JPS6342399B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crucible-shaped induction furnace for heating or melting a metal material to be heated or a metal material to be melted.

For example, taking a low frequency crucible induction furnace for melting cast iron as an example, its conventional configuration is shown in FIGS. 1 and 2.

1 and 2, 1 is an induction heating coil, 2 is a yoke provided on the outer circumferential side of the coil 1, and 3 is a yoke provided on the outer circumferential side of the coil 1.
In the melting pot, 4 is the magnetic flux generated by the coil 1, and 5 is the molten metal of the material to be melted. However, magnetic flux 4 only shows the left half. When the molten metal is maintained at the rated temperature in such a furnace, the instantaneous electrical efficiency is approximately
In the case of 82% Figure 2, it is about 80-81%. One of the causes of loss is that the magnetic flux passes through a non-magnetic material, that is, a crucible with high magnetic resistance.The longer the magnetic flux passes through the crucible, the greater the current flowing through the induction heating coil, and the coil resistance loss increases.

The present invention has been made in consideration of the above points, and its object is to provide a crucible-shaped induction furnace with improved electrical efficiency compared to conventional ones.

In order to achieve the above object, in this invention, in addition to a plurality of outer yokes provided outside the induction heating coil, a bottom yoke is provided at the lower part of the bottom of the crucible. Make it continuous with iron. By doing this, it is possible to reduce the magnetic resistance of the magnetic circuit to be excited by the current flowing through the induction coil by approximately 20%, thereby reducing the current flowing through the induction coil, and thereby reducing the magnetic resistance of the magnetic circuit to be excited by the current flowing through the induction coil. The resistance loss that occurs can be reduced.

The present invention will be described in detail below with reference to embodiments shown in the drawings.

FIG. 3 is a sectional view showing a schematic configuration of an embodiment of the present invention, in which 11 is an induction heating coil, 12 and 12' are yoke provided outside the coil 11, 13 is a crucible, 14 is a bottom yoke provided below the bottom of the crucible 13, 15 is a metal material to be melted or its molten metal, and 16 is a magnetic flux. However, only the left half of the magnetic flux was shown.

An example of the bottom yoke 14 is shown in FIG. Figure 4 is a top view of only the outer yoke and bottom yoke, 12,1
2', 12-a to 12-d are outer yokes, 13' is the outer periphery of the crucible 13, 14, 14-a
~b are the bottom yokes, respectively. 15 is the yoke 14
This is the convex part at the center of the .

First, a case where the convex portion 15 is not provided will be explained.

In Figure 3, only the left half of the magnetic flux 16 is shown, but
The magnetic fluxes a ₁ , b ₁ , c ₁ passing through the parts of the crucible 3 shown in FIGS. ₁ and ₂ ; magnetic fluxes a 3 , b passing through the crucible 13 in FIG. ₃ compared to a 2 , b 2 , c ₂ ; ₃ , the length of _c3 is quite short. This is because the portion of the magnetic flux 16 shown by the dotted line in FIG. 3 passes through the yoke 14 at the bottom.

Figure 5 shows the yokes 12, 12' and 14 of Figure 4.
This figure shows a case in which a convex portion 15 extending upward is provided in the center of the yoke 14.

FIG. 6 is a sectional view showing the general structure of an induction furnace using the yoke shown in FIG. 5. The difference from FIG. 3 is that the crucible 13 in FIG. It has a bent portion 13' toward the
The convex portion 15 of the bottom yoke 14 is only located in the inner cavity of the bent portion 13'. The shape of the inner vagina of the bent portion 13' may be such that the convex portion 15 can be inserted therein. 17 is a groove formed at the bottom of the inner cavity of the crucible 13, and if the outer shape of the bent part 13' is cylindrical, the groove 17 is formed.
becomes circular. Magnetic flux is relatively concentrated in this groove 17, which is effective in heating the contents of the crucible 13.

Now let the radius of the crucible 13 be d, and the bent portion 13'
If the outer shape of is cylindrical and its radius is a, groove 1
The width of 7 is a-d.

Assuming that the change in magnetic flux density from the left end of the groove 17 in FIG. 6 toward the center of the inner cavity of the crucible 13 is shown by the curve S in FIG. 7A, the area S _a is equal to the area S _b . The distance (distance from the left end of the groove 17) δ is referred to as the penetration depth of the magnetic flux. δ is Here, ρ is the specific resistance of the molten metal (ohm, mm ² /m), μ is the relative magnetic permeability, and ∫ is the power frequency applied to the coil 11. The width a-d of the groove 17 satisfies a-d≦2δ. For example, if the frequency of the power supply is 60Hz for molten cast iron, shall be. However, the deeper the groove, the better, but it cannot be made too high due to the strength of the refractory, and it is appropriate to make it approximately half the width of the groove.

Generally, as shown in FIG.
By providing a
Y' becomes shorter, so the magnetic resistance becomes smaller, and the current in the coil 11 can be reduced accordingly.

Therefore, when the groove width a-d is equal to δ, there is magnetic flux that enters the convex portion 15 from the upper surface and the outer surface of the convex portion 15 as shown in FIG. -X', Y-Y' pass through the yoke 14 extra.

When a-d is larger than δ, there is a magnetic flux entering the convex portion 15 from the upper part of the convex portion 15 as shown in FIG. 14 is the passage.

When a−d is 2δ, there is no particular effect as shown in FIG. 7D.

As explained above, according to the present invention, by providing the bottom yoke, the magnetic path of the magnetic flux passing through the crucible portion is shortened, and the magnetic resistance of the magnetic circuit can be reduced by about 20%. This has the effect of reducing the current flowing through the induction coil and reducing the resistance loss generated in this coil. Furthermore, in the present invention, since the lower yoke has an upwardly extending convex portion in its center, the magnetic path passing through the crucible becomes shorter, the magnetic resistance becomes smaller, and the current in the coil can be reduced accordingly.

[Brief explanation of the drawing]

Figures 1 and 2 are schematic sectional views of a conventional crucible induction furnace, Figure 3 is a schematic sectional view of an embodiment of the present invention, and Figure 4 is an example of the arrangement of yoke in the present invention. 5 is a front view of what is shown in FIG. 4, FIG. 6 is a schematic sectional view of another embodiment of the invention, and FIG. 7 is an explanatory graph. 11... Heating induction coil, 12, 12', 1
2-a to d...Outer yoke, 14...Bottom yoke, 1
5... Convex portion of the bottom yoke, 17... Groove formed at the bottom of the crucible.

Claims (1)

[Claims] 1. In addition to the plurality of outer yokes provided on the outer circumferential side of the heating induction coil, a bottom yoke is provided below the bottom of the crucible, and the outer yokes are connected at the lower end thereof by the bottom yoke, A crucible-shaped induction furnace characterized in that the bottom yoke has an upwardly extending convex portion at its center.