JP2005150066A - Efficient heater coil for induction heating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce loss of a heating coil in order to reduce power consumption of an induction heating device. <P>SOLUTION: The wall thickness of a part corresponding to the inner periphery of the coil of a hollow conductor for the heating coil of the induction heating device is made to be about two times or more of the permeation depth of electric current. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

Detailed Description of the Invention

Industrial application fields

  The present invention is used, for example, in an induction heating apparatus for heating a metal used for hot forging, in order to reduce the power consumption of the heating apparatus, and to improve the heating efficiency.

ここで１式のδを電流浸透深さと言い２式で求められる。

コイル内に流れる全電流Ｉは１式を積分する事によって求められ、３式に示す如くになる。

この式からコイル内に流れる電流は巾δの導体にｉ_０の電流が均等に流れると考えて良いと言う想定の基に、従来はコイル中空導体の肉厚ｔはｔ≒δに設定されている。但し周波数が４ＫＨｚ程度になると、中空導体の強度の問題からｔ＞δになる場合も有るが、これはあくまで強度上からの選定であり、効率を考慮したものではない。Normally, when a high-frequency current is applied to a coil, the current flows in a concentrated manner on the inner periphery of the coil due to the skin effect, and the current decreases exponentially as the distance from the inner periphery increases. Here, if the specific resistance of the conductor is ρ (μΩcm), the frequency is f (Hz), the current flowing through the innermost circumference of the coil is i ₀ , and the distance from the inner circumference of the conductor is x, the current distribution i in the conductor is It is expressed by one set.

Here, δ in equation (1) is called current penetration depth and is obtained by equation (2).

The total current I flowing in the coil is obtained by integrating the equation (1), as shown in the equation (3).

Based on the assumption that the current flowing in the coil can be considered to be equivalent to the current i ₀ flowing in the conductor of width δ from this equation, the thickness t of the coil hollow conductor is conventionally set to t≈δ. Yes. However, when the frequency is about 4 KHz, there may be a case where t> δ due to the problem of the strength of the hollow conductor, but this is a selection from the viewpoint of strength only and does not take efficiency into consideration.

Problems to be solved by the present invention

  According to the conventional method, the coil resistance is determined by the frequency, and further reduction of the coil loss cannot be expected. The present invention overcomes this point and intends to further reduce the loss due to coil resistance.

Means to solve the problem

  The present invention has been made in order to solve the above-mentioned problems. By reducing the thickness t of the hollow conductor at least at the portion corresponding to the inner circumference of the coil, the loss due to the coil resistance will be reduced. It is what.

Action

FIG. 1 shows a front view of a heating coil and a cross-sectional view of a hollow conductor used as a coil conductor. According to the conventional method, the thickness t of the hollow conductor is selected in the vicinity of δ, assuming that the current flows uniformly in the width of the penetration depth δ based on the three formulas. However, since the loss of each part of the coil is proportional to the square of the current, the total loss _Pc is expressed by the following equation (4).

ここで４式に６式を代入すると７式が得られる。

In Equation 3, the thickness of the hollow conductor was calculated as infinite. However, if the thickness of the hollow conductor is t and the current flowing through each part of the conductor is i ′, the formula 3 becomes the formula 5, and the current i ₀ ′ flowing in the innermost coil circumference at this time is between the current i ₀ ′ and the formula i _0. Holds the relationship of the six formulas.

Here, when formula 6 is substituted into formula 4, formula 7 is obtained.

７式と８式を比較すると９式が得られる。

９式を図示すると２図に示す如くになる。図において横軸は
（中空導体の肉厚ｔ／電流浸透深さδ）を表わし、縦軸は（本発明による計算で求めたコイル導体損失Ｐ_ｃ／従来計算で求めたコイル導体損失Ｐ_ｃ０）である。
図示のように中空導体の肉厚ｔをδの２倍以上に選べばコイルの抵抗損失はｔ≒δに選んだ場合に比べて６０％程度に低減し得る事がわかる。The calculated value of coil loss P _c0 by the conventional method is as follows:

Comparing formula 7 and formula 8, formula 9 is obtained.

The formula 9 is illustrated as shown in FIG. In the figure, the horizontal axis represents (thickness t of hollow conductor / current penetration depth δ), and the vertical axis (coil conductor loss P _c obtained by calculation according to the present invention / coil conductor loss P _c0 obtained by conventional calculation). It is.
As shown in the figure, it can be seen that if the thickness t of the hollow conductor is selected to be twice or more than δ, the resistance loss of the coil can be reduced to about 60% compared to the case where t≈δ is selected.

  In this case, when the thickness of the coil conductor is increased and the cooling water passage becomes narrow and the cooling water is insufficient, the thickness of only the portion corresponding to the inner circumference of the coil is formed using a modified copper pipe as shown in FIG. Choose bigger.

The invention's effect

  The effects of the present invention are as follows.

  The coil resistance loss of the induction heating device can be greatly reduced, and the power consumption can be reduced.

  By using an atypical copper tube, the amount of cooling water can be secured while reducing coil resistance loss.

  It is the front view of the heating coil of an induction heating apparatus, and sectional drawing of the hollow conductor for coils.   It is a graph which shows the relationship between the thickness of a hollow conductor, and the resistance loss of a coil.   It is sectional drawing of the atypical copper pipe used for Claim 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coil for induction heating 2 Cross section t of hollow conductor used for induction heating coil Thickness of hollow conductor t 'Thickness of a portion corresponding to the inner peripheral portion of a copper wire

Claims (2)

In the heating coil of the induction heating device used for heating metal, the thickness of at least the portion corresponding to the inner circumference of the coil hollow conductor is selected to be at least twice the current penetration depth. A heating coil for induction heating. In the heating coil of the induction heating device used for heating the metal, at least the thickness corresponding to the inner circumference of the hollow conductor for the heating coil is increased and only one side is thick in order to obtain a sufficient amount of cooling water. A heating coil for induction heating, characterized by using a thick rectangular irregular hollow conductor and selecting the thickness of the thick part to be at least twice the current penetration depth.

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