A method for continuous composite plating of low-tin tinplate with nickel base and trace tin plating

Abstract

This invention discloses a continuous composite plating method for low-tin-content tinplate with a nickel underlayer and micro-tin plating. The method first performs pre-plating treatment on a continuously operating steel strip, followed by continuous nickel plating to form a nickel underlayer. Before the nickel underlayer enters the micro-tin plating process, at least two of the following inter-tank state information are obtained: inter-tank dwell time, water washing residue state, and surface potential change state. Based on this, the tin nucleation compatibility state of the nickel underlayer is determined. Then, based on the tin nucleation compatibility state, an inter-tank treatment is performed using a direct transfer path, a weak acid reactivation path, or a cathodic protection path. Subsequently, the nickel underlayer undergoes micro-tin plating to form a continuous micro-tin layer. This method can reduce the risk of insufficient tin nucleation, discontinuous tin layer, and localized nickel exposure caused by the activation decay of the nickel underlayer, and improve the plating stability, welding consistency, and continuous production adaptability of low-tin-content tinplate.

Description

Technical Field

[0001] This application relates to the field of continuous electroplating technology for metal strips, and in particular to a method for continuous composite plating of low-tin tinplate with a nickel base and a small amount of tin plating. Background Technology

[0002] Tinplate typically refers to tin-plated steel sheets with a tin layer formed on the steel base. It possesses certain corrosion resistance, weldability, and can-making adaptability, and is widely used in food packaging, chemical packaging, and other metal packaging fields. Traditionally, tinplate uses a full-surface tin-plating process, where the tin layer on the steel base serves functions such as corrosion protection, welding wetting, and processing adaptability. Due to the high price and resource nature of tin, a high tin content across the entire surface can lead to significant material cost pressures.

[0003] To reduce tin consumption, existing processes can reduce the amount of tin layer applied or combine it with other metal layers to form a composite coating. Nickel layers have good adhesion and barrier properties, making them suitable as the underlayer between the steel base and the outer functional layer. However, when using only nickel layers, their surface welding wetting and can sealing adaptability cannot completely replace traditional tin layers; simply reducing the amount of tin layer applied can easily lead to problems such as discontinuous tin layer coverage, increased porosity, insufficient local protection after stamping, and decreased weld consistency.

[0004] In continuous composite plating processes involving nickel underlay and micro-tin plating, the nickel underlay typically requires washing, guiding, tension adjustment, and inter-tank transfer before proceeding to the subsequent micro-tin plating treatment. During inter-tank transfer, the nickel underlay may experience activation degradation due to increased residence time, residual liquid carryover, surface oxidation, or changes in electrochemical state. For traditional high-tin-weight tin plating processes, the tin layer thickness is relatively sufficient, providing some tolerance for slight fluctuations in the underlay surface. However, under micro-tin plating conditions, the initial deposition charge of the tin layer is low, and slight changes in the activation state of the nickel underlay surface can affect the number and distribution of tin nucleation points, leading to discontinuous deposition of the micro-tin layer, localized nickel exposure, or decreased solderability. Therefore, a continuous composite plating method for low-tin-weight tinplate is needed that can identify the inter-tank state of the nickel underlay during continuous production and select a suitable processing path based on this state. Summary of the Invention

[0005] This application provides a low-tin-content continuous composite plating method for tinplate with a nickel underlayer and a small amount of tin plating, which improves the problem of unstable initial nucleation of the small amount of tin layer when the nickel underlayer undergoes activation decay after nickel plating and before the small amount of tin plating.

[0006] In a first aspect, this application provides a method for continuous composite plating of low-tin-content tinplate with a nickel underlayer and micro-tin plating. The method includes: providing a continuously running steel strip and performing pre-plating treatment on the steel strip; performing continuous nickel plating on the pre-plating treated steel strip to form a nickel underlayer on the surface of the steel strip; before the nickel underlayer enters the micro-tin plating process, acquiring inter-tank state information of the nickel underlayer, the inter-tank state information including at least two of the following: inter-tank dwell time, water rinse residue state, and surface potential change state; and determining the nickel underlayer based on the inter-tank state information. Tin nucleation compatibility state is used to characterize whether the nickel substrate is suitable for initial nucleation of a trace tin layer before entering the trace tin plating process. Based on the tin nucleation compatibility state, an inter-tank treatment path is selected from the inter-tank treatment paths including the direct transfer path, the weak acid reactivation path, and the cathode activation path, and the nickel substrate is treated according to the selected inter-tank treatment path. The nickel substrate after inter-tank treatment is then subjected to trace tin plating to form a trace tin layer on the surface of the nickel substrate, resulting in low-tin-content tinplate with a nickel base and trace tin plating.

[0007] Using the above method, after the steel strip completes continuous nickel plating, this application does not directly send the nickel substrate into the micro-tin plating process, nor does it use a fixed single-tank treatment method. Instead, before the nickel substrate enters the micro-tin plating process, it first obtains the tank state information related to the activation state of the nickel substrate surface, and then determines whether the nickel substrate is suitable for the initial nucleation of the micro-tin layer based on the tank state information. The corresponding tank treatment path is then selected according to the determined tin nucleation suitability state. Since the deposition charge of the micro-tin layer is low and highly sensitive to the surface state of the nickel substrate, this application adds state judgment and path selection between the nickel plating process and the micro-tin plating process, enabling the micro-tin layer to form on the nickel substrate surface that is more suitable for initial tin nucleation. This helps reduce the risks of insufficient tin nucleation, discontinuous tin layer, localized nickel exposure, and decreased weld consistency.

[0008] In one possible implementation, obtaining the inter-tank state information of the nickel substrate includes: obtaining the inter-tank dwell time of the nickel substrate from leaving the nickel plating working area corresponding to the continuous nickel plating process to entering the micro-tin plating working area corresponding to the micro-tin plating process; obtaining the residual state of the nickel substrate after the final water wash, wherein the residual state of the water wash is characterized by at least one of the conductivity of the final water wash solution and the state of residual liquid carried out from the steel strip surface; and obtaining the surface potential change state of the nickel substrate, wherein the surface potential change state is characterized by the degree of deviation between the reference potential of the nickel substrate after the continuous nickel plating process and the potential to be tinned before entering the micro-tin plating process.

[0009] This implementation method can reflect the activation decay of the nickel substrate from three aspects: inter-tank residence time, water washing residue, and surface electrochemical state, avoiding the need to judge whether the nickel substrate is suitable for micro-tin nucleation based solely on a single time parameter or a single cleaning parameter.

[0010] In one possible implementation, determining the tin nucleation adaptation state of the nickel substrate based on the inter-tank state information includes: comparing the inter-tank residence time with preset residence conditions to obtain a residence state judgment result; comparing the water washing residue state with preset cleanliness conditions to obtain a water washing state judgment result; comparing the surface potential change state with preset potential conditions to obtain a potential state judgment result; and determining the tin nucleation adaptation state of the nickel substrate based on the residence state judgment result, the water washing state judgment result, and the potential state judgment result. Specifically, when the residence state judgment result, the water washing state judgment result, and the potential state judgment result all meet their corresponding conditions, the tin nucleation adaptation state is determined to be a direct adaptation state; when any one of the residence state judgment result, the water washing state judgment result, and the potential state judgment result does not meet its corresponding condition and does not reach the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation compensation state; when at least two of the residence state judgment result, the water washing state judgment result, and the potential state judgment result do not meet their corresponding conditions, or when any judgment result reaches the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation decay state.

[0011] This implementation method allows the tin nucleation adaptation state to be determined by multiple inter-cell states, reducing misjudgments caused by occasional fluctuations in a single indicator.

[0012] In one possible implementation, when the inter-tank state information includes two of the following: inter-tank dwell time, water washing residue state, and surface potential change state, the tin nucleation adaptation state can be determined based on the two acquired inter-tank state information items. Specifically, when both judgment results corresponding to the acquired inter-tank state information items meet the corresponding conditions, the tin nucleation adaptation state is determined to be a direct adaptation state; when one judgment result does not meet the corresponding condition and does not reach the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation compensation state; when neither of the acquired judgment results meets the corresponding condition, or when either judgment result reaches the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation decay state. Therefore, a judgment basis can be provided for continuous production scenarios where only two inter-tank state information items are acquired.

[0013] In one possible implementation, the inter-tank processing path is selected based on the tin nucleation adaptation state, including: when the tin nucleation adaptation state is a direct adaptation state, a direct transfer path is selected, so that the nickel substrate enters the micro-tin plating process after the final water wash; when the tin nucleation adaptation state is an activation compensation state, a weak acid reactivation path is selected, so that the nickel substrate undergoes a weak acid reactivation treatment before entering the micro-tin plating process; when the tin nucleation adaptation state is an activation decay state, a cathode retention path is selected, so that the nickel substrate undergoes a cathode retention treatment before entering the micro-tin plating process.

[0014] This implementation method allows for the selection of different processing paths based on the varying degrees of activation on the nickel substrate surface. It avoids applying high-intensity activation treatment to all steel strip segments and also prevents steel strip segments with severe activation degradation from undergoing micro-tin plating without prior treatment.

[0015] In one possible implementation, the weak acid reactivation treatment includes: contacting the nickel substrate with a weak acid activation solution to remove the oxide film or residual salt film on the surface of the nickel substrate; after the contact with the weak acid activation solution is completed, performing a final cleaning of the nickel substrate, and ensuring that the residual state of the nickel substrate meets preset cleanliness conditions. The cathodic hold-up treatment includes: immersing the nickel substrate in a hold-up solution and applying a cathodic hold-up current to the nickel substrate to maintain the nickel substrate in a cathodic polarization state before entering the micro-tin plating treatment; after the nickel substrate leaves the hold-up solution, allowing the nickel substrate to enter the tin nucleation region corresponding to the micro-tin plating treatment within a preset transfer time.

[0016] This implementation method allows for different degrees of surface state restoration of nickel substrates with moderate and high activation decay, ensuring that the nickel substrate remains in a suitable state for initial deposition of trace amounts of tin when it enters the tin nucleation region.

[0017] In one possible implementation, a micro-tin plating process is performed on the nickel substrate after inter-tank treatment, including: determining the initial nucleation method of the micro-tin plating process based on the tin nucleation adaptation state; performing tin nucleation treatment on the nickel substrate according to the initial nucleation method to form dispersed tin nucleation points on the surface of the nickel substrate; and performing a continuous tin coverage process on the nickel substrate after the formation of tin nucleation points to form a continuously connected micro-tin layer between adjacent tin nucleation points.

[0018] With this implementation method, the micro-tin plating process no longer uses the total amount of tin plating as the control target, but first forms tin nucleation points suitable for subsequent connections, and then forms a continuous micro-tin layer, which is beneficial to improve the continuity of the tin layer under low tin content conditions.

[0019] In one possible implementation, the initial nucleation method for the micro-tin plating treatment is determined based on the tin nucleation adaptation state, including: when the tin nucleation adaptation state is a direct adaptation state, a conventional initial nucleation method is used to perform tin nucleation treatment on the nickel substrate; when the tin nucleation adaptation state is an activation compensation state, a nucleation enhancement method is used to perform tin nucleation treatment on the nickel substrate, the nucleation enhancement method including at least one of increasing the initial current density of the tin nucleation stage, using a pulsed nucleation current, and increasing the renewal rate of the tin plating solution in the tin nucleation region; when the tin nucleation adaptation state is an activation decay state, a short-time tin pre-deposition treatment is first performed on the nickel substrate, followed by the tin nucleation treatment corresponding to the nucleation enhancement method, the short-time tin pre-deposition treatment being used to form transition deposition points on the surface of the nickel substrate.

[0020] This implementation method allows the results of inter-tank processing to be further transmitted to the initial stage of micro-tin plating, enabling continuous process linkage between inter-tank state judgment and tin nucleation method.

[0021] In one possible implementation, after obtaining the inter-tank state information of the nickel substrate, the method further includes: determining the expected time when the target steel strip segment will arrive at the inter-tank processing position and the tin nucleation area based on the running speed of the steel strip and the path length between the nickel plating working area corresponding to the continuous nickel plating process and the micro-tin plating working area corresponding to the micro-tin plating process; associating the tin nucleation adaptation state corresponding to the target steel strip segment with the target steel strip segment based on the expected time; and executing the corresponding inter-tank processing path according to the tin nucleation adaptation state associated with the target steel strip segment when the target steel strip segment arrives at the inter-tank processing position.

[0022] This implementation method allows for the mapping of tin nucleation adaptation states to specific steel strip segments in continuously operating steel strips, avoiding misalignment between state judgment results and actual processed steel strip segments, and improving processing accuracy in continuous production.

[0023] In one possible implementation, after forming a trace tin layer on the nickel substrate surface, the method further includes: obtaining an initial coverage detection result of the trace tin layer, the initial coverage detection result being used to characterize the continuous coverage state of the trace tin layer; when the initial coverage detection result does not meet preset coverage conditions, determining the inter-tank processing path used by the target steel strip segment corresponding to the initial coverage detection result before entering the trace tin plating process; and adjusting the tin nucleation adaptation state judgment conditions or inter-tank processing path of subsequent steel strip segments according to the inter-tank processing path corresponding to the target steel strip segment, so as to reduce the probability of discontinuous trace tin layer coverage in subsequent steel strip segments.

[0024] This implementation method allows for feedback correction of front-end inter-tank judgment and path selection using the detection results after the formation of a trace tin layer, enabling the judgment conditions in the continuous production process to be adjusted according to changes in operating conditions.

[0025] In one possible implementation, before the start of continuous composite plating production, or after adjustments are made to at least one of the nickel plating solution state, steel strip running speed, and water washing conditions, the method further includes: selecting a nickel underlayer formed under stable continuous nickel plating conditions as a reference nickel underlayer; obtaining a reference potential and a reference water washing state of the reference nickel underlayer after the continuous nickel plating process is completed; using the reference potential and reference water washing state to determine the inter-tank state information of the subsequent steel strip segment; wherein, when the tin-to-plate potential of the subsequent steel strip segment deviates from the reference potential, or the residual water washing state of the subsequent steel strip segment deviates from the reference water washing state, the tin nucleation adaptation state of the subsequent steel strip segment is updated according to the deviation.

[0026] This implementation method allows for the re-establishment of judgment criteria after changes in production line operating conditions, reducing judgment deviations caused by changes in nickel plating solution, water washing, or steel strip running speed. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0028] Figure 1 A schematic diagram of a continuous composite plating production line for nickel-based micro-tin plating provided in this application embodiment; Figure 2 A flowchart of a low-tin-content tinplate continuous composite plating method for nickel-based micro-tin plating provided in this application embodiment; Figure 3 A flowchart illustrating a method for acquiring inter-cell state information and determining tin nucleation adaptation state, provided in an embodiment of this application; Figure 4 A flowchart illustrating a method for selecting inter-slot processing paths provided in this application embodiment; Figure 5 A flowchart illustrating a micro-tin plating method provided in this application embodiment; Figure 6 A flowchart illustrating a continuous steel strip segment tracking method provided in this application embodiment; Figure 7 A flowchart illustrating a feedback correction method provided in an embodiment of this application; Figure 8 A flowchart illustrating a baseline state establishment and update method provided in this application embodiment; Figure 9 A schematic diagram of the process state of a direct transition path provided in an embodiment of this application; Figure 10 This is a schematic diagram of the process states for a weak acid reactivation path and a cathode retention path provided in the embodiments of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the embodiments of this application will be further described in detail below with reference to the accompanying drawings. The terms "first," "second," etc., used in the following embodiments are only used to distinguish different objects and should not be construed as indicating or implying relative importance, nor should they be construed as limiting the number of objects. "At least one" in the following embodiments can refer to a single item or any combination of multiple items.

[0030] In this embodiment, the steel strip can be a cold-rolled steel strip used for manufacturing tinplate. The nickel underlayer can be a nickel-based metal underlayer formed on the surface of the steel strip, which is used to improve the barrier protection capability of the steel strip surface and the basis for the adhesion of trace tin layers. In one embodiment, the amount of nickel adhering to one side of the nickel underlayer can be 0.05 g / m²-2.00 g / m², preferably 0.10 g / m²-1.20 g / m².

[0031] In this embodiment, the trace tin layer can be a low-adhesion tin layer formed on the outside of the nickel underlayer, primarily used to provide the surface tin function required for soldering wetting and can manufacturing. In one embodiment, the single-sided tin adhesion of the trace tin layer can be 0.05 g / m²-0.80 g / m², preferably 0.10 g / m²-0.50 g / m². This range is only an optional embodiment and does not mean that this application can only be used for products within this adhesion range.

[0032] In this embodiment, the inter-tank state information can be understood as information reflecting the change in the activation state of the nickel substrate surface after it leaves the nickel plating working area and before it enters the micro-tin plating working area. The inter-tank state information may include at least two of the following: inter-tank residence time, residual water washing state, and surface potential change state. The inter-tank residence time can be the time from when the nickel substrate leaves the nickel plating working area until it enters the micro-tin plating process; the residual water washing state can be characterized by at least one of the following: the conductivity of the final stage water washing solution, the state of residual liquid carried out from the steel strip surface, the amount of residual liquid on the surface, the continuity of the residual liquid film, the amount of liquid collected after purging, or the online wet film detection signal; the surface potential change state can be characterized by the degree of deviation of the tin-to-be-plated potential from the reference potential.

[0033] In this embodiment, the reference potential can be the surface potential of the nickel substrate after it leaves the nickel plating working area; the potential to be tinned can be the surface potential of the nickel substrate before it enters the micro-tin plating process; the surface potential change state can be the deviation state of the potential to be tinned relative to the reference potential. The reference water washing state can be the water washing residue state obtained under stable water washing conditions.

[0034] In one embodiment, the reference potential and the potential to be tinned can be obtained using potential detection electrodes located in the state detection area between the production lines. Potential detection can be performed by forming a detection circuit between a reference electrode and the steel strip surface. The reference electrode can be a silver / silver chloride reference electrode, a saturated calomel electrode, or other reference electrodes suitable for electroplating production lines. Preferably, the reference potential and the potential to be tinned are obtained using the same reference system and the same detection environment to reduce the impact of changes in the detection system on the determination of the degree of potential deviation. When the production line is not suitable for continuous contact potential detection, the correspondence between the reference potential and the potential to be tinned can also be established by sampling offline potential detection results of a steel strip section.

[0035] In this embodiment, the tin nucleation adaptation state can be understood as the result of judging whether the nickel substrate is suitable for the initial nucleation of trace tin. The tin nucleation adaptation state can include a direct adaptation state, an activation compensation state, and an activation decay state. The direct adaptation state indicates that the surface activity of the nickel substrate meets the requirements for the initial nucleation of trace tin; the activation compensation state indicates that the surface activity of the nickel substrate is slightly decayed, but can be restored by reactivation with a weak acid; the activation decay state indicates that the surface activity of the nickel substrate is significantly decayed, and needs to be maintained or restored by cathode activation.

[0036] In this embodiment, the inter-tank processing path may include a direct transfer path, a weak acid reactivation path, and a cathode retention path. The direct transfer path may be a path where the nickel substrate enters the micro-tin plating process after the final water wash; the weak acid reactivation path may be a path where the nickel substrate undergoes weak acid reactivation treatment before entering the micro-tin plating process; and the cathode retention path may be a path where the nickel substrate undergoes cathode retention treatment before entering the micro-tin plating process.

[0037] In this embodiment, the preset dwell conditions, preset cleanliness conditions, preset potential conditions, corresponding high-risk conditions, and preset coverage conditions can be set according to production line specifications, strip speed, nickel underlayer adhesion amount, target tin layer adhesion amount, and product quality requirements. In one embodiment, the preset dwell conditions can be set based on the path length from the nickel plating work area exit to the tin nucleation area entrance, the strip running speed, and the nickel underlayer surface potential decay test results. The preset cleanliness conditions can be set based on the correspondence between the conductivity of the final stage wash solution, the amount of residual liquid on the strip surface, and the tin layer coverage rate. The preset potential conditions can be set based on the reference potential of the reference nickel underlayer and the deviation degree of the tin-to-plate potential in subsequent strip sections. The corresponding high-risk conditions can be determined based on the correspondence between abnormal inter-tank dwell time, abnormal wash residue, or abnormal potential deviation and the initial tin layer coverage test results.

[0038] In one implementation, the upper limit of the preset dwell condition can be designated as the first dwell threshold, and the lower limit of the high-risk dwell condition can be designated as the second dwell threshold, with the second dwell threshold being greater than the first dwell threshold. Similarly, the upper limit of the preset cleanliness condition can be designated as the first cleanliness threshold, and the lower limit of the high-risk water washing condition can be designated as the second cleanliness threshold, with the second cleanliness threshold being greater than the first cleanliness threshold. Furthermore, the upper limit of the preset potential deviation can be designated as the first potential threshold, and the lower limit of the high-risk potential condition can be designated as the second potential threshold, with the second potential threshold being greater than the first potential threshold. This allows for a progressive relationship between normal and high-risk conditions, avoiding overlapping judgment intervals.

[0039] In one optional embodiment, the first residence threshold can be 3s-15s, and the second residence threshold can be 1.2-2.0 times the first residence threshold; the first cleanliness threshold can be 20μS / cm-100μS / cm, and the second cleanliness threshold can be 1.2-2.0 times the first cleanliness threshold; the first potential threshold can be 20mV-80mV, and the second potential threshold can be 1.2-2.5 times the first potential threshold. The above numerical ranges can be adjusted according to the actual steel strip speed, plating solution system, and target product specifications.

[0040] In one embodiment, the determination of the dwell state reaching the corresponding high-risk condition may include the dwell time between tanks exceeding a second dwell threshold; the determination of the water washing state reaching the corresponding high-risk condition may include the conductivity of the final water washing liquid exceeding a second cleanliness threshold, or the residual liquid carried out from the steel strip surface reaching a continuous residual liquid film state; the determination of the potential state reaching the corresponding high-risk condition may include the deviation of the potential to be tinned from the reference potential exceeding a second potential threshold.

[0041] In this embodiment, the residual liquid carry-out state on the steel strip surface can be divided into low residual state, medium residual state, and high residual state according to the residual liquid amount per unit area, the continuous length of the residual liquid film, or the online wet film signal intensity. The low residual state can correspond to preset cleanliness conditions, the medium residual state can correspond to not meeting the preset cleanliness conditions but not reaching the corresponding high-risk conditions, and the high residual state can correspond to the water washing state judgment result reaching the corresponding high-risk conditions.

[0042] In this embodiment, the micro-tin plating process may include tin nucleation treatment and tin continuous coverage treatment. Tin nucleation treatment is used to form dispersed tin nucleation points on the surface of the nickel substrate; tin continuous coverage treatment is used to form a continuous micro-tin layer between adjacent tin nucleation points. Tin nucleation points can be indirectly determined by surface microscopic observation, surface elemental distribution detection, or tin coverage detection; continuous connection can be determined by tin layer discontinuity rate, pinhole rate, nickel exposure rate, or solder wetting results.

[0043] In one embodiment, the micro-tin plating working area corresponding to the micro-tin plating process may include a tin nucleation region and a tin continuous coverage region. The tin nucleation region is used to form tin nucleation points on the surface of the nickel substrate, and the tin continuous coverage region is used to allow adjacent tin nucleation points to continue to grow and form a continuously connected micro-tin layer.

[0044] In this embodiment, the preset coverage conditions can be determined based on the coverage rate, pinhole rate, nickel exposure rate, or solder wetting requirements of the target trace tin layer. In one embodiment, the preset discontinuity rate can be 3%-10%, and the preset exposure rate can be 1%-5%. When the tin layer discontinuity rate of the trace tin layer is not higher than the preset discontinuity rate, and the nickel exposure rate is not higher than the preset exposure rate, it can be determined that the initial coverage test result meets the preset coverage conditions. In another embodiment, the preset coverage conditions can also be determined by combining the solder wetting angle, solder current window, or corrosion resistance sampling test results.

[0045] In this embodiment, the target steel strip segment can be a steel strip area divided according to the steel strip length, or it can be a steel strip area determined based on the detection time, encoder signal, and steel strip running speed. The length of the target steel strip segment can be determined based on the response time of the detection device, the production line speed, and the response time of the inter-tank processing actuator.

[0046] In this embodiment, the inter-tank treatment location can be situated within the inter-tank treatment area. The inter-tank treatment area may include a weak acid reactivation treatment location, a cathode retention treatment location, and a direct transfer channel. The direct transfer channel allows the nickel substrate in its directly adapted state to enter the micro-tin plating working area after a final water rinse; the weak acid reactivation treatment location is used to reactivate the nickel substrate in its activation compensation state with a weak acid; and the cathode retention treatment location is used to retain the nickel substrate in its activation decay state with a cathode.

[0047] Figure 1 A schematic diagram of a low-tin-content tinplate continuous composite plating production line can be provided for embodiments of this application. (Reference) Figure 1 The production line may include a pre-plating treatment area, a continuous nickel plating working area, an inter-tank condition detection area, an inter-tank treatment area, a micro-tin plating working area, and a post-treatment area. The steel strip runs continuously along the production line and passes through the above areas in sequence.

[0048] Figure 2 A flowchart illustrating a low-tin-content tinplate continuous composite plating method using a nickel-based undercoat and micro-tin plating method, which can be used as an embodiment of this application, is provided. (See reference) Figure 2 The method includes the following steps: S101: Provides continuously running steel strip and performs pre-plating treatment on the steel strip.

[0049] The pre-plating treatment may include at least one of degreasing, cleaning, pickling activation, and water rinsing. Through pre-plating treatment, oil, oxides, and impurities on the surface of the steel strip can be removed, making the surface of the steel strip suitable for subsequent continuous nickel plating.

[0050] S102: Continuous nickel plating is performed on the steel strip after pre-plating treatment to form a nickel underlayer on the surface of the steel strip.

[0051] In some implementations, a nickel underlayer can be formed using a nickel sulfate system, a nickel sulfamate system, or other nickel plating systems suitable for continuous steel strip electroplating. The nickel underlayer serves as a base for subsequent trace tin layers and provides barrier protection when the trace tin layer is locally thin or deformed after subsequent processing.

[0052] S103: Obtain the inter-tank state information of the nickel substrate before it enters the micro-tin plating process.

[0053] In this embodiment, the inter-tank state information is not simply equipment operating parameters, but rather information reflecting whether the surface activation state of the nickel substrate has decayed after leaving the nickel plating working area and before entering the micro-tin plating working area. The inter-tank state information includes at least two of the following: inter-tank residence time, water rinse residue state, and surface potential change state.

[0054] S104: Determine the tin nucleation and adaptation status of the nickel substrate based on the inter-tank status information.

[0055] The tin nucleation compatibility state is used to characterize whether the nickel substrate meets the surface activation conditions required for the initial nucleation of a trace tin layer. In conventional tin plating processes with high tin layer adhesion, slight surface state fluctuations may be covered by a thicker tin layer; however, under trace tin plating conditions, the initial deposition charge of the tin layer is low, and changes in the surface activation state of the nickel substrate directly affect the number and distribution of tin nucleation points. Therefore, in this embodiment, the tin nucleation compatibility state is determined before tin plating.

[0056] S105: Select the inter-tank processing path according to the tin nucleation and adaptation status, and perform inter-tank processing on the nickel bottom layer according to the selected inter-tank processing path.

[0057] In some implementations, the inter-tank treatment path may include a direct transfer path, a weak acid reactivation path, and a cathode retention path. Different paths are suitable for different degrees of activation state changes. By selecting the path, it is possible to avoid using the same treatment on all steel strip segments, and also to avoid directly introducing steel strip segments with significant activation degradation into the micro-tin plating process.

[0058] S106: The nickel substrate after the inter-tank treatment is subjected to micro-tin plating treatment to form a micro-tin layer on the surface of the nickel substrate, resulting in low-tin tinplate with nickel substrate and micro-tin plating.

[0059] Through the above S101 to S106, the embodiments of this application introduce inter-tank state information acquisition, tin nucleation adaptation state judgment and inter-tank processing path selection between nickel plating and micro-tin plating, so that the micro-tin layer is formed on the nickel bottom surface that is more suitable for the initial nucleation of tin, thereby reducing the risk of discontinuous micro-tin layer coverage and local nickel exposure.

[0060] Figure 3A flowchart illustrating a method for acquiring inter-cell state information and determining tin nucleation adaptation state, which can be provided for embodiments of this application, is available. (See reference...) Figure 3 This method can be performed in S103 and S104 of Example 1.

[0061] S201: Obtain the dwell time of the nickel substrate from leaving the nickel plating working area corresponding to the continuous nickel plating process to entering the micro-tin plating working area corresponding to the micro-tin plating process.

[0062] In some implementations, the dwell time between tanks can be determined based on the strip running speed and the path length from the exit of the nickel plating work area to the entrance of the micro-tin plating work area. Alternatively, the dwell time can be determined using a position detection device, encoder, or strip segment tracking marker installed on the production line.

[0063] S202: Obtain the residual state of the nickel substrate after the final water wash.

[0064] In some implementations, the residual state of the wash can be characterized by the conductivity of the final stage wash solution. A high conductivity of the final stage wash solution indicates a higher concentration of residual ions after washing, potentially suggesting a residual salt film or risk of carryover from the nickel substrate. The residual state can also be characterized by the carryover of residual liquid from the steel strip surface, for example, by assessing the amount of residual liquid, the dripping pattern, or the state of the wet film on the surface.

[0065] S203: Obtain the surface potential change state of the nickel substrate.

[0066] In some implementations, a reference potential can be obtained after the nickel substrate leaves the nickel plating working area, and a potential to be tinned can be obtained before the nickel substrate enters the micro-tin plating process. The degree of deviation between the reference potential and the potential to be tinned can be used to determine whether activation decay has occurred on the surface of the nickel substrate.

[0067] S204: Compare the dwell time between tanks with the preset dwell conditions to obtain the dwell state judgment result.

[0068] For example, if the dwell time between tanks does not exceed the first dwell threshold, the dwell status judgment result can be considered to meet the conditions; if the dwell time between tanks exceeds the first dwell threshold but does not reach the second dwell threshold, the dwell status judgment result can be considered to not meet the conditions but not reach the high risk level; if the dwell time between tanks exceeds the second dwell threshold, the dwell status judgment result can be considered to reach the corresponding high risk conditions.

[0069] S205: Compare the residual state of the water wash with the preset cleanliness conditions to obtain the water wash state judgment result.

[0070] For example, when the conductivity of the final stage washing liquid or the residual liquid carried out from the steel strip surface meets the preset cleanliness conditions corresponding to the first cleanliness threshold, the washing status judgment result can be considered to meet the conditions; when the conductivity of the final stage washing liquid is higher than the first cleanliness threshold but does not reach the second cleanliness threshold, or when there is a medium residual state on the steel strip surface, the washing status judgment result can be considered to not meet the conditions but not reach the high risk level; when the conductivity of the final stage washing liquid exceeds the second cleanliness threshold, or when the residual liquid carried out from the steel strip surface reaches the high residual state, the washing status judgment result can be considered to reach the corresponding high risk conditions.

[0071] S206: Compare the surface potential change state with the preset potential conditions to obtain the potential state judgment result.

[0072] For example, when the deviation of the potential to be tinned from the reference potential does not exceed the first potential threshold, the potential state judgment result can be considered to meet the conditions; when the deviation exceeds the first potential threshold but does not reach the second potential threshold, the potential state judgment result can be considered to not meet the conditions but not to reach high risk; when the deviation reaches the second potential threshold, the activation decay of the nickel underlayer surface can be considered to be significant.

[0073] S207: Determine the tin nucleation and adaptation state of the nickel substrate based on the results of the dwell state judgment, the water washing state judgment, and the potential state judgment.

[0074] In some implementations, when the results of the dwell state judgment, the water washing state judgment, and the potential state judgment all meet the corresponding conditions, the tin nucleation adaptation state is determined to be a direct adaptation state. When one of the above three judgment results does not meet the corresponding condition and does not reach the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation compensation state. When at least two of the above three judgment results do not meet the corresponding conditions, or when any judgment result reaches the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation decay state.

[0075] In other embodiments, when the inter-tank state information includes two of the following: inter-tank residence time, water washing residue state, and surface potential change state, the tin nucleation adaptation state can be determined based on the two acquired inter-tank state information items. When both judgment results corresponding to the acquired inter-tank state information items meet the corresponding conditions, the tin nucleation adaptation state is determined to be a direct adaptation state; when one judgment result does not meet the corresponding condition and does not reach the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation compensation state; when neither of the acquired judgment results meets the corresponding condition, or when either judgment result reaches the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation decay state.

[0076] In this embodiment, the determination of whether the nickel substrate can enter the micro-tin plating process is not based solely on the dwell time in the tank or a single water washing state, but rather on a combination of at least two types of tank state information, thereby improving the stability of the determination of the tin nucleation and adaptation state.

[0077] Figure 4 A flowchart illustrating a method for selecting inter-slot processing paths, which can be provided for embodiments of this application, is available. (See reference...) Figure 4 This method can be executed in S105 of Example 1.

[0078] S301: When the tin nucleation adaptation state is in the direct adaptation state, select the direct transfer path.

[0079] In the direct transfer path, the nickel substrate undergoes a final water rinse before entering the micro-tin plating process. This direct transfer path is suitable when the inter-tank dwell time, water rinse residue state, and surface potential change all meet the corresponding conditions, or when both acquired inter-tank state information meet the corresponding conditions. At this point, the nickel substrate surface still has a good activation state and can directly enter the tin nucleation region of the micro-tin plating process.

[0080] S302: When the tin nucleation adaptation state is the activation compensation state, the weak acid reactivation path is selected.

[0081] In the weak acid reactivation path, the nickel substrate undergoes a weak acid reactivation treatment before entering the micro-tin plating process. The weak acid reactivation treatment may include: contacting the nickel substrate with a weak acid activation solution to remove the oxide film or residual salt film on the surface of the nickel substrate; after the contact with the weak acid activation solution, performing a final cleaning of the nickel substrate, and ensuring that the residual state of the nickel substrate after water washing meets the preset cleanliness conditions.

[0082] In one embodiment, the weak acid activation solution can be dilute sulfuric acid, dilute hydrochloric acid, methanesulfonic acid, or a combination of the above acids. The pH of the weak acid activation solution can be 1.5-4.0, the contact time can be 0.5s-8s, and the treatment temperature can be 20℃-50℃. After the weak acid is reactivated, deionized water can be used for final rinsing to ensure that the conductivity of the final rinsing solution meets the preset cleanliness requirements.

[0083] S303: When the tin nucleation adaptation state is in the activation decay state, select the cathode survival path.

[0084] In the cathodic hold-on path, the nickel substrate undergoes a cathodic hold-on treatment before entering the micro-tin plating process. The cathodic hold-on treatment may include: immersing the nickel substrate in a hold-on solution and applying a cathodic hold current to the nickel substrate to maintain it in a cathodic polarized state before entering the micro-tin plating process; after the nickel substrate leaves the hold-on solution, it enters the tin nucleation region corresponding to the micro-tin plating process within a preset transfer time.

[0085] In one embodiment, the retaining solution can be a weakly acidic conductive solution, a dilute sulfuric acid aqueous solution, a methanesulfonic acid system conductive solution, or a low-concentration tin plating solution. The cathode holding current density can be 0.1 A / dm²-2.0 A / dm², and the retaining time can be 0.5 s-10 s. The preset transfer time for the nickel substrate to enter the tin nucleation region after leaving the retaining solution can be 0.5 s-5 s.

[0086] Through the above steps S301 to S303, different inter-tank treatment paths can be selected according to the degree of degradation of the nickel substrate surface condition. When the nickel substrate is in good condition, unnecessary activation treatment is avoided; when the nickel substrate shows slight activation degradation, the surface film or residual salt film is removed by reactivation with weak acid; when the nickel substrate shows significant activation degradation, a suitable surface condition for tin nucleation is maintained by cathode activation.

[0087] Figure 5 A flowchart illustrating a micro-tin plating method provided for embodiments of this application is available. (Reference) Figure 5 This method can be executed in S106 of Embodiment 1.

[0088] S401: Determine the initial nucleation method for micro-tin plating based on the tin nucleation adaptation state.

[0089] In some implementations, the initial nucleation method may include a conventional initial nucleation method, a nucleation enhancement method, and a short-time tin pre-deposition plus nucleation enhancement method. Different initial nucleation methods correspond to different nickel substrate surface states.

[0090] S402: When the tin nucleation adaptation state is the direct adaptation state, the nickel bottom layer is subjected to tin nucleation treatment using the conventional initial nucleation method.

[0091] Conventional nucleation initiation methods are suitable for nickel substrates with well-activated surfaces. In this case, tin nucleation points can be formed according to the initiation current and steel strip speed corresponding to the target amount of trace tin plating.

[0092] S403: When the tin nucleation adaptation state is the activation compensation state, the tin nucleation treatment is performed on the nickel substrate using the nucleation strengthening method.

[0093] Nucleation enhancement methods are used to increase the distribution density of tin nucleation sites without increasing the target adhesion amount of a trace tin layer. In some embodiments, nucleation enhancement methods may include at least one of increasing the initiation current density of the tin nucleation stage, using a pulsed nucleation current, and increasing the renewal rate of the tin plating solution in the tin nucleation region.

[0094] S404: When the tin nucleation adaptation state is the activation decay state, first perform short-time tin pre-deposition treatment on the nickel bottom layer, and then perform tin nucleation treatment corresponding to the nucleation enhancement mode.

[0095] Short-time tin pre-deposition treatment can be a low-current-density short-time tin deposition treatment performed before the formal tin nucleation treatment, or a short-time cathodic deposition treatment performed in a transition solution containing a low concentration of tin ions. The purpose of short-time tin pre-deposition treatment is not to form a complete tin layer, but to form transition deposition points on the surface of the nickel substrate to reduce the impact of the activation decay of the nickel substrate surface on the subsequent initial tin deposition.

[0096] S405: After the formation of tin nucleation points, a continuous tin covering process is applied to the nickel substrate to form a continuous micro-tin layer between adjacent tin nucleation points.

[0097] In this step, the continuous tin coating process allows existing tin nucleation sites to continue growing and connecting without increasing the target total tin adhesion, thus forming a continuous micro-tin layer. This micro-tin layer is located outside the nickel underlayer and provides solder wetting and can-making compatibility.

[0098] Through the above steps S401 to S405, the results of the inter-tank state judgment are not only used to determine whether activation is necessary, but also to further determine the initial nucleation method for the micro-tin plating treatment. Thus, the inter-tank state control after nickel plating and the initial control of micro-tin plating form a process linkage.

[0099] Figure 6 A flowchart illustrating a continuous steel strip segment tracking method provided for embodiments of this application is available. (Reference) Figure 6 This method can be used to support the correspondence between the tin nucleation and adaptation state and the actual steel strip segment in continuous production.

[0100] S501: Based on the running speed of the steel strip and the path length between the nickel plating working area corresponding to the continuous nickel plating process and the micro-tin plating working area corresponding to the micro-tin plating process, determine the expected time when the target steel strip segment will reach the inter-tank processing position and the tin nucleation area.

[0101] In some implementations, the target steel strip segment can be a steel strip unit divided by length on the production line, or a steel strip area determined based on the detection time and the steel strip running speed. The length of the target steel strip segment can be determined based on the response time of the detection device, the production line speed, and the response time of the actuator. By using the running speed and path length, the estimated time for the target steel strip segment to travel from the status detection position to the inter-tank processing position or the tin nucleation area can be determined.

[0102] S502: Based on the expected time, associate the tin nucleation and adaptation state corresponding to the target steel strip segment with the target steel strip segment.

[0103] In some implementations, the target steel strip segment's number, detection time, tin nucleation adaptation status, corresponding inter-tank processing path, and expected arrival time can be associated and stored. This allows the corresponding processing path to be invoked when the target steel strip segment subsequently arrives at different process locations.

[0104] S503: When the target steel strip reaches the inter-tank processing position, execute the corresponding inter-tank processing path according to the tin nucleation adaptation state associated with the target steel strip.

[0105] By employing steps S501 to S503 as described above, misalignment between the status detection object and the process processing object can be avoided. For example, when the steel strip speed changes, if processing is performed only based on a fixed delay, the detection status of one steel strip segment may be incorrectly applied to another steel strip segment. This application's embodiment improves processing accuracy in continuous production by associating target steel strip segments.

[0106] Figure 7 A flowchart of a feedback correction method provided for embodiments of this application is shown. (Reference) Figure 7 This method can be performed after a trace tin layer has been formed.

[0107] S601: Obtain the initial coverage test results of the trace tin layer.

[0108] Initial coverage detection results are used to characterize the continuous coverage status of trace tin layers. In some embodiments, initial coverage detection results may be characterized by at least one of the following: tin layer discontinuity rate, pinhole status, surface tin coverage, nickel exposure status, or online surface detection results.

[0109] In one implementation, the preset coverage conditions can be determined based on the coverage rate, pinhole rate, nickel exposure rate, or solder wetting requirements of the target trace tin layer. For example, the preset coverage conditions may include a tin layer discontinuity rate not exceeding a preset discontinuity rate, a nickel exposure rate not exceeding a preset exposure rate, or a solder wetting angle within a preset range.

[0110] S602: When the initial coverage test result does not meet the preset coverage conditions, determine the inter-tank processing path used by the target steel strip segment corresponding to the initial coverage test result before entering the micro-tin plating process.

[0111] For example, when the trace tin layer of the target steel strip is discontinuous, it is possible to trace whether the target steel strip used a direct transfer path, a weak acid reactivation path, or a cathode retention path at the front end. It is also possible to trace the inter-tank state information and tin nucleation adaptation state of the target steel strip.

[0112] S603: Adjust the tin nucleation adaptation state judgment conditions or inter-tank processing path of subsequent steel strip segments according to the inter-tank processing path corresponding to the target steel strip segment.

[0113] In one implementation, when a discontinuous trace tin layer coverage occurs in the target steel strip segment using the direct entry path, the subsequent steel strip segment corresponding to the same inter-tank state can be adjusted to a weak acid reactivation path. If the target steel strip segment using the weak acid reactivation path still exhibits a discontinuous trace tin layer coverage, the subsequent steel strip segment corresponding to the same inter-tank state can be adjusted to a cathodic protection path. When the trace tin layer coverage state of the target steel strip segment using the cathodic protection path meets preset coverage conditions, the same path can be maintained, or after multiple consecutive steel strip segments have met the preset coverage conditions, the corresponding judgment conditions can be appropriately relaxed.

[0114] In one implementation, adjusting the tin nucleation adaptation state judgment conditions may include lowering the first dwell threshold, lowering the first potential threshold, reducing the allowable range of water washing residue state, or adjusting the boundary condition that originally corresponded to the direct adaptation state to the activation compensation state. This allows subsequent steel strip segments to adopt a more reliable inter-tank treatment path under similar inter-tank conditions.

[0115] Through the above S601 to S603, the embodiments of this application feed back the detection results after the formation of a trace tin layer to the front-end inter-tank state judgment and path selection process, so that continuous production can be corrected according to the actual coverage results.

[0116] Figure 8 A flowchart illustrating a baseline state establishment and update method provided for embodiments of this application is available. (See reference...) Figure 8 This method can be performed before the start of continuous composite plating production, or after at least one of the following has been adjusted: the state of the nickel plating solution, the speed of the steel strip, and the washing conditions.

[0117] S701: Select the nickel underlayer formed under stable continuous nickel plating conditions as the reference nickel underlayer.

[0118] Stable continuous nickel plating conditions can be understood as conditions where the temperature of the nickel plating solution, current density, steel strip running speed, pH, and water washing status are within a preset stable range. In one embodiment, stable continuous nickel plating conditions can be conditions where, during continuous operation for 5-30 minutes, the steel strip speed fluctuation does not exceed ±5%, the nickel plating current density fluctuation does not exceed ±5%, the nickel plating solution temperature fluctuation does not exceed ±2°C, and the conductivity of the water washing solution remains within a preset range.

[0119] S702: Obtain the reference potential and reference water wash status of the reference nickel substrate after the continuous nickel plating process is completed.

[0120] The reference potential can be used to characterize the surface electrochemical state of the reference nickel underlayer immediately after continuous nickel plating. The reference water wash state can be used to characterize the surface residual state of the reference nickel underlayer under stable water wash conditions.

[0121] S703: Use the reference potential and reference water washing status for subsequent judgment of the inter-tank status information of the steel strip section.

[0122] In subsequent continuous production, the tin-plating potential of the subsequent steel strip segment can be compared with the reference potential, and the water washing residue state of the subsequent steel strip segment can be compared with the reference water washing state to determine whether there is a risk of activation degradation in the subsequent steel strip segment.

[0123] S704: When the tin plating potential of the subsequent steel strip segment deviates from the reference potential, or the water washing residue state of the subsequent steel strip segment deviates from the reference water washing state, the tin nucleation adaptation state of the subsequent steel strip segment is updated according to the deviation.

[0124] For example, when the deviation of the tin plating potential from the reference potential increases, or the residual state of the water wash deteriorates compared to the reference water wash state, the tin nucleation adaptation state of the subsequent steel strip segment can be adjusted from the direct adaptation state to the activation compensation state, or from the activation compensation state to the activation decay state.

[0125] Through the above S701 to S704, after the production line operating conditions change, the embodiments of this application can re-establish or update the judgment criteria, reducing the inaccuracy of judgment caused by changes in the state of the nickel plating solution, the running speed of the steel strip, or the water washing conditions.

[0126] In one embodiment, the steel strip undergoes degreasing, pickling activation, and water washing before entering the continuous nickel plating working area. After continuous nickel plating, a nickel underlayer is formed on the surface of the steel strip. The nickel adhesion amount on one side of the nickel underlayer is 0.30 g / m²-0.80 g / m². After leaving the nickel plating working area, the nickel underlayer undergoes a final water wash before entering the inter-tank condition detection area.

[0127] Under these conditions, the first residence threshold was set to 8 seconds, and the second residence threshold was set to 14 seconds; the first cleanliness threshold was set to 80 μS / cm, and the second cleanliness threshold was set to 140 μS / cm; the first potential threshold was set to 60 mV, and the second potential threshold was set to 110 mV. Actual measurements showed a residence time of 4-7 seconds, a final stage wash solution conductivity of 30-60 μS / cm, and a deviation of the tin plating potential from the reference potential of 20-50 mV. Based on the residence state, wash state, and potential state judgments, the tin nucleation adaptation state was determined to be a direct adaptation state. Therefore, a direct transition path was selected, allowing the nickel substrate to enter the micro-tin plating process after the final stage wash.

[0128] In the micro-tin plating process, tin nucleation points are formed using a conventional initial nucleation method, followed by continuous tin coverage to form a micro-tin layer on the nickel substrate surface. The single-sided tin adhesion of the micro-tin layer is 0.10 g / m²-0.35 g / m². Testing shows that the micro-tin layer coverage meets preset conditions, such as a tin layer discontinuity rate of no more than 5% and a nickel exposure rate of no more than 3%, which can be considered a normal production state for direct adaptation.

[0129] In another embodiment, after the steel strip completes the continuous nickel plating process, the single-sided nickel adhesion of the nickel substrate is 0.30 g / m²-0.90 g / m². The first residence threshold is set to 8 s, and the second residence threshold is set to 14 s; the first cleanliness threshold is set to 80 μS / cm, and the second cleanliness threshold is set to 140 μS / cm; the first potential threshold is set to 60 mV, and the second potential threshold is set to 110 mV. Due to adjustments in the production line speed or changes in the inter-tank rinsing conditions, the residence time of the nickel substrate from leaving the nickel plating working area to entering the micro-tin plating process is 9 s-11 s. The conductivity of the final rinsing solution is 60 μS / cm-75 μS / cm, and the deviation of the tin plating potential from the reference potential is 45 mV-58 mV.

[0130] Based on the inter-tank status information, the dwell state judgment result does not meet the corresponding conditions but does not reach the corresponding high-risk condition. The water washing state judgment result and the potential state judgment result meet the corresponding conditions. Therefore, the tin nucleation adaptation state is determined to be the activation compensation state. At this time, the weak acid reactivation path is selected.

[0131] In the weak acid reactivation path, the nickel substrate is contacted with a weak acid activation solution with a pH of 2.0-3.5 for 1-5 seconds, followed by a final rinse to restore the conductivity of the final rinse solution to the preset cleanliness conditions. Subsequently, the nickel substrate undergoes a micro-tin plating treatment, employing a nucleation enhancement method for tin nucleation. This nucleation enhancement method can involve appropriately increasing the initial current density during the tin nucleation stage or increasing the renewal rate of the tin plating solution in the tin nucleation region. This treatment improves the distribution of tin nucleation points without increasing the target adhesion amount of the micro-tin layer, ensuring that the tin layer discontinuity and nickel exposure rate meet preset coverage conditions.

[0132] Under the same production line conditions, if the steel strip segment in the above-mentioned activated compensation state is directly subjected to micro-tin plating without weak acid reactivation, the distribution of tin nucleation points may be sparse, and local nickel exposure may increase. By using the weak acid reactivation path, this type of steel strip segment can more stably meet the preset coverage conditions.

[0133] In another embodiment, after the steel strip completes the continuous nickel plating process, due to the extended inter-tank path, fluctuations in the final stage water washing state, or a short-term reduction in equipment speed, the first residence threshold is set to 8 seconds, and the second residence threshold is set to 14 seconds; the first cleanliness threshold is set to 80 μS / cm, and the second cleanliness threshold is set to 140 μS / cm; the first potential threshold is set to 60 mV, and the second potential threshold is set to 110 mV. Actual testing revealed that the residence time of the nickel substrate between tanks was 15-18 seconds, the conductivity of the final stage water washing solution was 95 μS / cm-130 μS / cm, and the deviation of the potential for tin plating from the reference potential was 90 mV-120 mV.

[0134] Based on the inter-tank status information, the dwell state assessment result meets the corresponding high-risk condition. The water washing state assessment result or the potential state assessment result also shows instances where the corresponding conditions are not met. Therefore, the tin nucleation adaptation state is determined to be the activation decay state. At this point, the cathode activation maintenance path is selected.

[0135] In the cathode holding process, the nickel substrate is immersed in a weakly acidic conductive holding solution, and a cathode holding current of 0.2 A / dm²-1.5 A / dm² is applied to the nickel substrate for a holding time of 1 s-6 s. After leaving the holding solution, the nickel substrate enters the tin nucleation region corresponding to the micro-tin plating treatment within 0.5 s-5 s. After entering the tin nucleation region, a short-time tin pre-deposition treatment is performed to form transition deposition points on the surface of the nickel substrate, followed by tin nucleation treatment corresponding to the nucleation strengthening method, and then continuous tin coverage treatment to form a micro-tin layer.

[0136] This treatment reduces the impact of nickel substrate surface activation decay on the initial deposition of trace tin, allowing the steel strip segment in the activation decay state to still form a relatively continuous trace tin layer. In one embodiment, the steel strip segment using the cathode activation retention path can meet the requirements that the tin layer discontinuity rate is not higher than a preset discontinuity rate and the nickel exposure rate is not higher than a preset exposure rate.

[0137] In one implementation, the production line does not have a continuous water washing residue online detection device, but it is equipped with inter-tank dwell time detection and surface potential detection devices. In this case, two inter-tank state information items, namely the inter-tank dwell time and the surface potential change status, can be obtained, and the tin nucleation adaptation status can be determined based on these two inter-tank state information items.

[0138] For example, the first dwell time threshold is set to 8 seconds, the second dwell time threshold is set to 14 seconds, the first potential threshold is set to 60 mV, and the second potential threshold is set to 110 mV. When the dwell time of the target steel strip segment between the tanks is 6 seconds and the deviation of the tin plating potential from the reference potential is 40 mV, both judgment results meet the corresponding conditions, and the tin nucleation adaptation state is determined to be the direct adaptation state. When the dwell time of the target steel strip segment between the tanks is 10 seconds and the deviation of the tin plating potential from the reference potential is 45 mV, the dwell state judgment result does not meet the corresponding conditions but does not reach the high-risk condition, and the potential state judgment result meets the corresponding conditions, and the tin nucleation adaptation state is determined to be the activation compensation state. When the dwell time of the target steel strip segment between the tanks is 15 seconds, or the deviation of the tin plating potential from the reference potential is 115 mV, the tin nucleation adaptation state is determined to be the activation decay state.

[0139] This embodiment demonstrates that even with only two pieces of inter-slot status information, this application can still complete the inter-slot processing path selection according to the progressive judgment logic.

[0140] In an optional embodiment, during continuous production, an initial coverage inspection can be performed on the formed trace tin layer. The initial coverage inspection can be performed through online surface inspection, sampling microscopic observation, tin layer discontinuity rate detection, nickel exposure rate detection, or solder wetting detection.

[0141] When a trace amount of tin layer in a target steel strip segment is detected to be inconsistent with the preset coverage conditions, the inter-tank status information and the inter-tank processing path used for that target steel strip segment can be traced. For example, if a steel strip segment using the direct transfer path exhibits a high tin layer discontinuity rate, subsequent steel strip segments with the same inter-tank status can be adjusted to a weak acid reactivation path. If a steel strip segment using the weak acid reactivation path still exhibits a high tin layer discontinuity rate, subsequent steel strip segments with the same inter-tank status can be adjusted to a cathodic protection path. When steel strip segments using the cathodic protection path continuously meet the preset coverage conditions, this path can be maintained, or after multiple consecutive steel strip segments have met the preset coverage conditions, some judgment conditions can be appropriately relaxed.

[0142] For example, if the first dwell threshold is 8 seconds and the first potential threshold is 60 mV, and multiple steel strip segments corresponding to direct entry paths exhibit tin layer discontinuity rates close to or exceeding the preset discontinuity rate, the first dwell threshold can be adjusted to 7 seconds, or the first potential threshold can be adjusted to 50 mV. This allows subsequent steel strip segments in boundary conditions to preferentially enter the weak acid reactivation path. This feedback correction process enables the state judgment and path selection in continuous production to form a closed loop with the actual trace tin layer coverage results, reducing batch differences caused by operating condition fluctuations.

[0143] In an optional embodiment, Figure 9 This can be used to illustrate the process status in a direct-fit configuration. (Reference) Figure 9 After continuous nickel plating, the steel strip forms a nickel underlayer. After a final water rinse, the nickel underlayer enters the inter-tank condition detection area. When the inter-tank condition information meets the judgment conditions for direct adaptation, the nickel underlayer enters the tin nucleation area in the micro-tin plating working area along the direct transfer path, and forms tin nucleation points in the tin nucleation area. Subsequently, it enters the tin continuous coverage area to form a micro-tin layer.

[0144] In an optional embodiment, Figure 10 This can be used to illustrate the process status of weak acid reactivation paths and cathode hold-up paths. (Reference) Figure 10 When the tin nucleation adaptation state is in the activation compensation state, the nickel substrate enters the weak acid reactivation treatment position, and after weak acid reactivation and end cleaning, it enters the tin nucleation region; when the tin nucleation adaptation state is in the activation decay state, the nickel substrate enters the cathode maintenance treatment position, maintains the cathode polarization state under the action of the cathode holding current, and enters the tin nucleation region within a preset transfer time. Figure 9 and Figure 10 This can intuitively illustrate the correspondence between different tin nucleation adaptation states and different inter-cell processing paths.

[0145] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0146] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A method for continuous composite plating of low-tin tinplate with a nickel undercoat and a small amount of tin plating, characterized in that, include: Provide a continuously running steel strip and perform pre-plating treatment on the steel strip; The steel strip after pre-plating treatment is subjected to continuous nickel plating to form a nickel underlayer on the surface of the steel strip. Before the nickel substrate enters the micro-tin plating process, the inter-tank state information of the nickel substrate is obtained. The inter-tank state information includes at least two of the following: inter-tank dwell time, water washing residue state, and surface potential change state. The tin nucleation adaptation state of the nickel substrate is determined based on the inter-tank state information. The tin nucleation adaptation state is used to characterize whether the nickel substrate is suitable for initial nucleation of a micro-tin layer before entering the micro-tin plating process. Based on the tin nucleation adaptation state, an inter-tank treatment path is selected from the inter-tank treatment paths including the direct transfer path, the weak acid reactivation path, and the cathode retention path, and the nickel bottom layer is subjected to inter-tank treatment according to the selected inter-tank treatment path. The nickel substrate after the inter-tank treatment is subjected to micro-tin plating to form a micro-tin layer on the surface of the nickel substrate, resulting in low-tin tinplate with nickel substrate and micro-tin plating.

2. The method as described in claim 1, characterized in that, The step of obtaining the inter-tank state information of the nickel substrate includes: The time the nickel substrate spends between leaving the nickel plating working area corresponding to the continuous nickel plating process and entering the micro-tin plating working area corresponding to the micro-tin plating process is obtained. The residual state of the nickel substrate after the final stage water washing is obtained, and the residual state of the water washing is characterized by at least one of the conductivity of the final stage water washing liquid and the state of residual liquid carried out from the surface of the steel strip. The surface potential change state of the nickel substrate is obtained, and the surface potential change state is characterized by the degree of deviation between the reference potential of the nickel substrate after the continuous nickel plating process and the potential to be tinned before entering the micro-tin plating process.

3. The method as described in claim 2, characterized in that, Determining the tin nucleation and adaptation state of the nickel substrate based on the inter-dip state information includes: The dwell time between the slots is compared with the preset dwell conditions to obtain the dwell state judgment result; The water washing residue state is compared with the preset cleanliness conditions to obtain the water washing state judgment result; The surface potential change state is compared with the preset potential conditions to obtain the potential state judgment result; Based on the results of the dwell state judgment, the results of the water washing state judgment, and the results of the potential state judgment, the tin nucleation and adaptation state of the nickel substrate is determined. When the dwell state judgment result, the water washing state judgment result and the potential state judgment result all meet the corresponding conditions, the tin nucleation adaptation state is determined to be the direct adaptation state. When any one of the dwell state judgment result, the water washing state judgment result and the potential state judgment result does not meet the corresponding condition and does not reach the corresponding high-risk condition, the tin nucleation adaptation state is determined to be the activation compensation state. When at least two of the following three conditions are not met: the dwell state judgment result, the water washing state judgment result, and the potential state judgment result, or when any judgment result reaches the corresponding high-risk condition, the tin nucleation adaptation state is determined to be an activation decay state.

4. The method as described in claim 3, characterized in that, The step of selecting an inter-tank treatment path from among the inter-tank treatment paths including a direct transfer path, a weak acid reactivation path, and a cathode retention path, based on the tin nucleation adaptation state, and performing inter-tank treatment on the nickel substrate according to the selected inter-tank treatment path, includes: When the tin nucleation adaptation state is the direct adaptation state, the direct transfer path is selected so that the nickel bottom layer enters the micro-tin plating process after the final water wash. When the tin nucleation adaptation state is the activation compensation state, a weak acid reactivation path is selected so that the nickel bottom layer undergoes a weak acid reactivation treatment before entering the micro-tin plating process. When the tin nucleation adaptation state is in the activation decay state, a cathode retention path is selected so that the nickel substrate undergoes cathode retention treatment before entering the micro-tin plating process.

5. The method as described in claim 4, characterized in that, The weak acid reactivation treatment includes: The nickel substrate is brought into contact with a weak acid activation solution to remove the oxide film or residual salt film on the surface of the nickel substrate. After the weak acid activation solution is applied, the nickel substrate is subjected to a final cleaning, and the residual state of the nickel substrate after water washing meets the preset cleanliness conditions. The cathode preservation process includes: The nickel substrate is immersed in a retaining solution, and a cathode holding current is applied to the nickel substrate to keep the nickel substrate in a cathode polarized state before entering the micro-tin plating process. After the nickel substrate leaves the activating solution, it is allowed to enter the tin nucleation region corresponding to the micro-tin plating treatment within a preset transfer time.

6. The method according to any one of claims 1-5, characterized in that, The process of performing a micro-tin plating on the nickel substrate after the inter-tank treatment includes: The initial nucleation method for micro-tin plating is determined based on the tin nucleation adaptation state. The nickel substrate is subjected to tin nucleation treatment according to the initial nucleation method described above, so that dispersed tin nucleation points are formed on the surface of the nickel substrate. After the tin nucleation sites are formed, the nickel substrate is subjected to a continuous tin covering process, so that a continuous micro-tin layer is formed between adjacent tin nucleation sites.

7. The method as described in claim 6, characterized in that, The step of determining the initial nucleation method for micro-tin plating based on the tin nucleation adaptation state includes: When the tin nucleation adaptation state is the direct adaptation state, the nickel substrate is subjected to tin nucleation treatment using a conventional initial nucleation method. When the tin nucleation adaptation state is the activation compensation state, the nickel substrate is subjected to tin nucleation treatment by a nucleation enhancement method. The nucleation enhancement method includes at least one of increasing the starting current density of the tin nucleation stage, using pulsed nucleation current, and increasing the renewal rate of the tin plating solution in the tin nucleation region. When the tin nucleation adaptation state is the activation decay state, the nickel substrate is first subjected to a short-time tin pre-deposition treatment, and then the tin nucleation treatment corresponding to the nucleation strengthening method is performed. The short-time tin pre-deposition treatment is used to form transition deposition points on the surface of the nickel substrate.

8. The method as described in claim 1, characterized in that, After obtaining the inter-tank state information of the nickel substrate, the method further includes: Based on the running speed of the steel strip and the path length between the nickel plating working area corresponding to the continuous nickel plating process and the micro tin plating working area corresponding to the micro tin plating process, the estimated time when the target steel strip segment reaches the inter-tank processing position and the tin nucleation area is determined. Based on the predicted time, the tin nucleation and adaptation state corresponding to the target steel strip segment is associated with the target steel strip segment; When the target steel strip segment reaches the inter-tank processing position, the corresponding inter-tank processing path is executed according to the tin nucleation adaptation state associated with the target steel strip segment.

9. The method as described in claim 1, characterized in that, After forming a trace tin layer on the surface of the nickel substrate, the method further includes: The initial coverage detection result of the trace tin layer is obtained, and the initial coverage detection result is used to characterize the continuous coverage state of the trace tin layer. When the initial coverage detection result does not meet the preset coverage conditions, determine the inter-tank processing path used by the target steel strip segment corresponding to the initial coverage detection result before entering the micro-tin plating process; Based on the inter-slot processing path corresponding to the target steel strip segment, adjust the tin nucleation adaptation state judgment conditions or inter-slot processing path of subsequent steel strip segments to reduce the probability of discontinuous micro-tin layer coverage in subsequent steel strip segments.

10. The method as described in claim 1, characterized in that, Before the start of continuous composite plating production, or after adjustments are made to at least one of the following: the state of the nickel plating solution, the speed of the steel strip, and the washing conditions: The nickel underlayer formed under stable and continuous nickel plating conditions was selected as the reference nickel underlayer. Obtain the reference potential and reference water wash status of the reference nickel substrate after the continuous nickel plating process is completed; The reference potential and the reference water washing state are used to determine the inter-tank state information of the subsequent steel strip segment; Specifically, when the tin-to-plate potential of the subsequent steel strip segment deviates from the reference potential, or when the residual water washing state of the subsequent steel strip segment deviates from the reference water washing state, the tin nucleation adaptation state of the subsequent steel strip segment is updated according to the deviation.

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