JP2012200729A - Gas blowing rotor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gas blowing rotor capable of supplying bubbles formed by fining down inert gas sufficiently into melted metal for a long time, and moreover, maintaining gas dispersibility for a long time.SOLUTION: The gas blowing rotor for blowing gas into the melted metal includes a rotary axis, a through-hole part formed with the rotary axis as its center, and a plurality of gas dispersing grooves extended radially toward an outer periphery when seen from the rotary axis, and is made of silicon nitride ceramics containing a main phase mainly constituted of a silicon nitride or sialon crystal and a grain boundary phase mainly constituted of a glassy or crystalline material. The surface of the gas dispersing groove is a fired surface or a surface similar to the fired surface. Moreover, the width of the gas dispersing groove is made to fall within the range of 10-20 mm, and the ratio between the depth and width thereof is made to fall within the range of 0.5-1.5.

Description

  The present invention is a gas that discharges and disperses an inert gas such as nitrogen or argon gas in a bubble state in a molten metal such as aluminum, and removes gas such as hydrogen and inclusions such as oxide in the molten metal. The present invention relates to a blowing rotor.

  For example, an aluminum product such as an aluminum wheel of an automobile is manufactured by casting aluminum or the like. In this case, high-temperature molten metal made of a metal material such as aluminum or an aluminum alloy is injected into the mold for forming. In this molten metal, an operation of bubbling an inert gas such as nitrogen or argon gas in the molten metal is performed in order to float and remove impurities such as hydrogen gas in the molten metal.

  In this operation, a gas blowing rotator (hereinafter sometimes referred to as a rotator) is used. A gas supply pipe for supplying an inert gas is connected to the center of the rotating body, and the gas supply pipe is disposed at the upper part of the molten metal. The rotating body is immersed in the molten metal and rotates around the gas supply pipe as a rotating shaft. The inert gas supplied to the rotating body through the gas supply pipe becomes fine bubbles from the periphery of the rotating body as the rotating body rotates, and is ejected while being dispersed in the molten metal. The bubbles reach the surface of the molten metal. At this time, hydrogen in the molten metal is removed.

  The temperature of the molten metal is as high as 650 ° C. or higher in the case of aluminum, and the rotating body is used therein. For this reason, the rotator and the gas supply pipe are required to have low reactivity with a metal material at a high temperature, the constituent material is not easily leached into the molten metal, and high mechanical strength. In addition, when the rotating body is immersed in a high-temperature molten metal, it is also required that cracking due to thermal stress due to a difference in thermal expansion at the time of rapid temperature rise hardly occurs, that is, that the thermal conductivity and fracture toughness are high. The

  As a material constituting the rotating body, for example, sintered graphite is known. However, graphite composed of carbon has a problem that durability is low because consumption in a molten metal is severe. In this respect, ceramics are advantageous because they have high durability.

  As this ceramic, for example, as described in Patent Document 1, there is a ceramic mainly composed of silicon nitride. As a shape of the rotating body, for example, as described in Patent Document 2, a radial gas dispersion groove is formed on a disk-shaped bottom surface, an inert gas flows through the gas dispersion groove, and dispersed fine bubbles are surrounded. There is a shape that erupts radially from. In the rotating body of Patent Document 2, the thickness of the disk in the radial direction is not uniform in order to prevent the cracking, and the thickness is gradually reduced from the center toward the outside.

Published Utility Heisei 4-15000 Public Utility No. Heisei 3-91161

  In recent years, fine bubbles can be stably supplied for a long time to a rotating body for gas blowing, which has a function of generating fine bubbles of inert gas as described above, and dispersing the bubbles into the molten metal. Realization of a rotating body for gas blowing is required. Here, in order to improve the dispersibility of the inert gas and generate finer bubbles, the shape of the cross section of the gas dispersion groove in the height direction of the rotating body is elongated, that is, (depth / width) of the gas dispersion groove. It is effective to increase the aspect ratio represented by

However, the surface of the conventional rotating body has high wettability of the surface of the rotating body with respect to the molten metal, and the molten metal may adhere to the surface of the gas dispersion groove when the rotating body is used or removed from the molten metal. It was. Further, when the molten metal is stirred, a powder component called a flux may be added to the molten metal in order to remove impurities (such as Mg) in the molten metal. This flux is stirred after being charged and dispersed in the molten metal, but this flux may adhere to the surface of the gas dispersion groove during use of the rotating body or when it is pulled up. If the molten metal or flux adheres to the surface of the gas dispersion groove whose aspect ratio is increased as described above to disperse the inert gas into fine bubbles, the cross-sectional area of the gas dispersion groove is reduced and the inert gas is inactive. The gas dispersibility (hereinafter sometimes referred to as gas dispersibility) cannot be maintained.

  In addition, cracks may occur in the rotating body due to thermal stress, and in order to cope with this, the rotating body of Patent Document 2 has a shape that is thicker at the center and thinner toward the outside. However, this crack is not determined only by the thickness of the rotating body. When the aspect ratio of the gas dispersion groove is increased as described above, cracks due to thermal stress tend to progress from the corner of the groove bottom where stress concentration occurs. At this time, this crack was more likely to occur as the aspect ratio of the gas dispersion groove where the wall thickness rapidly changed. In addition to the problem of maintaining gas dispersibility due to the clogging of the gas dispersion grooves, it is difficult to maintain gas dispersibility in a ceramic rotating body due to this cracking problem.

  For this reason, it has been difficult to obtain a gas blowing rotor capable of supplying gas bubbles made of sufficiently fine inert gas into the molten metal for a long period of time and maintaining gas dispersibility for a long period of time.

  The present invention has been made in view of such problems, and an object thereof is to provide an invention that solves the above problems.

In order to solve the above problems, the present invention has the following configurations.
The rotating body for gas blowing according to the present invention includes a rotation axis, a through-hole portion formed around the rotation axis, and a plurality of gas dispersion grooves extending radially from the rotation axis toward the outer periphery of view, A molten metal having a through-hole portion for supplying an inert gas and comprising a main phase mainly composed of silicon nitride or sialon crystals and a grain boundary phase mainly composed of vitreous or crystalline A rotating body for injecting an inert gas into the gas dispersion groove, wherein the surface of the gas dispersion groove is baked skin or skin similar to the baked skin, and the gas dispersion groove has a width of 10 to 20 mm. The depth / width ratio is in the range of 0.5 to 1.5.
The gas blowing rotator of the present invention has an average value of arithmetic mean roughness Ra according to JIS-B0601 of the surface of the gas dispersion groove at three points on the inner circumference side, the center, and the outer circumference side of the gas dispersion groove in the radial direction. Are both in the range of 0.9 to 2.1 μm.
In the gas blowing rotator according to the present invention, the silicon nitride ceramics includes fine particles selected from a boride, a nitride, or a carbide.
In the gas blowing rotator according to the present invention, the silicon nitride ceramics include fine particles made of hexagonal boron nitride.
In the gas blowing rotator of the present invention, the silicon nitride ceramic contains 2 to 15% by mass of rare earth elements and Mg in terms of oxides as grain boundary phases, and rare earth metals (RE) and Mg in terms of oxides. A mass ratio (RE ₂ O ₃ / MgO) is contained at a ratio of 0.1 to 10.
The gas blowing rotor of the present invention has a specific surface area of 20 to 50 m ² / g, an average particle size of 2 to 10 μm measured by a laser diffraction / scattering method, and particles having a particle size of 30 μm or more are 5% or less, The hexagonal boron nitride powder having an average primary particle size of 0.01 to 0.8 μm measured from the SEM photograph is 3 to 20 mass with respect to a total of 100 mass parts of the silicon nitride powder and the sintering aid powder. It is manufactured using the raw material powder which contains a part.
In the gas blowing rotator according to the present invention, the gas blowing rotator is configured to have a substantially bowl shape with one opening, and the gas dispersion groove is formed on one end surface of the gas blowing rotator, The through hole is formed on the other end surface.
In the gas blowing rotator according to the present invention, the gas blowing rotator is configured to have a substantially disk shape, and the gas dispersion groove is directly connected to the through hole. .
The gas blowing rotator according to the present invention is characterized in that R processing or chamfering is performed on an outer edge portion of the gas dispersion groove in a radial direction of the gas blowing rotator.
In the gas blowing rotator according to the present invention, an agitation groove for agitating the molten metal is formed on the outer peripheral surface of the rotating part.

  Since the present invention is configured as described above, it is possible to obtain a rotating body for blowing gas having sufficient durability and sufficient dispersibility of bubbles.

(A) is a bottom view of a rotating body for gas blowing according to an embodiment of the present invention, (b) is a sectional view taken along line AA in (a), and (c) is a sectional view taken along line BB in (a). is there. It is a perspective view of the rotary body for gas blowing of FIG. (A) is a bottom view of the modification of the rotary body for gas blowing used as embodiment of this invention, (b) is CC sectional drawing of (a). It is a perspective view of the modification of the rotary body for gas blowing of FIG.

  The present invention will be described below with reference to specific embodiments. However, the present invention is not limited to these embodiments. The gas blowing rotator according to the embodiment of the present invention can be applied as a gas blowing rotator immersed in a high-temperature molten metal.

  FIG. 1A is a bottom view of the gas blowing rotor, and FIG. 1B is a cross-sectional view taken along line AA including a gas dispersion groove 22 along the central axis of the rotor 20 in FIG. FIG.1 (c) is BB sectional drawing containing the stirring groove 23 along the central axis of the rotary body 20 of Fig.1 (a). FIG. 2 is a perspective view of the rotating body 20 of FIG.

  In the rotating body 20 for blowing gas supplied in a state where bubbles obtained by subdividing the inert gas are dispersed in the molten metal, argon / nitrogen or other inert gas (hereinafter simply referred to as gas) may be supplied to the rotating body 20. .) Is provided with a cylindrical gas supply pipe 30. As shown in FIG.1 (b), the left end part of the gas supply pipe 30 is fixed to the rotating shaft center of the rotary body 20 by fitting, and these are integrated. When the rotating body 20 rotates around the central axis of the gas supply pipe 30, the gas supplied from the gas supply pipe 30 is dispersed and ejected into the molten metal. In addition, a substantially cylindrical gas supply member 201 whose outer diameter is the same as that of the pipe is fitted into the pipe on one end side of the gas supply pipe 30 at the place where the gas supply pipe 30 is fitted to the rotating body 20. Are combined. A through-hole portion 21 is formed at the center of the gas supply member 201, and the gas passes through the through-hole portion 21 from the right side to the left side in FIGS. It spouts to 24. The rotating body 20 and the gas supply pipe 30 are manufactured at a low cost by reducing the number of parts, and from the viewpoint of preventing breakage of the rotating body from, for example, a female screw formed for screw fixing. It is preferable to fix by fitting. The same applies to the gas supply member 201 fitted in the flow path of the gas supply pipe 30.

  The gas supply pipe 30 is installed from the upper part of the molten metal to the inside of the molten metal, supplies gas to the rotating body 20 (gas supply member 201), and rotates the rotating body 20 in the molten metal. The arrow in FIG.1 (b) has shown the downward direction (side with the bottom of a molten metal) when this is installed. The lowermost end of the gas supply pipe 30 is integrated with the rotary body 20 and the gas supply member 201 at the center of the rotary body 20, and the other end protruding from the upper surface of the molten metal is connected to a rotation motor.

  The gas supply pipe 30 has a cylindrical shape having a flow path, and gas flows through the flow path. On the other hand, the rotator 20 has a substantially bowl shape having a hollow portion 24 opened on the lower side (the side where the bottom of the molten metal is present). Here, the center in FIG. 1 (a) is the rotation axis, and the rotating body 20 (gas supply member) extends in the vertical direction (the left / right direction in FIGS. 1 (b) and 1 (c)) around this rotation axis. 201) is provided. As shown in FIGS. 1B and 1C, the through-hole portion 21 is connected to the flow path of the gas supply pipe 30, and gas is supplied to the hollow portion 24 of the rotating body 20 through the through-hole portion 21. Is done. In the molten metal, the gas supplied to the rotating body 20 stays in the hollow portion 24 by buoyancy and is held. Hereinafter, the hollow portion 24 is referred to as a gas retention portion.

  On the circumference of the end surface (one end surface) on the opened side of the rotating body 20 of this embodiment, eight gas dispersion grooves 22 are provided so as to penetrate in the radial direction at an equal angle of 45 °. The width of the gas dispersion groove 22 is X in FIG. 1A, and the height (depth) is Y in FIG. The thickness of the rotating body 20 where the gas dispersion grooves 22 are formed is W in FIG.

  In addition, as a preferable element, the rotating body 20 of this embodiment has a stirring groove 23 that is 22.5 ° from the gas dispersion groove 22 from the upper surface (the right surface in FIGS. 1B and 1C) to the side surface. Eight are formed in a shifted form. The width of the stirring groove 23 is T in FIG. 1A, and the depth is Z in FIG. The stirring groove 23 does not penetrate through the members constituting the rotating body 20, and Z <W on the side surface, and the same applies to the upper surface.

  In the rotating body 20 having the above-described configuration, the gas flowed from above (the right side in FIGS. 1B and 1C) is the end surface (the other end surface) opposite to the side where the gas dispersion grooves 22 are formed. The rotating body 20 is reached through the through-hole portion 21 formed in the, and is held by a substantially bowl-shaped gas retention portion (hollow portion) 24. Thereafter, the gas flows outward and passes through the surrounding gas dispersion groove 22 by centrifugal force. At this time, the gas is dispersed as fine bubbles along with the rotation of the rotating body 20 and is released into the molten metal.

  On the other hand, as described above, the stirring groove 23 added as a preferable element in the rotating body 20 of the present embodiment is formed long from the upper surface to the side surface in the direction perpendicular to the rotating direction of the rotating body 20. When rotating, the action of stirring increases. In particular, if the material constituting the rotator 20 is thick, cracks are likely to occur due to thermal stress, and it is difficult to make this thick. On the other hand, sufficient stirring characteristics cannot be obtained unless the rotating body 20 is sufficiently thick in the vertical direction (the horizontal direction in FIG. 1B). In the rotating body 20, the rotating body 20 is thickened in the vertical direction while the material itself is thinned by having a substantially bowl shape. Further, since the stirring groove 23 is formed on the outer peripheral surface (side surface, upper surface) at this time, the action of stirring is particularly increased.

  The rotating body 20 having the above-described configuration is immersed in a high-temperature molten metal (for example, about 700 to 750 ° C. in the case of molten aluminum). For this reason, the material constituting the rotating body 20 is not deformed in the high-temperature molten metal, does not cause a chemical reaction or alloying with the molten metal, and is not heated in and out of the molten metal. It is required that no breakage (crack) due to stress occurs. Silicon nitride ceramics (ceramics containing silicon nitride as a main component) described in Patent Document 1 are generally known as materials that satisfy these requirements.

Here, as described above, when the gas dispersion groove 22 having a high aspect ratio (groove depth / groove width) is formed in the rotating body in consideration of the gas dispersibility that makes the gas fine bubbles, There is a problem that the molten aluminum, its oxide or slag adheres to the surface, and the gas dispersion groove 22 is easily blocked during use. When the gas dispersion groove 22 is blocked, the gas dispersibility cannot be maintained. As a result, an operation of removing the plug by pickling or the like is required. It is desired. The fine structure of the surface affects the blockage of the gas dispersion groove 22.

  In addition, in the case of the rotating body 20 immersed in a high-temperature molten metal, it is necessary to consider the breakage due to thermal stress. In addition to the thermal conductivity, fracture toughness, bending strength, and other material characteristics, the shape of the rotating body 20 such as the presence of a suddenly changed thickness portion that easily generates thermal stress affects the fracture. Here, in the rotating body 20, the portion where the wall thickness is abruptly changed and cracks are likely to occur is the corner at the bottom of the gas dispersion groove 22 or the stirring groove 23, and the gas dispersion groove 22 having a particularly high aspect ratio is thick. Destruction is likely to occur due to a large sudden change.

  Therefore, in the rotating body 20 of the present embodiment, considering mainly the maintenance of gas dispersibility and the thermal shock resistance, the inventors have used silicon nitride or sialon as the silicon nitride ceramics constituting the rotating body 20. It has been found that one containing a main phase mainly composed of crystals and a grain boundary phase mainly composed of glass or crystal is suitable. That is, if the silicon nitride ceramic is formed into the shape shown in FIG. 1 and sintered, the gas dispersibility can be maintained over a long period of time, and in addition, even if the aspect ratio (Y / X) of the gas dispersion groove 22 is high, it is sufficient. It has been found that a gas blowing rotor 10 having thermal shock resistance can be obtained. In this case, when the width X of the gas dispersion groove 22 is in the range of 10 to 20 mm and the ratio Y / X of the depth Y to the width X of the gas dispersion groove 22 is in the range of 0.5 to 1.5, Sufficient dispersibility can be obtained. When the width X of the gas dispersion groove 22 is less than 10 mm, the gas hardly enters the gas dispersion groove 22, and a desired amount of gas cannot be supplied into the molten metal. Further, when the width X of the gas dispersion groove 22 exceeds 20 mm, the gas spreads thinly in the gas dispersion groove 22, so that the gas cannot be dispersed as fine bubbles. Further, when the ratio Y / X of the depth Y to the width X of the gas dispersion groove 22 is less than 0.5, the gas dispersibility becomes insufficient, and when the value exceeds 1.5, gas dispersion due to thermal shock is caused. Damage from the groove 22 is likely to occur.

  Further, the rotating body 20 of this embodiment is composed of a silicon nitride ceramic including a main phase mainly composed of silicon nitride or sialon crystals extending in a columnar shape and a grain boundary phase mainly composed of vitreous or crystalline. Due to the presence of irregularities on the surface of the fired skin, adhesion of molten aluminum or the like hardly occurs. For this reason, the gas dispersion grooves 22 are not easily blocked, and the gas dispersibility can be maintained over a long period of time. In the present invention, the surface of the gas dispersion groove 22 is subjected not only to an unprocessed fired skin after sintering but also to shot blasting as long as it can prevent adhesion of molten aluminum, slag, and the like. Skin whose surface is adjusted to the level of fired skin, that is, skin similar to fired skin may be used.

  It is essential that the rotator 20 be composed of silicon nitride ceramics including a main phase mainly composed of silicon nitride or sialon crystals and a grain boundary phase mainly composed of glass or crystal. Since the pipe 30 is not particularly susceptible to cracking or blockage, other materials can be used for the gas supply pipe 30.

  Hereinafter, an example of the manufacturing method of the rotary body 20 using silicon nitride ceramics will be described. As this manufacturing method, a generally known method for manufacturing a sintered body can be used. That is, after raw material powder mainly composed of silicon nitride powder is wet mixed, a binder is added, mixed and dried to obtain granulated powder, and then a known press molding method, CIP molding method, extrusion molding method, etc. The molded body is formed by a known molding method such as an injection molding method. The green body is green processed as necessary, and after debinding in the air, sintered in a non-oxidizing atmosphere containing nitrogen at 1500 to 1900 ° C. under normal pressure or pressure. Get. The firing atmosphere is preferably normal pressure, and the firing temperature is preferably 1700 to 1780 ° C.

As the silicon nitride powder as the main raw material of this silicon nitride ceramic, the alpha conversion rate is 90% or more, the average particle diameter D ₅₀ : 0.3 to 0.8 μm, the oxygen content: 0.1 to 2.0% by mass, Al: 0.01% by mass or less, Fe: 0.01% by mass or less are preferable.

Here, even in the gas dispersion groove 22 having a high aspect ratio, hexagonal boron nitride (h-BN) is used in order to obtain the rotating body 20 in which the adhesion of molten metal is small and the gas dispersibility is maintained for a long time. Is preferably added. The hexagonal boron nitride powder used as the raw material powder has an average particle size of 2 to 10 μm measured by a laser diffraction / scattering method, an average particle size of primary particles measured from an SEM photograph of 0.01 to 0.8 μm, BET What has a specific surface area by a method of 20-50 m < ² > / g is preferable. The average particle diameter D ₅₀ measured by the laser diffraction / scattering method is in the range of 2 to 10 μm, and the particle having a particle diameter of 30 μm or more is preferably 5% or less. Here, this measurement is performed according to JIS R1622, 1629.

When the hexagonal boron nitride powder is contained in an amount of 3 to 20 parts by mass with respect to a total of 100 parts by mass of the silicon nitride powder and the sintering aid powder, the obtained rotating body 20 made of the silicon nitride-boron nitride composite ceramics is obtained. Even if it is repeatedly immersed in molten aluminum, molten aluminum, its oxides, slag, etc. are difficult to adhere and have the necessary strength as the rotating body 20 and can prevent damage due to mechanical impact. it can. In particular, in the silicon nitride-boron nitride composite ceramic, this hexagonal boron nitride forms an aggregate of fine primary particles. Since such an aggregate of fine primary particles of boron nitride is present in the silicon nitride-boron nitride composite ceramic as a dispersed phase, the molten aluminum is more formed by the unevenness formed by the primary particles in the boron nitride aggregate. In addition to being difficult to adhere, even if it adheres, it is possible to prevent adhesion of molten aluminum by peeling off at fine primary particle portions.

In hexagonal boron nitride powder, the average particle size measured by laser diffraction / scattering method is 2 to 10 μm, the average particle size of primary particles measured from SEM photograph is 0.01 to 0.8 μm, and the specific surface area is 20 to 50 m. ² / g is out of these ranges, the unevenness formed by the primary particles of boron nitride particles exposed on the surface of the silicon nitride-boron nitride ceramic is reduced, and the molten aluminum is liable to adhere. Because. The average particle diameter measured by the laser diffraction / scattering method is 2 to 10 μm. If the average particle size is less than 2 μm, the dispersed phase of hexagonal boron nitride becomes small and the molten aluminum tends to adhere, and if it is 10 μm or more, hexagonal boron nitride. This is because the dispersed phase becomes larger and the strength decreases. The average particle size measured by the laser diffraction / scattering method is preferably 3 to 8 μm for the same reason. Further, when the particle having a particle diameter of 30 μm or more exceeds 5% in the boron nitride powder, cracks are likely to occur in the silicon nitride-boron nitride composite ceramics where the particle is present. . For this reason, it is preferable that this ratio is 5% or less.

  Furthermore, when the addition ratio of the hexagonal silicon nitride is less than 3 parts by mass with respect to 100 parts by mass of the total of the silicon nitride powder and the sintering aid powder, the area ratio of the dispersed phase composed of an aggregate of hexagonal boron nitride Therefore, molten aluminum tends to adhere. If the amount exceeds 20 parts by mass, the proportion of silicon nitride decreases, so the strength decreases.

  The hexagonal boron nitride preferably has a crystallinity GI value of more than 5. The crystallinity GI value of boron nitride is the area of 102 diffraction lines [A (102)] in X-ray diffraction, and the area [A (100 + 101) of adding 100 diffraction lines and 101 diffraction lines as shown in the following equation. The lower the GI value, the more crystallization proceeds.

  When the crystallinity GI value exceeds 5, it means that the crystallinity is low. When the crystallinity GI value exceeds 5, the primary particles become smaller and the bonds between the primary particles become stronger. Therefore, the unevenness formed by the primary particles makes it difficult for the molten aluminum to adhere more reliably and prevents the molten aluminum from adhering. A more preferred crystallinity GI value is 5-10.

  Further, it is preferable that the amount of oxygen contained in the hexagonal boron nitride powder is 1.0 to 6.0% because it is easily fixed to the sintering aid component due to the influence of the oxygen component and the strength is improved. A more preferable range of the oxygen amount is 1.0 to 2.0%.

In addition, as the sintering aid powder mixed with the silicon nitride powder and the hexagonal boron nitride powder, the rare earth element and Mg are 2 to 15% by mass in terms of oxide, and the rare earth metal (RE) and Mg are in terms of oxide. those containing mass ratio _{(RE 2} O 3 / MgO) in a ratio to be 0.1 to 10 are preferred.

  The sintering aid component generates a liquid phase during the sintering process, and effectively acts on the densification of the silicon nitride-boron nitride composite ceramics. After firing, as a grain boundary phase of silicon nitride and / or boron nitride, glass It exists in a silicon nitride-boron nitride composite ceramic as a phase and / or a crystalline phase. A glass phase and / or a crystal phase composed of a rare earth element and Mg is effective because it hardly adheres to the molten aluminum. As the rare earth element, any element of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be preferably used. Among these, Y, Ce, Sm, Dy, Er, Yb, and Lu, especially Y and Er are preferable in terms of characteristics and cost. In addition, it is preferable that the rare earth elements and Mg as sintering aids both have an average particle size of 1 μm or less and a purity of 99% or more. In addition to these oxide powders, carbonates, acetates and the like are baked. It is added as a compound capable of forming an oxide.

The rare earth element and Mg are preferably contained in an amount of 2 to 15% by mass in terms of oxide, and more preferably in the range of 3 to 8% by mass. In addition, the rare earth element and Mg preferably have an oxide-converted mass ratio (RE ₂ O ₃ / MgO) of 0.1 to 10, more preferably 0.4 to 5 inclusive. . This is because if the rare earth oxide and Mg are less than 2% by mass in terms of oxides, the sinterability is insufficient and densification is insufficient and the strength may be lowered. In addition, the ratio of grain boundary phase mainly composed of rare earth elements and Mg in the silicon nitride-boron nitride composite ceramic and silicon nitride sintered body may be increased more than necessary, resulting in reduced strength and toughness. It is. Further, by setting the rare earth element and Mg to 2 to 15% by mass in terms of oxides, the thermal conductivity of the silicon nitride-boron nitride composite ceramic is increased and damage due to thermal shock can be prevented. Further, if the mass ratio of RE ₂ O ₃ / MgO exceeds 10 or is smaller than 0.1, the densification at the firing temperature of 1600 to 1900 ° C. becomes insufficient and the strength may be lowered. It is.

When an Al compound such as Al ₂ O ₃ is blended as a sintering aid component, it contributes to improvement in sinterability, but adhesion to molten aluminum, its oxide, slag, etc. is likely to occur, and nitriding As a result of Al dissolving in the silicon (Si ₃ N ₄ ) crystal and inhibiting the diffusion of phonons, the thermal conductivity of the sintered body is significantly lowered and the thermal shock resistance is also lowered. It is preferable not to contain more than 0.5 mass% in terms of conversion. Desirably, it is less than 0.1% by mass, more desirably less than 0.01% by mass.

In addition, the blending of Fe compounds such as Fe ₂ O ₃ also contributes to the improvement of sinterability, but adhesion with molten aluminum, its oxide, slag, etc. is likely to occur, so 0.5% by mass or more in terms of oxide It is preferable not to contain. Desirably, it is less than 0.1% by mass, more desirably less than 0.01% by mass.

  In addition to Al and Fe, Na, K, Li, Be, Mn, Ga, and the like as impurities that affect the thermal conductivity are not preferable because they reduce the thermal conductivity of the sintered body. The content of these impurity elements in the silicon nitride sintered body is sufficient if it is suppressed to 0.3 wt% or less, preferably 0.2 wt% or less in total.

In this sintered body, at least one of the metals in groups 4a, 5a, and 6a of the periodic table such as Ti, V, Nb, W, and Mo is in a ratio of 0.05 to 2% by mass in terms of oxide. The inclusion is preferable because it has an effect of improving strength and toughness.

  After mixing said raw material powder, a binder is added, it mixes and dries, and it is set as granulated powder. This is formed into a molded body by a known molding method such as a press molding method, a CIP molding method, an extrusion molding method, or an injection molding method. The molded body is appropriately processed to obtain the shape of the rotating body 20. Thereafter, the binder removal treatment is performed in the atmosphere.

  Thereafter, the gas dispersion groove 22 and the stirring groove 23 are formed by cutting or the like in a molded body having a desired shape, and firing is performed at a temperature of 1600 to 1900 ° C. in a normal pressure non-oxidizing atmosphere containing nitrogen. . Thereby, the rotary body 20 comprised with said silicon nitride ceramics can be obtained. The gas supply pipe 30 and the gas supply member 201 may be manufactured in the same manner, and then these may be attached to the rotating body 20.

  Here, when the rotating body 20 is made of silicon nitride ceramics, as described above, due to the unevenness of the fired skin, the wettability of the surface with respect to the molten metal (Al) or flux is low, so in the molten metal Even when the rotating body 20 is used and taken out from the molten metal, adhesion of the molten metal to the surface of the gas dispersion groove 22 is suppressed. In addition, when boron nitride powder is contained in the silicon nitride ceramic within the above range, fine irregularities caused by the boron nitride powder are formed on the surface of the silicon nitride ceramic. That is, the wettability of molten metal (Al), flux components, slag, etc. is further reduced by the surface irregularities formed by the boron nitride powder having a specific surface area, average particle diameter, and primary particle diameter in the above ranges. As a result, gas dispersibility can be maintained over a longer period.

  Moreover, silicon nitride becomes the main phase of this ceramic by setting the boron nitride powder to a ratio of 3 to 20 parts by mass with respect to a total of 100 parts by mass of the silicon nitride powder and the sintering aid powder. On the other hand, the sintering aid powder becomes a grain boundary phase existing at the grain boundary of the main phase, and the boron nitride powder exists at the grain boundary phase. This grain boundary phase is mainly composed of glass or crystal. That is, by adding the addition amount of boron nitride powder within the above range, such a main phase and a grain boundary phase can be obtained, and silicon nitride ceramics can be obtained by simply using a main phase consisting of silicon nitride or sialon crystals and a sintering aid. Compared with the case where it is composed of a grain boundary phase made of glassy or crystalline material, the wettability with the molten metal or the flux is further reduced, and the adhesion of the molten metal or the flux to the gas dispersion groove 22 can be suppressed. it can.

  The silicon nitride ceramic obtained by the above manufacturing method has the following characteristics. First, the water absorption is in the range of 0.1 to 10%. The thermal conductivity is 30 W / m / K or more, although it depends on additives such as a sintering aid as described above. The Young's modulus is in the range of 100 to 200 Pa. The thermal expansion coefficient is 3.5 ppm / ° C. or less in the range of 35 to 600 ° C. Although these values vary depending on the additive composition and the like, it is preferable that the thermal conductivity is high and the thermal expansion coefficient is small in order to suppress cracks that occur when the rotating body 20 is taken in and out of the molten metal.

  Further, as described above, the wettability of the molten metal is reduced by the unevenness of the surface of the gas dispersion groove 22. Surface roughness is an amount related to this unevenness. Here, the arithmetic average roughness Ra is in the range of 0.9 to 2.1 μm. The locations where the surface roughness is measured are the three surfaces on the inner peripheral side, the center, and the outer peripheral side of the gas dispersion groove 22, which are the locations where the above characteristics are most remarkably required. As described above, wettability decreases as the unevenness increases, but if the unevenness Ra is greater than 2.1 μm, cracks are likely to occur starting from this point. When the unevenness Ra is less than 0.9 μm, the effect of reducing wettability is insufficient.

  In the silicon nitride ceramics described above, the wettability of the surface decreases due to the unevenness of the fired skin. In addition to boron nitride, other borides, nitrides, or carbides can be used as materials for forming the irregularities as long as fracture toughness, thermal conductivity, and thermal expansion coefficient are kept equal.

  Also, the form of the gas dispersion groove 22 is arbitrary as long as it is a deep groove that exhibits the above-described effects. For example, an R process or a chamfering process can be performed at the corner of the outer edge of the gas dispersion groove 22 in the radial direction so as to keep the gas dispersibility high and the mechanical strength.

  As the form of the rotator, in addition to the forms shown in FIGS. 1 and 2, other forms of the rotator 120 shown in FIGS. 3 and 4 having high stirring ability and deep gas dispersion grooves can be used. Here, FIG. 3A is a bottom view of the rotator 120, and FIG. 3B is a CC cross-sectional view including the gas dispersion groove 122 along the central axis of the rotator in FIG. 3A. . FIG. 4 is a perspective view of the rotator 120.

  The rotator 120 is made of silicon nitride ceramics, like the rotator 20 of the above aspect. In the rotating body 120, instead of the stirring groove, eight stirring legs 121 are formed at 45 ° intervals radially from the rotation axis. As the rotating body 120 rotates, the molten metal is stirred by the stirring legs 121. Alternatively, this shape can be regarded as a shape in which a stirring groove penetrating in the thickness direction is formed radially in a disk shape thickened at the center. That is, the basic shape of the rotating body can be a disk shape, and radial stirring grooves (perpendicular to the rotation direction) can be appropriately formed thereon.

  A gas dispersion groove 122 is formed on the lower surface (left side in FIG. 3B) of each stirring leg 121. A gas supply member 140 is fitted inside the gas supply pipe 130 at a position where the gas supply pipe 130 is fitted to the rotating body 120. A through hole 123 is formed at the center of the gas supply member 140, and the gas passes through the through hole 123. The eight gas dispersion grooves 122 are connected to the through-hole portion 123 at the rotation axis, and the through-hole portion 123 is connected to the flow path of the gas supply pipe 130. For this reason, the gas that has passed through the flow path of the gas supply pipe 130 is discharged as bubbles from the tip of each gas dispersion groove 122 into the melt as the rotating body 120 rotates. The width of the gas dispersion groove 122 is X in FIG. 3A, and the height (depth) is Y in FIG. 3B. The thickness of the material constituting the rotating body 120 where the gas dispersion grooves 122 are formed is W in FIG.

  As described above, in the rotating body 120 made of silicon nitride ceramics, the width of the gas dispersion groove 122 is 10 to 20 mm and the depth / width ratio is 0.5 to 1.5, similarly to the rotating body 20. Since the surface of the gas dispersion groove 122 is fired skin, the gas dispersibility can be maintained over a long period of time.

  In this case, the rotating body 120 (stirring leg 121) is thick near the rotation axis and thin on the outside. Thereby, when the rotary body 120 is pulled up from the molten metal, the molten metal, flux, slag, and the like are less likely to adhere. In particular, in the silicon nitride ceramics described above, this effect is increased because the wettability of the surface is lowered.

  In this configuration, the stirring leg 121 near the rotation axis is particularly thick. As described above, the influence of thermal stress is particularly large at thick locations, and cracks are likely to occur. However, since the above silicon nitride ceramics have high fracture toughness, high thermal conductivity, and low thermal expansion coefficient, cracks are hardly generated even in the thickened portion.

  Hereinafter, the results of confirming the results of actually manufacturing the rotating bodies 20 and 120 with various aspect ratios of the gas dispersion grooves using silicon nitride ceramics having various compositions and actually using them in the molten aluminum will be described. In Examples and Comparative Examples described below, various types of silicon nitride formed by mixing eight types of hexagonal boron nitride powder, silicon nitride powder, and various types of sintering aid powders having different particle sizes and the like with various compositions. The rotating bodies 20 and 120 were formed using ceramics.

First, as the characteristics of silicon nitride ceramics themselves, the water absorption, bending strength, thermal conductivity, thermal expansion coefficient, Young's modulus, and thermal shock temperature are the characteristics of a rotating body made of silicon nitride ceramics. There is surface roughness of the grooves 22 and 122. Details of these evaluations are as follows.
(1) Water absorption rate From the sintered silicon nitride ceramics, a square-shaped test piece of 25 mm × 40 mm × 5 mm was manufactured, the weight of the test piece after drying at 110 ° C. for 24 hours was measured, and then in water After immersion for 24 hours, the test piece weight was measured again. The value obtained by dividing the weight difference before and after immersion in water by the weight after drying was defined as the water absorption rate.
(2) Bending strength Based on JISR1601, a test piece having a prism shape of 3 mm × 4 mm × 36 mm was manufactured, and a four-point bending test was performed under the condition of a load speed of 0.5 mm / min. Ten measurements were carried out for each example and comparative example, and the average value was taken as the bending strength.
(3) Thermal conductivity Based on JISR1611, the test piece of diameter 5mm x thickness 2mm was manufactured, and the thermal conductivity at room temperature was measured by the laser flash method.
(4) Thermal expansion coefficient Based on JISR1618, a 5 * 5 * 10 mm test piece was manufactured, and the average linear thermal expansion coefficient between 35 degreeC and 600 degreeC was measured with the thermomechanical analyzer (TMA).
(5) Young's modulus Based on JISR1602, a 10x10x10mm test piece was manufactured and the Young's modulus was measured by the ultrasonic pulse method.
(6) Thermal shock temperature ΔT
With respect to the thermal shock temperature ΔT, 25 mm × 25 mm × 4 mm test pieces were produced, the temperature was increased from 700 ° C. every 50 ° C., dropped into water at each temperature, rapidly cooled, and then checked for cracks. Cracks were confirmed by fluorescent flaw detection, and the temperature at which no cracks occurred was defined as the thermal shock temperature.
(7) Surface roughness Based on JIS-B0601, the arithmetic average roughness Ra of the surface of three points of the inner periphery side of the gas dispersion groove 22, the center, and an outer periphery side was calculated | required in the radial direction of the rotary body 20 * 120.

Next, the characteristics of the rotating bodies 20 and 120 were evaluated. As this evaluation item,
(1) Hydrogen removal ability in molten aluminum ○: Residual hydrogen amount less than 0.18 cc / 100 g, Δ: 0.18 to 0.2 cc / 100 g, x: more than 0.2 cc / 100 g,
(2) Adhesion rate of aluminum on the surface of the gas dispersion groove 22 after 100 hours of use: less than 25%, ◯: 25-40%, Δ: 40-60%, x: more than 60%,
(3) Continuous use period ◎: More than 1000 hours, ○: 500 to 1000 hours, Δ: 200 to 500 hours, ×: less than 200 hours,
(4) Causes of continuous use life,
It is.
Here, as the causes of the life, (a) blockage (the gas dispersion groove 22 is blocked by molten aluminum, slag, etc.), (b) peeling (local peeling occurs on the surface of the gas dispersion groove 22) And (c) Breakage (breakage of the rotating body itself). In the case of blockage, it can be reused by removing the blockage by pickling or the like, and in the case of peeling, it is possible to reuse it by regenerating the skin by shot blasting or the like, although this is not a preferable state. For this reason, if the lifetime is the same, clogging is the most preferable determinant of the lifetime, followed by peeling, and the most undesirable is damage that cannot be reused.

The hydrogen removal ability, the aluminum adhesion rate, and the continuous use period were evaluated by the following methods.
(1) Hydrogen removal ability A gas amount analyzer (model: ALFAITH M-DP MK2 manufactured by Eiko Engineering Co., Ltd.) that measures the hydrogen content of molten aluminum by an initial bubble method was used. With this analyzer, molten aluminum was collected in a 120 g crucible, this crucible was placed in a vacuum chamber, the vacuum chamber was gradually depressurized to 100 mmHg, and the time when bubbles were first observed was input. From the temperature and pressure, the hydrogen content in the molten aluminum was determined.
(2) Aluminum adhesion rate Rotating bodies 20 and 120 are immersed in molten aluminum heated and held at 750 ° C. in a holding furnace having a capacity of 1000 kg, and rotated at 600 rpm for 100 hours to degas. The area ratio of aluminum adhering to the surface of the gas dispersion groove 22 after the determination was obtained.
(3) Continuous use period Under the same operating conditions as in the above measurement of the aluminum adhesion rate, the rotating bodies 20 and 120 were rotated in molten aluminum to check the continuous use period. When the cause of the lifetime is clogging or peeling, the lifetime is defined as when the hydrogen removal ability exceeds 0.2 cc / 100 g, and the actual usage time from the start of use to the lifetime is defined as the continuous usage period (after regeneration). Does not include the period of use.) Moreover, when the cause of the life is damage, the actual use time from the start of use until the damage is determined as the continuous usable period.

  Table 1 shows the characteristics of eight types (BN1 to BN8) of hexagonal boron nitride powder used in the following examples and comparative examples. In Table 1, for each of BN1 to BN8, (1) the average particle diameter measured by the laser diffraction / scattering method, (2) the proportion of particles having a particle diameter of 30 μm or more, and (3) primary particles as seen from the SEM photograph (4) Specific surface area measured by BET method, (5) Crystallinity GI, (6) Oxygen content.

(Examples 1-4, 11, 13-15)
An average particle size of 0.6 μm, an oxygen content of 0.9%, an α conversion of 95% of silicon nitride powder of 95% by mass, an average particle size of 1 μm of Y ₂ O ₃ powder of 3% by mass, and an average particle size of 0.1 μm The hexagonal boron nitride powder BN1 in Table 1 is 0 parts by weight, 2.5 parts by weight with respect to Examples 1 to 4, 11, and 13 to 15 with respect to 100 parts by weight in total of 2% by weight of MgO powder. 3.5 parts by mass, 7.2, 11, 14.8, 18.9, 22.5 parts by mass were measured, ethyl alcohol was weighed as a solvent, and mixed in a ball mill using silicon nitride balls. After adding 1% polyvinyl butyral as a binder to the obtained slurry and mixing it to make a slurry, the slurry is dried with a spray dryer, and from a silicon nitride powder for molding, a sintering aid powder, and a hexagonal boron nitride powder. The resulting granulated powder was created.

After sieving the obtained granulated powder to an average particle diameter of 60 μm, a molded body having a length of 100 mm, a width of 100 mm, and a thickness of 20 mm is formed by cold isostatic pressing (CIP) at a pressure of 1000 kg / cm ^2. did. The molded body obtained by the CIP method was degreased in the atmosphere at 500 ° C. for 20 hours in the atmosphere, and sintered in the atmosphere of nitrogen and normal pressure at 1750 ° C. for 5 hours. Substantially bowl-shaped rotating bodies 20 shown in FIGS. The width of the gas dispersion groove in the rotating body was 10 mm, and the aspect ratio (depth / width) of the groove was 1.0.

(Examples 5 and 7)
The rotating body 20 of Examples 5 and 7 is obtained in the same manner as in Example 4 except that BN2 and BN3 are respectively used for the hexagonal boron nitride powder for the silicon nitride-boron nitride composite ceramic of Example 4. It was.

(Example 6)
In Example 6, Example ₂ was carried out in the same manner as Example 4 except that 7% by mass of Er ₂ O ₃ powder having an average particle size of 1.0 μm was added as a sintering aid instead of Y ₂ O ₃ powder. 6 of rotating bodies 20 were obtained.

(Examples 8 and 9)
Except that the mixing ratio of the sintering aid component (MgO, Y ₂ O ₃ ) was as shown in Table 1 with respect to the silicon nitride-boron nitride composite ceramic of Example 4, the same as in Example 4, The rotating body 20 of Examples 8 and 9 was obtained.

(Example 10)
0.5 mass% of TiO ₂ powder having an average particle size of 2.3 μm is further added to the silicon nitride-boron nitride composite ceramic of Example 4, and the mixing ratio of the sintering aid component is as shown in Table 1. A rotating body 120 of Example 10 was obtained in the same manner as in Example 4 except that the rotating body 120 had a substantially disk shape shown in FIGS.

(Example 12)
The rotating body 20 of Example 12 was obtained in the same manner as in Example 4 except that BN4 was used as the hexagonal boron nitride powder for the silicon nitride-boron nitride composite ceramic of Example 11.

(Example 16)
The same silicon nitride-boron nitride composite ceramic as in Example 9 was used, the gas dispersion groove width was kept at 10 mm, the width was reduced to 10 mm, and the groove aspect ratio (depth / width) was 0.5. The rotating body 20 of Example 16 was obtained.

(Example 17)
The same silicon nitride-boron nitride composite ceramic as in Examples 9 and 16 was used, the width was 10 mm, the groove aspect ratio was increased to 1.5, and the rotating body 20 of Example 17 was obtained.

(Example 18)
Using the same silicon nitride-boron nitride composite ceramics as in Examples 9, 16, and 17, the width was 20 mm, the groove aspect ratio was 0.5, and the rotating body 20 of Example 18 was obtained.

(Example 19)
Using the same silicon nitride-boron nitride composite ceramics as in Examples 9, 16, 17, and 18, the width was 20 mm, the groove aspect ratio was 1.5, and the rotating body 20 of Example 19 was obtained.

(Examples 20 to 23)
The rotating bodies of Examples 20 to 23 were the same as Example 4 except that BN5, BN6, BN7, and BN8 were used for the hexagonal boron nitride powder for the silicon nitride-boron nitride composite ceramics of Example 4, respectively. 20 was obtained.

(Examples 24-29)
Except that the mixing ratio of the sintering aid component (MgO, Y ₂ O ₃ ) was as shown in Table 1 with respect to the silicon nitride-boron nitride composite ceramic of Example 4, the same as in Example 4, The rotating body 20 of Examples 24-29 was obtained.

(Example 30)
To the silicon nitride-boron nitride composite ceramic of Example 4, 0.5% by mass of Al ₂ O ₃ powder having an average particle size of 0.5 μm was further added. Except this, it carried out similarly to Example 4, and obtained the rotary body 20 of Example 30.

(Comparative Example 1)
A rotating body 20 similar to that of Example 9 was used as Comparative Example 1 except that the surface of the gas dispersion groove of the rotating body 20 as a sintered body was ground to obtain a processed skin having a small surface roughness.

(Comparative Example 2)
A rotating body 20 similar to that of Example 9 was used as Comparative Example 2 except that the width of the gas dispersion groove was 5 mm and the aspect ratio was 0.3.

(Comparative Example 3)
A rotating body 20 similar to that of Example 9 was used as Comparative Example 3 except that the width of the gas dispersion groove was 5 mm and the aspect ratio was 1.7.

(Comparative Example 4)
A rotating body 20 similar to that of Example 9 was used as Comparative Example 4 except that the width of the gas dispersion groove was set to 25 mm and the aspect ratio was set to 0 and 3.

(Comparative Example 5)
A rotating body 20 similar to that of Example 9 was used as Comparative Example 5 except that the width of the gas dispersion groove was 25 mm and the aspect ratio was 1.7.

  Table 2 shows the production conditions of the above Examples and Comparative Examples, and Table 3 shows the characteristics of the obtained sintered bodies and the rotating bodies 20 and 120.

  From this result, as for the rotary body 20 * 120 of Examples 1-30, the surface of a gas dispersion groove is baking skin, the width | variety of a gas dispersion groove is 10-20 mm, and the (depth / width) is 0.5-1. Therefore, it was confirmed that the hydrogen removal ability was high and the gas dispersibility was excellent. In addition, since the surface of the gas dispersion groove 22 is a calcined skin, the area ratio of aluminum adhesion is uniformly as small as 40% or less by an evaluation of Δ or more, and the rotating bodies 20 and 120 of Examples 1 to 30 are gas dispersion. It was confirmed that the composition was suitable for maintaining the sex. On the other hand, the rotating body 20 of Comparative Example 1 has high hydrogen removal capability because the surface of the gas dispersion groove is processed skin, but it easily adheres molten aluminum, and the aluminum adhesion area ratio and the continuous use period are both x. there were. In addition, the rotating bodies 20 of Comparative Examples 2 to 4 have low gas dispersibility and did not reach the level where hydrogen removal ability is required in the first place. In addition, about Comparative Examples 2-4, since the hydrogen removal ability used as a premise was insufficient, the aluminum adhesion area rate and the continuous use period were not confirmed. Further, the rotating body 20 of Comparative Example 5 showed a hydrogen removal ability although its gas dispersion groove 22 had a constant width and aspect ratio, but it had a low aspect ratio, but had a high aspect ratio and a sudden change in thickness. Due to the existence, it has reached a short life due to breakage.

  In Examples 1 to 30, in Examples 3 to 14 and 16 to 30 in which hexagonal boron nitride powder is contained in an amount of 3 to 20 parts by mass with respect to a total of 100 parts by mass of the silicon nitride powder and the sintering aid powder. The surface roughness Ra of the baked skin is 0.9 to 2.1 μm, the hydrogen removal ability is all ◯, and the aluminum adhesion rate is all ◯ or more. That is, it was confirmed that the gas dispersibility can be more easily maintained by setting the surface roughness Ra of the fired skin to 0.9 to 2.1 μm. Further, the examples except for Example 15 containing a relatively large amount of hexagonal boron nitride powder BN1 and Example 20 mixed with BN5 containing coarse hexagonal boron nitride particles were continuously used under the above operating conditions. The period of use was Δ or more, and it was confirmed that the maintenance of gas dispersion and the thermal shock resistance were good from the practical viewpoint.

It contains 2 to 15% by mass of rare earth element and Mg in terms of oxide, and contains rare earth metal (RE) and Mg in a ratio such that the mass ratio in terms of oxide (RE ₂ O ₃ / MgO) is 0.1 to 10. Rotating bodies (Examples 1 to 23, 25, 26, and 28 to 30) using silicon nitride ceramics have also obtained particularly good results with respect to hydrogen removal ability and aluminum adhesion rate.

Further, the influence of the added hexagonal boron nitride powder will be examined in comparison with Examples 4, 5, 7, and 12 and Examples 20 to 23, in which the specifications other than the type of the powder are the same. In the rotating body 20 of Examples 4, 5, 7 and 12 including BN1 to BN4 shown in Table 1, the specific surface area of the hexagonal boron nitride powder is 20 to 50 m ² / g, and the average particle size measured by the laser diffraction / scattering method Particles having a diameter of 2 to 10 μm and a particle size of 30 μm or more are 5% or less, and the average particle size of primary particles measured from SEM photographs is 0.01 to 0.8 μm. As a result, hydrogen removal ability, aluminum The adhesion rate and the continuous use period were all ◯ or more, the cause of life was all clogging, and good characteristics were shown. On the other hand, the rotating body 20 of Example 20 has BN5 composed of hexagonal boron nitride powder containing coarser secondary particles than BN1 to BN4 and containing 5% or more of secondary particles of 30 μm or more. Although the roughness Ra was small and the aluminum adhesion area ratio was small, the life was reached in a relatively short time due to the damage caused by the coarse secondary particles. Further, the rotating body 20 of Example 21 includes BN6 made of hexagonal boron nitride powder having coarser primary particles and lower bonding degree between the primary particles than BN1 to BN4. Therefore, the primary particles are dispersed during use. As a result, the surface of the gas dispersion groove 22 is smoothed, and adhesion of molten aluminum proceeds, so that the continuous use period is Δ and the life is relatively short. Since the rotating body 20 of Example 22 includes BN7 composed of hexagonal boron nitride powder with finer primary particles than BN1 to BN4, the surface roughness Ra of the gas dispersion groove 22 is relatively small, and adhesion of molten aluminum Therefore, the continuous use period is Δ and the life is relatively short. The rotating body 20 of Example 23 includes BN8 having hexagonal boron nitride powder whose secondary particles are finer than those of BN1 to BN4, but the hexagonal boron nitride powder with fine secondary particles is composed of silicon nitride powder and a sintered body. It is difficult to uniformly mix with the binder powder and segregation of the hexagonal boron nitride powder occurs, resulting in a relatively short life due to breakage.

In Examples 24 and 25 in which the total amount of sintering aid components (MgO, RE ₂ O ₃ ) in the raw material powder is as low as 1.8% by mass and 2.9% by mass, the types and addition amounts of hexagonal boron nitride powder Compared with Example 4 in which the total amount of sintering aid components is 5% by mass and strength (bending strength Example 24: 300 MPa, Example 25: 340 MPa, Example 4: 390 MPa) and thermal conductivity (Example 24: 37 W / m / K, Example 25: 41 W / m / K, Example 4: 44 W / m / K) is decreased. Reflecting this, in Examples 24 and 25, the continuous use period was also shortened, and the cause of the lifetime was also clogged in Example 4, whereas it was broken in Example 24 and peeling in Example 25. .

  On the contrary, in Examples 26 and 27 where the total amount of the sintering aid component in the raw material powder is 11.0% by mass and 16.0% by mass, compared with Example 4, the strength (Example 26: 350 MPa, Example 27: 300 MPa) and thermal conductivity (Example 26: 40 W / m / K, Example 27: 36 W / m / K) are decreased. Reflecting this, even in Examples 26 and 27, the continuous use period was shortened, and the cause of the lifetime was peeling in Example 26 and damage in Example 27.

That is, when Examples 3 and 5 to 10 and Examples 24 to 27 having conditions similar to Example 4 and Example 4 are compared, the total amount of the sintering aid component (MgO, RE ₂ O ₃ ) in the raw material powder is 2 to 15% by mass is preferable, and 3 to 8% by mass is particularly preferable.

In addition, Example 28 having a large RE ₂ O ₃ / MgO ratio of 8.3 and Example 29 having a small RE ₂ O ₃ / MgO ratio of 0.1 have the same kind and addition amount of hexagonal boron nitride powder. Compared with Example 4 in which the addition amount of the sintering aid components (MgO, RE ₂ O ₃ ) is the same but the RE ₂ O ₃ / MgO ratio is 1.5, the strength (bending strength) ) Is reduced (Example 28, Example 29: 320 MPa). Reflecting this, in Examples 28 and 29, the continuous use period was shortened, and the cause of the life was also broken. That is, when Examples 3 and 5 to 10 and Examples 28 and 29 having conditions similar to Example 4 and Example 4 are compared, the value of RE ₂ O ₃ / MgO is in the range of 0.1 to 10.0. A range of 0.4 to 5.0 is particularly preferable.

In Example 10 in which 0.5% by mass of TiO ₂ which is a group 4a metal in the periodic table and has an effect of improving strength and toughness was added, the hydrogen removal ability and the aluminum adhesion rate were ○. In addition, the result of ◎ is also obtained for the continuous use period.

Moreover, although it contributes to the improvement of sinterability, the addition of Al ₂ O ₃ is not preferable because adhesion to molten aluminum, its oxide, slag, etc. easily occurs and thermal shock resistance is lowered. However, also in Example 30 to which 0.5% by mass of Al ₂ O ₃ was added, the hydrogen removal ability and the aluminum adhesion rate were “◯”, and the continuous use period was “Δ”. Moreover, since the cause of the lifetime is peeling, it does not substantially become a big problem regarding a continuous use period. That is, even when 0.5% by mass of Al ₂ O ₃ is added, good characteristics are obtained in all of the hydrogen removal ability, the aluminum adhesion rate, and the continuous use period. However, the thermal conductivity is reduced to 22 W / m / K. From the above, if _{the Al} 2 _{O 3} is added, the addition amount thereof is preferably not more than 0.5 mass%.

  In addition, the favorable hydrogen removal ability in the above embodiment is stably obtained because the form of the gas dispersion groove and the structure of the rotating body itself are stably maintained in the use environment. As described above, the characteristics of the silicon nitride ceramic itself and the fine shape of the surface are the dominant factors of these characteristics. For this reason, in the above example, the rotating body is used when stirring the molten aluminum. However, even when the rotating body is another molten metal, the above rotating body can achieve the same effect.

20, 120 (for gas blowing) Rotating body 21, 123 Through hole 22, 122 Gas dispersion groove 23 Stirring groove 24 Hollow part 30, 130 Gas supply pipe 121 Stirring leg 140, 201 Gas supply member

Claims (10)

A rotation axis, a through hole formed around the rotation axis, a plurality of gas dispersion grooves extending radially from the rotation axis toward the outer periphery of the view, and a through hole for supplying an inert gas Gas injection for injecting an inert gas into molten metal, comprising a silicon nitride ceramic comprising a main phase mainly composed of silicon nitride or sialon crystals and a grain boundary phase mainly composed of glassy or crystalline A rotating body for
The surface of the gas dispersion groove is fired skin or skin similar to fired skin, and the gas dispersion groove has a width in the range of 10 to 20 mm and a depth / width ratio of 0.5 to 1.5. A rotating body for blowing gas, characterized in that   In the radial direction, the arithmetic average roughness Ra according to JIS-B0601 of the surface of the gas dispersion groove at three points on the inner circumference side, the center, and the outer circumference side of the gas dispersion groove is in the range of 0.9 to 2.1 μm. The gas injection rotor according to claim 1, wherein the gas injection rotor is provided.   The gas blowing rotator according to claim 1 or 2, wherein the silicon nitride ceramic includes fine particles selected from a boride, a nitride, or a carbide.   The gas blowing rotator according to claim 3, wherein the silicon nitride ceramic contains fine particles made of hexagonal boron nitride. The silicon nitride ceramic contains 2 to 15% by mass of rare earth elements and Mg in terms of oxides as grain boundary phases, and a mass ratio of rare earth metals (RE) and Mg in terms of oxides (RE ₂ O ₃ / MgO). It contains in the ratio used as 0.1-10, The rotary body for gas blowing of any one of Claim 1- Claim 4 characterized by the above-mentioned. Specific surface area of 20-50 m ² / g, average particle diameter measured by laser diffraction / scattering method is 2-10 μm, particles having particle diameter of 30 μm or more are 5% or less, average particle of primary particles measured from SEM photograph Manufactured using raw material powder containing 3 to 20 parts by mass of hexagonal boron nitride powder having a size of 0.01 to 0.8 μm with respect to a total of 100 parts by mass of silicon nitride powder and sintering aid powder The rotating body for gas injection according to claim 5, wherein:   The gas blowing rotor is configured to have a substantially bowl shape with one opening, the gas dispersion groove is formed on one end surface, and the through hole is formed on the other end surface. The gas injection rotor according to any one of claims 1 to 6, wherein the gas injection rotor is provided.   The gas blowing rotor is configured to have a substantially disk shape, and the gas dispersion groove is directly connected to the through-hole portion. 2. A rotating body for gas injection according to item 1.   The R edge or the chamfering is given to the outer edge part of the said gas dispersion groove in the radial direction of the said rotary body for gas blowing, The any one of Claim 1-8 characterized by the above-mentioned. The rotating body for gas injection as described.   The rotation for gas injection according to any one of claims 1 to 9, wherein an agitation groove for agitating the molten metal is formed on an outer peripheral surface of the gas injection rotator. body.

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