JPH01321326A - Use of thermocouple protective pipe - Google Patents

Abstract

PURPOSE:To reduce thermometric cost and to enhance reliability by setting each of the immersing and taking-out speeds of a protective pipe composed of boride type ceramic with respect to a molten substance to 4m/min or less. CONSTITUTION:A thermometric protective pipe 1 is formed from a protective pipe main body 1a based on a Zr boride, the inner surface oxide layer 1b formed to the inner surface of said main body 1a, the outer vitreous layer 1c applied to the outer surface of said oxide layer 1b and heat-treated, and the ceramic fiber layer 1d applied to the outer surface of the layer 1c. A thermocouple 2, an Al2O3 insulating pipe 3 and an Al2O3 protective pipe 4 are incorporated in the protective pipe 1. When this protective pipe is used in a state inserted in a molten metal, each of the immersing and takng-out speeds thereof is set to 4m/min or less to secure the safety to a crack and cracking breakage due to a heat shock and high reliability is obtained in the response speed and thermometric accuracy of the thermocouple 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of using a temperature measuring protection tube for protecting a temperature measuring sensor that measures the temperature of a molten metal such as a molten metal.

[Prior Art] Conventionally, platinum is commonly used as a method for measuring the temperature of molten metals such as hot metal and molten steel.
It is a consumable thermometer that protects the tip of a rhodium-based thermocouple (hereinafter referred to as B thermocouple) with a quartz tube. Normally, when the thermocouple is immersed in hot metal, molten steel, etc., it takes an extremely short time (10 to 20 seconds).
Before long, the heat-sensitive part would melt and become unusable, so temperature measurements had to be completed in a short period of time, and the thermocouple had to be replaced after each measurement. For this reason, it is difficult to control quality and operation, and the temperature measurement cost is high, so there is a strong desire for a thermometer that can measure temperature continuously for a long time. Mo, ZrB
Thermocouple protection tubes such as a are provided.

[Problems to be solved by the invention] However, in the case of thermometers using these protective tubes, when continuously measuring the temperature of hot metal or molten steel, oxidation and corrosion resistance during preheating and temperature measurement during charging are significant. At worst, the lifespan is short because the protection tube is eroded after about 2 to 20 hours.

Also, when pouring into molten metal, Zr02-M□, A1.0
3-Thermocouple protection tubes using protective tubes such as C and BN have high thermal shock resistance, so they are used without sufficient preheating, but they are weak in strength, easily oxidized, and have low corrosion resistance. In this respect, there are few that can withstand temperature measurement for a sufficiently long period of time.

However, recently, boride-based ceramics have been provided as a preferred material for such protective tubes, that is, as having excellent corrosion resistance against molten metals, sufficient strength, heat resistance, and thermal conductivity. In particular, Zr1la best satisfies the material conditions described above and can be said to be a preferable material to which the present invention is applied.

However, boride ceramics have lower toughness and thermal shock resistance than ordinary metals, so they are difficult to measure when measuring high temperatures of molten metal, especially when the protective tube is suddenly immersed in the molten metal at an overall high temperature. However, there is a problem that thermal shock can cause cracks and shorten the lifespan due to breakage compared to when temperature measurements are taken continuously over a long period of time.There is a strong demand for technology that can stably measure temperatures over a long period of time even during such intermittent temperature measurement. It was rare.

[Means for Solving the Problems] The present invention has been made to solve the problems mentioned in 1'rlj, and it is possible to install a temperature sensor in a protective tube mainly composed of a boride such as Z'13□. Use of a thermocouple protection tube characterized by "IT" that reduces the immersion and removal speed of the protection tube into and out of molten material such as molten metal to 4 m/min or less when measuring the temperature of hot water continuously or intermittently while protecting the temperature. It is about the method.

The present invention will be explained below with reference to the drawings. FIG. 1 is a sectional view illustrating a preferred configuration of a protection tube used in the present invention.

Although various shapes and configurations 7 can be applied to the protective tube used in the present invention, the protective tube 1 of the present invention as a desirable typical example is a linear protective tube whose main component is Zr boride or the like. This protective tube is made up of an oxide layer 1b formed on the inner surface of a main body 1a, a vitreous layer film 1c coated and heat-treated on the outer surface, and an inorganic fiber layer 1d coated on the outer surface.

Inside this protective tube, there is a +1j thermocouple 2, an A1□03 insulation tube 3, and an A1□0. ! A protection tube 4 is incorporated and used. By inserting this protective tube 1 into molten metal, the device becomes capable of measuring temperature changes of the molten metal continuously or intermittently.

The method of the present invention will be explained below by taking such a protection tube as an example, but even if only the protection tube body 1a is used, it can be used under almost the same conditions as long as the wood is made of boride. is applicable.

Main body below! The protection tube 1 consisting of a, lb, lc, and Id will be further explained. In the present invention, the main body 1a is made of a non-oxide ceramic sintered body, and is mainly made of borides such as Zr[32 (zirconium diboride) and/or TiB2 (titanium diboride) from the viewpoint of high-temperature corrosion resistance against molten metal. It is best to use it as an ingredient.

A suitable boride sinter is as follows.

・The main component is boride of composition Zr, and SiC and I as subcomponents.
Those containing IN caps, for example, ZrB295-70 in weight%
%, SiC 1-15%, IIN4-29%, etc.

・Physical properties Bulk specific gravity 30-60 Breaking strength 10 kg/mm2 or more Coefficient of thermal expansion 0.6% or less (+000°C) Specific resistance 1
Thermal shock resistance (ΔT1
250 to 1000℃ Thermal shock resistance refers to the processing temperature at which the bending strength of the sample was measured after being rapidly heated to each temperature for 5 minutes in an electric furnace and rapidly cooled in water, and the strength suddenly decreased (△T 'C).

Specific resistance is f1500, which is the value measured at high temperature using the 4-terminal method.
°C) Ω・cm.

As the non-oxide sintered body in the present invention, 7. r
B In addition to the Z series, Tirlz series can also be used, but they are inferior in that they have lower corrosion resistance to slag and molten metal at high temperatures than the ZrB2 series, and for example, the TiB2 series has poor oxidation resistance. I can't deny it.

Next, an oxide layer 1b preferably formed on the inner surface
To explain, this oxide layer is as described above (, Zr
Prevents disconnection by reducing reducing gas that is thought to be generated due to non-oxide bodies such as the 82 layer.
It is necessary to form a stable oxide layer in order to obtain L.

It is desirable that this oxide layer 1b be integral with the main body 1a and as dense as possible. In order to be integral, it is desirable to use an oxide formed by oxidizing the metal component constituting the main body 1a, and in the case of ZrB2, this is a ZrO□ layer. Furthermore, in order to create a denser layer, it is desirable to use a film layer that includes SiO* components, since ZrO□ alone is somewhat brittle and may not be able to fully demonstrate the characteristics of ZrB* in terms of long-term durability. .

Considering the manufacturing method of the protective tube, it is preferable that this 5iOa component is produced by the oxidation of SiC contained as a metal component of the main body la, and from this point of view, Z
It can be said that it is preferable to use a material in which an SiC component, which serves as a Si source, is added as a separate component to the rBa-based main body.

Such an oxide layer containing ZrOz and/or Sin has a ZrL content of 50 to 10% by weight in terms of their mutual component ratios.
0%, Sin□ is about 0 to 50%, preferably Zr0
Z is about 90 to 70%, Sin, and power cylinder is about 30%.

Further, although this oxide layer has a certain effect even if it is thin, the thickness is preferably 30 μm or more, and the preferable range is about 50 to 500 μm.

A preferred method of manufacturing such a protection tube will be explained.

As mentioned above, it is preferable that the protective tube consists of an oxide layer formed integrally with the boride body, so it is preferable to oxidize a part of the boride body to form an oxide layer on the surface, that is, the inner surface. , this is a gas containing oxygen (
This can be done by heat-treating the protective tube itself in the presence of air (usually air is sufficient).

Specifically, the inner surface of the boride protective tube is generally heated to 1000°C.
Air may be actively introduced into the pipe while being heat-treated at the above temperature for about 1 to 5 hours.

By doing this, for example, the material of the protection tube body can be made of Si.
If it is a ZrB2-based product containing C, Zr and S on the surface
i is oxidized to form an oxide layer consisting of ZrO++ and SiO□.

Furthermore, it was confirmed that due to the formation of this oxide film, the deterioration or disconnection of the thermocouple over a long period of time is not dependent on the operating conditions, and continuous temperature measurement of the molten metal can be carried out stably. Also, due to the formation of this oxide film, there is no reaction between the A1□0° protection tube and the ZrBa protection tube at high temperatures (there is no welding, so the Al2O5 protection tube can be easily removed, and the Al20a protection tube can be reused). is also accepted.

Next, the glassy layer IC will be explained.

When such a protective tube containing a boride such as Zr as a main component is thrown into the molten metal, it is sufficiently preheated before being thrown into the molten metal because it has low thermal shock resistance. However, although the ZrBz protective tube has a certain degree of oxidation resistance, it gradually oxidizes when preheated for a long time, and becomes oxides of ZrO□, BJs, and 5iOa, and the oxidized structure becomes porous. B2O3 will scatter, but if the outer surface of the protective tube made of this porous composition is poured into the molten metal, it will be easily eroded, reducing the thickness of the protective tube and shortening its service life. It is preferable to prevent the outer surface layer of the ZrRg protective tube from forming during this preheating, and it is desirable that the protective tube used in the present invention also be provided with a vitreous layer for this purpose.

This glassy layer 1c will be specifically explained below.

This vitreous layer can be made of any material as long as it does not allow air to pass through, but it is desirable that it can be easily vitrified by heat treatment and has fire resistance at the same time. Something like this is appropriate.

・Physical properties of the glassy layer When treated at 1000℃ for 3 hours, the oxidation consumption rate of the ZrB material body is less than 1%, the oxidized thickness is less than 100μ, the softening point is more than 2000℃・The thickness of the glassy layer, softening Point 500 to 2000μ, softening point 7200°C or higher, Composition that gives a glassy quality. A coating material made of a vitrified refractory powder as a vitrified material and made into a slurry with a binder.

For example, the proportions of both are 50 to 85% by weight of refractory powder and 50 to 15% by weight of vitrified material.

Refractory powders include Al2O, powder, viscous powder, vitrified materials include p-plate glass powder, anhydrous borax, etc. This protective tube is made by coating the outer surface of the protective tube body with such refractory powders and vitrified materials in the form of a slurry. This is obtained by heat-treating this in an electric furnace at a temperature of 500°C or higher, preferably about 800 to 1200°C to form a vitrified film. This vitrified film is poured into the molten metal during preheating of the 11th edition, forming a glass film that does not allow air to pass through, so the ZrB2 protective tube will not be oxidized, and even if it is poured into the molten metal, the vitrified film will melt, but Since it is not oxidized, the dense composition and characteristics of ZrB2 can be exhibited as they are. This vitrified film also serves to alleviate thermal shock when the ZrB1 protective tube is rapidly heated and cooled. In addition, the ZrB2 protective tube has the ability to resist molten metal, but due to the formation of this vitrified film, a moderate amount of slag and base metal are present during immersion in hot water, resulting in thermal shock caused by rapid cooling during pulling. In other words, by forming this glass film, we can prevent oxidation and provide a highly durable thermocouple protection tube that is resistant to cracking and alleviates thermal shock resistance. This makes it easy to do so.

Next, the inorganic fiber layer 1d, such as ceramic fiber, as a desirable embodiment disposed on the outer surface of the protective tube body will be described.

As mentioned above, due to the non-oxide main body 1a such as ZrBz, when it is poured into a molten metal and the temperature rises and falls repeatedly, especially when the temperature drops from a high temperature range, the inside of the ceramic body 1a is often in the range of 500 to 600°C. Fine cracks occur in the structure of the ceramic, and if they are noticeable, they may lead to cracking of the entire ceramic. The cause of this is not clear, but it seems to be due to rapid changes in the coefficient of thermal expansion, oxidation properties, Young's modulus, etc.

However, when measuring the temperature of hot metal or molten steel in a blast furnace or continuous casting equipment, temperature measurement must be interrupted after each tap of pig iron is tapped and each liter of cast is cast. In many cases, the protection tube breaks at a time when Fd is faster than I.

In order to prevent this, the outer surface of the protective tube main body 1a is coated with an inorganic fiber layer 1d, so that the protective tube main body 121 remains stable without breaking even if the temperature repeatedly rises and falls intermittently. This makes it possible to easily measure temperature.

When the protective tube coated with this fibrous layer 1d is introduced into the molten metal and when it is removed from high temperature (for each tap of iron or I cast), this fibrous layer 1d is exposed to heat tit shock. It becomes a relaxation layer and easily shrinks with molten steel, forming an adhesion coat of slag and base metal during temperature measurement, and when cooling the protection tube, it is rapidly cooled and kept warm without 1. This prevents breakage.

This inorganic fiber layer 1d needs to be as heat resistant as possible in order to protect the protection tube main body 1a from thermal shock and thermal stress, so it is necessary to be an inorganic fiber, and in particular, the melting point It is preferable that the layer be a fibrous layer mainly composed of ceramic fibers with a temperature of 1400° C. or higher. In addition, as part of the fibrous material, clay, j! ! <Of course, there is no problem even if it contains organic light particles.

Hereinafter, a preferred embodiment of the ceramic fiber layer will be specifically explained by taking an example.

That is, a desirable ceramic fiber layer is Alz03
A blanket or sheet-like material mainly composed of -3iO□-based silica-based, zirconia-based, or alumina-based ceramic fibers, or a cylindrical molded object formed with an inorganic binder is suitable.

A suitable ceramic fiber layer is as follows.

・Composition A1□0s-3iOz fiber as main component, for example, Al2O, 40-55%, Si0□ 60-45% ・Physical properties Fiber specific gravity 2.5-6.0 g/am2 average fiber system
2.0~15.0μm Bulk Specific gravity 0.05~0.3 g/
cm3 thermal conductivity 0.1-0.4 kal/m, h
, °C (aL 1000 °C) Specifically, a ceramic fiber layer 1d having the above-mentioned composition is coated on the entire outer surface of the protective tube body 1a to a thickness of 5 to 50 °C.
The protective tube 1 is manufactured by covering the protective tube to a thickness of about 50 mm, preferably 20 to 30 mm. If it is in the form of a blanket or sheet, tie it in several places with wire to secure it. In some cases, the coating can also be applied by spraying.

Note that this coating layer 1d is desirably formed continuously over almost the entire outer circumference of the main body 1a, but of course the upper part of the main body 1a may be omitted depending on the purpose, but the radiation from the molten metal is also severe, It is preferable to form it over the entire outer periphery in order to protect 1a and metal fittings.

A desirable embodiment of the thermocouple protection tube I manufactured as described above is used in the apparatus shown in FIG. FIG. 2 will be explained below.

The thermocouple protection tube 1 is set at 600° in the heat insulation box 11 when measuring temperature.
After being sufficiently preheated with a heating burner 7 to a temperature of 1,000 to +20 degrees Celsius or above, it is placed into a tundish pot 9 using a discharging device 8 equipped with a guide rail 1o.

In this case, the temperature responsiveness, response speed, and temperature measurement accuracy of the temperature sensing thermocouple 2 when immersed in the molten metal of the thermocouple protection tube 1 are very important from the perspective of the reliability of the measured temperature. be.

The shape and thickness of the main body 1a of the thermocouple 1 capture tube 1, the AIzOi protection tube 4, etc. in FIG. 1 affect the temperature measurement accuracy response of -2. For example, Δ1□0. -The main body of the C-tube thermocouple protection tube is made of aluminum with a diameter of 4゜φmm, an inner diameter of 20φmm, and a wall thickness of 10φmm.
The 2O3 protection tube is 42m long to protect thermocouples from deterioration in reducing atmosphere.
They are used in three layers, and the response and temperature measurement accuracy are said to be slow and low. In order to provide a thermocouple protection tube with high responsiveness and temperature measurement accuracy, we conducted various studies and found that the structure shown in Figure 1 has a boride-based main body with a diameter of 25 mm, an inner diameter of 15 mm, and a wall thickness. 5 mm (appropriately, the wall thickness is about 3 to 8 mm). The dimensions and thickness are determined by the purpose of responsiveness, temperature measurement accuracy, and relaxation of thermal stress in the main body.

Figure 3 shows the relationship between thermal shock cracking and cracking when the thermocouple protection tube 1 shown in Figure 1 is immersed in molten metal and removed using the temperature measuring device shown in Figure 2. The temperature difference between the preheating temperature of No. 11 (that is, the temperature of the protective tube 1) and the molten metal temperature and the immersion removal speed are shown.

It is necessary to preheat the thermocouple protection tube as high as possible in order to alleviate thermal shock, but in reality, a heat insulating box is rarely installed, and it is preferable to use radiation preheating in a tundish pot or preheating with a burner, etc. In many cases, preheating to 1200°C or higher is difficult in terms of equipment.

As shown in Figure 3, if the preheating temperature is low, it is necessary to slow down the immersion and removal speeds sufficiently; if the preheating temperature is high, r7L
Although this is possible at a speed of 4 m/min or less, safety against cracking, cracking, and breakage due to thermal shock is ensured, and the response speed and temperature measurement accuracy of the thermocouple 2 are also highly reliable. At the preheating temperature and immersion removal speed in the dangerous area shown in Fig. 3, cracks and breakage of the protective tube l occur, the responsiveness of the thermometer 2,
It was also found that the reliability of temperature measurement accuracy was poor.

As can be seen from Figure 3, the desirable aspects are as follows, and in the case of boride-based protection tubes, there are almost no practical problems with the protection tubes, and this is due to the shape, wall thickness, etc. It can be applied as a common usable condition almost regardless of the situation.

That is, at any preheating temperature, the immersion and removal speed of the molten metal is required to be 4 m/min or less, and preferably 1 m/min if the difference between the preheating temperature and the molten metal temperature is 550°C or higher. It should be about the following.

This is because if the temperature difference is 550°C or less, a certain degree of reliability can be maintained even if the immersion or removal speed is relatively high, and even if this is the case, if the temperature difference is 550°C or more, sufficient reliability is maintained. This is because reliability will no longer be obtained, so the speed must be reduced.

Generally, the relationship between the difference between the preheating temperature and the molten metal temperature and the speed can be understood as follows.

In a boride-based protective tube whose main component is Zr 112,
Thermal shock resistance improves to zrBz-sic composite T-250~
300°C, ZrB, -BN-SiC composite system, △T=5
00 to 600°C1, and although it is difficult for the value of ΔT (°C) to match the actual temperature of molten steel when it is immersed in or taken out, the trend can be predicted sufficiently (in actual temperature measurements, molten steel and (It is not simple as the slag adheres to the protective tube and forms a protective layer.) That is, when measuring molten steel at about 1550°C, in the ZrBa-3iC system, unless the preheating temperature is about 1200°C, △T will exceed 250 to 300°C (for example, the molten steel temperature is 1550°C),
At a preheating temperature of 1000℃, the temperature difference is 500 to 600℃.
become. In this case, only ZrL-3iC system and △T =
If 250 to 300°C is used as a guideline, preheating and insulating at 1200°C is necessary, and sufficient reliability can be obtained at a speed of 4 m/min or less.

At 1000°C, the temperature difference becomes large, so it is necessary to slow down the speed to 05 m/min or less to prevent temperature distribution in the protection tube.

Note that the immersion and extraction means can be easily adjusted mechanically using normally preset automated equipment.

[Example] 10% of BN powder (1μ or less, purity 99% or more) was added to ZrB2 powder (1μ or less, purity 99% or more), and SiC
Using a Botmill with a ball and using ethanol solvent 3 +
: After being pulverized for J3 and taken out, an organic binder was added using a spray dryer and the product was granulated.

Using this powder, 2000 kg/c was produced using a rubber press.
A protective tube with an inner diameter of 15 φ, an outer diameter of 25 φ, and a length of 850 mm was manufactured by molding the tube at 2100°C for 3 hours in an Ar atmosphere. (Analysis value of the sintered body: ZrBg 85%.

8810%, SiC5%, Ichikawa%) Also, ZrBz powder (less than lμ, purity 99% or more) was
It was ground using a C ball to obtain a powder. After rubber pressing this powder, it is fired under normal pressure to create an inner diameter of 15φ and an outer diameter of 25φ.
A protection tube with a length of 850 mm°C was manufactured. (Analysis values of sintered body: Zr11295%, SiC5%, weight%) This protective tube contains 50% A1□03 powder (150 mesh passes), 20% temporary glass powder, and 15% clay as a binder.
A mixture of 5% anhydrous borax and a 3% PVA solution was mixed in a bot mill to obtain a slurry, which was applied to the outer surface of the protective tube body and dried.

This protective tube was placed in an electric furnace and gradually heated to 12DO"C.
The inner surface was forcibly oxidized by introducing air from the inlet of the protective tube body for 2 hours, and a glass tube coating layer was formed on the outer surface of the protective tube body (inner surface oxide layer 100μ, outer surface vitreous coating layer 1mm). (formed thickness). Inside this protection tube, a thermocouple (A1□03 insulation tube is placed in JIS-Bl)
A thermocouple protection tube was manufactured by incorporating the inner part of the 03 protection tube. The outer surface of this protective tube was covered with a blanket (bulk density 0.128 g/cm3) of alumina-silica fiber (trade name: Chikara Owl +400) to a thickness of 30 mm and fixed with a wire (analytical value of the fiber A1□0. 47.3
%SiC52,3%, heavy electric %). Using this protection tube, 4
The temperature was measured using a heat-retaining furnace in an on-tandish pot at 0 t. 1,200 yen with the heating burner type heat insulating box shown in Figure 2.
Heat at ℃ and pour into molten steel at 2 m/min and 4 m/min.
immersed at a speed of The temperature was measured 25 times for each casting, and the temperature of the protective tube was repeatedly raised and lowered, and the temperature was successfully measured within a total of 0 hours. The measured temperature value is 11 degrees higher than that of a consumable type immersion thermocouple, and the response is quick within 1 to 2 minutes, and it has been confirmed that temperature can be measured without damage such as cracks in the protective tube. Ta. Note that the melt w4 temperature was 1550°C on average.

When the immersion speed in molten steel was 5 m/min and the preheating temperature was 1200°C, temperature measurement was repeated 5 times each, resulting in intermittent temperature measurement for a total of 30 hours, but occasionally during 26 to 27 hours, An abnormal value was observed in the temperature measurement, so when it was taken out and examined 30 hours later, cracks were found and some molten steel had entered the inside of the protection tube, which is thought to be the reason why the temperature measurement abnormality was detected. .

Also, even at a preheating temperature of 1000°C, it is 0.5 m/m
Immersion and removal were repeated at a speed of 1 m/min, but at a speed of 1 m/min, the temperature was measured intermittently for 18 hours after every 3 castings, but the temperature was already in the protective tube. Damage occurred, and the measured temperature was unstable at 3:00 p.m. At a speed of 0.5 m/min, the temperature could be normally measured for 85 hours by repeated intermittent temperature measurements 20 times each, and the accuracy and responsiveness of the measured temperature were also normal.

[Effects of the Invention] As described above, according to the method of the present invention, the temperature of molten metal can be measured stably for a long period of time, so the cost of temperature measurement is reduced and the reliability of the thermometer is improved [1].

By using this, labor saving due to automated line,
It has great industrial value as it helps improve product quality, reduce costs, and save labor by adjusting hot water temperature, preparing ingredients, and predicting troubles.

[Brief explanation of the drawing]

FIG. 1 is an explanatory longitudinal cross-sectional view illustrating the Q-shaped side of the glue according to the present invention. 1...Temperature measuring cap, 1a...Main body, 1b...
・Inner surface oxide layer, IC...Outer surface glassy layer, 1d・
... Ceramic fiber layer, 2... Thermocouple,
3...A120i insulation tube, 4...A1□03 protection tube, 5...fixing metal fittings, 6...terminal box Figure 2 is a schematic diagram explaining the usage situation of the temperature measurement protection tube of the present invention. It is a diagram. I...Protection tube for temperature measurement, 7...Heating burner, 8.
・・Gastric excretion device, 9・Tandish pot, IO
. . . Guide rail, 11 . . Heat insulation box FIG. 3 is an explanatory diagram showing the relationship between the difference between the preheating temperature and the molten metal temperature of the temperature measuring protection tube of the present invention and the immersion removal speed. The danger in the figure indicates that there is a high possibility that damage to the protection tube will occur due to thermal stress if the immersion/removal rate exceeds this range. Safe means that if the immersion/removal speed is within this range, the protection tube will be less damaged and can withstand long-term adiabatic temperature measurement. i no IIZ

Claims (1)

[Claims] (1) When measuring the temperature of the molten material while protecting the temperature sensor with a protection tube made of boride-based ceramics, the immersion and/or removal speed of the protection tube into the molten material should be set at 4 m/min.
A method of using a thermocouple protection tube, which is characterized by a thermocouple protection tube of less than 1 minute.