JP7221498B2 - Ceramic filter and its manufacturing method - Google Patents

Description

The present invention relates to ceramic filters. More particularly, the present invention relates to improvement of a ceramic filter for removing unwanted substances from molten metal such as aluminum.

Ceramic filters are used to remove foreign matter from molten aluminum (including alloys; the same shall apply hereinafter).
A conventional ceramic filter is a plate-like member made by sintering an aggregate made of ceramic particles with a binder. These plate-like members are combined to form a bottomed cylindrical shape which is rectangular in plan view, that is, a cylindrical shape with an open top, and this is immersed in a molten aluminum metal bath.
Further, Patent Document 1 proposes a ceramic filter formed by integrally molding an upward-opening cylinder. The ceramic filter configured in this manner is mechanically more stable than a plate-shaped ceramic filter that is connected. Therefore, the durability is improved for use in the severe environment of molten aluminum metal.

Japanese Patent Application Laid-Open No. 2017-214268

However, according to the studies of the present inventors, when the manufacturing method described in Patent Document 1 was carried out, it was not possible to obtain a tall ceramic filter integrally molded with a three-dimensional structure. More specifically, when the height of the side wall was 300 mm or more, the side wall collapsed and the product could not be obtained.
A dough is prepared by kneading an aggregate consisting of ceramic particles, a binder, and water, and the dough is formed into an integrally molded three-dimensional structure, ie, an open top cylinder. At this time, the wall cannot be made thick in order to ensure the permeability of the molten aluminum metal. Therefore, the side walls made of the raw material before sintering are fragile and easily deformed or collapsed due to the convection of ambient air and changes in internal stress that occur during sintering. Therefore, if the height of the side wall is set to 300 mm or more at the raw material stage, the side wall will collapse during sintering.

The inventors of the present invention made intensive studies to solve the above problems, and as a result, reached the following aspects of the present invention.
A first aspect of the present invention is defined as follows. Namely
A method for manufacturing a ceramic filter, which is an integrally molded product with an upwardly open cylindrical shape, for removing unnecessary substances from molten metal,
kneading a mixture of an aggregate made of ceramic particles, a predetermined binder and water to form a dough;
integrally forming a precursor of an open-top cylindrical ceramic filter with the prepared fabric;
drying the precursor;
setting a retainer on the precursor for supporting sidewalls of the dried precursor;
then sintering the precursor;
removing the retainer after sintering;
A method of manufacturing a ceramic filter comprising:

According to the manufacturing method of the ceramic filter of the first aspect defined in this way, the side wall of the precursor is supported by the retainer during sintering. , which will never collapse.
Here, it is preferable to prepare a first retainer that supports the side wall from the outside and a second retainer that supports the side wall from the inside. Here, it is preferable that the first retainer that supports the side wall from the outside supports the entire circumference of the side wall. At this time, the second retainer may intermittently support the side wall.

A second aspect of the invention is defined as follows. That is, in the manufacturing method defined in the first aspect, after the drying step and before the firing step, the raw material of the precursor, which is a material stable to the molten metal and its oxides The step of coating sidewalls of the precursor with a layer of lower sintering temperature material is further included.
According to the manufacturing method defined in the second aspect defined in this way, since the sintering temperature of the material of the coating layer is lower than the sintering temperature of the raw material, the material of the coating layer is sintered first. Vitrification increases its mechanical rigidity. This vitrified coating layer supports the sidewalls of the precursor during sintering. This prevents the sidewalls from collapsing.

From this point of view, it is preferable that a continuous coating layer is formed on at least one side of all sidewalls of the precursor. More preferably, the covering layer is formed on the upper edge side of the outer surface and the inner surface of the side wall. The width of the coating layer is not particularly limited. For example, a coating layer can be laminated to the entire surface of the sidewalls. This is because the molten metal flows exclusively from the bottom wall to the inside of the upper-open cylindrical ceramic filter. The coating layer can also be wrapped around the peripheral edge of the bottom wall to the extent that it does not hinder the flow of hot water. A preferred width of the covering layer is 50 to 400 mm.
The thickness of the coating layer is not particularly limited as long as it has the mechanical strength to prevent the side walls from collapsing.
The material of the coating layer should not react with the molten metal and its oxides and should have a sintering temperature lower than that of the precursor material. When aluminum is selected as the molten metal, the material for the coating layer may be a binder in which zirconium oxide, zircon, or the like that does not react with aluminum and alumina is dispersed. This binder is mainly composed of, for example, alumina having a lower vitrification temperature than the vitrification temperature of the raw material.

A third aspect of the present invention is defined as follows: an integrally molded cylindrical ceramic filter with an open top, comprising a sintered body of ceramic particles through which molten metal can flow, and a bottom thereof; A ceramic filter having a sidewall rising vertically from the wall and having a height of 500 mm or more.
A ceramic filter having such a configuration can be obtained by carrying out the manufacturing methods of the first and second aspects described above. The side wall of this ceramic filter rises vertically from the bottom wall. This allows the area of the bottom wall to be maximized in a molten metal bath of limited area. When a ceramic filter is submerged in a bath of molten metal, the molten metal passes exclusively through its bottom wall. Therefore, by maximizing the area of the bottom wall, the filtering capability can be maximized.

In such a ceramic filter, the upper edge of the upwardly open opening is provided with a protective material that is stable against the molten metal and its oxides and has a sintering temperature lower than the sintering temperature of the ceramic particles. It is preferred to laminate the membranes.
An oxide is formed on the surface of the molten metal, and this metal oxide tends to react with the ceramic particles. Therefore, by covering the upper edge of the side wall with a protective film that is stable against the metal oxide and the molten metal itself, the independence of the ceramic filter in the molten metal can be ensured. In addition, as described in the second aspect, the production of the ceramic filter is stabilized by forming the coating layer with a material having a sintering temperature lower than the sintering temperature of the ceramic particles.

FIG. 1 is a cross-sectional view showing a precursor mold used in an embodiment of the present invention. FIG. 2 is a perspective view of the precursor. FIG. 3 is a cross-sectional view of a precursor with a protective coating. FIG. 4 is a cross-sectional view showing a retainer that supports the precursor during firing. FIG. 5 is a cross-sectional view showing a sintered state of a modified precursor. FIG. 6 is a schematic diagram showing the configuration of the side wall of the precursor of the modified embodiment.

The precursor dough material includes an aggregate of ceramic particles, a predetermined binder and water.
Here, as the material of the aggregate, for example, one or more selected from silicon carbide, silicon nitride, boron nitride, zirconium oxide (zirconia), aluminum oxide (alumina), and zircon may be used in an arbitrary mixing ratio. can be done.
The grain size of the aggregate can be arbitrarily selected according to the characteristics required for the ceramic filter, but is preferably 0.01 mm to 10 mm, more preferably 3 mm to 6 mm. This particle size can be determined by a common sieve.

Organic binders, inorganic cements and powdered glass can be used as binders.
The organic binder binds the aggregate together and retains its shape before sintering.
Water-soluble thickeners such as polyvinyl alcohol and starch can be used as the organic binder.
Inorganic cements are employed to hold the aggregates together during sintering, as the thickener is burned off during sintering. It is preferable to employ silica-free inorganic cement (alumina cement). This is to prevent reaction with the molten metal, especially its oxide.
The powdered glass is vitrified by sintering to finally bind the aggregate. The vitrification temperature (melting point) of such powdered glass should be sufficiently higher than the temperature of the molten metal.

These binders are dissolved or dispersed in a predetermined amount of water and mixed with the aggregate. The amount of the organic binder is preferably 0.1 to 0.5% by mass with respect to the total mass of the aggregate and the binder. Inorganic cement is preferably 0.5 to 10% by mass. It is preferable that the content of powdered glass is 0.5 to 10% by mass.
The amount of water is adjusted appropriately so that the viscosity of the mixture becomes the desired value.

The mixture obtained in this way has almost no fluidity. Such a mixture is filled into a mold to integrally form a ceramic filter precursor.
FIG. 1 shows a mold 10 forming a precursor 1 .
The mold 10 has an outer mold 11 and an inner mold 13 . Reference numeral 15 is the base. The outer mold 11 is a plate-like member and can be made of metal or ceramics. A release agent is applied to the cavity surface to facilitate release of the precursor 1 from the mold.
A foamed resin is used for the inner mold 13 . A protective film also made of resin is laminated on the cavity surface so that the mixture does not permeate. A heat-shrinkable tape or paint can be used as the protective film. The surface of the protective film is coated with a release agent to facilitate release of the precursor 1 from the mold.

In the present invention, the precursor 1 is dried prior to demolding, in other words, leaving at least the inner mold.
The drying conditions are general drying conditions of 80° C. to 100° C. for 5 hours to 15 hours. Under these conditions, the foamed resin material is thermally shrunk. Therefore, even if the side walls of the precursor 1 are high, the release work is easy.
The coefficient of thermal shrinkage of the foamed resin material may be about 1 to 10% as long as the inner mold can be released from the dried precursor 1 . Other materials with similar shrinkage coefficients can be used in place of the foamed resin material.

The entire precursor 1 after demolding is shown in FIG. The precursor 1 has vertical sidewalls 3, the height of which is greater than or equal to 500 mm. The thickness of the side wall 3 can be arbitrarily selected according to the characteristics required of the ceramic filter, but is set to 20 to 35 mm. The bottom wall 5 is also of the same thickness (see FIG. 3).
The upper edges of the side walls 3 of the precursor 1 are covered with a protective film 7 . The method of coating is by painting or spraying.
As described above, the protective film 7 is made of a material that is stable against molten metal and its oxides and has a sintering temperature lower than that of the precursor material. Although the range covered with the protective film 7 is arbitrary, it is preferable to have a margin of 100 mm or more above and below the draft surface of the molten metal. In addition, from the viewpoint of ease of application and imparting strength, it is preferable to cover the entire upper edge of the side wall.
This protective film 7 vitrifies before the raw material of the precursor 1, that is, the powdered glass, when the precursor 1 is fired.

The precursor 1 provided with the protective film 7 is placed in a firing furnace. At this time, a retainer 20 is set to prevent the sidewall 3 from collapsing (FIG. 4). The retainer 20 consists of a first retainer 21 that supports the side wall 3 from the outside and a second retainer 23 that supports the side wall 3 from the inside.
The first retainer 21 supports the entire outer surface of the side wall 3 . Preferably, the first retainer 21 is in intimate contact with the outer surface of the side wall 3 . Since the side wall tends to swell during firing, the first retainer 21 preferably faces the entire outer surface of the side wall.
The second retainer 23 prevents the sidewall from deforming inward. To prevent a side wall which is about to deform outward due to heat during firing from interfering with the first retainer 21 and rebounding inward. The second retainer need not face the entire inner surface of the sidewall, but in this example supports the inner surface at the upper edge of the sidewall. Alternatively, intermittent support may be used. In this example, L-shaped ceramic plates (width 100 mm) are arranged as the second retainer 23 as densely as possible, and the precursor 1 and the first retainer 21 are supported. Fitted to the rim.

When using such a retainer 20, the protective film 7 can be omitted.
On the other hand, if the protective film 7 is formed wider (in the vertical direction), the set of the second retainer 23 or all the retainers 20 can be omitted.
FIG. 5 shows an example of a precursor 31 with sidewalls 33 sloping outward. Such a precursor 31 can support deformation of the side wall 33 during sintering only with the first retainer 42 facing the outer surface of the side wall 33 .

In addition, the deformation of the side wall of the precursor during sintering is caused by its own weight due to its height exceeding 300 mm. On the other hand, the thickness of the side wall cannot be made thicker than a certain value because the thickness of the side wall is restricted by the permeability. Thus, as shown in FIG. 6A, sidewalls 57 can be bent to increase longitudinal stiffness. Further, as shown in FIG. 6B, a rib 67 may be provided on the side wall 63 so as to be continuous in the vertical direction.

Examples of the present invention will now be described.
First, the following mixture is obtained. The blending ratios below are expressed in parts by mass.
Aggregate 1 (silicon carbide, particle size: 3-6 mm): 70 parts by mass Aggregate 2 (silicon carbide, maximum particle size: 8 mm); 30 parts by mass Organic binder (polyvinyl acetate, model number: manufactured by Kuraray Co., Ltd. ISOBAN-110); 0.6 parts by mass Inorganic cement (alumina cement, model number: High Alumina Cement Super S manufactured by Denka Co., Ltd.): 5 parts by mass Powdered glass (glass fleet, model number: 4791 manufactured by Nippon Enamel Glaze Co., Ltd.) : 5.5 parts by mass Water (tap water): 3.8 parts by mass The mixture was kneaded with a universal mixing stirrer (manufactured by Sankei Seisakusho Co., Ltd.).

The mold 10 for the precursor 1 is prepared by setting the outer mold 11 and the inner mold 13 . Precursor 1 is an open-top box with a height of 500 mm, a width of 500 mm and a depth of 700 mm. The thickness of the side walls 2 and bottom wall 5 is 25 mm. Here, the outer mold 11 is entirely made of iron plate. The inner mold 13 was made of expanded polystyrene (EPS; expansion ratio of 90), and a tape (Piolan cloth adhesive tape manufactured by Nitoms Co., Ltd.) was attached to the entire surface of the inner mold 13 . Vaseline (manufactured by Chukyo Yushi Co., Ltd.) was applied as a release agent to the cavity forming surfaces of the outer frame 11 and the inner frame 13 .
The kneaded mixture was filled into the cavity of the mold 10 and dried under the conditions of 80° C. for 15 hours in a general-purpose drying oven with the mold 10 attached. As a result, the inner mold 13 was shrunk and the mold could be easily released.

A protective film 7 was applied to the upper edge of the side wall of the dried precursor 1 . The protective film 7 is made of zirconia particles dispersed in a binder. Here, as zirconia, product number: G325F of Fukushima Seiko Co., Ltd. was used. As the binding material, ALKONPATCH PT85U manufactured by Calderis Co., Ltd. was adopted. The mixing ratio of zirconia and binder was 3:7 (mass ratio). The coating thickness was visually 1 to 2 mm.
After the protective film 7 is dried, the precursor 1 is placed in a firing furnace. At this time, the retainer 20 was set as shown in FIG. Refractory bricks are used for the first retainer 21 and tightly abutted against the outer surface of the side wall 3 . The second retainer 23 was put over the first retainer 21 and the side wall 3 so as not to be a forced fit.
After that, firing was performed at a maximum temperature of 1100° C. for 27 hours. Conditions for temperature rise up to the maximum temperature and conditions for cooling after firing are general-purpose conditions and are not particularly limited.
The ceramic filter thus obtained maintained the shape of the precursor. This ceramic filter could be used in a molten aluminum bath. The ceramic filter of this example was superior in durability as compared with the conventional ceramic filter which is a combination of flat plates.

The present invention is by no means limited to the description of the above embodiments and modifications thereof. Various modifications are also included in the present invention without departing from the scope of the claims and within the scope that can be easily conceived by those skilled in the art.
The following items are disclosed below.
(1)
A method for manufacturing a ceramic filter, which is an integrally molded product with an upwardly open cylindrical shape, for removing unnecessary substances from molten metal,
kneading an aggregate composed of ceramic particles, a predetermined binder and water to form a mixture;
integrally forming a precursor of a top-opening cylindrical ceramic filter with the resulting mixture;
drying the precursor;
setting a retainer on the precursor for supporting sidewalls of the dried precursor;
then sintering the precursor;
removing the retainer after sintering;
A method of manufacturing a ceramic filter comprising:
(2)
after said drying step and before said firing step, a sidewall of said precursor with a layer of a material stable to said molten metal and its oxides and having a lower sintering temperature than said precursor mass; The manufacturing method according to (1), further comprising the step of coating the
(3)
A method for manufacturing a ceramic filter, which is an integrally molded product with an upwardly open cylindrical shape, for removing unnecessary substances from molten metal,
kneading a mixture of an aggregate made of ceramic particles, a predetermined binder and water to form a dough;
integrally forming a precursor of an open-top cylindrical ceramic filter with the prepared fabric;
drying the precursor;
coating the upper edges of the sidewalls of the precursor after drying with a layer of material that is stable to the molten metal and its oxides and has a lower sintering temperature than the bulk of the precursor; sintering the body;
A method of manufacturing a ceramic filter comprising:
(4)
A method for manufacturing a ceramic filter, which is an integrally molded product with an upwardly open cylindrical shape, for removing unnecessary substances from molten metal,
kneading an aggregate made of ceramic particles, a predetermined binder and water to form a mixture;
integrally forming a precursor of a top-opening cylindrical ceramic filter with the resulting mixture;
drying the precursor;
then sintering the precursor;
In a method for manufacturing a ceramic filter comprising
The step of integrally molding the precursor includes filling the mixture between an outer mold and an inner mold;
The method for manufacturing a ceramic filter, wherein in the drying step, the precursor is heated together with the inner mold to thermally shrink the inner mold.
(5)
The manufacturing method according to (4), wherein the inner mold is made of a foamed resin material and the surface thereof is coated.
(6)
The manufacturing method according to (4), wherein the surface of the inner mold made of the foamed resin material is coated with a heat-shrinkable resin tape.
(7)
The manufacturing method according to (4), wherein in the firing step, the sidewall is supported by another member.
(8)
An upwardly open cylindrical ceramic filter made of a sintered body of ceramic particles through which molten metal can flow, and having a side wall rising vertically from the bottom wall and having a height of 500 mm or more. is a ceramic filter.
(9)
The upper edge of the upwardly open opening is covered with a protective film made of a material that is stable against the molten metal and its oxides and has a sintering temperature lower than the sintering temperature of the ceramic particles. , (9).

1 Precursor 3, 33, 53, 63 Side Wall 7 Protective Film 10 Mold 11 Outer Mold 13 Inner Mold 20 Retainers 21, 42 First Retainer 23 Second Retainer

Claims (1)

A method for manufacturing a ceramic filter, which is an integrally molded product with an upwardly open cylindrical shape, for removing unnecessary substances from molten metal,
kneading an aggregate composed of ceramic particles, a predetermined binder and water to form a mixture;
integrally forming a precursor of a top-opening cylindrical ceramic filter with the resulting mixture;
drying the precursor;
setting a retainer on the precursor for supporting sidewalls of the dried precursor;
then sintering the precursor;
removing the retainer after sintering;
In a method for manufacturing a ceramic filter comprising
A method of manufacturing a ceramic filter, wherein the precursor has sidewalls inclined outward, and only the outside of the sidewalls is supported by the retainer.

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