JPS5819958B2 - Crucible for skull furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a skull furnace crucible used for melting active metals or high melting point metals.

Skull melting is a method of melting active metals with a strong affinity for oxygen, nitrogen, etc. (known as skull melting).When melted in a furnace made of ordinary refractory materials, the molten active metals and refractory materials react and the molten metal is melted. It was developed to solve the problem of contamination.

Crucibles for skull furnaces are generally water-cooled metal crucibles that can easily form a skull layer on the inner wall of the crucible, completely preventing contamination from the crucible during melting.

However, on the other hand, because the high-temperature molten metal or skull layer comes into direct contact with the water-cooled crucible, a large amount of heat is transferred to the crucible cooling water, resulting in the problem of extremely poor thermal efficiency compared to general melting furnaces. I'm holding it.

In order to address the above problems, the present inventors investigated various ways to improve thermal efficiency without impairing the original purpose of skull melting. He devised a crucible for skull furnaces with improved thermal efficiency by lining it with refractory material to an appropriate thickness, and filed an application as a utility model (Utility Model Application No. 171146/1989).
did.

After further investigation, it was discovered that in addition to the heat insulating effect of the lining, equalizing the temperature of the molten metal by stirring the molten metal was extremely effective in improving thermal efficiency.

Therefore, as a result of various studies on water-cooled crucibles that can sufficiently stir the molten metal during melting, we found that a magnetic field generating coil was placed around the side wall of the water-cooled crucible to generate a magnetic field perpendicular to the crucible surface, and the arc current was applied to the crucible. The inventors have discovered that if the molten metal is allowed to flow along the side wall, the molten metal can be sufficiently stirred by the electromagnetic effect of the magnetic field and the arc current component, leading to the present invention.

That is, the present invention uses Al2O3, Cab, etc., which have a high melting point and are difficult to react with molten metal, in the hole of a metal water-cooled crucible.
, lined with a refractory material of ZrO2, MgO, Y2O3, BeO alone or a mixture thereof to a thickness in the range of 5 to 30 mm.1. The crucible for a skull furnace is characterized in that a magnetic field generating coil is arranged around the side wall of the crucible.

In the present invention, if the refractory material is lined up to the upper part of the side wall of the crucible as in the earlier crucible mentioned above, the arc current will not flow to the side wall, there will be no electromagnetic effect, and the molten metal will not be stirred. The arc current flows only to the side wall.

Furthermore, the lining material, lining thickness, and lining area have important meanings in the construction of the crucible.

In other words, as a lining material, refractory materials that have a high melting point and are difficult to react with active metal molten metal, Al2O3, Ca
O9zrO29MgO9Y20. It has been experimentally confirmed that a lining thickness of 5 to 30 mm is suitable.

In addition, the electrically conductive part on the upper side wall of the crucible is an area where the plasma current can flow sufficiently, that is, an area (mm2) that is %x1 or more based on the normal plasma current I (ampere).
, (for example, an area of 101000i or more in the case of 2000A), and it is desirable to line the other parts.

The figure shows an example of a crucible for a skull furnace according to the present invention.

This water-cooled crucible has a structure in which the bottom of the water-cooled crucible 2 is lined with a refractory material 4, and a magnetic field generating coil 3 is installed around the side wall of the crucible.

During melting using the water-cooled crucible of the present invention, when a direct current is passed through the magnetic field generating coil 3 when the melted raw material begins to melt, a magnetic field perpendicular to the crucible surface is generated.

Next, when the arc current between the torch 1 and the molten metal 8 flows to the side wall of the crucible, a stirring force is generated in the molten metal due to the electromagnetic effect between the arc current component perpendicular to this and the magnetic field, and the temperature of the molten metal is made uniform. As a result, thermal efficiency can be greatly improved.

Furthermore, since a skull layer 9 is formed between the molten metal and the crucible, contamination of the molten metal can be completely prevented.

Next, the thermal efficiency when using the crucible of the present invention will be explained in detail using examples.

Example 1 Pure chromium was melted using a water-cooled copper crucible (container inner diameter: 800 mm) shown in the figure.

First, the bottom of the crucible was lined with a refractory material having a composition of MgO:A1203=8=2 to a thickness of about 20 yran.

A raw material of pure chromium was charged into this crucible, and after the inside of the furnace was evacuated to vacuum, it was replaced with Ar gas and a plasma arc was ignited to perform melting and scouring.

During melting, a direct current of 3OA is passed through the magnetic field generation coil to generate a magnetic field of 30 Gauss and stir the molten metal.
Ta.

Next, a pure chromium ingot was obtained by casting, but the ingot was extremely sound with no roughening of the surface and no slight cranking.However, unmelted raw material still remained on the lining surface of the crucible, and It was found that a skull layer with a thickness of several 10 mm was formed on top, and no reaction with the refractory occurred at all.

Next, in order to investigate the effect of improving the thermal efficiency and electric power consumption by using the crucible of the present invention, the amount of heat received by the crucible cooling water and the electric power consumption were examined.

For comparison, a conventional crucible (unlined crucible) and a prior application crucible (Utility Application 171146/1982)
We also investigated in the same way.

The results are shown in Table 1.

As shown in the table, by using the crucible of the present invention, the temperature difference between the cooling water inlet and the outlet is about the same as that of the earlier application crucible, but the power consumption per 1 kg melting (power unit) is lower. It turns out that it is even less than the Wish Crucible.

In other words, this shows that the crucible of the present invention has better thermal efficiency than the crucible of the prior application.

Example 2 Using a water-cooled copper crucible as shown in the figure, in which the bottom of the crucible was lined with ZR02 refractory with a purity of 99.9% (thickness: 10 mm), a raw material of pure titanium was charged and the inside of the furnace was evacuated to a vacuum. Afterwards, the gas was replaced with Ar gas, and a plasma arc was ignited to perform melting and scouring.

Note that a direct current of 50 A was passed through the magnetic field coil to generate a magnetic field of 50 Gauss to stir the molten metal.

The obtained ingot was extremely sound and had a purity of 99.9% or more.

In this example as well, it was confirmed that a sufficient amount of undissolved raw material remained on the lining surface of the crucible.

Next, in order to examine the improvement effect of the crucible of the present invention, the amount of heat received by the crucible cooling water during melting and the unit power area were examined in the same manner as in Example 1.

For comparison, a conventional crucible and a crucible of a prior application (Utility Model Application No. 171146/1983) were also examined in the same manner.

The results are shown in Table 2.

As shown in the same table, even in the case of pure titanium melting, by using the crucible of the present invention, the amount of heat received by the cooling water is about the same as that of the crucible of the prior application, but the amount of electricity used is clearly lower, and the thermal efficiency is even better. It shows.

As described above, the skull furnace crucible of the present invention can improve thermal efficiency (compared to conventional crucibles) without impairing product quality, and has economical value such as shortening melting time or reducing plasma output. This is a great invention.

In addition, although the example shows an example of melting pure chromium and pure titanium using a plasma arc as a heat source, the crucible of the present invention can also be used for melting high-melting point metals such as tungsten, niobium, tantalum, and molybdenum. can.

[Brief explanation of the drawing]

The figure is a diagram showing an embodiment of the crucible of the present invention. 1...Torch, 2...Metal water-cooled crucible, 3...Magnetic coil for stirring, 4...
Fireproof material, 5... Cooling water, 6... Cooling water inlet, 7... Cooling water outlet, 8...
- Molten metal, 9...Skull layer.

Claims (1)

[Claims] 1. The bottom of the metal water-cooled crucible has a high melting point and is difficult to react with the molten metal (Al2O3, CaO9ZrO2Mg).
A crucible for a skull furnace, characterized in that it is lined with a refractory material of O, Y2O3, and BeO alone or in a mixture thereof to a thickness in the range of 5 to 30 mm, and a magnetic field generating coil is arranged around the side wall of the crucible.