Manufacturing method of precious metal bars

Abstract

This invention provides a method for manufacturing precious metal ingots that maintains and improves the surface appearance of the precious metal ingots. [Solution] A method for manufacturing a precious metal bar, comprising a polishing step of polishing multiple surfaces of a precious metal ingot (bottom surface, top surface, left side surface, right side surface, back side surface, and front side surface) using two or more rotating cylindrical polishing rollers.

Description

Technical Field

[0001] The present invention relates to a method for producing noble metal bullion bars such as gold, silver, and platinum bullion bars.

Background Art

[0002] Noble metal bullion bars are required to have high purity as well as a favorable surface appearance.

[0003] Conventionally, for example, to produce a high-purity silver bullion bar, materials such as powder, plates, granules, and foil whose silver purity has been previously increased to 99.99% or higher are weighed to an appropriate weight, and then subjected to melting, casting, and solidification for forming.

[0004] However, in the above conventional production method, impurities are inevitably contained. Since these impurities are oxides such as calcium and have a lower specific gravity than silver, part of them floats on the surface of the molten bullion when the bullion is melted and cast, making it difficult to completely remove the impurities, and removing these impurities has been a challenge. Such a problem occurs not only in silver but also in other noble metals such as gold and platinum in the same manner.

[0005] Patent Document 1 describes a method for producing gold bullion, which is characterized by heating and removing impurity particles floating on the surface of the molten gold bullion together with carbon powder before the molten gold bullion is solidified after melting and casting.

[0006] Patent Document 2 describes a metal ingot polishing apparatus, which is configured to include a polisher frame, a polishing plate with metal brushes implanted on its surface and detachably attached to the polisher frame, and a polishing plate drive mechanism built in the polisher frame for rotating the polishing plate at a rotational speed of 100 to 150 rpm, wherein the metal brushes are formed by bundling 30 to 60 metal wires each having a thickness of 0.2 to 0.5 mm, bending the bundled wires into a U-shape, and implanting a plurality of the U-shaped bundled wires on the surface of the polishing plate at a height of 15 to 50 mm at a plurality of positions.

[0007] Patent Document 3 describes a grinding method in which an abrasive member having abrasive grains is primarily moved in the planar direction of the steel material, while the grinding member is moved relatively in the feed direction to expand the grinding area, thereby grinding off oxide scale adhering to the surface of the steel material. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 59-33067 [Patent Document 2] Japanese Patent Publication No. 2002-200549 [Patent Document 3] Japanese Patent Publication No. 2022-134390 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Conventional manufacturing methods may leave oxides or other contaminants on the surface of precious metal ingots.

[0010] Therefore, new manufacturing methods are needed to maintain and improve the surface appearance of precious metal bars.

[0011] The objective of this invention is to provide a novel manufacturing method for maintaining and improving the surface appearance of precious metal bullion bars. [Means for solving the problem]

[0012] The present invention A polishing process in which multiple surfaces of the precious metal ingot (bottom surface, top surface, left side surface, right side surface, back side surface, front side surface) are polished using two or more rotating cylindrical polishing rollers. This is a method for manufacturing precious metal bars, characterized by containing [the specified ingredient].

[0013] In the above manufacturing method, the polishing step is The left and right sides of the precious metal ingot are polished by the first rotating cylindrical polishing roller. The second rotating cylindrical polishing roller polishes the back and front sides of the precious metal ingot. A third rotating cylindrical polishing roller polishes the bottom and top surfaces of the precious metal ingot. The process may also include a polishing step.

[0014] In the above manufacturing method, The polishing step may include a step of polishing the R-shaped surface in the peripheral area of ​​the upper surface.

[0015] In the above manufacturing method, the polishing step may be performed such that the polishing direction for the finish polishing of the four surfaces (bottom surface, top surface, right side surface, and left side surface) is either the longitudinal direction or the short direction of each surface.

[0016] In the above manufacturing method, the polishing step includes two polishing stages for housing the precious metal ingot, and a chuck for gripping the precious metal ingot and transferring the precious metal ingot to the polishing stage, After polishing one of the two sides of the precious metal ingot, the left side or the right side, on the first polishing stage by the first rotating cylindrical polishing roller, the chuck inverts the ingot and transfers it to the first polishing stage, and then polishes the other of the two sides, the left side or the right side. After polishing one of the two sides of the precious metal ingot, the back side or the front side, on the first polishing stage with a second rotating cylindrical polishing roller, the polishing stage is reversed and the other side of the back side or front side is polished. After polishing either the "bottom surface" or the "top surface and the rounded edges of the top surface" of the precious metal ingot on the second polishing stage using a third rotating cylindrical polishing roller, the chuck inverts the ingot and transfers it to the second polishing stage, and then polishes the other surface of the "bottom surface" or the "top surface and the rounded edges of the top surface". You may do so.

[0017] In the above manufacturing method, A blending step of weighing a precious metal of a predetermined mass, a precious metal ingot manufacturing step of dissolving the precious metal of the predetermined mass and solidifying the molten metal in a mold, or dissolving and solidifying the precious metal of the predetermined mass in a mold to manufacture a precious metal ingot, may be included. Effects of the Invention

[0018] According to the present invention, it is possible to provide a novel manufacturing method that maintains and improves the surface appearance of a precious metal bullion bar. Brief Description of the Drawings

[0019] [Figure 1] This is an example of a perspective view of a precious metal bullion bar related to the manufacturing method of the present invention. [Figure 2] This is a developed view of the precious metal bullion bar of Figure 1. [Figure 3] This is a diagram for explaining an example of the polishing step of the present invention. Modes for Carrying Out the Invention

[0020] The present invention is a manufacturing method capable of suitably manufacturing a precious metal bullion bar having a mass of, for example, from 10 g to 40 kg. The precious metal can be gold, silver, or platinum.

[0021] The present invention can include a blending step of weighing a precious metal of a predetermined mass, and a precious metal ingot manufacturing step of dissolving the precious metal of the predetermined mass and solidifying the molten metal in a mold, or dissolving and solidifying the precious metal of the predetermined mass in a mold to manufacture a precious metal ingot.

[0022] For example, in the compounding process, a predetermined mass of precious metal with a purity of 99.99% or higher, such as granular precious metal, is weighed out using a balance. This precious metal is then inserted into a carbon mold, for example, with the bottom surface (engraving surface) of the precious metal ingot facing downwards. In the melting process, the carbon mold containing the precious metal is placed in a high-frequency melting furnace and melted under an argon atmosphere using high-frequency induction to obtain a precious metal ingot. After melting, the carbon mold is cooled with water-cooled copper. Alternatively, the precious metal ingot may be obtained by melting a carbon mold containing granular precious metal in an electric heater-type continuous furnace under a nitrogen atmosphere and then slowly cooling it during the melting process.

[0023] Figure 1 is an example of a perspective view of a precious metal bar according to the manufacturing method of the present invention, and Figure 2 is an unfolded view of the precious metal bar of Figure 1.

[0024] A precious metal bar is roughly rectangular and has six faces, as shown in Figures 1 and 2: a bottom face, a top face, a right side face, a left side face, a back side face, and a front side face face. In this specification, a precious metal bar is a precious metal bar that has been polished in the polishing process after being produced in the precious metal ingot manufacturing process.

[0025] The bottom surface (engraving surface) is the lower surface in the carbon mold. The top surface is the upper surface in the carbon mold. When the upper surface of the mold melts and solidifies, it becomes a surface with curvature (R) around its periphery due to the effect of surface tension. This curvatured surface around the periphery of the top surface is referred to as the R surface in this application. For example, after the weighing process, the bottom surface (engraving surface) of a precious metal ingot can be engraved with the product number, a mark indicating the manufacturer, the material name, purity information, mass, etc.

[0026] The present invention A polishing process in which multiple surfaces of a precious metal ingot (bottom, top, left, right, back, and front) are polished using two or more rotating cylindrical polishing rollers. Includes. The number of cylindrical polishing rollers is not particularly limited as long as it is two or more; for example, there may be three, or four or more. Also, the surfaces to be polished on the precious metal ingot are not particularly limited as long as there are two or more surfaces; for example, any two or more predetermined surfaces may be polished, or all six surfaces may be polished. Furthermore, the order in which each surface is polished in the polishing process is not particularly limited, nor is it limited to the order described in this application.

[0027] For example, the bottom surface of a precious metal ingot can be polished with one cylindrical polishing roller, and the top surface can be polished with another rotating cylindrical polishing roller. In this case, the order of polishing can be reversed.

[0028] Furthermore, for example, one cylindrical polishing roller can be used to polish the left side of a precious metal ingot, while another rotating cylindrical polishing roller can be used to polish the right side of the ingot. In this case, the order of polishing can be reversed.

[0029] Furthermore, for example, one cylindrical polishing roller can be used to polish the left and right sides of a precious metal ingot, while another rotating cylindrical polishing roller can be used to polish the bottom and top surfaces of the ingot. In this case, the order of polishing can be reversed.

[0030] Furthermore, for example, one cylindrical polishing roller can be used to polish the back and front sides of a precious metal ingot, while another rotating cylindrical polishing roller can be used to polish the bottom and top surfaces of the ingot. In this case, the order of polishing can be reversed.

[0031] In the above manufacturing method, the polishing step is: The first rotating cylindrical polishing roller polishes the left and right sides of the precious metal ingot. A second rotating cylindrical polishing roller polishes the back and front sides of the precious metal ingot. A third rotating cylindrical polishing roller polishes the bottom and top surfaces of the precious metal ingot. polishing process, It can include.

[0032] The order of polishing on the first rotating cylindrical polishing roller, the second rotating polishing roller, and the third polishing roller can be arbitrary. For example, the right side of the first polishing roller may be polished first, and then the left side may be polished.

[0033] The order in which the three polishing rollers are used to polish a precious metal ingot is not particularly limited and can be arbitrary. That is, the order may be first, second, and third polishing rollers, or second, third, and first polishing rollers, or any other order.

[0034] Figure 3 is a diagram illustrating one example of the polishing process of the present invention.

[0035] The polishing process shown in Figure 3 includes a first rotating cylindrical polishing roller, a second rotating cylindrical polishing roller, and a third rotating cylindrical polishing roller as polishing members. It also includes a first polishing stage, a second polishing stage, and a chuck section.

[0036] Furthermore, the control unit, which is not shown in the diagram, includes, for example, a CPU and a ROM for storing programs, and controls the polishing apparatus related to the polishing process using the control program stored in the ROM.

[0037] A cylindrical polishing roller is used as the polishing component. The cylindrical polishing roller only needs to be cylindrical overall. As the cylindrical polishing roller rotates, its circumferential surface polishes the surface to be polished. The fine shape and material of the cylindrical circumferential surface of the cylindrical polishing roller may be, for example, a metal brush, a nonwoven fabric such as nylon or cotton embedded with abrasive grains, or a resin embedded with abrasive grains formed into a brush shape. Abrasive grains such as alumina, silicon carbide, and diamond can be used. Because the fine shape and material of the cylindrical circumferential surface are as described above, it can follow slight irregularities, and even if the parallelism between the surface to be polished and the roller circumferential surface is insufficient, polishing unevenness is reduced. Also, over-polishing is prevented.

[0038] The cylindrical polishing roller performs the polishing action by rotating around the axis of the cylinder (axis of rotation) while the part to be polished moves vertically (the stage on which the part to be polished is placed moves). Furthermore, the roller's holding mechanism is configured so that the polishing roller can move parallel to its axial direction.

[0039] In the present invention, the polishing step in the above manufacturing method may include a step of polishing the R surface on the upper surface.

[0040] For example, a third rotating cylindrical polishing roller can be used to polish the bottom and top surfaces of the ingot, as well as the rounded edges (R-shaped surfaces) on the top surface. The top surface has four rounded edges. All four rounded edges on the top surface may be polished. When the upper part of the mold is melted and solidified, due to the effect of surface tension, it becomes a surface that is not flat but has rounded edges (curved surfaces) around its periphery. For example, if a carbon mold is used with the bottom surface of the precious metal ingot facing downwards, the top surface will have four rounded edges.

[0041] To accommodate the uneven surface and rounded edges of the top surface, the brush needs to be pressed more firmly against the bottom (engraved surface) and sides. The third rotating cylindrical polishing roller is narrower than the second polishing roller, reducing the overall brush weight and decreasing the contact surface with the precious metal ingot. This reduces the motor load, making it possible to press the brush more firmly.

[0042] The polishing process in the present invention includes two polishing stages for housing precious metal ingots, and a chuck for gripping the precious metal ingots and transferring them to the polishing stages. After polishing one of the two sides of the precious metal ingot, the left or right side, on the first polishing stage by the first rotating cylindrical polishing roller, the chuck inverts the ingot and transfers it to the first polishing stage, and then polishes the other side of the left or right side. After polishing one of the two sides of the precious metal ingot, the back side or the front side, on the first polishing stage, the polishing stage reverses and then polishes the other side of the back side or the front side. A third rotating cylindrical polishing roller polishes either the "bottom surface" or the "top surface and the rounded edges of the top surface" of the precious metal ingot on the second polishing stage. After the chuck inverts the ingot and transfers it to the second polishing stage, the other surface of the "bottom surface" or "top surface and the rounded edges of the top surface" can be polished.

[0043] The polishing stage is a stage on which precious metal ingots are placed (held). As shown in Figure 3, the polishing stage is movable in the Y-axis direction and can be reversed (rotated 180 degrees).

[0044] The chuck section can grip and rotate the precious metal ingot. Furthermore, the chuck section can transfer the precious metal ingot between the supply conveyor, the first polishing stage, the second polishing stage, and the discharge conveyor.

[0045] For example, it can consist of a first polishing stage and a second polishing stage. The polishing process of the present invention uses three rollers, but by arranging first and second rotating cylindrical polishing rollers around the first polishing stage, it can be configured as a first and second polishing stage. This reduces the number of polishing stages compared to the number of polishing rollers, thereby reducing the size of the apparatus.

[0046] First, a first rotating cylindrical polishing roller polishes one of the two longitudinal sides of the precious metal ingot on a first polishing stage. Then, the chuck inverts the ingot and transfers it to the first polishing stage, after which the other longitudinal side is polished.

[0047] Furthermore, a second rotating cylindrical polishing roller polishes one of the two short-side surfaces of the precious metal ingot on the first polishing stage. After the polishing stage is reversed, the other short-side surface is polished.

[0048] A third rotating cylindrical polishing roller polishes either the "bottom surface" or the "top surface and the rounded edges of the top surface" of the precious metal ingot on the second polishing stage. Then, the chuck inverts the precious metal ingot and transfers it to the polishing stage. After that, the same third rotating cylindrical polishing roller polishes the other surface of the precious metal ingot, either the "bottom surface" or the "top surface and the rounded edges of the top surface".

[0049] In the present invention, finish polishing may be further added to one or more of the four surfaces (bottom surface, top surface, right side surface, left side surface) during the polishing process.

[0050] Finish polishing is a polishing process that improves the smoothness of the surface after polishing compared to previous polishing processes. For example, finish polishing may be performed by restricting the polishing direction to only the longitudinal direction of the polished surface, or to only the short direction of the polished surface. That is, the roller polishes while the polished surface moves only in the longitudinal direction. Alternatively, the roller polishes while the polished surface moves only in the short direction. Furthermore, the brush rotation speed may be reduced in finish polishing compared to previous polishing processes. For example, finish polishing of the bottom surface may be performed immediately after the completion of the bottom surface polishing process. For example, finish polishing of the top surface may be performed immediately after the completion of the top surface polishing process. For example, finish polishing of the right side may be performed immediately after the completion of the right side polishing process. For example, finish polishing of the left side may be performed immediately after the completion of the left side polishing process. Finish polishing can further improve the smoothness of the polished surface.

[0051] The process may include a calibration step after polishing to confirm that the mass of the precious metal ingot falls within a predetermined mass range.

[0052] In this invention, the polishing process removes dirt and discoloration caused by oxides, creating a metallic luster and reliably maintaining the appearance of the precious metal bar. For example, in conventional manufacturing methods (where oxides were removed by applying a gas burner to the surface), dirt and discoloration may remain due to residual oxides, but in this invention, the polishing process reliably maintains a clean appearance free of dirt and discoloration on the surface of the precious metal bar. [Examples]

[0053] An example of the present invention will be described in the case of a silver bullion bar.

[0054] <Blending process, precious metal ingot manufacturing process> A predetermined mass of silver is weighed and placed into a carbon mold, which is then covered with a carbon lid. The mold with the lid is then placed into an ingot casting apparatus and melted using high-frequency induction in an argon atmosphere. After that, it is cooled and solidified in a water-cooled copper hearth to obtain a silver ingot.

[0055] <Polishing process> Figure 3, mentioned above, shows an example of the polishing process in this embodiment. Specifically, as previously described, the polishing members include a first rotating cylindrical polishing roller, a second rotating cylindrical polishing roller, and a third rotating cylindrical polishing roller. It also includes a first polishing stage, a second polishing stage, and a chuck section.

[0056] Furthermore, the control unit (not shown) comprehensively controls the operation of each part of the polishing apparatus. The specific objects controlled by the control unit are as follows:

[0057] The control unit controls the movement of the chuck in the X-axis direction, the movement of the Z-axis direction, the gripping and releasing of the ingot, and the rotational movement. Here, the movement in the X-axis direction is for transferring the ingot from the supply conveyor to the first polishing stage, from the first polishing stage to the second polishing stage, and from the second polishing stage to the discharge conveyor.

[0058] Furthermore, the control unit controls the Y-direction movement and reversal of the first polishing stage, as well as the Y-direction movement of the second polishing stage.

[0059] The control unit also controls the rotation speed, rotation time (polishing time), movement in the X-axis direction, and Z-axis position adjustment (contact with the ingot) of the first and third polishing rollers.

[0060] The control unit also controls the rotation speed, rotation time (polishing time), movement in the X-axis direction, movement in the Z-axis direction, and Y-axis position adjustment (contact with the ingot) of the second polishing roller.

[0061] Next, we will explain the polishing process step by step.

[0062] First, the silver ingot produced in the precious metal ingot manufacturing process is transported from the supply conveyor to the chuck section and transferred to the first polishing stage. In the embodiment illustrated in Figure 3, the silver ingot is transferred to the first polishing stage with its right side facing upwards.

[0063] Next, the right side of the silver ingot is polished on the first polishing stage by a first rotating cylindrical polishing roller.

[0064] Next, a second rotating cylindrical polishing roller polishes the back side of the silver ingot on the first polishing stage.

[0065] Next, a rotatably configured chuck grips the silver ingot, inverts it around the horizontal axis (Y-axis in Figure 3) (inverts it upside down), and transfers it to the first polishing stage. In other words, the chuck grips the silver ingot, inverts it, and places the silver ingot back onto the first polishing stage.

[0066] Next, the left side of the silver ingot is polished on the first polishing stage by a first rotating cylindrical polishing roller.

[0067] Next, the first polishing stage is configured to rotate with the silver ingot placed on it. After the first polishing stage has rotated around the vertical axis (Z-axis in Figure 3), the front side is polished by the second rotating cylindrical polishing roller.

[0068] Next, the chuck grips the silver ingot and transfers it to the second polishing stage. In the embodiment illustrated in Figure 3, the silver ingot is transferred to the second polishing stage with its bottom surface facing upwards.

[0069] Next, a third rotating cylindrical polishing roller polishes the bottom surface of the silver ingot on the second polishing stage.

[0070] Following the polishing of the bottom surface as described above, perform a final polishing of the bottom surface as needed.

[0071] The chuck grips the silver ingot, inverts it around the horizontal axis (Y-axis in Figure 3) (inverts it upside down), and transfers it to the second polishing stage. In other words, the chuck grips the silver ingot, inverts it, and places the silver ingot back onto the second polishing stage.

[0072] Next, a third rotating cylindrical polishing roller polishes the upper surface and the rounded edges around the upper surface of the silver ingot on the second polishing stage.

[0073] Next, once the polishing of the silver ingots is complete, they are transported from the second polishing stage to the discharge conveyor via a chuck.

[0074] <Comparative Example> The conventional manufacturing method involves placing a crucible containing granular silver into a gas furnace, tilting the crucible to pour the contents into a metal mold, and then slowly cooling the surface while applying a gas burner. Products manufactured using this method were used as a comparative example.

[0075] Silver bullion bars produced using the method described in the example and the conventional method were visually inspected for dirt, unevenness, and discoloration to distinguish between good and defective products, and the defect rates were compared as shown in Table 1.

[0076] [Table 1]

[0077] The silver bars produced by the method described in this example show a reduced defect rate and improved surface appearance compared to silver bars produced by the conventional method.

Claims

1. A polishing process in which multiple surfaces of a precious metal ingot (bottom, top, left, right, back, and front) are polished using two or more rotating cylindrical polishing rollers. A method for manufacturing precious metal bars, characterized by including the following:

2. The aforementioned polishing process is The left and right sides of the precious metal ingot are polished by the first rotating cylindrical polishing roller. The second rotating cylindrical polishing roller polishes the back and front sides of the precious metal ingot. A third rotating cylindrical polishing roller polishes the bottom and top surfaces of the precious metal ingot. polishing process, A method for manufacturing a precious metal bar according to claim 1, characterized by including the following:

3. The polishing step includes polishing the R-shaped surface in the peripheral portion of the upper surface. A method for manufacturing a precious metal bullion bar according to feature 1.

4. The polishing process includes two polishing stages for housing the precious metal ingot, and a chuck for gripping the precious metal ingot and transferring the precious metal ingot to the polishing stage. After polishing one of the two sides of the precious metal ingot, the left side or the right side, on the first polishing stage by the first rotating cylindrical polishing roller, the chuck inverts the ingot and transfers it to the first polishing stage, and then polishes the other of the two sides, the left side or the right side. After polishing one of the two sides of the precious metal ingot, the back side or the front side, on the first polishing stage with a second rotating cylindrical polishing roller, the polishing stage is reversed and the other side of the back side or front side is polished. After polishing either the "bottom surface" or the "top surface and the rounded edges of the top surface" of the precious metal ingot on the second polishing stage using a third rotating cylindrical polishing roller, the chuck inverts the ingot and transfers it to the second polishing stage, and then polishes the other surface of the "bottom surface" or the "top surface and the rounded edges of the top surface". A method for manufacturing a precious metal bullion bar according to claim 1 or 2.

5. The method for manufacturing a precious metal bar according to claim 1 or 2, characterized in that, in the polishing step, finish polishing is further applied to one or more of the four surfaces (bottom surface, top surface, right side surface, left side surface).

6. A compounding process in which a predetermined mass of precious metal is weighed, A precious metal ingot manufacturing process, which involves melting a predetermined mass of precious metal and solidifying the molten metal in a mold, or melting and solidifying a predetermined mass of precious metal in a mold to produce a precious metal ingot, and obtaining the precious metal ingot by this process. A method for manufacturing a precious metal bullion bar according to feature 1.

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