JPH0425834Y2 - - Google Patents

Description

[Detailed Description of the Invention] 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 locally heat-treats the vicinity of the welded part of a running electric resistance welded pipe by induction heating.
The inductor consists of a current-carrying conductor and an iron core surrounding the conductor, and a missing portion of the conductor is formed along the direction of movement of the electric resistance welded pipe at the center of the width of the surface facing the welded portion of the conductor. This enables uniform heating of the welded part to be heat treated and the surrounding heat affected zone,
As a result, heat treatment can be carried out smoothly with energy savings, and the overall length of the apparatus can be shortened.

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, the welded parts are hardened. Tempering heat treatment has also been carried out to improve low-temperature brittleness. For example, referring to FIGS. 8 and 9, 1 is an electric resistance welded tube running in the direction of the arrow, and a V-seam part is formed by gradually bending the strip plate on the left side of the figure as it runs. 2 is supplied with high frequency power by an induction coil 3, and a welding point 5 at the tip of the V-seam portion is welded by squeeze rolls 4, 4. 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, . This is to reduce the temperature difference between the inner and outer surfaces when increasing the temperature to the inner diameter surface by heat conduction to the inner surface.

By the way, the conventional inductor 7 is shown in FIGS. 10 and 11.
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. 10, 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. Figure 5 A shows inductor 7
Accordingly, the gap G between the ERW tube 1 and the inductor 7 (10th
The temperature distribution in the circumferential direction of the ERW tube 1 is shown when the electric resistance welded tube 1 is heated by changing the temperature (see FIGS. 1 and ₁₁ ).
As G ₂ and G ₃ are increased and heated, the temperature peak becomes gentler. However, the heating efficiency will of course deteriorate. FIG. 5B is a diagram showing the temperature distribution in the cross section of the electric resistance welded tube 1 using equal curves.

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 tube increases, the heat-affected zone becomes wider on both sides of the weld, and the heat treatment range becomes correspondingly wider. Further hardening. In the tempering heat treatment, 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 areas are graphically shown in FIG. 11 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. It is necessary to make the temperature at distant points B and C (this is T ₂ ) higher than the lower limit temperature for proper heat treatment (T ₁ >T ₂ ). Nahoko's
It is desirable that the temperature difference between T ₁ and T ₂ be 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 FIGS. 3 and 5, a sharp peak of temperature occurs at the center of the electric resistance welded tube 1 facing the inductor 7, so it is necessary to set point A in FIG. 11 to the appropriate temperature. If heated, the heating temperature at points B and C will be insufficient, and conversely, if points B and C are heated to the appropriate temperature, point A will be overheated, while the temperature at points D and E will rise. There was a delay. The conventional inductor 7 was not suitable for uniformly heating the heat-treated portion 12 in this manner.

In addition, conventionally, in order to compensate for the above-mentioned drawbacks, the only way to make the temperature uniform is through heat conduction in both the width direction and the wall thickness direction. A plurality of inductors 7, 7... are provided at large intervals in the running direction, but with this, it takes time to equalize the temperature in both the width direction and the wall thickness direction, and it is difficult to make the temperature uniform. It was difficult to achieve this, and the amount of heat dissipated during that time also increased, making it difficult to improve thermal efficiency. Also, a plurality of inductors 7,
There was also a drawback that the equipment line became long because 7... was used.

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 transducer 7 to effectively apply 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 includes a current-carrying conductor and an iron core surrounding the conductor. An inductor for a local heating device for a steel pipe, characterized in that a missing part of the conductor is formed along the traveling direction of the electric resistance welded pipe in the widthwise center of the surface facing the welded area of the conductor. It is.

F Example The present invention will be described below with reference to FIGS. 1 to 7.

1 and 2 show inductors 7 according to the first and second embodiments, and FIG. 3 shows a conventional inductor 7 for comparison with the above. Each figure also shows the current density IC distribution (in the X direction, that is, the circumferential direction of the ERW tube 1) flowing through the conductor 10, and the current density (IW) of the induced current flowing in the opposing portions of the ERW tube 1. It shows the distribution.

First, the conventional inductor 7 shown in FIG. 3 will be explained. Since the surface of the conductor 10 facing the ERW tube 1 is flat, the gap G between the conductor 7 and the ERW tube 1 is minimum at the center. , and due to the focusing effect of the high-frequency current, the induced current density iw forms a mountain shape with the maximum at the center. Due to this induced current, iw ² R
(R=resistance value of the part through which current flows) is generated, and the electric resistance welded tube 1 is heated. Therefore, in the temperature distribution in the circumferential direction (X direction) of the electric resistance welded tube 1, the iw distribution is further emphasized, resulting in a temperature distribution having a peak at the center as shown in FIG. 5A, and the temperature rises the most at the center of the outer surface. Therefore, the temperature at point A in the center shown in FIG.
Non-uniform heating occurs within 2.

On the other hand, the inductor 7 shown in FIG.
By forming a recess 13 in the center in the width direction of the surface facing the electric resistance welded pipe 1, a missing portion of the conductor where a part of the conductor is missing is provided. Therefore, the gap G between the concave portion 13 and the electric resistance welded tube 1 becomes large, so that the induced current flowing in the opposing portion of the electric resistance welded tube 1 is reduced. In other words, the iw distribution has a slightly concave central portion (or has a flat portion) as shown in the figure. As can be seen from FIG. 4, this indicates that the central portion A and the circumferentially outer portions B, C, D, and E of the heat-treated portion 12 can be heated relatively uniformly. 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 iw distribution widens.

Next, FIG. 2 shows a second embodiment, in which the conductor 10
is divided into left and right halves and an insulator 15 is sandwiched in the center, thereby providing a missing portion of the conductor corresponding to the recess 13 of the first embodiment at the center in the width direction of the conductor. Therefore, in this case as well, there is a part where no current flows at all in the center between the left and right conductors 10, and therefore the induced current density iw distribution induced in the electric resistance welded tube 1 is at the center as shown in the figure. has a concave distribution, and as in the first embodiment, the heat-treated portion 12
is heated evenly.

Note that each numerical value of the inductor 7 according to this embodiment may be determined from the following equation. To explain with reference to FIGS. 6 and 7, in FIG. 6, A (area when the conductor has no dent), B (relief area due to the curvature of the portion of the ERW pipe facing the conductor), C ( An inductor in which the area of the concave part of the conductor) is 0.9≧C-B/A≧0.1, and in Fig. 7, W (the length between the left and right conductors) and Z (the length of the missing part of the conductor) are 0.9≧W- The inductor satisfies Z/W≧0.1.

In addition, this is not limited to the case of the electric resistance welded pipe 1 having a circular cross section as described above. For example, there is 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, and the vicinity of the welded part is Also in the case of heat treatment, the third
When the conventional inductor 7 shown in the figure is used, the portion facing the center in the width direction of the conductor 10 becomes high in temperature due to the focusing effect of the high frequency current. Therefore, by using the inductor 7 according to the present invention shown in FIGS. 1 and 2, it is possible to uniformly heat the portion 12 to be heat treated.

G. Effects of the invention As described above, according to the invention, the parts to be heat-treated, which are mainly the welded parts and the heat-affected zones of the ERW pipe, can be uniformly heated in a short time, so that the heat treatment of these parts 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, use an ERW pipe with a wall thickness of 16 mm.
When running at a line speed of 10 m/min and heating the vicinity of the weld to a predetermined temperature range centered around 560°C, if three conventional inductors are placed at regular intervals, the frequency will be 300 Hz, A total power of 1110 Hz was required, but when the inductor of the present invention was used with the same specifications as above, it was achieved at 300 Hz and a total power of 890 Kw, a difference of 220 Kw.
This means energy savings of approximately 20%.

Furthermore, by using the inductor of the present invention, it is possible to uniformly inductively heat the outer circumference near the welded part of the ERW pipe and measure heat transfer in the wall thickness direction, as described above, making it possible to shorten the area near the welded part. Since the heat can be equalized in a short period of time, it is possible to shorten the distance between multiple inductors installed along the ERW pipe line, or reduce the number of inductors installed. The total length of the heat treatment equipment line can be shortened.

[Brief explanation of the drawing]

Figures 1, 2, and 3 show the first embodiment of the present invention, the second embodiment of the present invention, a conventional inductor, the current density distribution flowing through the conductor of each inductor, and the induced current flowing through the electric resistance welded pipe. Figures 4A and 5A are diagrams showing the distribution of current density, and Figure 4A is a diagram showing examples of temperature distribution in the circumferential direction of the tube when heated by the inductor of the present invention and the conventional inductor, respectively. , FIG. 5B is a diagram showing the temperature distribution in the cross section of the tube by isothermal lines corresponding to FIGS. 4A and 5A, respectively, and FIGS. 6 and 7 are diagrams showing the first and second embodiments of the present invention. Explanatory drawings showing predetermined areas and dimensions of the inductor according to the embodiment, FIGS. 8A and 9 are front and plan views of a conventional heat treatment apparatus using an inductor, and FIG. 8B is an illustration of an electric resistance welded pipe. 10 is a cross-sectional view, and FIG. 11 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.
The figure is an explanatory diagram showing a heat-treated portion near a welded portion of a tube heated by an inductor. 1... ERW pipe, 7... Inductor, 8... Welded part,
9... Iron core, 10... Conductor, 12... Part to be heat treated, 13... Conductor recess, 15... Insulator.

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 traveling ERW pipe by induction heating, the inductor includes a conductor having a rectangular cross section and a predetermined length that conducts current, and the conductor facing the ERW pipe. This conductor is parallel to the electric resistance welded pipe with a gap, and the central part of the conductor in the width direction of the face opposite to the welded part is wider than the both sides. 1. An inductor for a local heat treatment device for an electric resistance welded tube, characterized in that a missing portion of the conductor is formed in the central portion along the traveling direction of the electric resistance welded tube by recessing or cutting it out.