Porous ceramics for levitation transport devices

Abstract

This material achieves both buoyancy and product quality, which are particularly required properties for porous ceramics used in buoyancy conveying devices that levitate and convey web-type materials. [Solution] A porous ceramic 3 for a floating conveying device, used in a floating conveying device 1 in which at least a part of the floating conveying surface that levitates a web conveyed object is curved, wherein the average pore size is 0.1 to 10 μm, the bending strength is 50 MPa or more, the Mohs hardness is 3.5 or more, and the volume resistivity is 10 10 It is greater than Ω·cm.

Description

Technical Field

[0001] The present invention relates to porous ceramics for a levitation conveyor that levitates and conveys web conveyors.

Background Art

[0002] Web conveyance refers to a technology for conveying and storing thin sheet-like products (webs) wound in a roll shape such as films and foils, and web conveyors are a general term for conveyors conveyed by web conveyance. In such a technical field of web conveyance, in order to convey web conveyors without damaging them, attempts have been made to levitate and convey web conveyors, and for this purpose, attempts have been made to apply porous materials to levitation conveyor devices.

[0003] As examples of such porous materials, those obtained by processing pores in a metal material and porous carbon have been relatively widely studied. However, in the case of a metal material with pores processed therein, a large amount of fluid is required to ensure the levitation conveyance performance of the web conveyor, and as a result, a high-pressure fluid is required, etc., and there are problems from the viewpoint of levitation conveyance performance. Further, in a device using porous carbon, when the web conveyor comes into contact, the carbon main body is damaged due to wear, and the shaved carbon falls off from the device main body and contaminates the web conveyor, so the yield of the product originally manufactured in that process decreases. Furthermore, since carbon has conductivity, there are problems from the viewpoint of product quality, such as causing quality defects in the subsequent process in fields that dislike conductive contamination, such as products for electrical components.

[0004] On the other hand, Patent Document 1 cites porous carbon and porous alumina as examples of porous materials. However, as can be seen from the fact that porous alumina is exemplified alongside porous carbon in Patent Document 1, sufficient consideration was not given to achieving both the characteristics particularly required for porous ceramics for levitation conveying devices, such as levitation conveyance and product quality (hereinafter simply referred to as "product quality") such as wear resistance and insulation that can be achieved by using ceramics. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2020 / 138212 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The problem that this invention aims to solve is to achieve both buoyancy and product quality, which are particularly required properties for porous ceramics used in buoyancy conveying devices that convey web-type materials by levitation. [Means for solving the problem]

[0007] According to one aspect of the present invention, porous ceramics for the following levitation conveying device are provided. A porous ceramic for use in a levitation conveying device in which at least a portion of the levitation conveying surface that levitates a web conveyed object is curved, Average pore size 0.1-10 μm, bending strength 50 MPa or higher, Mohs hardness 3.5 or higher, volume resistivity 10 10 Porous ceramics for levitation conveying devices, with a density of Ω·cm or greater. [Effects of the Invention]

[0008] According to the present invention, it is possible to achieve both buoyancy and product quality, which are particularly required properties for porous ceramics used in buoyancy conveying devices that convey web-type materials by floating them. [Brief explanation of the drawing]

[0009] [Figure 1] The image shows a levitation conveying device using porous ceramics according to the present invention, where (a) is a plan view, (b) is a side view, and (c) is a front view. [Figure 2] A graph showing the measurement results of the flow characteristics of porous ceramics according to the present invention. [Modes for carrying out the invention]

[0010] The porous ceramics according to the present invention are for use in a floating conveying device that levitates and conveys web-carried materials, particularly a floating conveying device in which at least a portion of the floating conveying surface that levitates the web-carried material is curved. A key technical feature of these porous ceramics for such floating conveying devices is that the ranges of average pore diameter, bending strength, Mohs hardness, and volume resistivity are defined in order to achieve both floating conveying performance and product quality, which are particularly required for porous ceramics for such devices. A detailed explanation follows below.

[0011] The average pore size range is 0.1 to 10 μm. If the average pore size is less than 0.1 μm, the pressure loss of the fluid used for buoyancy transport becomes too large, making buoyancy transport difficult and thus preventing proper transport. On the other hand, if the average pore size is greater than 10 μm, the pressure loss of the fluid used for buoyancy transport becomes too small, making buoyancy transport difficult and thus preventing proper transport. The average pore size range is preferably 0.5 to 5 μm. Here, the average pore size is the value measured using a mercury intrusion porosimeter.

[0012] The bending strength range is 50 MPa or higher. If the bending strength is less than 50 MPa, the material becomes susceptible to damage from pressure and external forces during use, making it impossible to achieve both levitation transportability and product quality. There is no upper limit on the bending strength, but realistically, the upper limit for the bending strength of porous ceramics is around 120 MPa. Here, the bending strength is a value measured in accordance with JIS R1601.

[0013] The Mohs hardness range is 3.5 or higher. If the Mohs hardness is less than 3.5, the material is prone to damage and detachment due to abrasion when it comes into contact with the web material, resulting in contamination of the web material and making it impossible to ensure product quality. There is no particular upper limit to the Mohs hardness, but considering the machinability with carbide tools described later, the Mohs hardness is preferably 8 or lower, and more preferably 6 or lower. Here, Mohs hardness refers to the old Mohs hardness scale with a scale of 1 to 10, and is a value measured with a Mohs hardness tester.

[0014] The range of volume resistivity is 10 10 The resistance is greater than Ω·cm, which means it has insulating properties. The volume resistivity is 10 10 Below Ω·cm, product quality cannot be guaranteed due to the conductivity issues mentioned above. Here, the volume resistivity is a value measured in accordance with JIS C2141.

[0015] The material of the porous ceramic according to the present invention is not particularly limited as long as it can satisfy the above-mentioned ranges of average pore diameter, bending strength, Mohs hardness, and volume resistivity, but from the viewpoint of machinability with cemented carbide tools, it is preferable to use wollastonite as the base material. That is, a porous ceramic with wollastonite as the base material can satisfy the more preferable range of Mohs hardness of 3.5 to 6 while also satisfying the ranges of average pore diameter, bending strength, and volume resistivity. Note that porous ceramics with wollastonite as the base material itself and the method for manufacturing the same are publicly known and are disclosed, for example, in Japanese Patent Publication No. 4-21632. [Examples]

[0016] Table 1 shows the examples of the present invention together with comparative examples. In Table 1, Examples 1 to 3 and Comparative Example 1 are porous ceramics based on wollastonite, Examples 4 and Comparative Example 2 are porous alumina, and Comparative Example 3 is porous carbon. Samples were prepared by known manufacturing methods respectively.

[0017]

Table 1

[0018] Here, an example of the manufacturing method of the porous ceramics based on wollastonite is as follows. (1) The raw materials wollastonite, talc and nepheline are blended at a ratio of 100, 10, and 10 parts by mass respectively, and 120 parts of water is added and mixed together with a binder and an antifoaming agent. (2) After thoroughly stirring the obtained mixture, it is crushed and granulated by a spray dryer. (3) The obtained granules are molded at a predetermined molding pressure and fired at a predetermined temperature.

[0019] In addition, in Table 1, in Examples 1 to 3 and Comparative Example 1, the values of the average pore diameter, flexural strength and Mohs hardness of the porous ceramics based on wollastonite are changed, but these values can be changed by changing the above molding pressure or firing temperature.

[0020] Also, in Table 1, in Examples 4 and Comparative Example 2, the values of the average pore diameter and flexural strength of the porous alumina are changed, but these values can also be changed by changing the molding pressure or firing temperature in the manufacturing method of the porous alumina.

[0021] For the porous ceramics of each example shown in Table 1, the average pore diameter, flexural strength, Mohs hardness and volume resistivity were measured, and the floating transportability, abrasion resistance and machinability by a cemented carbide tool were evaluated. The measuring methods of the average pore diameter, flexural strength, Mohs hardness and volume resistivity are as described above. In addition, in Table 1, the measurement result of the volume resistivity is 10 10If it is Ω·cm or more, it is marked with ○ (Good), 10 10 Values ​​less than Ω·cm were indicated as × (defective).

[0022] The evaluation methods for levitation transportability, wear resistance, and machinability with carbide tools are as follows. <Floating transportability> Using the levitation conveying devices fabricated from porous ceramics for each example, the pressure of the fluid used for levitation conveying was varied, and the evaluation was conducted to see whether or not the web-transported material could be levitated. Specifically, if levitation conveying was possible at a fluid pressure of 0.1 MPa or higher, it was rated ◎ (Excellent), if levitation conveying was possible at a fluid pressure of 0.5 MPa or higher, it was rated ○ (Good), and if levitation conveying was not possible even at a fluid pressure of 0.5 MPa or higher, it was rated × (Poor). The shape of the levitation conveying device was the "semi-circular" shape described later, and the radius of curvature of the levitation conveying surface that levitates the web-transported material was set to R300. <Abrasion Resistance> Floating conveying tests were conducted using floating conveying devices made from porous ceramics for each example, and the performance was evaluated based on the presence or absence of wear on the floating conveying surface and the presence or absence of contamination of the web conveyed. Specifically, ◎ (Excellent) was used when there was no wear on the floating conveying surface and no contamination of the web conveyed; ○ (Good) was used when there was wear on the floating conveying surface but no contamination of the web conveyed; and × (Poor) was used when there was contamination of the web conveyed. In this test, the shape of the floating conveying device and the radius of curvature of the floating conveying surface were as described above, and the pressure of the fluid used for floating conveying was set to 0.5 MPa. This wear resistance correlates with the product quality described above; that is, the better the wear resistance, the better the product quality. <Machinability with carbide tools> The machinability of each porous ceramic material when fabricating the aforementioned levitation conveying device was evaluated using carbide tools. Specifically, ◎ (Excellent) was used when machinability with carbide tools was possible and tool wear was small, ○ (Good) was used when machinability with carbide tools was possible but tool wear was large, and × (Poor) was used when machinability with carbide tools was impossible. Carbide tools without diamond electroplating were used. It should be noted that this machinability with carbide tools is not an essential characteristic for solving the problems of the present invention described above. In other words, even if the evaluation of machinability with carbide tools is × (Poor), the problems of the present invention can still be solved.

[0023] Examples 1 to 4 in Table 1 show variations in average pore size, bending strength, and Mohs hardness, but all are within the scope of the present invention, and the evaluation results for buoyancy transportability and abrasion resistance were good.

[0024] In contrast, Comparative Example 1 was an example where the average pore diameter was below the lower limit of the present invention, and Comparative Example 2 was an example where the average pore diameter was above the upper limit of the present invention; in both cases, the buoyancy and transportability decreased.

[0025] Comparative Example 3, as described above, is an example of porous carbon, but its bending strength and Mohs hardness are below the lower limit of the present invention. Therefore, its wear resistance is reduced. In addition, Comparative Example 3 has a volume resistivity of 10 10 The conductivity is less than Ω·cm, and due to conductivity issues, product quality cannot be guaranteed.

[0026] Next, an example of the manufacturing of a levitation conveying device will be described. Figure 1 shows an example of the manufacturing of a levitation conveying device. The levitation conveying device 1 shown in the figure includes a flat substrate 2 and a semi-circular porous ceramic body 3 placed on the substrate 2. The upper surface of this porous ceramic body 3 is the levitation conveying surface 31, and at least a part of it is curved. Note that the fluid (air) supply path to the porous ceramic body 3 (levitation conveying surface 31) is not shown in Figure 1.

[0027] In this manufacturing example, the porous ceramic body 3 is made of the porous ceramic described in Example 2 above. The specific manufacturing method is as described above: a flat plate was formed using a uniaxial molding machine at a molding pressure of 49 MPa, and then fired at a firing temperature of 1170°C to produce a flat plate material of porous ceramic with wollastonite as the base material. This flat plate material was then processed with a carbide tool to produce a semi-circular porous ceramic body 3 as shown in Figure 1. Here, two types of radii of curvature, R300 and R600, were produced for the floating conveying surface 31 on the upper surface of the porous ceramic body 3.

[0028] In tests conducted by blowing air into these two types of floating conveying devices 1 underwater, it was confirmed that bubbles were generated from the entire surface of the floating conveying surface 31, regardless of whether the radius of curvature of the floating conveying surface 31 was R300 or R600. In this manufacturing example, although the thickness of the porous ceramic body 3 differs because the shape of the porous ceramic body 3 is semi-circular, it was confirmed that air was ejected from the entire surface of the floating conveying surface 31 without any bias.

[0029] Furthermore, Figure 2 shows the measurement results of the flow rate characteristics of the two types of levitation conveying devices 1 described above. It was confirmed that the flow rate at the same supply pressure increased slightly as the radius of curvature of the levitation conveying surface 31 increased from R300 to R600. In other words, it was confirmed that levitation conveying is possible with a larger flow rate of air by increasing the radius of curvature of the levitation conveying surface 31. [Explanation of Symbols]

[0030] 1. Levitation transport device 2 circuit boards 3. Porous ceramic body 31 Floating conveying surface

Claims

1. A porous ceramic for use in a levitation conveying device in which at least a portion of the levitation conveying surface that levitates a web conveyed object is curved, Average pore size 0.1-10 μm, bending strength 50 MPa or higher, Mohs hardness 3.5 or higher, volume resistivity 10 １０ Porous ceramics for levitation conveying devices, with a density of Ω·cm or greater.

2. A porous ceramic for a levitation conveying device according to claim 1, wherein wollastonite is used as the base material.

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