JPH0514471Y2 - - Google Patents

Description

[Detailed explanation of the idea]

A. Field of Industrial Application The present invention relates to an inductor for a local heat treatment device for electric resistance welded pipes. B. Summary of the invention This invention is an inductor for a device that heat-treats the vicinity of the welded part of a running electric resistance welded pipe by induction heating. By forming a notch along the traveling direction of the ERW tube in the part of the inductor surface that contacts the conductor of the iron core, the welded part to be heat-treated and the surrounding heat-affected zone can be uniformly heated. This makes it possible to perform heat treatment smoothly with energy savings, and to shorten the overall length of the apparatus. C. Prior Art It has already become common practice to provide an inductor in an ERW tube welding line to anneal or normalize the ERW tube welded portion to improve the quenched structure and hardened portion. Furthermore, in recent years, quenching and tempering heat treatments have been applied to welded parts to improve low-temperature embrittlement. For example, referring to FIGS. 11 and 12, 1
is an electric resistance welded tube that runs in the direction of the arrow, and on the left side of the figure, high-frequency power is supplied by an induction coil 3 to a V-seam portion 2 formed by gradually bending a strip plate while running it, and a squeeze roll 4, 4, welding point 5 at the tip of the V-seam portion is welded. 6
is a high frequency power source. Further, 7, 7, . . . are inductors for annealing or normalizing provided opposite to the welded portion 8.
The reason why a plurality of inductors 7, 7, etc. are provided at intervals is that while the electric resistance welded pipe 1 is running, the outer surface of the welded part 8 is heated by induction, and the temperature is increased, and the temperature is further increased in the thickness direction. This is to reduce the temperature difference between the inner and outer surfaces when the temperature is raised to the inner diameter surface by heat conduction. By the way, the conventional inductor 7 is shown in FIGS. 13 and 14.
As shown in the figure, the main part and cross section of which is shown, the conductor 10 through which current flows is surrounded by an iron core 9 (excluding the surface facing the welded part 8). Also, conductor 1
0 consists of a rectangular cross-section pipe with holes through which cooling water passes. Then, as shown in FIG. 13, both ends of the conductor 10 are connected to a power source, and an induced current induced by the alternating current flowing through the conductor 10 flows into the electric resistance welded tube 1, causing the inductor 7 to face each other. Since this induced current flows especially concentrated in the welding part 8, the temperature of the welding part increases. FIG. 10A shows a gap G (first
An example of the temperature distribution in the circumferential direction of the ERW tube 1 is shown when the ERW tube 1 is heated by changing the temperature (see FIGS. 3 and 14). is within the range corresponding to the conductor width WC. Then, a temperature peak occurs in the portion of the inductor 7 facing the center in the width direction of the conductor 10, and the gap G between the ERW tube 1 and the inductor 7 increases to G ₁ , G ₂ , and G ₃ . The more you do this, the more gradual this temperature peak becomes. However, the heating efficiency will of course deteriorate. Figure 10B
1 is a diagram showing an example of temperature distribution in a cross section of the electric resistance welded tube 1 using isothermal lines. D Problems to be solved by the invention By the way, the area to be heat treated is the welded part of the ERW tube and the heat-affected zone on both sides, but in order to completely cover this part, the actual heat treatment area is further circumferential. The area is rather wide on both sides of the direction. As the wall thickness of the pipe increases, the heat-affected zone also expands on both sides of the weld, and the range of heat treatment becomes correspondingly wider. Furthermore, in the quenching and tempering heat treatments, the quenching range is similarly wider than the heat-affected zone, and in order to completely cover this quenching range, the tempering range is wider in the circumferential direction. These heat-treated ranges are graphically shown in FIG. 14 as the welded portion 8 and the heat-treated portions 12 indicated by diagonal lines on both sides of the welded portion 8, which must be heated within a predetermined temperature range. The reason for this is that in order to perform heat treatment, the temperature of the heat-treated portion 12 must be raised to a predetermined heat treatment temperature or higher, but on the other hand, if the temperature is too high, the crystal grains will become coarse, which is inappropriate. Therefore, the temperature at point a, the center of the outer surface where the temperature rises most easily (this is referred to as T ₁ ), is kept below the upper limit temperature for proper heat treatment, and from the center on the inner diameter side, where the temperature rise is the slowest. The temperature at distant points _d1 and _d2 (these are referred to as _T2 ) needs to be higher than the lower limit temperature for proper heat treatment. (T ₁ > T ₂ ). It is desirable that the temperature difference between T ₁ and T ₂ of Nahoko is as small as possible. Therefore, temperature distribution not only in the thickness direction but also in the circumferential direction is important. However, in the conventional inductor 7, as shown in FIG. (shows the distribution in the circumferential direction of the ERW tube 1), as shown in FIG. 10, the inductor 7
It is within a range approximately corresponding to the width of the conductor 10 that an induced current is generated in the electric resistance welded tube 1 facing the conductor 10 and heating is effectively performed. Therefore, the conductor width Wc of the inductor in FIG.
It was necessary that Wc≧Wh for Wh. Furthermore, a peak of the induced current density occurs at the center in the circumferential direction of the heated portion of the ERW tube 1, and a dull peak of temperature occurs accordingly.
If point A in the figure is heated to the appropriate temperature, d ₁ point, d ₂
If the heating temperature at point A is insufficient and, conversely, points d ₁ and d ₂ are heated to the appropriate temperature, point A will be overheated, while the temperature rise at points a ₁ and a ₂ will be delayed. occurred. In this way, as the wall thickness of the ERW tube 1 increases and the area near the welded area undergoes quenching, tempering heat treatment, etc., the conductor width Wc becomes larger in order to uniformly heat the heat-treated area 12 which is wide in the circumferential direction. The conventional inductor 7 is not suitable because it is large in size and weight, and it is difficult to uniformly heat the inductor. In addition, conventionally, in order to compensate for the above-mentioned drawbacks, the only way to achieve uniformity of temperature was through heat conduction in both the width direction and the wall thickness direction.
As shown in the figure, a plurality of inductors 7, 7... are provided at large intervals in the running direction of the ERW tube 1.
According to this, it takes time to equalize the temperature in both the width direction and the wall thickness direction, and it is difficult to equalize the temperature, and the amount of heat dissipated in the meantime becomes large, making it difficult to improve thermal efficiency. Furthermore, since a plurality of inductors 7, 7, . . . are used at large intervals, the line of the device becomes long. However, as mentioned above, one of the reasons why the heating of the heat-treated part 12 is uneven is that the electric current penetration depth is shallow while the wall thickness of the ERW tube 1 is thick (for example, 16 mm or more). However, if the frequency is lowered in order to increase the penetration depth, it becomes difficult for the inductor 7 to effectively supply power to the electric resistance welded tube 1. In other words, there is a problem that the heating efficiency deteriorates. The object of the present invention is to provide an inductor for heat treatment of electric resistance welded pipes which solves the above-mentioned drawbacks. E. Means for Solving Problems The present invention is an inductor for a device that performs local heat treatment by induction heating near the welded part of a running electric resistance welded pipe, and the inductor has a conductor that carries current and an iron core that surrounds the conductor. An inductor for a local heating device for steel pipes, characterized in that a notch is formed along the traveling direction of the ERW pipe in the part of the inductor surface facing the welded part that is in contact with the conductor of the iron core. be. F Example The present invention will be described below with reference to FIGS. 1 to 10. 1, 2, 4 and 8 show the inductor 7 according to the first embodiment, FIGS. 3 and 9 show the inductor 7 according to the second embodiment, and FIG. 5 shows the inductor 7 according to the second embodiment. FIG. 10 shows a conventional inductor 7 for comparison with the present invention. In addition, Fig. 6A, Fig. 6B, and Fig. 7 show the first embodiment and the second embodiment.
Current density ic distribution (in the X direction, that is, the circumferential direction of the ERW tube 1) flowing through the conductor 10 of the embodiment and the conventional inductor, and the current density iW of the induced current flowing in the opposing portions of the ERW tube 1 It shows the distribution. The dotted line in FIG. 6A is drawn by overlapping ic and iw in FIG. 7 for comparison. First, the conventional inductor 7 shown in FIGS. 5, 7, and 10 will be explained.
is the current flowing through the portion of the conductor 10 facing the electric resistance welded tube 1, is the induced current flowing through the electric resistance welded tube 1, and 13 is the magnetic flux generated along the iron core 9. As can be seen from the figure, the range of the induced current flowing through the electric resistance welded tube 1 due to the magnetic flux 13 generated by the inductor 7 of the conventional structure is the conductor width Wc.
almost equal to To further explain this with reference to FIG. 7, since the surface of the conductor 10 facing the ERW pipe 1 is flat, the gap G between the conductor 10 and the ERW pipe 1 is minimum at the center, and Due to the focusing effect of the high-frequency current, the induced current density iw has a mountain-shaped distribution at the center and within a range in the circumferential direction that is approximately equal to the conductor width Wc. Due to this induced current
The electric resistance welded tube 1 is heated due to generation of Joule heat corresponding to iw ² R (R=resistance value of the part through which current flows). Therefore, in the temperature distribution in the circumferential direction (X direction) of the ERW tube 1, the iw distribution is further emphasized, and the
The temperature distribution has a peak at the center as shown in Figure A, and the temperature increases the most at the center of the outer surface. Therefore _{, the} temperature at _{point a} in the central part shown in FIG. becomes. FIG. 10B is a diagram showing an example of the temperature distribution in the cross section of the ERW tube 1 using isothermal lines, and shows that the temperature increase in the cross section is limited to a narrow range in the circumferential direction of the ERW tube 1. I understand. On the other hand, the inductor 7 according to the first embodiment shown in FIG. 1, FIG. 2, FIG. has been established. Explaining with reference to FIG. 4, X is the notch width and Y is the notch depth of the iron core. Also,
In FIG. 4, ○ is the current flowing through the conductor 10,
is an induced current flowing through the electric resistance welded tube 1, and 13 is a magnetic flux generated along the iron core 9. As can be seen from the figure, according to the inductor 7 according to the first embodiment, the magnetic flux 13 spreads left and right by the notch width X of the left and right notches 11 formed in the iron core 9, and is formed along the iron core 9. Therefore, the range of the induced current flowing in the ERW tube 1 (conductor width) is also Wc
+ (Left and right notch width) 2X wider than before.
To explain this in detail with reference to FIG. 6A, the induced current density iw flowing in the portion of the ERW pipe 1 facing the conductor 10 spreads laterally from iw in FIG. The left and right notch widths are distributed over a wider range approximately equivalent to 2X. Therefore, the eighth
As shown in Figure A, the temperature distribution in the circumferential direction on the outer surface of the ERW tube 1 also becomes a temperature distribution that widens on both sides, effectively making a range approximately equivalent to (conductor width) Wc + (left and right notch width) 2X. Inductor 7 because it can be heated
can be made smaller and lighter. FIG. 8B is a diagram showing an example of the temperature distribution in the cross section of the electric resistance welded tube 1 using isothermal lines, and it can be seen that the temperature distribution in the cross section also extends to both sides. Further, as can be seen from FIG. 8, point a at the center of the outer surface of the heat-treated portion 12 and points a ₁ , a ₂ , d ₁ , and d ₂ at the outer circumferential direction are similar to those of the conventional inductor 7. This shows that heating can be done much more uniformly than in the case shown in FIG. 10. Also in this case, it can be seen from the figure that as the gap G increases from G ₁ to G ₂ to G ₃ , the gentle range of the temperature distribution in the circumferential direction becomes wider. Next, the second
In the inductor 7 according to the embodiment, in addition to the above-mentioned notch 11 of the core, a recess 14 is further formed in the widthwise center of the surface of the conductor 10 facing the electric resistance welded tube 1. That is, as can be seen from FIG. 3, the gap G between the concave portion 14 and the electric resistance welded tube 1 becomes large, and therefore, as shown in FIG. 6B, the portion of the electric resistance welded tube 1 facing the conductor 10 induced current that flows
iw is reduced in the central part of the conductor facing the recess 14, and as a result, the central part is slightly concave (of course,
Both sides are gradually expanding as in Figure 6A),
Or a flat iw distribution will result. Therefore, the ninth
As shown in Figure A, the temperature distribution on the outer surface of the ERW tube 1 becomes a temperature distribution that spreads to both sides, and the temperature distribution becomes slightly concave or flat in the center, and the cross section shown in Figure 9B. The temperature distribution also becomes more widespread on both sides in the circumferential direction. this is,
As can be seen from FIG. 9, the portion to be heat treated 12
Point a at the center of the outer surface and the outer side in the circumferential direction
Points a ₁ , a ₂ , d ₁ , and d ₂ are the inductor 7 according to the first embodiment.
This shows that heating can be done even more uniformly than in the case shown in FIG. In this case as well, it can be seen from the figure that as the gap G increases from G ₁ to G ₂ to G ₃ , the gentle range of the temperature distribution in the circumferential direction expands. Note that this is not limited to the case of the electric resistance welded pipe 1 having a circular cross section as described above, but there may be a welded part in a part having a flat plate shape, such as a square pipe with a welded part in the center of the side, for example,
When heat-treating the vicinity of the welded part and using the conventional inductor 7 shown in Fig. 7, it is necessary that the conductor width Wc of the inductor 7 is larger than the width Wh of the treated part of the heat exchanger. Therefore, the inductor 7 becomes large, and the focusing effect of the high frequency current causes the conductor 10 to become large.
The part facing the center in the width direction becomes hot.
Therefore, the first
By using the inductor 7 according to the embodiment and the second embodiment, the inductor 7 can be similarly downsized and the portion 12 to be heat treated over a wide range in the width direction can be uniformly heated. Next, a comparative experiment was conducted using the inductors 7 according to the first and second embodiments of the present invention and the conventional inductor 7, and the following results were obtained. In addition, in the experiment, an electric resistance welded tube with a wall thickness of 16 mm was run at a line speed of 13 m/mm, and the consumption required to heat the heat-treated area 12 near the weld to a predetermined temperature range centered around 560°C was measured. I checked the electricity.

[Table] From the above experimental results, it was found that the use of the inductor 7 of the present invention provides the following effects compared to the conventional one. It is possible to uniformly heat a wide area near the welded part of the ERW pipe. Total power consumption is the first priority.
It can be reduced by 20% in the example and 33% in the second example,
It saves energy. The inductor is downsized and the device weight is reduced by approximately 85% in the first embodiment and approximately 70% in the second embodiment.
%, and accordingly, the manufacturing cost of the device can be significantly reduced. Heat treatment line length can be shortened. As a result of further experimental research, the code a 1 of the heat-treated portion ₁₂ indicated by diagonal lines in FIGS. 1 and 3,
The dimensions between the parts that are most difficult to heat, indicated by a ₂ , d ₁ , and d ₂ , that is, the desired circumferential width Wh for heat treatment and the conductor width Wc,
Set the wall thickness t of the ERW pipe to Wc≦Wh+t(max),
In addition, the width X and depth Y of the notch 11 are set so that X, Y≦t
(max), Wc+2X≧Wh was found to be most desirable in terms of uniformly heating the heat-treated portion 12 and in terms of total power consumption. G. Effects of the invention As described above, according to the invention, the parts to be heat treated, which are mainly the welded part and the heat affected zone of the ERW pipe, can be uniformly heated in a short time, so that the heat treatment of this part can be carried out smoothly. can be done. In addition, since heat can be soaked in a short time, less heat is radiated to the outside, making it possible to perform heat treatment with less energy. For example, an ERW tube with a wall thickness of 16 mm
When the inductor of this invention is run at a line speed of 13 m/mm and heats the area to be heat treated near the weld to a predetermined temperature range centered around 560°C, it takes about 200 m/mm compared to the conventional inductor. Energy savings of more than %. The inductor has also been made smaller, reducing the weight of the device.
This has enabled a reduction of more than 15%, making it possible to reduce manufacturing costs accordingly. Furthermore, by using the inductor of the present invention, as mentioned above, the outer circumference near the welded part of the ERW pipe can be widely and uniformly induction heated in the circumferential direction, and heat transfer in the inner thickness direction can be measured. Because the temperature near the welded area can be uniformized in a short time, it is possible to shorten the distance between multiple inductors installed along the ERW pipe line, or reduce the number of inductors installed. This makes it possible to shorten the total length of the heat treatment equipment line.

[Brief explanation of the drawing]

1 and 3 are front explanatory views of inductors according to the first and second embodiments of the present invention, FIG. 2 is a perspective view of the inductor shown in FIG. 1, and FIGS. 4 and 5. 6A, 6B, and 7 are magnetic flux distribution diagrams of the inductor according to the first embodiment and the conventional inductor, and FIG. 6A, FIG. 6B, and FIG. Figures 8A, 9A, and 10A are diagrams showing the current density distribution flowing through each conductor of the wire and the distribution of the induced current density flowing through the ERW tube, respectively. Figures 8B, 9B, and 10B are diagrams showing examples of temperature distribution in the circumferential direction of the tube when heated by the inductor of the second embodiment and the conventional example, respectively. Figure A, 1st
A diagram showing an example of temperature distribution in the cross section of the tube corresponding to Figure 0A using isothermal lines; Figures 11A and 12 are a front view and a plan view of a conventional heat treatment apparatus using an inductor;
Figure 1B is a cross-sectional view of the ERW tube, Figure 13 is a perspective view of the main parts of the heat treatment equipment with arrows indicating the current flowing in the inductor and the induced current flowing in the ERW tube, and Figure 14 is the heating by the inductor. FIG. 2 is an explanatory diagram showing a heat-treated portion near a welded portion of a pipe. 1... ERW pipe, 7... Inductor, 8... Welded part,
9... Iron core, 10... Conductor, 12... Heat treated portion, 11... Notch, 14... Recessed portion.

Claims (1)

[Scope of utility model registration request] In an inductor for a device that locally heat-treats the vicinity of a welded portion of a running electric resistance welded pipe by induction heating, the inductor includes a conductor having a rectangular cross section and a predetermined length that conducts current, and a conductor that is in contact with and conducts current through the conductor. It consists of an iron core that surrounds the ERW tube, leaving only the side facing the welded tube, and this conductor is arranged in parallel with the ERW tube with a gap, and the portion of the core that contacts the conductor of the iron core on the inductor surface facing the vicinity of the welded portion. 1. An inductor for an electric resistance welded tube local heat treatment device, characterized in that a notch is formed along the traveling direction of the electric resistance welded tube.