JPH04312788A - Induction furnace using graphite-type crucible - Google Patents

Abstract

PURPOSE:To prevent crack formation due to the temperature difference at the center part of a graphite-type crucible. CONSTITUTION:The pitch of a coil 3 to be wound on the circumference of a crucible is wound densely in the upper part and the lower part and sparsely in the center part. At that time, the coil 3b in the center part is made to have a larger cross-section size in the axial direction than a coil 3a in the upper part and the lower part or the coil 3b in the center part is made to have the same cross-section size as the coil 3a in the upper part and the lower part. In the case that the pitch of the coil 3b in the center part is made sparse, the current density is lowered and the temperature is made uniform in the upper and the lower sides, so that cracks due to thermal stress at the time of cooling are prevented and the reaction with a molten metal is also carried out uniformly and crack formation in the center part is prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction furnace using a graphite or graphite-based crucible, and more particularly to an induction furnace that uses a shaped crucible to heat copper alloys or non-conductive materials.

0002

[Prior Art] Although not necessarily an induction furnace using a graphite crucible, the conventional crucible type induction furnace is
As seen in Publication No. 15, Publication of Utility Model Publication No. 63-49678, etc., the coils are wound at equal pitches.

0003

The use of an induction furnace using a regular graphite crucible for melting copper alloys or non-conductive materials has the following benefits.

(a) Relining of refractories
The work is quick and easy as only the crucible needs to be replaced. (b) Since there is little crystallization water in the refractory, operation starts up quickly after relining, and there is no absorption of moisture, hydrogen gas, etc. into the molten metal. (c) Less slag is generated from materials that resist oxidation, such as copper alloys. (d) Even materials that do not self-heat, such as ceramics, can be indirectly heated by heating a crucible.

On the other hand, the disadvantages are (a) short life compared to monolithic refractories, (b) high cost, and (c)
It is difficult to form a large-capacity crucible with a capacity of 3 tons or more in terms of copper. Among these, regarding the lifespan, there is not necessarily a fixed usage period, and the lifespan often ends from the time the hot water is poured, and since it is a sudden accident, there is a problem in terms of stable operation.

When considering the lifespan of a graphite crucible, there are cases where the crucible itself reacts with the molten metal and wears out, becoming thinner and reaching the end of its lifespan, and cracks, especially in the center of the height of the crucible, which become hot water. It may reach the end of its life.

An object of the present invention is to provide an induction furnace using a graphite crucible that can prevent the occurrence of cracks due to temperature differences in the center of the graphite crucible.

[0008]

[Means for Solving the Problems] In an induction furnace using a graphite crucible of the present invention, the pitch of the coil wound around the crucible is set such that the coil is wound densely in the upper and lower parts and coarsely in the center part. It is. In this case, the central coil may have a larger axial cross-sectional dimension than the upper and lower coils, or the central coil, the upper coil, and the lower coil may have the same cross section. Make it.

[0009]

[Function] Considering a conventional coil crucible with equal pitch winding, the temperature in the center is higher than the top and bottom.
It turns out that the distribution of magnetic flux follows the same trend, and that there is also heat radiation into the atmosphere, especially in the upper part. When the center reaches a high temperature, the heat shrinkage during cooling is different from that in other parts, and cracks are more likely to occur due to thermal stress. In particular, as high-frequency furnaces become more advanced, full tapping becomes more frequent, and cracks tend to occur in the center due to repeated heating and cooling. In addition, reactions with the molten metal tend to proceed in the high-temperature parts.

[0010] If the pitch of the coil 3b in the central part is made rough as in invention 1, the current density is reduced, the temperature is made uniform in the upper and lower portions of the crucible 1, cracks due to thermal stress during cooling are prevented, and the contact with the molten metal is reduced. The reaction is also made more uniform and the occurrence of cracks in the center is prevented. In this case, invention 1 is embodied by inventions 2 and 3.

[0011]

Embodiment FIG. 1 is a sectional view of Embodiment 1, and FIG. 2 is a sectional view of Embodiment 2. In FIG. 1, a coil 3 is wound around a graphite crucible 1 via a back lining 2, and a yoke 4 is provided around the outer periphery of the coil 3.
The pitch of the coils 3b is closer than that of the central coil 3b. The height of the cross section in the axial direction is also larger in the coil 3b. When AC power is applied to such a coil 3, the current density of the central coil 3b can be reduced compared to that of the upper and lower coils 3a, and the coils 3a are closely spaced to improve coil efficiency. . Example 2 shown in Figure 2
The upper and lower coils 31a have the same cross section as shown in FIG.
The coil 31b may be wound densely and the coil 31b in the center may be wound loosely. In this way, by making the pitch of the central coil 3b coarse, the current density is reduced, the temperature is made uniform between the top and bottom of the crucible 1, cracks caused by thermal stress during cooling are prevented, and the reaction with the molten metal is made uniform. This prevents cracks from occurring in the center.

0012

[Effects of the Invention] In the induction furnace using the graphite crucible of the present invention, the pitch of the coils wound around the crucible is set such that the coils are wound densely in the upper and lower parts and coarsely in the central part. This has the effect of preventing cracks from occurring due to temperature differences in the center of the graphite crucible. In this case, the central coil may have a larger cross-sectional axial dimension than the upper and lower coils, or the central coil, the upper coil, and the lower coil may have the same cross section. It has a similar effect.

[Brief explanation of the drawing]

[Figure 1] Cross-sectional view of Example 1

[Fig. 2] Cross-sectional view of Example 2

[Explanation of symbols]

1 Graphite crucible 3 Coil 3a Coil 3b Coil 31 Coil

Claims (3)

[Claims] 1. An induction furnace using a graphite crucible, characterized in that the pitch of the coil wound around the crucible is set such that the pitch of the coil is densely wound in the upper and lower parts, and coarsely in the central part. 2. An induction furnace using a graphite crucible according to claim 1, wherein the central coil has a cross-sectional axial dimension larger than that of the upper and lower coils. An induction furnace that uses 3. An induction furnace using a graphite crucible according to claim 1, wherein the central coil, the upper coil, and the lower coil have the same cross section. Induction furnace used.