JP3820051B2 - Fluid detection tube for electromagnetic flow meter and method of manufacturing fluid detection tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fluid detection tube for an electromagnetic flowmeter that detects a flow rate of a fluid to be filled by a beverage filling machine or the like, and a method for manufacturing the fluid detection tube.
[0002]
[Prior art]
In a beverage filling machine, for example, when a beverage such as a glass bottle or a PET bottle is filled with a beverage, the flow rate of the beverage to be filled is measured with a flow meter, and the flow rate is set so that an appropriate amount of beverage is filled into the container based on the measurement result. Control is performed. An example of the flow meter is an electromagnetic flow meter that electromagnetically measures the flow rate. FIG. 6 shows a schematic configuration of an electromagnetic flow meter which is an object of the present invention.
[0003]
In FIG. 6, reference numeral 1 denotes a detection tube for detecting a fluid flow rate, and a fluid 2 such as a beverage flows in a flow path in the detection tube 1. A pair of electrodes 3a and 3b are attached to the detection tube 1 symmetrically with respect to the flow path in the diameter direction, that is, so as to face each other. In addition, a pair of electromagnetic coils 4a and 4b are attached to the outside of the detection tube 1 so as to face each other at a position shifted by 90 from the electrodes 3a and 3b. The electromagnetic coils 4 a and 4 b are excited by the excitation circuit 5. The excitation circuit 5 is supplied with DC power from a power line 6 and is grounded through a constant current circuit 7. The excitation circuit 5 supplies a sine wave or rectangular wave excitation signal to the electromagnetic coils 4a and 4b in accordance with an excitation command given from a CPU (microcomputer) 11 described later.
[0004]
When the electromagnetic coils 4a and 4b are excited, a voltage corresponding to the fluid velocity, the local strength, and the like is induced in the electrodes 3a and 3b of the detection tube 1. For example, the diameter of the detection tube 1 is d (m), the magnetic flux density provided by the electromagnetic coils 4a and 4b is B (T), the average flow velocity of the conductive fluid 2 is v (m / s), and the magnetic field is When the detection tube 1 is uniform and has an axisymmetric flow velocity distribution, the voltage e (v) generated in the fluid 2 is obtained by the following equation.
[0005]
e = B ・ d ・ v
The voltage e induced in the electrodes 3 a and 3 b is input to the differential amplifier circuit 8 and amplified, and then sent to the synchronization detection circuit 9. The synchronization detection circuit 9 detects the induced voltage applied to the electrodes 3 a and 3 b in synchronization with the excitation signal from the excitation circuit 5 and outputs it to the flow rate conversion circuit 10. The flow rate conversion circuit 10 converts the signal detected by the synchronization detection circuit 9 into a flow rate and outputs it to the CPU 11. The CPU 11 outputs an excitation command to the excitation circuit 5 as described above, and outputs a control signal to a beverage filling machine (not shown) according to the flow rate output from the flow rate conversion circuit 10.
[0006]
If the voltage e induced in the electrodes 3a and 3b of the detection tube 1 is measured as described above, the average flow velocity v can be uniquely obtained, and the flow rate of the fluid 2 can be calculated from the flow velocity v.
[0007]
The potential of the electrodes 3a and 3b is a voltage generated between the fluid 2 and the signal voltage generated by the movement of the fluid 2 is several mV, and noise is generated from several mV to several volt. Measurement is not possible, and measurement is performed by applying an alternating magnetic field as described above.
[0008]
Conventionally, the electrodes 3a and 3b of the detection tube 1 are flat, extrapolated, or pointed, as shown in FIGS. 7A to 7C show the cross-sectional structure of the electrode portion.
[0009]
In the flat shape shown in FIG. 7A, a hole for an electrode is formed in the tube wall 21 of the metal detection tube 1 and the lining 22 provided on the inside thereof, and the electrode 3 having a flat tip is inserted into the hole from the inside of the tube. Inserted and sealed with an insulator 23 interposed between the tube wall 21 and the electrode 3 from the outside of the tube.
[0010]
In the extrapolated form shown in FIG. 7B, the tip of the electrode 3 is formed in a small diameter, inserted into the hole provided in the tube wall 21 and the lining 22 from the outside of the tube, and the tip of the electrode is slightly protruded from the lining 22. Yes. The gap between the tube wall 21 and the electrode 3 is sealed with an insulator 23 interposed from the outside of the tube in the same manner as the flat shape.
[0011]
In the pointed shape shown in FIG. 7C, a flange portion 24 is formed in a portion near the tip of the electrode 3, and the center portion of the flange portion 24 is formed in a pointed shape. An insulating coating 25 is applied except for the pointed electrode portion. Then, the electrode 3 is inserted into the hole provided in the tube wall 21 and the lining 22 from the inside of the tube, the flange portion 24 is brought into contact with the inner wall of the lining 22, and the gap between the tube wall 21 and the electrode 3 is insulated from the outside of the tube. The body 23 is interposed and sealed.
[0012]
As the material of the electrode 3 (3a, 3b), SUS316 is usually used. However, in order to measure the particularly highly corrosive fluid 2, for example, platinum iridium, hastelloy B, hastelloy C, titanium, tantalum, monel, etc. As the lining material, neoprene, polyurethane, natural rubber, tetrafluoroethylene resin, trifluoride ethylene, glass or the like is used depending on conditions.
[0013]
[Problems to be solved by the invention]
As a material for the detection tube 1, conventionally, metals have been generally used as described above, but recently, ceramics having excellent corrosion resistance have been used.
[0014]
The detection tube 1 using the above ceramics is excellent in corrosion resistance, but has a problem that it is difficult to process. For example, when drilling for electrode insertion, the ceramics become very hard if fired after firing, making drilling difficult with a drill. There was a possibility of missing. Furthermore, if an electrode is inserted into an unsintered powder compact, the powder compact may be scraped when the electrode is inserted, resulting in a change in the hole diameter, resulting in gaps between the electrode and chipping after firing. was there.
[0015]
The combination of the ceramic detector tube and platinum (electrode) is excellent in terms of corrosion resistance, but there is still room for improvement in terms of thermal shock, bending strength, and adhesion.
[0016]
The present invention has been made to solve the above-mentioned problems, and is capable of reliably mounting an electrode, and manufacturing a fluid detection tube and a fluid detection tube for an electromagnetic flowmeter that are excellent in thermal shock, bending strength, corrosion resistance, and adhesion. It aims to provide a method.
[0017]
[Means for Solving the Problems]
1st invention is a manufacturing method of the fluid detection tube for electromagnetic flowmeters. The ceramic powder which has an alumina as a main component is compression-molded, The hole for electrode insertion is made in this compression-molded body, and the temperature of 600-1400 degreeC is formed. in calcined, the above electrode insertion hole after calcination by inserting the electrode of platinum or platinum alloy and the sintering at a temperature of 1400-1700 ° C., and said ceramic powder is heat than alumina and said alumina It is characterized in that it has a thermal expansion coefficient close to that of platinum by combining with ceramics having a large expansion coefficient .
[0018]
A second invention is a method of manufacturing a fluid detection tube for an electromagnetic flow meter, wherein a ceramic powder containing alumina as a main component is compression-molded, and a hole for electrode insertion is formed in the compression-molded body at a temperature of 600 to 1400 ° C. , Calcined at the temperature of 1400-1700 ° C. by inserting a platinum or platinum alloy electrode into the electrode insertion hole after the temporary firing , and the ceramic powder is partially stable based on alumina. Zirconia compounded in a range of 30 to 40% .
[0022]
A third invention is, in the fluid sensing tube for an electromagnetic flowmeter, and a platinum electrode, alumina and Sera Miku scan that by combining large Serra Miku scan of thermal expansion coefficient than the alumina and the thermal expansion coefficient close to platinum It consists of the produced tube.
[0023]
A fourth invention, in the fluid sensing tube for an electromagnetic flowmeter, and a platinum electrode, that made of zirconia in the range of 30-40% alumina as the base material and a tube manufactured in Sera Miku scan complexed Features.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0025]
(First embodiment)
FIGS. 1A to 1C show the manufacturing process of the fluid detection tube in the electromagnetic flow meter according to the first embodiment of the present invention. First, as shown in FIG. 1A, a raw powder of high-purity alumina (Al ₂ O ₃ ) is compression-molded, and this powder compact is processed into a schematic structure of the detection tube 30 with a lathe or a drill.
[0026]
Next, the powder molded body processed into the structure of the detection tube 30 is drilled with a drill to form an electrode insertion hole 31. Thereafter, the detection tube 30 is temporarily sintered at a pre-baking temperature of 600 to 1400 ° C., for example, 1000 ° C. to volatilize the binder, and is slightly sintered (hardened). The inner surface and end of the temporary sintered body are polished to improve the flow of the flow path, and then formed in the electrode insertion hole 31 with platinum or a platinum alloy as shown in FIG. The rod-shaped (columnar) electrode 32 is inserted. In this case, the insertion position is adjusted so that the tip of the electrode 32 is flush with the inner surface of the detection tube 30. The electrode insertion hole 31 is set in advance to a value slightly larger than the diameter of the electrode 32.
[0027]
Next, sintering is performed at a main firing temperature of 1400 to 1700 ° C., for example, 1600 ° C., with the electrode 32 inserted into the electrode insertion hole 31 of the detection tube 30 as described above. By performing this sintering process, the electrode insertion hole 31 of the detection tube 30 is narrowed as shown in FIG. 1C, and the outer peripheral surface of the electrode 32 is in close contact with the inner wall of the electrode insertion hole 31 and securely held. Is done. Thereafter, final polishing is performed to complete the detection tube 30.
[0028]
In the electromagnetic flow meter, in order to measure a voltage according to the magnetic field strength, it is necessary to cover at least the inside of the fluid detection tube with an insulator and to contact the electrode 32 for measuring the voltage. As shown in the above embodiment, when ceramic is used for the piping, the thermal expansion coefficient of the piping itself is “1 * 10 ⁻⁵ / ° C.” or less, and the measurement accuracy of the electromagnetic flowmeter is generally on the order of 0.1%. Therefore, the thermal expansion of the piping is hardly a problem and there is no need for temperature correction. Moreover, the corrosion resistance of ceramics is very good.
[0029]
When platinum is used for the electrode 32, the thermal expansion coefficient of platinum is “9 * 10 ⁻⁶ / ° C.”, and the thermal expansion coefficient of ceramics, for example, the thermal expansion coefficient of high-purity alumina is “8 * 10 ⁻⁶ / “° C.”, both of which are close to each other and cannot be a big problem. Moreover, platinum has excellent corrosion resistance.
[0030]
Then, as shown in the first embodiment, the ceramic powder is compression-molded, and the electrode insertion hole 31 is opened in a state where the ceramic powder is processed into the structure of the detection tube 30, so that the electrode is easily drilled. be able to. In addition, the detection tube 30 is temporarily sintered at an arbitrary temperature of 600 to 1400 ° C., and in a slightly hardened state, the electrode 32 is inserted into the slightly larger electrode insertion hole 31, and then the main firing process is performed. Therefore, it is possible to reduce the possibility of the powder molded body being scraped when the electrode is inserted and the occurrence of cracks, and to improve the adhesion between the outer peripheral surface of the electrode 32 and the inner wall of the electrode insertion hole 31.
[0031]
(Second embodiment)
35% of partially stabilized zirconia (ZrO ₂ ) containing 3 mol of yttria is added to alumina (Al ₂ O ₃ ), and the detection tube 30 is completed by the same method as in the first embodiment.
[0032]
The composite sintered body of alumina and zirconia (Al ₂ O ₃ / ZrO ₂ ) is also called zirconia toughened alumina, and alumina (Al ₂ O ₃ ) suppresses the phase transformation of zirconia (ZrO ₂ ) during the sintering process. On the contrary, zirconia slows the grain growth rate of alumina, which acts as a synergy effect and acts on toughening. This is also shown by Ryoichi Shikata, et al. “Evaluation of mechanical properties and structure of high-strength ZrO ₂ —Al ₂ O ₃ composite sintered body”. FIG. 2 is a characteristic curve diagram showing the relationship between the alumina content (% by weight) and the bending strength (MPa) in the alumina / zirconia composite sintered body. In particular, when the addition amount of zirconia is in the range of 30 to 40%, the particle diameter of zirconia gradually approaches 0.2 μm as shown in FIG. FIG. 3 shows the relationship between the alumina content and the particle sizes of alumina and zirconia in an alumina / zirconia composite sintered body. Furthermore, in Ryoichi Shikata and other authors, “Influence of the specific surface area of raw material powder on low temperature thermal degradation of zirconia”, the critical particle size not subject to thermal degradation at low temperature (200 ° C. hot water) is about 0.3 to 0.4 μm. If it is very fine, the corrosion resistance is said to increase. For this reason, the addition amount of zirconia is made 40% or less in the alumina / zirconia composite sintered body so that a grain size of 0.2 μm can be obtained with an allowance and the strength and thermal expansion coefficient can be arbitrarily selected. it is, it is possible to obtain a high strength sera Miku scan sensing tube in consideration of corrosion resistance and thermal expansion coefficient.
[0033]
The zirconia content is desirably 15% or more for the following reason.
The amount of the ceramics (alumina / zirconia composite sintered body) clamped to the electrode 3 is determined from cracks during sintering, but it is about 10 to 20% of the electrode diameter by experience. Adhesion is secured by this tightening. When the ceramics clamps the electrode 3, the internal stress due to plastic deformation is relaxed in a high temperature state, and the residual internal strain can be reduced by slowly cooling after firing. Although depending on the slow cooling conditions, the internal tensile stress is generated when the electrode (platinum) contracts from a certain temperature.
[0034]
For this reason, the temperature under the conditions of use is regarded as a problem. Usually, since an electromagnetic flowmeter is used at 200 degrees C or less at the maximum, the linear expansion coefficient of 0-200 degrees C of ceramics (alumina / zirconia composite sintered compact) is considered. The linear expansion coefficient of platinum is 9.6. FIG. 4 shows the relationship between the zirconia content and the linear expansion coefficient (10 ⁻⁶ / ° C.) of the alumina / zirconia composite sintered body. Curve a is 0 to 100 ° C., curve b is 0 to 200 ° C. A curve c is a characteristic diagram in the case of 0 to 300 ° C.
The difference in coefficient of linear expansion between platinum and ceramics also depends on the strength of the ceramics and the amount of tightening of platinum, but empirical values allow an alumina / zirconia composite sintered body up to about 15%. If the linear expansion coefficient difference is about 20%, the lower limit of the zirconia content is up to about 15%. Considering the variation in shrinkage, the lower limit of the zirconia content is 30%. As described above, the content of zirconia is preferably 15% to 40%, but considering the variation, the content of zirconia is appropriately 30 to 40%. For this reason, in this example, 35% was selected as the zirconia content.
[0035]
(Third embodiment)
75% of zirconia (ZrO ₂ ) containing 3 mol of yttrium is added to alumina (Al ₂ O ₃ ), and the detection tube 30 is completed by the same method as in the first embodiment.
[0036]
As shown in the first embodiment, the pipe portion is made of ceramics and the platinum electrode 32 is used to reduce the occurrence of cracks and eliminate gaps in the electrode portion, and has excellent corrosion resistance. 30 can be configured.
[0037]
However, when the temperature change is large, for example, when the detection tube 30 is rapidly cooled, the thermal shock is repeatedly applied even when the difference in thermal expansion coefficient between the pipe and the electrode is small as described above, and the possibility of cracking increases. Therefore, in the third embodiment, 75% of partially stabilized zirconia is added as a ceramic powder having a thermal expansion coefficient larger than that of alumina to increase the thermal expansion coefficient of alumina. The thermal expansion coefficient of the zirconia is “10 * 10 ⁻⁶ / ° C.”.
[0038]
By adding 75% of partially stabilized zirconia as shown in the third embodiment, the thermal expansion coefficient of alumina can be made close to “9 * 10 ⁻⁶ / ° C.” which is the thermal expansion coefficient of platinum. The difference in thermal expansion coefficient can be almost eliminated. As a result, even when a large temperature change is given to the detection tube 30, damage to the piping can be prevented.
[0039]
(Fourth embodiment)
FIG. 5 shows a main part of the fluid detection tube according to the fourth embodiment of the present invention before temporary firing. In the same manner as in the first embodiment, the raw material powder mainly composed of alumina is compression-molded, and then processed into a schematic structure of the detection tube 30 with a lathe or a drill. Next, the detection tube 30 is drilled with a drill to form an electrode insertion hole 31. Further, the detection tube 30 is temporarily sintered at a temporary firing temperature of 600 to 1400 ° C., for example, a temperature of 1000 ° C., and then the inner surface and end portions thereof are polished.
[0040]
On the other hand, with respect to a rod-like (columnar) electrode 32 formed of platinum or a platinum alloy, alumina 33 is deposited on the outer peripheral surface by 0.001 to 0.005 mm by a vapor deposition method. At this time, the alumina 33 partially creates 0.005 mm thickness unevenness at a pitch of 3 mm, for example. The alumina-deposited electrode 32 is inserted into the electrode insertion hole 31 of the temporarily fired detection tube 30 and sintered at a main firing temperature of 1400 to 1700 ° C., for example, 1600 ° C. By performing this sintering process, the electrode insertion hole 31 of the detection tube 30 is narrowed, and the outer peripheral surface of the electrode 32 is securely held in close contact with the inner wall of the electrode insertion hole 31. Thereafter, final polishing is performed to complete the detection tube 30.
[0041]
As described above, the alumina 33 is vapor-deposited on the outer peripheral surface of the electrode 32 and inserted into the electrode insertion hole 31, and then the sintering process is performed to improve the adhesion between the electrode 32 and the electrode insertion hole 31. In addition, it is possible to reliably prevent the electrode 32 from coming off.
[0042]
【The invention's effect】
As described above in detail, according to the present invention, since the ceramic powder is compression-molded and processed into the structure of the detection tube, the electrode insertion hole is formed, so that the electrode can be easily drilled. be able to. In addition, the compression-molded detection tube is temporarily calcined at an arbitrary temperature of 600 to 1400 ° C., and in a state of being slightly hardened, the electrode is inserted into the electrode insertion hole, and thereafter at a temperature of 1400 to 1700 ° C. Since the main firing process is performed, the possibility that the powder molded body is scraped during electrode insertion and the generation of cracks are reduced, and the adhesion between the outer peripheral surface of the electrode and the inner wall of the electrode insertion hole is improved. Can do.
[0043]
The ceramic powder composing the detection tube is composed of a composite of alumina and ceramic having a higher coefficient of thermal expansion than alumina. For example , by adding partially stabilized zirconia, the thermal expansion coefficient of alumina is changed to that of platinum. Therefore , the difference in thermal expansion coefficient between the ceramics detection tube and the platinum electrode can be almost eliminated, and damage can be prevented even when a large temperature change is given to the detection tube.
In addition, the powder ceramics that compose the detection tube is a composite of aluminum and partially stabilized zirconia in the range of 30 to 40%. The zirconia particles are refined to increase the corrosion resistance, resulting in corrosion resistance and thermal expansion coefficient. It is possible to obtain a high-strength ceramics detection tube in consideration of
[Brief description of the drawings]
FIG. 1 is a process diagram showing a method of manufacturing a fluid detection tube for an electromagnetic flow meter according to a first embodiment of the present invention.
FIG. 2 is a characteristic curve diagram showing the relationship between alumina content, alumina content, and bending strength of an alumina / zirconia composite sintered body in a second embodiment.
FIG. 3 is a characteristic curve diagram showing the relationship between the alumina content of the alumina / zirconia composite sintered body and the particle sizes of alumina and zirconia in the same example.
FIG. 4 is a characteristic diagram showing the relationship between the zirconia content of the alumina / zirconia composite sintered body and the linear expansion coefficient (10 ⁻⁶ / ° C.) in the same example.
FIG. 5 is a view showing a main part of a fluid detection tube according to a fourth embodiment of the present invention before temporary firing.
FIG. 6 is a diagram showing a schematic configuration of an electromagnetic flow meter that is an object of the present invention.
7A to 7C are views showing a cross-sectional structure of an electrode in a conventional fluid detection tube.
[Explanation of symbols]
30 Detection tube 31 Electrode insertion hole 32 Electrode 33 Alumina

Claims (4)

In the method of manufacturing a fluid detection tube for an electromagnetic flow meter, a ceramic powder containing alumina as a main component is compression-molded, and a hole for inserting an electrode is formed in the compression-molded body, and calcined at a temperature of 600 to 1400 ° C. An electrode made of platinum or a platinum alloy is inserted into the electrode insertion hole after the preliminary firing , and the main firing is performed at a temperature of 1400 to 1700 ° C. , and the ceramic powder is composed of alumina and a ceramic having a larger thermal expansion coefficient than the alumina. And a thermal expansion coefficient close to that of platinum . In the method of manufacturing a fluid detection tube for an electromagnetic flow meter, a ceramic powder containing alumina as a main component is compression-molded, and a hole for inserting an electrode is formed in the compression-molded body, and calcined at a temperature of 600 to 1400 ° C. An electrode made of platinum or a platinum alloy is inserted into the electrode insertion hole after the preliminary firing, and is finally fired at a temperature of 1400 to 1700 ° C. The ceramic powder is composed of 30 to 40 partially stabilized zirconia based on alumina. % . A method for producing a fluid detection tube for an electromagnetic flowmeter, characterized by being combined within a range of% . A fluid detection tube for an electromagnetic flow meter comprising a platinum electrode and a tube made of alumina and a ceramic having a thermal expansion coefficient close to that of platinum by combining ceramic and a ceramic having a thermal expansion coefficient larger than that of the alumina . A fluid detection tube for an electromagnetic flow meter comprising a platinum electrode and a tube made of ceramics in which the basic material is alumina and zirconia is combined in a range of 30 to 40% .

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