JPH0567162B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ceramic electromagnetic flowmeter having a measuring tube made of ceramics.

More specifically, the present invention relates to a method of manufacturing a measuring tube for a ceramic electromagnetic flowmeter.

(Prior Art) The conventional technology will be explained using FIGS. 3 to 6. In the following description, descriptions of parts other than the measurement tube, such as the excitation coil and core of the electromagnetic flowmeter, will be omitted because they are not characteristic parts of the present invention.

In FIG. 3, reference numeral 10 indicates a ceramic measuring tube through which the fluid to be measured flows. The measurement tube 10 has a cylindrical shape, and a fluid to be measured flows inside. A pair of electrodes 11 and 12 are formed in the center of the measuring tube 10 and are exposed inside. The electrodes 11 and 12 are formed by partially dispersing conductive ceramic or metal fine powder and sintering it into one body with the ceramic of the measuring tube 10.
The outer surface of the measuring tube 10 has a large wall thickness at both ends, and has a thick wall portion 1 for easy sealing with the mating pipe.
3 and 14 are formed.

Next, a method for manufacturing the measuring tube shown in FIG. 3 will be explained using FIGS. 4 and 5.

Reference numerals 15 and 16 indicate disc-shaped metal lids, and counterbore holes 18 and 19 are provided in the center thereof, respectively, so that a cylindrical metal core 17 can be inserted thereinto. 20 is a cylindrical rubber mold; lids 15 and 16;
It is adapted to fit into notches 21 and 22 formed on the peripheral edge of.

Hereinafter, the steps of manufacturing the measuring tube will be explained in order.

First, the core 17 is fitted into the counterbore 19 of the lower lid 16, and the temporary molded bodies 23 and 24, which are formed by temporarily molding conductive fine powder into a cylindrical shape, are adhered to the center of the core 17 using an adhesive or the like. In this case, the temporary compacts 23 and 24 may be a mixture of ceramic powder made of the same material as the measuring tube and conductive fine powder in an appropriate ratio.

Next, the rubber mold 20 is fitted into the lower lid 16 and ceramic powder 25 is filled from above, and the upper lid 15 is fitted into the core 17 and the rubber mold 20.

After that, hydrostatic pressure P is applied from the outside of the rubber mold 20, and the temporary molded bodies 23, 24 and the ceramic powder 25 are
and are integrally molded.

The measuring tube molded in this way is the fifth
The shape shown in the figure is obtained, which is cut as shown in FIG. 3 and then sintered at a predetermined temperature.

(Problems to be Solved by the Invention) However, such conventional ceramic measuring tubes have the following drawbacks.

This will be explained using the enlarged view shown in FIG.
The hydrostatic pressure P is applied to the filled ceramics 25 via the rubber mold 20, but the pre-formed body 24 is compressed by the surrounding ceramic powder 25.
Since it is difficult to deform compared to the ceramic powder 25, a large frictional force is generated between the ceramic powder 25 and the ceramic powder 25 on its side surface. The pressures P ₁ and P ₂ that have been propagated through the ceramic powder 25 due to this frictional force are gradually attenuated, and the core 1
Pressure is no longer sufficiently propagated to the X and Y portions near 7. For this reason, the molding density of the X and Y portions is lower than that of other portions, and the porosity increases even after sintering, or minute cracks occur due to the difference in shrinkage rate during sintering.

In this way, if there are minute cracks or areas with high porosity near the liquid contact side of the electrode,
During use, stress is generated due to an increase in the internal pressure of the measuring tube, for example, and cracks grow from this point, resulting in deterioration of airtight performance or damage to the measuring tube.

In addition, since the electrode temporary molded bodies 23 and 24 are made of compacted powder, they have low strength and are made of ceramic powder 2.
5 may break due to the load applied during filling, resulting in poor yield.

Further, since the electrode temporary molded bodies 23 and 24 have low strength, it is difficult to reduce the electrode diameter. Therefore, it is difficult to embed thin electrodes for micro-diameter electromagnetic pipes with small inner diameters, for example, for inner diameters of 2.5φ.

There were various problems as described above.

The present invention solves this problem.

An object of the present invention is to provide a method for manufacturing a ceramic measuring tube having highly reliable electrodes with a high yield.

(Means for solving the problem) In order to achieve this object, the present invention involves inserting a pipe perpendicularly to a predetermined position of a columnar rubber mold for molding a ceramic measuring tube, and inserting a conductive material into the pipe. Fine powder or a mixture of ceramic powder of the same material as the measuring tube and conductive fine powder in an appropriate ratio is either in a powder state or after forming a temporary molded body at a pressure sufficiently lower than the molding pressure of the measuring tube. ,
A method of manufacturing a ceramic electromagnetic flowmeter is carried out in which the rubber mold is filled with ceramic powder, the pipe is pulled out, the pipe is integrally formed, cut into a predetermined shape, and then integrally fired.

(Function) With this structure, the embedded conductive fine powder can be deformed to the same extent as the surrounding ceramic powder, and no large frictional force is generated at the boundary.
Areas with low molding density are less likely to form around the area.

Since the embedded conductive fine powder is protected by the pipe, it will not break when filling the ceramic powder.

Since the embedded conductive fine powder does not require strength, the electrode diameter can be made smaller.

Hereinafter, a detailed explanation will be given based on examples.

(Example) FIG. 1 is an explanatory diagram of an embodiment of the present invention.

In the figure, the same symbols as in FIG. 4 indicate the same functions.

Hereinafter, only the differences from FIG. 4 will be explained.

A pipe 27 having a thinner wall than the hole 29 provided in the rubber mold 20 is inserted so that its end is in contact with the core 17. A conductive fine powder 26 (which may be a mixture of ceramic powder made of the same material as the measuring tube 10 and conductive fine powder in an appropriate ratio) is further filled with ceramic powder 25 in a portion longer than the required length. and is held down by a rod 28 from the outside.

In this state, ceramic powder 25 is filled into the rubber mold 20 from above, and the upper lid 15 is fitted into the core 17 and the rubber mold 20.

After that, with the rod 28 fixed, the tube 2
7 is pulled out, and after that, the rod 28 is pulled out, the hole 29 is covered with a rubber screw 30, and the molding is performed by hydrostatic pressure P. After cutting this as shown in FIG. 3, it is sintered at a predetermined temperature.

If they are integrally molded using the method described above, the embedded conductive fine powder 26 can be easily deformed just like the surrounding ceramic powder 25, so a large frictional force will not be generated at the boundary. Non-uniform areas of molding density do not occur.

Furthermore, since the conductive fine powder 26 is protected by the pipe 27 during filling with the ceramic powder 25, there is no fear that it will break, unlike when the temporary molded bodies 23, 24 are bonded to the core 17.

Furthermore, by reducing the diameter of the pipe 27, it is also possible to reduce the electrode diameter.

Note that the conductive fine powder to be inserted into the pipe 27 is not in a complete powder state, and even if it is temporarily molded at a pressure sufficiently lower than the main molding pressure P (for example, about P/10), the same result will occur. Effects can be obtained.

(Effects of the Invention) As explained above, the present invention involves inserting a pipe orthogonally to a predetermined position of a columnar rubber mold for molding a ceramic measuring tube, and inserting conductive fine powder or measuring tube into the pipe. A mixture of ceramic powder of the same material and conductive fine powder in an appropriate ratio is formed into a powder state or a temporary molded body at a pressure sufficiently lower than the molding pressure of the measuring tube, and then placed in the rubber mold. After filling the pipe with ceramic powder and pulling it out, it is molded into one piece and cut into a predetermined shape.
Since we have implemented a manufacturing method for a ceramic electromagnetic flowmeter that is integrally fired, there is no large frictional force between the conductive fine powder and the ceramic powder.
It is difficult to form areas with low molding density around the electrode, making it possible to realize an electrode with high reliability.

Since the embedded conductive fine powder is protected by the pipe, it will not break when filling the ceramic powder, improving yield.

Since the embedded conductive fine powder does not require strength, the electrode diameter can be made smaller. Therefore, it is possible to embed electrodes in a measuring tube for a micro-diameter electromagnetic flowmeter.

Therefore, according to the present invention, it is possible to realize a method of manufacturing a ceramic measuring tube having highly reliable electrodes with a high yield.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams of an embodiment of the present invention,
FIG. 3 is a longitudinal sectional view showing the configuration of a conventional ceramic electromagnetic flowmeter, and FIG. FIG. 5 is a longitudinal sectional view showing a molded body formed by the manufacturing apparatus shown in FIG. 4, and FIG. 6 is a longitudinal sectional view of the molded body illustrating problems with the molded body shown in FIG. 5. 10... Measuring tube, 11, 12... Electrode, 15,
16... Lid, 17... Core, 20... Rubber mold, 2
3, 24... Temporary molded body, 25... Ceramics powder, 26... Conductive powder, 27... Pipe, 28
...rod, 29...hole, 30...rubber.

Claims (1)

[Claims] 1. Insert a pipe perpendicularly to a predetermined position of a columnar rubber mold for molding a ceramic measuring tube, and fill the pipe with conductive fine powder or ceramic powder made of the same material as the measuring tube and conductive fine powder. After forming a temporary molded body by mixing the mixture in powder form or at a pressure sufficiently lower than the molding pressure of the measuring tube, the rubber mold is filled with ceramic powder, and after the pipe is pulled out, A method of manufacturing a ceramic electromagnetic flowmeter, which is formed by molding, cutting into a predetermined shape, and then firing it as a unit.