JP3458431B2 - Ceramic porous body and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic porous body preferably used as a ceramic filter for removing and purifying inclusions in molten metal and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Non-ferrous metals,
When casting cast iron etc., using a ceramic porous body with a three-dimensional network skeleton structure for removing and refining inclusions in the molten metal
For example, it is known as disclosed in JP-A-51-142162.

[0003] In general, such a ceramic porous body is manufactured by immersing a synthetic resin foam having a three-dimensional reticulated skeleton structure having an internal communication space such as a flexible polyurethane foam without a cell membrane into a ceramic slurry to form a synthetic resin foam. After depositing the ceramic sludge, the excess sludge is removed, followed by drying and firing. In this case, the ceramic slurry adhered to the surface of the lattice of the foam is fired to form a lattice of the porous ceramic body, and the foam is burned off during the firing, so that the ceramic lattice of the porous ceramic body is formed. Is a state in which a cavity is formed inside.

By the way, in the production of the above-mentioned ceramic porous body, as a method for removing the excess sludge, a compression method using a roll, which is advantageous in terms of cost, is generally used.

However, in the roll compression method, since the skeleton does not become thick and the surface portion of the synthetic resin foam is rubbed directly with the roll, the adhered amount of the ceramic sludge to the surface portion of the synthetic resin foam is thin, and in some cases, There is also a portion that does not adhere to the top ridge of the skeleton of the foam surface portion, and after this, there is a problem that after the firing, vanishing holes of the synthetic resin foam are seen on the surface portion of the ceramic porous body, resulting in poor surface strength.

As a countermeasure for this, a method of widening the roll gap can be considered, but since excess sludge cannot be removed sufficiently, only the clogging part increases and the flowability of the molten metal becomes poor,
In addition, the portion that comes into contact with the roll, that is, the surface portion, exhibits the same phenomenon as described above in any case, and sufficient improvement cannot be achieved.

[0007] In such a porous ceramic body having a weak surface portion, when it is packaged and transported, the skeleton is chipped due to the vibration of transportation, and when it reaches the user, a considerable skeletal piece is found in the packaging box. If such a ceramic porous body contains a missing skeleton, it is necessary to remove the skeleton pieces with compressed air before using it as a filter material. However, it was not enough to remove the chipped skeleton, and it sometimes flowed into the cast product, and the cast product became defective.

When the ceramic porous body is used for filtering molten metal, the first requirement is a resistance to the impact of the molten metal, and a ceramic porous body having a weak surface portion has this resistance. The drag was insufficient.

Therefore, it is fully conceivable that such a problem will be reduced if the skeleton is thickened, but in the conventional method, if the skeleton is thickened, the flowability of the molten metal is deteriorated and the cost is increased. . For example, there is a method of removing excess sludge by centrifuging after impregnating a ceramic slurry with a synthetic resin foam. With this method, it is possible to obtain a ceramic porous body with a thick skeleton and no sharp corners. Since the amount is small, four steps of impregnation-centrifugation-drying are required.
It has to be repeated up to 5 times, resulting in increased man-hours and increased cost. Moreover, in this centrifugal separation method, since the entire skeleton of the ceramic porous body becomes thick, when the bulk specific gravity is increased, the bone becomes thicker, the voids are reduced, and the pressure loss increases.

On the other hand, when an inoculant such as copper or silicon is used during casting for the purpose of improving the mechanical properties of cast iron and improving the quality such as homogenizing the structure, the purpose is to improve the mechanical properties. , Casting is performed after adding an inoculant to the molten metal in the ladle. In this case, the effect of inoculation is seen at the beginning of casting,
Since the effect is rapidly lost with time, it is common to make a secondary inoculation. For this reason, a decrease in the molten metal temperature is unavoidable, which sometimes results in poor molten metal flow. In this case, if the surface strength of the ceramic porous body is high, it is expected that the inoculant can be directly placed on the surface of the ceramic porous body, and stable quality casting can be performed.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a ceramic porous body having excellent surface strength, less skeleton loss, and less pressure loss, and a method for producing the same.

[0012]

Means and Actions for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has dipped a synthetic resin foam having a three-dimensional net-like skeleton structure having an internal communication space into a ceramic slurry. After attaching ceramic sludge to the synthetic resin foam, remove excess sludge, then dry,
In a method for producing a ceramic porous body by firing to obtain a ceramic porous body having a three-dimensional network skeleton structure, the surface of a synthetic resin foam having ceramic slurry adhered thereto or a ceramic porous body substrate after firing has a viscosity of 8 to 30 poises and thixotropy. By a method such as spray coating a ceramic slurry having a tropic index of 1.5 to 5, drying and firing, the ceramic grid on the surface of the ceramic porous body has a ring-shaped main skeleton layer forming the grid, Formed by coating the main skeleton layer,
A virtual plane (a plane that passes through the center of the lattice and is orthogonal to the surface of the ceramic porous body) A located at the center of the ceramic lattice on the surface of the ceramic porous body of the ceramic lattice. 12 on each side as shafts
On the surface side defined by the ceramic porous body surface side between the virtual planes B and C displaced by 0 °, the average thickness is 0.2 to 2 times the thickness of the main skeleton layer, and the above 120 °
A ceramic porous body composed of a reinforcing layer having an average thickness of 0.1 times or less the thickness of the main skeleton layer on the back surface side defined by the ceramic porous body center layer side between the virtual planes B and C at the eccentric position. It has been found that this ceramic porous body is excellent in surface strength, has few skeleton defects, and has low pressure loss, since it has a bulk specific gravity as it is and only the surface portion is reinforced.

That is, ceramics progress to destruction by the occurrence of cracks with the cracks as cores. If the ceramic skeleton is thick, a larger force is required to generate the cracks, and as a result, the strength is high. become. However, since the present inventor only has to prevent the occurrence of cracks, even if the skeleton of the central layer is thin, the entire skeleton is necessarily thick in view of both crack generation due to chipping during transport and impact during casting. I thought that it was not necessary to do it and only the skeleton of the surface part should be thickened. For example, when used as a filter for molten metal, the relationship between the flowability of molten metal and the like and the thickness of the skeleton of the surface is advantageous in that the surface skeleton is thick on the inflow side and there is no acute angle portion, but It is not necessary to eliminate the sharp edges up to the back side, but rather it causes an increase in flow resistance. On the other hand, the outflow side is the opposite of the inflow side.
Based on such knowledge, the present inventor has conducted diligent studies in order to obtain a skeleton-shaped ceramic porous body having good flowability, and as a result, the ceramic porous body having the above-mentioned configuration simultaneously has contradictory characteristics of strength and pressure loss. The present inventors have completed the present invention by discovering that it has excellent performance as a filter for molten aluminum, cast iron and the like.

Therefore, the present invention provides a ceramic porous body having a three-dimensional net-like skeleton structure having an internal communication space and comprising a ceramic lattice having a cavity therein, wherein the ceramic lattice on the surface of the ceramic porous body is A ring-shaped main skeleton layer forming a lattice, and an imaginary plane formed by covering the main skeleton layer and located at the center of the ceramic porous body surface side of the ceramic lattice (passes through the center portion of the lattice, The surface of the ceramic porous body between the virtual planes B and C at a position deviated from the plane A orthogonal to the surface) A by 120 ° to both sides of the virtual plane A with the side passing through the center of the lattice as an axis. It has an average thickness of 0.2 to 2 times the thickness of the main skeleton layer on the defined surface side, and is defined on the ceramic porous body central layer side between the virtual planes B and C at the 120 ° deviation position. And a reinforcing layer having an average thickness not more than 0.1 times the thickness of the main skeleton layer on the back surface side, and a synthetic resin having a three-dimensional reticulated skeleton structure having an internal communication space. After immersing the foam in the ceramic slurry and adhering the ceramic slurry to the synthetic resin foam, removing the excess slurry, then drying and firing to obtain a ceramic porous body with a three-dimensional network skeleton structure. In the manufacturing method, a ceramic resin having a viscosity of 8 to 30 poise and a thixotropic index of 1.5 to 5 is spray-coated on the surface of the synthetic resin foam to which the ceramic sludge is adhered or the ceramic porous body substrate after firing,
Provided is a method for producing a ceramic porous body, which comprises drying and firing.

The present invention will be described in more detail below. As shown in FIGS. 1 to 4, the ceramic porous body of the present invention has a three-dimensional net-like skeleton structure having an internal communication space 2 and a cavity 3 inside. A ceramic porous body 1 comprising a ceramic grid 4 having the ceramic porous body 1
Of at least the surface portion 5, that is, when the ceramic porous body 1 is used as a molten metal filter, the molten metal inflow side ceramic grid 4a is provided with a ring-shaped main skeleton layer 6,
It is formed from the reinforcing layer 7, and in this case, the front surface side 7a of the reinforcing layer 7 is formed thicker than the back surface side 7b.

Here, the reinforcing layer 7 is formed on at least the surface portion 5 as described above,
If necessary, it can be performed on the back surface portion 9 and the side surface portions 10, 10, and particularly when the ceramic porous body 1 is used as a molten metal filter, it is recommended to form the reinforcing layer 7 also on the back surface portion 9. It

Further, the reinforcing layer 7 is formed such that the front surface side 7a thereof is thicker than the rear surface side 7b, so that the sharp corner portion of the top portion 11 of the lattice 4a on the front surface portion is covered and rounded. From this point as well, the surface strength is improved, but in this case, as shown in FIGS. 3 and 4, the surface side 7a is an imaginary plane (located at the center of the ceramic porous body 1 surface side of the lattice 4a). From the plane A which passes through the center of the lattice 4a and is orthogonal to the surface of the ceramic porous body 1, the virtual plane A is deviated by 120 ° on both sides with the side passing through the center of the lattice 4a as an axis. It is defined as the surface side of the ceramic porous body 1 between the virtual planes B and C at the position, and the thickness of the surface side 7a is preferably 0.2 to 2 times the average thickness of the main skeleton layer 6. , And the ceramic between the virtual planes B and C at the 120 ° deviation position. The thickness of the back surface side 7b defined by the central layer side of the porous body 1 preferably has an average thickness of 0.1 times or less the thickness of the main skeleton layer 6. If the average thickness of the front surface side 7a is less than 0.2 times, the above-mentioned acute angle portion remains, and if it is more than 2 times, the lattice 4a becomes too thick overall and pressure loss may increase. On the other hand, when the average thickness of the back surface side 7b is thicker than 0.1 times, since the ceramic sludge is sprayed from the front surface side of the ceramic porous body 1 as described later, the front surface side 7a becomes too thick.

After the reinforcing layer 7 is formed, the reinforcing layer 7 has no sharp corners and 70 to 1 convex portions in the lattice 4a.
It is preferable that the concave portion is 00% and the concave portion is about 0 to 40%. If the ratio of the convex portions is lower than 70%, it may be easily broken by the molten metal impact.

In the ceramic porous body as described above, a synthetic resin foam having a three-dimensional net-like skeleton structure having an internal communication space is immersed in the ceramic slurry to adhere the ceramic slurry to the synthetic resin foam, and then the excess slurry is removed. Then dried,
In the method for producing a ceramic porous body, which is obtained by firing to obtain a ceramic porous body having a three-dimensional network skeleton structure, a viscosity of 5 to 40 poises is applied to the surface of the synthetic resin foam to which the ceramic sludge is adhered or the fired ceramic porous body substrate. It can be obtained by spray-applying ceramic slurry having a thixotropic index of 1.5 to 5, drying and firing.

Here, the synthetic resin foam used in the present invention may be any one as long as it has a three-dimensional network skeleton structure having an internal communication space, for example, a flexible polyurethane foam, particularly a flexible polyurethane foam having no cell membrane. Can be preferably used. In this case, the number of vacancies (the number of cells) representing the degree of reticulation can be selected within a range generally used for this type of application, and is not particularly limited.

Next, the ceramic slurry used in the present invention is
A slurry prepared by suspending ceramic powder in water, which is generally used for producing a ceramic porous body, can be used. As the sludge characteristics, those exhibiting a weak thixotropic property are preferable, regardless of the type of oxide or non-oxide. Suitable oxide ceramics include, for example, alumina, cordierite, mullite, zirconia, and the like, and non-oxide ceramics include, for example, silicon carbide and silicon nitride. Further, regarding the preparation of sludge, a peptizer, an aqueous polymer or the like which adjusts sludge characteristics can be added if necessary.

The synthetic resin foam is soaked in this ceramic slurry, the ceramic slurry is attached to the synthetic resin foam, and the method for removing the excess slurry is not particularly limited, but the method for removing the excess slurry is produced. A method of compressing using a roll or the like can be suitably adopted because of its property.

Generally, the synthetic resin foam from which the excess sludge has been removed is subsequently dried and fired. In the present invention, however, the ceramic sludge is spray-applied and porous after removal of the excess sludge, drying, or firing. Treat the body surface.

In this case, as the ceramic slurry to be sprayed, it is preferable that the ceramic component has the same component as that of the lattice skeleton ceramic (main skeleton layer), or the difference between the coefficient of thermal expansion of the lattice skeleton ceramic is 18% or less. It is better to use a slurry consisting of the ingredients. If a ceramic component having a difference in thermal expansion coefficient of more than 18% is used, cracks may occur on the sprayed ceramic surface after firing (see JP-A-5-51278).

The target to be spray-applied is a synthetic resin foam in a wet state after removing excess sludge, a synthetic resin foam after drying, or a ceramic porous body after firing, but preferably after drying. Or after firing. In particular, it is preferable to dry the surface after removing excess sludge. Immediately after removing excess sludge, in a wet state, the basic sludge and sprayed sludge are easily assimilated, so unless the viscosity and thixotropy are increased, the surface lattice does not have the skeleton as described above, and the efficiency is improved. May be bad.

The characteristics of the ceramic slurry to be spray-coated are such that the viscosity at 25 ° C. is 5 to 40 poises, especially 8 to 30
It's a poise. If the viscosity is lower than 5 poise, the viscosity is small even when sprayed, so the sprayed sludge may flow down instead of staying on the surface of the lattice skeleton. There is a risk that On the other hand, if it exceeds 40 poise, the spraying operation is difficult and the spray nozzle may be clogged. The thixotropic index of this ceramic slurry is in the range of 1.5 to 5, particularly in the range of 2 to 4. If this value is less than 1.5, even if the viscosity is large, it may flow down instead of staying at the sprayed part. If it exceeds 5, the flowability is poor and the particles adhere as they are. It may be in a deposited state and may remain as a protrusion after firing. Such sludge characteristics can be adjusted by adding a polyacrylic acid-based thickener, a deflocculant, and an acid and an alkali agent, if necessary.

The thixotropic index is 6 _{r as} measured by a rotational viscometer at 25 ° C., where η _r is this value.
The viscosity ratio between pm and 60 rpm.

Η _r = η _{6 rpm} / η _{60 rpm}

The method of spray coating is not particularly limited, but the projection direction of the spray can be carried out within a range between positions displaced by 30 to 60 ° from the plane orthogonal to the surface of the porous body on each side. preferable. This allows the lattice of the surface portion to have the above-described structure. Further, the spray application may be performed on the entire surface of the porous body, or in the case of using as a filter, it may be performed on the surface on the fluid flow direction side. In particular, when a compression method such as a roll is adopted as a method for removing excess sludge, the contact surface of the roll may not have the sludge adhered thereto as described above, and therefore the roll contact surface is preferably spray-coated.

The spray coating amount is the amount by which the surface lattice has the above-mentioned structure, and specifically, it is 0.
03-0.2 g / cm ² , especially 0.05-0.18 g /
A range of cm ² is preferred. If the coating amount is less than 0.03 g / cm ² , sharp corners remain on the surface lattice, and 0.2 g / c
If it is larger than m ^2, the lattice skeleton forming the stitches may become too thick and block the openings.

When spray-applied, the ceramic sludge mainly adheres to the lattice of the surface portion, and the adhesion amount decreases toward the second layer and the third layer and the inside. In the present invention, the lattice of the surface portion is The structure described above may be used, but even if it is applied inside, it does not matter as long as the object of the present invention is not impaired.

After spray coating, the ceramic porous body of the present invention can be obtained by drying and firing as usual.

[0033]

EXAMPLES Hereinafter, the present invention will be specifically shown by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples. In addition, in the following example, a part shows a weight part.

Example 1 A synthetic resin foam having a ceramic slurry adhered thereto was obtained as follows. First, silicon carbide 75
Parts, 10 parts of alumina, 5 parts of kibushi clay, and 10 parts of primary aluminum phosphate were added with 11 parts of water to prepare a ceramic slurry. The viscosity of this ceramic slurry was 160 poise.

This slurry has a length and width of 75 mm and a thickness of 22 m.
A flexible polyurethane foam having a three-dimensional reticulated skeleton structure of m and 6 cells / inch was immersed. After the immersion, the excess sludge was removed using a roll. The adhesion amount at this time was 0.40 in terms of bulk specific gravity (0.32 after firing). As for the appearance, no clogging was observed, and the surface skeleton to which the sludge adhered had an acute angle.

Thereafter, the surface was dried by drying at 60 ° C. for 1 minute, and then spray coating was performed.

First, the slurry was diluted with water to 20 poise. The thixotropic index of this slurry was 3.4. Free-fall spray of this slurry (Iwata W7
7. Nozzle diameter of 1.5) was used to apply a coating amount of 0.1 g / cm to the front and back of the synthetic resin foam to which the ceramic sludge was adhered.
Sprayed at a rate of ² . Then, it dried at 60 degreeC for 16 hours, and baked at 1300 degreeC. The surface skeleton after firing was formed in a convex shape, and the convex portion was approximately 90% of the lattice.

[Example 2] The viscosity of sludge was adjusted to 1 in the spraying process.
A ceramic porous body was obtained in the same manner as in Example 1 except that 0 poise and thixotropic index were set to 2.9.

[Example 3] The viscosity of sludge was adjusted to 3 in the spraying process.
A ceramic porous body was obtained in the same manner as in Example 1 except that 0 poise and thixotropic index were set to 4.5.

[Comparative Examples 1, 2, 3] Ceramic porous bodies were obtained in the same manner as in Example 1 except that the spraying step was not performed. In this case, by adjusting the roll gap, the bulk specific gravity after removing the excess sludge is 0.45 (Comparative Example 1) and 0.35, respectively
(Comparative Example 2) and 0.41 (Comparative Example 3).

[Example 4] A synthetic resin foam having ceramic slurry adhered thereto was prepared in the same manner as in Example 1. To this ceramic slurry, 10 parts of alumina was added, and then water was added to adjust the viscosity to 11 poise and the thixotropic index to 2.4, and the slurry was sprayed by a free-falling spray as in Example 1. The amount of spray was 0.15 g / cm ² . Then, it was dried at 60 ° C. for 16 hours and calcined at 1300 ° C.

In this case, the average thermal expansion coefficient of the ceramic (main skeleton layer) forming the skeleton of the ceramic porous body from room temperature to 1000 ° C. is 6.3 × 10 ⁻⁶ , and the ceramic (reinforcing layer) in the spray coating part is the same. It was 6.5 × 10 ^-6 .

COMPARATIVE EXAMPLE 4 Example 1 was repeated except that the viscosity of the slurry for spraying was changed from 20 poise to 45 poise and the thixotropic index was changed from 3.4 to 4.5.
A ceramic porous body was obtained in the same manner as in.

Comparative Example 5 Ceramic porosity was the same as in Example 1 except that the viscosity of the slurry for spraying was changed from 20 poise to 3 poise and the thixotropic index was changed from 3.4 to 1.7. Got the body

The ceramic porous body thus obtained was evaluated as follows. <Skeleton thickness> The spray-treated sample was cut, and the average thicknesses of 0 ° (center on the surface side), 60 °, and 320 ° from the skeleton center were measured, and this value was set to A.
The average thickness of 0 ° and 270 ° was measured and this value was designated as A ′.

On the other hand, the average thickness of the non-spray-treated sample was similarly measured, and the average thickness of the portion corresponding to A was B, and the average thickness of the portion corresponding to A ′ was B ′.
The values of A / B and A '/ B' were obtained. This represents the difference in skeleton thickness between the front surface side and the back surface side. <Peeling test> Adhesive tape (trade name: Terraoka Tape, manufactured by Teraoka Seisakusho Co., Ltd.) was attached to both sides of the sample, and then peeled off from the sample. I asked. <Pressure Loss> A cylinder having a diameter of 40 mm was cut out from a sample having a length and width of 75 mm and a thickness of 22 mm, and the pressure loss at a wind speed of 20 mm / s was obtained. <Bending strength> Along the traveling direction of the synthetic resin foam at the time of roll compression, both sides of a sample measuring 75 mm in length and width and 22 mm in thickness are cut to have a width of 35 mm, a length of 75 mm, and a thickness of 25 m.
m samples were cut out. Three-point bending strength was measured for this sample at a span of 60 and a crosshead speed of 10 mm / min.

The results are shown in Table 1.

[0048]

[Table 1]

From the results shown in Table 1, the ceramic porous body of the present invention has very little peeling of the surface skeleton even when the bulk specific gravity is equal to that of the ceramic porous body of the present invention which does not have the reinforcing layer. It is recognized that the pressure loss is equivalent and the bending strength is also improved (Example 1 and Comparative Example 3, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 1). Plots of pressure loss with respect to bulk specific gravity and bending strength with respect to bulk specific gravity are shown in FIGS. 5 and 6, respectively. From these figures, it is recognized that the strength is improved without changing the pressure loss. Furthermore,
It is also recognized that the ceramic porous body of the present invention cannot be obtained when the slurry characteristics of the ceramic slurry to be sprayed are out of the preferable range (Comparative Examples 4 and 5).

[0050]

The ceramic porous body of the present invention has a high surface strength, very few defects in the lattice skeleton, and little pressure loss, and is therefore suitable as a filter for molten metal filtration and the like.

Further, according to the method for manufacturing a ceramic porous body of the present invention, the surface strength can be improved without increasing the pressure loss.

[Brief description of drawings]

FIG. 1 is a side view showing an example of a ceramic porous body of the present invention.

FIG. 2 is a partially enlarged side view of the same example.

FIG. 3 is an enlarged cross-sectional view of a ceramic grid on the surface of the example.

FIG. 4 is an enlarged cross-sectional view of another ceramic grid on the surface of the example.

FIG. 5 is a graph in which bending strength is plotted against bulk specific gravity of Examples and Comparative Examples.

FIG. 6 is a graph in which pressure loss is plotted against bulk specific gravity of Examples and Comparative Examples.

[Explanation of symbols]

1 Ceramic porous body 2 Internal communication space 3 cavity 4 ceramic grid 5 surface 6 Main skeleton layer 7 Reinforcement layer A surface center position B One position offset by 120 ° from the surface center position C The other position offset by 120 ° from the center position on the surface

Claims (2)

(57) [Claims] 1. A ceramic porous body comprising a ceramic lattice having a three-dimensional net-like skeleton structure having an internal communication space and having a cavity therein, wherein the ceramic lattice on the surface of the ceramic porous body forms the lattice. A ring-shaped main skeleton layer, and an imaginary plane formed by covering the main skeleton layer and located at the center of the ceramic porous body surface side of the ceramic lattice (passes through the center of the lattice and with respect to the surface of the ceramic porous body). A surface defined by the ceramic porous body surface side between the virtual planes B and C at a position deviated by 120 ° from both sides of the virtual plane A to the both sides of the virtual plane A as an axis. On the side, the thickness of the main skeleton layer is 0.2 to
It has a double average thickness and is 0.1 times or less of the thickness of the main skeleton layer on the back surface side defined by the ceramic porous body central layer side between the virtual surfaces B and C at the 120 ° deviation position. A ceramic porous body comprising a reinforcing layer having an average thickness. 2. A synthetic resin foam having a three-dimensional net-like skeleton structure having an internal communication space is immersed in ceramic slurry to adhere the ceramic slurry to the synthetic resin foam, and then excess slurry is removed and then dried. In a method for producing a ceramic porous body, which is obtained by firing to obtain a ceramic porous body having a three-dimensional network skeleton structure, a viscosity of 8 to 3 is applied to the surface of a synthetic resin foam to which ceramic sludge is adhered or a fired ceramic porous body substrate.
A method for producing a ceramic porous body, which comprises spray-coating a ceramic slurry having a poise of 0 and a thixotropic index of 1.5 to 5, drying and firing.