KR20080001021A - Method for producing alloy ribbons(or strips) by the centrifugal solidification process - Google Patents

Abstract

A method for manufacturing an alloy strip by a centrifugal solidification process is provided to improve magnetic characteristics of an alloy for a rare-earth permanent magnet. In a method for manufacturing an alloy strip by a centrifugal solidification process, a vacuum chamber(1) of a quenching system is connected with a rotary pump and a diffusion pump basically to remove oxygen and to substitute the oxygen into inert gas when manufacturing a magnet alloy which includes a rare-earth element which is oxidized easily. A cooling roll driving unit, an alloy melting high-frequency induction path, a cooling roll driving axis which is connected with a cool water supply unit are included. An adequate coolant is circulated at an inside of a cooling roll(3) to prevent temperature of an inner surface for the cooling roll from being increased in a continuous operation.

Description

Method for producing Alloy Ribbons (or Strips) by the Centrifugal solidification Process}

1 is a front view of the cooling roll and its main parts in the present invention;

Figure 2 is a perspective view of the cooling roll and its peripheral parts in the present invention

Figure 3 is a perspective view of the tundish and nozzle in the present invention

Figure 4 is a perspective view of the roller and the scraper in the present invention

5 is a strip outline photograph and thickness measurement results of the Nd-Fe-B magnet alloy prepared according to the present invention

6 is a measurement result of the relative density of the strip of Nd-Fe-B magnet alloy prepared by the present invention

7 is a microstructure of the strip of Nd-Fe-B magnet alloy prepared by the present invention

8 is an RXD measurement result of a strip of Nd-Fe-B magnet alloy prepared by the present invention

9 is a SEM analysis of the strip of Nd-Fe-B magnet alloy prepared by the present invention

10 is a VSM measurement result of the strip of Nd-Fe-B magnet alloy prepared by the present invention

[Explanation of symbols on the main parts of the drawings]

1 chamber 3 cooling roll

6: alloy ribbon (or strip) 9: tundish

10: nozzle 11: roller

11a: roller moving direction 11b: roller support shaft

12: scraper 12a: end of the scraper

12b: scraper support shaft 15: recovered alloy ribbon (or strip)

16: Guide for recovering alloy ribbon (or strip)

17: Alloy ribbon (or strip) recovery container 28: Weight for scraper contact

Generally high performance rare earth permanent magnet material (Sm-Co-based, Nd-), which is one of the rapid solidification methods (RSP), which is generally known for manufacturing magnetic materials (hard / soft various magnetic materials), hydrogen storage alloys, and anode materials for secondary batteries. Rapid solidification (Rapid), a well-known method of manufacturing Fe-B-based and Sm-Fe-N-based materials, soft magnetic materials (such as amorphous alloys, sand dust, permalloy, etc.), hydrogen storage alloys (LaNi5) and anode materials for secondary batteries The solidification process is roughly classified into two methods: gas atomizer and rotating chill roller. In particular, in the latter cooling roll method, the raw metal is melted using a high frequency induction furnace or an arc furnace in a vacuum or inert atmosphere chamber for the purpose of producing a master alloy powder of a functional material, respectively. After instantaneous contact with the outer circumference, it is first manufactured in the form of alloy ribbon (or strip), and finally powder is processed through coarse and fine grinding processes. However, both surfaces (cold roll contact surface and non-contact surface) and the internal microstructures of the mother alloy ribbon (or strip) thus manufactured are different from the cooling rate, that is, the microstructure of the ribbon (or strip) of the manufactured magnetic alloy. The thickness (range of 0.2-0.5mm) is not only different depending on the process variables such as the rotational speed of the cooling roll and the supply speed of the melt by the nozzle size or the melt temperature, but also because the control of their process variables is very difficult. The rapid cooling and solidification of the crystalline alloy ribbon (or strip) has been pointed out that the magnetic properties of the magnet alloy powder are deteriorated even after proper heat treatment because the microstructure is heterogeneous. As a practical example, when manufacturing practical Nd-Fe-B-based and Sm-Fe-N-based permanent magnet alloy ribbons or strips, α-Fe crystallization, coarsening of microstructures and micro segregation may occur. It is known that the magnetic properties of the magnet alloy are lowered.

Therefore, according to the US patent technique (US 6790296) by H. Kanekiyo et al., Developed as a means to improve such a problem, it rotates from the vertical upward direction of the cooling roll for the purpose of maintaining the contact time of the molten metal on the outer circumference of the rapid cooling roll. A method of contacting the molten metal as far back as possible (11 o'clock clockwise) is suggested. However, this method can increase the cooling rate of the alloy ribbon (or strip) by slightly increasing the contact time of the molten metal to the cooling roll compared to the conventional single roll method or twin roll method, but it scatters unstable as it cools in contact with the cooling roll. Considering the angle and the cooling rate of the alloy ribbon, it is not only difficult to adjust properly, but also the effect is considered to be insignificant. On the other hand, such a phenomenon is that when the Nd-Fe-B permanent magnet alloy ribbon (or strip) is manufactured, the cooling rate varies depending on the portion of the alloy ribbon (or strip). Compounds such as α-Fe, Nd ₂ Fe ₁₄ B, and Fe-B to be obtained are formed in the non-contact surface with the cooling roll) and the lower portion (contact surface with the cooling roll), but their compounds are hardly present in the center even after the heat treatment. In addition, segregation of added elements, coarsening of microstructures, and heterogeneity are known to reduce magnetic properties of the magnet alloy. It is known to be obtained. Therefore, according to a technique known as Japanese Patent Application Laid-Open No. Hei 11-238612 as part of a practical technique for improving such a problem, an alloy particle (or strip) obtained by rapid solidification is first pulverized and improper particles by magnetic screening. As a method of improving the magnetic properties by removing (for example, powder particles having low magnetic properties), it is considered that there is a problem in the manufacturing process cost due to the decrease in productivity due to the increase in the process.

In addition, according to techniques known in Japanese Patent Applications (Japanese Patent Laid-Open Nos. 11-209804 and 11-297519), as an example of a technique using a conventional centrifugal casting method, a finer structure of a magnetic alloy can be obtained by centrifugal force. It is a disadvantage that the production cost increases due to the increase in the manufacturing process such as coarse pulverization by separating and recovering the solidified alloy from the mold as well as a large difference in the microstructure due to the cooling rate depending on the thickness of the alloy solidifying inside the cylinder. In fact, there is no report on the specific effectiveness or adoption of the above patented technology.

The present invention is a means for solving the problems of the conventional rapid solidification apparatus as described above, by supplying the molten alloy to the inner circumference, not the outer circumference of the rotating cooling roll, so that centrifugal force is added and stable for a relatively long time. After contact is allowed to cool to solidify and then the strip (or ribbon) is removed using a scraper to recover.

The present invention, in particular, when cooling the molten alloy, according to the effect of increasing the cooling rate, densification and miniaturization of the alloy structure, improve the unidirectional coagulation characteristics and decrease the segregation of the alloy (magnetic material, hydrogen storage alloy, secondary It can be used as a manufacturing method suitable for the production of battery negative electrode material, etc., in particular, the magnetic properties of the rare earth permanent magnet alloy is expected to improve.

1 is a front view schematically showing a vacuum chamber 1, a cooling roll 3, a tundish 9, a nozzle 10, a roller 11, a scraper 12 and main components according to the present invention. The vacuum chamber of the quenching apparatus according to the present invention basically requires a connection with a general rotary pump and a diffusion pump in order to remove oxygen and replace with an inert gas when manufacturing a magnetic alloy containing rare earth elements that are easily oxidized. It consists of a roll drive device, a high frequency induction furnace for alloy melting, a cooling roll drive shaft connected to a cooling water supply device, and the like. In particular, the cooling roll is preferably designed to circulate a suitable refrigerant (water, air, liquid nitrogen, etc.) in order to avoid the temperature rise of the inner surface of the cooling roll due to the cooling effect or continuous operation.

2 is a perspective view partially showing the components of a cooling device composed of a cooling roll 3, a roller 11, a scraper 12, a tundish 9 and the like in the present invention. The materials of the cooling roll 3 and the roller 11 are preferably thermally conductive Cu and Cu alloy (Cu-Be alloy, etc.) capable of withstanding thermal shock, and the inside diameter of the cooling roll is a target alloy ribbon (or strip). ) Can directly affect manufacturing process variables such as operating capacity, cooling roll rotation speed, and microstructure of alloy ribbons (or strips). Therefore, the size can be adjusted according to the operation amount (kg / day) of the target alloy, and for optimal operating conditions is made by adjusting the rotational speed and nozzle size, etc. according to the inner size of the cooling roll.

In the roller 11 installed inside the cooling roll 3, the molten alloy 8 passes through the tundish 9 and the nozzle 10 to stably contact and cool the inside of the cooling roll so that the alloy ribbon (or strip) As a means for stably contacting until it is removed by the scraper 12 in the form (15), it is installed so as to contact the middle lower end (3 o'clock-4 o'clock direction of the clock) of the inner circumference of the cooling roll. However, it is preferable to install the roller 11 and the roller holder so as to move from side to side like a clock weight using the weight or weight (or spring) of the roller holder without fixing the roller support shaft 11b. It is also preferable that the material thereof is not overheated by using a material similar to that of the material of the cooling roll.

The scraper 12 is for removing the rapidly cooled solidified alloy ribbon (or strip) from the inside of the cooling roll. The scraper 12 must be installed at the lower end of the roller. use. In addition, the scraper 12 is in contact with the inside of the cooling roll 3 by using the weight or weight 28 of the scraper itself and the alloy ribbon ( Or strips 6 and 15 to effectively remove the strips.

FIG. 3 shows the tundish 9 and the nozzle 10 for supplying the molten alloy for the purpose to the inner circumference of the cooling roll 3 in the present invention. In this case, the inner diameter of the nozzle 10 should be appropriately designed in consideration of the size of the cooling roll 3 and the operation amount of the alloy ribbon. In particular, the nozzle 10 may be manufactured in a rectangular shape rather than a cylindrical shape so that the molten metal is as flat as possible on the inner circumference of the cooling roll. Allow for supply and contact, but be careful not to set the nozzle bottom and the cooling roll contact distance too far.

Figure 4 shows the assembly of the cooling roll 3 and the scraper 12, in particular, the roller support shaft (11b) and the scraper support shaft (12b) is preferably manufactured using a bearing for their smooth drive and operation Do.

5 and 6 is an embodiment according to the present invention, the sample shape and thickness of the (a) Nd-Fe-B alloy ribbon (or strip) prepared by changing the cooling roll rotational speed from 300rpm to 700rpm, and ( b) shows the result of measuring specific gravity. As expected, although the thickness of the alloy ribbon (or strip) sample 15 decreased as the rotational speed of the cooling roll 3 increased, the specific gravity of these samples increased inversely. Such a reason can be said to be evidence of the change of centrifugal force due to the cooling roll rotational speed.

7 and 8 show the microstructure and the XRD pattern of the above-described Nd-Fe-B-based alloy ribbon (strip) sample, the crystalline quality of the alloy ribbon (strip) sample with the increase of the cooling rate according to the increase in the rotational speed of the cooling roll It could be confirmed that the microstructure becomes more fine.

In addition, FIG. 9 shows that the Nd ₂ Fe ₁₄ B phase and the Nd-rich phase phase that can be obtained from the Nd-Fe-B magnet alloy are obtained as a result of the phase analysis of the sample by XRD. In addition, these phases were almost in agreement with the chemical composition by EDX point analysis of electron microscope.

10 is a result of measuring the magnetic properties by using a vibrating specimen type magnetic measuring device (VSM) by grinding all the above samples in a mortar, especially when the rotational speed is increased from 300rpm to 600rpm at a relatively low speed Although this increased, samples of more than 700 rpm were rather reduced.

The quenching apparatus according to the present invention is a primary means for pulverizing various functional material alloys such as alloys for rare earth permanent magnets containing rare earth elements as active metals, hydrogen storage materials and negative electrode materials for secondary batteries. By contacting the molten metal to the inside of the cooling roll, which rotates at a relatively low speed, and rapidly solidifying the molten metal without contacting the outer circumference of the roll, the high quality of the product due to the miniaturization, densification, segregation, and unidirectional solidification characteristics of the alloy are improved. As well as homogenization, it is very advantageous for the economic effect of the increase of product productivity and the reduction of equipment cost.

In addition, the quenching apparatus according to the present invention is improved in productivity since the alloy ribbon (or strip) having a thickness of 0.5 mm or more can be manufactured by the synergistic effect of the cooling effect as compared to the quenching apparatus by the cooling rolls fed to the outer circumference. Of course, the cooling roll rotational speed can be operated even at a relatively low speed of less than 1000rpm can be expected economic effects due to the reduction of the manufacturing apparatus and equipment costs accordingly.

Claims (4)

The molten metal (8) is contacted and cooled at the lower end of the inner circumference of the cooling roll (3) which is filled to circulate the refrigerant and rotates at a relatively low speed so that the tundish (9) and the nozzle (10) capable of supplying a predetermined amount are fixed. And a roller 11 for supporting the solidified alloy ribbon (or strip) 6 to be stably contacted and cooled inside the cooling roll, and the solidified alloy ribbon (or strip) is cooled. Various magnetic materials (rare earth magnets, alico magnets, amorphous alloys, sendusts, permalloys) and functional materials (water tank storage alloys, secondary batteries), which are recovered by using the scraper 12 as a means for removing them from the inside of the rolls. Cathode material and the like) and its manufacturing apparatus. The roller 11 is installed so as to contact the lower and middle ends (3 o'clock-4 o'clock direction of the clock) of the inner circumference of the cooling roll 3, but without fixing the roller 11 around the support shaft 11b. ) And various magnetic materials (rare earth magnets, alico), which support alloy ribbons (or strips) while moving left and right (11a) like watch weights using the weight or weight (28) (or spring) of the holder. Magnets, amorphous alloys, sendust, permalloy) and functional materials (water tank storage alloys, secondary battery negative electrode materials, etc.) and apparatuses for manufacturing the same. 2. The scraper (12) according to claim 1, wherein the scraper (12) is formed with the roller of claim 2 about its support shaft (12b) to remove the rapidly cooled solidified alloy ribbon (or strip) 6 from the inside of the cooling roll (3). Similarly, by using the weight of the scraper 12 itself or the weight 28, etc. to be in contact with the inside of the cooling roll to be installed on the lower end of the center of the cooling roll as possible to effectively remove the alloy ribbon (or strip) (6), Various magnetic materials (rare earth magnets, alico magnets, amorphous alloys, sendust, permalloy) and functional materials (tank storage alloys), characterized in that the tip portion must be partially mounted and used with high speed tool steel (or cemented carbide) 12a. A secondary battery negative electrode material, etc.) and a method for manufacturing the same. [2] The magnetic material of claim 1, wherein a stopper 13 is installed so as to be detachable from the upper portion of the tundish so that the molten metal supplied to the tundish 9 is not suddenly supplied to the nozzle portion. (Rare earth magnets, alico magnets, amorphous alloys, sendust, permalloy) and functional materials (water tank storage alloys, secondary battery negative electrode materials, etc.) and manufacturing apparatus thereof.

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