Patent Application
20210291401
The present invention relates to methods for producing a ceramic molded body and a ceramic structure.
Ceramic structures are used for various applications. For example, a honeycomb-shaped ceramic structure having partition walls that define a plurality of cells each extending from a first end face to a second end face is widely used for catalyst supports, and for various filters such as diesel particulate filters (DPFs), and gasoline particulate filters (GPFs).
The ceramic structure is produced by extruding a ceramic molding material (kneading material) containing ceramic raw materials to obtain a ceramic molded body, and then cutting the ceramic molded body to have a predetermined length, drying and firing it. As used herein, the ceramic molded body refer to a material in a state before firing, and the ceramic structure refers to a material in a state after firing.
In recent years, there is a requirement for improvement of dimensional accuracy of the ceramic structure from the viewpoint of increasing productivity of the ceramic structure or the like. To address the requirement, a method for improving the dimensional accuracy of the ceramic molded body before firing has been proposed. For example, Patent Literature 1 proposes a method of controlling extrusion molding process parameters (e.g., an extrusion pressure) by acquiring a shape signal of an outer peripheral surface of a ceramic molded body obtained by extrusion molding, and comparing in real-time the shape signal with a reference shape signal. Further, Patent Literature 2 proposes a method of measuring a dimension of a ceramic molded body that has been extruded and dried, and adjusting an amount of liquid to be added to a kneading material based on the measurement result.
The present invention relates to a method for producing a ceramic molded body, the method comprising:
a molding step of subjecting a ceramic molding material to extrusion molding using an extrusion molding machine equipped with a temperature control portion to provide a ceramic molded body;
a cutting step of cutting the ceramic molded body to have a predetermined length; and
a dimension measuring step of measure a dimension of the cut ceramic molded body;
wherein a relationship between a temperature of the temperature control portion and the dimension of the cut ceramic molded body is previously obtained, and based on the relationship, an appropriate temperature of the temperature control portion is calculated from the dimension of the ceramic molded body measured in the dimension measuring step, and the temperature control portion is controlled to the appropriate temperature in the molding step.
Also, the present invention relates to a method for producing a ceramic structure, the method comprising:
a drying step of drying the ceramic molded body obtained by the method for producing the ceramic molded body; and
a firing step of firing the dried ceramic molded body.
When the ceramic molded body obtained by extrusion molding is cut to have a predetermined length, the shape may be deformed due to the stress accumulated during extrusion molding. Therefore, in the method disclosed in Patent Literature 1 which controls the extrusion process parameters by measuring the shape immediately after extrusion molding, the deformation caused by cutting cannot be considered, and the dimensional accuracy of the ceramic molded body cannot be stably improved.
Further, since the drying of the ceramic molded body requires a long period of time, the method disclosed in Patent Literature 2 which measures the shape of the ceramic molded body after drying and adjusts the amount of the liquid to be added to the kneading material requires a long period of time until the adjustment is reflected. Therefore, in some cases, the produced ceramic molded bodies may be wasted until the adjustment is reflected.
The present invention has been made to solve the above problems. An object of the present invention is to provide a method for producing a ceramic molded body, which can quickly and stably improve dimensional accuracy of the ceramic molded body.
Another object of the present invention is to provide a method for producing a ceramic structure, which can stably improve dimensional accuracy of the ceramic structure.
As a result of intensive studies to solve the above problems, the present inventors have found that there is a correlation between a dimension of a ceramic molded body cut in a cutting step and a temperature of a temperature control portion in a molding process, and based on this finding, the dimension of the ceramic molded body cut in the cutting step is measured, and the temperature of the temperature control portion in the molding step is controlled based on the measured dimension, whereby the dimensional accuracy of the ceramic molded body can be quickly and stably improved, and they have completed the present invention.
According to the present invention, it is possible to provide a method for producing a ceramic molded body, which can quickly and stably improve dimensional accuracy of the ceramic molded body.
Also, according to the present invention, it is possible to provide a method for producing a ceramic structure, which can stably improve dimensional accuracy of the ceramic structure.
Hereinafter, embodiments of the present invention will be specifically described. It is to understand that the present invention is not limited to the following embodiments, and those which appropriately added changes, improvements and the like to the following embodiments based on knowledge of a person skilled in the art without departing from the spirit of the present invention fall within the scope of the present invention.
A method for producing a ceramic molded body according to an embodiment of the present invention includes: a molding step of subjecting a ceramic molding material to extrusion molding using an extrusion molding machine equipped with a temperature control portion to provide a ceramic molded body; a cutting step of cutting the ceramic molded body to have a predetermined length; and a dimension measuring step of measure a dimension of the cut ceramic molded body.
The molding step is to extrude a ceramic molding material using an extrusion molding machine equipped with a temperature control portion to obtain a ceramic molded body.
The extrusion molding machine is not particularly limited as long as it has a temperature control portion, and a machine known in the art can be used. Here,
As shown in
The extruding portion 10 is not particularly limited as long as it has the screw 11 and the barrel 12 capable of housing the screw 11. Any member known in the art can be used.
The screw 11 preferably has a screw shaft 14 and a blade portion 15 that is spirally formed along the screw shaft 14.
Further, the screw 11 is preferably a biaxial screw that rotates in the same direction, from the viewpoint of kneading properties of the ceramic molding material, and more preferably a meshing type biaxial screw. In this case, a pair of screws 11 are arranged in parallel inside the barrel 12.
A base portion of the screw 11 is connected to a drive device 16. The drive device 16 includes a motor and a gearbox (not shown), and controls a rotation speed so as to obtain a predetermined extrusion pressure and rotates the screw 11.
Provided on an upstream side of the extruding portion 10 is a material introducing portion 17 for feeding a ceramic raw material mixture into the extruding portion 10. The ceramic raw material mixture fed from the material introducing portion 17 is kneaded by the screw 11 to form a ceramic molding material, which is fed to the molding portion 20.
The molding portion 20 includes a drum 22 having a space therein. One end of the molding portion 20 has a die 21, and the other end is connected to the extruding portion 13 of the extruding portion 10.
A shape of the drum 22 is not particularly limited, and a part of the dram 22 may have a decreased diameter portion or an increased diameter portion. For example, as shown in
A shape of the die 21 is not particularly limited, and it can be appropriately set according to the shape of the ceramic molded body to be produced. For example, when producing a ceramic molded body having a honeycomb shape, the die 21 having slits corresponding to the thickness of the partition walls in the form of honeycomb is used.
The screen 23 is provided in the drum 22 (molding portion 20), and is formed of a material in the form of mesh. The screen 23 can remove coarse particles or other impurities mixed in the ceramic molding material to stabilize the ceramic molding material fed to the die 21.
The temperature control portion 24 is arranged between the screen 23 and the die 21.
The temperature control portion 24 is not particularly limited as long as it can control the temperature of the ceramic molding material. Any temperature controller known in the art can be used. Among others, it is preferable to use a temperature control drum through which a fluid can flow, as the temperature control portion 24. Since the temperature control drum can control the temperature by adjusting the temperature of the fluid, it is possible to reduce the consumption of electricity as compared with a case where a heating means such as a heating element is used. For example, the ceramic molding material can be easily and efficiently heated by circulating hot water having a temperature controlled by using a boiler or the like through the temperature control drum.
Here,
The temperature of the temperature control portion 24 is determined based on results of the dimension measured in the dimension measuring step. More particularly, a relationship between the temperature of the temperature control portion 24 and the dimension of the ceramic molded body cut to have a predetermined length (which may, hereinafter, be abbreviated as a “cut ceramic molded body”) is previously obtained. Based on the relationship, an appropriate temperature of the temperature control portion 24 is calculated from the dimension of the ceramic molded body measured in the dimensional measuring step as described later, and the temperature control portion 24 is controlled to the appropriate temperature.
The relationship between the temperature of the temperature control portion 24 and the dimension of the cut ceramic molded body can be obtained based on the past data accumulated by producing the ceramic molded bodies. Further, the relationship can be optimized in real-time by reflecting the data obtained by continuously carrying out the method for producing the ceramic molded body according to the embodiment of the present invention.
The relationship between the temperature of the temperature control portion 24 and the dimension of the cut ceramic molded body may differ depending on conditions such as a material and size of the ceramic molded body and a type of the extrusion molding machine 1. Therefore, it is preferable that the relationship is determined by rendering each of these conditions identical.
The dimension of the cut ceramic molded body used to obtain the relationship is not particularly limited. A diameter of a cut surface of the cut ceramic molded body (for example, a radius or diameter when the ceramic molded body has a circular pillar shape) is preferably used, and a value (ΔR) obtained by subtracting a previously defined reference value of a diameter of a cut surface of a reference ceramic molded body from the measured value of the measured diameter of the cut surface of the cut ceramic molded body is more preferably used. The use of these dimensions can allow the correlation of the relationship to be easily obtained.
In addition, as used herein, the “reference ceramic molded body” refers to a ceramic molded body having an ideal (target) dimension.
Here,
The dimension of the cut ceramic molded body used to obtain the relationship as shown in
Using a cordierite-forming raw material containing alumina, kaolin and talc mixed together as a ceramic raw material, the cordierite-forming raw material was mixed with a binder including an organic binder, a water-absorbent resin as a pore former, and water (42% by mass) as a dispersion medium to form a ceramic raw material mixture, which was fed to the material introducing portion 17 of the extrusion molding machine 1 as shown in
For the cut ceramic molded body obtained above, a radius of an upper half of the cut surface was measured while maintaining the axial direction of the cut ceramic molded body in the horizontal direction, using a method employing an end face inspection machine as described later. The value (ΔR) was calculated by subtracting the previously defined reference value of the radius of the cut surface of the reference ceramic molded body from the measured value of the radius of the cut surface of the cut ceramic molded body thus measured. A plurality of cut ceramic molded bodies were produced by changing the temperatures of the temperature control portion 24, and the relationship between the temperatures of the temperature control portion 24 and the dimensions (ΔR) of the cut ceramic molded bodies was obtained. A graph showing the relationship is shown in
The value of ΔR has a relationship that changes as shown in
As shown in
Optionally, an outer circumference of the drum 22 (molding portion 20) may preferably be covered with a heat insulating sheet (not shown). Such a configuration can allow the temperature inside the drum 22 to be maintained at a predetermined temperature, so that the effect of improving the dimensional accuracy of the ceramic molded body can be enhanced.
The molding step can carry out using the extrusion molding machine 1 having the structure as described above. In the molding step, a ceramic raw material mixture is fed from the material introducing portion 17 to the interior of the barrel 12. The ceramic raw material mixture is kneaded while being subjected to shearing force by the rotation of the screw 11 to form a ceramic molding material, which is conveyed to the extruding port 13 side at the tip of the barrel 12. The ceramic molding material extruded from the extruding port 13 of the barrel 12 passes through the through holes of the rectifier 30, and passes through the screen 23 to be fed to the die 21. The ceramic molding material is extruded through the die 21 into a desired shape.
The ceramic molding material can be obtained by kneading the ceramic raw material mixture.
The ceramic raw material mixture may contain ceramic raw materials and water, although not particularly limited thereto.
Examples of the ceramic raw materials that can be used include, but not particularly limited to, cordierite-forming raw materials, cordierite, silicon carbide, silicon-silicon carbide composite materials, mullite, aluminum titanate, and the like. These can be used alone or in combination of two or more. As used herein, the cordierite-forming raw material refers to a ceramic raw material formulated so as to have a chemical composition in which silica is in a range of from 42 to 56% by mass, alumina is in a range of from 30 to 45% by mass, and magnesia is in a range of from 12 to 16% by mass. The cordierite-forming raw material is calcined to form cordierite.
In addition to the ceramic raw materials and water, the ceramic raw material mixture may also contain a dispersion medium other than water, a binder (for example, an organic binder, an inorganic binder, or the like), a pore former, a surfactant, and the like. Each raw material has any composition ratio, and preferably has a composition ratio according to the structure, material, and the like of the ceramic molded body to be produced.
The ceramic molded body obtained by extrusion molding preferably has a water content of from 10 to 50%. The ceramic molded body having the water content in such a range can allow the dimensional accuracy of the ceramic molded body to be stably improved by the method for producing the ceramic molded body according to the embodiment of the present invention.
As used herein, the water content of the ceramic molded body refers to a water content measured by an infrared heating type moisture meter.
The cutting step is to cut the ceramic molded body obtained by extrusion molding to have a predetermined length.
The cutting method is not particularly limited, and a method known in the art can be used. For example, the ceramic molded body can be cut by using a wire rod hung between a pair of bobbins.
The length of the ceramic molded body to be cut is not particularly limited, and the ceramic molded body may be cut to have an appropriate length depending on applications.
The structure of the cut ceramic molded body preferably has a honeycomb structure including partition walls that define a plurality of cells each extending from a first end face to a second end face, although not particularly limited thereto.
The ceramic molded body having a honeycomb structure (hereinafter referred to as a “honeycomb molded body”) may have a non-limiting shape, including a circular pillar shape, an elliptical pillar shape, and a polygonal pillar shape having end faces in the form of square, rectangular, triangular, pentagonal, hexagonal, octagonal, and the like.
Further, the honeycomb molded body may have a non-limiting cell shape (a cell shape in the cross section orthogonal to the cell extending direction), including a triangle, a quadrangle, a hexagon, an octagon, a circle, or a combination thereof.
The dimensional measuring step is to measure the dimension of the cut ceramic molded body.
The method for measuring the dimension of the cut ceramic molded body is not particularly limited, and a method known in the art can be used. For example, the dimension of the cut ceramic molded body can be measured using an end face inspection machine, a laser type outer diameter dimension measuring device, or the like.
However, it is preferable that the measuring method used in the dimension measuring step is the same as the measuring method for the dimension of the ceramic molded body used to obtain the relationship between the temperature of the temperature control portion 24 and the dimension of the cut ceramic molded body. Further, the dimension of the cut ceramic molded body measured in the dimension measuring step is preferably the same as the dimension of the ceramic molded body used to obtain the relationship between the temperature of the temperature control portion 24 and the dimension of the cut ceramic molded body.
The dimension of the cut ceramic molded body measured in the dimension measuring step is not particularly limited. A diameter of a cut surface of the cut ceramic molded body (for example, a radius or diameter of the cut surface when the ceramic molded body has a circular pillar shape) is preferably used, and a value (ΔR) obtained by subtracting a previously defined reference value of a diameter of a cut surface of a reference ceramic molded body from the measured value of the measured diameter of the cut surface of the cut ceramic molded body is more preferably used. The diameter of the cut surface of the cut ceramic molded body can be calculated by measuring the radii at a plurality of positions after a correction process of a center position as described later and averaging the measured values.
The dimension of the cut ceramic molded body can be measured at the end face (cut surface) or the side surface of the cut ceramic molded body.
Further, the dimension of the cut ceramic molded body may be measured over the entire end face or the entire side surface of the cut ceramic molded body, but it is preferably measured at a part of the end face or the side surface of the cut ceramic molded body.
When measuring the dimension of the entire end face or the entire side surface of the cut ceramic molded body, an axial direction (extrusion molding direction) of the cut ceramic molded body should be matched to a vertical direction, so that the cut ceramic molded body has to be rotated by 90° to measure the dimension, which requires a long period of time. Therefore, it is preferable to leave the axial direction (extrusion molding direction) of the cut ceramic molded body in the horizontal direction and measure the dimension a part (for example, an upper half) of the end face or the side surface of the cut ceramic molded body from the upper direction. Such a measuring method can allow a measurement time to be shortened. In this case, it is preferable to perform a correction process of the center position of the measured shape so that an error from a reference shape is minimized.
When measuring the dimension of the end face of the cut ceramic molded body, an end face image of the cut ceramic molded body is taken by an imaging camera of the end face inspection machine. The contour of the cut ceramic molded body may be detected from the obtained end face image by means of image analysis, and the dimension (outer diameter, radius) of the cut ceramic molded body may be calculated.
When measuring the dimension of the side surface of the cut ceramic molded body, the side surface of the cut ceramic molded body is irradiated with a laser from a laser displacement meter of a laser type outer diameter dimension measuring device. The laser oscillated from the laser displacement meter reaches the side surface of the cut ceramic molded body and is reflected. The reflected laser may be detected by a light receiving element, and the dimension of the cut ceramic molded body may be calculated based on the principle of the triangulation ranging method.
In the method for producing the ceramic molded body according to the embodiment of the present invention including the above steps, the temperature of the temperature control portion 24 in the molding step is controlled to the appropriate temperature based on the measurement result of the dimension of the cut ceramic molded body. Therefore, the dimensional accuracy of the ceramic molded body can be quickly and stably improved.
The method for producing the ceramic structure according to the embodiment of the present invention includes a drying step of drying the ceramic molded body obtained by the method for producing the ceramic molded body as described above, and a firing step of firing the dried ceramic molded body.
The drying step is to dry the ceramic molded body.
The method for drying the ceramic molded body is not particularly limited, and a method known in the art can be used. For example, the ceramic molded body may be placed on a drying cradle, conveyed between a pair of electrodes, and subjected to dielectric drying by passing an electric current between the electrodes. The dielectric drying is to subject dipoles of water in the ceramic molding body to molecular motion by a high frequency energy generated by passing the electric current between the pair of electrodes, and dry the ceramic molding body by frictional heat caused by the molecular motion.
In addition, as the drying conditions, known conditions can be appropriately selected according to the outer shape and material of the honeycomb structure to be produced.
The firing step is to fire the dried ceramic molded body.
The method for firing the ceramic molded body is not particularly limited, and a method known in the art can be used. For example, the ceramic molded body may be fired in a firing furnace.
In addition, as the firing conditions, known conditions can be appropriately selected according to the outer shape and material of the honeycomb structure to be produced. Further, organic substances such as the binder may be removed by calcination prior to the firing.
Since the method for producing the ceramic structure according to the embodiment of the present invention including the above steps uses the ceramic molded body obtained by the method for producing the ceramic molded body as described above, the dimensional accuracy of the ceramic structure can be stably improved.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2020/012764 | Mar 2020 | US |
| Child | 17136390 | US |
