Method for repairing bolt with rusted surface

Abstract

The invention discloses a method for repairing a bolt with a rusted surface. The method comprises the following steps that the bolt with the rusted surface to be repaired is placed in a cleaning tank containing acid cleaning liquid; the sound velocity and the conductivity of tank liquid are monitored in real time through a cooperative sensing system arranged in a circulation loop of the cleaning tank; calculating the concentration of acid in the acidic cleaning solution and the concentration of dissolved iron generated by dissolution of the rust in real time; calculating the instantaneous dissolution reaction rate of the rust in the acidic cleaning solution; an end point of the cleaning process is determined based on a variation trend of the instantaneous dissolution reaction rate, and the cleaning step is terminated when the end point is reached. According to the method, the reaction rate is monitored in real time, the optimal end point of rust removal is automatically judged, it is guaranteed that rust is thoroughly removed, meanwhile, the situation that bolt base metal is damaged due to excessive cleaning is avoided, and therefore the high consistency of repairing quality is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment and repair technology, and in particular to a method for repairing bolts with surface rust. Background Technology

[0002] In modern industrial production and equipment repair, surface cleaning of large quantities of fasteners such as bolts is a fundamental and crucial process. These processes aim to remove scale, rust, and contaminants formed during heat treatment or long-term service, providing a clean and activated metal substrate for subsequent repair, painting, or assembly steps. Currently, the control methods for batch cleaning processes such as industrial pickling largely rely on experience and indirect parameters. The most common method is timed immersion, which involves setting a fixed treatment time based on historical data. This method cannot accommodate differences in scale thickness, composition, and adhesion between different batches of bolts, nor can it compensate for changes in the chemical composition of the cleaning solution due to continuous use. This often leads to two undesirable consequences: insufficient treatment, resulting in incomplete scale removal and affecting the quality of subsequent processes; or over-treatment, i.e., over-pickling, which not only corrodes the bolt base metal, causing dimensional deviations and decreased mechanical properties, but also unnecessarily consumes large amounts of acid and energy, increasing production costs and environmental burden.

[0003] To compensate for the shortcomings of timed methods, some factories employ periodic manual sampling and chemical titration to monitor the acid concentration and dissolved metal ion content in the bath solution. While this method represents an improvement over simple timed methods, it remains essentially a passive, offline control approach. The sampling and analysis frequency is limited, with significant time delays, making it impossible to capture the dynamic processes of bath solution changes. Consequently, operator adjustments are often delayed, hindering precise control of the cleaning process and ultimately leading to product quality fluctuations and resource waste. Therefore, it is necessary to research a repair method for surface-corroded bolts that allows for precise control of the treatment process. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for repairing surface-corroded bolts. By monitoring the reaction rate in real time, the optimal endpoint for rust removal is automatically determined, ensuring that the rust is completely removed while avoiding damage to the bolt base metal due to excessive cleaning, thereby guaranteeing a high degree of consistency in repair quality.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for repairing bolts with surface rust includes the following steps:

[0007] S1. Place the bolts with surface rust to be repaired into a cleaning tank containing acidic cleaning solution;

[0008] S2. During the cleaning process, the sound velocity and conductivity of the tank liquid are monitored in real time by a collaborative sensing system installed in the circulation loop of the cleaning tank.

[0009] S3. Based on real-time measurements of sound velocity and electrical conductivity, calculate in real-time the acid concentration in the acidic cleaning solution and the concentration of dissolved iron produced by the dissolution of rust.

[0010] S4. Calculate the instantaneous dissolution rate of rust in acidic cleaning solution based on the real-time change data of dissolved iron concentration.

[0011] S5. Determine the endpoint of the cleaning process based on the changing trend of the instantaneous dissolution reaction rate, and terminate the cleaning step when the endpoint is reached.

[0012] Preferably, in the aforementioned step S2, the collaborative sensing system includes an online sound velocity sensor and a four-electrode conductivity sensor. The sound velocity sensor is used to primarily reflect changes in acid concentration, and the conductivity sensor is used to primarily reflect changes in dissolved iron salt concentration.

[0013] Preferably, in the aforementioned step S5, the change in the instantaneous dissolution reaction rate is continuously monitored, and the optimal endpoint of the cleaning process is determined when the reaction rate drops significantly from a high-speed plateau or peak.

[0014] Preferably, in step S5, when the optimal endpoint is reached, the control system automatically triggers subsequent process instructions, which include stopping cleaning, draining the used acidic cleaning solution, and initiating at least one rinsing step.

[0015] Preferably, the method further includes a post-processing step performed after step S5:

[0016] (1) Neutralization treatment: Use an alkaline solution to treat the bolt surface to neutralize the residual acid;

[0017] (2) Passivation treatment: The neutralized bolts are immersed in passivation solution for passivation treatment.

[0018] Preferably, the passivation solution is a citric acid passivation solution or a molybdate / phosphate composite conversion membrane solution.

[0019] Preferably, the aforementioned acidic cleaning solution comprises the following components by mass fraction: 10%-50% acid, 0.1%-5% corrosion inhibitor, 0.1%-15% surfactant, and the remainder is water.

[0020] Preferably, the aforementioned acid is selected from one or more of hydrochloric acid, phosphoric acid, and citric acid, the corrosion inhibitor is an imidazoline derivative or hexamethylenetetramine, and the surfactant is one of alkylphenol polyoxyethylene ether, alcohol ether, or sodium lauryl sulfate.

[0021] Preferably, in step S5 above, the model for determining the endpoint of the cleaning process is:

[0022]

[0023] Where R(t) is the instantaneous reaction rate; C acid (t) represents the real-time concentration of acid in the cleaning solution; C Fe (t) represents the real-time concentration of iron ions dissolved in the cleaning solution; α is the first parameter to be fitted, representing the theoretical maximum reaction rate without product inhibition, characterizing the inherent reactivity of the rust layer; β is the second parameter to be fitted, representing the competitive inhibition coefficient, characterizing the relative strength of the adsorption capacity of dissolved iron ions and acid on the active sites of the rust surface.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) This invention monitors the reaction rate in real time and automatically determines the optimal endpoint for rust removal, ensuring that the rust is completely removed while avoiding damage to the bolt base metal due to excessive cleaning. This ensures a high degree of consistency in repair quality and effectively shortens the processing time, saving chemicals and energy consumption.

[0026] (2) The physical sensor combination (sound velocity / conductivity) used in this invention can provide real-time concentration data of acid and dissolved iron ions in a strong acid and highly polluted cleaning tank solution for a long time, which solves the technical problem of easy failure of traditional chemical sensors.

[0027] (3) The competitive inhibition kinetic model used in this invention is derived from the chemical reaction mechanism. It can not only accurately predict the reaction endpoint, but its fitting parameters can also reflect the characteristics of the batch of rust. Attached Figure Description

[0028] Figure 1 This is a graph showing the change in sound velocity measured during the processing in Example 1.

[0029] Figure 2 This is a graph showing the change in conductivity measured during the processing of Example 1.

[0030] Figure 3 This is a graph showing the change in acid concentration calculated in Example 1;

[0031] Figure 4 This is a graph showing the change in dissolved iron concentration calculated in Example 1;

[0032] Figure 5 This is a graph showing the change in the instantaneous reaction rate calculated in Example 1. Detailed Implementation

[0033] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution.

[0034] A method for repairing bolts with surface rust includes the following steps:

[0035] S1. Place the bolts with surface rust to be repaired in a cleaning tank containing an acidic cleaning solution. The acidic cleaning solution contains the following components by mass fraction: 10%-50% acid, 0.1%-5% corrosion inhibitor, 0.1%-15% surfactant, and the remainder is water. The acid is selected from one or more of hydrochloric acid, phosphoric acid, and citric acid; the corrosion inhibitor is an imidazoline derivative or hexamethylenetetramine; and the surfactant is one of alkylphenol polyoxyethylene ether, alcohol ether, or sodium lauryl sulfate.

[0036] S2. During the cleaning process, the sound velocity and conductivity of the tank liquid are monitored in real time by a collaborative sensing system set in the circulation loop of the cleaning tank. The collaborative sensing system includes an online sound velocity sensor and a four-electrode conductivity sensor. The sound velocity sensor is mainly used to reflect changes in acid concentration, and the conductivity sensor is mainly used to reflect changes in dissolved iron salt concentration.

[0037] S3. Based on real-time measurements of sound velocity and electrical conductivity, calculate in real-time the acid concentration in the acidic cleaning solution and the concentration of dissolved iron produced by the dissolution of rust.

[0038] S4. Calculate the instantaneous dissolution rate of rust in acidic cleaning solution based on the real-time change data of dissolved iron concentration.

[0039] S5. Continuously monitor the change in the instantaneous dissolution reaction rate. The optimal endpoint of the cleaning process is determined when the reaction rate reaches a high plateau or a significant decrease from its peak value. The cleaning step is terminated upon reaching this endpoint. Upon reaching the optimal endpoint, the control system automatically triggers subsequent process commands, including stopping cleaning, draining the used acidic cleaning solution, and initiating at least one rinsing step. Then, the post-treatment steps are performed.

[0040] (1) Neutralization treatment: Use an alkaline solution to treat the bolt surface to neutralize the residual acid;

[0041] (2) Passivation treatment: The neutralized bolts are immersed in a passivation solution for passivation treatment. The passivation solution is either citric acid passivation solution or molybdate / phosphate composite conversion membrane solution.

[0042] Pickling bath solution is itself a dynamic, evolving multi-component system. In a typical hydrochloric acid pickling process, this system mainly consists of three key components: acid as an surfactant, water as a solvent, and the continuously accumulating byproduct—dissolved ferrous salts. The effectiveness of the process depends not only on the acid concentration but also significantly on the accumulation of dissolved metal salts. As the oxide scale and some of the metal matrix react with the acid, the FeCl2 concentration in the bath continuously increases. This change has several effects: first, it alters the physical properties of the solution, such as density, viscosity, and conductivity; second, according to the principle of chemical equilibrium, the increase in product concentration inhibits the forward reaction, thereby reducing the pickling rate; finally, high concentrations of metal salts interfere with the measurement accuracy of many traditional sensors, making the monitoring of a single parameter unreliable. Therefore, the control model must be able to simultaneously, independently, and accurately measure the two key variables: acid concentration and dissolved ferrous salt concentration.

[0043] To address the challenges of real-time monitoring of multiple components, this solution proposes a collaborative sensing technology based on physical measurements. This technology uses the measurement of two independent physical quantities to inversely determine the concentrations of two key chemicals. This method is more robust and reliable than directly using chemical sensors, and is particularly suitable for harsh industrial environments. However, a single conductivity measurement cannot distinguish the contributions of acid and iron salt, and a single sound velocity measurement is also susceptible to slight interference from iron salt. Therefore, when combining these two real-time measurements, a pre-defined computational model is used. This model, based on laboratory-calibrated data, describes how sound velocity and conductivity respond to changes in acid and iron salt concentrations, respectively. After receiving the original sound velocity and conductivity signals, the controller solves this computational model to accurately and in real-time calculate the concentrations of acid and iron salt.

[0044] Rust removal is a heterogeneous reaction occurring at the solid-liquid interface. Its reaction rate primarily depends on the effective contact between the reactant (acid) and the solid (rust layer) surface. It can be assumed that the reaction occurs only at specific active sites (denoted by S) on the rusted surface. The acid (denoted by A) must first adsorb onto these sites, forming an activated intermediate complex (S·A), which then decomposes to generate the products. Therefore, the overall reaction rate is related to the fraction of active sites occupied by the acid (i.e., surface coverage θ). A It is directly proportional to.

[0045] The overall reaction rate (R(t) is expressed as the rate of change of dissolved iron ion concentration). (This can be written as:)

[0046] R(t) = k rxn ·θ A (t) (1);

[0047] Where: k rxnIt is the surface reaction rate constant (unit: mol·L). -1 ·s -1 ), representing when all active sites are occupied by acids (θ) A =1) maximum reaction rate; θ A (t) is the fraction of the total active sites occupied by acid molecules at time t (dimensionless).

[0048] This formula forms the foundation for subsequent derivations. However, θ A (t) is a microscopic quantity that cannot be directly measured, and requires a macroscopically measurable variable, namely the acid concentration C in the solution. acid (t) and the concentration of dissolved iron ions C Fe (t) is used to represent θ A (t).

[0049] Assuming that not only can the reactant (acid, A) reversibly adsorb onto the active site S, but the reaction product (dissolved iron ions, denoted by P) can also reversibly adsorb onto the same active site, forming a non-reactive complex (S·P), this means that the acid and the product iron ions are competing for limited reaction sites. In this case, there are two parallel adsorption / desorption processes that rapidly reach equilibrium:

[0050] Acid adsorption:

[0051] Inhibitory adsorption of the product:

[0052] These two equilibrium processes are each described by their respective equilibrium constants (adsorption constants):

[0053]

[0054] Where: K A K is the adsorption equilibrium constant of the acid. P It is the adsorption equilibrium constant of the product (iron ions), θ A It is the fraction occupied by acid, θ P It is the fraction occupied by the product, θ free This refers to the free site fraction, where [A] and [P] represent the concentrations of acid and product in the solution, respectively, i.e., the measurable C. acid (t) and C Fe (t).

[0055] Establishing these two equilibrium relationships lays the foundation for quantitatively describing the inhibitory effect of the product. P A higher value means the product more easily occupies the reaction site, resulting in stronger inhibition. The sum of all active sites is fixed. The total site fraction equals the free site fraction (θ). free The fraction occupied by acid (θ)A ) and the fraction occupied by the product (θ) P The sum of these () equals 1. Using this conservation relationship and the equilibrium equations, we can solve for θ. A :

[0056] θ free +θ A +θ P =1 (4);

[0057] According to formulas (2) and (3), θ can be used free To represent θ A and θ P :

[0058] θ A =K A ·θ free ·C acid (t);

[0059] θ P =K P ·θ free ·C Fe (t);

[0060] Substitute these two expressions into formula (4):

[0061] θ free +(K A ·θ free ·C acid (t))+(K P ·θ free ·C Fe (t))=1;

[0062] Factor out the common factor θ free :

[0063] θ free ·(1+K A ·C acid (t)+K P ·C Fe (t))=1;

[0064] Solve for the fraction of free sites:

[0065]

[0066] Finally, θ free Substitute the expression back to θ A From the relational formula, we obtain the final required fraction of sites occupied by acid:

[0067]

[0068] This step is the mathematical core of the entire derivation process, successfully converting the microscopic surface coverage θ A (t) represents the two macroscopically measurable concentrations C. acid (t) and C Fe The formula is a function of (t). This formula clearly reflects the meaning of competition, with K in the denominator. P ·C Fe Term (t) indicates that increasing the product concentration reduces the acid coverage on the surface, even if the acid concentration itself C acid (t) remains unchanged.

[0069] Construct a complete macroscopic dynamic model by substituting equation (5) into equation (1):

[0070]

[0071] After sorting, we get:

[0072]

[0073] Equation (6) is a complete kinetic model derived from the competitive inhibition mechanism, describing how the instantaneous reaction rate R(t) depends simultaneously on the reactant concentration C. acid (t) and product concentration C Fe (t).

[0074] To facilitate data fitting and parameter interpretation in practical applications, the fundamental constants in formula (6) are combined and defined as two new parameters to be fitted with clear physical meaning. In typical pickling processes, the concentration of acid is usually much higher than the reciprocal of its adsorption equilibrium constant (i.e., K). A ·C acid (t)>>1), which means that the surface is almost saturated with acid in the early stage of the reaction.

[0075] Starting from formula (6), in K A ·C acid Under the condition that (t) >> 1, the 1 in the denominator can be ignored:

[0076]

[0077] Divide both the numerator and denominator by K. A :

[0078]

[0079] Where, let α = k rxn This parameter represents the condition without any product inhibition (C). Fe (t)→0), the theoretical upper limit of the reaction rate that can be reached, directly reflects the inherent reactivity of the rust layer itself, and the unit is mol·L.-1 ·s -1 Let β = K P / K A β is a dimensionless parameter that represents the relative strength of the adsorption capacity of the product (iron ions) and the reactant (acid) on the active site. The larger the β value, the more significant the inhibitory effect of the product.

[0080] Final formula model:

[0081]

[0082] Where R(t) is the instantaneous reaction rate, i.e. C acid (t) is the acid concentration as a function of time; C Fe (t) is the dissolved iron concentration as a function of time; α (theoretical maximum rate) is the parameter to be fitted, representing the inherent maximum reaction rate of the system, which is related to the type of rust and temperature; β (competition inhibition coefficient) is the parameter to be fitted, representing the inhibitory strength of the product on the reaction, reflecting the ability of the product to compete with the reactants for reaction sites.

[0083] After fitting the running data, the regression values ​​were α = 6.096478 and β = 0.005527. The model predictions and experimental values ​​were compared, and the results are shown in Table 1.

[0084] Table 1. Actual and model-predicted values ​​of instantaneous reaction rate

[0085]

[0086]

[0087] As shown in Table 1, the model proposed in this invention can effectively predict the instantaneous reaction rate, with a determination coefficient R0. 2 A value of 0.998 indicates that the model has a high goodness of fit and good predictive consistency.

[0088] Example 1

[0089] High-strength carbon steel bolts were selected for treatment. After 12 months of outdoor storage, an uneven reddish-brown and dark brown composite rust layer formed on the bolt surface, mainly composed of ferric oxide and magnetite. This type of high-strength material is extremely sensitive to over-pickling during the pickling process; excessive treatment can easily induce hydrogen embrittlement, leading to a severe decline in the mechanical properties of the bolts and even rendering them unusable. The specific treatment steps are as follows:

[0090] (1) Preparation of cleaning solution:

[0091] A 500L acidic cleaning solution was prepared, with the following components and mass fractions: Acid: Industrial-grade hydrochloric acid (HCl, 37% mass fraction), added at 243kg (48.6% of total mass), ensuring an effective HCl mass fraction of 18% in the cleaning solution; Corrosion inhibitor: Hexamethylenetetramine, added at 6kg (1.2% of total mass), used to slow down the corrosion of the bolt steel substrate while removing rust; Surfactant: Alkylphenol polyoxyethylene ether (OP-10), added at 2.5kg (0.5% of total mass), used to reduce the surface tension of the solution and enhance the wetting and penetration ability of the cleaning solution on the rust layer and oil stains; Solvent: Deionized water, added at 248.5kg (49.7% of total mass). The above components were added sequentially to the cleaning tank under stirring and mixed thoroughly to obtain the initial cleaning solution.

[0092] (2) Process equipment and sensing systems:

[0093] This embodiment employs an integrated automated cleaning system, with the following key equipment configurations: a 600L corrosion-resistant polypropylene (PP) cleaning tank equipped with an electric heating system to maintain a constant process temperature; a circulation loop driven by a corrosion-resistant magnetic pump, which extracts liquid from the tank at a constant flow rate of 30L / min, passes it through a sensing system, and then returns it to the tank. This circulation loop ensures that the liquid sample measured by the sensing system can represent the average chemical state of the entire tank liquid in real time, avoiding measurement errors caused by local concentration gradients near the bolts; and a collaborative sensing system, in which an online sound velocity sensor (Germany) is connected in series on the straight section of the circulation loop. A 40-type ultrasonic sensor and a four-electrode conductivity sensor (German Knick SE 656N inductive conductivity sensor) are installed downstream of the sound velocity sensor; control system.

[0094] (3) Process execution and real-time data acquisition

[0095] A basket containing 500 kg of bolts to be repaired was lowered into the cleaning tank. The heating system was activated to heat the cleaning solution and maintain it at a constant temperature of 45±1℃. The circulation pump was started, and the PLC began acquiring and storing real-time data from the sound velocity and conductivity sensors at a frequency of 0.2 Hz (i.e., recording data every 5 seconds). The real-time sensor data recording process started at t=0, and the control system continuously recorded the sensor readings. The data showed that as the reaction proceeded, the sound velocity continuously decreased due to the consumption of hydrochloric acid, while the conductivity steadily increased due to the continuous formation of dissolved iron salts. See [link to specific data] for details. Figure 1 and Figure 2 .

[0096] The collected raw physical data is converted into chemical concentration and reaction rate information in real time. The specific steps are as follows: The real-time readings of the sensors (sound velocity v(t) and conductivity κ(t)) are converted into acid concentration C. acid (t) and dissolved iron concentration C Fe (t). The specific form of this model at 45℃ is a system of two linear equations:

[0097]

[0098] Where v0 and κ0 are the initial sound velocity and conductivity readings at the start of the process (t=0), respectively. Coefficient matrix [k ij [ ] represents the sensitivity coefficient obtained through calibration, characterizing the contribution of unit concentrations of acid and iron ions to the sound velocity and conductivity, respectively. In this embodiment, the inverse matrix of this matrix is ​​determined through calibration. The controller can obtain the accurate C at each sampling time by solving this system of equations. acid (t) and C Fe (t), see details in (t), Figure 3 and Figure 4 .

[0099] (4) Calculation of instantaneous reaction rate

[0100] The instantaneous reaction rate R(t) is defined as the rate of change of dissolved iron concentration per unit time. The control system uses the central difference method to analyze the discrete C... Fe (t) Numerical differentiation is performed on the time series data to obtain smoother and more accurate rate values:

[0101]

[0102] Among them, t i t is the current sampling time point. i+1 and t i-1 These are the sampling time points before and after the sampling point, respectively. The calculated R(t) is in mol / L·s. See the detailed results below. Figure 5 .

[0103] Depend on Figure 5 Three kinetic stages of the rust removal process can be clearly observed: The first stage is the induction period, t = 0–45 s, during which the reaction rate R(t) rapidly increases from 0. This is because the surfactant begins to wet the bolt surface, the acid penetrates into the porous rust layer, and the effective reaction area rapidly increases. The second stage is the plateau period, t = 45–310 s, during which the reaction rate reaches and remains at approximately 1.5 × 10⁻⁶. -3 mol·L -1 ·s -1The high-speed, stable platform corresponds to the rapid dissolution of a large amount of readily accessible, loose rust layer. The third stage is the decay period, t>310s, where the reaction rate begins to decline sharply. This kinetic behavior is consistent with the competitive inhibition kinetic model proposed in this invention. Highly consistent. During the plateau phase, the acid concentration C... acid (t) remains high, while the iron ion concentration C of the product is high. Fe (t) is relatively low, resulting in β·C in the denominator Fe The (t) term is much smaller than C. acid (t) term. At this point, the model simplifies to R(t)≈α, meaning the reaction rate is approximately equal to the theoretical maximum reaction rate α. Therefore, the rate value during this plateau period directly reflects the inherent reactivity of the rust layer on this batch of bolts. By fitting the data from this embodiment, the kinetic parameters of this batch of rust layer can be obtained: α≈1.52×10 -3 mol·L -1 ·s -1 The competition inhibition coefficient β≈4.2. These parameters can be used for process quality traceability and diagnosis.

[0104] According to the endpoint determination criterion of this invention, the turning point when the reaction rate significantly decreases from the high-speed plateau phase is the kinetic inflection point, indicating that most of the rust layer has been removed, and the subsequent reaction will mainly be a slow erosion of the metal matrix. The control system algorithm continuously monitors the rate of change of R(t). At t = 310 s, the rate R(t) is 1.45 × 10⁻⁶. -3 mol·L -1 ·s -1 It is still at the end of the plateau period. At t = 315s, the rate drops sharply to 0.95 × 10⁻⁶. -3 mol·L -1 ·s -1 At t = 320 s, the rate had dropped to 0.40 × 10⁻⁶. -3 mol·L -1 ·s -1 Within a mere 10 seconds, the reaction rate decreased by over 70%. This sharp decline in rate was accurately identified by the system as a kinetic inflection point. Physically, this inflection point corresponds to the near depletion of the readily reactive rust layer, a significant increase in the exposed surface area of ​​the metal matrix, and a more pronounced inhibitory effect of accumulated iron ions on the reaction. Based on this analysis, the control system determined the optimal process endpoint to be t = 315 seconds.

[0105] To verify the effectiveness and superiority of the method of this invention, the results of this embodiment are compared with two comparative examples using the traditional fixed-time method. After 315 seconds of automated control processing, bolts were randomly selected for inspection, and the specific results are as follows:

[0106] (1) Macroscopic inspection: The bolt surface has a uniform grayish-white metallic luster and no visible rust residue. It is especially clean in hard-to-treat areas such as the root of the thread.

[0107] (2) Microscopic inspection: Under a 200x metallographic microscope, the bolt surface was smooth and no pitting or excessive etching caused by over-corrosion was found.

[0108] (3) Mechanical performance test: The bolts were subjected to torque and tensile tests. Their mechanical properties were not significantly different from those of untreated new products, and no signs of hydrogen embrittlement were observed.

[0109] Comparative Example 1

[0110] Another batch of bolts in the same condition were processed under the same conditions for a fixed empirical time (240 seconds).

[0111] Inspection revealed that the bolt surfaces, particularly at the junction of the head and shank, still had noticeable black and red rust spots. This batch of bolts was deemed substandard and could not proceed to the subsequent painting process. This demonstrates that the timed method is inadequate for uneven rust formation and can easily lead to insufficient treatment.

[0112] Comparative Example 2

[0113] The third batch of bolts in the same condition were treated under the same conditions for an extended fixing time (450 seconds) to ensure complete removal of rust.

[0114] Inspection revealed that although the rust had been completely removed, the bolt surface had a dull luster and exhibited a rough, etched texture, with measurable dimensional reduction in some thread edges. Subsequent stress tests showed a significantly higher failure rate in this batch of bolts, exhibiting typical hydrogen embrittlement symptoms. This demonstrates that extending the processing time in the timed method to ensure rust removal inevitably leads to over-pickling, severely damaging the workpiece's performance and value.

[0115] This embodiment, by monitoring reaction kinetics in real time and automatically determining the endpoint, precisely terminates the pickling process at 315 seconds. This achieves thorough removal of rust while maximizing the protection of the metal substrate, ensuring a high degree of consistency in repair quality, and avoiding waste of chemicals and energy. Its effect is significantly better than traditional timed treatment methods.

[0116] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for repairing bolts with surface rust, characterized in that, Includes the following steps: S1. Place the bolts with surface rust to be repaired into a cleaning tank containing acidic cleaning solution; S2. During the cleaning process, the sound velocity and conductivity of the tank liquid are monitored in real time by a collaborative sensing system installed in the circulation loop of the cleaning tank. S3. Based on real-time measurements of sound velocity and electrical conductivity, calculate in real-time the acid concentration in the acidic cleaning solution and the concentration of dissolved iron produced by the dissolution of rust. S4. Calculate the instantaneous dissolution rate of rust in acidic cleaning solution based on the real-time change data of dissolved iron concentration. S5. Determine the endpoint of the cleaning process based on the changing trend of the instantaneous dissolution reaction rate, and terminate the cleaning step when the endpoint is reached.

2. The method for repairing surface-corroded bolts according to claim 1, characterized in that, In step S2, the collaborative sensing system includes an online sound velocity sensor and a four-electrode conductivity sensor. The sound velocity sensor is mainly used to reflect changes in acid concentration, and the conductivity sensor is mainly used to reflect changes in dissolved iron salt concentration.

3. The method for repairing surface-corroded bolts according to claim 1, characterized in that, In step S5, the change in the instantaneous dissolution reaction rate is continuously monitored, and the optimal endpoint of the cleaning process is determined when the reaction rate drops significantly from a high-speed plateau or peak.

4. The method for repairing surface-corroded bolts according to claim 1, characterized in that, In step S5, when the optimal endpoint is reached, the control system automatically triggers subsequent process instructions, which include stopping cleaning, draining the used acidic cleaning solution, and initiating at least one rinsing step.

5. The method for repairing surface-corroded bolts according to claim 1, characterized in that, It also includes post-processing steps performed after step S5: (1) Neutralization treatment: Use an alkaline solution to treat the bolt surface to neutralize the residual acid; (2) Passivation treatment: The neutralized bolts are immersed in passivation solution for passivation treatment.

6. The method for repairing surface-corroded bolts according to claim 5, characterized in that, The passivation solution is either citric acid passivation solution or molybdate / phosphate composite conversion membrane solution.

7. The method for repairing surface-corroded bolts according to claim 1, characterized in that, The acidic cleaning solution comprises the following components by mass fraction: 10%-50% acid, 0.1%-5% corrosion inhibitor, 0.1%-15% surfactant, and the remainder is water.

8. The method for repairing surface-corroded bolts according to claim 7, characterized in that, The acid is selected from one or more of hydrochloric acid, phosphoric acid, and citric acid; the corrosion inhibitor is an imidazoline derivative or hexamethylenetetramine; and the surfactant is one of alkylphenol polyoxyethylene ether, alcohol ether, or sodium lauryl sulfate.

9. The method for repairing surface-corroded bolts according to claim 1, characterized in that, In step S5, the model for determining the endpoint of the cleaning process is: in, This refers to the instantaneous reaction rate; This represents the real-time concentration of acid in the cleaning solution; This represents the real-time concentration of iron ions dissolved in the cleaning solution. The first parameter to be fitted represents the theoretical maximum reaction rate without product inhibition, and characterizes the inherent reactivity of the rust layer. The second parameter to be fitted represents the competitive inhibition coefficient, which characterizes the relative strength of the adsorption capacity of dissolved iron ions and acid on the active sites of rusted surfaces.

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