JP2012170998A - Jig for forming metal ball, method of forming metal ball using the same, and metal ball produced by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a jig for forming metal balls, capable of effectively forming not only a noble metal but also the other metals into extremely large sized metal balls, while having a plane plate-like shape, without any special processing; to provide a method of forming the metal balls, capable of making the sizes of metal particles uniform by uniforming weights of solid metal pieces to be placed on the jig for forming the metal balls and further capable of adjusting the sizes of the metal balls to be produced by adjusting the weights from the densities of the metals to be melted; and to provide the metal balls formed by this method.SOLUTION: The jig 1 for forming the metal balls includes a part for mounting a solid metal, the part being used in the method in which the solid metal mounted is melted to produce liquid metal 2 and then the metal ball is formed by surface tension of the liquid metal. The jig is formed of ceramics so as to have a wetting angle θ of 90° or more with the liquid metals.

Description

  The present invention relates to a forming jig used for forming a metal sphere, a method for forming a metal sphere using the jig, and a metal sphere obtained by the forming method.

  Conventionally, metal balls have been used in various fields, for example, bearing balls, ornaments, ball milling balls, pumps and check valves for valves, and raw balls for making porous bodies. Yes.

  Various methods for producing such metal spheres are known, and one of them is an atomizing method in which molten metal is formed into droplets and solidified into a sphere that is the most stable shape while falling in the air. There is.

  This atomization method is a process for solidifying metals, and is roughly divided into a gas atomization method using an inert gas and a water atomization method using water, but the metal spheres that can be obtained by either method are deformed. It is difficult to obtain the target metal sphere.

  In addition, there is a large variation in the size of the metal spheres obtained by the atomization method, and classification with a sieve is necessary to obtain a metal sphere of the desired size. Therefore, all metal balls other than the target size may be redissolved or unusable.

  Furthermore, a plasma rotating electrode process (PREP) is also known as a method for obtaining fine metal spheres. In this method, a metal sphere is obtained by rotating an electrode, dissolving the electrode with plasma, and further miniaturizing a droplet blown off by centrifugal force with a gas jet.

  However, since such a method uses free fall, a considerably large system is required to produce a metal ball. Further, the size of the metal spheres obtained is such that the maximum particle size is about several hundreds μm because the melted raw material is sprayed from the nozzle tip, and it is difficult to obtain a larger size.

  A forging method is known as a method for producing a metal ball having a large size. In this method, a metal lump is divided into several stages, forged, gradually brought close to a spherical shape, and finally polished to obtain a target metal sphere. Such a method is costly due to various processes. In addition, since a large press is used, the manufacturing equipment becomes large.

  Therefore, as a method of forming a relatively large size metal sphere with a simple apparatus, a method using a surface tension between the jig and a liquid metal obtained by melting a solid metal has been proposed. (See Patent Documents 1 to 3).

  These methods can form metal balls having a relatively large size without requiring a large-scale apparatus as compared with the conventional atomizing method, plasma rotating electrode method, forging method and the like.

  However, since the jig is formed of a carbon material, there is a risk of causing an undesirable reaction such as a carbonization reaction or a reduction reaction with the jig in the process of melting the solid metal. In some cases, the desired high-purity metal spheres cannot be obtained.

  Moreover, since there is a limit to the metal having a large wetting angle with respect to the carbon material, the metal balls that can be produced by this jig are limited.

  For this reason, the metal spheres produced by the above method are mainly those containing a large amount of precious metals that are relatively difficult to react with other substances, and other pure metal spheres such as iron, cobalt, nickel, and copper. It was difficult to apply to the process.

  Further, when using a jig made of ordinary ceramics or metal other than carbon, the same problem as that naturally occurs.

  Furthermore, in these methods, there is a problem that it is necessary to provide a recess in the jig, or to form the recess in a circular shape having a diameter larger than the depth, and it takes time and labor to form the jig.

JP-A-6-264113 JP-A-2005-139526 Japanese Examined Patent Publication No. 7-91561

  The present invention has been made in view of the above-described prior art, and has a plate-like shape without special processing, and not only precious metals but also other metals are efficiently very large in size. By aligning the weight of the metal sphere forming jig that can be a sphere and the weight of the solid metal piece placed on the metal forming jig, the size of the obtained metal particles can be made uniform, It is an object of the present invention to provide a method for forming a metal sphere capable of adjusting the size of the metal sphere obtained by adjusting the weight from the density of the molten metal, and a metal sphere formed by this method.

  In order to solve the above problems, the present inventors have found that the wetting angle between the jig and the liquid metal obtained by melting the solid metal (the wetting angle is a figure when a molten metal droplet is placed on the jig. The contact angle θ between the jig and the molten metal droplet as shown in FIG. 1) is a result of intensive investigations, and as a result, the metal formed from a material having a specific wetting angle with respect to the molten liquid metal. It has been found that by melting a solid metal in the tool, the molten liquid metal is efficiently spherical due to the influence of surface tension, and the desired metal sphere can be obtained.

  That is, the present invention is characterized by the following.

  The first is a metal sphere forming jig provided with a solid metal placement portion, which is used in a method of melting a placed solid metal to form a liquid metal and forming a metal sphere by its surface tension. The jig is made of ceramics having a wetting angle with the liquid metal of 90 ° or more.

  Second, in the metal ball forming jig of the first invention, the ceramic contains titanium nitride.

  Third, the metal ball forming jig of the first or second invention includes ceramics and metal.

  Fourth, in the metal ball forming jig of the third invention, the metal is iron, nickel, cobalt, or copper.

  Fifth, in the metal sphere forming jig of the third or fourth invention, the compounding ratio of titanium nitride and metal is 90% by mass or more of titanium nitride and the balance is metal.

  Sixth, in the metal ball forming jig of the first to fifth inventions, the relative density is 80% or more.

  Seventh, in the metal ball forming jig according to the first to sixth inventions, a recess for placing a solid metal is formed on at least a part of the surface of the jig.

  Eighth, the solid metal placed on the surface of the metal ball forming jig of the first to seventh inventions is melted to form a liquid metal, and the metal ball is formed by the surface tension, and then cooled. This is a method for forming a metal sphere.

  Ninth, in the method for forming a metal sphere according to the eighth aspect of the invention, the atmosphere for melting the solid metal is a vacuum of 100 Pa or less.

  Tenth, in the metal sphere forming method of the eighth or ninth invention, the surface of the metal sphere is rapidly cooled by introducing an inert gas and / or an active gas.

  Eleventh, a metal sphere having a diameter of 0.1 mm or more obtained by the method for forming a metal sphere of the eighth to tenth inventions.

  Twelfth, in the metal sphere of the eleventh aspect, the average diameter variation of the metal sphere is within 10% of the diameter of the target metal sphere.

  According to the present invention, a metal forming jig provided with a solid metal placement portion, used in a method of melting a placed solid metal into a liquid metal and forming a metal ball by its surface tension, Without special processing, while having a flat plate shape, not only precious metals but also other metals can be efficiently made into extremely large metal balls.

  Further, according to the metal ball forming method using the metal forming jig, the size of the obtained metal particles is made uniform by making the weight of the solid metal pieces placed on the metal forming jig uniform. In addition, the size of the resulting metal sphere can be adjusted based on the density and weight of the metal to be melted.

  Furthermore, since a simple process of melting and cooling after placing a metal piece on a jig, the apparatus can be simplified and miniaturized as compared with the atomizing method and the plasma rotating electrode method.

It is a schematic explanatory drawing which shows the contact angle (theta) of a jig | tool and a molten metal droplet. It is a photograph which shows the state of the nickel (Ni) fuse | melted on the jig | tool for titanium nitride (TiN) metal ball forming. It is a photograph which shows the state of the tin (Sn) fuse | melted on the jig | tool for titanium nitride (TiN) metal ball forming. It is a photograph which shows the state of the iron (Fe) fuse | melted on the jig | tool for titanium nitride (TiN) metal ball forming. It is a photograph which shows the state of the cobalt (Co) fuse | melted on the jig | tool for titanium nitride (TiN) metal ball forming. It is a photograph which shows the state of the nickel (Ni) fuse | melted on the jig | tool for metal sphere formation of a titanium nitride (TiN) group composite material.

  The metal sphere forming jig having a solid metal placement portion according to the present invention is used in a method of melting a placed solid metal to form a liquid metal and forming a metal sphere by its surface tension. The material is ceramics having a wetting angle with the liquid metal of 90 ° or more, preferably 120 ° or more.

  Here, the wetting angle is a contact angle θ between the jig and the molten metal droplet as shown in FIG. 1 when the molten metal droplet is placed on the jig.

  In the present invention, the reason why the wetting angle is 90 ° or more is that the contact angle with the jig needs to be at least 90 ° or more in order for the molten metal to be a sphere.

  As the ceramic used in the present invention, any ceramic can be used as long as the wetting angle is 90 ° or more, but it is preferable to use a ceramic whose melting point is higher than that of the metal to be spheroidized.

  Examples of such ceramics include ceramics such as titanium nitride (hereinafter abbreviated as TiN) and titanium boride.

  Among these, TiN ceramics can be preferably used. This is because the TiN ceramics have a wetting angle of more than 90 ° with various metals, the melting point is about 2900 ° C, which is very high compared to the melting point of many metals, and it is difficult to react with metals. It depends on.

  Moreover, in order to improve the intensity | strength and toughness, ceramics elements, such as iron, cobalt, nickel, copper, can be mix | blended with ceramics.

  In the case of using TiN-based ceramics, it is desirable from the viewpoint of strength and toughness that the mixing ratio of TiN and metal is such that TiN is 90% by mass or more, preferably 95% by weight, and the balance is metal.

  The relative density of the ceramic is preferably 80% or more, and preferably 95% or more from the viewpoint of strength.

  The metal ball forming jig of the present invention can fully exhibit its function even when it is flat, but can form a recess for placing a solid metal on a part of its surface. By providing the concave portion on a part of the surface, the position of the metal sphere can be stabilized when the solid metal is melted.

  Further, by forming a polygonal groove in a part of the surface, the contact point with the metal sphere at the time of melting increases, and it is possible to make the metal sphere easier to produce.

  Thus, the cross-sectional shape of the recess is not particularly limited, and may be a cross-sectional shape such as a circle, an ellipse, a V shape, or a polygon.

  Hereinafter, a specific method for producing the metal ball forming jig of the present invention will be described.

  After mixing TiN powder or TiN powder and metal powder, press molding is performed to obtain a predetermined shape. By heating this press-molded body to 1100 ° C. or higher under pressure, a molded body of a metal ball forming jig can be produced.

  Next, the metal ball forming method of the present invention will be described.

  In the metal sphere forming method of the present invention, after placing a solid metal on the surface of the above-described metal sphere forming jig, the metal sphere is melted to form a liquid metal, and the metal sphere is formed by the surface tension and then cooled. Consists of.

  The solid metal used in the present invention is not particularly limited, and is a base metal or a simple substance of gold, silver, platinum group element, aluminum, silicon, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, Any of simple metals such as zinc, gallium, germanium, zirconium, indium, tin, and lead, or alloys thereof can be used.

  The shape of the solid metal is not particularly limited, such as a metal piece, metal powder, etc., but a metal having a uniform weight by cutting a wire, rod, plate, strip or the like to a certain length or a certain area It is preferable to use it as a piece.

  The method for placing the solid metal on the surface of the metal ball forming jig is not particularly limited, and may be any distance as long as the solid metal pieces do not contact each other after melting. Solid metal may be arranged in a plane on a metal ball forming jig, but a plurality of jigs may be arranged three-dimensionally, or arranged in a tray-like container in a plane. May be stacked in several layers.

  In the metal ball forming method of the present invention, the solid metal placed on the metal ball forming jig is heated to the melting point of the solid metal or higher. As the heating means, a conventionally known heating furnace or the like can be used. The heating atmosphere may be normal pressure, pressurization, or reduced pressure, but from the viewpoint of oxidation, the reduced pressure is 100 Pa or less, preferably 10 Pa or less.

  A solid metal melts at a temperature equal to or higher than its melting point, and spheroidizes into each metal piece due to its surface tension. If this is cooled, a desired metal sphere can be obtained. The cooling means is not particularly limited, and means such as natural cooling can be used, but the surface of the metal sphere is intentionally cooled by introducing an inert gas and / or an active gas to rapidly cool the surface of the metal sphere. Effects such as formation of a hardened phase and refinement of crystal grains can be obtained.

  As described above, the metal ball forming method of the present invention is a simple process of melting and cooling after placing a metal piece on a metal ball forming jig, and therefore, compared to the atomizing method and the plasma rotating electrode method. Thus, the apparatus can be simply and miniaturized.

  In addition, according to the present invention, the size of the metal particles obtained by aligning the weight of the solid metal piece placed on the jig can be made uniform, and the variation in the average diameter of the metal spheres is the target metal. It can be within 10% of the diameter of the sphere.

  Further, the size of the metal sphere obtained can be adjusted from the density and weight of the molten metal. That is, in the method of the present invention, it is possible to obtain a metal sphere of 0.1 mm or more, and further 2 mm or more and 5 mm or more.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all.
<Example 1>
(Preparation of TiN metal ball forming jig)
TiN powder was press-molded so as to have a predetermined shape, and heated to 1100 ° C. or higher under pressure to produce a TiN compact.

The produced TiN metal sphere forming jig was a flat plate with a diameter of 15 mm and a thickness of 5 mm, and the relative density was 99%.
(Production of metal balls)
On the produced TiN metal ball forming jig, 0.3 g of a nickel piece having a cylindrical shape was placed and placed in a vacuum furnace, and the inside of the furnace was evacuated to 10 Pa. Heating to 0 ° C. confirmed that the nickel had melted. The wetting angle at this time was 130 °.

  Thereafter, cooling was performed under furnace cooling conditions to obtain metal balls.

A photograph of the state in the melting furnace is shown in FIG. It was confirmed that the molten nickel had a spherical shape, and the diameter of the extracted nickel sphere was about 2 to 3 mm.
<Example 2>
(Production of metal balls)
After placing 0.3 g of a cylindrical tin piece on the TiN metal sphere forming jig produced in Example 1 and placing it in a vacuum furnace, the inside of the furnace was evacuated to 10 Pa, and then tin It was confirmed that the tin was melted by heating to a melting point of 231.93 ° C. The wetting angle at this time was 135 °.

  Thereafter, cooling was performed under furnace cooling conditions to obtain metal balls.

A photograph of the state in the vacuum furnace is shown in FIG. It was confirmed that the molten tin was spherical, and the diameter of the extracted tin sphere was about 2 mm.
<Example 3>
A cylindrical iron piece 1 g was placed on the TiN metal ball forming jig produced in Example 1 and placed in a vacuum furnace, and the inside of the furnace was evacuated to 10 Pa. Then, the melting point of iron 1535 Heating to 0 ° C. confirmed that the iron was melted. The wetting angle at this time was 100 °.

  Thereafter, cooling was performed under furnace cooling conditions to obtain metal balls.

A photograph of the state in the vacuum furnace is shown in FIG. It was confirmed that the molten iron was spherical, and the diameter of the extracted iron ball was about 5 mm.
<Example 4>
After placing 0.7 g of cylindrical cobalt pieces on the TiN metal sphere forming jig produced in Example 1 and placing it in a vacuum furnace, and evacuating the furnace to 10 Pa, cobalt It was confirmed that the cobalt was melted by heating to a melting point of 1494 ° C. The wetting angle at this time was 110 °.

  Thereafter, cooling was performed under furnace cooling conditions to obtain metal balls.

A photograph of the state in the vacuum furnace is shown in FIG. It was confirmed that the molten cobalt was spherical, and the diameter of the extracted cobalt sphere was about 3 mm.
<Example 5>
(Preparation of TiN-based composite metal ball forming jig)
After mixing the TiN powder and the metal powder, it was press-molded so as to have a predetermined shape, and heated to 1100 ° C. or higher under pressure to produce a metal ball molding jig of a TiN-based composite material.

The produced TiN-based composite metal ball forming jig was a flat plate having a diameter of 15 mm and a thickness of 5 mm, and its relative density was 98%.
(Production of metal balls)
1 g of a cylindrical nickel piece was placed on the TiN-based composite metal ball forming jig, placed in a vacuum furnace, the inside of the furnace was evacuated to 10 Pa, and then the melting point of nickel It heated to 1455 degreeC and it confirmed that nickel was fuse | melted. The wetting angle at this time was 130 °.

  Then, it cooled on the conditions of natural cooling in the vacuum, and obtained the metal sphere.

  A photograph of the state in the vacuum furnace is shown in FIG. It was confirmed that the molten nickel was spherical, and the diameter of the extracted nickel sphere was about 5 mm.

  By using metal balls formed using the metal ball forming jig of the present invention, bearing balls, decorative articles using precious metals, ball milling balls, check valves for pumps and valves, and porous body production It is possible to manufacture such raw material balls.

1 Jig 2 Molten metal droplet

Claims (12)

  A metal ball forming jig provided with a solid metal mounting portion, which is used in a method of melting a placed solid metal to form a liquid metal and forming a metal ball by its surface tension. The tool is formed of a ceramic having a wetting angle with a liquid metal of 90 ° or more.   2. The metal ball forming jig according to claim 1, wherein the ceramic includes titanium nitride.   The metal ball forming jig according to claim 1 or 2, wherein the ceramic further contains a metal.   The metal ball forming jig according to claim 3, wherein the metal is iron, cobalt, nickel, or copper.   5. The metal ball forming jig according to claim 3, wherein the titanium nitride and metal contents are 90% by mass or more of titanium nitride and the remainder is metal.   6. The metal ball forming jig according to claim 1, wherein a relative density is 80% or more.   The metal ball forming jig according to claim 1, wherein a recess for placing a solid metal is formed on at least a part of the surface of the metal ball forming jig.   The solid metal placed on the surface of the metal sphere forming jig according to claim 1 is melted to form a liquid metal, and the metal sphere is formed by the surface tension, and then cooled. A method for forming a metal sphere, which is characterized.   The method for forming a metal sphere according to claim 8, wherein the atmosphere for melting the solid metal is a vacuum of 100 Pa or less.   The method for forming a metal sphere according to claim 8 or 9, wherein the surface of the metal sphere is rapidly cooled by introducing an inert gas and / or an active gas.   A metal sphere having a diameter of 0.1 mm or more, obtained by the molding method according to claim 8.   The metal sphere according to claim 11, wherein the variation of the average diameter of the metal sphere is within 10% of the diameter of the target metal sphere.