JPH03755B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention compensates for the temperature drop at the edge of a plate-shaped material to be heated, such as a steel strip or steel plate during hot rolling, by using a transverse induction heating method, for example, to heat the material to be heated. This relates to an induction heating method for achieving a uniform temperature distribution in the width direction of the material, and in particular, by appropriately selecting the frequency of the power supply current flowing through the inductor, it is possible to increase the temperature distribution in the width direction of the edge of the material to be heated. The present invention aims to provide an induction heating method that optimizes temperature distribution characteristics. [Prior Art] In general, the temperature of a steel plate or the like during a hot rolling process gradually decreases while being conveyed by a roller table, etc., but in particular, the temperature decrease at the side edges of the rolled material is greater than the temperature decrease at the center in the width direction. For example, as shown in FIG. It is very clear that during such a hot rolling process, if the temperature distribution in the width direction of the material to be rolled is not uniform, the quality of the product will be adversely affected. Attempts to flatten the temperature distribution in the width direction of the plate by heating the side edges of the heating plate during conveyance using an auxiliary induction heating device are disclosed in, for example, Japanese Patent Publication No. 50-22741 or Japanese Patent Publication No. This method is already known from, for example, Japanese Patent No. 55-36250. [Problem to be Solved by the Invention] The present invention performs auxiliary heating of the edge of a heated plate-shaped material to be heated in order to flatten the temperature distribution in the width direction with respect to the material to be heated by using alternating magnetic flux in the thickness direction. The purpose of the present invention is to provide a method that can perform compensatory heating with optimum efficiency according to the thickness of the material to be heated when performing induction heating by infiltrating the material. [Means for Solving the Problems] That is, in the induction heating method of the present invention, during conveyance of a plate-shaped material to be heated such as a heated plate material or a band material, a side edge portion of the material to be heated is By injecting alternating magnetic flux from the inductor in the plate thickness direction, the side edges of the heated material are compensated for the temperature drop at the side edges of the heated material to provide a flat temperature distribution in the plate width direction. When inductively heating the edges,
The following formula, δ=50.3×(ρ/μ _r f), is used so that the ratio t/δ of the plate thickness of the heated material t [mm] and the current penetration depth δ [mm] into the heated material is approximately 1. ^1/2 (where ρ is the resistivity of the heated material [μΩcm], μ _r
(also the relative magnetic permeability of the heated material) is the power supply frequency f [Hz] that provides the alternating magnetic flux based on
The purpose is to select the following. [Function] As is well known to those skilled in the art, the current penetration depth δ [mm] from the surface of the material to be heated in induction heating is δ = 50.3 x (ρ/μ _r f) ^1/2 (however, ρ is the resistivity of the specific heating material [μΩcm], μ _r
is also expressed by the relative magnetic permeability, and f is the power supply frequency [Hz] that provides the alternating magnetic flux, and this can be said to be a function of the power supply frequency f. ρ and μ are physical property values specific to the material to be heated, and have specific values depending on the material to be heated. On the other hand, t is the thickness of the material to be heated, and varies depending on specifications. In reality, t during heating usually falls within a certain range, so once the value of t is determined, the frequency f at which t/δ is approximately 1 can be determined from the previous equation. Become. The condition that t/δ is approximately 1 is the characteristic function of the temperature rise distribution in the width direction of the edge portion due to the induction heating inductor Δθ=Ae ^-x/ 〓 ...[1] (However, Δθ is the temperature rise , A is a constant determined by the power supplied to the inductor, the conveyance speed of the heated material, etc., x is the distance from the edge of the heated material [mm]),
Characteristic function of the temperature distribution in the width direction of the edge portion according to the plate thickness t of the heated material θ=θo−Be ^-x/ 〓 ...[2] (However, θ is the temperature of the heated material, θo is The temperature (constant) at approximately the center of the heated material, B is a constant determined by the heat radiation state and heat radiation time, and α is a characteristic constant of an exponential function, which has a value approximately equal to the thickness t of the heated material. ) gives the width direction temperature distribution after heating, this can be said to be a condition for substantially compensating (-Be ^-x/ 〓) by (Ae ^-x/ 〓). In this case, the constants A and B should be made to be approximately the same, that is, the temperature distribution in the width direction of the edge portion of the heated material according to the plate thickness t of the heated material should be compensated for to achieve a flat temperature distribution. It is natural to set the level of temperature increase distribution in the width direction of the edge portion by the inductor so as to give the temperature distribution in the width direction of the edge portion. Since it is determined almost uniquely depending on the plate thickness t of the heating material, compensation heating at the optimum temperature level can be provided by appropriately selecting the power supplied to the inductor and/or the conveyance speed according to the plate thickness. Often, this temperature level is not influenced by the power supply frequency f which gives the optimum efficiency at that time. [Example] Fig. 1 shows an example of the main part of an apparatus for carrying out the method of the present invention, in which a material to be heated 1 being transported is heated, such as a steel plate in a hot rolling process. A pair of inductors 2, 3 consisting of transverse inductor coils 2a, 3a and laminated cores 2b, 3b are arranged on the front and back surfaces of the side edges, and an alternating current is applied to the inductor coils 2a, 3a. The edge portion of the material to be heated 1 is compensated and heated by the electromagnetic induction effect thereof, and the temperature distribution in the width direction of the material to be heated 1 during conveyance is made uniform. Although FIG. 1 shows a pair of opposing inductors 2 and 3 at the edge of one side of the material to be heated 1, in reality, they are also provided at the edge of the other side of the material to be heated 1. Needless to say, a similar pair of opposing inductors are arranged to perform auxiliary induction heating of the edge portions on both sides of the material to be heated 1 during conveyance. FIG. 2 is a diagram showing actually measured temperature rise characteristics in the board width direction due to induction heating of the material to be heated using the induction heating means as shown in FIG. 1 above. The inventor of this invention succeeded in finding the experimental formula Δθ=Ae ^-x/ 〓 from the above characteristic diagram. As shown in FIG. 2 above, the distribution of the temperature rise of the heated material 1 shows a characteristic curve that can be expressed approximately as an exponential function in the width direction of the plate, and this characteristic function is as shown in equation [1] above. The parameter δ of the characteristic function in equation [1] is a function of the power supply frequency f. In other words, as is well known, the ratio of the absolute value of the current density i _a at the surface of the heated material caused by the alternating magnetic flux from the inductor to the current density i _r at an internal position at a distance x from the surface is expressed as i _r /i _a ≒e ^-x/ 〓, and the current penetration depth δ in this equation is the internal current density i _r at the position of δ = x from the surface compared to the current density i _a at the surface. 1/e≒0.368 (e is Napier's number)
The resistivity (volume specific resistance) of the heated material is ρ [μΩcm], the relative magnetic permeability of the heated material is μr, and the power frequency of the current supplied to the inductor is f
[Hz], it is expressed as δ=50.3(ρ/μrf) ^1/2 [mm]. Here, μr and ρ are specific values specific to the material to be heated, so δ is a function of the power supply frequency f. For example, if we consider the case where it is applied to the general hot rolling process of steel plates, the heated material loses its magnetism due to the high temperature during the hot rolling process, so μr = 1, and ρ
is a value of about 120 [μΩcm] for a general steel plate, so for example, the current penetration depth δ [mm] depending on the power supply frequency f [Hz] in this case is tabulated as follows.

[Table] Now, as mentioned above, the temperature distribution in the width direction of the plate-shaped material to be heated 1 during transportation is such that the temperature is lower at both side edges than at the center of the plate width, as shown in Figure 3. However, there is generally a difference in the temperature distribution at the edge depending on the thickness of the material to be heated 1, and for thinner plates, the temperature distribution at the edge changes. It is steep, and changes relatively slowly in thick plates. Figure 4 is a characteristic diagram showing the difference in temperature distribution due to the difference in plate thickness of the heated material.
As is clear from this, this temperature distribution can be approximately expressed by the characteristic function of the above-mentioned equation [2]. According to the present invention, the material 1 to be heated having the temperature distribution expressed by the above formula [2] is subjected to compensatory induction heating of the edge portion by the inductors 2 and 3, thereby achieving the above [1].
A uniform temperature distribution in the width direction of the plate is obtained by heating with a temperature increase characteristic as expressed by the following formula. In this case, the temperature distribution characteristic of the heated material 1 after compensation heating is [1] The sum of equation and [2], that is, Θ=θ+Δθ=θ ₀ −Be ^-x/ 〓+Ae ^-x/ 〓 ...[3]. In this equation [3], if A=B and δ=α, Θ is equal to θ ₀ , and it can therefore be seen that a uniform temperature distribution is obtained from edge to edge at a temperature of θ ₀ . Regarding the condition A=B, B is that, as mentioned above, for the conveyance equipment that handles the material to be heated, the distribution of the temperature drop at the edge of the material in the width direction is uniquely determined by the thickness of the material to be heated. Therefore, A can be made approximately equal to B by adjusting the amount of heating by setting the heating power and conveying speed accordingly in a conventional manner. This invention is characterized in that it not only sets the heating level but also satisfies the condition δ=α in equation [3]. That is, as described above, α has a value approximately equal to the plate thickness t, and therefore, the power supply frequency f is selected so that δ≈t, in other words, δ/t≈1. In this case, the heating level is set (heating power,
Changes in the power supply frequency f are irrelevant to changes in the power supply frequency f (conveying speed, etc.), and by selecting the power supply frequency f in this way and satisfying the condition of δ/t≒1, the best compensation induction heating of the edge can be achieved. It gives efficiency. In addition, if the relationship between the plate thickness t of the material to be heated and the induction heating power supply frequency f for compensation heating of the edge portion is directly shown, from the condition of δ/t≒1 and the above-mentioned formula for δ, t≒50.3 (ρ/μrf) ^1/2 , and if μ _r = 1, then f≒(50.3) ² ρ/t ² ... [4] The optimum power supply frequency f can be found from the plate thickness t. . Furthermore, if the thickness of the target material to be heated varies within a certain range, the average thickness value may be used as t in equation [4]. [Effects of the Invention] As described above, according to the present invention, compensatory heating of the edge portion of the material to be heated is performed using a transverse type inductor to obtain a uniform temperature distribution in the width direction of the material. In this case, the power supply frequency is selected so as to give a current penetration depth that is approximately equal to the thickness of the material to be heated. By setting the power supply frequency to the device power supply, ideal compensation heating can always be performed under optimal heating conditions.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the main parts of the apparatus configuration for carrying out the method of the present invention, FIG. The figure is a diagram showing the temperature distribution in the width direction of the heated plate-shaped material to be heated during transportation, and Figure 4 is the temperature distribution in the width direction of the heated plate-shaped material to be heated during transportation depending on the plate thickness. FIG. 3 is a diagram showing differences in characteristics. (Explanation of symbols of main parts) In the drawings, 1 is a heated material, 2 and 3 are inductors, 2a and 3a are inductor coils, and 2b and 3b are laminated iron cores.
Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. During transportation of a plate-shaped material to be heated such as a heated plate material or a band material, an alternating magnetic flux is caused to enter the side edge portion of the material to be heated from an inductor in the thickness direction of the material. By this, when induction heating the side edges of the heated material to compensate for the temperature drop at the side edges of the heated material and give a flat temperature distribution in the width direction of the heated material, The ratio t/δ of the plate thickness t [mm] and the current penetration depth δ [mm] into the heated material is approximately 1.
The formula below is δ=50.3×(ρ/μ _r f) ^1/2 (where ρ is the resistivity of the heated material [μΩcm], μ _r
(also the relative magnetic permeability of the heated material) is the power supply frequency f that provides the alternating magnetic flux based on
An induction heating method characterized by selecting [Hz].