Patent Application
20190176224
The present invention relates to an apparatus for producing a thin metal strip and a method for producing a thin metal strip using the apparatus.
It is known that rapid solidification process can provide metal materials with various properties. The rapid solidification process refers to a process for solidifying molten metal at a certain cooling rate or higher. The rapid solidification process enables, for example, refining crystal structures of a metal material, homogenizing a solute distribution, increasing a solid-solubility limit, producing amorphous layers (amorphous), and producing thermodynamic non-equilibrium phases. Specifically, known methods for producing a cast piece by the rapid solidification process include the strip casting process, the melt spinning process, the atomization process, the melt spinning process, and the like.
For example, International Application Publication No. WO2012/099056 (Patent Literature 1) describes producing Si alloy by the atomization process. For another example, Japanese Patent Application Publication No. 2013-161785 (Patent Literature 2) describes producing Si alloy by the melt spinning process.
In the rapid solidification processes, the higher the cooling rate of molten metal is, the finer the resultant grains become. Among the rapid solidification processes, one producing method with a particularly high cooling rate is, for example, the melt spinning process. The melt spinning process is a method in which molten metal is jetted and rapidly cooled on a roll rotating at high speed to produce a ribbon-shaped thin metal strip in a flying manner. In the melt spinning process, a jet of a small amount of molten metal is supplied onto the roll. Therefore, the cooling rate is high.
The melt spinning process enables the production of a thin metal strip including fine grains. However, in the melt spinning process, a small amount of the molten metal is supplied onto the roll. Therefore, the melt spinning process has its limitation in production capability and has a difficulty of producing a thin metal strip in volume.
Meanwhile, in the rapid solidification processes, a method capable of producing a thin metal strip in volume is, for example, a single roll strip casting process. The single roll strip casting process is a method for producing a thin metal strip by continuously supplying molten metal onto a rotating roll to rapidly cool the molten metal. Methods for producing a cast piece using the strip casting process are, for example, described in Japanese Patent Application Publication No. 2011-206835 (Patent Literature 3) and Japanese Patent Application Publication No. 2001-291514 (Patent Literature 4).
The producing apparatus described in Japanese Patent Application Publication No. 2011-206835 (Patent Literature 3) is a producing apparatus for an aluminum clad plate. This producing apparatus includes a first roll with a cooling capability and a first pool for storing first molten alloy. The first pool is surrounded by a surface of the first roll, a first front plate, a rear member, and both-side members. The first front plate lies forward of the first roll in a rotation direction. The rear member lies rearward of the first roll in the rotation direction. The first front plate includes a front edge portion and is movably provided such that the distance between the front edge portion and the surface of the first roll can vary. The first roll cools the first molten alloy in the first pool to form a first metallic layer in a semi-solidified state or a solidified state on the surface of the first roll and rotates with the first metallic layer. The first front plate is urged so that the front edge portion of the first front plate always abuts against a semi-solidified surface of the first metallic layer moving with the rotation of the first roll, at given force.
The producing method described in Japanese Patent Application Publication No. 2001-291514 (Patent Literature 4) is a producing method for a negative electrode material for a non-aqueous electrolyte secondary battery. This producing method is characterized by melting an alloy raw material having a composition selected such that a Si phase and intermetallic compounds of Si and other metallic elements are crystallized in solidification, and then solidifying the alloy raw material using the strip casting process or the centrifugal casting process to form a columnar structure.
In the strip casting process, the amount of molten metal supplied onto a roll is large as compared with the melt spinning process. Therefore, the strip casting process enables the production of a thin metal strip in large volume. However, in the strip casting process, the cooling rate of the molten metal is low as compared with the melt spinning process. Therefore, the strip casting process has a difficulty of refining grains. For that reason, the strip casting process is requested to provide more refined grains.
Patent Literature 1: International Application Publication No. WO2012/099056
The production methods disclosed in the Patent Literatures described above fail in some cases to efficiently produce thin metal strips including fine grains.
An objective of the present invention is to provide an apparatus for producing a thin metal strip that is capable of efficiently producing a thin metal strip including fine grains.
A producing apparatus according to the present embodiment is an apparatus for producing a thin metal strip by a single roll strip casting process. The producing apparatus includes a cooling roll, a tundish, and a molten metal remover. The cooling roll includes an outer peripheral surface and is configured to cool and solidify molten metal on the outer peripheral surface while rotating. The tundish can accommodate the molten metal and is configured to supply the molten metal onto the outer peripheral surface of the cooling roll. The molten metal remover is disposed downstream of the tundish in the rotating direction of the cooling roll with a gap provided between the molten metal remover and the outer peripheral surface of the cooling roll. The molten metal remover is configured to remove a portion of a thickness of the molten metal on the outer peripheral surface of the cooling roll that is larger than the width of the gap described above. As a result, the thickness of the molten metal on the outer peripheral surface of the cooling roll is cut down to the width of the gap between the outer peripheral surface of the cooling roll and the molten metal remover.
A method for producing a thin metal strip according to the present embodiment is a method for producing a thin metal strip by a single roll strip casting process using the producing apparatus described above. The producing method includes a supplying step, a rapid cooling step, and a thickness adjustment step. In the supplying step, the molten metal in the tundish is supplied onto the outer peripheral surface of the cooling roll. In the rapid cooling step, the molten metal on the outer peripheral surface is rapidly cooled with the cooling roll to be formed into the thin metal strip. In the thickness adjustment step, a portion of a thickness of the molten metal on the outer peripheral surface of the cooling roll that is larger than the width of the gap described above is removed by the molten metal remover. As a result, the thickness of the molten metal on the outer peripheral surface is cut down to the width of the gap between the outer peripheral surface of the cooling roll and the molten metal remover.
Using the apparatus for producing a thin metal strip according to the present embodiment enables a thin metal strip including fine grains to be produced efficiently.
A producing apparatus according to the present embodiment is an apparatus for producing a thin metal strip by a single roll strip casting process. The producing apparatus includes a cooling roll, a tundish, and a molten metal remover. The cooling roll includes an outer peripheral surface and is configured to cool and solidify molten metal on the outer peripheral surface while rotating. The tundish can accommodate the molten metal and is configured to supply the molten metal onto the outer peripheral surface of the cooling roll. The molten metal remover is disposed downstream of the tundish in the rotating direction of the cooling roll with a gap provided between the molten metal remover and the outer peripheral surface of the cooling roll. The molten metal remover is configured to remove a portion of a thickness of the molten metal that is larger than the width of the gap described above (hereafter, also referred to as a surface portion). As a result, the thickness of the molten metal on the outer peripheral surface of the cooling roll is cut down to the width of the gap between the outer peripheral surface of the cooling roll and the molten metal remover.
The producing apparatus according to the present embodiment includes a molten metal remover. The molten metal remover is configured to be in contact with the molten metal when a free surface of the molten metal (a surface of the molten metal on a side on which the molten metal is not in contact with the cooling roll) in a liquid state or a semi-solidified state. The molten metal remover is configured to remove the surface portion of the molten metal on the outer peripheral surface. As a result, the thickness of the molten metal on the outer peripheral surface of the cooling roll is cut down to the width of the gap between the outer peripheral surface of the cooling roll and the molten metal remover. As a result, the molten metal on the outer peripheral surface of the cooling roll becomes thin. As the molten metal becomes thin, the cooling rate of the molten metal increases. As a result, grains in the thin metal strip become small. In other words, by using the strip casting, it is possible to efficiently produce a thin metal strip including fine grains. In addition, by cutting down the width of the thickness of the molten metal to the width of the gap as described above, it is possible to perform rapid solidification without being affected not much by viscosity of the molten metal, wettability to the roll material, supply amount of the molten metal, and the like.
It is preferable that the width of a gap between the outer peripheral surface of the cooling roll and the molten metal remover is smaller than the thickness of the molten metal on the outer peripheral surface of the cooling roll on an upstream side of the molten metal remover in the rotating direction of the cooling roll.
In this case, the molten metal on the outer peripheral surface of the cooling roll becomes thinner. Therefore, the cooling rate of the molten metal becomes higher. As a result, the grains in the thin metal strip are more refined.
It is preferable that the tundish is disposed in the vicinity of the outer peripheral surface of the cooling roll and includes a supply end configured to guide the molten metal onto the outer peripheral surface of the cooling roll. In addition, the molten metal remover is disposed above the supply end of the tundish.
In this case, the molten metal is cooled while being wound up by the cooling roll. Therefore, the time for which the molten metal is in contact with the outer peripheral surface of the cooling roll is long, and the cooling time of the molten metal is long. As a result, the grains in the thin metal strip are more refined.
It is preferable that molten metal remover is disposed opposite to the outer peripheral surface of the cooling roll and includes a heat dissipation surface configured to be in contact with the molten metal passing through the gap between the outer peripheral surface of the cooling roll and the molten metal remover.
In this case, the molten metal is subjected to heat dissipation from a surface in contact with the molten metal remover, as well as a surface in contact with the cooling roll (hereafter, also referred to as a solidified portion). Therefore, the cooling rate of the molten metal becomes high. As a result, the grains in the thin metal strip are more refined.
A method for producing a thin metal strip according to the present embodiment is a method for producing a thin metal strip by a single roll strip casting process using the producing apparatus described above. The producing method includes a supplying step, a rapid cooling step, and a thickness adjustment step. In the supplying step, the molten metal in the tundish is supplied onto the outer peripheral surface of the cooling roll. In the rapid cooling step, the molten metal on the outer peripheral surface is rapidly cooled with the cooling roll to be formed into the thin metal strip. In the thickness adjustment step, a portion of a thickness of the molten metal on the outer peripheral surface of the cooling roll that is larger than the width of the gap described above is removed by the molten metal remover. As a result, the thickness of the molten metal on the outer peripheral surface is cut down to the width of the gap between the outer peripheral surface of the cooling roll and the molten metal remover.
The producing method according to the present embodiment includes the thickness adjustment step. Through the thickness adjustment step, the molten metal on the outer peripheral surface of the cooling roll becomes thin. Therefore, the cooling rate of the molten metal becomes high. As a result, the grains in the thin metal strip are refined. In other words, by using the strip casting process, it is possible to efficiently produce a thin metal strip including fine grains.
The thin metal strip produced by the above production method of a thin metal strip may contain a chemical composition that includes Cu and Sn, and may contain a phase having D03 structure in the Strukturbericht notation. The powder obtained by pulverizing this thin metal strip can be used as a negative electrode active material for a nonaqueous electrolyte secondary battery, such as a lithium ion secondary battery. This negative electrode active material has excellent charge-discharge capacity and capacity retention characteristics. A chemical composition of the above thin metal strip consists of, for example, 10 to 20 at % or 21 to 27 at % of Sn, with the balance being Cu and impurities. The chemical composition of the above thin metal strip may further contain one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B, and C in place of a part of Cu.
With the producing method according to the present embodiment, in case of the above chemical composition, the ratio of the phase having D03 structure (hereinafter referred to as D03 phase) can be increased. Therefore, battery characteristics (capacity retention rate etc.) are increased.
The present embodiment will be described below in detail with reference to the accompanying drawings. The same or equivalent elements will be denoted by the same reference numerals, and the description thereof will not be repeated.
[Producing Apparatus]
[Cooling Roll]
The cooling roll 2 has an outer peripheral surface and is configured to cool and solidify molten metal 3 on the outer peripheral surface while rotating. The cooling roll 2 includes a column-shaped barrel portion and a shaft portion not illustrated. The barrel portion includes the outer peripheral surface described above. The shaft portion is disposed at a central axis position of the barrel portion and attached to a driving source not illustrated. The cooling roll 2 is configured to be rotated about a central axis 9 of the cooling roll 2 by the driving source.
The starting material of the cooling roll 2 is preferably a material having a high hardness and a high thermal conductivity. The starting material of the cooling roll 2 is, for example, one selected from the group consisting of copper and copper alloys. The starting material of the cooling roll 2 is preferably copper. The cooling roll 2 may further include a coating on its surface. This inclusion of the coating increases the hardness of the cooling roll 2. Therefore, it is advantageous, particularly in mass production. The coating is, for example, one or two selected from the group consisting of plating coating and cermet coating. The plating coating is, for example, one or two selected from the group consisting of chromium plating and nickel plating. The cermet coating contains, for example, one, or two or more selected from the group consisting of tungsten (W), cobalt (Co), titanium (Ti), chromium (Cr), nickel (Ni), silicon (Si), aluminum (Al), boron (B), and carbides, nitrides, and carbo-nitrides of these elements. It is preferable that the outer layer of the cooling roll 2 is made of copper, and the cooling roll 2 further includes a chromium plating coating on its surface.
Reference character X illustrated in
The cooling roll 2 includes a cooling zone that lies downstream of the tundish 4 to be described later in the rotating direction of the cooling roll 2 but does not reach the molten metal remover 5 to be described later. In the cooling zone, the molten metal 3 supplied onto the outer peripheral surface of the cooling roll 2 has a free surface. Therefore, rapid cooling is enabled. If the molten metal 3 has no free surface, that is, if a solidified portion of the molten metal 3 is covered with another portion of molten metal 3, the solidified portion cannot be subjected to sufficient heat dissipation. This is because heat is continuously added to the solidified portion from the molten metal 3 lying on the solidified portion. In the cooling zone, the molten metal 3 is made to have the free surface by being supplied onto the outer peripheral surface of the cooling roll 2. Therefore, the solidified portion can be subjected to sufficient heat dissipation, which enables the rapid cooling. As a result, it is possible to obtain the thin metal strip 6 including more refined grains.
The roll peripheral speed of the cooling roll 2 is set as appropriate in consideration of the cooling rate and the efficiency of manufacturing of the molten metal 3. The higher the roll peripheral speed is, the more easily the thin metal strip 6 peels off from the outer peripheral surface of the cooling roll 2. Therefore, the lower limit of the roll peripheral speed is preferably 50 m/min, more preferably 80 m/min, and still more preferably 120 m/min. The upper limit of the roll peripheral speed is not particularly limited but, for example, 500 m/min in consideration of a plant capacity. The roll peripheral speed can be determined from the diameter and the number of revolutions of the roll.
The inside of the cooling roll 2 may be filled with solvent for the heat dissipation. It is thereby possible to subject the molten metal 3 to the heat dissipation efficiently. The solvent is, for example, one, or two or more selected from the group consisting of water, organic solvent, and oil. The solvent may stay inside the cooling roll 2 or may be circulated through the outside.
[Tundish]
The tundish 4 can accommodate the molten metal 3 and is configured to supply the molten metal 3 onto the outer peripheral surface of the cooling roll 2.
In the present embodiment, the tundish 4 may always be heated. In this case, the melted state of the molten metal 3 having a high fusing point can be maintained. As a result, the molten metal 3 can be removed remaining in the melted state, with the molten metal remover 5 to be described later. A heating temperature is not particularly limited as long as the heating temperature is equal to or higher than the liquidus temperature of a raw material. In a case of producing a Si alloy, the heating temperature is, for example, 1200° C. or more, and a more preferable heating temperature is 1500° C. or more. In a case of producing an alloy material for a magnet, the heating temperature is, for example, 1000° C. or more.
The shape of the tundish 4 is not particularly limited as long as the molten metal 3 can be supplied onto the outer peripheral surface of the cooling roll 2. As shown in
The tundish 4 includes a supply end 7 for guiding the molten metal 3 on the outer peripheral surface of the cooling roll 2. The molten metal 3 is supplied from a crucible (not shown) to the tundish 4, and then supplied to the outer peripheral surface of the cooling roll 2 through the supply end 7. The shape of the supply end 7 is not particularly limited. The cross section of the supply end 7 may be rectangular as shown in
Preferably, the tundish 4 is disposed in the vicinity of the outer peripheral surface of the cooling roll 2. Thereby, the molten metal 3 can be stably supplied onto the outer peripheral surface of the cooling roll 2. The gap between the tundish 4 and the cooling roll 2 is appropriately set within a range where the molten metal 3 does not leak.
The material of the tundish 4 is preferably refractory. The tundish 4 is made of, for example, one or more selected from the group consisting of aluminum oxide (Al2O3), silicon monoxide (SiO), silicon dioxide (SiO2), chromium oxide (Cr2O3), magnesium oxide (MgO), titanium oxide (TiO2), aluminum titanate (Al2TiO5), And zirconium oxide (ZrO2).
[Molten Metal Remover]
The molten metal remover 5 is a member that extends along the shaft direction of the cooling roll 2. An example of the molten metal remover 5 is a plate-shaped member that is disposed in parallel to the shaft direction of the cooling roll 2, as illustrated in
The width of the gap A is preferably smaller than a thickness B of the molten metal 3 on the outer peripheral surface on an upstream side of the molten metal remover 5 in the rotating direction of the cooling roll 2. In this case, the molten metal 3 on the outer peripheral surface of the cooling roll 2 becomes thinner. Therefore, the cooling rate of the molten metal 3 becomes higher. As a result, the grains in the thin metal strip 6 are more refined.
The width of the gap A between the outer peripheral surface of the cooling roll 2 and the molten metal remover 5 is a shortest distance between the molten metal remover 5 and the outer peripheral surface of the cooling roll 2. The width of the gap A is set as appropriate in accordance with a target cooling rate and a target efficiency of manufacturing. The smaller the width of the gap A, the thinner the molten metal 3 subjected to thickness adjustment. Therefore, the cooling rate of the molten metal 3 becomes higher. As a result, the grains in the thin metal strip 6 are more easily refined. Consequently, the upper limit of the gap A is preferably 400 more preferably 250 μm, still more preferably 100 μm, even still more preferably 50 μm, even still more preferably 30 μm. In a case where the cooling roll 2 includes chromium plating and nickel plating on its surface, the cooling rate is slow as compared with a case where the surface of the cooling roll 2 is made of copper. Therefore, in this case, the gap A is preferably narrowed. The lower limit of the gap A is not particularly limited but, for example to, 10 μm.
Of the outer peripheral surface of the cooling roll 2, the distance between a location where the molten metal 3 is supplied from the tundish 4 and a location where the molten metal remover 5 is disposed is set as appropriate. The molten metal remover 5 may be disposed in a region where the free surface of the molten metal 3 (a surface of the molten metal 3 on a side on which the molten metal 3 is not in contact with the cooling roll 2) is in contact with the molten metal remover 5 in the liquid state or the semi-solidified state.
Referring to
The starting material of the molten metal remover 5 is preferably a refractory material. The molten metal remover 5 contains, for example, one, or two or more selected from the group consisting of aluminum oxide (Al2O3), silicon monoxide (SiO), silicon dioxide (SiO2), chromium oxide (Cr2O3), magnesium oxide (MgO), titanium oxide (TiO2), aluminum titanate (Al2TiO5), and zirconium oxide (ZrO2). It is preferable that the molten metal remover 5 contains one, or two or more selected from the group consisting of aluminum oxide (Al2O3), silicon dioxide (SiO2), aluminum titanate (Al2TiO5), and magnesium oxide (MgO).
In the producing apparatus 1 described above, the molten metal remover 5 removes a surface portion of the molten metal 3 on the outer peripheral surface of the cooling roll 2. The surface portion of the molten metal 3 means a portion of a thickness of the molten metal 3 on the outer peripheral surface of the cooling roll 2 that is larger than the width of the gap A between the outer peripheral surface of the cooling roll 2 and the molten metal remover 5. This cuts down the thickness of the molten metal 3 on the outer peripheral surface of the cooling roll 2. As a result, the molten metal 3 on the outer peripheral surface of the cooling roll 2 becomes thin. The reduction of the molten metal 3 in thickness makes the cooling rate of the molten metal 3 higher. Therefore, by producing a thin metal strip using the producing apparatus 1, it is possible to obtain the thin metal strip 6 including more refined grains.
The apparatus for producing a thin metal strip according to the present embodiment is not limited to the producing apparatus 1 described above.
In the producing apparatus 1 illustrated in
In the producing apparatus 10, the molten metal 3 is cooled while descending from the top of the cooling roll 2 along the outer peripheral surface of the cooling roll 2. Meanwhile, in the producing apparatus 1 illustrated in
The number of molten metal removers 5 to be disposed may be one as illustrated in
The molten metal remover 5 may be disposed in a direction along a normal line of the cooling roll 2 as illustrated in
The cross sectional shape of the front edge portion 50 of the molten metal remover 5 (an edge of the molten metal remover 5 to be in contact with the molten metal 3) in a cross section perpendicular to the shaft of the roll may be a rectangle as illustrated in
[Producing Method]
A method for producing the thin metal strip 6 according to the present embodiment is a producing method using the producing apparatus 1 or 10 described above. The producing method includes a supplying step, a rapid cooling step, and a thickness adjustment step.
First, the molten metal 3 is prepared. The composition of the molten metal 3 is set as appropriate in accordance with an intended composition of the thin metal strip 6. For example, in a case of producing Si alloy, the molten metal 3 contains, for example, one, or two or more selected from the group consisting of silicon (Si), titanium (Ti), chromium (Cr), vanadium (vanadium), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), copper (Cu), and tin (Sn), with the balance being impurities. In the case of producing a metal ribbon for a negative electrode active material used in a lithium secondary battery or the like, it is preferable to produce the molten metal 3 so as to obtain a metal ribbon having the chemical composition described below. Alternatively, in a case of producing an alloy material for a neodymium magnet, the molten metal 3 consists, for example, neodymium (Nd), boron (B), and iron (Fe), with the balance being impurities. The molten metal 3 is produced by heating a raw material having the chemical composition described above to the fusing point of the raw material or higher.
By putting the raw material having the chemical composition described above in a crucible and heating the raw material, the molten metal 3 is produced. Examples of the method of the heating include high-frequency induction heating, arc heating, plasma arc heating, electric resistance heating, and electron beam heating. A heating temperature is not particularly limited as long as the heating temperature is equal to or higher than the liquidus temperature of the raw material. In a case of producing a Si alloy, the heating temperature is, for example, 1200° C. or more, more preferably 1500° C. or more. In a case of producing an alloy material for a magnet, the heating temperature is, for example, 1000° C. or more.
[Supplying Step]
In the supplying step, the molten metal 3 in the tundish 4 is supplied onto the outer peripheral surface of the cooling roll 2. First, the molten metal 3 is supplied from the crucible to the tundish 4. The supply of the molten metal 3 from the crucible to the tundish 4 may be made by tilting the crucible to pour the molten metal 3 directly. Alternatively, a nozzle or the like may be used to supply the molten metal 3 from the crucible to the tundish 4. Subsequently, from the supply end 7 of the tundish 4, the molten metal 3 is supplied onto the outer peripheral surface of the cooling roll 2. The cooling roll 2 rotates, as described above, about the central axis 9 of the cooling roll 2 at a given speed. When the molten metal 3 supplied from the tundish 4 comes into contact with the outer peripheral surface of the cooling roll 2, the molten metal 3 is partially solidified to be transferred to the cooling roll 2. The molten metal 3 moves with the rotation of the cooling roll 2. At this point, a surface of the molten metal 3 not in contact with the outer peripheral surface of the cooling roll 2 (free surface) is in a liquid state or a semi-solidified state.
In the supplying step, the tundish 4 may always be heated. In this case, the melted state of the molten metal 3 having a high fusing point can be maintained. Therefore, the molten metal 3 can be removed by the molten metal remover 5 while being in the melted state. A heating temperature is not particularly limited as long as the heating temperature is equal to or higher than the liquidus temperature of the raw material. In a case of producing a Si alloy, the heating temperature is, for example, 1200° C. or more, and a more preferable heating temperature is 1500° C. or more. In a case of producing an alloy material for a magnet, the heating temperature is, for example, 1000° C. or more.
[Rapid Cooling Step]
In the rapid cooling step, the molten metal 3 on the outer peripheral surface is rapidly cooled with the cooling roll 2 to be formed into the thin metal strip 6. The rapid cooling step is started when the molten metal 3 is supplied onto the outer peripheral surface of the cooling roll 2 in the supplying step described above. In the rapid cooling process, the molten metal 3 is cooled from a solidified portion.
In the rapid cooling step, the cooling roll 2 includes a cooling zone that lies downstream of the tundish 4 in the rotating direction of the cooling roll 2 but does not reach the molten metal remover 5. In the cooling zone, the molten metal 3 supplied onto the outer peripheral surface of the cooling roll 2 includes a free surface. Therefore, rapid cooling is enabled. If the molten metal 3 has no free surface, that is, if the solidified portion is covered with another portion of molten metal 3, the solidified portion cannot be subjected to sufficient heat dissipation. This is because heat is continuously added to the solidified portion from the molten metal 3 lying on the solidified portion. In the cooling zone, the molten metal 3 is made to have the free surface by being supplied onto the outer peripheral surface of the cooling roll 2. Therefore, the solidified portion can be subjected to sufficient heat dissipation, which enables the rapid cooling. As a result, the thin metal strip 6 including more refined grains can be produced.
[Thickness Adjustment Step]
In the thickness adjustment step, the thickness of the molten metal 3 on the outer peripheral surface of the cooling roll 2 is cut down by the molten metal remover 5, in the middle of the rapid cooling step, to the width of the gap A between the outer peripheral surface of the cooling roll 2 and the molten metal remover 5. Immediately after supplied onto the outer peripheral surface of the cooling roll 2, the molten metal 3 is not solidified as a whole but gradually solidified from a solidified portion. The free surface of the molten metal 3 comes into contact with the molten metal remover 5, in a liquid state or a semi-solidified state. The hardness of the molten metal 3 in the liquid state or the semi-solidified state is low. Therefore, when the thickness of the molten metal 3 is larger than the width of the gap A, the free surface of the molten metal 3 in the liquid state or the semi-solidified state is blocked or removed. The molten metal 3 thereby becomes thin. As the molten metal 3 is thinner, the cooling rate of the molten metal 3 increases. As a result, the thin metal strip 6 including more refined grains can be produced.
The disposition of the heat dissipation surface 8 enables the molten metal 3 to be subjected to heat dissipation from the heat dissipation surface 8 as well as the solidified portion. In this case, the cooling rate of the molten metal 3 becomes high. The area and shape of the heat dissipation surface 8 are set as appropriate. For example, as illustrated in
The molten metal 3 reduced in thickness through the thickness adjustment step is subsequently cooled on the cooling roll 2. At this point, the molten metal 3 is thin. Therefore, the cooling rate is remarkably high. As a result, grains in the thin metal strip 6 are fine. The entire molten metal 3 is solidified into the thin metal strip 6. The thin metal strip 6 is separated from the outer peripheral surface of the cooling roll 2 and collected. Through the above steps, the thin metal strip 6 according to the present embodiment can be produced.
[Production of Thin Metal Strip for Negative Electrode Active Material]
As a negative electrode active material made of a metal, it is preferable that the ratio of a phase having D03 structure in Strukturbericht notation (hereinafter also referred to as D03 phase) is large. When pulverizing the thin metal strip and using it as a negative electrode active material (powder) for a lithium secondary battery, the D03 phase acts as a host for occlusion and release a lithium. Therefore, the greater the ratio of D03 phase in the metal strip is, the better the electric capacity and the cycle life of a battery are.
In the manufacturing method of this embodiment, it is easy to generate D03 phase. Therefore, it is suitable for the production of a metal ribbon for a negative electrode active material used in a lithium secondary battery.
A preferable chemical composition of the thin metal strip as a negative electrode active material is Sn, with the balance being Cu and impurities. More preferably, the chemical composition of the thin metal strip contains 10 to 20 at % or 21 to 27 at % of Sn, with the balance being Cu and impurities. In the chemical composition of the thin metal strip, the more preferable Sn content is 13 to 16 at %, 18.5 to 20 at %, or 21 to 27 at %.
The chemical composition may contain 10 to 20 at % or 21 to 27 at % of Sn, and one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B, and C, with the balance being Cu and impurities. More specifically, the above chemical composition may contain: Sn: 10 to 20 at % or 21 to 27 at % of Sn, and one or more selected from the group consisting of Ti: 9.0 at % or less, V: 49.0 at % or less, Cr: 49.0 at % or less, Mn: 9.0 at % or less, Fe: 49.0 at % or less, Co: 49.0 at % or less, Ni: 9.0 at % or less, Zn: 29.0 at % or less, Al: 49.0 at % or less, Si: 49.0 at % or less, B: 5.0 at % or less, and C: 5.0 at % or less, with the balance being Cu and impurities.
Using a producing apparatus described in the following Example 1 to Example 3, thin metal strips made of Si alloy were produced. A raw material contained nickel (Ni), titanium (Ti), and silicon (Si). The composition of the raw material was, in mass ratio, Ni:Ti:Si=25:17:58. One kilogram of the raw material in a mixed state was heated to 1450° C. to be produced into molten metal. The molten metal was supplied from the tundish onto the cooling roll. The cooling roll was one the outer peripheral surface of which is covered with copper and the inside of which is cooled by water. The cooling roll had a diameter of 20 cm and a width of 18 cm. The peripheral speed of the roll was 120 m/min. The thin metal strips made of Si alloy obtained in Example 1 to Example 3 were cut, and cross sections were observed under a scanning electron microscope (SEM).
In Example 1, the producing apparatus according to the present embodiment was used to produce a thin metal strip made of Si alloy. In other words, the thin metal strip made of Si alloy was produced using the molten metal remover. The molten metal remover was a flat alumina plate having a thickness of 3 mm. The width of the gap between the molten metal remover and the outer peripheral surface of the cooling roll was 80 μm.
In Example 2, a thin metal strip made of Si alloy was produced using the producing apparatus according to the present embodiment from which the molten metal remover was detached. In other words, the thin metal strip made of Si alloy was produced without using the molten metal remover.
In Example 3, a thin metal strip made of Si alloy was produced under the same conditions as those of Example 1 except that a producing apparatus with no cooling zone on the cooling roll in a region between the tundish and the molten metal remover was used. In other words, without the free surface, the molten metal was supplied to the molten metal remover.
In Example 3, in which the production was made by removing the molten metal without the free surface with the molten metal remover, the size of a grain in a Si phase of the thin metal strip was 10 to 15 μm.
From the above, the method according to the present embodiment provides a thin metal strip with finer crystal grain than the conventional method.
Metallic ribbons were produced under various producing conditions. Each of the thin metal strip had a chemical composition, containing 20.0 at % of Sn and 8.0 at % of Si, with the balance being Cu and impurities. The ratio (mass %) of D03 phase (phase having D03 structure) in the produced thin metal strip was determined.
[Experimental Method]
Initially, molten metals with the chemical composition of test numbers 1 to 8 shown in Table 1 were prepared.
The composition of raw material of the molten metal was Cu:Sn:Si=63.8:33.1:3.1 by mass ratio at each test number. 1 kg of the raw material was heated to 1250° C. to produce molten metal.
Using the molten metal described above, in test numbers 1 to 3 and 5 to 8, thin metal strips were produced by the production method (with a blade member) of this embodiment. In test number 4, a thin metal strip was produced by a conventional manufacturing method (without a blade member).
Specifically, molten metal of each test number was provided onto the cooling roll from the tundish. The composition of the coating film on the surface of the cooling roll used was as shown in Table 1. That is, in test numbers. 1 and 2, the surface of the cooling roll was Cu, and in test numbers 3 and 4, the surface of the cooling roll was a Cr plating film. The interior of the cooling roll was cooled with water. The diameter of the cooling roll was 20 cm, and the width was 18 cm.
With the peripheral velocity of the cooling roll shown in Table 1, molten metal was provided onto the cooling role at the temperature shown in Table 1 to produce a thin metal strip. At this time, in test numbers. 1 to 3, a blade member was used. The material of the blade member was alumina and the blade member was a flat plate having a thickness of 3 mm. The gap between the blade member and the cooling roll of each test numbers 1 to 3 was as shown in Table 1. In test number 4, no blade member was used.
The ratio occupied by D03 phase in the produced thin metal strips of each test numbers 1 to 8 was determined by the following method.
X-ray diffraction measurement was conducted on the thin metal strips and measurement data of the X-ray diffraction profile was obtained. Specifically, an X-ray diffraction profile of the thin metal strip was obtained, using a SmartLab (rotor target maximum output 9 KW; 45 kV-200 mA) manufactured by Rigaku Corporation. Based on the obtained X-ray diffraction profile (measured data), the crystal structure in the thin metal strip was analyzed by the Rietveld method. The X-ray diffraction apparatus and measurement conditions are described below.
(X-Ray Diffraction Apparatus and Measurement Conditions)
The crystal structure of D03 phase is cubic, and in terms of classification of a space group, No. 225(Fm-3m) of International Table (Volume-A).
Accordingly, with the structure model of this space group number being as the initial structure model of Rietveld analysis, a calculated value of diffraction profile (hereinafter, referred to as a calculated profile) of each thin metal strip was found by Rietveld method. Rietan-2000 (program name) was used for Rietveld analysis.
From the each diffraction peaks at the powder X-ray diffraction profile and the Rietveld method, the existence of D03 phase in the thin metal strips was confirmed. When the D03 phase was present, the ratio (mass %) of the D03 phase was determined.
[Result of Evaluation]
The ratio of D03 phase is shown in Table 1. Referring to Table 1, the ratio of D03 phase in the thin metal strips of test numbers 1 to 3 and 5 to 8 produced by the product method (with a blade member) of the present embodiment was higher than the ration of D03 phase in the thin metal strip of test number 4 produced by the conventional production method).
Furthermore, when comparing test numbers 1 to 3 and 5 to 8, when the surface of the cooling roll was Cu, the ratio of D03 phase was higher as compared with the case of the Cr plating film on the surface of the cooling roll. It is thought that Cu had a higher heat transfer property than the Cr plating film and it was easy to quench the molten metal.
The embodiment according to the present invention has been described above. However, the aforementioned embodiment is merely an example for practicing the present invention. Therefore, the present invention is not limited to the aforementioned embodiment, and the aforementioned embodiment can be modified and implemented as appropriate without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-233354 | Nov 2015 | JP | national |
| 2016-099864 | May 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/085458 | 11/29/2016 | WO | 00 |
