阅读说明：本技术 热电偶绝缘材料防吸潮的高温封接材料及其制备方法 (Thermocouple insulating material moisture absorption preventing high-temperature sealing material and preparation method thereof ) 是由 王晓春 蒲健 冯江涛 池波 于 2021-09-26 设计创作，主要内容包括：本发明涉及热电偶的技术领域,尤其涉及一种热电偶绝缘材料防吸潮的高温封接材料及其制备方法。包括离子键和共价键共存的混合键体系的玻璃微粉,粘结剂材料。高温玻璃封接材料软化温度与粘流温度均高于现有环氧树脂的可靠工作温度,可有效改善高温状态下氧化镁由于吸潮而降低绝缘电阻值。高温玻璃密封材料在600～( o)C以上工作,部分析晶的状态使之在其内部形成均匀分散的陶瓷相以提供封接材料支撑力,外部低粘度的玻璃使之与热电偶其他材料包括填充材料氧化镁粉体及不锈钢套管紧密结合,提高其与界面间的浸润性与密封性。高温玻璃封接材料可以通过后期的热处理工艺使之适度析晶,形成玻璃-陶瓷复合材料,进一步提高玻璃陶瓷封接材料的强度与可靠性。(The invention relates to the technical field of thermocouples, in particular to a high-temperature sealing material for preventing thermocouple insulating materials from absorbing moisture and a preparation method thereof. The glass powder comprises glass micropowder of a mixed bond system with coexisting ionic bonds and covalent bonds and a binder material. The softening temperature and the viscous flow temperature of the high-temperature glass sealing material are both higher than the reliable working temperature of the existing epoxy resin, and the insulation resistance value of the magnesium oxide can be effectively reduced due to moisture absorption under the high-temperature state. High temperature glass sealing material at 600 o And C, working above, forming a uniformly dispersed ceramic phase in the glass in a partially crystallized state to provide a sealing material supporting force, and tightly combining the glass with low viscosity at the outer part with other materials of the thermocouple, including filling material magnesium oxide powder and a stainless steel sleeve, so that the wettability and the sealing property between the glass and an interface are improved. High temperature glassThe sealing material can be properly crystallized through a later heat treatment process to form a glass-ceramic composite material, so that the strength and the reliability of the glass-ceramic sealing material are further improved.)

1. The high temperature sealing material for preventing thermocouple insulating material from absorbing moisture is characterized by comprising glass micropowder of a mixed bond system with coexisting ionic bond and covalent bond and a binder material.

2. The thermocouple insulating material moisture absorption resistant high temperature sealing material of claim 1, wherein the glass micropowder is a solid particle having a size of 5 to 8 μm and a coefficient of thermal expansion CTE of 10.3 x 10^-6 K^-1。

3. The thermocouple insulating material moisture absorption preventing high temperature sealing material according to claim 1, wherein the glass fine powder is SiO₂CaO-MgO system.

4. The method for preparing a high-temperature sealing material for preventing moisture absorption of a thermocouple insulating material according to claim 1, wherein the preparation method comprises the following steps:

step one, uniformly mixing glass micropowder and terpineol;

step two, grinding the mixed powder in the step one by using an agate mortar to be finer;

and step three, respectively weighing the mixed powder with the medium weight in the step two, placing the mixed powder into a tablet press, and respectively pressing and molding to prepare the sealing material block.

And step four, penetrating the thermocouple wire into the block sealing material obtained in the step three, then penetrating a thermocouple wire and block sealing material combination into a stainless steel sleeve, and connecting the thermocouple wire and the block sealing material combination with a compensating lead at the tail of the probe and then heating at a high temperature.

5. The method for preparing a high-temperature sealing material for preventing moisture absorption of a thermocouple insulating material according to claim 4, wherein the method comprises the following steps: the pressure molding process is an extrusion, filling or injection process to obtain a block with a length-diameter ratio.

Technical Field

The invention relates to a sealing material, in particular to a high-temperature sealing material for preventing thermocouple insulating materials from absorbing moisture and a preparation method thereof.

Background

The thermocouple is a sensing device which directly converts heat energy into an electric signal and outputs a direct current voltage signal to realize rapid display, record and transmission of temperature data. The working principle is that the electromotive force generated by the temperature difference between the thermocouple wire normal temperature environment (cold end for short) and the temperature measuring port of the test object environment (hot end for short) is calculated through the thermoelectric effect linear relation, and then the temperature value of the detected object is obtained. The thermocouple is widely used by various industries due to the characteristics of simple assembly, convenient replacement, good shock resistance, high measurement precision, fast thermal response, good pressure resistance and the like. At present, the structures of the thermocouples mainly comprise two types of standard thermocouples and non-standard thermocouples. The standard thermocouple mainly comprises a thermocouple wire, an insulating filling material, a high-temperature sealing material, a protective sleeve and a junction box, the test temperature is between 0 and 1800 ℃, and the dual functions of sealing and moisture prevention are realized between the thermocouple wire and a thermocouple probe tail compensation lead by applying the high-temperature sealing material. In addition, the sealing material also needs to have the characteristics of resistance wire obstruction, thermal stress absorption, moisture resistance, low manufacturing cost, high reliability and the like.

At present, the sealing materials of the thermocouple are mainly divided into two types, namely epoxy resin and glass powder. Due to the chemical activity of the epoxy group, the epoxy resin can be subjected to ring opening by using a plurality of compounds containing active hydrogen, is cured and crosslinked to generate a network structure, is a thermosetting resin, has the unique advantages of high insulating property, large structural strength, good sealing property and the like, and is widely applied to the insulating and packaging process of conventional thermocouples and electronic components. Epoxy resin is a sealing material which is used in a thermocouple at present. However, since the epoxy resin is a high molecular polymer, the temperature resistance is poor, and the working temperature range is-40 to 245 ℃, so that the working temperature range of the thermocouple is narrow and has large limitation. In addition, when the tail end of the thermocouple probe is encapsulated by epoxy resin, the air leakage phenomenon is easy to occur, so that the filling material magnesium oxide is prone to moisture absorption and failure, the product is scrapped or reworked, and the product yield is reduced.

Disclosure of Invention

The invention aims to solve the defects and provides a high-temperature sealing material for preventing moisture absorption of a thermocouple insulating material and a preparation method thereof.

In order to overcome the defects in the background art, the technical scheme adopted by the invention for solving the technical problems is as follows: the high-temperature sealing material for preventing the thermocouple insulating material from absorbing moisture comprises glass micropowder of a mixed bond system coexisting with ionic bonds and covalent bonds and a binder material.

According to another embodiment of the present invention, it is further included that the glass micropowder is solid particles having a size of 5 to 8 μm and a coefficient of thermal expansion CTE of 10.3X 10^-6 K^-1。

According to another embodiment of the present invention, further comprising the glass micropowder is SiO₂CaO-MgO system.

A method for preparing a high-temperature sealing material for preventing thermocouple insulating material from absorbing moisture,

step one, uniformly mixing glass micropowder and terpineol according to a certain mass ratio;

step two, grinding the mixed powder in the step one by using an agate mortar to be finer;

and step three, respectively weighing the mixed powder with the medium weight in the step two, placing the mixed powder into a tablet press, and respectively pressing and molding to prepare the sealing material block.

And step four, penetrating the thermocouple wire into the block sealing material obtained in the step three, then penetrating a thermocouple wire and block sealing material combination into a stainless steel sleeve, and connecting the thermocouple wire and the block sealing material combination with a compensating lead at the tail of the probe and then heating at a high temperature.

According to another embodiment of the present invention, the pressure molding process is extrusion, filling or injection to obtain the block with the aspect ratio.

The invention has the beneficial effects that: the glass of the high-temperature sealing material for preventing the thermocouple insulating material from absorbing moisture belongs to a thermodynamically metastable phase, is high-temperature resistant and easy to flow, has good sealing performance, prevents moisture absorption, is simple to prepare, and has low cost, so the glass powder is considered to be the better high-temperature sealing material for preventing the thermocouple insulating material from absorbing moisture. Four important performance criteria need to be considered when selecting glass sealing materials: glass transition temperature T_gGlass softening temperature T_sAnd the coefficient of thermal expansion CTE and the glass particle size. The inherent property of glass is that the glass tends to be transformed (crystallized) into a more stable crystalline phase under a long-term high-temperature condition, so that the change of volume, thermal expansion coefficient, internal stress and the like can be brought, and the service life of the glass is shortened. Therefore, the crystallization process of the glass can be controlled through a proper heat treatment process, so that the glass ceramic composite sealing material is formed to have certain high-temperature strength and is not easy to break and fail under the bending use condition. In addition, the glass transition temperature T is due to the glass frit_gGlass softening temperature T_sThe flowing property and the crystallinity of the glass can be influenced, so that the glass for thermocouple high-temperature sealing can be prepared by regulating and controlling the components, is favorable for gas to escape and has certain supporting force. The granularity of the glass needs to be controlled within a certain range, so that the glass can be extruded into a block more easily and then gas can be ensured to escape completely during sintering, and the prepared glass block sealing material can enlarge the sealing space of glass powder and provide conditions for the flow of the glass powder; on the other hand, glass powder with larger particle size will also inhibit the devitrification behavior of the glass to some extent. The thermal expansion coefficient of the glass is adjusted to be as close as possible to that of the stainless steel sleeve of the thermocouple, so that the thermal stress generated by the sealing material in the working process of the thermocouple can be effectively reduced, and the stability and the reliability of the cold-hot circulation of the sealing material are further ensured. The glass sealing material formed by extrusion molding is used as a high-temperature sealing material of the thermocouple, and has good infiltration effect with the filling material magnesium oxide powder and the armored stainless steel sleeve. By adjusting the glass at a later stageThe glass heat treatment process promotes the glass to be properly crystallized to form the glass-ceramic composite sealing material, and can improve the properties of the glass-based sealing material, such as strength, high-temperature insulation, structural stability, interface sealing property, reliability and the like. The glass sealing material and the sealing method have the advantages of low cost, simple preparation and stable and reliable quality, and are suitable for industrialized batch preparation.

Drawings

The invention is further illustrated with reference to the following figures and examples.

FIG. 1 is a schematic structural view of an armored thermocouple;

FIG. 2 is a schematic view of the structure within the metal casing of FIG. 1;

FIG. 3 is a microscopic topography of the glass;

FIG. 4 is a graph showing the variation of the gas leakage rate of the glass sealing material with temperature at different operating temperatures;

FIG. 5 is a TEM image of the glass after high temperature treatment;

wherein: the protection device comprises a protection device, a thermocouple, a compensation lead wire, a glass sealing material, a sealing plug, an upper sleeve, a hexagonal seat, a main sleeve, a metal sleeve, a thermocouple wire, a magnesium oxide insulation filling powder, a metal sleeve, a thermocouple wire, a metal sleeve, a thermocouple wire, a glass sealing material, a sealing plug, a metal sleeve, a thermocouple wire, a magnesium oxide insulation filling powder, a metal sleeve, a thermocouple wire, a metal sleeve and a protection device.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the high-temperature working state of the thermocouple, the glass micro powder boundary is softened and flows, and the high-viscosity glass liquid-phase film can infiltrate the magnesium oxide filling powder and the surface of the ferrite stainless steel sleeve, so that good interface connection and sealing are realized, and the air tightness of the glass sealing material is improved. In addition, the glass component in the glass micro powder sealing material generates crystallization phenomenon under the working state to form a glass-ceramic composite material, which has certain high-temperature strength, is not easy to break and lose efficacy under the bending use condition, and improves the strength and reliability of the glass sealing material. The softened glass facilitates uniform deformation of the integrity of the sheathed thermocouple.

In order to obtain a material having the above structure, the present invention can obtain by this method: glass micro powder is added, and because the selected glass can be softened at the working temperature of the thermocouple, the glass powder bodies are tightly combined with each other under the action of external pressure, so that the fracture energy of the sealing material is improved; on the other hand, the bond energy of the covalent bond and the ionic bond in the glass is large, and the bonding strength between the glass and the ceramic particles is improved, so that the mechanical property of the material is further improved. The glass sealing material can be prepared by adjusting the glass components to seal the tail end of the thermocouple probe, so that the phenomenon that the insulation resistance is reduced due to moisture absorption of magnesium oxide powder caused by the failure of glass sealing is avoided.

Weighing a certain mass of glass micropowder and terpineol, uniformly mixing and grinding the glass micropowder and the terpineol in an agate mortar, then weighing the mixed powder with the same weight, putting the mixed powder in a tablet press, pressing and forming to prepare a sealing material block, finally penetrating a thermocouple wire into the glass sealing material block, and putting the block in a metal sleeve for heat treatment and drawing.

The thermocouple insulating material moisture absorption preventing high-temperature sealing material combines the advantages of a glass-based sealing material and a ceramic-based sealing material, can effectively reduce the air leakage rate of the sealing material, improves the high-temperature mechanical property of the sealing material, and further provides an excellent sealing effect.

The glass micropowder is a compound of ionic bonds and polar covalent bonds, and molten glass and crystalline glass simultaneously have ionic bonds and polar covalent bonds to form a three-dimensional space developed frame structure, so that the characteristics of high viscosity and high mechanical strength of the glass are determined. Therefore, the glass micropowder is used as a moisture absorption-proof high-temperature sealing material of the thermocouple insulating material, and has high insulativity and sealing property in the process from low temperature to high temperature. In addition, in the atomic crystal, the melting point of a substance is inversely proportional to the atomic radius and the bond length, and the shorter the covalent bond is, the larger the bond energy is, the more difficult the bond energy is to break, so that the melting point of the glass can be kept by adjusting the components of the glass to effectively seal the tail end of the thermocouple probe, and the phenomenon that the insulation resistance is reduced due to moisture absorption of magnesium oxide powder caused by the sealing failure of the glass is avoided.

At the working temperature of the thermocouple, the glass micro powder is partially sintered and softened, so that the glass powder is tightly combined, and the softened glass is continuously promoted to move and block an air leakage channel of the sealing material under the action of thermal stress. The glass powder improves the sealing performance of the sealing material and enhances the rheological capability of the sealing material to a certain extent. In addition, the glass softening temperature is about 600 ℃, the initial viscous flow temperature is about 700 ℃, and the magnesium oxide powder and the stainless steel sleeve have good infiltration effect.

Wherein the glass micropowder is solid particles with the size of 5-8 μm and the coefficient of thermal expansion CTE of 10.3 x 10 < -6 > K < -1 >.

Wherein the glass micro powder is a SiO2-CaO-MgO system. The SiO2-CaO-MgO glass sealing material has good thermal expansion coefficient matching with the adjacent components in the thermocouple. From room temperature to 750 ℃, the glass has a coefficient of thermal expansion of about 10.3X 10-6K-1, which is similar to the 13.8X 10-6K-1 of MgO powdered and 12.5X 10-6K-1 of ferritic stainless steel, and is effective in mitigating thermal stress concentrations and thus interface gas leakage caused by thermal expansion mismatch between adjacent components. In addition, the glass powder can be pressed into a round glass block with two thermocouple wire holes, then the round glass block is placed at the sealing position of a thermocouple, and the sealing and glass crystallization processes are completed under a certain heat treatment system.

The preparation method of the high-temperature sealing material for preventing the thermocouple insulating material from absorbing moisture comprises the following steps:

step one, uniformly mixing glass micropowder and terpineol according to a certain mass ratio;

step two, grinding the mixed powder in the step one by using an agate mortar to be finer;

and step three, respectively weighing the mixed powder with the medium weight in the step two, placing the mixed powder into a tablet press, and respectively pressing and molding to prepare the sealing material block.

And step four, penetrating the thermocouple wire into the block sealing material obtained in the step three, then penetrating a thermocouple wire and block sealing material combination into a stainless steel sleeve, and connecting the thermocouple wire and the block sealing material combination with a compensating lead at the tail of the probe and then heating at a high temperature. After the high-temperature glass sealing work is finished, the high-temperature glass can be properly crystallized through a later-stage glass heat treatment process to form a glass-ceramic composite material, so that the glass-ceramic composite material has certain high-temperature strength, is not easy to break and lose efficacy under the bending use condition, and improves the strength and reliability of the glass sealing material.

Wherein, the compression molding process is extrusion, filling or injection process to obtain the block with the length-diameter ratio. The extrusion forming process has the best effect.

Examples

FIG. 1 is a schematic structural view of an armored thermocouple showing the shapes and relative positions of glass sealing material, wire and ferritic stainless steel sleeve according to the present invention. The armored thermocouple is formed by thermocouple metal wire, ceramic filling material, glass sealing material and alloy sleeve, the glass sealing material is used for sealing between magnesium oxide powder and a ferrite stainless steel sleeve, and then proper heat treatment process is applied to draw and produce armored thermocouples with different specifications. The reliability and the insulation of the magnesium oxide powder in the armored thermocouple can be ensured by taking the glass micro powder as the sealing material.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.