A composite ceramic filter for metal casting and its preparation method

Abstract

The present invention relates to a composite ceramic filter for metal casting and a preparation method thereof, belonging to the technical field of liquid metal filters. The preparation method includes: preparing an aqueous solution of a composite surfactant of sodium methyl cellulose and polyethyleneimine; mixing basic aggregate α-Al2O3, toughening aggregate ZrO2, sintering aid Fe2O3, rheological agent clay, binder dextrin and water to form a slurry; surface-activating reticulated polyurethane foam and high-silica fiber grid cloth in the aqueous solution of the composite surface activator, then fully absorbing the slurry, and extruding the excess slurry of the reticulated polyurethane foam; laminating and compounding the reticulated polyurethane foam impregnated with the slurry and the high-silica fiber grid cloth to obtain a laminated green body; pre-sintering the laminated green body; diluting the slurry with water; immersing the laminated green body in the diluted slurry, and then performing secondary sintering on the laminated green body to form a filter. The filter prepared by the present invention is not easily broken.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid metal filters, and particularly to a composite ceramic filter for metal casting and a preparation method thereof. Background Art

[0002] Slag in the process of metal melting accounts for a large proportion of casting defects. Filtering liquid metal with a filter can effectively intercept inclusions in the liquid metal and greatly reduce casting rejects caused by slag and impurities.

[0003] Commonly used casting filters include: refractory fiber mesh filters, straight-hole filters, and foam ceramic filters. Among these three filters, the refractory fiber mesh filter has a short filtration process, the straight-hole filter has a straight filtration channel, while the foam ceramic filter has a filter cake mechanism, surface effect, rectification effect, etc. due to its unique structure, and its filtration effect is the best. However, the foam ceramic filter has problems such as low strength and easy fragmentation during use. In addition, there is also a high-silica corrugated cloth laminate filter, which has better filtration performance than ordinary refractory fiber mesh filters and improves the resistance to liquid metal impact. However, compared with the foam ceramic filter, the surface area (including the inner surface area) of this laminate filter is still small, and the surface effect is not obvious. Summary of the Invention

[0004] In view of the above problems, the first object of the present invention is to provide a preparation method for a composite ceramic filter for metal casting, which composites a refractory fiber mesh filter and a foam ceramic filter to solve the problems of poor performance such as low strength of existing products.

[0005] Another object of the present invention is to provide a composite ceramic filter for metal casting prepared by the above preparation method.

[0006] To achieve the above objects, the specific solutions adopted by the present invention are as follows:

[0007] A preparation method for a composite ceramic filter for metal casting includes:

[0008] Providing reticulated polyurethane foam plastic and high-silica fiber mesh cloth as ceramic carriers;

[0009] According to the specifications (pore density and size) of the filter to be prepared, select reticulated polyurethane foam plastic with a certain pore density, and cut a foam plastic ceramic carrier with a certain length, width, and thickness thereon; cut out a high-silica fiber mesh cloth ceramic carrier with the same length and width as the foam plastic ceramic carrier;

[0010] Preparation of composite surfactant. Sodium carboxymethyl cellulose (CMC) and polyethyleneimine (PEI) were added to water respectively and stirred evenly to prepare an aqueous solution of composite surfactant, in which the mass ratio of sodium carboxymethyl cellulose (CMC) to polyethyleneimine (PEI) was 1:1, and the concentration of the aqueous solution was 1.0wt%-2.5wt%;

[0011] The ceramic carrier was surface-activated with the aqueous solution of the composite surfactant; during the activation treatment, two ceramic carriers were immersed in the surfactant aqueous solution for 2 - 3 hours;

[0012] Slurry preparation: The basic aggregate α-Al2O3, toughening aggregate ZrO2, sintering aid Fe2O3, rheological agent clay (sodium bentonite), binder dextrin and water were mixed to form a slurry, where ZrO2 was 10wt% - 15wt% of the basic aggregate, Fe2O3 was 2wt% - 2.5wt% of the basic aggregate, clay was 4wt% - 5wt% of the basic aggregate, dextrin was 2.5wt% - 3wt% of the basic aggregate, and the water addition was 35wt% - 45wt% of the basic aggregate; the purity of α-Al2O3 and ZrO2 > 99wt%, the average particle size was 45 μm, and other raw materials were of industrial purity;

[0013] The foamed plastic ceramic carrier and the high-silica fiber mesh ceramic carrier after surface activation treatment were immersed in the slurry and allowed to fully absorb the slurry. The foamed plastic ceramic carrier and the high-silica fiber mesh ceramic carrier could be directly immersed in the slurry after being taken out of the aqueous solution of the composite surfactant, or could be appropriately air-dried after being taken out of the aqueous solution of the composite surfactant and then immersed in the slurry;

[0014] The foamed plastic ceramic carrier that had fully absorbed the slurry was subjected to double-roll extrusion to remove the excess slurry; among them, during double-roll extrusion, the two rolls rotated in opposite directions, the roll spacing could be adjusted, and the roll spacing during extrusion was 2 / 3 - 1 / 2 of the thickness of the foamed plastic;

[0015] The upper and lower surfaces (the four sides other than the thickness) of the foamed plastic ceramic carrier after double-roll extrusion were respectively attached to the high-silica fiber mesh ceramic carrier impregnated with the slurry, and placed between two plates for extrusion. The minimum gap between the plates during extrusion was equal to the roll gap when removing the excess slurry in the foamed plastic ceramic carrier by double-roll extrusion, so that the high-silica fiber mesh ceramic carrier and the foamed plastic ceramic carrier were closely attached to form a laminated green body;

[0016] The laminated green body was dried and pre-sintered, where the drying was natural drying for 36 - 48 hours; the pre-sintering temperature was 800 - 1000°C, and the pre-sintering time was 2 - 3 hours;

[0017] Dilute the slurry with water having a weight of 25 wt% - 30 wt% of the weight of the slurry;

[0018] Immerse the pre-sintered laminated blank into the diluted slurry and allow it to fully absorb the diluted slurry. The laminated blank can be appropriately shaken in the slurry;

[0019] Take out the pre-sintered laminated blank from the diluted slurry and perform a drying treatment; and then sinter the laminated blank again to form a liquid metal filter; the drying is natural drying for 36 - 48 hours; the re-sintering temperature is 1350 - 1450 °C, and the re-sintering time is 1 - 2 hours.

[0020] Preferably, the pore density of the foamed plastic ceramic carrier is 10 - 40 pores per inch (i.e., 10 - 40 PPI. The number of pores per inch is usually represented by PPI. For example, 10 pores per inch is expressed as 10 PPI). The pore density is selected according to the filter specifications to be prepared.

[0021] Preferably, the high-silica fiber mesh ceramic carrier is woven from high-silica fiber wires with a diameter of 0.3 - 0.5 mm, and the side length of the square holes of the high-silica fiber mesh ceramic carrier is 2 - 4 mm.

[0022] The present invention also provides a filter for composite material metal casting, which is prepared according to the above preparation method.

[0023] Advantageous effects: The present invention uses a composite of polyurethane foam plastic and high-silica fiber mesh cloth as the carrier, solving the technical problems of the existing foam filters such as low strength, easy fragmentation, and poor thermal shock stability, thereby improving the service performance. Description of the Drawings

[0024] Figure 1 is a schematic flow chart of a preparation method of a filter for composite material metal casting provided by the present invention.

[0025] Figure 2 is a schematic cross-sectional view of the laminated blank in the present invention. In the figure, 1 is the reticulated polyurethane foam plastic impregnated with the slurry; 2 is the high-silica fiber mesh cloth impregnated with the slurry. Detailed Embodiments

[0026] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention.

[0027] Provide ceramic carriers: Provide reticulated polyurethane foam and high-silica fiber mesh cloth as ceramic carriers. According to the filter specifications to be prepared (pore density and size), such as size 100mm×100mm×15mm and pore density of 20 pores per inch. Select commercially available reticulated polyurethane foam with a pore density of 20 pores per inch (20PPI), and cut a piece with a length of 100mm, a width of 100mm, and a thickness of 15mm on it as the foam plastic ceramic carrier. Use commercially available high-silica fiber wire, such as high-silica fiber wire with a diameter of 0.5 mm, to weave a high-silica fiber mesh cloth with square holes, such as the side length of the square hole is 3mm. Cut out two pieces with a length of 100mm and a width of 100mm from the mesh cloth as the high-silica fiber mesh cloth ceramic carrier.

[0028] Preparation of composite surfactant: Add sodium carboxymethyl cellulose (CMC) and polyethyleneimine (PEI) into water respectively, stir evenly to prepare an aqueous solution of composite surfactant, in which the mass ratio of sodium carboxymethyl cellulose (CMC) to polyethyleneimine (PEI) is 1:1, such as the aqueous solution concentration is 2.0wt%.

[0029] Surface activation: Use the aqueous solution of the composite surfactant to perform surface activation treatment on the two ceramic carriers; during the activation treatment, immerse the two ceramic carriers in the surfactant aqueous solution, such as activate for 2 hours, and take them out of the aqueous solution and dry them properly.

[0030] Slurry preparation: Mix basic aggregate α-Al2O3, toughening aggregate ZrO2, sintering aid Fe2O3, rheological agent clay (sodium bentonite), binder dextrin and water to form a slurry; add a certain amount of water into the container of the stirrer, and sequentially add dextrin, sodium bentonite, Fe2O3, ZrO2, α-Al2O3 while stirring.

[0031] Impregnate the slurry: Immerse the two ceramic carriers that have been surface-activated in the slurry and make them fully absorb the slurry.

[0032] Extrude the excess slurry: Perform double-roll extrusion on the foam plastic ceramic carrier that has fully absorbed the slurry to remove the excess slurry; among them, during double-roll extrusion, the two rolls rotate in opposite directions, and the roll spacing can be adjusted. During extrusion, the roll spacing is 2 / 3 - 1 / 2 of the thickness of the foam plastic ceramic carrier, such as 2 / 3.

[0033] Laminated green body: Attach the impregnated mesh cloth ceramic carrier 2 to the upper and lower surfaces (the four sides other than the thickness) of the foam plastic ceramic carrier 1 after double-roll extrusion, and place it between two plates for extrusion. The minimum gap during extrusion is equal to the gap during double-roll extrusion to remove the excess slurry in the foam plastic ceramic carrier, so that the silica fiber mesh cloth ceramic carrier and the foam plastic ceramic carrier are closely attached to form a laminated green body, such as Figure 2As shown; when extruding, the roller spacing is 2 / 3 of the thickness of the foam ceramic carrier, and the extrusion gap between the two plates is also 2 / 3 of the thickness of the foam ceramic carrier.

[0034] Dry and pre-sinter the laminated green body: The drying is natural drying for 36 - 48 hours, such as 36 hours. The pre-sintering temperature is 800 - 1000 °C, such as 900 °C, and the pre-sintering time is 2 - 3 hours, such as 2 hours.

[0035] Immerse in slurry again: Dilute the slurry with water weighing 25wt% - 30wt% of the weight of the slurry and stir evenly. Immerse the pre-sintered laminated green body in the diluted slurry and shake it appropriately in the slurry. Take out the pre-sintered laminated green body from the diluted slurry and conduct a drying treatment, and the drying is natural drying for 36 - 48 hours.

[0036] Sinter again: Sinter the laminated green body again to form a liquid metal filter; the re-sintering temperature is 1350 - 1450 °C, and the re-sintering time is 1 - 2 hours.

[0037] The following examples list the specific parameters involved in the method steps of the present invention. However, those skilled in the art should understand that these examples are only used to illustrate the present invention and not to impose any limitations on it.

[0038] Example 1

[0039] Activate a 100mm×100mm×15mm, 10PPI reticulated polyurethane foam and a high-silica fiber mesh cloth with a square hole side length of 4mm (size 100mm×100mm) woven from high-silica fiber wires with a diameter of 0.5 mm in a 2.5wt% CMC + PEI aqueous solution for 2 hours.

[0040] Mix α-Al2O3, ZrO2, Fe2O3, sodium-based bentonite, dextrin and water and stir into a slurry. ZrO2 is 10wt% of α-Al2O3, Fe2O3 is 2wt% of α-Al2O3, sodium-based bentonite is 4wt% of α-Al2O3, dextrin is 2.5wt% of α-Al2O3, and the water addition amount is 45wt% of α-Al2O3.

[0041] Immerse the surface-activated reticulated polyurethane foam and the high-silica fiber mesh cloth in the slurry and make them fully absorb the slurry; conduct double-roll extrusion on the reticulated polyurethane foam that has fully absorbed the slurry to remove the excess slurry; wherein the two rollers rotate in opposite directions, and the roller spacing during extrusion is 1 / 2 of the thickness of the foam, that is, 7.5 mm.

[0042] For the upper and lower surfaces of the reticulated polyurethane foam 1 after double-roll extrusion, that is, the two surfaces with a side length of 100 mm, impregnated high-silica fiber mesh cloth 2 is respectively adhered, and it is placed between two plates for extrusion. The minimum gap during extrusion is 7.5 mm, so that the high-silica fiber mesh cloth 2 and the reticulated polyurethane foam 1 are closely attached to form a laminated blank.

[0043] Dry and pre-sinter the laminated blank; naturally dry for 36 hours, the pre-sintering temperature is 800 °C, and the pre-sintering time is 2 hours.

[0044] Dilute the slurry with water with a weight of 25 wt% of the weight of the slurry, and stir evenly; immerse the pre-sintered laminated blank in the diluted slurry and shake it appropriately in the slurry; take out the pre-sintered laminated blank from the diluted slurry and naturally dry for 36 hours.

[0045] Sinter the laminated blank again (final sintering) to form a liquid metal filter; the re-sintering temperature is 1350 °C, and the re-sintering time is 1 hour, thereby obtaining a ceramic filter.

[0046] Performance comparison of the filter prepared in Example 1 and the filters prepared under other conditions:

[0047] (1) Activation in a CMC + PEI aqueous solution with a composite concentration of 2.5 wt% for 2 hours, compared with activation in a 2.5 wt% CMC aqueous solution for 2 hours and activation in a 2.5 wt% PEI aqueous solution for 2 hours, the slurry hanging amount is shown in Table 1 (other components of the slurry are the same, and the activation process is the same). The slurry hanging amount (expressed by bulk density, the larger the bulk density, the more the slurry hanging amount) has increased, and the activation effect is obvious.

[0048] Table 1 Slurry hanging amount of different activators (10 PPI).

[0049] Surfactant CMC PEI CMC + PEI <![CDATA[Bulk density (g / cm 3 )]]> 0.34 0.31 0.41

[0050] (2) Compared with the foam ceramic filter prepared with the same specification of foam plastic (10 PPI) as the carrier using the same activator, slurry and sintering process, the composite ceramic filter of the present invention has high strength and good thermal shock resistance (1100 °C heating and water cooling thermal cycle method). The specific comparison is shown in Table 2.

[0051] Table 2 Performance comparison of ceramic filters (10 PPI).

[0052] Filter type Compressive strength (MPa) Number of thermal shock performances at 1100 °C (times) Composite ceramic filter 1.9 20 Foam ceramic filter (not composite with fiber mesh) 1.7 16

[0053] Example 2

[0054] A 150mm×150mm×20mm, 40PPI reticulated polyurethane foam and a high-silica fiber mesh cloth (sized 150mm×150mm) woven from high-silica fiber wires with a diameter of 0.3 mm and a square hole side length of 2 mm were activated in a 1.0 wt% CMC + PEI aqueous solution for 3 hours.

[0055] α-Al2O3, ZrO2, Fe2O3, sodium-based bentonite, dextrin, and water were mixed and stirred into a slurry; ZrO2 was 15 wt% of α-Al2O3, Fe2O3 was 2.5 wt% of α-Al2O3, sodium-based bentonite was 5 wt% of α-Al2O3, dextrin was 3.0 wt% of α-Al2O3, and the water addition was 35 wt% of α-Al2O3.

[0056] The surface-activated reticulated polyurethane foam and the high-silica fiber mesh cloth were impregnated in the slurry and allowed to fully absorb the slurry. The reticulated polyurethane foam that had fully absorbed the slurry was subjected to double-roll extrusion to remove the excess slurry; the two rolls rotated in opposite directions, and the roll spacing during extrusion was 2 / 3 of the reticulated polyurethane foam, i.e., 13 mm.

[0057] For the upper and lower surfaces of the reticulated polyurethane foam 1 after double-roll extrusion, i.e., the two surfaces with side lengths of 150 mm each, the impregnated high-silica fiber mesh cloth 2 was respectively adhered, and it was placed between two plates and extruded. The minimum gap during extrusion was 13 mm to make the high-silica fiber mesh cloth and the reticulated polyurethane foam stick tightly, forming a laminated blank.

[0058] The laminated blank was dried and pre-sintered; it was naturally dried for 48 hours, the pre-sintering temperature was 1000 °C, and the pre-sintering time was 3 hours.

[0059] The slurry was diluted with water weighing 30 wt% of the weight of the slurry and stirred evenly. The pre-sintered laminated blank was immersed in the diluted slurry and shaken appropriately in the slurry. The pre-sintered laminated blank was taken out of the diluted slurry and naturally dried for 48 hours.

[0060] The laminated blank was sintered again (final sintering) to form a liquid metal filter; the re-sintering temperature was 1450 °C, and the re-sintering time was 2 hours.

[0061] Performance of the filter prepared in Example 2 and comparison with the performance of filters prepared under other conditions:

[0062] (1)Activated in an aqueous solution of CMC + PEI with a composite concentration of 1.0 wt% for 3 hours, the amount of slurry coating compared with that activated in an aqueous solution of 1.0 wt% CMC for 3 hours and that activated in an aqueous solution of 1.0 wt% PEI for 3 hours is shown in Table 3 (other components of the slurry are the same and the activation process is the same). The amount of slurry coating (represented by bulk density, the greater the bulk density, the more the slurry coating) has increased, and the activation effect is obvious.

[0063] Table 3 Amount of Slurry Coating with Different Activators (40 PPI)

[0064] Surfactant CMC PEI CMC + PEI <![CDATA[Bulk density (g / cm 3 )]]> 0.51 0.49 0.55

[0065] (2)Compared with the foam ceramic filter prepared with the same specification of foam plastic (40 PPI) as the carrier using the same activator, slurry and sintering process, the composite ceramic filter of the present invention has high strength and good thermal shock resistance (1100 °C heating and water cooling thermal cycling method). The specific comparison is shown in Table 4.

[0066] Table 4 Performance Comparison of Ceramic Filters (40 PPI)

[0067] Filter type Compressive strength (MPa) Number of thermal shock performances at 1100 °C (times) Composite ceramic filter 3.2 17 Foam ceramic filter (not composite with fiber mesh) 2.7 12

[0068] It should be noted that the above-described embodiments should be understood as illustrative and not limiting the scope of protection of the present invention. The scope of protection of the present invention is subject to the claims. For those skilled in the art, without departing from the essence and scope of the present invention, some non-essential improvements and adjustments made to the present invention still fall within the scope of protection of the present invention.

Claims

1. A preparation method of a composite ceramic filter for metal casting, comprising the following steps: Providing reticulated polyurethane foam and high-silica fiber mesh cloth as ceramic carriers; Adding sodium carboxymethyl cellulose and polyethyleneimine into water respectively to prepare an aqueous solution of a composite surface activator, wherein the mass ratio of sodium carboxymethyl cellulose to polyethyleneimine is 1:1, and the concentration of the aqueous solution of the composite surface activator is 1.0 wt% - 2.5 wt%; using the aqueous solution of the composite surface activator to perform surface activation treatment on the ceramic carrier; Slurry preparation: Mixing basic aggregate α-Al2O3, toughening aggregate ZrO2, sintering aid Fe2O3, rheological agent clay, binder dextrin and water to form a slurry; in the slurry preparation, ZrO2 is 10 wt% - 15 wt% of the basic aggregate, Fe2O3 is 2 wt% - 2.5 wt% of the basic aggregate, clay is 4 wt% - 5 wt% of the basic aggregate, dextrin is 2.5 wt% - 3 wt% of the basic aggregate, and the water addition amount is 35 wt% - 45 wt% of the basic aggregate; Immersing the ceramic carrier subjected to surface activation treatment in the slurry and allowing it to fully absorb the slurry; Performing double-roll extrusion on the reticulated polyurethane foam that has fully absorbed the slurry; Respectively laminating the upper and lower surfaces of the reticulated polyurethane foam after double-roll extrusion with the high-silica fiber mesh cloth impregnated with the slurry, and extruding to make the high-silica fiber mesh cloth and the foam plastic adhere tightly to form a laminated blank; Drying and pre-sintering the laminated blank; Diluting the slurry with water having a weight of 25 wt% - 30 wt% of the weight of the slurry; immersing the laminated blank subjected to pre-sintering in the diluted slurry and allowing it to fully absorb the diluted slurry; Taking out the laminated blank from the diluted slurry and performing a drying treatment; and re-sintering the laminated blank to form a liquid metal filter; Wherein, the pre-sintering temperature is 800 - 1000 °C, and the pre-sintering time is 2 - 3 hours; the re-sintering temperature is 1350 - 1450 °C, and the re-sintering time is 1 - 2 hours.

2. The preparation method according to claim 1, characterized in that: The reticulated polyurethane foam has a pore density of 10 - 40 pores per inch.

3. The preparation method according to claim 1, characterized in that: The high-silica fiber mesh cloth is woven from high-silica fiber wires with a diameter of 0.3 - 0.5 mm, and the side length of the square holes of the high-silica fiber mesh cloth is 2 - 4 mm.

4. The preparation method according to claim 1, characterized in that: The concentration of the aqueous solution of the composite surface activator is 1.0 wt%.

5. The preparation method according to claim 1, wherein: The surface activation treatment is to immerse the ceramic carrier in the aqueous solution of the composite surface activator for 2 - 3 hours.

6. The preparation method according to claim 1, characterized in that: The drying is natural drying, and the drying time is 36 - 48 hours.

7. The preparation method according to claim 1, characterized in that: When making the laminated blank, the minimum gap of extrusion is the same as the double-roll spacing when double-roll extruding the reticulated polyurethane foam.

8. A composite ceramic filter for metal casting, prepared by using the preparation method described in any one of claims 1 - 7.

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