Graphite silver special roll plating equipment and electroplating process thereof

Abstract

The application discloses a special barrel plating equipment for graphite and silver and an electroplating process thereof, and belongs to the technical field of electroplating equipment and electroplating process.The barrel plating equipment comprises an electroplating tank body, a high-frequency bidirectional pulse power supply, a hollow anti-corrosion roller, symmetrical anodes, a central cathode and a built-in positive pressure circulation and vortex stirring mechanism, and is matched with a temperature control assembly to realize full-process uniform suspension and no sedimentation and stratification of graphite particles in plating solution; the process adopts high-frequency bidirectional pulse current, realizes fine and dense nucleation through forward high peak current, realizes diffusion replenishment through off-interval, realizes reverse micro-dissolution and flattening and purifying, and combines with low-speed tumbling and position changing of the roller, so that the graphite particles are uniformly embedded in the silver matrix.The composite coating prepared by the application has the characteristics of high conductivity, self-lubrication, high wear resistance and sulfurization discoloration resistance, the contact resistance is stable, the plugging life is improved, the coating is dense and uniform, the batch consistency is good, the coating thickness can be reduced, the noble metal silver is saved, the application is suitable for mass production of small workpieces, the cost is reduced, and industrial production is realized.

Description

Technical Field

[0001] This invention relates to the technical field of precision electronic component processing equipment, specifically to a graphite silver barrel plating equipment and its electroplating process. Background Technology

[0002] Conventional barrel plating of pure silver for small parts can only produce a single metallic silver plating layer. Although the silver plating layer has excellent conductivity, it has problems such as high coefficient of friction, poor wear resistance, easy sulfidation and blackening, and easy wear and detachment of the contact interface after frequent plugging and unplugging. After long-term service, the electrical contact resistance drifts greatly and the service life is short, which cannot meet the high-frequency plugging and unplugging, wear resistance, low friction and high stability requirements of high-end precision electronic components.

[0003] Existing graphite-silver composite plating processes mostly employ rack plating, which is only suitable for large-scale single-piece production and cannot achieve large-scale barrel plating production for small and micro-sized batches of workpieces. Traditional DC barrel plating composite plating processes have significant technical shortcomings: continuous deposition with constant DC current results in severe concentration polarization at the cathode interface, leading to an imbalance in the co-deposition ratio of graphite particles and silver ions. This results in insufficient graphite doping in the workpiece stacking shielding area and uneven coating composition. Furthermore, DC deposition produces coarse grains and severe graphite particle agglomeration, resulting in a loose coating with poor adhesion, easy peeling and flaking, and high porosity, leading to poor corrosion resistance and discoloration resistance. In addition, traditional barrel plating equipment lacks a dedicated graphite particle dispersion and circulation replenishment structure, resulting in severe sedimentation and stratification of graphite particles in the plating solution. This further leads to poor batch product consistency and low yield, making it impossible to achieve stable mass production of high-quality graphite-silver composite coatings. Summary of the Invention

[0004] The purpose of this invention is to provide a dedicated barrel plating equipment for graphite silver, which solves the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a graphite silver dedicated barrel plating equipment, comprising an electroplating tank, a high-frequency bidirectional pulse power supply system, an electroplating drum, a transmission mechanism, a symmetrical pure silver anode plate assembly, a centrally built-in cathode conductive assembly, a plating solution positive pressure circulation mechanism, a graphite particle vortex dispersion mechanism, and a temperature control mechanism.

[0006] The electroplating tank is a sealed, corrosion-resistant structure that holds the graphite-silver composite plating solution.

[0007] The electroplating roller is suspended in the electroplating tank and located in the composite plating solution. The electroplating roller is driven to rotate at a constant speed by a transmission mechanism.

[0008] The pure silver anode plate assembly includes two pure silver anode plates symmetrically fixed on both sides of the inner wall of the electroplating tank. The central cathode conductive component penetrates the interior of the electroplating drum and is electrically connected to the cathode of the pulse power system. The two anode plates are electrically connected to the anode of the pulse power system.

[0009] The positive pressure circulation mechanism for the plating solution includes a circulation pump, a filter, and an inlet pressure pipe. The outlet of the inlet pressure pipe extends into the interior of the electroplating drum, pumping the filtered plating solution into the electroplating drum under positive pressure.

[0010] The graphite particle vortex dispersion mechanism includes a vortex ring island disposed at the bottom of the electroplating tank, and the graphite particle vortex dispersion mechanism also includes a vortex stirring water pump connected to the vortex ring island, which generates a rotating vortex by directional spraying of plating solution.

[0011] The temperature control mechanism includes a cooling pipe, a chiller, and a temperature sensor.

[0012] In this invention, the electroplating roller has an opening that communicates with the interior and a roller door that covers the opening, through which the workpiece to be electroplated passes.

[0013] The electroplating roller has several evenly arranged hollow holes, and the size of the hollow holes is smaller than the minimum size of the workpiece. The inner wall of the electroplating roller is provided with guide ribs, which enhance the tumbling effect of the workpiece as the electroplating roller rotates.

[0014] The transmission mechanism includes a rolling main motor, a rolling motor controller, and a gear transmission module. The rolling main motor is electrically connected to the rolling motor controller. The moving end of the rolling main motor is connected in sequence to the gear transmission module and the electroplating drum. The rolling main motor drives the drum to rotate at a steplessly adjustable speed within the range of 1 to 30 rpm.

[0015] In this invention, the vortex island is an annular guide channel structure. Its inlet is connected to the outlet of the vortex stirring water pump, and the outlet is arranged along the tangential direction of the island, so that the sprayed plating solution forms a continuously rotating annular vortex at the bottom of the tank. The vortex intensity is sufficient to lift up the graphite particles that have settled at the bottom and evenly disperse them in the main body of the plating solution.

[0016] In this invention, the outlet end of the liquid inlet pressure pipe is rotatably connected to one side of the electroplating drum, and the liquid inlet pressure pipe outputs along the axial direction of the electroplating drum, so that the positive pressure plating solution pumped into the electroplating drum is evenly distributed throughout the entire internal space of the electroplating drum, and drives the plating solution inside the electroplating drum to seep outward, forming a continuous forced exchange flow.

[0017] In this invention, the high-frequency bidirectional pulse power supply system includes a rectifier, a pulse generation module, and a control center, and can output a positive pulse with a frequency of 50-1000Hz, a duty cycle of 10%-45%, and a peak current density of 8-100A / dm², as well as a short-time reverse pulse with a reverse voltage amplitude of 20%-50% of the positive amplitude and a reverse conduction time of 5%-20% of the forward conduction time.

[0018] An electroplating process using a dedicated graphite silver barrel plating equipment includes the following steps:

[0019] In the pretreatment process, the workpiece undergoes alkaline degreasing, hot water cleaning, acid pickling activation, and multi-stage pure water rinsing in sequence to remove oil and oxide scale from the workpiece surface.

[0020] The plating solution preparation and equipment pre-running process involves preparing a composite plating solution containing silver complex main salt, nano or micron-sized graphite particles, dispersant, complexing agent, brightener, and buffer. The circulation and vortex dispersion mechanisms are turned on and pre-run for 10 to 20 minutes to ensure uniform suspension of the graphite particles, and the plating solution temperature is stabilized at 35 to 55°C.

[0021] The main process of pulsed barrel plating of graphite silver involves loading the workpiece into the plating drum, controlling the drum to rotate at a speed of 1 to 30 rpm, turning on the high-frequency bidirectional pulse power supply system, setting the pulse frequency to 50 to 1000 Hz, the duty cycle to 10% to 45%, the peak current density to 8 to 100 A / dm², and alternating between forward conduction, off-off intermittent and reverse conduction, with a plating time of 1 to 10000 min.

[0022] In the post-processing stage, after electroplating, the workpiece is removed and sequentially subjected to multi-stage pure water rinsing, neutral anti-discoloration passivation, hot air drying, and screening inspection.

[0023] In this invention, the silver ion concentration in the graphite-silver composite plating solution is 20–60 g / L, the amount of graphite particles added is 5–30 g / L, the average particle size of the graphite particles is 0.2–5 μm, the dispersant is polyvinylpyrrolidone, sodium dodecyl sulfate, or polyethylene glycol, and the amount added is 0.5–5 g / L, the complexing agent is sodium citrate, disodium ethylenediaminetetraacetate, or potassium sodium tartrate, and the amount added is 10–50 g / L, the brightener is saccharin, sodium benzenesulfinate, or an alkynyl alcohol compound, and the amount added is 0.1–2 g / L, the buffer is boric acid or sodium acetate, and the amount added is 10–30 g / L, and the pH value of the plating solution is controlled at 6–9.

[0024] In this invention, the forward conduction stage realizes the reduction of silver ions and the co-deposition of graphite particles, the turn-off intermittent stage reduces the current to zero to eliminate concentration polarization and allow particle diffusion replenishment, and the reverse conduction stage causes a small amount of dissolution in the high current density area on the workpiece surface to level the coating and remove impurities. The three sub-stages constitute a complete pulse cycle and are repeated cyclically.

[0025] In this invention, the neutral anti-discoloration passivation uses a passivation solution containing benzotriazole or thiazole compounds, with a concentration of 0.5-3 g / L, a temperature of 40-60°C, and a time of 1-5 min, to form an organic complex protective film on the coating surface; the hot air drying temperature is 80-120°C, and the time is 5-15 min.

[0026] In this invention, the positive pressure circulation mechanism and the vortex dispersion mechanism of the plating solution operate continuously throughout the electroplating process to ensure the uniformity of the concentration and suspension stability of the graphite particles in the plating solution. At the same time, the temperature control mechanism controls the temperature fluctuation of the plating solution within ±1℃ to ensure the stable progress of the composite deposition reaction.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention, by setting up a positive pressure circulation mechanism for the plating solution and a graphite particle vortex dispersion mechanism, and through the synergistic effect of the positive pressure circulation dispersion and the bottom vortex dispersion structure of the electroplating drum, completely solves the problems of sedimentation, agglomeration, and stratification of graphite particles in the plating solution from the root of the equipment structure. This ensures that the concentration of graphite particles in the plating solution remains stable and uniform throughout the entire process, ensuring a high degree of consistency in the graphite doping amount in the composite coating on the workpiece surface. It eliminates the defects of uneven composition caused by local graphite deficiency or excessive graphite agglomeration in traditional processes, and significantly improves the consistency and yield of batch products.

[0029] This invention achieves significant grain refinement of the composite coating by setting up a high-frequency bidirectional pulse power supply system and adopting a high-frequency bidirectional pulse co-deposition mechanism, combined with the dynamic mass transfer capability of the equipment. Graphite microparticles are uniformly embedded in the silver substrate, resulting in a dense, non-porous, and agglomerated coating structure. The bonding force between the coating and the substrate is greatly enhanced, effectively avoiding problems such as peeling, flaking, and wear failure. At the same time, the graphite-silver composite coating combines the ultra-high conductivity of metallic silver with the self-lubricating, high wear-resistant, and low-friction properties of graphite. The contact resistance of the workpiece remains stable over a long period, and the high-frequency insertion and removal service life is more than five times longer than that of pure silver coating. Furthermore, its resistance to sulfidation and blackening is significantly better than that of pure silver coating.

[0030] This invention, by setting up an electroplating drum and relying on the dynamic tumbling mass transfer and pulse polarization elimination technology of the drum, completely solves the stubborn problems of traditional barrel plating such as small part stacking shielding, thin plating in gaps, and uneven thickness. The coating thickness and composition of the entire batch of workpieces are extremely consistent, and the coating thinning design can be realized to significantly reduce the consumption of precious metal silver. The equipment has a high degree of automation, can be used as a single machine or multi-machine line, and its modular design is compatible with all barrel plating process products. It has high production efficiency and low operation and maintenance costs, and is perfectly suited to the industrial mass production needs of precision electronic parts with large volume, high quality, and low cost. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the present invention;

[0032] Figure 2 This is a partial structural schematic diagram of the present invention;

[0033] Figure 3 This is a front sectional view of the machine tool of the present invention;

[0034] Figure 4This is a side sectional view of the machine tool of the present invention. Detailed Implementation

[0035] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "horizontal," "vertical," "top," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] Please see Figures 1 to 4 This invention provides an embodiment of a graphite silver dedicated barrel plating equipment and its electroplating process. The equipment includes a machine base 100, wherein an electroplating tank 1, a high-frequency bidirectional pulse power supply system, an electroplating roller 2, a transmission mechanism, a symmetrical pure silver anode plate assembly, a centrally built-in cathode conductive assembly, a plating solution positive pressure circulation mechanism, and a graphite particle vortex dispersion mechanism are arranged on the same machine base 100. The electroplating tank 1 is a container for holding the plating solution, which is a graphite silver composite plating solution. The electroplating roller 2 is suspended inside the electroplating tank 1 and rotatably connected to the electroplating tank 1. The electroplating roller 2 is linked to the transmission mechanism. The electroplating drum 2 is driven to rotate at a speed of 1 to 30 rpm and is immersed in the plating solution. The symmetrical pure silver anode plate assembly includes two pure silver anode plates (not shown) that are fixed on the inner walls of both sides of the electroplating tank 1. The anode plates are electrically connected to the positive electrode of the dual-pulse power supply system through wires. When energized, they undergo oxidation and dissolution, continuously replenishing silver ions to the plating solution to maintain a stable main salt concentration. A central cathode conductive component (not shown) is installed inside the electroplating drum 2 along the axis. This central cathode conductive component is electrically connected to the negative electrode of the dual-pulse power supply system and serves as the working cathode in the electroplating process.

[0038] The transmission mechanism includes a rolling main motor 31, a rolling motor controller 32, and a gear transmission module 33. The rolling main motor 31 is electrically connected to the rolling motor controller 32, which controls the rotational speed of the rolling main motor 31. The movable end of the rolling main motor 31 is connected to the gear transmission module 32 and the electroplating drum 2 in sequence. When the shaft of the rolling main motor 31 rotates, it drives the gear transmission module 33 and the electroplating drum 2 to rotate in sequence, so that the rotational speed of the electroplating drum 2 can be infinitely adjusted within the range of 1 to 30 rpm. The rolling motor controller 32 precisely adjusts the rotational speed of the electroplating drum 2, so that the electroplating drum 2 rotates at a uniform speed within the speed range required by the process, thereby driving the workpieces inside the drum to continuously tumble, change position, and loosely stack, avoiding the shielding effect caused by the workpieces sticking to each other for a long time, and ensuring that the surface of each workpiece is evenly exposed to the plating solution.

[0039] The electroplating roller 2 has an opening that connects to the interior and a roller door 21 covering the opening, through which the workpiece to be electroplated passes. The electroplating roller 2 has several evenly arranged hollow holes 22, and the size of the hollow holes 22 is smaller than the minimum size of the workpiece. This setting ensures that the workpiece is always kept inside the electroplating roller 2. The inner wall of the electroplating roller 2 is provided with guide ribs 23, which enhance the tumbling effect of the workpiece as the electroplating roller 2 rotates.

[0040] The positive pressure circulation mechanism for the plating solution includes a circulation pump 41, a filter (not shown), and an inlet pressure pipe 42. The output end of the circulation pump 41 is sequentially connected to the filter and the inlet pressure pipe 42. The inlet pressure pipe 42 is rotatably connected to the side end of the electroplating drum 2. Simultaneously, the outlet 42 of the inlet pressure pipe extends into the interior of the electroplating drum 2, pumping the filtered plating solution into the electroplating drum 2 under positive pressure. The plating solution is output along the axial direction of the electroplating drum 2, ensuring that the positive pressure plating solution pumped into the electroplating drum 2 is evenly distributed throughout the entire interior space of the electroplating drum 2, and driving the plating solution inside the electroplating drum 2 to seep outward, forming a continuous forced exchange flow. Furthermore, the circulation pump 41... The input end is connected to the inside of the electroplating tank 1 through a pipe. The plating solution in the electroplating tank 1 is drawn out under negative pressure and then switched to positive pressure plating solution pumped into the electroplating drum 2, realizing the recycling of the plating solution. The plating solution inside the electroplating drum 2 is kept at a higher level and pressure than the external tank solution. This positive pressure replenishment not only ensures that the inside of the drum is always filled with fresh and uniform graphite-containing plating solution, but also drives the plating solution to flow out from the hollow holes of the drum through the pressure difference, forming a continuous internal and external exchange, avoiding the inside of the drum from becoming a dead zone for plating solution retention and particle sedimentation. A filter is also installed in the circulation pipeline to remove solid impurities and large agglomerates in the plating solution, ensuring the cleanliness of the plating solution.

[0041] The graphite particle vortex dispersion mechanism includes a vortex ring island 51 located at the bottom of the electroplating tank 1 and a vortex-initiating stirring water pump 52 connected to the vortex ring island 51. The vortex ring island 51 is a flow guide structure, and its inlet is connected to the outlet of the vortex-initiating stirring water pump 52. Furthermore, the inlet of the vortex-initiating stirring water pump 52 is connected to the inside of the electroplating tank 1 through a pipe. The plating solution is drawn under negative pressure and sprayed into the inside of the vortex ring island 51 at a specific angle and flow rate. Under the guidance of the ring island, a rotating vortex is formed. This vortex continuously scours the bottom area of ​​the tank, raising the graphite particles deposited at the bottom and dispersing them evenly in the main body of the plating solution. At the same time, the shear force of the vortex effectively breaks up the aggregated graphite particle clusters, achieving primary dispersion of the particles.

[0042] The temperature control mechanism includes a cooling pipe 61, a chiller 62, and a temperature sensor (not shown). The cooling pipe 61 is located inside the electroplating tank 1, and both ends of the cooling pipe 61 are connected to the chiller 62 to form a water-cooled circulation system. The chiller 62 and the temperature sensor are electrically connected. The temperature sensor is installed inside the electroplating tank 1 to detect the temperature of the plating solution in real time and feeds back to the chiller 62 via an electrical signal. In this embodiment, the cooling pipe 61 spirals around the vortex island 51, while the chiller 62 is a device independent of the machine 100. Both ends of the cooling pipe 61 penetrate the side wall of the electroplating tank 1 and are connected to the chiller 61.

[0043] The chiller 61 regulates the cooling water flow rate according to the temperature signal from the temperature sensor controller, and precisely controls the temperature of the plating solution within the process setting range. Because the composite electrodeposition process is sensitive to temperature, a suitable temperature is conducive to the migration of silver ions and the adsorption of graphite particles.

[0044] Furthermore, the electroplating tank 1 is made of several corrosion-resistant and temperature-sensitive polymer materials or metal materials with an anti-corrosion lining.

[0045] In this embodiment, the electroplating tank 1 is also equipped with a low liquid level controller (not shown) and a high liquid level controller (not shown), which are used to monitor the minimum and maximum liquid levels of the plating solution in the tank, respectively. When the liquid level is abnormal, an alarm is issued or the plating solution is automatically replenished to ensure the safe operation of the equipment.

[0046] The high-frequency bidirectional pulse power supply system includes a rectifier 7, a pulse generation module (not shown in the figure), and a control center 8. The rectifier 7 provides a stable power supply for the entire equipment. The control center 8 serves as the core of human-machine interaction, integrating all control functions such as pulse power parameter setting, drum speed adjustment, temperature control, liquid level monitoring, and circulation pump start / stop. The pulse generation module is located inside the rectifier 7, which supplies power to the pulse generation module and outputs pulse current to the plating solution in the electroplating tank 1 through the anode plate or the central cathode conductive component.

[0047] The operator sets the output mode, frequency, duty cycle, and peak current density of the pulse power supply through the control center 8. The main motor 31 drives the electroplating drum 2 to rotate at a constant speed, and the workpiece continuously tumbles inside the drum. The vortex stirring water pump 52 and the circulation pump 41 start simultaneously to complete the vortex dispersion at the bottom of the tank and the positive pressure supply inside the electroplating drum 2, respectively. The pulse power supply outputs a high-frequency bidirectional pulse current according to the set program, forming a periodic electric field on the surface of the workpiece through the anode plate and the central cathode. The temperature control system adjusts the cooling or heating power in real time to maintain a constant temperature of the plating solution. Throughout the process, the subsystems cooperate with each other to create an electroplating environment with uniform suspension of graphite particles, efficient ion mass transfer, and optimized current distribution, ensuring that each workpiece can obtain a high-quality composite coating with consistent composition and thickness.

[0048] The first stage is the pretreatment of the workpieces. Operators perform alkaline degreasing on batches of small, precision workpieces by immersing them in an alkaline degreasing solution containing sodium hydroxide, sodium carbonate, and sodium phosphate at a temperature controlled between 60 and 80 degrees Celsius for 5 to 15 minutes. This process utilizes saponification and emulsification to remove grease and organic contaminants from the workpiece surface. After degreasing, the workpieces are rinsed at least twice with hot water at a temperature of 50 to 70 degrees Celsius to thoroughly remove residual alkali and saponification products. Next, an acid pickling and activation treatment is performed by immersing the workpieces in a dilute sulfuric acid or dilute hydrochloric acid solution (5% to 15% concentration) at room temperature for 30 seconds to 2 minutes. This removes the oxide film and minor rust from the workpiece surface and activates the base metal surface, providing a fresh and clean active surface for subsequent electroplating. After acid pickling, multi-stage pure water rinsing is required, typically using a three-stage countercurrent rinsing process. Each rinsing time is no less than 30 seconds, and the resistivity of the pure water is no less than 15 megohm-cm to ensure that acid and metal ion residues are minimized, preventing contamination of subsequent plating solutions.

[0049] The workpiece should be kept moist to prevent secondary oxidation between pretreatment steps. If there is a delay between processes, the workpiece can be temporarily stored in a pure water protection tank.

[0050] Secondly, during the preparation of the plating solution and the pre-operation stage of the equipment, the graphite-silver composite plating solution needs to be prepared in a dedicated mixing tank. The basic components of the plating solution include a silver complex main salt, with the silver ion concentration controlled at 20-60 g / L, and the amount of nano or micron-sized graphite particles added at 5-30 g / L, with the average particle size of the graphite particles in the range of 0.2-5 μm. Dispersants, complexing agents, brighteners, and buffers also need to be added to the plating solution.

[0051] The dispersant is polyvinylpyrrolidone, sodium dodecyl sulfate, or polyethylene glycol, with an addition amount of 0.5–5 g / L. Its function is to adsorb onto the surface of graphite particles, inhibit particle aggregation through steric hindrance or electrostatic repulsion, and maintain its stable dispersion in the plating solution.

[0052] The complexing agent is sodium citrate, disodium ethylenediaminetetraacetate, or potassium sodium tartrate, with an addition amount of 10-50 g / L. Its function is to form a stable complex ion with silver ions, reduce the free concentration of silver ions, improve cathode polarization, and promote grain refinement.

[0053] The brightener is saccharin, sodium benzenesulfinate, or alkynyl alcohol compound, added at a rate of 0.1–2 g / L, to improve the appearance and leveling of the coating.

[0054] The buffer is boric acid or sodium acetate, with an addition amount of 10-30 g / L. The pH value of the plating solution is controlled within the range of 6-9 to ensure the stability of the electrodeposition process.

[0055] After the plating solution is prepared, it is injected into the electroplating tank 1. The vortex stirring water pump 52 and the circulation pump 41 are started, and the filter is opened at the same time, so that the plating solution continuously circulates between the electroplating tank 1 and the electroplating drum 2. The pre-running time is ten to twenty minutes. During this time, the rotating vortex generated by the vortex island 51 and the positive pressure circulation work together to gradually disperse the graphite particles from the initial aggregated state and suspend them evenly in the entire plating solution system.

[0056] Operators can confirm the dispersion effect by observing the appearance of the plating solution and taking samples for testing. The qualified standard is that the plating solution is uniformly blackish-gray and there are no visible sediment layers or large particle agglomerates.

[0057] At the same time, the temperature control system is turned on, and the temperature is set within the range of 35 to 55 degrees Celsius. The chiller 61 automatically adjusts according to the signal fed back by the temperature sensor, so that the temperature of the plating solution reaches and stabilizes at the set value before the end of the pre-run.

[0058] In the main process stage of pulse barrel plating of graphite silver, the pre-treated workpiece is loaded into the electroplating drum 2 through the opening on the drum 2. Then, the drum door 21 covers the opening and locks it, so that the workpiece is always inside the electroplating drum 2. The rotation speed of the electroplating drum 2 is set by the control center 8, with a speed range of one to thirty revolutions per minute. The specific value is adjusted according to the size, shape and loading of the workpiece. The rolling main motor 31 is started, and the electroplating drum 2 begins to rotate at a uniform speed. The workpiece is continuously tumbled and repositioned. Then, the high-frequency bidirectional pulse power supply system is turned on, and the pulse parameters are set as follows: pulse frequency of fifty to one kilohertz, duty cycle of ten percent to forty-five percent, and peak current density of eight to one hundred amperes per square decimeter. Then, reverse conduction is performed, and the reverse current amplitude is twenty percent to fifty percent of the forward amplitude.

[0059] Specifically, during the forward conduction phase within one pulse cycle, the cathode acquires a high negative potential, and silver complex ions are reduced to silver atoms and deposited on the workpiece surface. Simultaneously, positively charged or electrically neutral graphite particles migrate to the cathode interface under the combined action of electric field force, fluid force, and adsorption force, and are encapsulated and embedded by the growing silver grains. After the forward conduction ends, the workpiece enters a turn-off interval, at which point the current is zero, and the silver ion concentration at the cathode interface rapidly recovers through diffusion. Graphite particles also take this time to migrate to the cathode surface and the gap area of ​​the workpiece. Subsequently, a short reverse pulse is applied, and the workpiece becomes the anode. The silver in the high current density area on the surface undergoes slight dissolution, smoothing out rough protrusions and peeling off poorly adsorbed impurities and bubbles.

[0060] The three sub-stages of forward conduction, intermittent shutdown, and reverse dissolution repeat cyclically, forming a complete pulse cycle. The total electroplating time is determined based on the required coating thickness, generally ranging from ten to one thousand minutes. For the typically required thickness of 0.5 to 5 micrometers, the electroplating time is approximately thirty to one hundred and twenty minutes. Throughout the electroplating process, the circulating pump 41 and the vortex-stirring water pump 52 operate continuously to ensure that the concentration of graphite particles in the plating solution remains uniform. Simultaneously, the positive pressure inlet pipe 42 continuously replenishes fresh plating solution into the drum, maintaining the graphite particle concentration inside the electroplating drum 2 consistent with that of the main body of the electroplating tank 1. This prevents a decrease in internal concentration due to the workpiece consuming silver ions and adsorbing graphite particles within the electroplating drum.

[0061] Operators can monitor real-time parameters such as current, voltage, temperature, liquid level, and drum speed through the control center 8, and make fine adjustments when necessary to ensure the stability of process conditions.

[0062] In the post-processing stage, after electroplating is completed, the bidirectional pulse power system is first turned off to stop the rotation of the electroplating drum 2. However, the circulation pump 41 and the vortex stirring water pump 52 continue to run for three to five minutes to rinse the residual plating solution and loosely adsorbed graphite particles on the surface of the workpiece. Then, the drum door is opened, the workpiece is taken out, and it immediately enters the multi-stage pure water rinsing process. At least three stages of pure water countercurrent rinsing are used, with each rinsing time being thirty seconds to two minutes and the pure water temperature being room temperature to forty degrees Celsius to thoroughly remove the residual plating solution components on the surface of the workpiece.

[0063] After rinsing, a neutral anti-discoloration passivation treatment is performed. The workpiece is immersed in a passivation solution containing benzotriazole or thiazole compounds at a concentration of 0.5 to 3 grams per liter, a temperature of 40 to 60 degrees Celsius, and a time of 1 to 5 minutes. This forms an extremely thin organic complex film on the coating surface, which effectively blocks the corrosion of sulfides and moisture, and significantly improves the resistance to sulfide discoloration.

[0064] After passivation, rinse again with pure water, and then dry with hot air at a temperature of 80 to 120 degrees Celsius for 5 to 15 minutes until the workpiece surface is completely dry and there is no moisture residue.

[0065] Finally, screening and inspection are carried out. The inspection items include appearance color uniformity, coating thickness, adhesion, contact resistance, and salt spray test resistance to discoloration. Qualified products are packaged and put into storage.

[0066] In each of the above process steps, the selection of all equipment parameters and process conditions should be appropriately adjusted according to the specific workpiece shape, size, batch size and the required coating performance. Those skilled in the art can optimize and modify these parameters without departing from the core concept of this invention.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A graphite silver barrel plating equipment, characterized in that, It includes an electroplating tank, a high-frequency bidirectional pulse power supply system, an electroplating drum, a transmission mechanism, a symmetrical pure silver anode plate assembly, a centrally built-in cathode conductive assembly, a positive pressure circulation mechanism for the plating solution, a graphite particle vortex dispersion mechanism, and a temperature control mechanism. The electroplating tank is a sealed, corrosion-resistant structure that holds the graphite-silver composite plating solution. The electroplating roller is suspended in the electroplating tank and located in the composite plating solution. The electroplating roller is driven to rotate at a constant speed by a transmission mechanism. The pure silver anode plate assembly includes two pure silver anode plates symmetrically fixed on both sides of the inner wall of the electroplating tank. The central cathode conductive component penetrates the interior of the electroplating drum and is electrically connected to the cathode of the pulse power system. The two anode plates are electrically connected to the anode of the pulse power system. The positive pressure circulation mechanism for the plating solution includes a circulation pump, a filter, and an inlet pressure pipe. The outlet of the inlet pressure pipe extends into the interior of the electroplating drum, pumping the filtered plating solution into the electroplating drum under positive pressure. The graphite particle vortex dispersion mechanism includes a vortex ring island disposed at the bottom of the electroplating tank, and the graphite particle vortex dispersion mechanism also includes a vortex stirring water pump connected to the vortex ring island, which generates a rotating vortex by directional spraying of plating solution. The temperature control mechanism includes a cooling pipe, a chiller, and a temperature sensor.

2. The graphite silver barrel plating equipment according to claim 1, characterized in that, The electroplating roller has an opening that connects to the interior and a roller door that covers the opening, through which the workpiece to be electroplated passes. The electroplating roller has several evenly arranged hollow holes, and the size of the hollow holes is smaller than the minimum size of the workpiece. The inner wall of the electroplating roller is provided with guide ribs, which enhance the tumbling effect of the workpiece as the electroplating roller rotates. The transmission mechanism includes a rolling main motor, a rolling motor controller, and a gear transmission module. The rolling main motor is electrically connected to the rolling motor controller. The moving end of the rolling main motor is connected in sequence to the gear transmission module and the electroplating drum. The rolling main motor drives the drum to rotate at a steplessly adjustable speed within the range of 1 to 30 rpm.

3. The graphite silver barrel plating equipment according to claim 1, characterized in that, The vortex island is an annular guide channel structure. Its inlet is connected to the outlet of the vortex stirring water pump, and the outlet is arranged along the tangent of the island, so that the sprayed plating solution forms a continuously rotating annular vortex at the bottom of the tank. The vortex intensity is sufficient to lift up the graphite particles that have settled at the bottom and evenly disperse them in the main body of the plating solution.

4. The graphite silver barrel plating equipment according to claim 1, characterized in that, The outlet end of the liquid inlet pressure pipe is rotatably connected to one side of the electroplating drum, and the liquid inlet pressure pipe outputs along the axis of the electroplating drum, so that the positive pressure plating solution pumped into the electroplating drum is evenly distributed throughout the entire internal space of the electroplating drum, and drives the plating solution inside the electroplating drum to seep outward, forming a continuous forced exchange flow.

5. The graphite silver barrel plating equipment according to claim 1, characterized in that, The high-frequency bidirectional pulse power supply system includes a rectifier, a pulse generation module, and a control center. It can output a forward pulse with a frequency of 50-1000Hz, a duty cycle of 10%-45%, and a peak current density of 8-100A / dm², as well as a short-time reverse pulse with a reverse voltage amplitude of 20%-50% of the forward amplitude and a reverse conduction time of 5%-20% of the forward conduction time.

6. An electroplating process using a graphite silver barrel plating apparatus as described in any one of claims 1 to 5, characterized in that, The process includes the following steps: In the pretreatment process, the workpiece undergoes alkaline degreasing, hot water cleaning, acid pickling activation, and multi-stage pure water rinsing in sequence to remove oil and oxide scale from the workpiece surface. The plating solution preparation and equipment pre-running process involves preparing a composite plating solution containing silver complex main salt, nano or micron-sized graphite particles, dispersant, complexing agent, brightener, and buffer. The circulation and vortex dispersion mechanisms are turned on and pre-run for 10 to 20 minutes to ensure uniform suspension of the graphite particles, and the plating solution temperature is stabilized at 35 to 55°C. The main process of pulsed barrel plating of graphite silver involves loading the workpiece into the plating drum, controlling the drum to rotate at a speed of 1 to 30 rpm, turning on the high-frequency bidirectional pulse power supply system, setting the pulse frequency to 50 to 1000 Hz, the duty cycle to 10% to 45%, the peak current density to 8 to 100 A / dm², and alternating between forward conduction, off-off intermittent and reverse conduction, with a plating time of 1 to 10000 min. In the post-processing stage, after electroplating, the workpiece is removed and sequentially subjected to multi-stage pure water rinsing, neutral anti-discoloration passivation, hot air drying, and screening inspection.

7. The electroplating process according to claim 6, characterized in that, The silver ion concentration in the graphite-silver composite plating solution is 20–60 g / L, the amount of graphite microparticles added is 5–30 g / L, the average particle size of the graphite microparticles is 0.2–5 μm, the dispersant is polyvinylpyrrolidone, sodium dodecyl sulfate, or polyethylene glycol, and the amount added is 0.5–5 g / L, the complexing agent is sodium citrate, disodium ethylenediaminetetraacetate, or potassium sodium tartrate, and the amount added is 10–50 g / L, the brightener is saccharin, sodium benzenesulfinate, or alkynyl alcohol compounds, and the amount added is 0.1–2 g / L, the buffer is boric acid or sodium acetate, and the amount added is 10–30 g / L. The pH value of the plating solution is controlled at 6–9.

8. The electroplating process according to claim 6, characterized in that, The forward conduction stage enables silver ion reduction and graphite microparticle co-deposition. The off-intermittent stage returns the current to zero to eliminate concentration polarization and allow microparticle diffusion replenishment. The reverse conduction stage causes micro-dissolution in the high current density area on the workpiece surface to level the coating and remove impurities. The three sub-stages constitute a complete pulse cycle and repeat cyclically.

9. The electroplating process according to claim 6, characterized in that, The neutral anti-discoloration passivation uses a passivation solution containing benzotriazole or thiazole compounds at a concentration of 0.5–3 g / L, a temperature of 40–60°C, and a time of 1–5 min to form an organic complex protective film on the coating surface; the hot air drying temperature is 80–120°C, and the time is 5–15 min.

10. The electroplating process according to claim 6, characterized in that, Throughout the electroplating process, the positive pressure circulation mechanism and the vortex dispersion mechanism of the plating solution operate continuously to ensure the uniformity of the concentration and suspension stability of the graphite particles in the plating solution. At the same time, the temperature control mechanism controls the temperature fluctuation of the plating solution within ±1℃ to ensure the stable progress of the composite deposition reaction.

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