JPS6146767B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for non-contact temperature measurement of tubular objects. When performing heat treatment such as quenching or tempering after forming a tubular object, such as a seamless steel pipe, the temperature of the steel pipe is measured in the heat treatment furnace to reach a predetermined set temperature, and the amount of combustion gas and time in the furnace are measured. need to be controlled. Possible methods for measuring the temperature of steel pipes in a heat treatment furnace include a method in which a thermocouple or the like is brought into direct contact with the steel pipe, and a non-contact method in which a radiometer (or radiation thermometer) is used. Measurement methods using contact sensors such as thermocouples require a device mechanism to properly contact the sensor with the steel pipe, and the high temperature inside the heat treatment furnace poses problems in protecting and deteriorating the sensor and device mechanism. Furthermore, when the steel pipe moves, it is often difficult to measure the temperature by contact method. On the other hand, if a transmission window is installed in a part of the furnace wall and the radiant energy from the steel pipe is guided to a radiometer (or radiation thermometer), it is possible to measure the temperature of the steel pipe without contact. The currently used method has the following problems, making accurate measurement difficult in practice. FIG. 1 shows a conceptual diagram of a conventional method for measuring steel pipe temperature. A steel pipe 1 is placed inside a heat treatment furnace 5, and a radiometer 3 detects the radiant energy from a measurement point 2 on the steel pipe through a transmission window 4 provided in a part of the furnace wall to measure the temperature of the steel pipe. do. however,
In addition to the problem of changes in the emissivity of steel pipes, in heat treatment furnaces used industrially, the temperature of the inner wall of the furnace is generally higher than the temperature of the steel pipe, and the radiation emitted from the inner wall of the furnace is higher than that of the steel pipe. Radiant energy is reflected at the measurement point 2, and the magnitude of the noise component 10 detected by the radiometer 3 is not negligible compared to the magnitude of the radiation component 9 from the steel pipe itself detected by the radiometer 3. can be the value of
In such a case, accurate temperature measurement cannot be expected. In addition, coke gas or the like may be burned in the furnace to heat the steel pipe, and in that case, the radiant energy from the combustion flame 6 becomes an extremely large noise component 11, making it impossible to expect accurate temperature measurement. That is, in the conventional temperature measuring method, the radiant energy signal E detected by the radiometer 3 is expressed by the following equation. E=ε・Eb(T)+E'...(1) However, E: Detection signal of the radiometer T: Temperature of the steel pipe Eb(T): Blackbody radiant energy at temperature T ε: Emissivity of the surface of the steel pipe E': Noise signal components from the furnace inner wall, flame, etc. Therefore, in general industrial heat treatment furnaces where ε and E' are considered to be variable or unknown, accurate temperature measurement using conventional methods is extremely difficult. be. The present invention relates to a radiation thermometry method that solves such problems in radiation thermometry, namely changes in emissivity and the presence of noise, and accurately measures the temperature of steel pipes in a heat treatment furnace. FIG. 2 shows an overview of the measurement method according to the present invention. A steel pipe 1 is placed inside a heat treatment furnace 5 having an effective temperature Tn, and is heated to a temperature T. A measurement point 2 inside the steel pipe is measured with a radiometer 3 through a transmission window 4 provided in a part of the furnace wall. The detection value E of the radiometer at this time is given by the following equation. E=εaBb(T)+(1-εa)Eb(Tn)...(2) However, εa in the first term on the right side is the effective emissivity of measurement point 2, including the contribution from the entire inner surface of the steel pipe. , the second term is the noise signal component from the furnace inner wall.
In addition, εa is the material of the pipe, the geometrical condition in Fig. 2,
It is a function of θ, L/D, a/D, etc., and the relationship between εa and these conditions is shown in FIGS. 3 and 4.
Here, θ is the angle between the line connecting the measurement point and the radiometer and the surface normal N set at the measurement point. Further, L is the length of the tubular object from the measurement point to the end opposite to the radiometer side, D is the pipe diameter, and a is the length from the end of the tubular object on the radiometer side to the measurement point. The detection element of the radiometer is a silicon (Si) element, and its detection wavelength is 1 μm. The sample to be measured was a steel pipe. As is clear from Figures 3 and 4, L/D,
The larger a/D is, the larger εa becomes, and if θ is set appropriately, the temperature of the steel pipe can be measured under εa1, that is, under conditions that can be considered to be almost a black body cavity. That is, according to the present invention, the temperature of a steel pipe can be accurately measured regardless of changes in emissivity or the presence of noise signals. For seamless steel pipes and electric resistance welded pipes, L/D is about 100, so even if the conditions of θ and a/D are set roughly, it is possible to create a state where εa = 1. Therefore, the method according to the present invention is not easy. However, it is a very effective method of measuring temperature. Also, even if L/D cannot be large, a/
By setting D and θ appropriately, εa can be made sufficiently large, and the noise component (1-εa) Eb (Tn)
can be made smaller. Note that the energy input to the radiometer reflects multiple times on the inner surface of the tubular object, and the closer it reaches the radiometer, the closer it becomes to the blackbody cavity condition. Therefore, if the temperature Tn of the furnace wall, the temperature T of the steel pipe, and the allowable temperature measurement error ΔT are given, the minimum necessary value of εa, εa=εamin, can be found using equation (2), and then θ, a/D, The L/D conditions can be determined using FIGS. 3 and 4. When actually measuring a tubular object, the direction in which the measurement point is measured by the radiometer 3 is mirror-symmetric with respect to the normal N drawn to the measurement point 2 as shown in FIG. If the angle θ of the radiometer is set so that the inner surface of the tubular object lies on the line of direction, it can be set to approximately εa1, and disturbance noise from the inner wall 5 of the heat treatment furnace etc. can be prevented. This is D.
This can be achieved by selecting θ such that tanθ<L. FIG. 6 shows an example of measurement according to the present invention. The seamless steel pipe 1 is charged into the heating furnace, and the radiometer 3
Measurement point 2 on the inner surface of the steel pipe was measured. Also,
The temperatures at measurement point 2 and point 5 on the inner wall of the furnace on the opposite side of the radiometer on the central axis of the steel tube were measured by embedding thermocouples. The radiometer uses a Si cell detection element with a detection wavelength of 0.65 μm, and εa =
Measured as 1.0. The inner diameter of the steel pipe was D = 50 mm, and the length L = 1000 mm. Also, the position of the measurement point is a
= 50mm. The angle θ was set to 75°. At this time, D・tanθ=50×tan75゜=187mm and D・tanθ
The condition <L is fully satisfied. Measurement results first
Shown in the table. As can be seen in Table 1, even when the temperature on the inner wall of the furnace is much higher than the temperature at the measurement point, the measurement error ΔT = Ta - T is within about 10°C, which is similar to the radiation temperature measurement in industrial furnaces. This is a very small error value.

[Table] As described above, according to the present invention, it is possible to accurately measure the temperature of a tubular object regardless of surrounding disturbances, and the temperature can always be measured within the allowable temperature measurement error range. It is clear that the present invention can be applied to temperature measurement of not only seamless steel pipes but also pipe-like objects of any shape and material in general. Furthermore, the present invention is particularly effective when the object to be measured is inside the furnace and is moving, and of course it is possible to more easily measure objects outside the furnace or at rest.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an example of a conventionally used measurement method, Fig. 2 is an explanatory diagram showing the principle of the present invention,
3 and 4 are diagrams showing the relationship between emissivity and dimensions (length, diameter) of a tubular object in the present invention,
FIGS. 5 and 6 are explanatory diagrams showing an example of measuring the inner surface temperature of a steel pipe according to the present invention. In the drawing, 1 is a tubular object, 2 is a measurement point, 3 is a radiometer, N is a normal line, and 5 is a heat treatment furnace.

Claims (1)

[Claims] 1. A measurement point is provided on the inner surface of a tubular object, a radiometer is directed to the measurement point from outside the tubular object, and the angle formed between the normal line erected to the measurement point and the pointing direction of the radiometer. θ
A method for measuring temperature of a tubular object, characterized in that the angle θ is set so that a mirror-symmetrical direction exists on the inner surface of the tubular object. 2. A method for measuring the temperature of a tubular object according to claim 1, wherein the temperature is measured while the tubular object is in a furnace such as a heat treatment furnace. 3. A method for measuring the temperature of a tubular object according to claim 1, characterized in that the temperature is measured while the tubular object is moving.