High-brightness polishing method for spherical pure gold material

Abstract

The invention relates to the technical field of metal polishing, in particular to a high-brightness polishing method for a spherical pure gold material, which comprises the following steps: S1, hardening the material; s2, preparing a hard grinding disc; s3, rough grinding; s4, rough polishing; s5, fine polishing; s6, repeated soft polishing is conducted, specifically, the gold piece obtained after fine polishing is slightly wiped clean with soft cloth, the gold piece is soaked or smeared with aqua regia at the normal temperature for 20-30 s and then washed clean with purified water, a soft polishing disc is used for continuous soft polishing of the gold piece for 2-3 min, and the position of the gold piece is continuously changed during the period; repeating the step S6 for 6-8 times; and S7, cleaning, wherein the gold part with the high-quality mirror surface effect is obtained after the gold part is wiped dry with purified water. The concave grinding disc used in the polishing method is simple in structure and easy to manufacture, and the method is high in operability and controllability, low in machining cost, high in machining efficiency, good in machining precision and easy to popularize and use in the industry.

Description

Technical Field

[0001] This invention relates to the field of metal polishing technology, specifically to a high-gloss polishing method for spherical pure gold materials. Background Technology

[0002] Gold, due to its extremely stable chemical properties, excellent electrical and thermal conductivity, and unparalleled ductility, plays an irreplaceable and crucial role in industrial and consumer fields such as aerospace, precision electronics, high-end jewelry, and medical devices. However, the inherent low hardness of pure gold (Mohs hardness approximately 2.5-3) poses a significant challenge to precision polishing processes that pursue ultra-high surface quality, a contradiction particularly pronounced on workpieces with complex geometries. Currently, the industry typically employs the following methods for surface treatment of pure gold materials, but all of them have significant limitations when applied to high-gloss mirror polishing of spherical pure gold workpieces: 1. Traditional mechanical polishing: This is the most common method, relying on the mechanical friction between abrasive and the workpiece to remove material. However, for soft materials like pure gold, this method is prone to producing fine scratches, an "orange peel" effect, and even deformation. Especially when processing spherical surfaces, general-purpose flat or flexible polishing wheels struggle to maintain an ideal match with the curvature of the sphere, resulting in uneven polishing pressure distribution. This easily leads to over-polishing or under-polishing at the poles or equator of the sphere, making it difficult to achieve a uniform mirror finish. The final surface roughness is typically difficult to exceed 100 nanometers (nm), failing to meet the nanometer-level smoothness requirements of high-end applications.

[0003] 2. Chemical Polishing and Electrochemical Polishing: These methods smooth surfaces through chemical or anodic dissolution, theoretically avoiding mechanical damage. However, chemical polishing is extremely sensitive to solution concentration, temperature, and stirring speed, has a narrow process window, poor controllability, and is prone to surface roughness or anisotropic corrosion. Electrochemical polishing requires the development of specialized electrolytes for specific gold alloy compositions. For pure gold, its polishing efficiency is low, and for gold layers on non-conductive substrates or complex inner spherical surfaces, there are challenges in uneven electric field distribution and application. Furthermore, both methods involve hazardous chemicals such as strong acids or cyanides, imposing higher requirements on environmental protection and equipment.

[0004] 3. Advanced polishing technologies, such as ion beam polishing and laser polishing, can achieve extremely high surface quality, but their equipment is expensive, operation is complex, and processing costs are extremely high. They are usually suitable for small areas or workpieces with specific shapes, and it is difficult to achieve high-efficiency, low-cost uniform processing on the entire spherical surface. Therefore, they are not economically viable for large-scale industrial promotion.

[0005] In summary, existing technologies lack a polishing method specifically designed for spherical pure gold workpieces that can simultaneously achieve high quality, high controllability, and good economic efficiency. The softness of pure gold and the curvature of the spherical geometry constitute a long-standing technical bottleneck in this field, making high-gloss mirror polishing of spherical pure gold materials a significant technological challenge. Therefore, there is an urgent need for an innovative technical solution that can overcome these limitations and achieve a significant reduction in surface roughness and a substantial improvement in mirror gloss of spherical pure gold workpieces. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a high-gloss polishing method for spherical pure gold materials, which has advantages such as strong operability, low cost, and good results.

[0007] This invention is achieved through the following technical solution: A method for high-gloss polishing of spherical pure gold material is provided, including the following steps: S1. Material hardening: Pure gold raw materials are extruded or hammered into the desired shape using mechanical methods, resulting in a significant shape change since the last quenching. No heat treatment is required afterward to improve the strength of the gold parts. S2. Preparation of hard grinding disc: For the processing of convex spherical surfaces of gold parts: use ceramic to process a spherical concave grinding disc, the inner diameter of the concave spherical surface is 25% larger than the inner diameter of the spherical surface of the gold part to be polished, fix the grinding disc with the concave opening facing upward on a conventional polishing disc, and make the diameter direction of the concave spherical surface of the grinding disc the rotation axis direction of the grinding disc, so that the grinding disc is always in stable contact with the gold part when it rotates. S3. Coarse grinding: A mixture of corundum fine powder abrasive and water is applied to the center of a concave grinding disc. The gold part is placed inside the concave grinding disc, keeping the gold part in contact with the concave grinding disc. The concave grinding disc is rotated for coarse grinding, and the mixture is continuously added to the center of the concave grinding disc. S4. Rough polishing: After rinsing the rough-polished gold parts and concave grinding disc with pure water and wiping them clean, repeat step S3. Replace the rough polishing mixture with polishing liquid containing polishing powder. During polishing, continuously change the contact position between the gold parts and the concave grinding disc until the surface of the gold parts has a mirror effect. S5. Fine polishing: Repeat step S4, replacing the polishing liquid containing polishing powder with ultrafine hydrophilic precipitated silica slurry. During the polishing process, continuously change the position of the gold parts and continuously add ultrafine hydrophilic precipitated silica slurry. S6. Repeated soft polishing: After fine polishing, wipe the gold piece clean with a soft cloth, immerse it in or apply aqua regia at room temperature for 20-30 seconds, then rinse it with pure water. Use a soft polishing pad to continuously soft polish the gold piece for 2-3 minutes, changing the position of the gold piece continuously during this period; repeat step S6 6-8 times. S7. Cleaning: The gold pieces have a high-quality mirror finish after being wiped dry with pure water.

[0008] In this scheme, a mixture of corundum fine powder abrasive and water is used for coarse grinding. Due to the high hardness of corundum, the sample surface can be polished quickly. The ultrafine hydrophilic precipitated silica slurry has a Mohs hardness of 7, which is lower than that of commonly used polishing agents. It is also a very fine powder slurry with a large polishing contact area, which can achieve the effect of fine polishing.

[0009] Furthermore, in step S1, during material hardening, a trace amount of hard gold filler can be added by doping to improve the hardness of the material, including the addition of one or more of beryllium, sodium, and calcium.

[0010] Furthermore, in step S1, during material hardening, the sample can be heated to a red-hot state and held for a period of time, and then rapidly cooled and quenched with cold water.

[0011] Furthermore, in step S2, the rotation speed of the concave grinding disc does not exceed 1000 r / min, and the grinding disc rotation is stopped every 0.5 min to allow the polishing liquid in the groove of the grinding disc to flow back.

[0012] Furthermore, step S2 also includes the inner spherical processing of the gold part: a spherical grinding disc is made of ceramic, the spherical diameter of the grinding disc is about 75% of the spherical diameter of the gold part being polished, and the rotating polishing disc is designed to hang from the top and droop from the bottom, with the polishing liquid placed inside the stationary concave gold part.

[0013] Preferably, in step S6, the soft polishing disc is formed by lining the inner wall of the concave polishing disc with leather or felt.

[0014] Furthermore, in step S2, the contact force between the metal part and the grinding disc is maintained at 5~10N.

[0015] Furthermore, in steps S3 and S4, the polishing agent used for coarse grinding and coarse polishing adopts the particle size commonly used for metal polishing; the fine polishing agent is a slurry fluid made by mixing ultrafine hydrophilic precipitated silica with a mesh size of not less than 2000 mesh and pure water in a ratio of 1:5.

[0016] Preferably, in step S2, the inner surface of the concave grinding disc is polished, and a groove is left near the outer edge of the grinding disc.

[0017] The groove is designed to prevent the polishing liquid from overflowing and can flow back towards the axis of rotation when the rotation stops.

[0018] The beneficial effects of this invention are: The polishing method of the present invention uses a concave grinding disc with a simple structure that is easy to manufacture. It has strong overall operability and controllability, low processing cost, high processing efficiency, and good processing accuracy.

[0019] I. Significantly improves surface quality, achieving a high-precision mirror finish. The surface roughness of gold parts treated by the method of this invention can reach 20nm, which is an order of magnitude improvement compared with the prior art, indicating that the method can effectively eliminate surface micro-irregularities and obtain extremely high surface smoothness.

[0020] The method of this invention uses a multi-stage progressive process of "rough grinding - rough polishing - fine polishing - repeated soft polishing" to gradually remove scratches left by previous processes, ultimately making the surface of the gold part "uniformly present a mirror effect". Specifically addressing the two major challenges of "low hardness of gold" and "spherical geometry", the "material hardening" in step S1 increases the strength of the workpiece substrate to resist polishing force and reduce deformation; the specially designed concave grinding disc in step S2 ensures a high degree of fit and stable contact between the polishing tool and the spherical workpiece, thereby effectively avoiding surface unevenness caused by tool mismatch.

[0021] II. Optimize the process flow to enhance operational controllability and stability. The tool is ingeniously designed and simplifies operation: the concave grinding disc has a simple structure and is easy to manufacture. Its unique design (such as grooves and specific size ratios) effectively prevents polishing fluid from overflowing and allows it to flow back during intermittent periods, ensuring a continuous and uniform supply of polishing media, reducing the need for frequent manual additions, and improving process stability.

[0022] The parameters are clearly defined and highly controllable, reducing the risk of failure due to improper operation. This demonstrates the method's strong controllability and repeatability, and it covers both internal and external spherical surface processing, making it widely applicable.

[0023] Third, it possesses good economic viability and promotion potential. Low processing cost: This method mainly relies on the principle of mechanical polishing. The equipment (conventional polishing discs) and materials (ceramic grinding discs, corundum, silicon dioxide, etc.) used are all common or universal industrial raw materials. It does not rely on expensive special equipment (such as ion beam polishing machines and laser polishing machines), which greatly reduces equipment investment costs and maintenance costs.

[0024] High processing efficiency: The multi-step assembly line polishing process is reasonably designed, with clear division of labor between rough grinding, rough polishing and fine polishing. Compared with some precision methods that require repeated adjustments or have a long processing time per cycle, it can help improve the overall processing efficiency.

[0025] Easy to promote and use in the industry: In summary, due to the simple structure, low cost and strong controllability of the above points, this method is very suitable for rapid deployment and application in existing metal processing, especially in factories that process gold products such as jewelry and precision instruments, and has great potential for technology transfer and market promotion.

[0026] In summary, this invention, through innovative tool design and refined process parameter control, successfully solves the industry challenge of high-precision polishing of pure gold spherical materials. Ultimately, it achieves a superior mirror finish while maintaining the method's economy, stability, and ease of implementation. These advantages collectively constitute the significant advancement and practical value of this invention compared to existing technologies. Attached Figure Description

[0027] Figure 1 This is a schematic diagram showing the positional relationship between the concave grinding disc and the metal part in Embodiment 1 of the present invention.

[0028] Figure 2 Features of the electron microscope sample that was not polished using the present invention.

[0029] Figure 3 The optical microscope features of the sample polished using Example 1 of the present invention.

[0030] Figure 4 The features of the sample polished using Example 1 of the present invention are shown under a scanning electron microscope.

[0031] In the picture: 1. Concave grinding disc, 2. Metal part. Detailed Implementation

[0032] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution.

[0033] Example 1: A high-gloss polishing method for spherical pure gold materials, for processing convex spherical gold parts, includes the following steps: S1. Material hardening: Pure gold raw materials are mechanically extruded or hammered into the desired shape, resulting in a significant shape change since the last quenching. No further heat treatment is required to enhance the strength of the gold parts. The performance of the gold parts is mainly determined by their dimensions. For parts combined with other materials, the performance of those materials must also be considered, such as the inability to be heated or subjected to excessive pressure.

[0034] S2. Preparation of the hard grinding disc: A spherical concave grinding disc 1 is fabricated from ceramic. The inner diameter of the concave spherical surface is 25% larger than the inner diameter of the spherical surface of the gold part to be polished. The grinding disc is fixed on a conventional polishing disc with the concave opening facing upwards, and the diameter direction of the concave spherical surface of the grinding disc is used as the rotation axis of the grinding disc, ensuring stable contact with the gold part during rotation. The rotation speed of the concave grinding disc 1 does not exceed 1000 r / min, and the rotation is stopped every 0.5 min to allow the polishing fluid in the groove of the grinding disc to flow back. The contact force between the gold part 2 and the grinding disc is maintained at 5~10N. If the device is heavy, additional force should be applied to reduce the pressure of contact between the two.

[0035] The inner surface of the concave grinding disc 1 is polished, and a groove is left near the outer edge of the grinding disc. The groove is designed to prevent the polishing liquid from overflowing and can flow back towards the axis of rotation when rotation stops.

[0036] S3. Coarse grinding: A mixture of corundum fine powder abrasive and water is applied to the center of a concave grinding disc. The gold part is placed inside the concave grinding disc 1, keeping the gold part 2 in contact with and attached to the concave grinding disc 1. The concave grinding disc 1 is rotated for coarse grinding, and the mixture is continuously added to the center of the concave grinding disc 1. S4. Rough polishing: After rinsing the rough-polished gold part 2 and concave grinding disc 1 with pure water and wiping them clean, repeat step S3. Replace the rough polishing mixture with polishing liquid containing polishing powder. During polishing, continuously change the contact position between the gold part and the concave grinding disc 1 until the surface of the gold part shows a mirror effect. S5. Fine polishing: Repeat step S4, replace the polishing liquid containing polishing powder with ultrafine hydrophilic precipitated silica slurry, continuously change the position of the gold part 2 during the polishing process, and continuously add ultrafine hydrophilic precipitated silica slurry. The polishing agent used for coarse grinding and coarse polishing adopts the particle size commonly used for metal polishing; the fine polishing agent is made by mixing ultrafine hydrophilic precipitated silica with pure water at a ratio of 1:5 with a mesh size of not less than 2000 to form a thin slurry fluid.

[0037] S6. Repeated soft polishing: Wipe the finely polished gold piece 2 clean with a soft cloth, immerse it in aqua regia for 20 seconds at room temperature, then rinse it with pure water. Use a soft polishing disc to continuously soft polish the gold piece for 2-3 minutes, changing the position of the gold piece continuously during this period. Repeat step S6 6 times. The soft polishing disc is formed by lining the inner wall of the concave grinding disc with leather or felt.

[0038] S7. Cleaning: The gold pieces have a high-quality mirror finish after being wiped dry with pure water.

[0039] The surface roughness of the gold parts prepared by this invention can reach about 20 nm. In contrast, the roughness of conventionally polished gold parts is generally about 100 nm.

[0040] like Figure 4 As shown, under high magnification of SEM, a high-quality mirror surface that achieves nanoscale roughness exhibits an extremely flat and smooth morphology, and the surface should be free of obvious grain boundary protrusions, tiny scratches (polishing marks), pitting, or contaminant particles. Figure 4 To verify the precision and final quality of the polishing method of this invention, SEM images can intuitively reveal microscopic defects that are indistinguishable to the naked eye and optical microscopes.

[0041] After processing using the method of this invention, the average surface roughness Ra of three points measured using a stylus-type surface profilometer (Taylor Hobson Talysurf) was 18.5 nm, 21.2 nm, and 19.8 nm (see [link to invention]). Figure 3 (marked area); as a comparative example, the Ra value of the same batch of gold parts treated with traditional pure mechanical polishing is 95nm~110nm.

[0042] Example 2: A high-gloss polishing method for spherical pure gold material. For the inner spherical processing of gold parts, the processing steps are generally the same as in Example 1. The difference is that in step S2, when preparing the hard grinding disc, ceramic is used to process the spherical grinding disc. The spherical diameter of the grinding disc is about 75% of the spherical diameter of the gold part being polished. The rotating polishing disc is designed to be hanging from the top and pendant. The polishing liquid is placed inside the stationary concave gold part.

[0043] Example 3: The only difference between this embodiment and Embodiment 1 is that, in step S1, instead of mechanical hardening, a trace amount of hard gold is added to improve the hardness of the material by doping, including the addition of one or more of beryllium, sodium, and calcium.

[0044] Example 4: The only difference between this embodiment and Embodiment 1 is that in step S1, the mechanical hardening method is replaced. The material hardening method involves heating the sample to a red-hot state and holding it for a period of time, followed by rapid cooling and quenching with cold water.

[0045] Of course, the above description is not limited to the examples above. Technical features not described in this invention can be implemented by or using existing technology, and will not be repeated here. The above embodiments and drawings are only used to illustrate the technical solutions of this invention and are not intended to limit this invention. This invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention do not depart from the spirit of this invention and should also fall within the scope of protection of the claims of this invention.

Claims

1. A method for high-gloss polishing of spherical pure gold material, characterized in that: Includes the following steps: S1. Material hardening: Cold working hardens the pure gold raw material. The cold working should be carried out in the annealed state of the workpiece, and stress-relief annealing should not be performed after processing. S2. Preparation of hard grinding disc: For the processing of convex spherical surfaces of gold parts: use ceramic to process a spherical concave grinding disc, the inner diameter of the concave spherical surface is 25% larger than the inner diameter of the spherical surface of the gold part to be polished, fix the grinding disc with the concave opening facing upward on a conventional polishing disc, and make the diameter direction of the concave spherical surface of the grinding disc the rotation axis direction of the grinding disc, so that the grinding disc is always in stable contact with the gold part when it rotates. S3. Coarse grinding: A mixture of fine corundum powder and water is applied to the center of a concave grinding disc. The gold part is placed inside the concave grinding disc, keeping it in contact with the disc. The disc is rotated for coarse grinding, and the mixture is continuously added to the center of the disc. S4. Rough polishing: After rinsing the rough-polished gold parts and concave grinding disc with pure water and wiping them clean, repeat step S3. Replace the rough polishing mixture with polishing liquid containing polishing powder. During polishing, continuously change the contact position between the gold parts and the concave grinding disc until the surface of the gold parts has a mirror effect. S5. Fine polishing: Repeat step S4, replacing the polishing liquid containing polishing powder with ultrafine hydrophilic precipitated silica slurry. During the polishing process, continuously change the position of the gold parts and continuously add ultrafine hydrophilic precipitated silica slurry. S6. Repeated soft polishing: After fine polishing, wipe the gold piece clean with a soft cloth, immerse it in or apply aqua regia at room temperature for 20-30 seconds, then rinse it with pure water. Use a soft polishing pad to continuously soft polish the gold piece for 2-3 minutes, changing the position of the gold piece continuously during this period; repeat step S6 6-8 times. S7. Cleaning: The gold pieces are dried with pure water to achieve a high-quality mirror finish.

2. The high-gloss polishing method for spherical pure gold material according to claim 1, characterized in that: In step S1, the hardness of the material can be improved by adding a trace amount of hard gold filler during the material hardening process, including adding a trace amount of one or more of beryllium, sodium, and calcium.

3. The high-gloss polishing method for spherical pure gold material according to claim 1, characterized in that: In step S1, when the material is hardening, the sample can be heated to a red-hot state and held for a period of time, and then quickly cooled and quenched with cold water.

4. The high-gloss polishing method for spherical pure gold material according to claim 1, characterized in that: In step S2, the rotation speed of the concave grinding disc does not exceed 1000 r / min, and the grinding disc rotation is stopped every 0.5 min to allow the polishing liquid in the groove of the grinding disc to flow back.

5. The high-gloss polishing method for spherical pure gold material according to claim 1, characterized in that: Step S2 also includes the inner spherical processing of the gold part: a spherical grinding disc is made of ceramic, the spherical diameter of the grinding disc is about 75% of the spherical diameter of the gold part being polished; and the rotating polishing disc is designed to hang from the top and hang down, with the polishing liquid placed inside the stationary concave gold part.

6. The high-gloss polishing method for spherical pure gold material according to claim 1, characterized in that: In step S6, the soft polishing disc is formed by lining the inner wall of the concave polishing disc with leather or felt.

7. The high-gloss polishing method for spherical pure gold material according to claim 1, characterized in that: In step S2, the contact force between the metal part and the grinding disc is maintained at 5~10N.

8. The high-gloss polishing method for spherical pure gold material according to claim 1, characterized in that: In steps S3 and S4, the polishing agent used for coarse grinding and coarse polishing adopts the particle size commonly used for metal polishing; the fine polishing agent is a slurry fluid made by mixing ultrafine hydrophilic precipitated silica with a mesh size of not less than 2000 mesh and pure water in a ratio of 1:

5.

9. The high-gloss polishing method for spherical pure gold material according to claim 1, characterized in that: In step S2, the inner surface of the concave grinding disc is polished, and a groove is left near the outer edge of the grinding disc.

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