A copper hammer repairing method based on segmented heat treatment and phase change control

Abstract

This invention discloses a method for repairing gongs based on segmented heat treatment and phase change control. The method involves cleaning and / or crack-stopping treatment of the crack location, followed by heating the area to be repaired within a first temperature range for stress relief and toughening. After a first holding time, the area to be repaired is brought into contact with and cooled by a first cooling medium. Molten synthetic copper repair material is then filled along the crack trajectory, and a brief impact pressure or continuous bonding pressure is applied to ensure the synthetic copper repair material fully fuses with the crack. After cooling, all cracks and the synthetic copper repair material are polished until the synthetic copper repair material is flush with the gong surface or conforms to the same curvature. Finally, the entire gong is heated to a second temperature range and held for a second time before being brought into contact with and cooled by a second cooling medium. Compared to existing technologies, this invention improves existing gong repair techniques, enhancing the quality of gong repair and improving its mechanical and acoustic properties.

Description

Technical Field

[0001] This invention relates to the field of musical instrument restoration technology, and in particular to a method for restoring gongs based on segmented heat treatment and phase change control. Background Technology

[0002] The gong is a traditional percussion instrument that plays a vital role in folk performances. Before a performance, the operator suspends the gong and allows it to swing freely. During the performance, the gong is struck directly with sticks or other striking tools. Due to the resonance of its internal metal structure, the gong produces a loud and resonant sound, achieving specific promotional or performance effects.

[0003] However, the impact of the stick on the gong is usually concentrated in the center. After prolonged impact, this can cause material wear on the gong's surface and even metal fatigue in the center, leading to internal cracks. If these structural defects are not detected and repaired promptly, the gong may break or detach during a subsequent strike. In recent years, with the continuous rise in copper prices both domestically and internationally, directly replacing a structurally defective, repairable gong would significantly increase the cost of a new purchase. Repair is a relatively better option.

[0004] Observing the overall structure of a gong, we can see that it typically consists of a central copper plate and outer copper plates. Current techniques for repairing structural defects involve directly welding repair materials to cover cracks, then grinding the welds smooth. While this appears to completely repair the cracks, internal stress remains between the welded material and the original gong material. This results in a dull tone or a short, weak sound, lacking the sustained resonance expected in performances. Furthermore, this repair method is prone to causing severe stress fractures at the transition point between the new weld and the original gong structure during subsequent short-term use, leading to more extensive damage or even rendering the gong unusable.

[0005] Therefore, it is of great significance to optimize the existing gong repair techniques so that the repaired gong can achieve or even surpass the tone before the structural defects occurred. Summary of the Invention

[0006] The main objective of this invention is to propose a gong repair method based on segmented heat treatment and phase change control, which aims to improve existing gong repair technology, enhance the quality of gong repair, and improve its mechanical and acoustic properties.

[0007] To achieve the above objectives, this invention proposes a method for repairing gongs based on segmented heat treatment and phase change control, characterized by comprising the following steps:

[0008] Step S1: Clean and / or stop the crack in the gong.

[0009] Step S2: The local area to be repaired is heated within a first temperature range to relieve stress and toughen it. After the first heat preservation time, the local area to be repaired is brought into contact with and cooled by the first cooling medium.

[0010] Step S3: Fill the crack with molten synthetic copper repair material and apply short-term impact pressure or continuous bonding pressure to fully fuse the synthetic copper repair material with the crack. After cooling, polish all cracks and synthetic copper repair material. The synthetic copper repair material should be flush with the surface of the gong or follow the same curvature.

[0011] Step S4: After heating the entire gong to the second temperature range and holding it for the second time, bring the entire gong into contact with the second cooling medium and cool it.

[0012] Preferably, in step S1, the crack-stopping treatment involves scanning the trajectory of the crack to determine all ends of the crack and the intersection positions of different cracks, and then creating crack-stopping holes at the end positions and intersection positions respectively.

[0013] Preferably, the anti-crack hole penetrates the plate structure of the gong, and the anti-crack hole has inwardly tapering chamfers on both the front and back sides of the plate.

[0014] Preferably, in step S2, the first temperature range is 400-450℃, and the first heat preservation time is 10-20 minutes.

[0015] Preferably, in step S4, the second temperature range is 700-750℃, and the second heat preservation time is 15-30 minutes.

[0016] Preferably, step S2 further includes the following steps:

[0017] Step S21: Before repair, cracks at different locations on the surface of the gong are detected by scanning. Cracks that intersect at some locations are classified into the same crack group. If there is an intersection between two adjacent crack groups, the two adjacent crack groups are merged. Cracks that do not intersect at any location are classified into a single crack group.

[0018] Step S22: Within the same crack group, extract the end positions and intersection positions of different cracks to define the initial contour of the same crack group, and extend it outward at the same distance to define the final contour.

[0019] Step S23: Based on the final contour, a filling mold for filling the first cooling medium is made. The filling mold has a hollow area in the center. The boundary of the hollow area can cover all the cracks in the same crack group. The hollow area has multiple layers of staggered honeycomb filler, which contains the first cooling medium.

[0020] Preferably, step S3 further includes the following step:

[0021] Step S31: Divide the gong into a central copper plate and an outer copper plate, and measure and calculate the area ratio of the central copper plate and the outer copper plate;

[0022] Step S32: Before repairing the crack, use a spectrometer to collect at least one parameter of the copper-tin composition ratio at any position on the surface of the central copper plate and the outer copper plate.

[0023] Step S33: If the copper-tin ratio of the central copper plate and the outer copper plate is consistent, then adjust the material to repair the crack according to the copper-tin ratio.

[0024] Step S34: If the copper-tin ratio of the central copper plate and the outer copper plate is not exactly the same and exceeds the limit error threshold, the weight is corrected by referring to the area ratio and the corrected copper-tin ratio is obtained. The material is then prepared to repair the cracks using the corrected copper-tin ratio.

[0025] Preferably, in step S31, the area ratio of the central copper plate to the outer peripheral copper plate is 3-4:2-3.

[0026] The technical solution of this invention has the following advantages over the prior art:

[0027] The technical solution of this invention uses a two-stage heat treatment process combined with two water cooling cycles to achieve atomic-level diffusion bonding between the filler material and the matrix. The tensile strength and fatigue life are close to the level of the parent material. The first low-temperature treatment eliminates the initial stress, and the second high-temperature solid solution eliminates microscopic defects. Combined with the surface compressive stress generated by water cooling, it effectively prevents secondary cracking at the repair site. The temperature range is scientifically set, avoiding the brittle temperature range and melting zone of copper-tin composite copper. It is suitable for industrial promotion and fine manual operation, restoring the mechanical properties and acoustic quality of gongs. It is applicable to the field of musical instrument repair and protection made of copper-tin materials. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0029] Figure 1 The flowchart shows the gong repair method based on segmented heat treatment and phase change control of the present invention.

[0030] Figure 2 This is a schematic diagram of the external structure of the gong of the present invention;

[0031] Figure 3 This is a schematic diagram of the crack and crack-stopping hole structure of the present invention;

[0032] Figure 4 A cross-sectional view of the repair synthetic copper material filling the crack arrest hole and the crack arrest hole fitting together, according to the present invention.

[0033] Figure 5 A schematic diagram illustrating the crack area confirmation principle in the crack repair process of this invention.

[0034] Figure 6 This is a schematic diagram of the filling mold and porous filler used for the first cooling of the present invention.

[0035] Explanation of icon numbers:

[0036] 1. Gong; 11. Center copper plate; 12. Outer copper plate; 2. Crack; 21. Crack end position; 22. Crack intersection position; 23. Initial outline; 24. Final outline; 3. Crack stop hole; 31. Chamfer; 4. Repair synthetic copper material; 5. Filling mold; 51. Hollow area; 6. Porous filler;

[0037] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] This invention proposes a method for repairing gongs based on segmented heat treatment and phase change control.

[0040] Please see Figure 1-4In the gong repair method based on segmented heat treatment and phase change control in this embodiment of the invention, the crack 2 and surrounding area of ​​the gong 1 to be repaired are first mechanically ground to remove the oxide layer and oil stains on the surface of the gong 1, which may affect subsequent welding. After determining the path of the crack 2, corresponding anti-crack holes 3 are drilled at the crack end position 21 and the intersection position 22 of multiple cracks. During the subsequent welding process, the repair synthetic copper material 4 enters into the anti-crack holes 3 to prevent the crack 2 from continuing to expand and extend.

[0041] Please see Figure 3 and Figure 4 Preferably, since the central copper plate 11 or the outer peripheral copper plate 12 of the gong 1 are both plate structures, after opening the crack-stopping hole 3 at the crack end position 21 and the crack intersection position 22, the corresponding concave chamfer 31 is made on the front and back sides of the copper plate corresponding to the crack-stopping hole 3 by using a chamfering tool. Therefore, after the repair synthetic copper material 4 is completely cured at the chamfer 31 position, the repair synthetic copper material 4 includes two frustum structures connected vertically. It can not only press the plate structure of the gong 1, but also increase the contact area so that the repair synthetic copper material 4 can better contact and connect with the raw material of the gong 1. In addition, when the operator uses it later, the sound and impact force transmission between the repair synthetic copper material 4 and the raw material of the gong 1 are released radially, which can effectively improve the sound display effect of the repaired gong 1.

[0042] In the first heat treatment stage, the area corresponding to the crack 2 to be repaired is heated to 400-450℃ and held at that temperature for 10-20 minutes. Since the main material of the gong 1 is copper-tin composite copper, heating and holding the crack area of ​​the gong to be repaired within the above temperature range gradually eliminates the residual tensile stress caused by work hardening during the manufacturing process of the gong, which is below the recrystallization temperature of copper and above the stress-relief annealing temperature. This not only improves the plasticity and toughness of the gong matrix material, but also provides a relatively soft base material for the subsequent filling process and avoids grain growth.

[0043] Specifically, an infrared heating lamp can be used to heat the center trajectory of the crack 2 in the gong and the area extending outward by 1-2 cm. Alternatively, the relatively stable distance between the heating source and the surface of the gong 1 can be controlled, and the actual heat coverage width of the heating source can be controlled. The heating source can then be moved back and forth along the trajectory of the crack 2. A thermocouple can also be used to monitor the surface temperature around the crack 2. The heating and monitoring temperature is set to 420℃. After heating and holding for 15 minutes, the surface of the gong 1 will turn dark red.

[0044] After the first heat treatment stage is completed, the locally heated gong 1 is brought into contact with a first cooling medium for rapid cooling. The first cooling medium can be room temperature water or warm water containing a corrosion inhibitor, with a temperature of 20-50°C. The area to be repaired on the gong 1 is cooled by contact with the first cooling medium, and the surface temperature of the area to be repaired is controlled to rapidly decrease to room temperature. After cooling with the first cooling medium, a fine-grained structure is formed in the area to be repaired on the gong during the first heat treatment stage, preventing the further expansion of oxides generated at high temperatures and providing a stable basic interface for subsequent filler materials.

[0045] Please see Figure 5 Preferably, before repairing the gong, all cracks at different locations on the surface of the gong 1 are detected by scanning. This can be done by an operator visually inspecting the surface of the gong 1 and tracing the cracks with a developing pen. Alternatively, after clarifying the surface of the gong 1, a suitable developing agent is applied to highlight the crack paths on the surface of the gong 1.

[0046] For cracks in different locations, cracks that partially intersect are grouped into the same crack group. For example, if the path of the first crack intersects with the path of the second crack, then the first and second cracks are classified as the same crack. This process is repeated for subsequent cracks, such as the third, fourth, and Nth cracks, merging them into the same group as much as possible. Through this initial classification, several crack groups may be obtained. If adjacent crack groups also partially intersect, these two groups are merged to group as many cracks as possible into the same group. Additionally, cracks that do not intersect at all should be classified into a separate crack group.

[0047] For the same group of cracks, different crack end positions 21 and crack intersection positions 22 are extracted. Each crack end position 21 is used as a positioning point, and each crack intersection position 22 is used as another positioning point. Furthermore, if a positioning point is located in a closed area where at least three cracks intersect and connect sequentially, this positioning point needs to be removed. This is because a closed area formed by at least three sequentially intersecting and connecting cracks poses a serious risk of crack separation, and this area needs to be completely separated from other locations. Deep cleaning of the crack edges is also required, as well as separate welding of the internal structure to ensure reliability after normal use.

[0048] Then, for different positioning points within the same crack group, all positioning points on the outermost edge need to be connected to form the initial contour 23 of the same crack group. This is then expanded outwards at equal distances to define the final contour 24. Based on the final contour 24, a filling mold 5 for filling the first cooling medium is fabricated. (See [link to relevant documentation]). Figure 5 , 6 The filling mold 5 can be printed with a specific structure using 3D printing. The filling mold 5 has a hollow area 51 at its center. The inner boundary of the central control area 51 can cover all the cracks in the same crack group. The hollow area 51 has multiple layers of staggered porous filler 6 inside. The porous filler 6 contains a first cooling medium, which can be quenching oil, polymer aqueous solution, molten salt, fluidized solid particle medium, etc.

[0049] Therefore, after the first heat treatment stage is completed, the filling mold, which has a porous filler 6 and is filled with the first cooling medium, is directly placed over the corresponding crack group to rapidly cool the area. Cooling by the filling mold 5 corresponding to the contour of the same crack group can prevent other parts of the gong that are not in the same crack group from being disturbed by rapid heat changes. Furthermore, during the first heating stage, it is necessary to strictly control the heating path. Combining a specific heating path with the filling mold 5 set according to the contour ensures that the area to be repaired meets the requirements of subsequent accurate processing.

[0050] During the repair process, copper-tin synthetic copper powder or repair synthetic copper material 4, which matches the composition of the gong matrix, is filled into the crack. Utilizing the already toughened substrate, the molten repair synthetic copper material 4 is hammered and compacted, or low-temperature brazing is used to fill the crack 2. As the temperature at the welded area gradually cools, the protruding structure in the filled area is then finely polished to make its surface flush with the surrounding gong 1 surface, thus eliminating stress concentration. For surfaces of the gong 1 with significant variations, manual or relatively fine polishing methods are required to ensure a smooth transition between the repair synthetic copper material 4 and the surrounding surface of the gong 1, or to allow for a transition along the same curvature.

[0051] Specifically, Cu-15%Sn synthetic copper wire can be heated and melted, allowing the molten synthetic copper material 4 to directly enter the crack 2. While maintaining a high temperature, the synthetic copper material 4 is compacted using a special chisel, ensuring that it is fully immersed in the crack. After cooling, it is polished with an oilstone or high-grit sandpaper until it is completely flush with the surface of the gong 1.

[0052] Please see Figure 2 Preferably, the technical solution of the present invention can also divide the gong 1 into a central copper plate 11 and an outer peripheral copper plate 12, and measure and calculate the area ratio of the central copper plate 11 and the outer peripheral copper plate 12, wherein the area ratio of the central copper plate 11 and the outer peripheral copper plate 12 is 3-4:2-3.

[0053] Before repairing the crack, a spectrometer was used to collect at least one copper-tin composition ratio data at any position on the central copper plate 11 and the outer peripheral copper plate 12.

[0054] In the first scenario, if the copper-tin ratio in the two areas is consistent (i.e., the data is the same or the error is less than 1%), the repair material is prepared according to this ratio to repair the cracks. The consistent copper-tin ratio in the two areas suggests that the central and outer copper plates of the gong were made from the same copper-tin sheet during manufacturing, resulting in good consistency. Even after repair, using the same material will ensure good consistency in acoustic performance.

[0055] In the second scenario, if the copper-tin ratios of the two regions are not exactly the same, such cases may be that the copper-tin ratios of the central copper plate and the outer peripheral copper plate are completely different or the error exceeds 1%, which is considered as the two being made of copper-tin plates with different properties. In this case, it is necessary to repair the cracks in different locations to ensure acoustic consistency after repair, and it is also necessary to formulate a repair synthetic copper material 4 that harmonizes the acoustic properties of different regions.

[0056] For the second scenario, the copper-tin ratio used in the actual repair application is adjusted based on the area ratio. The following example further illustrates this second scenario:

[0057] The copper-tin composition ratio of the central copper plate is 84% ​​copper and 14% tin, while that of the outer copper plate is 80% copper and 19% tin. It can be observed that the copper material composition error is 5%, and the tin material composition error is 28%, exceeding the aforementioned 1% benchmark. Furthermore, assuming the area ratio of the central copper plate to the outer copper plate is 3:2, the process for calculating the corrected copper-tin composition ratio is as follows:

[0058] The proportion of copper material = (84%*3 + 80%*2) / (3+2) = 82.4%;

[0059] Tin material ratio = (14%*3 + 19%*2) / (3+2) = 16.0%.

[0060] Therefore, the final corrected copper-tin ratio is (82.4% copper, 16.0% tin), and the material for crack repair is finally prepared based on the corrected copper-tin ratio.

[0061] In the second heat treatment stage, the repaired gong is placed in a heating furnace and heated to 700-750℃, then held at that temperature for 15-30 minutes. This temperature range is close to the solidus of copper-tin composite copper, but does not reach the melting point of the copper-tin composite copper in the gong. Therefore, at this temperature, the repair composite copper material 4 at the crack location and the gong matrix 1 undergo interdiffusion, forming a dense composite copper structure. It should be noted that because the tin element in the copper-tin composite copper fully melts within the copper matrix, it can eliminate microscopic segregation of tin and refine the grains. These steps improve the gong's elastic modulus and internal friction characteristics.

[0062] Specifically, the entire gong was suspended inside a box-type resistance furnace and heated to 720°C. After holding at that temperature for 20 minutes, the surface of the gong 1 turned a bright cherry red and did not melt or flow.

[0063] After the second heat treatment stage, the copper gong is rapidly immersed in a second cooling medium for rapid cooling. This can be achieved by spraying the gong with flowing water or by immersion quenching, with the cooling rate controlled at 50°C / s or higher. This process suppresses abnormal grain growth at high temperatures and cools the single-phase solid solution structure to room temperature, resulting in high hardness, high performance, and good acoustic response characteristics.

[0064] Specifically, the heated gong can be removed and quenched by spraying 20°C flowing water evenly on both sides of the gong with a high-pressure spray device until it is completely cooled.

[0065] After the above processing steps, the gong can be placed at room temperature for 24-48 hours, or in an environment of 150-200℃ for a relatively long period of time, to stabilize the internal structure of the gong. Finally, it can be fine-tuned by tapping. To further confirm the surface or internal quality of the repaired gong, the surface can be visually inspected to ensure that there are no obvious cracks or fissures. Microscopic inspection can also be used to ensure that the synthetic copper material at the repair site has fine and uniform grains and no coarse casting structure under metallographic visualization. The repaired gong can also be tapped to ensure that the fundamental frequency and overtone series basically coincide with the undamaged area, and the quality factor is restored to 95% or more of the original.

[0066] This invention employs a two-stage heat treatment process for repairing gongs. First, the area to be repaired is heated within the range of 400-450℃ to improve the structural toughness between the repaired part and other parts of the gong. Within this relatively low heating temperature range, initial stress at the repair location is eliminated, providing a good welding foundation for subsequent welding. Then, within the range of 700-750℃, the welded material undergoes a relatively high-temperature solidification process with the main structure of the gong, eliminating microscopic defects. The entire process is further enhanced by two cooling media applications, achieving material diffusion and bonding between the filler material and the substrate. The repaired gong exhibits overall tensile strength and fatigue life approaching the performance level of the base material, and effectively prevents secondary cracking and other repair defects at the repaired location during long-term use.

[0067] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made under the concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for repairing a gong based on segmented heat treatment and phase change control, characterized in that, Includes the following steps: Step S1: Clean and / or stop the crack in the gong. Step S2: The local area to be repaired is heated within a first temperature range to relieve stress and toughen it. After the first heat preservation time, the local area to be repaired is brought into contact with and cooled by the first cooling medium. Step S3: Fill the crack with molten synthetic copper repair material and apply short-term impact pressure or continuous bonding pressure to fully fuse the synthetic copper repair material with the crack. After cooling, polish all cracks and synthetic copper repair material. The synthetic copper repair material should be flush with the surface of the gong or follow the same curvature. Step S4: After heating the entire gong to the second temperature range and holding it for the second time, bring the entire gong into contact with the second cooling medium and cool it.

2. The method for repairing a gong based on segmented heat treatment and phase change control as described in claim 1, characterized in that, In step S1, the crack-stopping treatment involves scanning the trajectory of the crack to determine all ends of the crack and the intersection positions of different cracks, and then creating crack-stopping holes at the end positions and intersection positions respectively.

3. The method for repairing a gong based on segmented heat treatment and phase change control as described in claim 2, characterized in that, The anti-crack hole penetrates the plate structure of the gong, and the anti-crack hole has inwardly tapering chamfers on both the front and back sides of the plate.

4. The method for repairing a gong based on segmented heat treatment and phase change control as described in claim 1, characterized in that, In step S2, the first temperature range is 400-450℃, and the first heat preservation time is 10-20 minutes.

5. The method for repairing a gong based on segmented heat treatment and phase change control as described in claim 1, characterized in that, In step S4, the second temperature range is 700-750℃, and the second heat preservation time is 15-30 minutes.

6. The method for repairing a gong based on segmented heat treatment and phase change control as described in claim 1, characterized in that, Step S2 further includes the following steps: Step S21: Before repair, cracks at different locations on the surface of the gong are detected by scanning. Cracks that intersect at some locations are classified into the same crack group. If there is an intersection between two adjacent crack groups, the two adjacent crack groups are merged. Cracks that do not intersect at any location are classified into a single crack group. Step S22: Within the same crack group, extract the end positions and intersection positions of different cracks to define the initial contour of the same crack group, and extend it outward at the same distance to define the final contour. Step S23: Based on the final contour, a filling mold for filling the first cooling medium is made. The filling mold has a hollow area in the center. The boundary of the hollow area can cover all the cracks in the same crack group. The hollow area has multiple layers of staggered honeycomb filler, which contains the first cooling medium.

7. The method for repairing a gong based on segmented heat treatment and phase change control as described in claim 1, characterized in that, Step S3 further includes the following steps: Step S31: Divide the gong into a central copper plate and an outer copper plate, and measure and calculate the area ratio of the central copper plate and the outer copper plate; Step S32: Before repairing the crack, use a spectrometer to collect at least one parameter of the copper-tin composition ratio at any position on the surface of the central copper plate and the outer copper plate. Step S33: If the copper-tin ratio of the central copper plate and the outer copper plate is consistent, then adjust the material to repair the crack according to the copper-tin ratio. Step S34: If the copper-tin ratio of the central copper plate and the outer copper plate is not exactly the same and exceeds the limit error threshold, the weight is corrected by referring to the area ratio and the corrected copper-tin ratio is obtained. The material is then prepared to repair the cracks using the corrected copper-tin ratio.

8. The method for repairing a gong based on segmented heat treatment and phase change control as described in claim 7, characterized in that, In step S31, the area ratio of the central copper plate to the outer peripheral copper plate is 3-4:2-3.

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