JPH0442596B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a winding structure for a crucible induction furnace.

It is desirable that the crucible-type induction furnace be capable of melting metal in a short time by inputting electric power as effectively as possible.

[Prior art and its problems]

The conventional crucible induction furnace is shown in Figure 2.
A coil 2 is wound around the outer periphery of a furnace body 1 made of a refractory material. The coil 2 is generally made of a water-cooled coil insulated with a heat-resistant insulator. When a metal (iron, aluminum, copper, etc.) is placed in the furnace and an alternating current is passed through the coil 2, an eddy current flows through the metal due to electromagnetic induction, and the metal is melted by the heat. The furnace melting procedure is as shown in Figure 2, when dividing the space inside the furnace into the lower part A and the upper part B, a cold lump of metal is first inserted into part A, and once the cold lump is melted, it enters the molten metal. Additional cold lumps are added and the coil is energized until part B is filled with molten metal. When all parts A and B are filled with molten metal, turn off the electricity, tilt the furnace body, take out the molten metal and use it, leaving some molten metal at the bottom and charge the cold metal lump to melt it. The process is becoming repeated. By the way, since this induction furnace has no iron core, the absorption power effective for melting is P,
When the voltage is E, the current is I, and the power factor is cosφ, P=EIcosφ, and this absorbed power is equal to the magnetomotive force of the N-turn coil, where N is the number of turns of the coil in contact with the metal to be melted across the furnace wall. i.e.
Almost proportional to NI. Furthermore, the resistivity and permeability of the metal differ between the cold lump state and the molten state, and therefore the penetration depth of the eddy current differs. In the molten state, the penetration depth was greater, so the absorption power was also greater. During the melting process, the cold metal mass remains in part A for a long time, and in this state, the only coil that contributes to melting is the part Na in contact with part A, and the absorption power is small, so it takes even more time. . When molten metal rises to part B, the absorption power increases and it is filled with molten metal in a short time, but the molten metal is immediately taken out and used, so in the end, the Nb coils in contact with part B only help melting. However, the overall efficiency was low and the dissolution process took a long time.

As another conventional example that improves the above-mentioned drawbacks, as shown in Fig. 8, an intermediate tap is provided on the coil 2, and when there is no metal to be melted in the upper part, the tap is switched and the upper coil is disconnected. However, large current tap switching switches S ₁ and S ₂ are required, and the impedance decreases too much if only the lower coil is applied, and excessive current will flow if full voltage is applied, so it is necessary to combine it with a tap transformer Tv. The voltage must be adjusted, and the current capacity of the lower coil cannot be changed, so the absorption power cannot be increased.Although it may save power, it does not improve melting efficiency, and it is expensive. It was hot.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a crucible-type induction furnace which eliminates the above-mentioned drawbacks, has a simple structure, and improves melting efficiency.

[Key points of the invention]

The present invention divides the coil of a crucible-shaped induction furnace into upper and lower parts, the lower coil has fewer turns than the upper coil, has a larger current capacity, and is connected to an AC power source in parallel, so that the lower part of the furnace is larger than the upper part. This is an attempt to improve the dissolution efficiency by heating with electricity.

[Embodiments of the invention]

FIG. 1 shows an outline of a coil of a crucible-type induction furnace according to an embodiment of the present invention, in which a coil 2 wound around a furnace body 1 is divided into upper and lower halves, and the number of turns of the lower coil is N _1.
is smaller than the number of turns N ₂ of the upper coil, and the conductor cross section of the lower coil is larger than that of the upper coil, and each coil is connected in parallel to an AC power source. Assuming that the power supply voltage is E, the power absorbed by the lower coil is P ₁ , the current i ₁ is, the power factor is cosφ ₁ , the absorbed power of the upper coil is P ₂ , the current i ₂ and the power factor cosφ ₂ , P ₁ = Ei ₁ cosφ ₁ ∽ i ₁ N ₁ P ₂ = Ei ₂ cosφ ₂ ∽i ₂ N ₂ .

Since N ₁ <N ₂ , the impedance of the N ₁ coil decreases and i ₁ increases. The conductor of the N ₁ coil is made thick to withstand i ₁ . Since the rate of decrease in impedance is greater than the decrease in the number of coil turns, the magnetomotive force
i ₁ N ₁ > i ₂ N ₂ . Therefore, the input power of the lower coil is higher than that of the upper part, and the melting efficiency of the lower part of the furnace increases, so that the melting efficiency of the furnace as a whole increases and the melting time can be shortened.

〔Effect of the invention〕

According to the present invention, by increasing the power input to the lower part of the furnace than to the upper part, melting efficiency is improved, the melting process is shortened, and workability is improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a coil of a crucible induction furnace according to an embodiment of the present invention, Fig. 2 is a sectional view showing the general structure of a conventional crucible induction furnace, and Fig. 3 is a schematic diagram of a coil with a switching tap. be. 1...furnace body, 2...coil, Tr...transformer,
S ₁ , S ₂ ... changeover switch.

Claims (1)

[Claims] 1 Coils wound around the outer circumference of the furnace body are placed 2 times above and below the furnace body.
A crucible-shaped induction furnace is characterized in that the lower coil has fewer turns than the upper coil, the conductor has a larger cross section, and each coil is connected in parallel to an AC power source.