JPH0269627A - Protective tube for thermocouple - Google Patents

Abstract

PURPOSE:To improve the durability of a protective tube for thermocouple by making a fiber layer wound around the outer periphery of the tubular body of the tube more flexible compared with the tubular body and a refractory layer formed on the outer periphery of the tubular body and composed of fine powder of refractories and larger-size particles of refractories so that the fiber layer can work as a cushion against the contraction stress caused by a heat shock and adhesion of slag. CONSTITUTION:A thermocouple is inserted into the tubular body 1 of a protective tube for thermocouple which is used when the temperature of a high- temperature of molten metal, etc., is measured with the thermocouple after the front end of the body 1 is hermetically sealed and a fiber layer 6 used refractory fibers as a base material is wound around the body 1. Then a refractory layer 3 constituted by alternately laminated layers of fine powder 4 of refractories and layers of larger-size particles 5 of refractories is formed on the outer peripheral surface of the layer 6. The fiber layer 6 is made more flexible than the refractory layer 3 so that the layer 6 can work as a cushion material against contraction stress.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermocouple protection tube used when measuring the temperature of a high-temperature liquid such as molten metal with a thermocouple.

[Prior Art] Thermocouples such as platinum-platinum rhodium or alumel-chromel are widely used to measure the temperature of high-temperature liquids such as molten metals or other high-temperature gases.

In order to maintain the contacts of these thermocouples at the same temperature as the object to be measured when measuring temperature, the contacts must be immersed in high-temperature liquid or exposed to high-temperature gas. However, when the bare wires of these thermocouples are brought into contact with the object to be measured, they are subject to oxidation, erosion, and contamination by molten metal and slag, resulting in severe physical and chemical deterioration and an extremely short lifespan. . Therefore, the contact portion of the thermocouple is usually housed in a protection tube.

Metal tubes are often used as protection tubes for thermocouples, but metal protection tubes lack heat resistance, especially when the temperature to be measured is high-temperature molten metal such as iron or nickel. Therefore, non-metallic protection tubes are used.

[Problem to be solved by the invention] When it is desired to continuously measure the temperature of high-temperature molten metal such as iron-based molten metal or nickel-based molten metal, it is necessary to protect zirconia or recrystallized alumina, etc., which have a high maximum operating temperature. It is necessary to use a tube. However, when using these protective tubes, if they are not sufficiently preheated before use, they may crack due to heat shock when immersed in molten metal, or cracks may occur when the protective tube is removed from molten metal. The drawback was that the shrinkage stress caused by the cooling of the slag adhering to the periphery of the protective tube could cause it to crack, making it difficult to reuse the protective tube.

One method for solving the above problems is to form a refractory layer on the surface of the protective tube. That is, on the outer periphery of a cylindrical body made of ceramic such as recrystallized alumina or mullite, a refractory layer is formed by depositing a slurry of II Km large-sized powder and large-diameter refractory particles alternately several times. This is a thermocouple protection tube.

However, even in the above-mentioned proposal in which a refractory layer is formed on the surface (hereinafter referred to as coated protection tube), there are several problems as described below.

a) If the material of the V&fine refractory particles and large-diameter refractory particles to be attached to the outer periphery of the protection tube is not very high in fire resistance, such as zircon or mullite, 80%
It is necessary to bake the coated protective tube at 0°C or higher to strengthen the bonds between large and small refractories, or to preheat the coated protective tube to 500°C or higher just before immersion in the molten metal, which increases operating costs. are doing.

b) If a refractory such as zirconia, which has a higher refractoriness than the zircon or mullite used in a), is used, α
Although there is no need for firing or preheating as described in ), the cost of using zirconia is higher than that of other low-grade refractories.

C) Even if a refractory with a high degree of fire resistance is used, the number of times the refractory is applied (the number of layers) must be increased considerably, which is disadvantageous in terms of time and material cost.

The present invention has been made in view of the above-mentioned problems of conventional coated protective tubes, and uses a refractory layer that is made of low-grade refractory material and has a reduced number of adhesion layers, and is better than conventional coated protective tubes. The purpose of the present invention is to provide a protective tube for thermocouples with excellent durability.

[Means for Solving the Problems] The thermocouple protection tube of the present invention includes a cylindrical body whose tip is sealed and into which a thermocouple can be inserted, and a fire-resistant fiber wrapped around the outer periphery of the cylindrical body. and a refractory layer formed on the surface of the fiber layer by alternately laminating fine refractory powder layers and large refractory particle layers.

The cylindrical body whose tip is sealed and into which a thermocouple can be inserted is made of ceramics such as recrystallized alumina or mullite, which have been conventionally used as protective tube materials. The refractory fibers wound around the outer periphery of the cylindrical body may be of any type as long as they are made of refractory ceramic fibers that can withstand temperatures of 1000° C. or higher.

In addition, the shape of the refractory fiber may be in the form of a fiber, or may be in the form of a sheet or ribbon, as long as it can be wrapped around the outer periphery of a cylindrical body to form a delamination layer. good.

As the fine refractory powder and large-diameter refractory particles forming the refractory layer, it is desirable to use one or more selected from zircon, high alumina, mullite, and zirconia. Fine refractory powder is 50-500
The particle size is within the range of mesh, and the slurry is made using colloidal silica or ethyl silicate hydrolyzate as a binder. This slurry of fine refractory powder and 01
Large-diameter refractory particles having a particle size in the range of ~2+61 mm are alternately deposited on the fiber layer in multiple layers.

It is desirable that the formed refractory layer be fired at a temperature of 600°C or higher. Since it is more flexible than a refractory layer made of refractory particles, it acts as a cushioning material against shrinkage stress due to heat shock and adhesion of slag, increasing durability.

Moreover, since the fiber layer itself has fire resistance, it is possible to reduce the number of laminated refractory layers.

[Example] A preferred example of the present invention will be described below based on the drawings.

1 is a longitudinal cross-sectional view of one embodiment of the present invention, FIG. 2 is a cross-sectional view of the embodiment of FIG. 1, and FIG. 3 is a partially enlarged view of FIG. 1. Cylindrical body 1 has an outer diameter of 13 m+n, an inner diameter of 9 Inm, and a length of 5
It is a tube with a sealed tip and is made of remelted alumina. A sheet made of fire-resistant fiber (Kao Wool Ace Paper manufactured by Isolite Bevcock, 2,5+n+nl!) is wrapped once around the outer periphery of the cylindrical body as a separation layer 6.

The fine refractory particles 4 constituting the refractory layer 3 are selected from among zircon, high alumina sand, light, and zirconia. It is a powder with a particle size of 200 to 400 mesh. Further, the large-diameter refractory particles 5 constituting the refractory layer 3 are selected from zircon, high alumina sand, porcelain, and zirconia, and have a particle size of 0.3 to 1.5 m.
m particles.

The fine refractory particles 4 are made into a slurry using colloidal silica with a 10% SiO2 concentration as a binder, and the slurry consisting of the fine refractory particles 4 and large-diameter refractory particles 5 are alternately placed on the fiber layer 6 in four layers. Alternatively, the refractory layer 3 is formed by depositing six layers.

Some of the protective tubes in which the fiber layer 6 and the refractory layer 3 are formed on the cylindrical body 1 have a diameter of 900 mm.
It was subjected to baking treatment at ℃ for 1 hour.

For comparison, a coated protection tube was also prepared. Figure 4 is a longitudinal cross-sectional view of a conventional coated protective tube.
5UA is a cross-sectional view of the 411A tabulation tube, 6I71
FIG. 1 is a partially enlarged sectional view of FIG. 4th [21st to 6th
As is clear from r3, the coated protective tube of the ratio I bite was produced by the same method as the method of the present invention except that the fiber layer 6 was not formed, and some of the tubes were subjected to firing 3 times.

Regarding the protective tube of the present invention example prepared as described above and the IX protective tube of the comparative example, the molten metal erosion resistance (
Erosion resistance) and heat 1R impact resistance were tested.

That is, each protective tube was immersed for 24 hours in a molten stainless steel cast steel equivalent to JIS 5C313 maintained at 1400 to 1450°C, and its melt damage was examined.

In addition, each protective tube was preheated to 500° C. and immersed in the molten metal at 1400 to 1450° C. The presence or absence of cracks due to heat cracks was examined for each protective tube. Furthermore, after preheating each 1'R3ff tube to 1000°C, it was immersed in the molten metal maintained at L -100 to 1450°C for 8 hours, taken out from the molten metal, left to cool, and then heated again for 100°C.
The number of times the protective tube could be used repeatedly was investigated by repeating the cycle of preheating to 00°C, immersing it in the molten metal for 8 hours as described above, taking it out and letting it cool. The evaluation results are shown in Table 1 for the present invention examples and in Table 2 for the comparative examples, along with the IP formation conditions of each protection tube.

The evaluation method here is to prepare three protective tubes for each planning item that were created under the same conditions, and mark the amount of erosion loss as ○ if almost no erosion was observed, and indicate that it cannot be replaced again. The case where the melting loss was severe was evaluated by the mark "X", and the case in between was marked by the mark "Δ". Also,
Regarding cracking due to heat cracking, the marks were ○ if no cracks occurred in any of the three trees, Δ marks if cracks occurred in one or two trees, and X marks if the three favorite parts were cracked. In addition, the number of times that can be used repeatedly is the average of the three trees.

However, this repeat test was repeated only up to 5 times.

As is clear from the first person and the second No. 7, in the thermocouple IZ protection tubes (No. 1 to 16) of the examples of the present invention, the patterned R refractories forming the refractory layer are Although there are differences depending on the type of refractory and large-diameter refractory particles, JΔ number, and presence or absence of firing, none of them form a fiber flf layer. It was confirmed that the thermocouple protection tube of the present invention is less likely to crack due to heat shock and can be used repeatedly, and the durability of the protection tube is significantly improved.2 [Effects of the Invention] The thermocouple protection tube of the present invention This is a significant improvement in the durability and corrosion resistance of the protective tube compared to conventional coatings (protective tubes), which improves the durability of the protective tube and increases the service life and number of times the protective tube can be used. Effects can be obtained.

In addition, the thermocouple 1'A protection tube according to the present invention can be made by winding a fiber layer made of fire-resistant fiber and cutting it by one inch.
The layer acts as a cushioning material against the shrinkage stress caused by heat shock and slag build-up, increasing durability, allowing the use of relatively low-grade, low-cost ceramics for the cylindrical body, and making it fire-resistant. As for the fine refractory powder and large-diameter refractory particles that form the material layer, it is possible to use relatively low-grade and low-cost refractories. Furthermore, it is possible to reduce the number of times the fine refractory powder and large-diameter refractory particles that form the refractory layer are laminated, and therefore the overall cost does not increase, making it possible to manufacture thermocouple protection tubes at low cost. .

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of one embodiment of the present invention, and FIG.
3 is a partially enlarged sectional view of 111N, FIG. 4 is a vertical sectional view of a conventional coated protection tube, and FIG. 5 is a cross sectional view of the protection tube shown in FIG. 4. FIG. 6 is a partially enlarged sectional view of FIG. 4. 1 - Cylindrical body, 3 - Refractory layer, 4 Fine refractory powder, 5 - Large diameter refractory particles, 6 - Fiber H1 layer Figure 1 Figure 2

Claims (1)

[Claims] (1) A cylindrical body whose tip is sealed and into which a thermocouple can be inserted, a fiber layer made of refractory fibers wrapped around the outer periphery of the cylindrical body, a fine refractory powder layer, and large refractory particles. 1. A protective tube for a thermocouple, comprising a refractory layer formed on the surface of the fibrous layer, the layer being alternately laminated.