as 5SiO ₂ ) and zirconia (ZrO ₂ ) are used. Filters using these ceramic materials have a controlled filtration diameter, and have an optimum diameter depending on the amount of molten metal that can be processed and the size of massive inclusions floating in the molten metal.

On the other hand, impurities such as phosphorus and sulfur contained in a casting different from the massive inclusions cause a change in the microstructure of the casting, that is, cause structural defects and the like, and cause various deteriorations in performance. . Phosphorus causes deterioration of low-temperature brittleness. Sulfur also reduces red hot brittleness, and particularly in ductile cast iron, sulfur inhibits carbon spheroidization and lowers quality. The above-described ceramics filter for removing inclusions floating in the molten metal has almost no ability to remove phosphorus or sulfur. Therefore, in order to obtain castings with no deterioration in performance, high quality pig iron with low impurity concentration must be selected, which limits the selection range of raw materials, such as the inability to use scrap, the availability of raw materials, and economical aspects. There's a problem.

[0004]

SUMMARY OF THE INVENTION The present invention provides a filter for removing high-quality castings by removing phosphorus and sulfur from castings without using special equipment, in addition to the conventional ability to remove suspended inclusions. The purpose is to provide.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a filter having a ceramic containing calcium and carbon.

The ceramic containing calcium is xC
filter represented by _{aO · yAl 2 O 3 (x} / y = 0.125~4.0), ceramic content of 10 to 90 wt% of the filter in the filter, and, of carbon in the filter The filter preferably has a content of 10 to 90% by weight.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A ceramic containing a calcium compound used in a filter of the present invention is essential as a component for removing phosphorus and sulfur in a molten metal. That is, it is considered that phosphorus and sulfur in the molten metal react with the calcium compound during the filtration and change into insoluble components, so that they can be removed from the metal. The calcium compound in the filter exists in a sufficiently large amount with respect to the amount of phosphorus and sulfur in the molten metal, and the filtration of the molten metal can remove phosphorus and sulfur in the molten metal for a long time.

[0008] The calcium compound is preferably a compound that does not change its form due to adsorption of water vapor or carbon dioxide gas, and is more preferably an oxide, carbide or double oxide from the viewpoint of fire resistance because it is used at a high temperature. For example, calcium aluminate _{(xCaO · yAl 2 O 3)} , calcium silicate (xCaO · zSiO _2), calcium aluminate silicate (xCaO · yAl ₂ O ₃ ·
zSiO ₂ ) or a mixture thereof (x, y, and z in the composition formula are integers of 1 or more). In particular, calcium aluminate is preferred from the viewpoint of heat resistance.

Although the effect of the present invention can be obtained by using calcia (CaO) alone, calcia easily reacts with water vapor or carbon dioxide gas in the air. And
In some cases, it is difficult to maintain the shape of the filter due to expansion due to hydration or the like. Therefore, it is preferable to use another calcium compound from the viewpoint of handling and durability.

From the viewpoint of removing phosphorus and sulfur, the content of the calcium compound is 50 to 100% by weight in the ceramics.
Is preferable, 70 to 100% by weight is more preferable, and 9
0-100% by weight is particularly preferred. The content as calcium oxide is 10 to 90% by weight in the ceramics.
Is preferably 20 to 80% by weight, more preferably 50 to 80% by weight.
-75% by weight is particularly preferred.

A preferred composition of calcium aluminate is represented by xCaO.yAl ₂ O ₃ , where x / y = 0.1
25 to 4.0. More preferably, x / y = 0.2
It is 5 to 3.5, particularly preferably 0.5 to 3.0. As a typical compound, a stoichiometric compound of calcia and alumina is known, and 3CaO.Al ₂ O _3, 12Ca
_{O · Al2O 3, CaO · Al} 2 O 3, CaO · 2Al
₂ O _{3 and the} like.

The ceramics are mixed, for example, in a predetermined ratio with ceramic constituents containing calcium, and are mixed at a ratio of 300-17.
It is obtained by baking in the air or an inert gas at 00 ° C. for 0.5 to 24 hours. For example, calcium aluminate is obtained by mixing a calcium compound such as calcium hydroxide and calcium carbonate with an aluminum compound such as aluminum hydroxide and aluminum sulfate at a predetermined ratio, and
１1600 ° C. for 0.5-24 hours, preferably 1-12
It can be obtained by firing for a time. The optimal firing temperature is
It is appropriately selected according to the composition of calcium aluminate and the type of raw material.

Preferred calcium silicate and calcium
The composition of the aluminum silicate is 3CaO.Si
O_Two、 2CaO ・ SiO_Two3CaO.2SiO_Two, C
aO ・ SiO_Two, 2CaO · Al_TwoO_Three・ SiO_Two, C
aO ・ Al_TwoO_Three・ 2SiO _TwoAnd the like. these
Is the same as for calcium aluminate
You can get more.

The content of ceramics in the filter is preferably from 10 to 90% by weight, more preferably from 50 to 90% by weight, particularly preferably from 70 to 90% by weight, from the viewpoint of removing phosphorus and sulfur.
% By weight is preferred.

In order to enhance the thermal shock resistance of the filter, a ceramic containing a calcium compound is combined with carbon.
If the thermal shock resistance is low, the filter is destroyed during the pouring of the molten metal, and the filter itself and phosphorus or sulfur that could not be removed are mixed into the casting to cause defects. The content of carbon in the filter is preferably from 10 to 90% by weight, more preferably from 10 to 50% by weight, particularly preferably from 10 to 30% by weight from the viewpoint of strength.
% By weight is preferred. The composite carbon may be in the form of graphitic, amorphous, or a mixture thereof. The state of dispersion of carbon is not limited, but is preferably uniform with ceramics from the viewpoint of thermal shock resistance and strength.

In the filter, (1) oxides or double oxides such as MgO and TiO ₂ , and (2) SiC, TiC, BN, Si ₃ N _{4 and the} like, as long as the effects of the present invention are not impaired. Other components such as non-oxides, (3) metals such as iron and ferromanganese may be combined.

The filter of the present invention can be obtained, for example, by the following method. The above-described ceramic containing a calcium compound is mixed with graphite powder or carbon powder, and an organic compound such as resin and pitch which is converted into carbon after firing, and then shaped into a filter. When the ceramic is not in a powder form, it is preferable to pulverize the ceramic and then mix carbon from the viewpoint of uniform dispersion. Then 1
It is obtained by firing (heat treatment) in the range of 50 to 1500 ° C. for 0.5 to 24 hours, preferably 1 to 12 hours, under an inert atmosphere or a reducing atmosphere. This firing (heat treatment) develops the strength of the filter.

The form of the filter is not particularly limited as long as it has continuous holes. For example, a lotus root type, a straight-hole honeycomb type, a three-dimensional honeycomb type, and the like can be given. The pore size is selected according to the casting conditions from the viewpoint of securing the flow rate of the molten metal during filtration and the ability to remove inclusions. Preferably 0.2 to
It is 20 mm, more preferably 1 to 10 mm.

[0019]

EXAMPLE 1 1000 g of calcium carbonate and 520 of aluminum hydroxide
g and water (1800 g) were wet-mixed with a ball mill for 24 hours, and the water in the dispersion medium was removed and dried. The resulting mixture is
The powder was fired in the air at 00 ° C. for 4 hours to obtain a powdery ceramic. In a ball mill, 80 parts of the obtained ceramics were dry-processed with 20 parts of graphitic carbon (artificial graphite; carbon purity 98.5%, particle size 80 to 150 mesh) and 5 parts of a phenol resin (resole type, fixed carbon 46%). For 5 hours. The obtained mixture was molded at a pressure of 98 MPa.
(Shape: Disk shape with outer diameter φ60mm, thickness 15mm, φ1
Lotus root type with seven 0 mm holes, appearance is shown in FIG. 1). The molded body is fired at 1500 ° C. for 1 hour in a nitrogen atmosphere, and 78% of calcium aluminate (3CaO.Al ₂ O ₃ )
A test filter with 22% carbon was obtained.

A cast iron FC-15 composition (phosphorus: 0.234)
% By weight, sulfur: 0.079% by weight)
It was melted at 400 ° C. and subjected to a filtration test. 10 molten metal
As a result of pouring kg, there was no damage due to thermal shock.

Example 2 1000 g of calcium carbonate and 780 of aluminum hydroxide
g and 2000 g of water were mixed and dried in the same manner as in Example 1 to obtain a mixture. The mixture was fired at 1500 ° C. in the air for 4 hours to obtain a massive ceramic. 1mm for fired product
After pulverization, 70 parts of the obtained pulverized ceramics were treated with 20 parts of coal pitch (fixed carbon: 61%) and 10 parts of phenol resin (resole type, fixed carbon: 46%) in the same manner as in Example 1 by using Aluminate (12C
_{aO · 7Al 2 O 3) 81} %, to obtain a test filter of 19% carbon. As a result of performing the same filtration test as in Example 1,
There was no damage due to thermal shock.

Comparative Example 1 Mullite (3Al ₂ O ₃ .2Si) having the same shape as in Example 1
Using a filter of O ₂ ), the same filtration test as in Example 1 was carried out. As a result, cracks were formed after the test.

Comparative Example 2 The same filtration test as in Example 1 was performed using a SiC filter having three-dimensional continuous holes.

Table 1 shows the strength deterioration rate of the filter after the casting test and the phosphorus and sulfur contents of the obtained casting.

<Quantitative Determination of Phosphorus and Sulfur>
Cut out to × 20 × 7mm, mirror polished flat plate surface,
X-ray fluorescence (Rigaku Denki, 3371E) was used.

<Measurement of Strength Deterioration Rate> The compressive strength in the thickness direction of a filter that was not poured and a filter that was poured were measured and determined by the following equation. The compressive strength was measured at a crosshead speed of 0.2 mm / min (Shimadzu Corporation, Autograph DCS). Strength degradation rate (%) = [(filter strength before pouring)-(filter strength after pouring)] / (filter strength before pouring) x 100

[0027]

[Table 1]

[0028]

The filter of the present invention has an effect of reducing strength deterioration and reducing phosphorus and sulfur in a casting. Phosphorus in molten metal without using special equipment,
It is useful for producing high quality castings by removing sulfur.

[Brief description of the drawings]

FIG. 1 is a view showing the appearance of filters of Examples 1 and 2 of the present application and Comparative Example 1. FIG.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B22D 43/00 B22D 43/00 C C04B 35/44 C04B 35/44 35/52 35/52 B (72) Inventor Shigeo Nakai 4-51 Akami-cho, Toyohashi-shi, Aichi Prefecture Kao Co., Ltd. Laboratory F-term (reference) 4D019 AA03 BA03 BA05 BB06 BC05 CA01 4E014 NA08 4G031 AA04 AA29 AA40 BA26 GA04 GA08 4G032 AA22 BA00 GA12 4G066 AAAAAAAAAAAB20AA20A BA07 CA22 CA41 DA20 FA02 FA03 FA22 FA23 FA25 FA28

Claims (4)

[Claims] 1. A filter comprising a ceramic containing a calcium compound and carbon. 2. A ceramic containing a calcium compound is xCaO.yAl ₂ O ₃ (x / y = 0.125 to 4.25).
2. The filter according to claim 1, wherein the filter is represented by 0). 3. The filter according to claim 1, wherein the content of the ceramic is 10 to 90% by weight. 4. The filter according to claim 1, wherein the content of carbon is 10 to 90% by weight.