JP3100773B2 - Electromagnetic flowmeter using capacitance electrodes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, about the electromagnetic flowmeter using a capacitive electrode.

[0002]

2. Description of the Related Art A conventional capacitance type electromagnetic flowmeter of this type has a structure in which an electrode is incorporated into an unfired ceramic pipe, which is a green pipe, and an electrode member is sealed in the fired ceramic by a firing treatment. (Japanese Patent Publication No. 2-29170, Japanese Utility Model Publication No. 63-1215).

[0003] Specifically, this capacitance type electromagnetic flowmeter is provided with a metallization process on the outer periphery of an unsintered ceramic pipe, or the application of a paste containing metal powder, and the outer side of an unsintered ceramic sheet (green sheet). ) Is fired and fired.

The unfired ceramic pipe is an unfired ceramic obtained by dispersing ceramic fine powder in a so-called water-soluble binder mainly composed of, for example, an aqueous solution of vinyl alcohol or vinyl acetate, and solidifying it at room temperature. The properties of the unfired ceramic pipe are a seemingly blackish substance having no flexibility, and contain a considerable amount of moisture. Therefore, not only can the metallization process of adding a full-scale heating step to the surface of such a chalk-like substance be performed, but it tends to be thick, and a considerable gap is required when a plurality of pipes are superimposed. In some cases, when almost the same shrinkage material is used, there is a problem that the defective rate continues.

[0005] On the other hand, the unsintered ceramic sheet is a flexible sheet made by mixing ceramic fine powder into a so-called oil-soluble binder obtained by dissolving a resin such as polyvinyl butyral with MEK, ie, methyl ethyl ketone, and kneading the mixture at room temperature. It is a non-fired ceramic sheet with a high content, and contains a considerable amount of organic solvents. Therefore, a metallizing treatment for adding a heating step cannot be performed on the surface of the material.

Therefore, when a metal film is formed on the surface of the unfired ceramic pipe or the unfired ceramic sheet as described above, a paint-like substance obtained by mixing metal powder into an oil-soluble binder is applied to the surface of the pipe or sheet. However, it is common that the unfired ceramics are fired together when firing. This baking produces a metal film.

In the case of mounting a metal electrode on an unfired ceramic pipe, in a conventional manufacturing method, after a measurement electrode is metallized on the unfired ceramic pipe, a paste-like conductive material is applied, and then the unfired ceramic material is applied. After covering with a ceramic sheet, the process of baking is taken.

[0008]

However, as described above, the method of forming a metal film on the surface of an unsintered ceramic pipe or an unsintered ceramic sheet is performed by an unsintered ceramic pipe using a water-soluble binder. And an unfired ceramic sheet using an oil-soluble binder, the overall thickness is increased, and the binder diverges or decomposes by heating even in the debinding step, which is a weak heating step, and this becomes a gas. Therefore, when the ceramics escape from the unfired ceramics, it becomes difficult to remove the ceramics, and when the ceramics are heated too much, the ceramics are likely to be in a void (hollow) state. As a result, many cavities are formed in the unfired ceramic pipe or the like, and there is a problem that when the internal pressure of the fluid is applied as a complete internal defect, it breaks.

Next, when the metal electrode is mounted on the unfired ceramic pipe, when the unfired ceramic pipe or the unfired ceramic sheet is fired, the linear shrinkage is 16% or less.
As it contracts about 26%, 41% to 60% in body contraction rate,
It is unlikely that the metal electrode is accurately positioned at the required position, which is an inappropriate manufacturing method when a high-precision electromagnetic flowmeter is to be manufactured.

Further, for example, metallized metal which is applied by spraying a metal melted by heating and deposited from a distance or a metal coated with a paste-like conductive material is overlapped during firing between a pipe and a sheet of unfired ceramics, resulting in thermal expansion. If a different layer is formed and the amount is large, there is a high possibility that destruction will occur due to a change in the temperature of the measurement fluid of the electromagnetic flowmeter, or triggering will occur due to internal pressure.

The present invention has been made in view of the above circumstances. Therefore, a metal pipe can be easily and appropriately attached to a ceramic pipe, and a stable measuring pipe section having few defects such as pores is realized. Electrode using capacitance electrode
It is to provide a magnetic flow meter . Another object of the present invention is to provide a capacitance capable of mounting an electrode at an appropriate position.
An object of the present invention is to provide an electromagnetic flowmeter using electrodes . Further, another object of the present invention is to provide an electrode using a capacitance electrode for realizing a measurement tube portion that is less likely to cause defects using ceramics.
It is to provide a magnetic flow meter .

[0012]

According to a first aspect of the present invention, at least one pair of measurement electrodes or at least one pair of measurement electrodes and a pair of shield drive electrodes are arranged in a fired ceramic tube. And the outside of the fired ceramic tube containing these electrodes
The unfired ceramic diffusion bonded to the fired ceramic tube by firing of the green ceramics which are applied so as to cover, and an electromagnetic flow using an electrostatic capacitance electrode having a measurement tube portion formed by encapsulates the electrode It is total .

According to a second aspect of the present invention , at least one pair of measurement electrodes or at least one pair of measurement electrodes and a pair of shield drive electrodes are arranged in a fired ceramic tube, and the fired ceramic tube including these electrodes is provided. On the outside, the electrode is embedded by dispersing and precipitating unfired ceramic fine powder in a binder solution, diffusion bonding the unfired ceramic to the fired ceramic tube by desolvation and firing , and capacitance electrodes which have a measuring pipe portion which is formed by the containment
This is the electromagnetic flow meter used .

Furthermore, the invention is greater plurality of unfired ceramic shrinkage during firing as the outer side corresponding to claim 3
Superposed tube was placed and fired is interposed at least one pair of measurement electrodes between the two unfired ceramic tube
Using a capacitance electrode with a measuring tube section formed by
It is an electromagnetic flow meter .

Further, the invention according to claim 4 is that the unfired ceramic tube includes at least one pair of measurement electrodes or at least one pair of measurement electrodes and a pair of shield drive electrodes, and includes the electrodes. On the outside of the tube, the electrode is embedded by dispersing and precipitating unfired ceramic fine powder in a binder solution, and the unfired ceramic is fired by firing the unfired ceramic tube by removing the solution and firing. Diffusion bonding , and enclosing the electrode
Electromagnetic flow using an electrostatic capacitance electrodes which have a form with the measurement pipe section
It is a meter .

Furthermore, the invention is greater multilayer unsintered ceramic shrinkage during firing as the outer side corresponding to claim 5
Tubes are placed one on top of the other and have a measuring tube part formed by diffusion bonding of unfired multilayer ceramic tubes by firing
This is an electromagnetic flowmeter using a capacitance electrode .

Furthermore, corresponding to claim 6 invention, covering the outside of the firing ceramic tube to remove defects elements of strength
Electrostatic using an electrostatic capacitance electrodes having a measuring tube section the unfired ceramic formed diffusion bonded to the fired ceramic tube by firing the unfired ceramics decorated with Migihitsuji
It is a magnetic flow meter .

[0018]

Therefore, according to the invention corresponding to claim 1, by taking the above means, after arranging at least one pair of measurement electrodes outside the fired ceramic tube, the unfired ceramic is covered outside the measurement electrode. If fired, the fired ceramic wraps around the measurement electrode and is diffused and bonded to the fired ceramic tube to be integrated, so that the metal electrode can be securely attached to the ceramic pipe and the gas, liquid, etc. can pass through the fired ceramic tube. After confirming that there is no defect, the unfired ceramic is diffusion-bonded, so that a measuring tube portion of the ceramic with few defects can be obtained.

Next, in the invention corresponding to claim 2, after arranging at least a pair of measuring electrodes outside the fired ceramic tube, the unfired ceramic fine powder is placed in a binder solution using a mold on the outside. The electrode is buried by dispersing and precipitating, and thereafter, the unfired ceramic is diffused and bonded to the fired ceramic tube by desolvation and firing, so that the same as the invention corresponding to claim 1 In addition, it is easy to mount the metal electrode, and it is possible to obtain a ceramic measuring tube having few defects.

Further, according to the invention, a plurality of unfired ceramic pipes are polymerized so that the outer side thereof has a larger shrinkage rate during firing, and at least one pair of unfired ceramic pipes is provided between the two unfired ceramic pipes. Since the measurement tube portion is obtained by firing with the measurement electrode interposed, a measurement tube portion having stable mechanical dimensions can be obtained, and the electrode can be mounted at an appropriate position.

Further, according to a fourth aspect of the present invention, at least a pair of measurement electrodes are arranged outside a green ceramic tube, and a binder solution is placed outside the green ceramic tube containing these electrodes. The method according to claim 1, wherein the electrode is buried by dispersing and precipitating unfired ceramic fine powder, and the unfired ceramic is diffused and bonded to the fired ceramic tube by desolvation and firing, so that the invention according to claim 1 and Similarly, it is easy to mount the metal electrode, and it is possible to obtain a ceramic measuring tube having stable mechanical dimensions with few defects.

Further, the invention according to claim 5 is to superimpose a multilayer unfired ceramic pipe, arrange a pipe having a larger shrinkage rate at the time of firing at the outer side, and fire the multilayer unfired ceramic pipe by firing. Diffusion bonding is integrated to form a measurement tube section, so that the thickness of each unfired ceramic is reduced, so that gases and the like inside the unfired ceramic can be extracted during firing, and a measurement tube section with few defects is used. Obtainable.

Further, the invention according to claim 6 is that, after covering the outside of the fired ceramic from which the defective element on the strength has been removed with the unfired ceramic, the unfired ceramic is diffusion-bonded to the fired ceramic by firing and integrated. By doing so, a measurement tube section can be obtained, so that a measurement tube section with few defects can be obtained.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a front sectional view showing an embodiment of an electromagnetic flow meter according to the present invention, FIG. 2A is a side sectional view of FIG. 1 when using an outer casing that also serves as a feedback magnetic path, and FIG. FIG. 2 is a side sectional view of FIG. 1 when a non-magnetic material outer casing is used.

In these figures, reference numeral 1a denotes a fired ceramic pipe having a relatively small thickness. An outer surface of the fired ceramic pipe 1a is opposed to a capacitance measuring electrode 2, and an unfired ceramic 1b is covered on the outside. ing.

Such a fired ceramic pipe 1a is used because of its small temperature deformation, heat resistance, easy metallization, property of forming a metal thin film by spraying molten metal, and stability of mechanical dimensions after metallization. This is based on the characteristics and the like. Moreover, the reason why the thickness is reduced is to confirm that there are no transmission defects such as gas and liquid inside.

On the other hand, the capacitance measuring electrode 2 is made of a material that can sufficiently withstand the firing in the subsequent step, and is as close as possible to the fluid to be measured from the viewpoint of reducing the impedance between the electrode and the fluid to be measured. And place it. For this purpose, it is desirable to arrange the surface of the fired ceramic pipe 1a or within the thickness of the fired ceramic pipe 1a.

Further, a shield drive capacitance electrode 3 is arranged outside the green ceramics 1b so as to cover the capacitance measurement electrode 2 from outside. In addition,
When the capacitance measurement electrode 2 and the shield drive capacitance electrode 3 are embedded in the ceramics pipe, they are made of a material in which metal and ceramics are mixed in order to match the thermal expansion coefficient as much as possible and to increase the bonding force. The formation of the cermet-shaped electrode facilitates the integration of the electrode and the ceramic. These components 1a, 1b, 2, 3 are referred to as a measuring tube 1.

As shown in FIG. 2A, an exciting coil 6 is provided outside the measuring tube 1 obtained as described above.
2 and a return magnetic path / external housing 7 made of a magnetic material is provided via an exciting coil 6 and a ring-shaped core 8 of a magnetic material wound around a thin silicon steel strip, for example, as shown in FIG. An outer casing 7a made of a non-magnetic material is provided. Reference numeral 3a denotes a shield for shield drive, and 9 denotes a shield of the same potential. This shield keeps a noise source away from the capacitance measuring electrode 2 and the shield driving capacitance electrode 3, and also prevents electrostatic discharge from the fluid to be measured. It has a function of setting the exciting coil 6 to the same potential as the outer casings 7 and 7a in order to reduce the coupling. Reference numeral 10 denotes an excitation signal line of the coil, and reference numeral 11 denotes a coil mounting adhesive layer.

In the above embodiment, the shield drive capacitance electrode 3 is disposed outside the unfired ceramics 1b. However, from the viewpoint of preventing noise from entering from outside, the capacitance measurement electrode 3 is actually used. Since it is not necessary to dispose the ceramic pipe 2 close to the ceramic pipe 2, the ceramic pipe may be disposed within the thickness of the ceramic pipe composed of the fired ceramic pipe 1a and the unfired ceramic 1b, as shown in FIG. When the double electrode is embedded in the ceramic pipe, the above-described manufacturing procedure is repeated twice or the capacitance measuring electrode 2
An insulating layer such as a ceramic may be formed on the surface of the substrate, and the shield drive capacitance electrode 3 may be formed thereon by thermal spraying or the like. Further, as shown in FIG. 4, a plurality of pairs of capacitance measuring electrodes 2a-2 are provided inside the ceramic pipe.
a, 2b-2b, capacitance electrode 3a for shield drive
a-3aa, 3bb-3bb may be used.

FIG. 5 shows an example in which the measuring tube including the measuring tube unit 1 obtained as described above is connected to the signal conversion processing system 20. That is, the signal conversion processing system 20 includes the excitation power supply 2
An excitation signal is applied to the excitation coil 6 from 1 to form a magnetic field in the measurement tube section 1. At this time, a signal proportional to the flow velocity of the fluid is taken out from the pair of capacitance measuring electrodes 2 and is sent via the signal taking-out line 2a. Introduced to the preamplifier 22.

Reference numeral 23 denotes a clock generation source for generating a clock signal of a predetermined period. The preamplifier 22 samples a measurement signal using the clock signal from the clock generation source 23, And output it. 25 is a shield drive feedback signal. Next, a method of manufacturing the measurement tube unit 1 will be described with reference to FIGS.

First, as shown in FIG. 6, the capacitance measuring electrode 2 or the capacitance measuring electrode 2 and the shield driving capacitance electrode 3 are provided outside the fired ceramic pipe 1a.
(Not shown), and an unfired ceramic pipe 1b having an inner diameter that flexibly adheres to the fired ceramic pipe 1a in consideration of the shrinkage force during firing. At this time, the signal output line 2a or the contact electrode 2c with the signal output line 2a is arranged inside the unfired ceramic pipe 1b and firing is performed.

By this firing treatment, the unfired ceramic pipe 1b shrinks, adheres to the fired ceramic pipe 1a by diffusion bonding and is integrated, and the electrode members and the like are sealed in the ceramic pipe. At this time, the diffusion bonding of the fired ceramic pipe 1a and the unfired ceramic 1b is performed by performing a heat treatment at a temperature lower than the melting of the ceramic for a long time.

At this time, for example, in the case of the contact electrode 2c with the signal extraction line 2a, the contact electrode 2c arranged inside the unfired ceramic pipe 1b is
, And a signal can be taken out.

Although the gap between the fired ceramic pipe 1a and the unfired ceramic pipe 1b may be close to each other, for example, low temperature baking (about 100 to
In the case of 200 ° C.), it is better to have a gap because the binder is easily scattered.

Further, at the time of firing, the fired ceramic pipe 1
In order to exclude gas from between a and the unfired ceramics pipe 1b, the fired ceramics pipe 1a and the unfired ceramics pipe 1b in the form shown in FIGS. Thereafter, a configuration may be adopted in which gas generated during diffusion bonding during firing is released to the outside. For example, as shown in FIG. 7A, an unfired ceramic pipe 1b having a tapered diameter in one direction is disposed outside a fired ceramic pipe 1a having no taper, or as shown in FIG. An unfired ceramic pipe 1b having a tapered diameter that expands in both directions from the portion is disposed. Further, FIG.
Conversely, as shown in (c), a tapered shape is formed so as to be narrowed from the central portion of the outer shape of the fired ceramic pipe 1a toward both ends, or the fired ceramic pipe 1a as shown in FIG. The outer diameter of the ceramic pipe 1b is tapered in directions different from each other.

Further, as shown in FIG. 8 (a), a recessed portion having both sides tapered is formed at the center of the outside of the fired ceramic pipe 1a, and the outside of the recessed portion is formed outside the fired ceramic pipe 1a. An unfired ceramic pipe 1b having an outer diameter larger than the diameter is disposed, and the fired ceramic pipe 1a and the unfired ceramic pipe 1b are integrated by diffusion bonding by firing as shown in FIG. Is what you do.

Further, the measuring tube section 1 can be made by using another manufacturing method. That is, after the capacitance measuring electrode 2 or the capacitance measuring electrode 2 and the shield driving capacitance electrode 3 are arranged outside the fired ceramic pipe 1a, the unfired ceramic is dispersed and precipitated in a binder solution. After the electrodes 2 and 3 are buried, the solution is removed, and the unfired ceramic is fired while being diffused and integrated with the fired ceramic pipe 1a to seal the electrode members and the like in the ceramic.

As shown in FIGS. 9 (a) and 9 (b), this manufacturing method employs a metallization, metallikon, reductive plating, electrospraying after carbon spraying, etc. on the outside of the fired ceramic 1a. The capacitance measuring electrode 2 is arranged. At this time, the signal output line 2a is attached to the capacitance measuring electrode 2 at the same time.

Thereafter, as shown in FIG. 4C, the fired ceramic pipe 1a with the electrode 2 is erected on the outer die 41a of the bottom plate with an adhesive 42 such as putty or cement, and then fixed to the outside of the ceramic pipe 1a. Cylindrical outer mold 4 to cover
1b is attached to the bottom plate outer die 41a. Further, a core 43 is fixed to the opposite surface side of the ceramic pipe 1a via a fixing agent 42 such as putty or cement. And core 4
A fluid 44 in which ceramic powder is dispersed is poured into a gap between the outer mold 3 and the outer mold 41b.

As the liquid at this time, for example, an aqueous solution of polyvinyl alcohol is used when it is water-soluble, and a solution of methyl ethyl ketone of polyvinyl butyral is used when it is non-aqueous. Further, the fixing agent 42 used is one that cannot be dissolved with a solution, such as putty or cement. An aqueous putty is used for a non-aqueous solution, and an oily putty is used for an aqueous solution.

After the unfired ceramic is solidified as described above, the mold is removed, and cut into necessary lengths as shown in FIG.
Finally, as shown in FIG. 3 (f), it is processed into a measuring tube having a required final dimension.

As oxide ceramics, alumina Al ₂ O ₃ (melting point: 1999-2032 ° C.), zirconia ZrO ₂ (melting point: 2700 ° C.), beryllia Be
O (melting point: 2585 ° C.), etc., and firing is performed in an oxygen or air atmosphere. The maximum heating temperature in the firing step is about 1800 ° C. for typical alumina, but when Pt (melting point: 1755 ° C.) is used as the electrode material, the maximum heating temperature is about 1500 ° C. Sintering to cover a low sintering temperature. In the case of nitride ceramics or non-oxide ceramics, the treatment is performed with H ₂ or in a nitrogen atmosphere.

Next, another embodiment of the present invention will be described. This embodiment has exactly the same configuration and manufacturing steps as those of the above-described embodiment, but in particular, uses unfired ceramics in place of the fired ceramics 1a and manufactures in exactly the same manner as in FIGS.

More specifically, at least a pair of capacitance measuring electrodes 2 are disposed between the inner unfired ceramic pipe 1a 'and the outer unfired ceramic pipe 1b, for example, with the signal output line 2a attached. At this time, a pipe having a larger shrinkage rate at the time of sintering is arranged in the outer pipe. The shrinkage is determined by the cohesive force when the unfired ceramic powder is fired. As a general property, the smaller the particle size of the unfired ceramic, the lower the shrinkage.

At this time, as for the outer unfired ceramic pipe 1b, the unfired ceramic fine powder is dispersed and precipitated in a binder solution, the electrodes 2 and 3 are buried, then the solution is removed, and firing is performed. Thus, an integrated fired ceramic pipe having the capacitance measuring electrode 2 built therein is produced. That is, the connection between the inner unfired ceramic pipe 1a 'and the outer unfired ceramic pipe 1b is diffused and integrated between the two by heating for a long time at a temperature lower than the melting of the ceramic.

It should be noted that the smaller the amount of the water-soluble and oil-soluble binder, the smaller the shrinkage ratio. In the case of an unfired ceramic pipe formed by high-pressure pressing in a dry state using a small amount of a dry binder, the shrinkage ratio is the linear shrinkage ratio It can be suppressed to about 5%, and in the case of a wet method, the shrinkage ratio in the production process of a general commercial product is about 16% to 26%. Therefore, the degree of shrinkage can be selected by changing the composition.

Further, as another embodiment, an outer unfired ceramic pipe 1b having an inner diameter that is softly adhered to the outer shape of the inner unfired ceramic pipe 1a 'is arranged and fired, whereby the both are adhered during firing. To form a measurement tube 1 in which the electrode member is sealed in a ceramic pipe.

As shown in FIG. 6, the capacitance measuring electrode 2 or the capacitance measuring electrode 2 and the shield driving capacitance electrode 3 (not shown) are provided outside the inner unfired ceramic pipe 1a '. And an unfired ceramic pipe 1b is disposed outside of the pipe in consideration of the shrinkage force during firing. At this time, the signal extraction line 2a or the contact electrode 2c with the signal extraction line 2a is arranged inside the unfired ceramic pipe 1b, and firing is performed. As a result of this firing treatment, the unfired ceramic pipe 1b shrinks, adheres tightly to the unfired ceramic pipe 1a 'by diffusion bonding, and integrates the electrode member and the like into the ceramic pipe.

At this time, for example, in the case of the contact electrode 2c with the signal extraction line 2a, the contact electrode 2c arranged inside the unfired ceramic pipe 1b is
And the signal can be taken out. Next, the ceramic pipe will be described.

This ceramic pipe is made of a high-pressure fluid capable of withstanding a high-pressure fluid, such as a wetted electrode type electromagnetic flowmeter, a wetted electrode type electric conductivity meter, a capacitance type electromagnetic flowmeter, and a capacitance type electric conductivity meter. It is intended for measuring pipes.

Conventional ceramic pipes are excellent in mechanical properties, such as bending strength and tensile strength, but these mechanical strengths may be reduced to several times due to defects on the ceramic surface or inside. The main causes of this decrease are roughly classified into surface defects and internal defects. This surface defect is caused by "grain boundaries" generated in the surface structure,
"Heterogeneous heterogeneous structure due to surface diffusion, grain boundary diffusion, lattice diffusion anomaly", "Drag phenomenon due to the type, size, concentration, etc. of heterogeneous (solute) atoms, intervening particles, cavities, etc. at or near the grain interface. On the other hand, the latter internal defects include cavities caused by rapid air diffusion of the binder during the binder removal operation, cavities caused by generation of gaps due to coalescence with large ultrafine particles, and the like.

Therefore, in the present invention, even with various measuring instruments handling high-pressure fluid as described above, it is possible to eliminate the above-mentioned defects and to realize a ceramic pipe having sufficient mechanical strength inherent in ceramics. It is in. First,
Various investigations into the state of occurrence of internal defects in the ceramic pipe revealed that the thinner the wall, the more difficult it is to form a cavity inside the pipe.

Therefore, in order to obtain a ceramic pipe having a target thickness, the necessary thickness of the unfired ceramic pipe is divided into a plurality of pieces, and as shown in FIG. ', 51b', 5
1c 'is arranged concentrically in a multilayer pipe, while an unfired ceramics pipe having a larger shrinkage ratio during firing is arranged closer to the outer pipe.

Thereafter, the multi-layer unfired ceramic pipe 51 'is fired to obtain the multilayer unfired ceramic pipe 51', as shown in FIG.
As shown in (c), the ceramic pipes are made into an integral body by diffusion bonding between the ceramic pipes. Next, an example of removing a defect of the pipe will be described.

First, with respect to the internal defects of the ceramic pipe, if the thickness of the ceramic pipe is reduced,
A binder (water-soluble, oil-soluble, etc.) that is heated and eluted during baking, has low resistance when gas is released when it is thermally decomposed, and has a low possibility of generating voids in meat due to bumping or bump decomposition. Moreover, the temperature can be significantly reduced by performing hot pressing or hot isostatic pressing. Therefore, these measures are performed with due consideration.

On the other hand, the surface defects of the ceramic pipe are as follows:
Due to the extremely large surface area of the inner and outer surfaces of the multi-layer pipe, the location of occurrence may occur more than in a single piece pipe. In order to prevent this surface defect from occurring, the following firing treatment is performed. In other words, since the aggregation of the ultrafine particles is suppressed at the stage of the initial sintering and the middle sintering, and the low-temperature coalescence with the large particles is difficult to be performed, a sintering aid is used, or before the coalescence between the layers during the firing of each pipe. The temperature is allowed to elapse in a short period of time at a high temperature to prevent surface defects in a portion sealed between the pipe layers.

The initial sintering referred to here is a stage in which a neck grows at a contact point of each ceramic particle.
Mid-term sintering refers to the process of shrinking the tubular open pores at each ridge where particles are multifaceted. AL ₂ O ₃ is used as a sintering aid.
Is called a sintering aid when a small amount of MgO is added to prevent agglomeration as described above.

When the above-mentioned middle sintering stage is completed, the second stage sintering is started. This late sintering is a pore shrinkage disappearance process in which the tubular pores are closed. The firing is completed by the latter sintering. By maintaining the temperature during the sintering as described above, the ceramic pipes are diffusion-bonded to each other, and the multilayer pipe is integrated.

The surface defects on the inner and outer end faces of the united pipe generated until the end of the latter sintering step are removed as necessary. This surface defect may be due to the existence of grain boundaries where the ceramic fine powder agglomerates and grows into a crystalline form. In this case, when high pressure is applied to the pipe, the grain boundaries may trigger and break the ceramic pipe. Is high.

Therefore, these surface defects such as grain boundaries are removed by using a chemical method or a mechanical method. For example, the chemical method applies a vitreous material to the surface at a relatively low temperature (about 600 °).
C, the temperature differs depending on the glass component), the grain boundaries are dissolved in the glass, the glass is removed with alkali or hydrofluoric acid, etc. By doing so, the grain boundaries are removed. Another chemical method is to use hydrofluoric acid (HF) or 50% to 60% without using vitreous material.
% HF and nitric acid (HNO ₃ ) or HF: HNO ₃ : H ₂
The surface is etched by immersing in SO ₄ (sulfuric acid) = 1: 1: 1 at room temperature for several seconds to remove defects. On the other hand, as a mechanical method, the cloth is polished after the grinding, or the defect is removed by directly polishing the cloth.

When the multilayer ceramic pipe 51 obtained as described above is applied to a wetted electrode type electromagnetic flowmeter, a wetted electrode type electric conductivity meter, etc., as shown in FIG. Holes 52 are opened at opposing portions of the ceramics pipe 51, and the holes 52 are inserted with the liquid-contact type electrodes 54 through the packing 53, and are fixed by bolts 56 from outside the pipes through the washers 55.

If the electrode mounting hole 52 is provided with a heat treatment for stress relaxation and a step of removing surface defect elements in the same manner as in the firing step after the hole is formed, a pipe with even more reliable electrode holes can be obtained. it can. Grinding using ultrasonic vibration is suitable for drilling holes in the firing pipe.

FIG. 11B shows a multilayer ceramic pipe 5.
This is an example in which a capacitance type electrode 57 is interposed between the reference numerals 1 and a shield drive shield 58 is provided so as to surround the capacitance type electrode 57 from outside. This is used for a capacitance type electromagnetic flow meter, a capacitance type electric conductivity meter and the like. Next, FIG. 12 is a view showing an example of manufacturing a two-layer ceramic pipe.

First, an unfired ceramic pipe 51a 'as shown in FIG. After a while, FIG.
After the unfired ceramic pipe 51a 'is erected and fixed to the bottom plate outer mold 61a with an adhesive 62 such as putty or cement, a cylindrical outer mold 61b is provided so as to cover the outside of the unfired ceramic pipe 51a'. Is attached to the bottom plate outer die 61a. Further, the core 6 is placed on the opposite side of the ceramic pipe 51a 'via a fixing agent 62 such as putty or cement.
3 is fixed. Then, a fluid 64 in which ceramic powder is suspended is poured into a gap between the core 63 and the outer mold 61b.
After solidifying the unfired ceramics, the mold is removed, cut into necessary lengths as shown in FIG. 12 (c), further fired to form a desired shape, and finally a measuring tube of required final dimensions Part.

Further, as another embodiment, after removing and correcting an element which causes a defect in the strength of the outer surface layer of the fired ceramic pipe, the outside of the fired ceramic pipe is covered with an unfired ceramic pipe. It is also possible to manufacture an integrated fired ceramic pipe by diffusion bonding while firing the ceramic pipe.

In some cases, after the manufacturing process of the multilayer ceramic pipe having two or more layers is completed, a surface element which becomes a defect in strength on both the inner surface, the outer surface, and the inner and outer surfaces is removed and corrected. In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[0069]

As described above, according to the present invention, the following various effects can be obtained.

First, according to the first and second aspects of the present invention, a capacitance electrode having a stable measuring tube portion with a small number of defects such as pores can be easily and appropriately attached to a ceramic pipe. It can provide an electromagnetic flow meter was used.

Next, according to the third aspect of the present invention, it is possible to obtain a measuring tube section having stable mechanical dimensions and to mount an electrode at an appropriate position. Can be easily attached, and a ceramic measuring tube portion having stable mechanical dimensions with few defects can be obtained. Further, the invention according to claims 5 and 6 can easily realize a measuring tube portion in which defects are less likely to occur. it can.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing one embodiment of a physical quantity measuring device according to the present invention.

FIG. 2A is a side sectional view using a magnetic material outer case, and FIG. 2B is a side sectional view using a nonmagnetic material outer case.

FIG. 3 is a front sectional view in which electrodes are embedded in a ceramic pipe.

FIG. 4 is a front sectional view in which a plurality of pairs of electrodes are embedded in a ceramic pipe.

FIG. 5 is a configuration diagram in which a signal conversion system is connected to the measurement tube of FIG. 1;

FIG. 6 is a diagram for embedding an electrode in a ceramic pipe and attaching a signal output line at the same time.

FIG. 7 is a diagram showing a tapered fired and unfired ceramic pipe for eliminating gas when the unfired ceramic shrinks during firing.

FIG. 8 is a diagram showing how a signal output line is attached to an electrode by utilizing shrinkage of unfired ceramics during firing on a ceramics pipe.

FIG. 9 is a diagram showing a method for forming a ceramic pipe by embedding electrodes while dispersing and precipitating ceramic fine powder in a binder solution using a mold outside a fired ceramic pipe.

FIG. 10 is a diagram showing a method of manufacturing a measurement tube section using a multilayer unfired ceramic pipe.

FIG. 11 is a diagram showing how a measurement electrode is attached to the measurement tube manufactured according to FIG. 10;

FIG. 12 is a diagram showing a method of manufacturing a ceramic pipe by dispersing and precipitating ceramic fine powder in a binder solution using a mold outside a green ceramic pipe;

[Explanation of symbols]

Reference numeral 1 denotes a measuring tube portion, 1a denotes a fired ceramic pipe, and 1b denotes a pipe.
Unfired ceramic, 2 ... measurement electrode, 2a ... signal extraction line, 2c ... contact electrode, 3 ... shield drive electrode, 6 ... excitation coil, 7, 7a ... outer casing, 8 ... same potential shield, 20 ... signal processing conversion 44, a fluid in which ceramic powder is dispersed, 51 ', a multilayer unfired ceramic pipe, 51a', 51b ', 51c', an unfired ceramic pipe, 51, a multilayer ceramic pipe,

Claims (6)

(57) [Claims] 1. A with placing at least a pair of measurement electrodes or at least a pair of measurement electrodes and the pair of shield drive electrode firing ceramic tube, subjected to cover the outside of the firing ceramic tube comprising electrodes
Unfired ceramics by Ri is diffusion bonded prior SL-fired ceramics tube baked formation of and form and encapsulates the electrodes
Capacitance electrodes, characterized in that have a measurement pipe section which forms
Electromagnetic flowmeter using . With wherein placing at least a pair of measurement electrodes or at least the pair of measurement electrodes and the pair of shield drive electrode firing ceramic tube, the outside of the firing ceramic tube containing the electrodes, non-in binder solution the electrode buried by dispersing the calcined ceramic powder is precipitated, the unfired ceramic diffusion bonded to the fired ceramic tube with de solution and calcined, and the measurement tube portion formed by encapsulates the electrode
Electromagnetic flow using a capacitive electrode, characterized in that the chromatic
Total . Wherein during firing as the outer side shrinkage plurality of large
Place superimposed unfired ceramic tube, and a capacitance electrode, characterized in that the perforated flow tube portion formed by firing is interposed at least one pair of measurement electrodes between the two unfired ceramic tube The electromagnetic flow meter used . Wherein with placing at least a pair of measurement electrodes or at least the pair of measurement electrodes and the pair of shield drive electrode into a green ceramic tube, the outside of the unfired ceramic tube containing the electrodes, in the binder solution The electrode is buried by dispersing and precipitating the unfired ceramic fine powder into the unfired ceramic tube, and the unfired ceramic is removed from the unfired ceramic tube by removing the solution and firing .
Diffusion bonded to the fired fired ceramic tube, and an electromagnetic flowmeter using a capacitive electrode, characterized in that the perforated flow tube portion formed by encapsulates the electrode. Wherein the shrinkage during firing as the outer side larger multilayered
Place superimposed unfired ceramic tube, the multilayer unsintered ceramic tube each other diffusion bonded to form by firing
Use the capacitance electrodes characterized by have a measuring tube portions
Electromagnetic flow meter . 6. An unfired ceramic applied to cover the outside of a fired ceramic tube from which a defect element on strength has been removed.
Scan electromagnetic flowmeter using a capacitive electrode, characterized in Rukoto to have a the unfired ceramic was diffusion bonded to the fired ceramic tube formed by the measuring pipe portion by firing.