JPS5814037B2 - multilayer heating coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer heating coil used in an induction heating device that utilizes induction heating by electromagnetic induction.

Generally, single-layer coils wound in a cylindrical shape are often used as heating coils in induction heating devices such as billet heaters. In order to avoid this problem and reduce copper loss in the coil, it is possible to adopt a multilayer coil.

However, when a multilayer coil is used, an induced current is generated in the inner layer due to the alternating magnetic flux generated by the outer layer coil.
This causes increased copper loss in the coil.

For example, as shown in Fig. 1, an inner layer coil 1 and an outer layer coil 2
In a two-layer coil connected in series to an AC power supply (not shown), an induced current flows in the path shown by the dotted line in addition to the current shown by the solid arrow in the inner layer coil 1, which increases copper loss. Layer winding does not necessarily reduce copper loss.

The present invention aims to improve electrical efficiency by minimizing copper loss by suppressing the increase in induced current as much as possible.One embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a sectional view showing a part of the case where the present invention is applied to a two-layer coil;
The conductor thickness t of each inner layer coil 3 of the outer layer coils is set to be smaller than the effective conductor thickness t' of each outer layer coil 4.

Reference numerals 5 and 6 denote water holes for circulating cooling water provided in each inner and outer layer coil, respectively.

In this embodiment of the present invention, the thickness t of the five conductors of the inner layer coil 3 is made smaller than that of the outer layer coil 4, and the copper loss of the inner layer coil 3 is now shown in FIG. Considering the figure, in the same figure, curve a shows resistance loss, curve b shows inductive loss, and curve C shows the composite value of these.As the conductor thickness t of the coil becomes thinner, Resistive loss increases, and as the conductor thickness t increases, inductive loss increases.

Therefore, the sum of both, and therefore the copper loss of the inner layer coil 3, takes a minimum value at a certain thickness, and this thickness is near the point where the resistance loss and the induction loss take equal values, as seen in curve C. It becomes T.

At commercial frequencies, the thickness range is approximately 8 mm.

Also at this time, the effective conductor thickness t' of the outer layer coil 4
As for the copper loss of the coil, it is only necessary to consider the resistance loss, so the dimensions and shape that have traditionally been considered optimal for single-layer heating coils are applied, and this thickness t
' is about 10g.

Therefore, even if the minimum value of copper loss in the inner layer coil increases slightly due to the presence of the cooling water passage holes 5, the coil can be made to Overall copper loss can be minimized and heating coil efficiency can be increased.

Although the embodiment described a two-layer coil, as the number of winding layers increases, the curve showing the induction loss in FIG. The point T indicating the thickness will move to the left, and the total copper loss of the coil can be reduced by sequentially decreasing the conductor thickness toward the inner layer of the coil.

According to experimental examples, the electrical efficiency of a conventional single-layer aluminum heating coil was 55%, but by applying the present invention to a two-layer coil, it was possible to increase the electrical efficiency to 60% or more.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the induced current of a two-layer heating coil, Fig. 2 is a partial cross-sectional view of a two-layer heating coil showing an embodiment of the present invention, and Fig. 3 is a diagram showing the copper loss and thickness of the coil. It is a curve diagram showing a relationship. 3... Inner layer coil, 4... Outer layer coil.

Claims (1)

[Claims] 1. A multilayer heating coil characterized in that the thickness of the coil conductor is gradually reduced from the outer layer to the inner layer.