JPS6322525B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wall thickness measuring device for a tubular material that can measure the average wall thickness of a tubular material in a non-contact manner.

Generally, in the manufacturing (rolling) process of tubular materials in the steel industry, when controlling the wall thickness, highly accurate wall thickness measurement is required. In addition, in order to increase productivity, without stopping the manufacturing flow process,
It is important to be able to measure wall thickness online, and in hot processes where tubular materials reach high temperatures, it is not only possible to measure without contact, but also from a position as far away from the tubular material as possible. It is desired that

FIG. 1 shows an outline of the configuration of a conventional tubular material thickness measuring device that satisfies these conditions. In the same figure,
1, 2, and 3 are γ-ray sources that each emit radiation; 4 to 6 are radiation detection devices (hereinafter also referred to as sensors); 7 is a fixed frame; 8 is a movable frame; 9 is a conveyor roller for the tubular material 11; 1
0 is a movable frame drive device.

In the measuring device shown in FIG.
γ-ray sources 1, 2 and sensors 4, 5 installed above
The gamma ray source 3 and sensor 6 installed on the movable frame 8 measure the wall thickness of the tubular material 11 carried on the conveying rollers 9. The relative positional relationship between the sensor and the tubular material has an important meaning.

That is, as shown in FIG. 2, a beam emitted from the gamma ray source 1 and incident on the sensor 4, a beam also emitted from the source 2 and incident on the sensor 5, and a beam emitted from the source 3 and incident on the sensor 6. Each vertex of the equilateral triangle EFG formed by the incident beam is
It is necessary to position the movable frame 8 in FIG. 1 so that it is on the circumference of a circle whose diameter is the average value of the nominal outer diameter and inner diameter (hereinafter referred to as the center diameter) of the tubular material 11 (in addition, For details on the measurement principle, please refer to JP-A-Sho.
56-46406, and is not essential for understanding the present invention,
(The explanation is omitted.)

However, since the tubular material 11 is transported by the transport rollers ₉ , in _{FIG .}
It constantly vibrates in each direction of _{the 4} Z axes, and it is difficult to accurately maintain each vertex of the equilateral triangle EFG formed by the three radiation beams on the circumference of the 11 center diameter of the tubular material, even if it is transported. Even if measures such as adding an anti-vibration roller (not shown) to the roller 9 are taken, it is quite difficult. Additionally, additional equipment such as anti-vibration rollers itself has technical and cost problems, but unless sufficient anti-vibration measures are taken for the transport rollers, the conventional measurements shown in Figs. The device has a drawback in that an error due to vibration (referred to as a run-out error) occurs due to the principle of measurement. Therefore, as a practical matter, by using a vibration-proof roller (not shown) in conjunction with the conveying roller 9, the tubular material 11
Attempts are being made to suppress the run-out of the machine as much as possible and to minimize the occurrence of run-out errors as much as possible.

Furthermore, another previously proposed method for measuring the wall thickness of steel pipes using radiation is described in Japanese Patent Application Laid-Open No. 114263/1983.

This method is based on the fact that radiation irradiated from the outside of a steel pipe has the maximum amount of attenuation when it comes into contact with the inner surface of the steel pipe and passes through it, and has the minimum amount of attenuation when it comes into contact with the outside surface and passes through it. This method detects the maximum and minimum points of attenuation and measures the wall thickness of the steel pipe from the distance between the two.

However, in this method, 30C _{i is} used as the radiation source.
Even if we use a radioactive substance as small as Kyuri,
When measuring a steel pipe with a wall thickness of several mm to 40 mm, taking into account statistical fluctuations in the radiation dose from radioactive materials, the measurement inevitably takes about 20 mm seconds to 1 second. steel pipes are required to remain stationary. For this reason, the above-mentioned measuring method has the disadvantage that it cannot be used for online wall thickness measurement of steel pipes that are transported with vibrations. Not only that, but the width of the slit for projecting radiation from the radiation source is 2 mm.
If we use a TV camera to take images of radiation transmitted through steel pipes, the resolution of the TV camera can only be expected to be about 1 mm, so in the end, the accuracy of measuring the wall thickness of steel pipes using this method is about 10 μm compared to that of a steel plate thickness meter. It is understood that the measurement accuracy must be significantly inferior to that of the above measurement accuracy.

The present invention has been made in view of the conventional technical circumstances as described above, and therefore, an object of the present invention is to eliminate the run-out error in the wall thickness measurement results even if run-out occurs in the tubular material during transportation. without occurring in principle,
Moreover, it is an object of the present invention to provide a tubular material wall thickness measuring device with high measurement accuracy.

Next, the measurement principle of the present invention will be explained.

3A and 3B are explanatory diagrams of the measurement principle of the wall thickness measuring device according to the present invention. In Figure 3 A, 21
is a line array of γ-ray sources (hereinafter referred to as a line-shaped source), and 22 is a collection of many sensors arranged in a line (hereinafter referred to as a line-shaped sensor).
and 11 is a tubular material.

That is, in FIG. 3A, the length l of the linear radiation source 21 and the linear sensor 22, which are placed opposite to each other with the tubular material 11 in between, is made sufficiently larger than the outer diameter of the tubular material 11, and the sensor 22 measures the amount of attenuation of the γ-rays emitted from the radiation source 21, thereby determining the average wall thickness of the tubular material 11 in the cross section. In FIG. 3B, N ₀ is when the tubular material 11 is not present.
It represents the total number of counts of radiation (gamma rays) detected by the sensor 22, and N _S represents the total number of counts of radiation (gamma rays) detected by the sensor 22 when the tubular material 11 is present. The average wall thickness of the tubular material 11 can be determined from the values of N ₀ and N _S .
Moreover, if the length l of the linear radiation source 21 and the sensor 22 is made sufficiently larger than the outer diameter of the tubular material 11, even if the tubular material 11 is caused to run out,
Since the value of the total number of counts _N3 does not change, the tubular material 1 can be
The average wall thickness dimension of 1 can be determined.

Note that, in one embodiment of the present invention, the linear radiation source 21 can be configured as shown in FIG. 3A. Here, FIGS. 3A and 3A are a cross-sectional configuration diagram showing an example of a linear radiation source and a front view of a collimator.

That is, a radiation source container 210 having a cavity 216
A radiation source holder 211 is placed inside. This radiation source holder 211 has a plurality of cesium 1
37 radiation source capsules 212 are arranged in a row (line shape). And the radiation source container 21
A rotary shutter 213 is disposed in the empty space 216 at 0, and a collimator 214 is attached to the radiation source 210. This collimator 214 has a large number of collimator holes 215 formed in a staggered manner. The rotary shutter 213 is rotationally driven by a rotation drive mechanism (not shown), and the shutter plate 217 is made parallel to the plane of the paper in the figure when performing measurements, and directs the radiation emitted from the source capsule 212 to the collimator 214. When not making measurements, it is perpendicular to the plane of the paper in the figure to block that radiation. Radiation is emitted radially from each source capsule 212, but during measurement, it is formed into a parallel beam by passing through the collimator hole 214 of the collimator 215. It is well known that in a collimator, if the collimator holes are arranged in a staggered manner, it is possible to prevent the mixture of oblique beams and eliminate the influence of radiation scattering, which is useful for improving accuracy.

Furthermore, the line-shaped sensor 2 in FIG.
2 can be constructed as shown in FIG. 3B in one embodiment of the present invention. Here, FIGS. 3B and 3B are a schematic side view and a front view of a collimator, respectively, showing an example of a line-shaped sensor.

That is, one rectangular collimator hole 22
4, a plastic scintillator 221 made of polyvinyl toluene or the like is attached after this collimator 220,
A light guide 222 made of acrylic or the like is attached after the plastic scintillator 221. The light guide 222 is provided with a photomultiplier tube 223, the output of which is guided to an amplifier (not shown). The radiation made into a parallel beam by passing through the collimator hole 215 of the collimator 214 of the linear radiation source 21 passes through the tubular material, and then passes through the collimator hole 2 of the collimator 220 of the linear sensor 22.
24. Although this collimator hole 224 is shown for one rectangular one, the collimator hole 215 of the collimator 214 of the line-shaped radiation source 21
In order to improve measurement accuracy, it is convenient to arrange a large number of collimator holes in a staggered manner as shown in FIG.

Next, the principle of a measurement method for determining the wall thickness of a tubular material by measuring radiation attenuation will be explained.

In general, it is known that the following equation holds true as a basic equation for a radiation transmission type thickness meter, where N is the detection force of a sensor for radiation that passes through an object to be measured having a thickness dimension t.

N=N ₀ EXP (-μt) ...(1) However, N ₀ represents the output (reference output) detected by the sensor when there is no object to be measured (thickness dimension t = 0), and μ is the absorption coefficient It is a constant called .

Now, as shown in FIG. 4, if we define the x-axis and the y-axis that are orthogonal to each other in the cross section of the tubular material 11, the wall thickness dimension t _i of the tubular material 11 along the y-axis direction can be determined by the x coordinate x _i
It can be expressed as a function of

t=f(x)...(2) Therefore, the force _Ns detected by the linear sensor 22 in FIG. 3A is given by the following equation.

N _S =∫ ^l ₀ N ₀ EXP (-μ・f(x)) dx …(3) Calculate the wall thickness dimension t at each x-coordinate from the above equation (3), and calculate the relationship between it and the detected force N _S. Figure 5 shows the obtained graph.

According to the graph shown in Figure 5, the value taken on the vertical axis
It can be seen that when l _o (N _S /N ₀ ) decreases from a certain value to half of this value, the amount of change S in the wall thickness dimension (this is called the half-value layer) is about 4.5 mm.

In general, measurement becomes difficult if the half-value layer is too large or too small, but the half-value layer of a normal flat plate, which is measured by the already widely used transmission type thickness gauge for flat plates, is approximately 11 mm. Compared to this value, the above-mentioned value of 4.5 mm is about 1/2 of that value, so the wall thickness measuring device for tubular materials based on the above-mentioned principle can be fully put into practical use. It can be seen that measurement accuracy comparable to that of a thickness gauge can be expected.

In addition, as shown in Figure 5, in the range of wall thickness 3 mm to 15 mm (approximately 0.03 to 0.1 in terms of the ratio of wall thickness t to diameter D (t/D)), which requires measurement for ordinary pipes, the attenuation Since the curve representing the characteristic is linear, there is no need for correction that would be required if the curve were nonlinear, and the average wall thickness of the tubular material can be immediately determined from the detection force of the linear sensor.

In addition, in the method of the present invention, the half-value layer is about 1/1 of the flat plate.
I explained earlier that it is 2. This thing is flat plate 1
This means that the change in radiation dose due to a change in thickness per mm is equal to the change in radiation dose due to a change in thickness per approximately 0.5 mm of the pipe. Therefore, in this method,
Thickness changes can be measured with approximately twice the fineness of a flat plate, and it can be said that the measurement accuracy is that much higher.

It can be said that the apparatus for measuring the wall thickness of a tubular material according to the present invention is particularly suitable when used in a stretch reducer. A stretch reducer is a mill used in the rolling finishing process, and its outline will be explained below.

Stretch reducers are used in most of the final finishing processes for small-diameter joint pipes, and because of their excellent efficiency, they are often used in the finishing process for small-diameter welded pipes. A stretch reducer consists of 14 to 20 roll housings of two or three rolls arranged continuously along a pipe, and while rolling the outside diameter of the pipe sequentially, the difference in the circumferential speed of the rolls of adjacent stands is applied. The wall thickness is controlled by applying tensile force in the longitudinal direction of the tube during rolling.
Therefore, by preparing several types of raw pipes, it is possible to finish pipes of various sizes.

6A and 6B are a side view and a front view of the above-mentioned two-roll reducer, and FIGS. 7A and 7B are a side view and a front view of the three-roll reducer. In these figures, 31 indicates a roll, and 32 indicates a pipe during rolling.

Now, with the stretch reducer as mentioned above,
Since the wall thickness is changed by pulling the pipe in the longitudinal direction, in order to control the mill or improve the operation method, it is necessary to find out the average wall thickness in the longitudinal direction of the pipe rather than knowing the uneven thickness within the pipe cross section. need to know. This is particularly noticeable in the case of welded steel pipes made from plate materials of uniform thickness.

Furthermore, when attempting to control the wall thickness by changing the tension on the pipe by changing the rotational speed of the multi-stage mill, the faster the response of the wall thickness measuring device, the better. Furthermore, when applying a wall thickness measurement device to a stretch reducer, it must be installed on the inlet or outlet side of the mill, and the vibration of the pipe in this area is generally very large. In addition, even if you try to install a pinch roller for vibration isolation, there is no place for it. As described above, when the wall thickness measuring device according to the present invention is applied to a stretch reducer, the advantages of being completely unaffected by runout and the ability to expect high-speed response are particularly effective. Although it is possible to measure the thickness unevenness in the longitudinal direction, that is, the average thickness of the cross section, using conventional techniques,
However, this device requires only one radiation source and one detector, so the cost is low.

The present invention is applicable not only to steel pipes, but also to various metals, plastics, glass, cement, and other materials.
By using rays, X-rays, β-rays, ultraviolet rays, visible light, infrared rays, etc., it can be widely used to measure the wall thickness of general tubular materials.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a conventional tubular material thickness measuring device, FIG. 2 is a diagram explaining the principle of the same device, and FIGS. 3A A and B are a cross-sectional configuration diagram showing a linear radiation source and a front view of a collimator in an embodiment of the present invention, and FIGS. 3B A and B are schematic side views showing a linear sensor in an embodiment of the present invention. and a front view of the collimator, Figure 4 is an explanatory diagram of the functional relationship between the wall thickness and position of the tubular material, Figure 5 is a graph showing the relationship between the wall thickness and the radiation detection force of the sensor, and Figure 6 is , B are a side view and a front view of a two-roll reducer, and FIGS. 7A and 7B are a side view and a front view of a three-roll reducer. Explanation of symbols, 1 to 3...γ-ray source, 4 to 6...sensor, 7...fixed frame, 8...movable frame,
9... Conveyance roller, 10... Movable frame drive device, 11... Tubular material, 21... Line array of γ-ray sources, 22... Sensors arranged in a line, 3
1...Roll, 32...Pipe being rolled.

Claims (1)

[Scope of Claims] 1. Consists of a radiation source and a radiation detector that are placed opposite to each other with a tubular material in between and have lengths exceeding the outer diameter of the tubular material, and the beam emitted from the radiation source is In an apparatus for measuring an average wall thickness dimension of the tubular material from the amount of radiation attenuation that is incident on the detector after passing through at least the entire cross section of the tubular material and detected by the detector, the radiation source side and the detector side a collimator plate member having collimator holes arranged in a staggered manner in the outer diameter dimension direction of the tubular material,
A wall thickness measuring device for a tubular material, characterized in that the beam emitted from the radiation source is emitted through a collimator plate member on the radiation source side and is incident on a detector through a collimator plate member on the detector side. .