WO2012011160A1

WO2012011160A1 - Electromagnetic casting device for silicon ingots

Info

Publication number: WO2012011160A1
Application number: PCT/JP2010/006739
Authority: WO
Inventors: 宣正内藤; 草場　辰己; 伸一宮本
Original assignee: 株式会社Sumco
Priority date: 2010-07-21
Filing date: 2010-11-17
Publication date: 2012-01-26
Also published as: TW201204884A; JP2012025600A

Abstract

Disclosed is an electromagnetic casting device for continuously casting silicon ingots by introducing a silicon material into a bottomless cooling crucible that is arranged inside a chamber, melting the silicon material through induction heating caused by an induction coil, and solidifying the molten silicon while lowering same from the cooling crucible. The electromagnetic casting device includes a ventilation pipe that is connected to the upper and lower sections of the side wall of the chamber, and that takes in atmospheric gas above the cooling crucible and sends out the atmospheric gas below the cooling crucible. A dust collector and a magnetic separator are provided on the path of the ventilation pipe. Thus, during continuous casting, the molten silicon can be prevented from being contaminated by metal impurities due to the free convection of the atmospheric gas inside the chamber.

Description

Silicon ingot electromagnetic casting equipment

The present invention relates to an electromagnetic casting apparatus for continuously casting a silicon ingot that is a material of a substrate for a solar cell.

In recent years, the problem of global warming due to CO ₂ emissions and the problem of depletion of energy resources have become serious, and solar power generation that uses solar energy that falls indefinitely is attracting attention as one of the countermeasures against these problems. . Photovoltaic power generation is a power generation method in which solar energy is directly converted into electric power using a solar cell, and a polycrystalline silicon wafer is mainly used as a substrate of the solar cell.

A polycrystalline silicon wafer for solar cells is manufactured by slicing a unidirectionally solidified silicon ingot. For this reason, in order to promote the spread of solar cells, it is necessary to secure the quality of the silicon wafer and reduce the cost, and it is required to manufacture a high-quality silicon ingot at a low cost in the previous stage. As a method that can meet this requirement, for example, as disclosed in Patent Document 1, a continuous casting method using electromagnetic induction (hereinafter also referred to as “electromagnetic casting method”) has been put into practical use.

FIG. 6 is a diagram schematically showing a configuration of a conventional typical electromagnetic casting apparatus used in the electromagnetic casting method. As shown in FIG. 1, the electromagnetic casting apparatus includes a chamber 1. The chamber 1 is a water-cooled container having a double wall structure in which the inside is isolated from the outside air and maintained in an inert gas atmosphere suitable for casting. A raw material supply device (not shown) is connected to the upper wall of the chamber 1 via an openable / closable shutter 2. The chamber 1 is provided with an inert gas introduction port 5, and an exhaust port 6 is provided in a lower side wall.

In the chamber 1, a bottomless cooling crucible 7, an induction coil 8, and an after heater 9 are arranged. The cooling crucible 7 functions not only as a melting vessel but also as a mold and is a rectangular tube made of metal (for example, copper) excellent in thermal conductivity and conductivity, and is suspended in the chamber 1. The cooling crucible 7 is divided into a plurality of strip-shaped pieces in the circumferential direction, leaving the upper part, and is forcibly cooled by cooling water flowing through the inside.

The induction coil 8 is provided concentrically with the cooling crucible 7 so as to surround the cooling crucible 7 and is connected to a power supply device (not shown). A plurality of after-heaters 9 are concentrically connected to the cooling crucible 7 below the cooling crucible 7 and heat the silicon ingot 3 pulled down from the cooling crucible 7 to provide an appropriate temperature gradient in the axial direction thereof.

In the chamber 1, a raw material introduction pipe 10 is attached below the shutter 2 connected to the raw material supply device. Along with opening and closing of the shutter 2, granular or lump silicon raw material 11 is supplied from the raw material supply device into the raw material introduction pipe 10 and charged into the cooling crucible 7.

In the bottom wall of the chamber 1, an outlet 4 for extracting the ingot 3 is provided directly under the after heater 9, and this outlet 4 is sealed with gas. The ingot 3 is pulled down while being supported by a support base 14 that descends through the drawer opening 4.

A plasma torch 13 is provided directly above the cooling crucible 7 so as to be movable up and down. The plasma torch 13 is connected to one pole of a plasma power supply device (not shown), and the other pole is connected to the ingot 3 side. The plasma torch 13 is inserted into the cooling crucible 7 while being lowered.

In the electromagnetic casting method using such an electromagnetic casting apparatus, the silicon raw material 11 is inserted into the cooling crucible 7, an alternating current is applied to the induction coil 8, and the lowered plasma torch 13 is energized. At this time, since the strip-shaped pieces constituting the cooling crucible 7 are electrically divided from each other, an eddy current is generated in each piece due to electromagnetic induction by the induction coil 8, and the cooling crucible 7 The eddy current on the inner wall side generates a magnetic field in the cooling crucible 7. As a result, the silicon raw material 11 in the cooling crucible 7 is melted by electromagnetic induction heating to form molten silicon 12. In addition, a plasma arc is generated between the plasma torch 13 and the silicon raw material 11 and further the molten silicon 12, and the silicon raw material 11 is also heated and melted by the Joule heat, thereby reducing the burden of electromagnetic induction heating. The molten silicon 12 is efficiently formed.

The molten silicon 12 has a force (pinch force) in the inner normal direction of the surface of the molten silicon 12 due to the interaction between the magnetic field generated along with the eddy current on the inner wall of the cooling crucible 7 and the current generated on the surface of the molten silicon 12. ) Is held in a non-contact state with the cooling crucible 7. When the support 14 supporting the molten silicon 12 is gradually lowered while melting the silicon raw material 11 in the cooling crucible 7, the induction magnetic field decreases as the distance from the lower end of the induction coil 8 decreases. Further, the molten silicon 12 is solidified from the outer peripheral portion by cooling from the cooling crucible 7. Then, the silicon raw material 11 is continuously charged as the support base 14 is lowered, and the melting and solidification are continued, whereby the molten silicon 12 is solidified in one direction, and the ingot 3 can be continuously cast.

During casting, in order to maintain the inside of the chamber 1 in an inert gas atmosphere, the inert gas is sequentially supplied from the inert gas inlet 5 at the top of the chamber 1 to fill the chamber 1. The inert gas in the chamber 1 is sequentially discharged from the exhaust port 6 on the lower side wall of the chamber 1. At this time, SiO (silicon oxide) is vigorously evaporated from the molten silicon 12 by the plasma arc from the plasma torch 13, and this SiO gas is discharged from the exhaust port 6 together with the inert gas.

According to such an electromagnetic casting apparatus, contact between the molten silicon 12 and the cooling crucible 7 is reduced, so that impurity contamination from the cooling crucible 7 due to the contact is prevented, and a high-quality ingot 3 can be obtained. it can. And since it is continuous casting, it becomes possible to manufacture the ingot 3 at low cost.

International Publication WO02 / 053496 Pamphlet

In the electromagnetic casting apparatus described above, the atmospheric temperature in the chamber 1 is high at the central portion where the ingot 3 exists, decreases as the side wall of the chamber 1 is approached, and increases toward the upper portion where the molten silicon 12 exists even at the same central portion. Due to this temperature difference, natural convection of the atmospheric gas occurs in the chamber 1 as shown by the solid line arrow in FIG. Specifically, it rises between the outer periphery of the ingot 3 and the inner periphery of the after heater 9, passes through the gap between the upper end of the uppermost after heater 9 and the lower end of the cooling crucible 7, further outside the cooling crucible 7. After rising, convection of the atmospheric gas descending near the side wall of the chamber 1 occurs. A part of the atmospheric gas that convects and rises outside the cooling crucible 7 also flows directly above the cooling crucible 7 as indicated by a dotted arrow in FIG.

Then, when a metal impurity is contained in the convection atmosphere gas, the impurity is carried to a position just above the cooling crucible 7 along with the flow of the atmosphere gas, falls into the cooling crucible 7 and falls into the molten silicon 12. May be mixed. In this case, since the molten silicon 12 is contaminated with metal impurities, the quality of the ingot 3 cast from the molten silicon 12 is deteriorated. For example, when a heat-resistant alloy containing Fe or Cr is used as a constituent member of the after heater 9, the metal impurities are easily taken into the atmosphere gas in the process in which the atmosphere gas rises along the after heater 9.

The present invention has been made in view of the above problems, and when silicon ingots are continuously cast by an electromagnetic casting method, molten silicon is contaminated with metal impurities due to the atmospheric gas that naturally convects in the chamber. An object of the present invention is to provide an electromagnetic casting apparatus for a silicon ingot that can prevent this.

In order to achieve the above-mentioned object, the present inventors made extensive studies by paying attention to the flow of atmospheric gas that naturally convects in the chamber during casting, and conducted various tests. As a result, the metal impurities are removed from the atmosphere gas that has reached the upper side of the cooling crucible due to natural convection, or the atmosphere gas containing the metal impurities is forcibly exhausted, resulting in the convection atmosphere gas. As a result, it was found that impurity contamination of the molten silicon was prevented, and the present invention was completed.

The gist of the present invention resides in a silicon ingot electromagnetic casting apparatus shown in the following (1) and (2).

(1) A silicon raw material is charged into a conductive bottomless cooling crucible disposed in the chamber, and the silicon raw material is melted by electromagnetic induction heating from an induction coil surrounding the bottomless cooling crucible. In an electromagnetic casting apparatus that continuously solidifies a silicon ingot by pulling it down from the bottom cooling crucible, it is connected to the upper and lower portions of the side wall of the chamber, and the atmosphere gas above the bottomless cooling crucible is introduced to the bottom of the bottomless cooling crucible. The silicon ingot electromagnetic casting apparatus is characterized in that a vent pipe for feeding out to the pipe is provided, and a dust collector is provided in the path of the vent pipe.

In the electromagnetic casting apparatus of (1), it is preferable that a magnetic separator is provided in the path of the vent pipe or a blower is provided in the path of the vent pipe.

(2) A silicon raw material is charged into a conductive bottomless cooling crucible disposed in the chamber, and the silicon raw material is melted by electromagnetic induction heating from an induction coil surrounding the bottomless cooling crucible. In an electromagnetic casting apparatus for continuously casting a silicon ingot by solidifying while pulling down from the bottom cooling crucible, it is connected to the upper part of the side wall of the chamber, and has an upper exhaust pipe for introducing and discharging the atmospheric gas above the bottomless cooling crucible, A silicon ingot electromagnetic casting apparatus comprising a lower exhaust pipe connected to a lower portion of a side wall of a chamber and introducing and discharging an atmospheric gas below a bottomless cooling crucible.

According to the electromagnetic casting apparatus for a silicon ingot of the present invention, even if the atmospheric gas is convected under the cooling crucible and the metallic gas is contained in the atmospheric gas, the metallic impurity is removed from the atmospheric gas and reduced. Since the atmospheric gas containing the metal impurities can be forcibly exhausted, it is possible to prevent the impurity contamination of the molten silicon due to the convective atmospheric gas.

FIG. 1 is a diagram schematically showing the configuration of the electromagnetic casting apparatus of the first embodiment. FIG. 2 is a diagram schematically illustrating a configuration of a modified example of the electromagnetic casting apparatus according to the first embodiment. FIG. 3 is a diagram schematically showing the configuration of the electromagnetic casting apparatus of the second embodiment. FIG. 4 is a diagram schematically showing a configuration of an electromagnetic casting apparatus used for comparison. FIG. 5 is a diagram showing the measurement results of the Fe concentration in the silicon ingots in the present invention example and the comparative example. FIG. 6 is a diagram schematically showing a configuration of a typical representative electromagnetic casting apparatus used in the electromagnetic casting method.

Hereinafter, an electromagnetic casting apparatus for a silicon ingot according to the present invention will be described in detail by dividing the embodiment into a first embodiment and a second embodiment.

<First Embodiment>
FIG. 1 is a diagram schematically showing the configuration of the electromagnetic casting apparatus of the first embodiment. The electromagnetic casting apparatus according to the first embodiment of the present invention shown in the figure is based on the configuration of the electromagnetic casting apparatus shown in FIG. 6, and the same components are denoted by the same reference numerals, and repeated description is omitted as appropriate. .

As shown in FIG. 1, the electromagnetic casting apparatus of the first embodiment has a vent pipe 15 connected to the upper and lower portions of the side wall of the chamber 1. The upper and lower ends of the ventilation pipe 15 are opened at positions corresponding to the upper side of the cooling crucible 7 and positions corresponding to the lower side of the cooling crucible 7, respectively. Although FIG. 1 shows an example in which the ventilation pipes 15 are provided on both sides sandwiching the central axis of the chamber 1, the ventilation pipe 15 may be installed only at one place or at three or more places.

In the electromagnetic casting apparatus of the first embodiment, a dust collector 20 is provided in the path of each vent pipe 15. As the dust collector 20, a dust collector such as a cyclone method, a filter method, or an electric dust collection method can be adopted. Further, a magnetic separator 21 is provided along with a dust collector 20 in the path of each vent pipe 15. As the magnetic separator 21, a magnetic separator using a magnet filter, a magnet bar, an electromagnet, or the like can be employed.

An inert gas inlet 5 for introducing an inert gas into the chamber 1 is provided on the upper wall of the chamber 1, and an inert gas inlet pipe 17 is connected to the inert gas inlet 5. Yes. The exhaust port 6 for exhausting the atmospheric gas in the chamber 1 is provided in the lower side wall of the chamber 1 as in the electromagnetic casting apparatus shown in FIG. 6, and an exhaust pipe 16 is connected to the exhaust port 6. Yes. In FIG. 1, for convenience, an exhaust port 6 is shown in the bottom wall of the chamber 1. The exhaust amount of the atmospheric gas from the exhaust port 6 through the exhaust pipe 16 is adjusted by a flow rate adjusting valve (not shown) installed in the exhaust pipe 16.

In the electromagnetic casting using the electromagnetic casting apparatus of the first embodiment having such a configuration, the atmospheric gas existing above the cooling crucible 7 in the chamber 1 is a part thereof as shown by the solid line arrow in FIG. Is introduced into the vent pipe 15 from the upper end of the vent pipe 15 that opens here, and after descending the vent pipe 15, it is fed into the lower portion of the chamber 1 corresponding to the lower part of the cooling crucible 7, and into the vent pipe 15. The remainder that has not been introduced descends near the side wall of the chamber 1.

The atmospheric gas introduced into the lower portion of the chamber 1 through the vent pipe 15 and the atmospheric gas descending in the vicinity of the side wall of the chamber 1 are finally discharged from the exhaust port 6 to the outside of the chamber 1. Natural convection within 1. That is, the atmospheric gas present in the lower portion of the chamber 1 enters the inside of the after heater 9 through the gap between the adjacent upper and lower after heaters 9 as indicated by solid arrows in FIG. After rising between the outer periphery of the heater and the inner periphery of the after-heater 9, it passes through the gap between the upper end of the uppermost after-heater 9 and the lower end of the cooling crucible 7 and reaches the outside of the cooling crucible 7. Then, the atmospheric gas that has reached the outside of the cooling crucible 7 further rises, part of which is introduced into the vent pipe 15, and the rest descends again near the side wall of the chamber 1. Such natural convection of the atmospheric gas occurs.

At that time, when the convection atmosphere gas contains metal impurities, the metal impurities are captured and removed by the dust collector 20 in the process of passing through the dust collector 20 and the purified atmosphere gas is removed. It is sent out to the lower part of the chamber 1. At this time, even if the impurity removal by the dust collector 20 is not complete, the atmospheric gas that has passed through the dust collector 20 further passes through the magnetic separator 21 so that the metal impurities are selectively captured by the magnetic separator 21, so that the metal impurities are effectively removed. Can be removed.

Therefore, according to the electromagnetic casting apparatus of the first embodiment of the present invention, even when the convection atmosphere gas contains metal impurities, the atmosphere gas reaching the upper side of the magnetic cooling crucible 7 is introduced into the vent pipe 15. Since the dust collector 20 and possibly the magnetic separator 21 remove metal impurities from the atmospheric gas and the purified atmospheric gas is sent out to the lower part of the chamber 1, the circulation is repeated. As a result, the amount of metal impurities carried directly above the cooling crucible 7 can be remarkably suppressed. As a result, impurity contamination of the molten silicon 12 due to the convection atmosphere gas can be prevented, and the ingot 3 having excellent quality can be manufactured.

FIG. 2 is a diagram schematically showing a configuration of a modified example of the electromagnetic casting apparatus of the first embodiment. The electromagnetic casting apparatus shown in the figure has a configuration in which a blower 22 is added to the path of each ventilation pipe 15 in the electromagnetic casting apparatus shown in FIG. A fan or a blower can be adopted as the blower 22. In the electromagnetic casting apparatus shown in FIG. 1, the flow of the atmospheric gas in the ventilation pipe 15 relies on natural convection, but in the electromagnetic casting apparatus shown in FIG. 2, the gas flow is forced by the installation of the blower 22. As a result, metal impurities can be efficiently removed by the dust collector 20 and the magnetic separator 21.

Second Embodiment
FIG. 3 is a diagram schematically showing the configuration of the electromagnetic casting apparatus of the second embodiment. The electromagnetic casting apparatus according to the second embodiment of the present invention shown in the figure is different from the electromagnetic casting apparatus according to the first embodiment shown in FIG. 1 in the following points.

As shown in FIG. 3, the electromagnetic casting apparatus of the second embodiment has an upper exhaust pipe 23 connected to the upper side wall of the chamber 1 instead of the vent pipe 15 in the electromagnetic casting apparatus shown in FIG. A lower exhaust pipe 24 connected to the lower side wall of the chamber 1 is provided. The upper exhaust pipe 23 is opened at a position corresponding to the upper side of the cooling crucible 7, and introduces and discharges the atmospheric gas existing in the upper part of the chamber 1. On the other hand, the lower exhaust pipe 24 opens at a position corresponding to the lower side of the cooling crucible 7, and introduces and discharges the atmospheric gas existing in the lower part of the chamber 1. The exhaust amount of the atmospheric gas through each of the upper exhaust pipe 23 and the lower exhaust pipe 24 is adjusted by a flow rate adjusting valve (not shown) installed in each.

FIG. 3 shows an example in which the upper exhaust pipe 23 and the lower exhaust pipe 24 are provided on both sides sandwiching the central axis of the chamber 1, but the

exhaust pipes

23 and 24 may be installed at only one place. And it does not matter even if it is three or more places.

In the electromagnetic casting using the electromagnetic casting apparatus according to the second embodiment having such a configuration, the atmospheric gas existing above the cooling crucible 7 in the chamber 1 is partially a part as shown by the solid line arrow in FIG. However, it is introduced into the upper exhaust pipe 23 opened here and discharged to the outside, and the remainder not introduced into the upper exhaust pipe 23 descends in the vicinity of the side wall of the chamber 1.

The atmospheric gas that descends near the side wall of the chamber 1 and reaches the lower portion of the chamber 1 is finally discharged to the outside also from the exhaust port 6 on the bottom wall of the chamber 1, but most of it naturally convects in the chamber 1. . That is, as indicated by the solid line arrow in FIG. 3, a part of the atmospheric gas existing in the lower part in the chamber 1 is introduced into the lower exhaust pipe 24 opened here and discharged to the outside, and the lower exhaust The remainder that was not introduced into the pipe 24 entered the inside of the after heater 9 through the gap between the adjacent upper and lower after heaters 9 and ascended between the outer periphery of the ingot 3 and the inner periphery of the after heater 9 as it was. After that, it passes through the gap between the upper end of the uppermost after-heater 9 and the lower end of the cooling crucible 7 and reaches the outside of the cooling crucible 7. Then, the atmospheric gas that has reached the outside of the cooling crucible 7 further rises, part of which is discharged from the upper exhaust pipe 23, and the rest descends again near the side wall of the chamber 1. Such natural convection of the atmospheric gas occurs.

Therefore, according to the electromagnetic casting apparatus of the first embodiment of the present invention, the atmosphere gas reaching the upper side of the cooling crucible 7 is forced through the upper exhaust pipe 23 even when the convection atmosphere gas contains metal impurities. Since the exhaust gas is exhausted, the metal impurities contained in the atmospheric gas in the chamber 1 can be reduced, and accordingly, the amount of metal impurities carried directly above the cooling crucible 7 can be remarkably suppressed. As a result, impurity contamination of the molten silicon 12 due to the convection atmosphere gas can be prevented, and the ingot 3 having excellent quality can be manufactured.

In order to confirm the effect of the electromagnetic casting apparatus of the present invention, a silicon ingot was electromagnetically cast using various electromagnetic casting apparatuses having different configurations. The electromagnetic casting apparatus used in the present invention example 1 is the apparatus shown in FIG. 1 provided with only the dust collector of the dust collector and magnetic separator, in the present invention example 2, the apparatus shown in FIG. 1 and in the present invention example 3. The apparatus shown in FIG. 2 and the apparatus shown in FIG. A cyclone type dust collector was adopted, a magnetic separator using a magnet filter was adopted, and a fan was adopted as a blower.

In each manufactured ingot, sample wafers are taken from the corresponding positions when the solidification rate is 0%, 10%, 30%, 50%, 70% and 90%, and the Fe concentration in each sample wafer is measured. A test was conducted. The solidification rate here represents the ratio of the weight of the solidified ingot to the total weight of the charged silicon raw material, and corresponds to the length from the lower end of the ingot (the first position of continuous casting). For comparison, a silicon ingot was continuously cast using the electromagnetic casting apparatus shown in FIG. 4 below, and a sample wafer was similarly collected from this ingot to measure the Fe concentration.

FIG. 4 is a diagram schematically showing the configuration of an electromagnetic casting apparatus used for comparison. The electromagnetic casting apparatus used in the comparative example shown in the same drawing is compared with the electromagnetic casting apparatus used in the inventive examples 1 to 3 shown in FIG. However, the vent pipe 15 is different in that it does not include any of a dust collector, a magnetic separator, and a blower.

FIG. 5 is a diagram showing the measurement results of the Fe concentration in the silicon ingot in the present invention example and the comparative example. The Fe concentration shown in the same figure is a relative value indexed with the minimum Fe concentration of 10 (reference) among the Fe concentrations obtained in the test of the comparative example. From the results shown in the figure, it is clear that the Fe concentration is reduced in all of the inventive examples 1 to 4 and the impurity contamination of the molten silicon can be prevented as compared with the comparative example using the electromagnetic casting apparatus having only the vent pipe. became.

According to the electromagnetic casting apparatus of the silicon ingot of the present invention, even if the metal gas is contained in the atmospheric gas convection below the cooling crucible, it can be reduced by removing the metal impurity from the atmospheric gas, Alternatively, the atmospheric gas containing the metal impurities can be forcibly exhausted, and it is possible to prevent the molten silicon from being contaminated with the metal impurities due to the convective atmospheric gas. Therefore, the continuous casting method of the present invention is extremely useful in that a silicon ingot for a solar cell excellent in quality can be produced.

1: chamber, 2: shutter, 3: silicon ingot,
4: Drawer port, 5: Inert gas inlet port, 6: Exhaust port,
7: Bottomless cooling crucible, 8: Induction coil,
9: After heater, 10: Raw material introduction pipe,
11: Silicon raw material, 12: Molten silicon,
13: Plasma torch, 14: Support base, 15: Vent pipe,
16: exhaust pipe, 17: inert gas introduction pipe,
20: Dust collector, 21: Magnetic separator, 22: Blower
23: Upper exhaust pipe, 24: Lower exhaust pipe

Claims

A silicon raw material is charged into a conductive bottomless cooling crucible disposed in the chamber, and the silicon raw material is melted by electromagnetic induction heating from an induction coil surrounding the bottomless cooling crucible. In an electromagnetic casting apparatus that continuously solidifies a silicon ingot by lowering it from
It is connected to the upper and lower sides of the side wall of the chamber, and has a vent pipe that introduces atmospheric gas above the bottomless cooling crucible and sends it out below the bottomless cooling crucible,
An electromagnetic casting apparatus for a silicon ingot, characterized in that a dust collector is provided in the path of the vent pipe.
2. The electromagnetic casting apparatus for a silicon ingot according to claim 1, further comprising a magnetic separator provided in a path of the vent pipe.
Furthermore, the silicon ingot electromagnetic casting apparatus according to claim 1, wherein a blower is provided in a path of the vent pipe.
A silicon raw material is charged into a conductive bottomless cooling crucible disposed in the chamber, and the silicon raw material is melted by electromagnetic induction heating from an induction coil surrounding the bottomless cooling crucible. In an electromagnetic casting apparatus that continuously solidifies a silicon ingot by lowering it from
An upper exhaust pipe connected to the upper part of the side wall of the chamber, for introducing and discharging the atmospheric gas above the bottomless cooling crucible;
A silicon ingot electromagnetic casting apparatus comprising a lower exhaust pipe connected to a lower portion of a side wall of a chamber and for introducing and discharging an atmospheric gas below a bottomless cooling crucible.