JPH0610257Y2 - Ceramic electromagnetic flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a ceramics electromagnetic flowmeter having a ceramics measuring tube.

More specifically, the present invention relates to improvement of an electrode portion of a ceramics electromagnetic flowmeter having a ceramics measuring tube.

<Prior Art> FIG. 2 is an explanatory view of a configuration of a conventional example which is generally used in the past.

In the figure, 1 is a cylindrical measuring tube made of ceramics. The measuring tube 1 is, in this case, alumina (Al ₂ O ₃ ).
Is used. Reference numerals 21 and 22 denote columnar cermet electrode portions which are arranged so as to face the measurement tube 1 and which are formed by mixing conductive powder and firing the mixture together with the measurement tube 1.

<Problems to be Solved by the Invention> In such a ceramic electromagnetic flowmeter, if there is a difference in thermal conductivity and thermal expansion coefficient between the measuring tube 1 and the electrode parts 21 and 22, thermal shock is applied to the inner surface of the measuring tube 1. Is applied, a larger stress is generated at the boundary between the measuring tube 1 and the electrode portions 21 and 22 and in the vicinity thereof than in the other inner surface of the measuring tube 1.

For example, alumina _(Al 2 _{O 3)} in the measuring tube 1, platinum and alumina _(Pt-Al 2 _{O 3)} of the cermet of the electrode portion 2
When 1 and 22 are embedded, the coefficient of thermal expansion of alumina 7 to 8 × 10 ⁻⁶ / ° C. <The coefficient of thermal expansion of platinum 8.9 × 10 ⁻⁶ / ° C. Thermal conductivity of alumina 21 (W / m · k) <Since platinum has a thermal conductivity of 72 (W / m · k), the inner surface of the measuring tube 1 is rapidly heated (becomes a thermal shock).
In that case, a large stress is generated at the boundary between the measuring tube 1 and the electrode portions 21 and 22 and in the vicinity thereof due to the difference in thermal conductivity.

Usually plant equipment, especially in the case of food equipment,
Steam cleaning of the piping is often required, for which it must withstand about 150 ° C.

In the conventional example of FIG. 2, when a rapid thermal shock is applied to the inner surface of the measuring tube 1, for example, a thermal shock of about 100 ° C.
A crack is generated in the measuring tube 1 due to the stress generated at the boundary surface between the electrodes 21 and 22.

From the above, there is a problem that a ceramic electromagnetic flowmeter having high thermal shock resistance cannot be obtained.

The present invention solves this problem.

An object of the present invention is to provide an inexpensive ceramics electromagnetic flowmeter having good thermal shock resistance.

<Means for Solving the Problem> In order to achieve this object, the present invention provides a ceramics electromagnetic flowmeter in which a conductive substance is embedded and fired in an electrode portion of a ceramics measuring tube in which a measuring fluid flows. A columnar electrode body made of a composite ceramic powder in which a conductive ceramic powder and an insulating ceramic powder are mixed, and a concentric closed curve provided around the electrode body, and the insulating ceramic powder is electrically conductive from the inner circumference to the outer circumference. Of the conductive ceramic powder mixed so as to lower the thermal conductivity and the insulating ceramic powder of high thermal conductivity mixed such that the thermal conductivity is substantially equal to that of the electrode body from the inner circumference to the outer circumference. An electrode part having a cylindrical buffer body and an insulating ceramic powder are mixed so that the thermal conductivity of the buffer body is substantially equal to that of the buffer body. Is obtained by constituting the ceramic electromagnetic flowmeter characterized by comprising a measuring tube of high thermal conductivity insulating ceramic powder comprising a composite ceramic which.

<Operation> In the above configuration, when the inner surface of the measuring tube is rapidly heated, a large stress may occur at the boundary between the measuring tube and the electrode part and in the vicinity thereof. Since the body is provided, the measuring tube does not break.

<Embodiment> FIG. 1 is an explanatory view of a main part configuration of an embodiment of the present invention.
Is a front view and (B) is a plan view.

In the figure, the same symbols as in FIG. 2 represent the same functions.

1 is made of silicon nitride (Si ₃ N ₄ ) made of insulating ceramic powder having good thermal shock resistance and aluminum nitride (AlN) made of insulating ceramic powder having high thermal conductivity,
A cylindrical measuring tube made of composite ceramics having a required thermal conductivity.

In this case, the volume content is 77.3% of silicon nitride (Si ₃ N ₄ ) and 22.7% of aluminum nitride (AlN).

Reference numeral 3 is an electrode portion including an electrode body 31 and a buffer body 32.

Reference numeral 31 is a columnar electrode body made of a composite ceramic in which a required volume content of a conductive ceramic powder and an insulating ceramic powder are mixed so as to have substantially the same thermal conductivity as that of the measuring tube 1.

In this case, the volume content is 30% of silicon carbide (SiC) made of conductive ceramic powder and 70% of silicon nitride (Si ₃ N ₄ ) made of insulating ceramic powder.

The buffer body 32 includes the first, second and third buffer layers 32.
1, 322, 333, which are provided in a concentric closed curve shape around the electrode body 31, and are mixed with the insulating ceramic powder so that the conductivity decreases from the inner circumference toward the outer circumference. From the outer circumference to the electrode body 31
And a highly heat-conductive insulating ceramic powder mixed so that their thermal conductivity is almost equal to each other.

In this case, silicon nitride (Si ₃ N ₄ ) is used as the insulating ceramic powder, silicon carbide (SiC) is used as the conductive ceramic powder, and aluminum nitride (AlN) is used as the highly thermally conductive insulating ceramic powder.

The first buffer layer 321 is made of silicon carbide (SiC) 20%, aluminum nitride (AlN) 7.6%, and silicon nitride (Si ₃ N ₄ ).
72.4% is used.

The second buffer layer 322 is made of silicon carbide (SiC) 10%, aluminum nitride (AlN) 15.1%, and silicon nitride (Si).
₃ N ₄ ) 74.9% is used.

The third buffer layer 323 is made of silicon carbide (SiC) 5%, aluminum nitride (AlN) 18.9%, and silicon nitride (Si ₃ N ₄ ).
76.1% is used.

Silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), and aluminum nitride (AlN) have the same coefficient of thermal expansion and different thermal conductivity as described below. Can improve thermal shock resistance.

Thermal conductivity of silicon nitride 15 to 20 (W / m · k) Thermal conductivity of silicon carbide 60 to 160 (W / m · k) Thermal conductivity of aluminum nitride 100 to 180 (W / m · k) Silicon nitride Coefficient of thermal expansion of 3-4 × 10 ^-6 / ° C. coefficient of thermal expansion of silicon carbide 4 × 10 ^-6 / ° C. aluminum nitride coefficient of thermal expansion 4-6 × 10 ^-6 / ° C. Now, when the thermal conductivity of each component is calculated, Thermal conductivity of measuring tube 1 45.3 (W / m · k) Thermal conductivity of electrode body 31 45.25 (W / m · k) 321 Thermal conductivity of first buffer layer 45.31 (W / m)・
k) The thermal conductivity of the second buffer layer 322 is 45.25 (W / m ·
k) The thermal conductivity of the third buffer layer 323 is 45.28 (W / m ·
It is almost equal to k).

In the above configuration, even when the inner surface of the measuring tube 1 is rapidly heated, the buffer body 32 is provided around the electrode body 31, so that the thermal conductivity between the measuring tube 1 and the electrode body 31 is high. Are almost equal, and cracks or the like due to the difference in thermal conductivity do not occur.

As a result, generation of stress between the electrode body 31 and the measuring tube 1 is small, and heat resistance can be improved.

As the conductive ceramic powder, silicon carbide (Si
Instead of C), titanium carbide (TiC), tungsten carbide (WC), titanium nitride (TiN), holon carbide (B ₄ C) or the like may be used.

Further, as the high thermal conductive ceramic powder, beryllia (BeO) or the like may be used instead of aluminum nitride (AlN).

<Effects of the Invention> As described above, the present invention is a ceramics electromagnetic flowmeter in which a conductive substance is embedded in the electrode part of a ceramic measuring tube through which a measurement fluid flows and fired. A columnar electrode body made of a composite ceramics powder mixed with ceramics powder and a concentric closed curve provided around the electrode body and mixed with an insulating ceramics powder so that the conductivity decreases from the inner circumference to the outer circumference. And a cylindrical buffer body of a composite ceramics composed of a conductive ceramics powder and an insulating ceramics powder having a high thermal conductivity, which is mixed from the inner circumference to the outer circumference so as to have substantially the same thermal conductivity as the electrode body. Insulating material with high thermal conductivity mixed with insulating ceramic powder so that the thermal conductivity is almost equal to that of the buffer body. It was equipped with a measuring tube of a composite ceramic comprising a ceramic powder composed of ceramic electromagnetic flowmeter according to claim.

As a result, the thermal conductivity of the electrode body and the measuring tube are almost equal, the stress between the electrode body and the measuring tube is small,
The thermal shock resistance can be improved.

Therefore, according to the present invention, it is possible to realize an inexpensive ceramics electromagnetic flowmeter having good thermal shock resistance.

[Brief description of drawings]

FIG. 1 is an explanatory view of a main part configuration of an embodiment of the present invention.
Is a front view, (B) is a plan view, and FIG. 2 is a configuration explanatory view of a conventional example which is generally used in the past. 1 ... Measuring tube, 21, 22 ... Electrode part, 3 ... Electrode, 3
1 ... Electrode body, 32 ... Buffer body, 321 ... First
... buffer layer, 322 ... second buffer layer, 323 ...
… Third buffer layer.

Claims (1)

[Scope of utility model registration request] 1. A ceramic electromagnetic flowmeter in which a conductive substance is embedded in an electrode portion of a ceramic measuring tube through which a measuring fluid flows and baked, and a composite ceramic powder in which a conductive ceramic powder and an insulating ceramic powder are mixed. A columnar electrode body made of, and a conductive ceramic powder mixed in a concentric closed curve around the electrode body with the insulating ceramic powder so that the conductivity decreases from the inner circumference to the outer circumference, and from the inner circumference to the outer circumference. In the insulating ceramic powder, an electrode portion including a cylindrical buffer body of a composite ceramics, which is composed of a high thermal conductivity insulating ceramics powder mixed so that its thermal conductivity is substantially equal to that of the electrode main body. A composite consisting of the above-mentioned buffer body and an insulating ceramic powder having a high thermal conductivity mixed so that the thermal conductivity thereof is almost equal. Ceramic electromagnetic flowmeter characterized by comprising a measuring tube of La mix.